How can we help?

You can also find more resources in our Help Center.

529 terms

Neuroscience Exam 1

STUDY
PLAY
Synaptic Transmission
The process of information transfer at a synapse
Electrical Synapses
Synapse where an electrical current is transfered from one neuron to another which occurs at gap junctions and are usually bidirectional. Common in the mammalian brain and in every part of the mammalian CNS.
Chemical Synapses
Synapse where a chemical neurotransmitter transfered information from one neuron to another
Gap Junctions
Location where electrical synapses happen. The membrane of two cells are about 3 nm apart and has clusters of specialized proteins called connexins. Two connexins combine to form a gap junction channel.
Postsynaptic Potential (PSP)
An action potential in the second neuron caused by an action potential in the first neuron to send a small amount of ion current to flow through the gap junction channels.
Usually small so several PSPs are required to excite a neuron.
Synaptic Cleft
Region between the presynaptic and postsynaptic membrane thats about 20-50nm apart filled with a matrix of fibrous extracellular protein.
Synaptic Vesicles
Vesicles that store neurotransmitters on on the presynaptic side (usually an axon terminal)
Secretory Granules
Larger vesicles in the axon terminals that contain soluble protein.
Dense-core Vesicles
Another name for Secretory Granules
Membrane Differentiations
Dense regions of the presynaptic and postsynaptic membranes packed with proteins
Active Zones
The membrane differentiation of the presynaptic membrane that contains pyramid-like proteins where neurotransmitters are released
Postsynaptic Density
membrane differentiation of the postsynaptic membrane that contains a lot of NT receptors which convert intercellular chemical signals into an intracellular signal
Axodendritic
The synapse in the CNS if the postsynaptic membrane is on a dendrite
Axoaxonic
The synapse in the CNS if the postsynaptic membrane is on a axon
Axosomatic
The synapse in the CNS if the postsynaptic membrane is on a soma
Dendrodendritic Synapses
The synapse in the CNS if the presynaptic and postsynaptic membrane are on dendrites
Gray's Type I Synapses
Synapses where the membrane differentiations of the presynaptic membrane is thinner than of the postsynaptic membrane. Usually means synapse is excitatory.
Gray's Type II Synapses
Synapses where the membrane differentiations is of similar thickness. Usually means synapse is inhibitory.
Neuromuscular Junction
Synapse between the axons of a motor neuron of the spinal cord and skeletal muscle. It has many of the structural features of chemical synapses in the CNS.
One of the largest synapses in the body
Motor end-plate
Post-synaptic membrane of the muscle that contains a series of shallow folds so more receptors can be there.
What are the three categories of neurotransmitters?
amino acids, amines, and peptides
What are the major amino acid neurotransmitters? (3)
Gamma-amino-butyric Acid (GABA), Glutamate (Glu), Glycine (Gly)
What are the major amine neurotransmitters? (6)
Acetylcholine (Ach), Dopamin (DA), Epinephrine, Histamine, Norepinephrine (NE), Serotonin (5-HT)
What are the major peptide neurotransmitters? (9)
Cholecystokinin (CCK), Dynorphin, Enkephalins (Enk), N-acetlaspartylglutamate (NAAG), Neuropeptide Y, Somatostatin, Substance P, Thyrotropin-releasing hormone, Vasoactive intestinal polypeptide (VIP)
Which neurotransmitters are in fast synaptic transmissions at most CNS synapses?
Gamma-amino-butyric Acid (GABA), Glutamate (Glu), Glycine (Gly)
What neurotransmitter mediates fast synaptic transmission at all neuromuscular junctions?
Acetylcholine (ACh)
Which neurotransmitters are in slower forms of synaptic transmissions in the CNS and in the periphery?
All.
Transporters
Special proteins embedded in the vesicle membrane that transports NTs into the vesicles
How are peptides put in the secretory granules?
Budded off from the Golgi apparatus.
Voltage-Gated Calcium Channels
Permeable to calcium which allows calcium into the presynaptic membrane that causes NTs to be released from synaptic vesicles
Exocytosis
The process by which vesicles release their content
Endocytosis
The process where the vesicle membrane is recovered and refilled with NTs
What are the two types of NTs receptors?
Transmitter-gated ion channels and G-protein-coupled receptors
Transmitter-gated ion channels
Membrane-spanning proteins with four or five subunits that when activated, allows pore to be open to let specific ions in/out.
Excitatory Post-synaptic Potential (ESSP)
When the presynaptic NTs causes a depolarization in the postsynaptic membrane.
Synaptic activation of ACh-activated and glutamate-gated ion channels causes them.
Inhibitory Post-Synaptic Potential (IPSP)
When te presynaptic NTs causes hyperpolarization in the postsynaptic membrane.
Synaptic activation of Glycine-activated and GABA-gated ion channels causes them.
G-Protein Coupled Receptors
Receptors that can have a slower, longer-lasting and much more diverse postsynaptic actions.
G-proteins
small proteins that are free to move along the intracelular face of the postsynaptic membrane that can activate "effector" proteins to lead to postsynaptic actions
Second messengers
molecules that diffuse away and activate additional enzymes in the cytosol that can regulate ion channels and alter cellular metabolism.
Metabotropic Receptors
Another word for G-Protein Coupled Receptors because they can trigger widespread metabolic effects
Autoreceptors
Presynaptic receptors that are sensitive to the NT released by the presynaptic terminal.
Used to regular itself so it doesn't release too much NT
Why must NTs be recovered and degraded quickly after its been released and how?
Ot must be cleared so that the next action potential can cause another synaptic transmission.
There are NT transports on the presynaptic membrane that allows for re-uptake so enzyme can destroy them or be released back into vesicles. Glial cells also have these so that they can regular the cleft. There also could be enzymes in the cleft that destroys the NTs.
This prevents desensitization where the transmitter-gated channels won't respond to the NTs on the postsynaptic side.
Neuropharmacology
Study of the effects of drugs on nervous system tissue
Inhibitors
Drugs that inhibit the normal function of specific proteins
Receptor Antagonists
Inhibitors of NT receptors that bind to and block the receptors
Receptor Agonists
Drugs that mimic the normal actions of the naturally occurring NT
Synaptic Integration
Process where multiple postsynaptic potentials combine within one postsynaptic neuron.
Why at NTs quantally released?
A single vesicle has the same number of NT molecules (several thousands) so depending on how many vesicles are released, it will always be a multiple of that number.
Miniature PostSynaptic Potential
A response generated by one vesicle of NTs
Quantal Analysis
We can compare the amplitudes of miniature and evoked postsynaptic potentials to figure out how many vesicles is released during a synapse transmission.
Neuromuscular = about 200 vesicles
CNS = about 1 vesicle
EPSP Summation
The simplest form of synaptic integration in the CNS. There are two types: spatial and temporal
Spatial Summation
addition of EPSPs generated simultaneously at many different synapses on a dendrite
Temporal Summation
addition of EPSPs generated at the same synapses as they occur in rapid succession (1/15 m sec apart)
Length Constant (λ)
Distance from the synapse where the depolarization is 37% of that at the origin
Internal resistance
The resistance of current flowing longitudinally down the dendrite. It depends only on the diameter of the dendrite & electrical properties of the cytoplasm (constant)
Higher = Lower λ
Membrane resistance
The resistance of current flowing across the membrane. It depends on the number of ion channels number (changes)
Higher = Higher λ
Why do some dendrites have VG ion channels?
They can act as small postsynaptic potential amplifiers generated far out on dendrites
What factors effect an EPSP's output on a neuron?
Number of coactive excitatory synapses, the distance the synapse is form the spike-initiation zone, and the properties of the dendritic membrane.
Shunting Inhibition
When an inhibitory synapse acts as an electrical shunt and prevents current from flowing through the soma to the axon hillock which is usually inward movement of negatively charged Cl- ions.
Where are inhibitory synapses located usually?
On the soma and near the axon hillock where they have a powerful position to affect the neuron action
Modulation
A synapse where it affects the effectiveness of EPSPs generated by other synapses with transmitter-gated channels
Norepinephrine (NE)
an amine NT that binds to ß receptors and triggers a cascade of biochemical events within the cell that leads to modulation
Adenylyl Cyclase
enzyme that catalyzes the reaction to convert ATP into cAMP
Cyclic Adenosine Monophosphate (cAMP)
a second messenger molecule that can stimulate other enzymes such as a protein kinase
Protein Kinases
enzyme that catalyzes phosphorylation to change another protein
Phosphorylation
process that transfers phosphate groups from ATP to a specific site on cell proteins to change its conformation and activity
What is an important effect of phosphorylation in neurons?
It can close a particular type of K channels and thus lowering the membrane's K+ conductance which increases the dendritic membrane resistance and increases λ
Otto Loewi
Discovered effect of acetylcholine, ACh (vagusstoff) through experiments with frog hearts...He used this discovery to prove chemical synapses
Cholinergic
Introduced by Henry Dale. Described cells that produce and release ACh as this.
Noradrenergic
Dale termed neurons that use the amine neurotransmitter norepinephrine this...
Glutamatergic
Synapses that use glutamate
GABAergic
Synapses that use GABA
Peptidergic
Synapses that use peptides
Criteria for a neurotransmitter
Must be synthesized and stored in the presynaptic neuron.
Must be released by presynaptic axon terminal upon stimulation
When experimentally applied, must produce a response in postsynaptic cell that minus the response produced by the release of neurotransmitter from presynaptic neuron
Important techniques to satisfy criteria for neurotransmitter
Immunuocytochemistry and in situ hybridization
Immunochemistry: method for viewing location of specific molecules in sections of brain tissue
In situ hybridization: Method for localizing specific mRNa transcripts for proteins. Together, these methods enable us to see whether a neuron contains and synthesizes a transmitter candidate.
Immunocytochemistry
Used to anatomically localize particular molecules to particular cells. Once neurotransmitter candidate has been chemically purified, it is injected into the bloodstream of an animal where it stimulates an immune response (to evoke response, molecule is chemically coupled to larger molecule). One aspect of immune response is generation of antibodies which tightly bind to specific sites of foreign molecule (transmitter candidate). Better antibodies bind tightly to transmitter of interest and very little or not at all to other chemicals. Antibodies are recovered from blood sample of immunized animal and chemically tagged with marker to see under microscope. Used to localize molecule for which antibody can be generated (synthesizing enzymes for transmitter candidates). Demonstration that transmitter candidate and its synthesizing enzyme are contained in the same neuron or axon terminal can help satisfy criterion. http://o.quizlet.com/i/EMbNpIVPpPEq01qOZ_9LBQ.jpg
In Situ Hybridization
Chemically label probe (complementary strand of mRNA), apply it to section of brain tissue, allow time for probes to stick to any complementary RNA strands, then wash away all extra probes that haven't stuck. Finally, search for neurons that contain label. Probes are usually labeled by making them radioactive.
Technique for viewing distribution of radioactivity
autoradiography
Stimulate release in in vitro brains
Slices bathed in solution containing hihg potassium concentration. Causes large membrane depolarization, stimulating transmitter release from axon terminals in the tissue.
Microinophoresis
Assesses postsynaptic actions of transmitter candidate. Inject charged candidate ions next to postsynaptic membrane and use microelectrode to record effects on membrane potential.
No two neurotransmitters
bind to the same receptor
One neurotransmitter
can bind to many different receptors.
Receptor subtype
Each of the different receptors a neurotransmitter binds to. ACh acts on two different cholinergic receptor subtypes: One present in skeletal muscle and the other in heart muscle. Both subtypes are also present in many other organs and within the CNS
Neuropharmacological Analysis
Distinguishing receptor types through the use of drugs
Nicotinic ACh receptors
Skeletal muscle. Also exists in brain.
Muscarinic ACh receptors
Heart muscle. Also exists in brain.
Selective Antagonists
Inhibit action of certain receptors to distinguish receptor subtypes
Subtypes of glutamate receptors
Meidate much of synaptic excitation in CNS. AMPA receptors, NMDA receptors, kainate receptors (named for different chemical agonists. Glutamate activates all three receptor subtypes, but AMPA acts only at AMPA receptor, NMDA at NMDA receptor, etc.
Opiates
Broad class of drugs that are both medically important and commonly abused. Effects include pain relief, euphoria, depressed breathing, and constipation
Ligand
Any chemical compound that binds to a specific site ona receptor
Ligand binding method
Technique of studying receptors using radioactively labeled ligands. Specific ligands were invaluable for isolating neurotransmitter receptors and determining their chemical structure. Important for mapping anatomical distribution of different neurotransmitters.
Molecular Analysis
Discovered that each subunit could be replaced/substituted by different polypeptides...leading to a very large diversity of receptors
Dale's Principle
The idea that a neuron has only one neurotransmitter. Many peptide containing neurons violate Dale's principle because these cells usually release more than one transmitter: an amino acid or amine AND a peptide. True for most cases, though.
Co-transmitters
When two or more transmitters are released from one nerve terminal, they are called...
Acetylcholine
Neurotransmitter at neuromuscular junction. Synthesized by all motor neurons int he spinal cord and brain stem. Other cholinergenic cells contribute to functions of specific circuits in PNS and CNS.
ACh synthesis
Requires choline acetyltransferase ChAT (manufactured in soma and transported to axon terminal) Only cholinergic neurons contain ChAT, so this enzyme is a good marker for cells that use ACh. Ex: Immunocytochem with ChAT specific antibodies can identify cholinergic neurons. ChAT synthesizes ACh in cytosol of axon terminal, and neurotransmitter is concentrated in synaptic vesicles by ACh transporter. ChAT transfers acetyl group from acetyl CoA to choline(from extracellular fluid taken up by transporter).
Rate Limiting Step in ACh synthesis
Transport of choline into neuron. (Availability of chlorine limits how much ACh can be made)
AChE (Acetylcholinesterase)
degradative enzyme. secreted into synaptic cleft and is associated with cholinergic axon terminal membranes. Also manufactured by some noncholinergic neurons (not useful as a market for cholinergic synapses)
Catecholaminergic Neurons
Amino acid(Tyrosine) is a precursor for three different amine neurotransmitters that contain a chemical structure called a catechol. Called catecholamines: Dopamine, norepinephrine, epinephrine. Found in regions of nervous system involved in the regulation of movement, mood, attention, and visceral attention. All catecholaminergic neurons contain tyrosine hydroxylase (TH [activity of this is rate limiting step for synthesis]), which catalyzes the firs step in catecholamine synthesis (conversion of tyrosine to dopa which is converted into dopamine via dopa decarboxylase).
Parkinson's disease
Dopaminergic neurons in brain slowly degenerate and eventually die.
Dopamine B-hydroxylase
Converts dopamine to norepinephrine. Located in synaptic vesicles
Phentolamine N Methyltransferase
Converts norepinephrone to epinephrine. In cytosol.
Monoamine oxidase (MAO)
enzyme found on outer membrane of mitochondria that functions in enzymatic destruction of catecholamines and serotonin once inside axon terminal
Serotonin
Amine neurotransmitter (also called 5 hydroxyltryptamine) and abbreviated 5-HT and derived from tryptophan amino acid.
Serotonergic Neurons
Few in number but regulate mood, emotional behavior, and sleep
Synthesis of serotonin
1) Tryptophan converted into intermediary (5 HTP) through tryptophan hydroxylase
2) 5 HTP converted to 5 HT by 5 HTP decarboxylase
* Synthesis is limited by availability of tryptophan in extracellular fluid bathing neurons. Dietary.
Glutamate, glycine, GABA
Serve as neurotransmitters at most CNS synapses
GABA
Unique to neurons that use it as neurotransmitter; synthesized only in neurons that use it since it's not one of the 20 amino acids used in protein syntehsis. Precursor: glutamate...Glutamic acid decarboxylase.
GABAergic neurons
Marked well by GAD. Distributed widely in brain. Major source of synaptic inhibition in ervous system.
GABA transaminase
Enzyme that metabolizes GABA.
ATP as a neurotransmitter
Concentrated in vesicles at many synapses (CNS and PNS). Released into cleft through spikes in Ca-dependent manner. Packaged in vesicles along with another transmitter. (Co transmitter with catecholamine) directly excites some neurons by gating cation channel...function similarly like glutamate) Binds to purinergic receptors
Endocannabinoids
Can be released from postsynaptic neurons. Act on presynaptic terminals.Retrograde messengers. Serve as feedback system to regulate conventional forms of synaptic transmission. Vigorous firing of action potentials in postsynaptic neuron causes voltage gated CA channels to open, Ca enters cell and intracellular Ca rises. Elevated Ca stimulates synthesis of endo-cannabinoid from membrane lipids. http://o.quizlet.com/i/t-QPpMXfmyB2vg5ka5-LAQ.jpg
Retrograde signaling
Communication from post to presynpatic.
Unusual qualities about endocannabinoids
They are not packaged in vesicles like most other neurotransmitters; manufactured rapidly on demand
They are small and membrane permeable; can diffuse rapidly across membrane of cell origin to contact neighboring cells
Bind selectively to CB1 type of cannabinoid receptor located on presynaptic terminals
CB1 Receptors
G protein coupled receptors. Main effect is to reduce opening of presynaptic calcium channels. Slows down neurotransmitter release.
Cannabis Sativa
Botanical name for hemp, fibrous plant used through ages for making rope and cloth. Active gredient is THC. It binds to specific G-Protein cannabinoid receptors in brain (particularly motor control, cerebral cortex, pain pathways). Led to discovery of THC like neurotransmitters called endocannabinoids (anandamide and arachidonylglycerol. Potentially useful for relieving nausea, suppressing pain, relaxing muscles, treating seizures, decreasing intraocular pressure of glaucoma.
Nitrous oxide
Gaseous molecule. Interceullular communication. May be another example of retrograde messenger. Since it's small and membrane permeable, it can diffuse more freely than most other transmitter molecules. Also evanescent and breaks down very rapidly.
Dual function
Some neurotransmitters may exist elsewhere other than nervous system and serve another purpose. For example, amino acids and ATP serve other acids other than being neurotransmitters.
Transmitter Gated Channels
Most studied is nicotinic ACh receptor at neuromuscular junction in skeletal muscle. Each receptor subunit has different primary structure (some portions are similar). Pentameric complexes (mostly) minus glutamate which are tetramers. Different transmitter binding sites let one channel respond to Glu while another respond to GABA.. http://o.quizlet.com/i/dBDypivQJVIFCsQpipzopg.jpg
Similarities in structure of subunits for different transmitter gated ion channels
http://o.quizlet.com/i/_7ay-Hy9-TT-2rkXBnQ-qw.jpg
Amino acid gated channels
Mediate most of the fast synaptic transmission in the CNS.
1) Pharmacology of their binding sites describes which transmitters affect them and how drugs interact with them.
2) Kinetics of the transmitter binding process and channel gating determine the duration fo their effect
3) Selectivity of ion channels determines whether they produce excitation or inhibition and whether Ca enters the cell in significant amounts
4) conductance of open channels helps determine the magnitude of their effects
Glutamate-Gated channels
Three glubtamate receptor subytpes: AMPA, NMDA, kainate. AMPA and NMDA mediate bulk of fast excitatory synaptic transmission in the brain. Kainate receptors also exist but functions are not understood. *AMPA permeable to both sodium and potassium, most aren't permeable to calcium. Net effect at rest: admit Na into cell, causing rapid depolarization. AMPA receptors at CNS synapses mediate excitatory transmission in same way as nicotinic receptors at neuromuscular junctions. http://o.quizlet.com/i/Bz2rp4jxyPfvaViyjl3W-A.jpg
AMPA Receptors
Permeable to both sodium and potassium, most aren't permeable to calcium. Net effect at rest: admit Na into cell, causing rapid depolarization. AMPA receptors at CNS synapses mediate excitatory transmission in same way as nicotinic receptors at neuromuscular junctions.
NMDA Receptors
Permeable to calcium, inward ionic current through NMDA gated channels is voltage dependent. When NMDA gated channels open, Ca and Na enter cell while K leaves. Magnitude of inward current depends on postsynaptic membrane potential. When glutamate binds to NMDA receptor, pore opens as usual but at normal negatie resting membrane potentials, channel becomes clogged by Mg ions (magnesium block prevents other ions from passing freely through NMDA channel). Mg pops out only when depolarized. Therefore, both glutamate and depolarization must coincide before the channel passes current. http://o.quizlet.com/i/YU9vvbwHHbKzC-v9OHLDcw.jpg
Excitotoxins
Toxins that overstimulate glutamate release and cause neuron suicide.
GABA Gated channels
GABA mediates most of the synaptic inhibition in the CNS. Gates a chlorine channel. Similar structure to nicotinic ACh receptors despite different ion selectivity.
Glycine gated channels
Glycine mediates most of the rest of the inhibition of the CNS after GABA. Gates a chlorine channel. Similar structure to nicotinic ACh receptors despite different ion selectivity.
Benzodiazepines (diazepam, Valium)
Binds to specific site on outside face of GABA A channel. With GABA present, increase frequency of channel openings. Cause stronger inhibitory signals. Only receptors with gamma GABAA subnit (in addition to alpha and beta subunits) respond to these
Barbituates (phenobarbital, sedatives)
Binds to own distinct site on outside face of GABA A channel. With GABA present, increase duration of channel openings. Cause stronger inhibitory singals.
Ethanol
Affects NMDA, glycine, ACh, and serotonin receptors. Effects on GABA A channels depends on specific structure. *alpha, beta, and gamma sub units necessary for ethanol sensitive ethanol GABA A receptor. Enhances inhibition on some brain areas but not others.
Neurosteroids
Natural metabolites of steroid hormones that are synthesized from cholesterol primarily in gonads and adrenal glands but also glial cells of brain. Some enhance inhibitory function while others suppress it. Bind to own site on GABA A receptor.
Structure of G Protein coupled receptors
Single poly peptide containing seven membrane spanning alpha helices. Two extracellular loops form transmitter binding sites. Two intracellular loops bind to and activate G Proteins. http://o.quizlet.com/i/2JvvnePySAjcwQsZSDIx-A.jpg
G-proteins
Guanosine triphosphate binding protein. Some types of g proteins can be activated by many receptors.
1) Each G protein has three subunits, alpha, beta, gamma. In resting state, GDP molecule is bound to G alpha subunit and the whole complex floats around on inner surface of membrane
2) If this GDP bound G protein bumps into proper type of receptor and that receptor has a transmitter molecule bound to it, G protein releases GDP and exchanges it for GTP from cytosol
3) The activated GTP bound G protein splits into two parts: G alpha subunit + GTP, and G beta-gamma complex. Both move on to influence effector proteins
4) G alpha subunit is itself an enzyme that eventually breaks down GTP into GDP. Terminates its own activity by converting bound GTP to GDP
5) G alpha and G beta-gamma subunits come back together, allowing cycle to begin again
Gs and Gi
Stimulatory and inhibitory G-proteins
The Shortcut Pathway
Fastest of G protein coupled systems (response 30-100 msec of neurotransmitter binding) Not as fast as transmitter gated, and very localized.
Example: Muscarinic receptors in heart. ACh receptors coupled via G proteins to potassium channels, explaining why ACh slows heart rate. Beta=gamma subunits migrate laterally along membrane until they bind to right type of potassium channel.
Another example: Neuronal GABA B receptors..coupled by shortcut pathway to potassium channels.
Fastest of G protein coupled systems.
Second Messenger Cascades
Happen when G proteins exert effects by activating certain enzymes, which trigger series of biochemical reactions. Second messengers are between first and last enzyme. The whole process that couples neurotransmitter, via multiple steps, to activation of a downstream is called this...
Protein Kinase A
Downstream enzyme activated by rise in cAMP in cytosol
Protein phosphatases
Act rapidly to remove phosphate groups from phosphorylated proteins
Channel phosphorylation
when ATP is bound and changes the conformation of protein channels to inhibit or excite
Signal amplification
Activation of one G protein coupled receptor can lead to activation of many ion channels http://o.quizlet.com/i/Eq_hAGGQGZdDCDM_iZWOww.jpg
Signal cascade benefits
Allows signaling at a distance, signal amplification, provides more sites of regulation, and generation of long lasting chemical changes are possible
Divergence
Ability of one transmitter to activate mor ethan one subtype of receptor and cause more than one type of postsynaptic response http://o.quizlet.com/i/_uQ0TxXq1JwWVcg3O-p7rg.jpg
Convergence
Multiple transmitters, each activating their own receptor type, converge to affect the same effector systems. Can occur at level of G protein, second messenger cascade, or type of ion channel. http://o.quizlet.com/i/KzJn2-BoH2khFlcoy7QcVw.jpg
Diffusion:
A. Carries particles away from equilibrium
B. Requires energy
c. occurs due to random motion of particles
d. is a type of active transport
e. only occurs in biological systems
c. Diffusion occurs due to random motion of particles
The Nernst equation
a. Calculates equilibrium potential across the membrane
b. Takes into account ionic concentration
c. Does not take into account the permeability of the membrane
d. Both a and b
e. All of the above
e. The nernst equation calculates equilibrium potential across the membrane, takes into account ionic concentration, and does not take into account the permeability of the membrane
An example of a neurotransmitter that is typically released at excititory synapses is:
a. Glutamate
b. Acetyl choline
c. dopamine
d. Both a and b.
e. all of the above
e. glutamate, acetyl choline, and dopamine are all examples of neurotransmitters that are typically released at excitatory synapses
Action potentials are propagated along an axon due to the
a. opening of voltage-gated Na+ channels
b. passive diffusion of electrical current
c. membrane depolarization
d. all of the above
e. none of the above
d. action potentials are propagated along an axon due to the opening of voltage-gated Na+ channels, passive diffusion of electrical current, and membrane depolarization
When a muscle cell is held at its reversal potential of 0 mV, the release of Ach no longer produces a current because:
a. nicotinic AchRs won't open unless the membrane depolarizes past 0 mV
b. The rate of Ach degradation is increased
c. The equilibrium potential for Na+ (Ena) and for K+ (Ek) is 0 mV in muscle cells
d. an influx of Na+ is balanced by an equal efflux of K+
e. none of the above - d. When a muscle cell is held at its reversal potential of 0 mV, the release of ACh no longer produces current because an influx of Na+ is balanced by an equal efflux of K+
...
Ionotropic receptors:
a. are ion channels.
b. produce slower, longer lasting postsynaptic responses compared to metabotropic receptors.
c. cause ion channels to open or close by activating intermediate proteins.
d. All of the above
e. None of the above
a. Ionotropic receptors are ion channels.
A negative resting membrane potential is generated by
a. A high extracellular concentration of K+ and a membrane that is permeable to K+.
b. A high intracellular concentration of K+ and a membrane that is permeable to K+.
c. The expenditure of ATP.
d. Both a and c
e. Both b and c
e. A negative resting membrane potential is generated by a high intracellular concentration of K+ and a membrane that is permeable to K+ and The expenditure of ATP.
The inactivation of voltage-gated Na+ channels
a. is voltage-dependent.
b. prevents the action potential from traveling 'back up' the axon towards the cell body.
c. relies on the conformation of voltage-gated K+ channels.
d. causes the neuronal membrane to depolarize.
e. All of the above
b. The inactivation of voltage-gated Na+ channels prevents the action potential from traveling 'back up' the axon towards the cell body.
Methamphetamine
a. increases the local concentration of dopamine in the synaptic cleft.
b. reverses the direction of the VMAT transporter.
c. reverses the direction of the DAT transporter.
d. causes degradation of dopaminergic neurons.
e. All of the above
e. Methamphetamine increases the local concentration of dopamine in the synaptic cleft, reverses the direction of the VMAT transporter, reverses the direction of the DAT transporter and causes degradation of dopaminergic neurons.
Small molecule neurotransmitters are
a. synthesized in the nucleus.
b. transported to the synaptic terminal along microtubules.
c. packaged into synaptic vesicles in the synaptic terminal.
d. never packaged with other types of neurotransmitters.
e. All of the above
c. Small molecule neurotransmitters are packaged into synaptic vesicles in the synaptic terminal.
Glial cells
a. increase the conduction velocity of neurons.
b. remove cellular debris.
c. remove neurotransmitters from the extracellular environment.
d. provide a scaffold for neural development.
e. All of the above
e. Glial cells increase the conduction velocity of neurons, remove cellular debris, remove neurotransmitters from the extracellular environment and provide a scaffold for neural development.
Movement of ions by pumps (active transport) differs from movement of ions by channels in what way?
a. Only channels require the hydrolysis of ATP.
b. Only pumps can move ions against their concentration gradient.
c. Only pumps can be gated.
d. Only ion channels are proteins that span the membrane.
e. Only pumps are selective for certain ions.
b. Only pumps can move ions against their concentration gradient
GAP junctions
a. consist of the hexameric arrangement of subunits called synapsins.
b. are only found at electrical synapses.
c. allow ions to flow in one direction between cells.
d. open in response to membrane depolarization.
e. are paired channels that form pores between cells.
e. GAP junctions are paired channels that form pores between cells.
Action potentials
a. always occur with the same frequency.
b. increase in amplitude in response to stronger stimuli.
c. occur when the influx of Na+ is greater than the efflux of K+.
d. All of the above
e. None of the above
c. Action potentials occur when the influx of Na+ is greater than the efflux of K+.
Compared with small molecule neurotransmitters, peptide neurotransmitters are released in response to (a)
a. high frequency stimulation, resulting in more diffuse intracellular Ca2+.
b. high frequency stimulation, resulting in more localized intracellular Ca2+.
c. low frequency stimulation, resulting in resulting in more diffuse intracellular Ca2+.
d. low frequency stimulation, resulting in more localized intraceullular Ca2+.
e. None of the above
a. Compared with small molecule neurotransmitters, peptide neurotransmitters are released in response to high frequency stimulation, resulting in more diffuse intracellular Ca2+.
An inhibitory postsynaptic potential (IPSP) can be depolarizing. True / False
True
Hodgkin & Katz found that increasing external K+ caused the resting membrane potential in the squid giant axon to decrease, or hyperpolarize. True / False
False
Ions can diffuse across phospholipid bilayers. True / False
False
Ca2+ triggers synaptic vesicles to dock with the plasma membrane via binding to SNARE proteins in the vesicular membrane. True / False
False
Conotoxins are a mix of peptides, some of which bind to and block nicotinic AChRs. True / False
True
Neurotransmitter removal from the synaptic cleft occurs by several mechanisms, including degradation and transport into the postsynaptic terminal. True / False
False
Voltage-gated ion channels open and close in response to changes in membrane potential. True / False
True
Myelination speeds up the conduction velocity of an action potential by increasing the distance that a local current can passively travel. True / False
True
Endocannabinoids are released from the presynaptic terminal in response to an influx of Ca2+. True / False
False
At the equilibrium potential for an ion, the ________________________ is balanced by the _________________________.
At the equilibrium potential for an ion, the concentration gradient is balanced by the membrane potential
Two examples of biogenic amines are ________________________ and ________________________.
Two examples of biogenic amines are dopamine and Serotonin
Multiple presynaptic neurons can synapse with one postsynaptic neuron. The sum of the postsynaptic potentials in _________________________, ________________________, and magnitude decides whether or not an action potential occurs in the postsynaptic neuron.
Multiple presynaptic neurons can synapse with one postsynaptic neuron. The sum of the postsynaptic potentials in space, time, and magnitude decides whether or not an action potential occurs in the postsynaptic neuron
The ________________________ experiment allows measurement of ionic current through a single ion channel
The patch-clamp experiment allows measurement of ionic current through a single ion channel
An inward current is defined as an influx of __________________________ ions.
An inward current is defined as an influx of positive ions.
After an action potential has occurred, the period of time during which that axon is resistant to further excitation is called the _____________________________.
After an action potential has occurred, the period of time during which that axon is resistant to further excitation is called the Refractory period.
Multiple sclerosis is an autoimmune disease that results in the destruction of ______________________ .
Multiple sclerosis is an autoimmune disease that results in the destruction of myelin.
Describe the state of voltage-gated Na+ and K+ channels during the phases of an action potential. Explain why action potentials move in one direction along the axon.

At rest _______________
At rest, both voltage-gated Na+ and K+ channels are closed
Describe the state of voltage-gated Na+ and K+ channels during the phases of an action potential. Explain why action potentials move in one direction along the axon.

Threshold
enough v-g _____ channels open so that the ______ influx is greater than the _______ efflux through _________ leak channels - Na+, Na+, K+, K+
Describe the state of voltage-gated Na+ and K+ channels during the phases of an action potential. Explain why action potentials move in one direction along the axon.

Depolarization
Most v-g _______ channels are open and intial ones start to ________, v-g _____ channels are just begining to open - Na+, inactivate, K+
Describe the state of voltage-gated Na+ and K+ channels during the phases of an action potential. Explain why action potentials move in one direction along the axon.

Repolarization and hyperpolarization
v-g ____ channels are open, v-g ______ channels are either ________ or are ________ - K+, Na+, inactive, closed
As an action potential travels down an axon, the Na+ channels that have just opened are_______(time-dependent) and cannot respond to further membrane depolarization. So, even though passive current can flow in both directions along an axon, only the v-g ______ channels that haven't recently opened can respond
Inactive, Na+
At a postsynaptic synapse that has both NMDA and AMPA receptors, explain what happens when glutamate is released. Include in your answer the properties of both types of receptors and the resulting current

Both receptors are glutamate-gated cation channels (ionotropic receptors). Once glutamate is released, it binds to _____ receptors. AMPA opens once it binds _________ , and there is an influx of _________ that causes the membrane to depolarize. The ion channel pore in NMDA receptors is normally blocked by ______. If there is enough of a membrane depolarization from the AMPA receptors opening, this causes the ______ to be dispelled. This, plus the binding of glutamate causes the channel to open. NMDA receptors allow ____ and _______ into the cell (depolarization) and remain open ________ than AMPA receptors. So, the excitatory current caused by NMDA activation is slower but lasts longer than that caused by AMPA receptors. NMDA also triggers intracellular signaling pathways because it allows______ into the cell.
Both, glutamate, Na+, Mg2+, Mg2+, Na+, Ca2+, longer, Ca2+
Describe the sequence of events that occur during chemical transmission at a synaptic terminal.

An action potential ________ the presynaptic membrane.
Voltage-gated _______ channels open.
_______ flows into the presynaptic terminal.
Ca2+ binds to _________ on synaptic vesicles
The synaptic vesicles that are docked at the plasma membrane are triggered to fuse with the plasma membrane upon ______ binding.
As a result of vesicle fusion, the neurotransmitter contained within the synaptic vesicles is released into the _____ _____.
Neurotransmitters diffuse across the cleft and bind to ________ receptors.
Neurotransmitter binding often triggers ion channels to open, resulting in an _____ flux that causes the membrane potential to change
Depolarizes, Ca2+, Ca2+, Synaptotagmin, Ca2+, synaptic cleft, postsynaptic, ion,
It has been demonstrated that a rise in presynaptic Ca2+ is necessary and sufficient for neurotransmitter release. Describe experimental evidence that supports the claim that Ca2+ is necessary and that Ca2+ is sufficient

_________: Injecting a Ca2+ chelator (or something that binds/removes Ca2+) into the presynaptic terminal blocks postsynaptic membrane depolarization in response to a presynaptic action potential

_________: Injecting Ca2+ into the presynaptic terminal causes the postsynaptic cell to depolarize in the absence of an action potential in the presynaptic neuron
Necessary, sufficient
what type of signal is neurotransmitter?
chemical signal
what type of info is in the nervous sstem
qualitative and quantitattive
qualitative info?
cold, hot, bright, soft, et
quantitative info
how cold, how hot, etc...
what are the domains of the neuron?
somatodendritic domain, axon hillock, axon, nerve termini
somtodendritic domain has the dendrites which do what
receive incoming signals
incoming signal to dendrites come from what type of neuron
presynaptic
the cell body is also in the somatodendritic domain, what is it for?
biosynthesis and signal integration
what type of channels are on the dendrites. therefore,
what are the receptors for signals sent to the dendrites?
ligand gated and/or GPCR gated channels;
therefore, mebrane proteins are the receptors of the signals
the axon hillock is the zone for what?
action potential generation zone
the axon is for what?
impulse conduction
what type of channels are on the axon
voltage gated sodium and potassium channels. for action potentials...
what is the nerve termini domain for?
secretion of neurotransmitter
neurotransmitter is secreted to what type of neuron
a postsynaptic neuron
what type of channels are in the nerve termini, what channel is unique to the nerve termini (compared to the rest of the neuron)
voltage gated channels, sodium, potassium and calcium.
calcium is unique and for release of neuortransmitter
what type of response occurs in the dendrites and cell body
a graded response, which is due to opening of channels that are not voltage gated
what type of voltage spread is in the graded response
passive spread of voltage
where is the all or non response
axon hillock to terminus
why is there a different type of response for all or none, what channels is this due to
its due to the voltage gated sodium and potassium channels
resting potential?
potential maintained across the membrane of excitable cells
hyperpolarization
membrane potential gets more polarized, or more negative
depolarization
membrane potential gets less polarized, less negative, or more positive
threshold potential
the level of depolarization that triggers an action potential
action potential
rapid, large, regenerative depolarization
in a graded potential how does the amplitude of voltage deflection related to the amplitude of the stimulus pulse
they are proportional
where can graded potentials occur
in any part of the membrane in any cell
can summation occur in graded potentials?
yes
how do graded potentials affect action potentials
graded potentials can cause the cell to reach a particular threshold, once that threshold is reached, an action potential is developed
therefore, in an action potential, what type of voltage deflection is there
all or none
where does a graded potential occur for what we are dealing with
in the dendrites and cell body
where does the action potential occur
in the trigger zone through the axon
what initiates the graded potential signal
entry of ions through channels
what initiates the action potential signal
when threshold is reached due to the graded potential at the trigger zone
action potentials travel along the axon without decay and require what two things
presence of voltage gated sodium and potassium channels, and maintenance of the resting Vm (membrane potential)
in a hypokalemic patient, what is the membrane potential, and how does this affect the action potential
membrane potential is hyper polarized because of less potassium; therefore, it is more difficult to generate an action potential.
in resting state, what are the sodium and potassium channels
closed
what gives nerves their resting potential
potassium leak channels
at threshold, what happens
depolarization occurs due to opening of sodium channels and influx of sodium
why don't potassium channels open right away even though they respond to the same stimulus
they are slower to open and slower to close, don't know why
the repolarization phase includes what
inactivation of sodium channels and opening of potassium channels
the hyperpolarization phase is next, what happens?
potassium channels begin to slowly close, while the inactivation particle keeps the sodium channels inactive
change in conductance is the reason for differences in sodium and potassium conductance during an action potential (seemingly).
change in conductance is due to what?
change in permeability
therefore, there is a point when the sodium conductance decreases, and the potassium conductance?
increases
permeability changes cause what
cause the membrane potential to change
the actual current/cponductance that develops is the sum of what
all of the individual openings and closings of the channels
during the rising phase, what has increased permeability due to what and what is the relative permeability of potassium and sodium
sodium has increased permeability due to opening of more sodium channels.
sodium permeabilty = 400
potassium = 40
during the falling phase, what permeability increases. what is the relative permeability
potassium channels open, thus increase permeability, while sodium channels are inactivated.
potassium permeabilty = 100
sodium = 1
TETRODOTOXIN (TTX) does what
blocks the fast voltage gated sodium channels of neurons and striated muscle causing a hyper polarization because potassium channels are still open...
what is the voltage gated sodium channel composed of?
a single large alpha subunit with four transmembrane domains
each of the four transmembrane domains are comprised of?
six membrane spanning regions
which membraning spanning helix contains the voltage sensor
the 4th membrane spanning helix
voltage gated sodium channels may also have one or more smaller Beta subunits that are specific to a given channel, why?
regualtion specific to that cell type... ish...
what is the most stable configuration of the voltage gated sodium channel?
its closed configuration
depolarization causes the channel to
open, which is not a stable configuration
what stabilizes the unstable open configuration of the sodium channel
inactivation via the inactivation protein
what are the three stages of the voltage gated sodium channels
closed, open, inactivated
the inactivation stage is the basis for what?
the refractory period where the channel cannot be induced to produce an aciton potential because the channel is inactivated by the inactivation protein
the action potential or Hodgkin cycle (voltage gated sodium channels) is what type of feedback
positive feedback
what must happen to stop positive feedback systems
an outside mechanism is needed to stop the process
what mechanism stops the sodium channel positive feedback...
spontaneous inactivation via inactivation protein
will a larger stimulus induce another action potential during the absoulute refractory period?
no
what about during the relative refractory period. explain
yes, but the response will be smaller, and will need to be induced by a larger stimulus.
threshold is dependent upon?
the number of channels that can respond
in relative refractory, what's happening to the channels
some channels have closed, and thus can respond, but some channels are still inactivated, hence the larger stimulus needed to create a smaller than normal action potential
Cells of Nervous System
Neurons, glia, Schwann
Majority of Neuron Shape
Multipolar
Majority of Sensory shapes
Bipolar or pseudo-unipolar
Which shapes have no dendrites (per se)
Bipolar and pseudo-unipolar
____ carries info to other neurons
Axons
____ receive synapses from other neurons
Dendrites
Bipolar cells are for what special sense
optic and olfactory
___ is the primary sensory neuron type and located in ____
Psudo-unipolar; DRG
The shape of a neuron is maintained by?
cytoskeleton
Cytoskeleton is composed of
microtublues, neurofilaments, and microfilaments
Which component of the cytoskeleton is the largest?
microtubules
function of MAPS
assembly and disassembly of microtubules
What is a common target for immunocytochemical stains specific for neurons?
MAPS
Which cells do not contain microtubules and MAPS?
glia and schwann
Which component of the cytoskeleton is composed of cytokeratins?
neurofilaments
Which components of the cytoskeleton are involved in axoplasmic flow?
Neuronfilaments and microtubules
what are neurofibrillary tangles (as in Alzheimer's Disease)
a dense build-up of disorganized filaments resulting from a disruption of the assembly/disassembly of neurofilaments
Which components of the cytoskeleton is the smallest
microfilaments
Microfilaments are made up of?
actin
Microfilaments are involved in?
growth and remodeling, including formation of growth cones
axon segment closest to the soma aries from
axon hillock
The axon hillock is densely populated with ____ ____ and are important for _____ ___
ion channels; action potentials
Do axons branch?
yes
two most common synapse types
axo-dendritic (most common), axosomatic
axo-axonic and dedro-dendritic are thought to
allow groups of neurons with similar function and location to influence each other
Fast anterograde transports:
vesicles and organelles
Slow anterograde transports:
cytoskeleton components, proteins
fast retrograde transports:
lysosomes, organelles and proteins
Where are neurotransmitters made?
soma and terminal boutons
In a cortical or hippocampal pyramidal neuron myelin covers only:
the axon proper
Dale's principle states:
each terminal can only express one transmitter
Is Dale's principle still true?
no
What modification was made to Dale's principle?
all terminal release the same "profile of transmitters (even this may not be true)
Which synapses is + or -
axosomatic and axodendritic
which synapse is mostly -
axoaxonic
What is the most abundant type of glia
Astrocytes
What are the two types of astrocytes
protoplasmic and fibrous
which type of astrocyte is found in contact with the neuronal somata and dendrites?
protoplasmic
which type of astrocyte provides structural and metabolic support
protoplasmic
which type of astrocyte is found in the CNS white matter
Fibrous
which type of astrocyte is in contact with axons and to a lesser extent dendrites
fibrous
Which type of astrocyte is composed of GFAP
Both
what is the job of the astrocyte?
removing K+ and transmitter or transmitter components from the extracellular fluid.
The function of astrocytes is facilitated by what?
gap junctions
Astrocyte "end feet" + Blood vessel =
Glial limitans
Nuerovascular unit (NVU) is composed of:
Astrocyte is the bridge b/w the blood supply and the neuron.
What is a critical site of inflammation and changes to the BBB associated with strokes
NVU
The Gilal limitans is a part of what structure?
BBB
Astrocyte can form a syncytium. What is a syncytium?
a continous network via gap junctions
Can proteins and enzymes pass through the astrocyte syncytium?
no
oligodendrocytes exist primarily where?
CNS white matter
oliogodendrocytes are intimately associated with
neuronal axons
What is responsible for myelinating axons in the CNS?
oligodendrocytes
What is responsible for myelinating axons in the PNS
Schwann cells
What is an internode?
area of axon coated by myelin
What is a node of ranvier
short regions of bare axons
Which only myelinates only a single internode of a given axon?
both
Which can myelinate many axons
oligodendrocytes
Which is the least abundant glia cell
microglia
Where are microglia found?
white and gray matter of CNS
which glia cell can transform to a phagocyte
microglia
microglia are responsible for
removing dead cells and debris from the area of injury or inflammations
Which glia cell can myelinate more than one internode?
none.
MS involves which type of glia cell
oligodendrocytes
Schwann cells that do not from myelin and simply surround the axon in the DRG are called
satellite cells
which glia cells secrete neurotrophic factors
schwann and astrocytes
ependymal cells create what?
barriers between compartments
Which gila cell can exhibit auto florescence?
microglia
Are there cells in the brain that can give rise to new neurons in vivo?
yes
Where are the neural precursors located?
subventricular zone(SVZ)
Where is the SVZ
just beneath the lateral ventricles next to the striatum
neuronal precursors can give rise to
neurons, astrocytes, oligodendrocytes in the CNS
a stem cell must be ____ and ____
self-renewing and totipotent
self-renewing means
the ability to give rise to daughter cells that retain the equivalent "stem-ness"
totipotent means
the cell can give rise to every tissue in the body
new neurons are thought to be in greater number following:
voluntary activity; running for example
Proof of new neurons was first found in what special sense
olfactory
New neurons can be found where in the adult rat and sub-human primate
hippocampus, in particular the denate gyrus
New neurons in human migrate from ____ to ___ ___ and ____ ____
SVZ; olfactory bulb; olfactory epithelium
Cells of Nervous System
Neurons, glia, Schwann
Majority of Neuron Shape
Multipolar
Majority of Sensory shapes
Bipolar or pseudo-unipolar
Which shapes have no dendrites (per se)
Bipolar and pseudo-unipolar
____ carries info to other neurons
Axons
____ receive synapses from other neurons
Dendrites
Bipolar cells are for what special sense
optic and olfactory
___ is the primary sensory neuron type and located in ____
Psudo-unipolar; DRG
The shape of a neuron is maintained by?
cytoskeleton
Cytoskeleton is composed of
microtublues, neurofilaments, and microfilaments
Which component of the cytoskeleton is the largest?
microtubules
function of MAPS
assembly and disassembly of microtubules
What is a common target for immunocytochemical stains specific for neurons?
MAPS
Which cells do not contain microtubules and MAPS?
glia and schwann
Which component of the cytoskeleton is composed of cytokeratins?
neurofilaments
Which components of the cytoskeleton are involved in axoplasmic flow?
Neuronfilaments and microtubules
what are neurofibrillary tangles (as in Alzheimer's Disease)
a dense build-up of disorganized filaments resulting from a disruption of the assembly/disassembly of neurofilaments
Which components of the cytoskeleton is the smallest
microfilaments
Microfilaments are made up of?
actin
Microfilaments are involved in?
growth and remodeling, including formation of growth cones
axon segment closest to the soma aries from
axon hillock
The axon hillock is densely populated with ____ ____ and are important for _____ ___
ion channels; action potentials
Do axons branch?
yes
two most common synapse types
axo-dendritic (most common), axosomatic
axo-axonic and dedro-dendritic are thought to
allow groups of neurons with similar function and location to influence each other
Fast anterograde transports:
vesicles and organelles
Slow anterograde transports:
cytoskeleton components, proteins
fast retrograde transports:
lysosomes, organelles and proteins
Where are neurotransmitters made?
soma and terminal boutons
In a cortical or hippocampal pyramidal neuron myelin covers only:
the axon proper
Dale's principle states:
each terminal can only express one transmitter
Is Dale's principle still true?
no
What modification was made to Dale's principle?
all terminal release the same "profile of transmitters (even this may not be true)
Which synapses is + or -
axosomatic and axodendritic
which synapse is mostly -
axoaxonic
What is the most abundant type of glia
Astrocytes
What are the two types of astrocytes
protoplasmic and fibrous
which type of astrocyte is found in contact with the neuronal somata and dendrites?
protoplasmic
which type of astrocyte provides structural and metabolic support
protoplasmic
which type of astrocyte is found in the CNS white matter
Fibrous
which type of astrocyte is in contact with axons and to a lesser extent dendrites
fibrous
Which type of astrocyte is composed of GFAP
Both
what is the job of the astrocyte?
removing K+ and transmitter or transmitter components from the extracellular fluid.
The function of astrocytes is facilitated by what?
gap junctions
Astrocyte "end feet" + Blood vessel =
Glial limitans
Nuerovascular unit (NVU) is composed of:
Astrocyte is the bridge b/w the blood supply and the neuron.
What is a critical site of inflammation and changes to the BBB associated with strokes
NVU
The Gilal limitans is a part of what structure?
BBB
Astrocyte can form a syncytium. What is a syncytium?
a continous network via gap junctions
Can proteins and enzymes pass through the astrocyte syncytium?
no
oligodendrocytes exist primarily where?
CNS white matter
oliogodendrocytes are intimately associated with
neuronal axons
What is responsible for myelinating axons in the CNS?
oligodendrocytes
What is responsible for myelinating axons in the PNS
Schwann cells
What is an internode?
area of axon coated by myelin
What is a node of ranvier
short regions of bare axons
Which only myelinates only a single internode of a given axon?
both
Which can myelinate many axons
oligodendrocytes
Which is the least abundant glia cell
microglia
Where are microglia found?
white and gray matter of CNS
which glia cell can transform to a phagocyte
microglia
microglia are responsible for
removing dead cells and debris from the area of injury or inflammations
Which glia cell can myelinate more than one internode?
none.
MS involves which type of glia cell
oligodendrocytes
Schwann cells that do not from myelin and simply surround the axon in the DRG are called
satellite cells
which glia cells secrete neurotrophic factors
schwann and astrocytes
ependymal cells create what?
barriers between compartments
Which gila cell can exhibit auto florescence?
microglia
Are there cells in the brain that can give rise to new neurons in vivo?
yes
Where are the neural precursors located?
subventricular zone(SVZ)
Where is the SVZ
just beneath the lateral ventricles next to the striatum
neuronal precursors can give rise to
neurons, astrocytes, oligodendrocytes in the CNS
a stem cell must be ____ and ____
self-renewing and totipotent
self-renewing means
the ability to give rise to daughter cells that retain the equivalent "stem-ness"
totipotent means
the cell can give rise to every tissue in the body
new neurons are thought to be in greater number following:
voluntary activity; running for example
Proof of new neurons was first found in what special sense
olfactory
New neurons can be found where in the adult rat and sub-human primate
hippocampus, in particular the denate gyrus
New neurons in human migrate from ____ to ___ ___ and ____ ____
SVZ; olfactory bulb; olfactory epithelium
Neurons
Receive and transmit information
cellular organelles
carry out functions in the soma
Plasma membrane
permeable
cytoplasm
fluid that fills the cell
nucleus
"brain" of the cell, holds DNA
mitochondria
Creates energy for the cell, requires oxygen to function, does contain some DNA inherited from mom
Lysosomes
processes cellular waste
microtubules
transporters, tubes that carry info throughout the cell
neuronal specialization
how neurons are different from other cells in the body
Dendrites
sites of incoming info called receptors
spines
cover dendrites & mediate learning and memory
more surface area
more information received
Axons
1 per neuron
Axon Hillock
junction between soma and axon (may be a meter or more in length)
Myelin Sheath
fatty insulator speeding up signal
nodes of Ranvier
space between myelin
terminal bouton
releases chemical messages
Bundles of axons
PNS- nerve
CNS- tract
Types of neurons
motor neurons, sensory neurons, interneurons,
motor neurons
CNS--> PNA : brain to muscles
runs from spinal cord to muscle
soma in the spine
Sensory neurons
PNS--> CNS: muscles to brain
dendrites with specialized receptors for sensory info
interneurons
facilitates communication between neurons, small axons because contained in a single brain region
Glia
Smaller than neurons, outnumber neurons, Exchange chemical messages to adjacent neurons
types of glia
microglia, astrocytes, schwann cells, oligodentrocytes
microglia
part of the immune system: phagocytes- assassinates invaders by digestion, proliferate in response to injury or disease to help remove waste
astrocytes
facilitate neuronal communication, divide in response to injury or disease, provide neurotrophins to neurons, remove wastes and excess neurotransmitter, clean-up crew
Schwann Cells
myelinate axons in the PNS (ex: motor neurons) - causes multiple sclerosis
oligodendrocytes
myelinate axons in the CNS
The Blood-Brain Barrier
Protection from viruses, bacteria & chemicals
cannot protect from rabies
Endothelial Cells
make up brain blood vessels are rightly packed
What gets passed the BBB
small, uncharged molecules (ex= oxygen, carbon dioxide & water), fat-soluble (molecules ex: drugs)
Active Transport
protein-mediated pump
requires energy
glucose, amino acids, vitamins, hormones
area postrema
base of the brain, guards the BBB, toxin detection includes vomiting
Action potential
Nerve impulse from axonal membrane that enables it to conduct a special type of signal that overcomes biological constraints. Action potentials do not diminish over distance and they are signals of fixed size and duration. Information is encoded in the frequency of action potentials as well as in the distribution and number of neurons firing action potentials in a given nerve. The action potential causes the resting membrane to become positively charged with respect to the outside- about a thousandth of a second.
Excitable Membrane
Cells capable of generating and conducting action potentials which include both nerve and muscle cells.
Resting Membrane Potential
In a resting neuron, the cytosol along the inside surface of the membrane has a negative electrical charge compare to the outside.
Intracellular fluid and Extracellular Fluid
Water is the main ingredient in intracellular and the fluid that bathes the neurons is the most important in extracellular.
Water
The most important property of H2O is its uneven distribution of electrical charge. H2O is a polar molecule held together by polar covalent bonds. This electrical polarity makes water an effective solvent of other charged or polar molecules; that is, other polar molecules tend to dissolve in water.
Ionic Bonds
NaCl is an ionic bond because they are electrically attracted to each other. NaCl or salt readily dissolvs in water because the charged portions of the water molecule have a stronger attraction for the ions than they have for each other. When broken apart the Na+ will be covered by water molecules oriented so that the oxygen atom will face the ion and the hydrogen atoms face the chloride ions
Monovalent
When the difference in the ion is 1
Divalent
When the ion difference is 2
Cations & Anions
Cations are positively charged and Anions are negatively charged.
Hydrophillic
"Water loving compounds like polar molecules or ions
Hyrophobic
Water fearing compounds like non-polar covalent bonds. Olive oli and water dont mix. Also lipids, a class of water insoluble bioliglc molecules important to the structure of cell membranes. Lipids form a barrier to the water and water ions.
Phospholipid
The main chemical building blocks of cell membranes are phospholipids. They contain long nonpolar chains of carbon atoms bonded to hydrogen atoms. In addition, it contains a polar phosphate group. Phospholipids contain a polar head which has the phosphate and a nonpolar tail which contains the hydrocarbons.
Phospholipid bilayer
it effectively isolates the cytosol of the neuron from the extracellular fluid.
Protein
The type and distribution of protein molecules distinguish neurons from other types of cells. Enzymes, cytoskeleton and receptors are all made of protein. The resting and action potential depend on special proteins that span the phospholipid bilayer. These proteins provide routs for ions to cross the neuronal membrane.
Amino Acid Structure
All have a central carbon ato (alpha carbon) which is covalently bonded to four molecular groups, a hydrogen atom, an amino group (NH3+), a carboxyl group (COO-) and a variable group called the R group.
Peptide bonds
Proteins are synthesized by the ribosomes of the neuronal cell body. Amino acids assemble into a chain.
Polypeptides
Proteins made of a single chain of amino acids are also called polypeptides.
How many levels of protein structure are there?
Four
Primary Structure of Proteins:
It is like a chain, in which the amino acids are linked together by peptide bonds.
Secondary Structure of Proteins
As the protein molecule, the polypeptide chain can coil into a spiral-like configuration called an alpha helix.
Tertiary Structure of Proteins
Interactions among the R groups can cause the molecule to change even further. Proteins can bend, fold, and assume a globular shape.
Quarternary Structure of Proteins
Different polypeptide chains can bond together to form a larger molecule. One it gets into the quarternary structure it is called a subunit.
Ion Channels
Are made from just these sorts of membrane-spanning molecules. Typically a functional channel across the membrane require that 4-6 similar protein molecules assemble to form a pore between them
Ion Selectivity & Gating
One important property of most ion channels, specified by the diameter of the pore and the nature of the R groups linking. Another important property of many channels is gating
Ion Pumps
Enzymes that use the energy released by the breakdown of ATP to transport certain ions across the membrane.
What influences ionic movements through channels?
Diffusion and Electricity
Diffusion
A net movement of ions from regions of high concentration to regions of low concentration. Ions typically do not move through a phospholipid bilayer but diffusion will cause ions to be pushed through channels in the membrane.
Concentration Gradient
Differences in concentration
Driving ions across the membrane by diffusion happens when...
The membrane possess channels permeable to the ions and there is a concentration gradient across the membrane.
Electrical Current (I)
The movement of electrical charge.
Two Important Factors of Electrical Current
Electrical Potential & Electrical Conductance
Electrical Potential (V)
Also called voltage is the force exerted on a charged particle, and it reflects the difference in charge between the anode and the cathode. More current will flow as this differance is increased.
Electrical Conductance (g)
Is the relative ability of an electrical charge to migrate from one point to another.
Electrical Resistance (R)
The relative inability of an electrical charge to migrate.
Ohm's Law
The relationship among potential (V), conductance (g) and current (I). Current is the product of the conductance and the potential difference
Ohm's Law I=gV
Driving an ion across a membrane electrically requires...
The membrane possesses channels permeable to that ion and that there is an electrical potential difference across the membrane.
Membrane Potential
The voltage across the neuronal membrane at any moment, represented by the symbol Vm. Sometimes it is "at rest" other times it is not (during an action potential.
Microelectrode
A thin glass tube with an extremely fine tip that van measure the Vm. By using an electrode to measure potential the method reveals that the electrical charge is unevenly distributed across the neuronal membrane
Resting Membrane Potential of a typical neuron
It is about -65 millivolts. It needs to be negative because it is the absolute requirement for a functioning nervous system.
Ionic Equilibrium Potential
The electrical potential difference that exactly balances an ionic concentration gradient.
Four Important Points about Membrane Potentials
Large changes in membrane potential are caused by miniscule changes in ionic concentrations. The net difference in electrical charge occurs at the inside and outside surfaces of the membrane. Ions are driven across the membrane at a rate proportional to the difference between the membrane potential and the equilibrium potential. And If the concentration difference across the membrane is known for an ion, an equilibrium potential can be calculated for that ion.
Ionic Driving Force
The difference between the real membrane potential and the equilibrium potential.
Distribution of Ions Across the Membrane
K+ is more concentrated on the inside and Na+ and Ca2+ are more concentrated on the outside.
How do concentration gradients arise?
Ionic concentration gradients are established by the actions of ion pumps in the neuronal membrane.
Sodium-Potassium Pump
Is an enzyme that breaks down ATP in the presence of internal Na+. The chemical energy released by this reaction drives, this pump, exchanges internal Na+ for external K+. The actions of this pump ensure that K+ is concentrated inside the neuron and that Na+. The pump pushes these ions across the membrane against their concentration gradients. Expends about 70% of the total amount of ATP utilized.
Calcium Pump
Is also an enzyme that actively transports Ca2+ out of the cytosol across the cell membrane. Without ion pumps the resting membrane potential would not exist and the brain would not function. .
Why the resting membrane potential is not -80mV like K+?
The resting membrane potential of -65 mV appraoches, but does not achieve the potassium equilibrium potential of -80mV . This difference arises because although the membrane at rest is higly permeable to K+ there is also a steady leak of Na+ into the cell.
Goldmann equation
A mathematical formula that takes into consideration the relative permeability of the membrane to different ions. If we concern ourselves only with K+ and Na+, use the ionic concentraions and assume that the resting membrane permeability to K+ is fortyfold greater than it is to Na+ then the Goldman equation predicts a resting membrane potential of -65 mV the observed value.
UCSF
Student succeeded in determining the amino acid sequences of a family of potassium channels. The search was conducted using the fruit fly Drosophila Melanogaster.
Membrane Potential Permeability
Because the neuronal membrane at rest is mostly permeable to K+ the membrane potential is close to Ek. Membrane potential is particularly sensitive to changes in the concentration of extracellular potassium.
Depolarization
A change in membrane potential from the normal resting value -65 mV to a less negative value.
Blood-brain barrier & Glia
A specialization of the walls of brain capillaries that limits the movement of potassium and other bloodborne substances into the extracellular fluid of the brain. Glia, particulary astrocytes also possess efficient mechanisms to take up extracellular K+ whenever concentrations rise, as they normally do during periods of neural activity. Astrocytes have membrane potassium pumps that concentrate K+ in their cytosol andthey also have potassium channels
Potassium Spatial Buffering
The mechanism for the regulation of initial K+ by astrocytes.
Astrocytes
provide physical support and TRANSPORT nutrients to neurons
Oligodendroglia
Provide physical support and form the myelin sheath CNS axons
Schwann Cells
form myelin for PNS axons
Microglia
involved in Phagocytosis and brain immune function
Peripheral nerves
the parallel bundles of axons surrounded by connective tissue sheaths
Endoneurium
separates individual axons
Perineurium
surrounds fascicles (bundles of axons)
Epineurium
encloses entire nerve trunk
Leak Channels
a small number of ions diffuse across the cell membrane
Modality Channels
sensory neuron reacting to detecting Mechanical Force, temperature, or chemical changes
Ligand-gated Channels
Channel opens when neurotransmitter binds to receptor site, generates Local Potential
Voltage-gated channels
structural change of the channel due to the Electrical potential. opens and closes quickly
Electrical Potential
the difference in electrical charge across the membrane, 3 types of electrical potential: resting membrane potential, local potential, and action potential
Resting Membrane Potential
Difference in voltage between the inside and outside of the axon membrane when the neuron is not transmitting any information, no net change in ions across the membrane
Local potential
the change in voltage that spreads only a short distance, originates at receiving sites: sensory neurons-- sensory receptors, and motor neurons & interneurons -- at post synaptic membrane
Action potentials
a large depolarizing signal along the axon, starts at the axon hillock, all or none, sudden influx of Na+ through voltage-gated channels. Depolarization must reach threshold of -55 mV
Electrochemical transmission
Dendrites receive chemical message from adjoining cells, chemical messangers activate receptors on the dendritic membrane, receptor activation opens ion channels, which can alter membrane potential, action potential can result which is propegated down the membrane, presynaptic terminal depolarizes opening voltage-gated CA++ channels, CA++ triggers movement of neurotransmitter vesicles, synaptic vessicles fuse with presynaptic terminal, Action Potential causes RELEASE of transmitter from Axon terminals
Neurotransmitter Release
influenced by: the number of action potentials, duration of the stimulus to presynaptic cell, increase in the level of the strength of the stimulus
Excitatory postsynaptic potential (EPSP)
Depolarization, Na+ or CA++ i.e. Acetylcholine at the neuromuscular junction
Inhibitory Postsynaptic Potential (IPSP)
Cl- flow into neuron or K+ flow out of neuron, hyperpolarization* i.e. GABA
Axodendritic synapse
synaptic contact between axon and dendrite
Axosomatic synapse
synaptic contact between axon and soma
Axoaxonic synapse
synaptic contact between axon and axon
Rising Phase
Phase after neuron reaches threshold where it is rapidly depolarized by voltage gated sodium channels opening
Overshoot
When the neuron is positively charged which comes after the rising phase
Falling Phase
When the neuron re-polarizes after hitting the over shoot. Caused by VG sodium channels closing and VG potassium channels opening
Undershoot
When the neuron's potential is lower than the resting potential which comes after the falling phase.
After-hyperpolarization
Another word for undershoot
Threshold
The minimum potential a neuron needs to reach to release an action potential
Absolute refractory period
The period of time after an action potential is sent where it is impossible to send another action potential
Relative refractory period
The period of time after an action potential is sent where it is harder but not impossible to send another action potential. Comes after the absolute refractory period
Voltage Clamp
device by Kenneth C. Cole that allowed the membrane potential of an axon at any value they close. Used it to deduce changes in membrane conductance at different membrane potential.
Voltage-Gated Sodium Channel
Protein that creates a pore that's highly selective to Na+ ions and opens/closes by changes in electrical potential of the membrane.
Reason why rise phase is so fast after threshold
Patch Clamp
New method by Neher to study the functional properties of the VG sodium channel by studying the ionic currents passing through one channel
Channelopathy
Human genetic diseases such as epilepsy that is due to a change in the structure or function of ion channels
Tetrodotoxin (TTX)
A toxin that blocks VG sodium channels by binding tightly to a specific site outside of the channel
Voltage-gated Potassium Channel
Protein that creates a pore that's highly selective to potassium ions and opens/closes by changes in electrical potential of the membrane.
One of the reasons why the falling phase occurs
Saltatory Conduction
The action potential propagation where it leaps from node to node.
Spike-initiation Zone
Region where the action potential starts. Typically at the axon hillock but on sensory neurons, its on the sensory nerve ending so that it can propagate up.