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Chapter 8-Neurons: Cellular and Network Properties

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Action potential
AP, spike, nerve impulse, conduction signal
Autonomic nervous system
Visceral nervous system
Axon
Nerve fiber
Axonal transport
Axoplasmic flow
Axon Terminal
Synaptic knob, synaptic bouton, presynaptic terminal
Axoplasm
Cytoplasm of an axon
Cell Body
Cell soma, nerve cell body
Cell membrane of an axon
Axolemma
Glial cells
Neuroglia, glia
Interneuron
Association neuron
Rough endoplasmic reticulum
Nissl substance, Nissl body
Sensory neuron
Afferent neuron, afferent
Central Nervous System (CNS)
consists of the brain and the spinal cord
Peripheral Nervous System (PNS)
consists of sensory (afferent) neurons and efferent neurons.
1. Sensory afferents carry messages from sensory receptors to CNS. Their cell bodies are located close to the CNS.

2. Interneurons are completely contained within the CNS are often extensively branched.

3. Efferents carry signals from the CNS to the effectors. They have short, branched dendrites and long axons.
List the three functional classes of neurons and explain how they differ structurally and functionally.
skeletal muscles
Somatic motor neurons control_________.
autonomic
_________ neurons control smooth and cardiac muscles, glands and some adipose tissue.
sympathetic or parasympathetic
Autonomic neurons are classified as either _______ or ________ neurons.
3. long process that transmits signals to the target cell.
Match the term with its description

A. axon

1. process of a neuron that receives incoming signals.
2. sensory neuron, transmits information to CNS
3. long process that transmits signals to the target cell.
4. region of neuron where action potential begins.
5. neuron that transmits information from CNS to the rest of the body.
1. process of a neuron that receives incoming signals.
Match the term with its description

B. dendrite

1. process of a neuron that receives incoming signals.
2. sensory neuron, transmits information to CNS
3. long process that transmits signals to the target cell.
4. region of neuron where action potential begins.
5. neuron that transmits information from CNS to the rest of the body.
2. sensory neuron, transmits information to CNS
Match the term with its description

C. afferent

1. process of a neuron that receives incoming signals.
2. sensory neuron, transmits information to CNS
3. long process that transmits signals to the target cell.
4. region of neuron where action potential begins.
5. neuron that transmits information from CNS to the rest of the body.
5. neuron that transmits information from CNS to the rest of the body.
Match the term with its description

D. efferent

1. process of a neuron that receives incoming signals.
2. sensory neuron, transmits information to CNS
3. long process that transmits signals to the target cell.
4. region of neuron where action potential begins.
5. neuron that transmits information from CNS to the rest of the body.
4. region of neuron where action potential begins.
Match the term with its description

E. trigger zone

1. process of a neuron that receives incoming signals.
2. sensory neuron, transmits information to CNS
3. long process that transmits signals to the target cell.
4. region of neuron where action potential begins.
5. neuron that transmits information from CNS to the rest of the body.
C. movement of organelles and cytoplasm up and down the axon.
Axonal transport refers to the

A. release of neurotransmitters into the synaptic cleft.
B. use of microtubules to send secretions from the cell body to the axon terminal.
C. movement of organelles and cytoplasm up and down the axon.
D. movement of the axon terminal to synapse with a new postsynaptic cell.
E. None of these.
1. all-or-none
4. exhibits a refractory period
Match the numbers of the appropriate characteristics with the two types of potentials. Characteristics may apply to one or both types.

A. Action Potential

1. all-or-none
2. can be summed
3. amplitude decreases with distance
4. exhibits a refractory period
5. amplitude depends on strength of stimulus
6. has no threshold
2. can be summed
3. amplitude decreases with distance
5. amplitude depends on strength of stimulus
6. has no threshold
Match the numbers of the appropriate characteristics with the two types of potentials. Characteristics may apply to one or both types.

B. Graded potential

1. all-or-none
2. can be summed
3. amplitude decreases with distance
4. exhibits a refractory period
5. amplitude depends on strength of stimulus
6. has no threshold
1. astrocytes
4. oligodendrocytes
Match the glial cell on the right to the functions on the left. There may be more than one correct answer for each function.

A. modified immune cells

1. astrocytes
2. ependymal cells
3. microglia
4. oligodendrocytes
5. satellite cells
6. Schwann cells
1. astrocytes
Match the glial cell on the right to the functions on the left. There may be more than one correct answer for each function.

B. help form the blood-brain barrier

1. astrocytes
2. ependymal cells
3. microglia
4. oligodendrocytes
5. satellite cells
6. Schwann cells
4. oligodendrocytes
6. Schwann cells
Match the glial cell on the right to the functions on the left. There may be more than one correct answer for each function.

C. form myelin

1. astrocytes
2. ependymal cells
3. microglia
4. oligodendrocytes
5. satellite cells
6. Schwann cells
2. ependymal cells
Match the glial cell on the right to the functions on the left. There may be more than one correct answer for each function.

D. separate CNS fluid compartments

1. astrocytes
2. ependymal cells
3. microglia
4. oligodendrocytes
5. satellite cells
6. Schwann cells
5. satellite cells
6. Schwann cells
Match the glial cell on the right to the functions on the left. There may be more than one correct answer for each function.

E. found in peripheral nervous system

1. astrocytes
2. ependymal cells
3. microglia
4. oligodendrocytes
5. satellite cells
6. Schwann cells
5. satellite cells
Match the glial cell on the right to the functions on the left. There may be more than one correct answer for each function.

F. found in ganglia

1. astrocytes
2. ependymal cells
3. microglia
4. oligodendrocytes
5. satellite cells
6. Schwann cells
1. Na+ channels (voltage-gated alon axon; any type of gating on dendrites)

2. Voltage gated K+ channels along axon

3. Voltage-gated CA2+ channels in axon terminal

4. Chemically gated Cl- channels
List the four types of ion channels found in neurons. Are they chemically gated, mechanically gated, or voltage-gated?
E. Sensory organ detects change in the environment.

B. Afferent neuron reaches threshold and fires an action potential.

D. Integrating center reaches decision about response.

A. Efferent neuron reaches threshold and fires an action potential.

C. Effector organ responds by performing output.
Arrange the following events in the proper sequence:

A. Efferent neuron reaches threshold and fires an action potential.
B. Afferent neuron reaches threshold and fires an action potential.
C. Effector organ responds by performing output.
D. Integrating center reaches decision about response.
E. Sensory organ detects change in the environment.
B. the same size and shape at the beginning and end of the axon.

D. transmitted to the distal end of a neuron and causes release of neurotransmitter.
An action potential is (can be more than one.)

A. a reversal of the Na+ and K+ concentrations inside and outside the neuron.
B. the same size and shape at the beginning and end of the axon.
C. initiated by inhibitory postsynaptic graded potentials.
D. transmitted to the distal end of a neuron and causes release of neurotransmitter.
The resting cell membrane is more permeable to__K+__ than to___Na+___. Although __Na+___ contributes little to the resting membrane, potential they play a key role in generating electric signals in excitable tissues.
Choose from the following ions to fill in the blanks correctly: Na+, K+, Ca (2+), Cl-

A. The resting cell membrane is more permeable to__________ than to____________. Although _________ contribute little to the resting membrane, potential they play a key role in generating electric signals in excitable tissues.
The concentration of ___Na+_ is 12 times greater outside the cell than inside.
Choose from the following ions to fill in the blanks correctly: Na+, K+, Ca (2+), Cl-

B. The concentration of _______ is 12 times greater outside the cell than inside.
The concentration of ___K+__ is 30 times greater inside the cell than outside.
Choose from the following ions to fill in the blanks correctly: Na+, K+, Ca (2+), Cl-

C. The concentration of ________ is 30 times greater inside the cell than outside.
An action potential occurs when __Na+__ enter the cell.
Choose from the following ions to fill in the blanks correctly: Na+, K+, Ca (2+), Cl-

D. An action potential occurs when _______ enter the cell.
The resting membrane potential is due to the high __K+__ permeability of the cell.
Choose from the following ions to fill in the blanks correctly: Na+, K+, Ca (2+), Cl-

E. The resting membrane potential is due to the high _______ permeability of the cell.
Insulating membranes around neurons that prevent current leak.
What is the myelin sheath?
1. Larger axon diameter
2. the presence of myelin
List two factors that enhance conduction speed.
1. enzymatic degradation
2. reabsorption
3. diffusion
List three ways neurotransmitters are removed from the synapse.
Threshold
Label 1
Depolarization
Label 2
Repolarization
Label 3
Refractory Period
Label 4
D. Na+ entering the cell through voltage-gated channels
What causes the depolarization phase of an action potential? (Can be more than one answer)

A. K+ leaving the cell through voltage-gated channels
B. K+ being pumped into the cell by the Na+ -K+ -ATPase
C. Na+ being pumped into the cell by the Na+-K+-ATPase
D. Na+ entering the cell through voltage-gated channels
E. opening of the Na+ channel inactivation gate
1
2
3
4
20 Name any four neurotransmitters, their receptor(s), and tell whether the receptor is an ion channel or a GPCR.
F. ligand-gated ion channel opens

C. cell depolarizes

G. local current flow occurs

E. graded potential occurs

B. trigger zone reaches threshold

K. voltage-gated Na+ channels open.

C. cell depolarizes

A. action potential fires at axon hillock.

H. salutatory conduction occurs

J. voltage-gated K+ channels open

I. Voltage-gated Ca2+ channels open

D. exocytosis
Arrange the following terms to describe the sequence of events after a neurotransmitter binds to the receptor on the postsynaptic neuron. Terms may be used more than once or not at all.

A. action potential fires at axon hillock.
B. trigger zone reaches threshold
C. cell depolarizes
D. exocytosis
E. graded potential occurs
F. ligand-gated ion channel opens
G. local current flow occurs
H. salutatory conduction occurs
I. Voltage-gated Ca2+ channels open
J. voltage-gated K+ channels open
K. voltage-gated Na+ channels open.
depolarize
Match the best term (hyperpolarize, depolarize, repolarize) to the following events. The cell in question has a resting membrane potential of -70 mV.

A. membrane potential changes from -70 mV to -50 mV
hyperpolarize
Match the best term (hyperpolarize, depolarize, repolarize) to the following events. The cell in question has a resting membrane potential of -70 mV.

B. membrane potential changes from -70 mV to -90 mV
repolarize
Match the best term (hyperpolarize, depolarize, repolarize) to the following events. The cell in question has a resting membrane potential of -70 mV.

C. membrane potential changes from +20 mV to -60 mV
depolarize
Match the best term (hyperpolarize, depolarize, repolarize) to the following events. The cell in question has a resting membrane potential of -70 mV.

D. membrane potential changes from -80 mV to -70 mV
Depolarize
A neuron has a resting membrane potential of -70 mV. Will the neuron hyperpolarize or depolarize when each of the following events occurs? (More than one answer may apply; list all those that are correct)

A. Na+ enters the cell
Hyperpolarize
A neuron has a resting membrane potential of -70 mV. Will the neuron hyperpolarize or depolarize when each of the following events occurs? (More than one answer may apply; list all those that are correct)

B. K+ leaves the cell
Hyperpolarize
A neuron has a resting membrane potential of -70 mV. Will the neuron hyperpolarize or depolarize when each of the following events occurs? (More than one answer may apply; list all those that are correct)

C. Cl- enters the cell
Depolarize
A neuron has a resting membrane potential of -70 mV. Will the neuron hyperpolarize or depolarize when each of the following events occurs? (More than one answer may apply; list all those that are correct)

D. Ca2+ enters the cell
Strength is coded by the frequency of action potentials; duration is coded by the duration of a train of repeated action potentials.
If all action potentials within a given neuron are identical, how does the neuron transmit information about the strength and duration of the stimulus.
B. conduct impulses more rapidly.
The presence of myelin allows an axon to

A. produce more frequent action potentials.
B. conduct impulses more rapidly.
C. produce action potentials of larger amplitude.
D. produce action potentials of longer duration.
neurons and glial cells
Name the two primary cell types found in the nervous system.
somatic motor division
Controls skeletal muscles
autonomic division
Controls smooth and cardiac muscles, exocrine glands, some endocrine glands, and some types of adipose tissue.
sympathetic branch
"fight or flight"
conditions of high stress
mostly stimulatory

Speeds up and energy is used.
parasympathic branch
Division of the autonomic nervous system that is responsible for the day-to-day activities activities.

Slows down and energy is conserved.
Dendritic spines
Identify 1
cell body
Identify 2
Axon
Identify 3
Telodendria
Identify 4
Synaptic terminals
Identify 5
fast axonal transport
Moves organelles at rates of up to 400 mm per day. Uses stationary microtubules as tracks along which transported vesicles and mitochondria "walk" with the aid of attached footlike motor proteins powered by ATP.
slow axonal transport
Moves material by axoplasmic flow from the cell body to the axon terminal. Can be used only for components that are not consumed rapidly by the cell, such as enzymes and cytoskeleton proteins.
Anterograde Flow
Forward flow. Moves synaptic and secretory vesicles and mitochondria from the cell body to the axon terminal.
Retrograde Flow
Backward flow. Returns old cellular components from the axon terminal to the cell body for recycling.
Synapse
Site of intracellular communication. The region where an axon terminal meets its target cell. The neuron that delivers a signal to the synapse is the presynaptic cell and the cell that receives the signal is the postsynaptic cell. The narrow space between the two cells is the synaptic cleft.
List all the types of Neuroglia
1. Satellite cells
2. Schwann Cells
3. Oligodendrocytes
4. Astrocytes
5. Microglia
6. Ependymal cells
Which types of Neuroglia are found in the PNS
1. Satellite cells
2. Schwann cells
Which types of Neuroglia are found in the CNS
1. Oligodendrocytes
2. Astrocytes
3. Microglia
4. Ependymal cells

"Only Anna Makes Empanada"
What is one function of a satellite cells?
What is one function of a schwann cells?
What is one function of an oligodendrocytes?
What is one function of an astrocyte?
What is one function of a Microglia?
What is one function of an ependymal cells?
What cells do the equivalent of the Schwann cell in the CNS?
oligodendrocytes
What is a nerve impulse?
Electrical messages produced and conducted by neurons. Nerve impulses result from movement of ions (electrically charged particles) in and out through the plasma membrane of neurons.
What are the types of gated ion channels?
1. Mechanically gated
2. Chemically Gated
3. Voltage-Gated
Mechanically gated
Found in sensory neurons and open in response to physical forces such as pressure or stretch.
Chemically gated
In most neurons, respond to a variety of ligands, such as extracellular neurotransmitters and neuromodulators or intracellular signal molecules.
Voltage-Gated
Respond to changes in the cell's membrane potential.
Resting Membrane Potential
is determined by the K+ concentration gradient and the cell's resting permeability to K+, Na+, and Cl-. Difference in charge on either side of the resting neuron membrane.
What causes depolarization?
loss (sometimes even reversal) of polarization due to
rapid opening of Na+ channels
What causes repolarization?
recovery of the resting membrane potential due
to the slower opening of K+ channels and the closing of Na+ channels
What causes hyperpolarization?
increase in the negativity of the resting potential
(K+ channels open)
Graded Potentials
variable strength signals that travel over short distances and lose strength as they travel through the cell.
Action Potentials
brief large depolarizations that travel for long distances through a neuron without losing strength. Appears in the initial segment of the axon.
Compare action and graded potentials.
Stages of action potential.
Step One of Action Potential
"Depolarization to Threshold"

A graded depolarization brings an area of excitable mebrane to threshold (-60mV)
Step Two of Action Potential
"Activation of Sodium Channels and Rapid Depolarization"

1. The voltage-regulated sodium channels open (sodium channel activation)
2. Sodium ions, driven by electrical attraction and the chemical gradient, flood into the cell.
3. The transmembrane potential goes from -60 mV, the threshold level, toward +30 mV.
Step Three of Action Potential
"Inactivation of Sodium Channels and Activation of Potassium Channels"

1. the voltage-regulated sodium channels close (sodium channel inactivation occurs) at +30 mV.
2. The voltage-regulated potassium channels are now open, and the potassium ions diffuse out of the cell.
3. Repolarization begins.
Step Four of Action Potential
"Return to Normal Permeability"

1. The voltage regulated sodium channels regain their normal properties in 0.4-1.0 msec. The membrane is now capable of generating another action potential if a larger than normal stimulus is provided.

2. The voltage regulated potassium channels begin closing at -70 mV. Because they do not all close at the same time, potassium loss continues and a temporary hyperpolarization to approximately -90 mV occurs.

3. At the end of the relative refractory period, all voltage-regulated channels have closed and the membrane is back to its resting state.
Hyperkalemia
Shifts the resting membrane potential of a neuron closer to threshold and causes the cells to fire action potentials in response to smaller graded potentials.
Saltatory Conduction
Meaning to leap. Apparent jump of the action potential from node to node.
Continuous Conduction
signals that are conducted down unmyelinated axons :are slower
Information flow through the nervous system follows the basic pattern of a reflex:
Stimulus--- sensor--- input signal--- integrating center--- output signal--- target--- response
Dendrites:
Thin, branched processes that receive and transfer incoming information to an integrating region within the neuron.
Cell body:
Part of the cell that contains the nucleus and many organelles
Axon:
An extension of a neuron that carries signals to the target cell
axon terminal
swelling at each collateral end, contains mitochondria and membrane bound vesicles filled with neurocrine molecules
Synapse:
Region where an axon terminal meets its target cell
Myelin Sheath
Concentric layers of cell membrane that wrap around and insulate axons.
Axon hillock:
Region of the axon where it joins the cell body. Often contains the trigger zone.
Schwann cell
Cell that forms myelin around a a peripheral neuron axon
Sensory Neurons:
Pseudounipolar and bipolar. Dendrites, schwann cells, cell body, and axon
Interneurons of CNS
Anaxonic and multipolar. Dendrites, axon, and cell body
Efferent neurons
Multipolar. Dendrites, axon, cell body, schwann cells
axon transport
a process that moves proteins down the axon
Fast axonal transport:
Rapid movement of particles along an axon using microtubules and kinesin foot proteins. Neuron uses stationary microtubules as tracks along which transported vesicles and mitochondria walk with the aid of attached footlike motor proteins. Goes 2 directions, forward and backwards
Slow axonal transport:
Moves material by axoplasmic (cytoplasmic) flow from the cell body to the axon terminal. Used only for components that are not consumed rapidly by the cell like enzymes and cytoskeleton proteins.
Anterograde flow:
(forward) fast transport of vesicles and mitochondria from cell body to axon terminal
Retrograde flow:
(backward) transport returns old cellular components from the axon terminal to the cell body for recycling.
Main components of the synapse
presynaptic cell, postsynaptic cell, synaptic cleft
Presynaptic cell
Neuron that delivers a signal to the synapse
Postsynaptic cell
the cell that receives the signal
Synaptic cleft
narrow space between the two cells
Glial cells-(glia-glue)
non-excitable support cells of the CNS (communicate, biochemical support), only communicate through chemical signals
Peripheral Nerve injury is facilitated by what cells?
Schwann Cells
Cells that have an equivalent job in the CNS as schwann cells are...
Oligodendrocytes (both form myelin sheaths). PNS, myelinate one axon and (Oligodendrocytes)-CNS, myelinate several axons
Nerve Impulse
electrical messages produced and conducted by neurons. Result from movement of ions (electrically charged particles) in and out through the plasma membrane of neurons
Factors causing the difference in charge (4):
1. 30 times more K+ on the inside
2. 15 times more Na+ on the outside
3. Large negative ions (ex: proteins) trapped inside the cell
4. K+ leaks out much more quickly than Na+ leaks in
How does graded potential initiate an action potential?
If a depolarizing graded potential is strong enough when it reaches an integrating region within a neuron it then initiates it.
Comparing Graded and Action potential slide 26
GP:
-input signal
-usually dendrites and cell body
-mechanically, chemically, or voltage gated channels
-sodium, chloride, and calcium
-depolarization or hyperpolarization
-depends on stimulus, can be summed
-no min levl required to initiate
-2 signals coming close together in time will sum
-initial stimulus strength is indicated by frequency of a series of action potentials
AP:
-regenerating conduction signal
-trigger zone through axon
-voltage gated channels
-sodium and potassium
-depolarizing
-all or none phenomenon; cannot be summed
-above threshold graded potential at the trigger zone opens ion channels
-threshold stimulus required to initiate
-refractory period: two signals too close together in time cannot sum
Electrical synapse
pass an electrical signal, or current, directly from the cytoplasm of one cell to another through the pores of gap junction proteins (mainly in CNS)
Chemical synapses
vast majority of synapses in NS, which use neurocrine molecules to carry information from one cell to the next (Chemical synapses use neurotransmitters that cross synaptic clefts)
Neurotransmitter release (sequence of events)
1.An AP depolarizes the axon terminal
2.Depolarization opens voltage gated Ca2+ channels, and Ca2+ enters the cell
3.Calcium entering the cell binds to regulatory proteins and initiates exocytosis synaptic vesicle contents
4.Neurotransmitter diffuses across the synaptic cleft and binds with receptors on the postsynaptic cell
5.Neurotransmitter binding initiates a response in the postsynaptic cell
How can the neurotransmitter be removed from the synaptic cleft?
1.) Neurotransmitters can be returned to axon terminals for reuse or transported into glial cells
2.) Enzymes inactivate neurotransmitters breaking them down to acetyl CoA and choline by acetyl cholinesterase
3.) Neurotransmitters can diffuse out of the synaptic cleft
what happens to acetylcholine after it leaves the synapse?
Synthesis and recycling of acetylcholine
1.) Ach is made from choline and acetyl CoA
2.) In the synaptic cleft ACh is rapidly broken down by the enzyme acetylcholinesterase
3.) Choline is transported back into the axon terminal by cotransport with Na+
4.) Recycled choline is used to make more ACh
explain the statement "The stronger the stimulus the more neurotransmitter is released"
A stronger stimulus causes more action potentials per second to arrive at the axon terminal, which in turn results in more neurotransmitter release
Divergence pathway:
a single presynaptic neuron brances, and its collaterals synapse on multiple target neurons (Purkinje cell)
Convergence pathway:
a group of presynaptic neurons provide input to a smaller number of postsynaptic neurons (somatic motor neuron)
Explain how postsynaptic response can be slow or fast depending on the signaling pathway used
-Fast postsynaptic response is always associated with the opening of ion channels
-Fast synaptic potential begins quickly and lasts only a few milliseconds
-Slow postsynaptic response are mediated by G protein-coupled receptors linked to second messenger systems
-Slow synaptic potentials the response of the second messenger pathway takes longer than the direct opening or closing of a channel and last longer seconds to minutes
Excitatory postsynaptic potential EPSP
synaptic potential is depolarizing because it makes the cell more likely to fire an AP
Inhibitory postsynaptic potential IPSP
synaptic potential is hyperpolarizing because hyperpolarization moves the membrane potential farther from threshold and makes the cell less likely to fire an AP
Spatial summation
(spatium-space) occurs when the currents from the graded potentials originate at different locations that nearly simultaneously combines
Temporal summation
occurs when two graded potentials from one presynaptic neuron occur close together in time
Post synaptic inhibition-occur when a
presynaptic neuron releases an inhibitory neurotransmitter onto a postsynaptic cell and alters its response. (2 EPSP and 1 IPSP=No AP)
Presynaptic inhibition-
if activity in an inhibitory neuron decreases neurotransmitter release, allows selective modulation of collaterals and their targets, one collateral can be inhibited while others remain unaffected
Postsynaptic inhibition
if a neuron synapses on the dendrites and cell body of a neuron, the responsiveness of the entire postsynaptic neuron is altered, all target cells are affected equally