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141 terms

Module 11: Neuron Anatomy & Physiology

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What are the 2 basic types of cells nervous tissue contains?
neurons and neuroglia
What are neurons?
Individual nerves cells that conduct signals in the NS.
How many neurons are in the human brain?
100 billion
What do nerve cell serve?
sensorimotor activities and higher mental functions (e.g., memory, thought, language, reasoning and calculation.)
What are neuroglia cells?
supporting and insulating cells. also interstitial cells
What is the function of neuroglia cells?
they hold neurons in place.
Where are neurons not encapsulated/insulated from each other?
at the synapses
By providing insulation, glial cells prevent _____
abberant spread of signals
_____ cells far outnumber neurons by __-__ times.
Glial cells far outnumber neurons by 5-50 times.
What makes up half of the CNS volume?
Glial cells
What are equivalent to glial cells in the PNS?
Schwann Cells
What forms myelin in the PNS?
Schwann cells
What forms the axon covering in the PNS?
Schwann cells
What is neurolemma known as?
Schwann cells
What forms myelin in the CNS?
Oligodendroglia
When does myelination begin?
prenatal
When are pathways in the CNS fully myelinated?
2 years of age
What are the 3 types of glia in the CNS?
Oligodendroglia
Astroglia
Microglia
What are Oligodendroglia?
Equivalent to Schwann Cell in the PNS
lay down the myelin sheath in the CNS
What has sheet like processes that extend out among neurons?
astroglia
What occupies spaces between neural processes in the gray matter?
astroglia
What insulates the synapse?
astroglia
Why are astroglia believed to play a role in transport of substances between capillaries and neurons and in the blood brain barrier?
Because they have end-feet that contact capillaries
What are the largest and most numerous of the glial cells?
astroglia
What are the cells that remove cell debris generated in normal cell death and in degenerating brain tissue/cell death due to brain injury?
microglia
What cells look like Halloween ghosts?
microglia
Where are microglia found?
in choroid plexus and other structures related to the ventricles
What is composed of glial cells that line the ventricles and choroid plexus?
ependyma
What functions as phagocytes (macrophages)?
microglia
When do microglia remove cell debris?
in normal death or in cell death due to injury
What is a soma?
cell body
What is the metabolic center of the neuron?
soma
What is known as the receiving tree?
dendrites
What are the neoplasms?
Tumors
What is glioma?
tumor involving glia
What is glioblastoma?
most frequent type of tumor in adults
What is are three types of glia tumors?
glioma, glioblastoma, astrocytoma
What do dendrites receive?
integrative synaptic input from other neurons
Together with the ___ ___, dendrites constitute the ______ segment of the neuron
Together with the cell body, dendrites constitute the receptive segment of the neuron.
What unit is specialized as a receptor and integrator of info received from other neurons?
dendrite-cell body
What is a single process?
axon
What conveys coded info from the dendrite cell body unit to synaptic junctions?
conductile segment
What is called initial segment where action potential is initiated?
axon hillcock
Each main axon or its collaterals, terminates by branching into several terminal filaments called _______
teledendria
Where does each telodendron end?
at the terminal bouton
What is part of the synaptic junction?
terminal bouton
What constitutes the transmissive segment of the neuron?
boutons
What does a bouton contain?
presynaptic vessicles with neurotransmitter
What determines if a neuron will have an excitatory or inhibitory effect on the neuron with which it synapses?
neurotransmitter
What is another name for pre-synaptic terminal?
axon terminal
What is another name for the synaptic knob?
bouton
Axon length can vary from ___ ____ (in the brain) to as long as __ ______ (in the spinal cord)
Axon length can vary from a few micrometers (in the brain) to as long as 2 meters (in the spinal cord)
What are the 3 types of neurons?
Multipolar
Bipolar
Unipolar
What has many dendrites and one axon?
multipolar neurons
What is the most typical neuron?
multipolar
Which neuron is found in the brain?
multipolar
What are bipolar neurons?
have 2 processes extending from each pole of the body
In bipolar neurons, what is the peripheral process?
dendrite
In bipolar neurons, what is the axon?
central process
What is an example of a bipolar neuron?
rods and cones of eye, visual receptor cells
What neuron is T-shaped?
unipolar
What has one process extending from the body and divides into central and peripheral processes?
unipolar neurons
What kind of neurons are the cells in the dorsal/sensory roots of the spinal cord?
unipolar or pseudopolar
What is the effector segment?
synapse
What is the synapse?
site of contact with one neuron with another
What is neurosomatic?
neuron to cell body (soma) or dendrite of a neuron
What is neuroaxonal?
neuron to axon of a second neuron
What is nerve to muscle fiber synapse?
neuromuscular
What is the synaptic cleft?
space between the
bouton of one neuron and the cell body, dendrite or axon or another neuron
or the space between the bouton and the cell membrane of a muscle fiber neuron to muscle synapse
What is the cell membrane of the bouton?
pre-synaptic membrane
What is the cell membrane of the other cell body, dendrite, axon, or muscle fiber?
post-synaptic membrane
How many micrometers is a myelinated neuron?
greater than 2 micrometers in diameter
How many micrometers is an unmylinated neuron?
less than 2 micrometers
What is the range of conduction speed for myelinated neurons?
2 - 100 meters/sec.
What interrupts the myelin sheath?
nodes of ranvier
What is an internode?
distance from one node of ranvier to the next along the course of the axon fiber
The _____ is porportional to the diameter of the fiber.
internode
The thicker the fiber, the longer the _____
internodes
Where are neurotransmitter contained?
in synaptic vessicles of the bouton
When are they released?
at a synapse
What are neurotransmitters?
chemical messengers that transmit signals between neurons and between neurons and muscle
What are alpha motor neurons and all the muscle fibers it innervates?
motor units
What is the nerve to muscle ratio?
describes how many muscle fibers are innervated by a single motor neuron
What are lower motor neurons?
alpha motor neurons
The more precise (fine) a movement, the ____ the ratio
The more precise a movement, the smaller the ratio.
i.e. tongue muscle 1:5
Gross movement has a ____ ratio.
larger ratio
i.e. calf muscle 1:1900
What is the termination of a nerve fiber (and its branches) on a muscle?
neuromuscular (myoneural) junction
What is the synapse of each axon terminal (bouton) of a motor neuron on a voluntary muscle fiber?
motor end-plate
Neuron fluid inside is more _____ than fluid ____ a neuron
Neuron fluid inside is more negative than fluid outside a neuron.
How is electrical potential measured?
voltage across 2 points of the cell membrane
What is the measure across 2 points?
membrane potential
When a cell fires, what happens?
It depolarizes
The membrane potential is always ____
negative in resting cell
What is the membrane potential in neurons?
-70mV
What is the membrane potential in muscle fibers?
around m-90mV
How is the potential (or voltage) measured?
from the cell membrane
How is the membrane potential created?
by differences in ion concentrations across the cell membrane (between the intra vs. extracellular fluid)
cell metabolic activity (diffusion of potassium)
selective transport (gated channels in the cell membrane)
What is there a high concentration of INSIDE the cell?
potassium ions (K+) and anions
What is their a high concentration of OUTSIDE the cell?
sodium ions (NA+) and chloride (C1-)
What is continuously leaking out of cell?
potassium ions (K+)
What is left behind when potassium (K+) leaks out?
anions (large quantities of (-) charged protein molecules that cannot leak out)
which is why the inside of the cell is negative relative to the outside
When a signal is transmitted over a nerve fiber, the membrane potential goes through a series of changes called the ____ ________
Action potential
What does an action potential do to the cell membrane?
any factor that suddenly increase the permeability of the membrane to sodium ions
What are two stimuli that can elicit an action potential?
physical stimulus - sensory nerve ending such as pressure on skin
chemical stimulus - neurotransmitter
How does CNS transmission of information occur?
neurotransmitter
What happens when the action potential permeates?
positively charged sodium ions leak into the cell in great numbers and membrane becomes more positive/less negative by at least 30 mV
Action potential and associated events happen very _____
fast
NA+ leakage lasts for less than a _____ of a second
thousandth
The sodium-potassium pump drives sodium out and _____ ___
potassium in
When is the cell membrane polarized?
at -70mV, in its resting state
What is the initial positive change in the membrane potential?
depolarization (where the normal negatively polarized state no longer exists)
What is the return of membrane potential to its resting state called?
repolarization
What is saltatory conduction?
takes place in myelinated axons. the Action potential jumps from node to node
What occurs immediately after action potential is triggered?
refractory period
How do action potentials code info?
by response frequency
A weak stimulus will evoke only a ____ APs per unit of ___
few APs per unit of time
A strong stimulus will evoke generation of ____ APs per units of time
many APs per unit of time
How long does the absolute refractory period last?
8 milliseconds
During the absolute refractory period, ___ ____ cannot be generated
Action Potential
When the the neuron is hyperpolarized, what is happening to the membrane potential?
it becomes more negative from -70 to -90
What follows the absolute refractory period?
relative refractory period
What is the relative refractory period?
membrane is not fully repolarized but a strong (suprathreshold) stimulus can cause new AP
The _________ period is shorter in larger diameter fibers.
refractory
What is the all-or-none principle?
adequate stimulus causes the entire fiber to fire
What has an all-or-none phenomenon?
Action Potential
The ____ acts as a one way connector
synapse
________ are chemical agents released at the presynaptic terminal.
Neurotransmitters
What influences the postsynaptic membrane
neurotransmitters
What are the steps in the process of synapse and neurotransmitter release?
1. AP arrives at the terminal bouton
2. this causes depolarization of presynaptic membrane
3. Influx of calcium (CA++) from synaptic cleft
activates neurotransmitter release from the synaptic vessicles
What is the main transmitter at neuromuscular junctions within the PNS?
acetycholine
What is graded depolarization?
generator potential
Generator potential relies on _________ of arriving stimuli, which is a local graded response.
summation
What has to happen for the stimulus to to reach the initial segment (axon hillock) and generate a new AP?
Generator potentials need to sum
What are the 2 types of neural summation for GP?
temporal summation
spatial summation
What is temporal summation?
several subthreshold stimuli must sum within a critical time period to initiate new AP
What type of neural summation requires many stimuli to converge on postsynaptic membrane simultaneously to initiate new AP?
spatial summation
Generator potentials code info by response amplitude that is by _____ of the stimulus.
intensity
A weak stimulus evokes a _____ potential
small
small voltage change
A _____ stimulus evokes a large (er) potential
stronger
large voltage change
What is EPSP?
excitation of receptor membrane
What is IPSP?
creates state in which neuron is prevented from firing neurotransmitter substance hyperpolarizes the receptor membrane