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104 terms

Nervous System Cells

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Divisions of the Nervous system:
CNS, PNS, ANS:
Central Nervous System (CNS):
-Structure and Function center of the entire nervous system
-Consists of the brain and the spinal cord.
-Integrates sensory information, evaluates in and sends out a response.
Peripheral Nervous System (PNS):
-Nerves that lie in outer regoins of the nervous system.
-Cranial nerves comes from the brain
-Spinal nerves comes from the spinal cord.
Afferent division:
consists of all incoming sensory pathways
More information about the different primary afferent axons:
A-alpha nerve fibers carry information related to muscle sense.
A-beta nerve fibers carry information related to touch.
A-delta nerve fibers carry information related to pain and temperature.
C-nerve fibers carry information related to pain, temperature and itch.
Efferent division:
consists of all outgoing motor pathways
Autonomic Nervous System (ANS):
carries information to the autonomic (involuntary) effectors (smooth and cardiac muscles). -Efferent division of the ANS carries information to the autonomic (involuntary) effectors (smooth and cardiac muscles).
Two divisions in the ANS:
Sympathetic division
Parasympathetic division
Sympathetic division:
prepares body to deal with immediate threats. Flight-or-fight response.
Parasympathetic division:
coordinates bodies normal resting activities. Called the "rest-and-repair" division.
Neuroglia: types/functions: Neuroglia is also known as "Glia".
Glia cells helps support neurons. 5 major types:
Astrocytes (in CNS)
Star-shaped cell, largest and most numerous type of glia.
-transfer nutrients from blood to neurons
-extends to connect neurons and capillaries.
-forms tight sheets around brain capillaries, constitutes the blood brain barrier.
Microglia
-small, stationary cells usually in inflamed brain tissue.
-they enlarge and carry out phagocytosis (engulfing inflammatory products)
Ependymal cells (in CNS)
-form thin fluid-filled cavities in the CNS
-some produce the actual fluid, others just aid in circulation of the fluid
Oligodendrocytes (in CNS)
-hold nerve fibers together and produce the "myelin sheath."
Schwann cells (in PNS)
-found only in peripheral neurons
-supoports nerve fibers and form myelin sheaths
-Myelin sheath gaps known as Nodes of Ravier.
-"Satellite cells" are schwann cells that cover and support cell bodies in the PNS.
Functional/structural classification of cells in nervous system
o Afferent (sensory) neurons
o Efferent (motor) neurons
o Neuron types: structure/function
-"Satellite cells"
are schwann cells that cover and support cell bodies in the PNS.
Neurons
-Excitable cells that initiate and conduct impulses that makes the nervous system possible.
4 Structure/components of Neurons:
Cell body: Dendrites:Axon:Cytoskeleton
Cell body:
-ribosome, mitochondria rough ER
Dendrites:
Dendrites are treelike extensions at the beginning of a neuron that help increase the surface area of the cell body and are covered with synapses. These tiny protrusions receive information from other neurons and transmit electrical stimulation to the soma
Axon:
-single process extending from the axon hillock, sometimes covered with myelin sheath
-conducts nerve impulses away from the cell body of the neuron
Cytoskeleton:
-microtubules and microfilaments
-allows for rapid transport of small organelles
Functional regions of the Neuron:
-Input zone: dendrites and cell body
-Summation zone: axon hillock
-Conduction zone: axon
-Output zone: telodendria and synaptic knobs of axon
Structural classification:
goes by the number of things extending off it's body)
Multipolar nueron
one axon, several dendrites.
Bipolar nueron
only one axon and one dendrite.
Unipolar:
one process comes off the body, but then immediately divides into two fibers, central fiber and peripheral fiber.
Functional classification-
-Afferent (sensory) neurons: -Efferent (motor) neurons:
Interneurons:
Afferent (sensory neurons)
conduct impulses to spinal cord or brain.
Efferent
motor) neurons: conduct impulses away from spinal cord or brain toward muscles or glandular tissues
Interneurons:
conduct impulses from sensory neurons to or toward motor neurons. Only in the CNS*
Resting Membrane Potential
-this is a membrane potential at rest. No conducting of electrical impulses are happening.
-A neurons resting potential is usually resting at -70mV. (slight excess of positive ions on the outer surface of the neuron).
-The neuron makes this possible balance of staying at -70mV by using a transport mechanism. The neurons plasma membrane barrier is selectively permeable, only allowing in certain ions, leaving a positive charge to the outside. The next pump is an example.
Sodium potassium pump
-Active transport mechanism on neuron.
-Transports sodium and postassium in opposite directions across the plasma membrane, all at different rates an amount.
-This maintains an imbalance in the distribution of positive ions, resulting in the inside surface being slightly negative and the outer surface slightly positive.*3 na goes up 2 K go down*
Action Potential/Nerve Impulse
-also known as a nerve impulse is when the membrane potential conducts an impulse. ( not at rest anymore, something trigger electrical impulse on membrane)
-When an adequate amount of stimulus excites the membrane, stimulus-gated sodium (Na+) channels open, allowing Na+ to diffuse into the cell at a very fast rate.
-Having Na+ rapidly diffuse into the cells, the membrane potential quickly moves towards being zero or neutral. (Remember the membrane at rest has a charge of -70mV. When the Na+ floods in, this moves to closer to zero instead, -70mV to 0).
-This movement, an change in charge is known at Depolarization.
-As the threshold of the potential is reached, voltage-gated Na+ gates open up, an even more Na+ enters the cell, causing even further Depolarization.
-*THIS ACTION POTENTIAL IS AN ALL OR NOTHING RESPONSE. If it does not reach it's threshold, it will not trigger an action potential.
-Eventually once the action potential peaks, the membrane will start to return to it's resting membrane potential (-70mV)
-This process is helped when potassium (K+) channels open, allowing K+ to diffuse outwardly of the membrane. The K+ moving out of the cell is known as Repolarization.
Electrical synapses
occurs when cells joined by the gap junctions allows the action potential to carrier along to the postsynaptic membrane.
Chemical synapses:
occur when presynaptic cells release chemical transmitters (neurotransmitters) across a tiny gap to a postsynaptic cell, possibly creating an action potential.
How many structures of a chemical synapse:
3
1 Synaptic knob:
-tiny bulge at the end of the presynaptic nerve that contains neurotransmitters.
2-Synaptic cleft:
space between a synaptic knob and the plasma membrane of the postsynaptic neuron.
3 -Postsynaptic
neuron has receptors for neurotransmitters on it's plasma membrane.
Neurotransmitters:
the means by which neurons communicate with one another. -50 compounds known to be neurotransmitters
The function of the neurotransmitter soley depends on the neuron it is being release to, (the postsynaptic neuron.) But mainly neurotransmitters have two main functions.
To act either as:1. -An excitatory neurotransmitter
2.-Or An Inhibitory neurotransmitter
Acetylcholine
is an example of a small-molecule neurotransmitter.
Associated with memory, muscle contractions, and learning. A lack of acetylcholine in the brain is associated with Alzheimer's disease.
Saltatory Conduction
In myelinated fibers, the action potentials of the membrane only occurs in the Nodes of Ravier; this type of impulse conduction is known as Saltatory conduction.
-The speed of the nerve conduction
depends on the diameter or thickness of the myelin sheath.
soma
is where the signals from the dendrites are joined and passed on. The soma and the nucleus do not play an active role in the transmission of the neural signal. Instead, these two structures serve to maintain the cell and keep the neuron functional.
axon hillock
is located at the end of the soma and controls the firing of the neuron. If the total strength of the signal exceeds the threshold limit of the axon hillock, the structure will fire a signal (known as an action potential) down the axon.
Electrical and Chemical Synapses
a. electrical synapses involve gap junctions that allow action potentials to move from cell to cell directly by allowing electrical current to flow between cells
b. Chemical synapses involves tramitter chemicals/neurotransmitters that signal post synaptic cells, possibly inducing an action potential.
dopamine
Associated with thought and pleasurable feelings. Parkinson's disease is one illness associated with deficits in dopamine, while schizophrenia is strongly linked to excessive amounts of this chemical messenger.
Endorphins:
Associated with emotions and pain perception. The body releases endorphins in response to fear or trauma. These chemical messengers are similar to opiate drugs such as morphine, but are significantly stronger.
afferent division
consists of all incoming sensory pathways
More information about the different primary afferent axons:
A-alpha nerve fibers carry information related to muscle sense.
A-beta nerve fibers carry information related to touch.
A-delta nerve fibers carry information related to pain and temperature.
C-nerve fibers carry information related to pain, temperature and itch.
absolute refractory period
time during which the local area of the membrane has surpassed the threshold potential and will not respond to any stimulus
amine
organic compound containing nitrogen; nuerotransmitter synthesizes from amino acid molecules
axon transport
process of transporting vesicles, small organelles, and other structures along pathways inside the axon of a neuron
catecholamine
chemical category of neurotransmitters that include norepinephrine, epinephrine and dopamine
convergence
a coming together, as in when one or more presynaptic axon synapses with a single postsynaptic neuron
depolarization
electrical activity that triggers a contraction of the heart muscle
divergence
when a single presynaptic axon synapses with more then one different postsynaptic nueron
endoneurium
thin wrapping of fibrous connective tissue that surrounds each axon in a nerve
epineurium
fibrous coat surrounding a bundle of nerve fibers(tough fibrous sheath that covers the whole nerve)
excitatory postsynaptic potential (EPSP)
temporary depolarization of postsynaptic membrane following stimulation
G-Protein-coupled receptor
A signal receptor protein in the plasma membrane that responds to the binding of a signaling molecule by activating a G protein. Also called a G protein-linked receptor.
glia
Cells found throughout the nervous system that provide various types of support for neurons.
gray matter
Brain and spinal cord tissue that appears gray with the naked eye; consists mainly of neuronal cell bodies (nuclei) and lacks myelinated axons.
hyperpolarization
increase in electrical charges separated by the cell membrane; causes change further below 0 mV
inhibitory postsynaptic potentional (IPSP)
temporary hyperpolarization that makes the inside of the membrane even more negative than at the resting potential
local potential
slight shift from resting membrane potential in a specific region of the plasma membrane
membrane potential
The charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.
monoamine
a molecule containing one amine group (especially one that is a neurotransmitter)
myelin
a layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next
myelin sheath
a layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next; produced by Schwann cells
myelinated fiber
axon surrounded by a sheath of myelin formed by Schwann cells or oligodentrocytes
nerve
bundle of nerve fibers, plus surrounding connective tissue, located outside the brain or spinal cord
nerve fiber
axon of a neuron
nervous system
the body's speedy, electrochemical communication system, consisting of all the nerve cells of the peripheral and central nervous systems
neurilemma
additional sheath external to myelin that is formed by schwann cells and found only on axons in the peripheral nervous system
neurofibril
Cytoskeletal structure in a neuron composed of microtubules and intermediate filaments.
neuroglobin (Ngb)
a protein molecule very similar to hemoglobin used to temporarily store a "back-up" supply of oxygen
neuromodulator
"cotransmitter"that regulates the effects of nuerotransmitters released along with it
neuropeptide
neurotransmitter with short strands of plypeptides
neurotrophin
nerve growth factor
nitric oxide(NO)
small gas moecule used as a neurotransmitter that diffuses backward from a postsynaptic cell toward the presynapptic neuron, where it has its biochemical effects and gives the opportunity for feedback
node of Ranvier
short space of myelin sheath between adjacent Schwann cells, myelin sheath gap
perikaryon
Cell body of a neuron
perineurium
connective tissue that covers a bundle of nerve fibers
postsynaptic potentional
local potential produced by opening of ion channels in the postsynaptic membrane
presynaptic
adjective describing any structure before a synapse (junction) of one neuron to another or any function that occurs before synaptic transmission
reflex arc
impulse conduction route to and from the CNS; smallest portion of nervous system that can receive a stimulus and generate a response
relative refractory period
a period after firing when a neuron is returning to its normal polarize state and will only fire again if the incoming message ( impulse) is stronger than usual; returning to arresting state
repolarization
phase of the action potential in which the membrane potential changes from it maximum degree of depolarization toward the resting state potential
retrograde signaling
type of synaptic transmission in which chemical signals are sent from the postsynaptic neuron back to the presynaptic neuron, usually to facilitate or inhibit further synaptic signals
somatic nervous system (SNS)
motor neurons that control voluntary actions of skeletal muscles
somatic sensory division
division of the nervous system made up of afferent pathways from somatic sensory receptors ( receptors involved in conscious perception)
spatial summation
ability of the postsyaptic neuron to add together the inhibitory and stimulatory input recieved from numerous different presynaptic neurons and produce an action potential based on the collation of information
stimulus-gated channel
...
synapse
the junction between two neurons (axon-to-dendrite) or between a neuron and a muscle
telodendrion
Each of the small branches that come off the axon and collateral axons. Terminate in the synaptic knob
temporal summation
when synaptic knobs stimulate a postsynaptic neuron in rapid succession and the effects add up over time to produce an action potential
threshold potential
...
tract
a bundle of mylenated nerve fibers following a path through the CNS; unlike a nerve, a tract does not have connective tissue coverings
visceral sensory division
division of the nervous system made up of afferent pathways from autonomic sensory receptors of the internal organs
voltage-gated channel
type of cell-membrane channel for the transport of molecules that is controlled by a gate that responds to a change in voltage (difference in charge across the cell membrane)
white matter
nerves covered with white myelin sheath