CNS Overview Flashcards
1
Q
sensory input
A
sensory (afferent) signals are picked up by sensory receptors throughout the body and are carried by nerve fibers of the PNS to the CNS
2
Q
motor output
A
motor (efferent) signals are carried away from the CNS by nerve fibers of the PNS to innervate muscles to contract and/or glands to secrete
3
Q
peripheral nervous system
A
links all parts of the body to the CNS
includes both cranial nerves and spinal nerves
cranial nerves - extend from the brain and carry signals to and from the brain
spinal nerves - extend from the spinal cord and carry signals to and from the spinal cord
ganglia - clusters of neuronal cell bodies outside of the CNS
4
Q
cranial nerves
A
extend from the brain
carry signals to and from the brain
part of the PNS
5
Q
spinal nerves
A
extend from the spinal cord
carry signals to and from the spinal cord
part of the PNS
6
Q
ganglia
A
clusters of neuronal cell bodies outside the CNS
part of the PNS
7
Q
integration
A
nervous system processes and interprets sensory input and makes decisions on what should be done
dictates a response by activating effector organs to produce a motor output response
8
Q
nervous tissue cell types
A
neuron: excitatory cells
neuroglial cells: nonconducting cells that wrap around, nourish, insulate, and protect the delicate neurons
9
Q
the neuron
A
large complex cells
contain a cell body
arm-like neuron processes (axons and dendrites) extend from cell bodies
conduct electrical impulses from one part of the body to another
signals travel very rapidly and are transmitted along the plasma membrane in the form of nerve impulses (action potentials)
10
Q
action potentials
A
neuron signals travel very rapidly and are transmitted along the plasma membrane in the form of nerve impulses
11
Q
the cell body
A
size varies from 5-140 um
plasma membrane of the cell body acts as a receptive surface for signals from other neurons
has a single nucleus surrounded by cytoplasm
cytoplasm contains all the usual organelles as well as chromatophilic (Nissl) bodies
12
Q
Nissl bodies
A
chromatophilic bodies
clusters of rough endoplasmic reticulum and free ribosomes
found in cytoplasm of neuronal cell body
13
Q
neurofibrils
A
bundles of intermediate filaments which form a network between chromatophilic bodies and prevent the cell from being pulled apart when subjected to tensile forces
14
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dendrites
A
neuron processes that extensively branch from the cell body
function as receptive sites for receiving signals from other neurons
transmit electrical signals toward the cell body
15
Q
axon
A
neuron has one axon which arises from cone-shaped region of the cell body called axon hillock
have a uniform diameter throughout length
impulse generator and conductor
transmits impulses away from cell body
16
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axon structural support
A
neurofilaments, actin microfilaments, and microtubules provide structural strength along length of axon
this structural support aids in axonal transport of substances to and from the cell body
17
Q
axon length
A
neurons may be long or short
axons of motor nerves innervating the foot extend from the lumbar spine to the foot and can be 3-4 feet long
18
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axon diameter
A
axons with larger diameters conduct impulses faster because the resistance to passage of an electrical current decreases as diameter increases
19
Q
axon branching
A
axons branch far less frequently than dendrites
branches develop at more or less 90 degree angles to prevent axon collaterals
branches usually occur at the terminus of the axon (terminal branches)
branches end in knobs called axon terminals, also called end bulbs or boutons
20
Q
axon hillock
A
cone-shaped region of neuronal cell body from which axon arises
21
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terminal branches
A
axon branches usually occur at the terminus of the axon
22
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axon terminals
A
knobs at the end of axon branches
also called end bulbs or boutons
23
Q
neuron, nerve fiber, nerve
A
neuron: nerve cell
nerve fiber: long axon of a neuron
nerve: collection of parallel running nerve fibers in the PNS
24
Q
nerve impulse
A
generated where the axon extends from the axon hillock
conducted along the axon to the axon terminals
releases neurotransmitters from axon terminals into extracellular space (synaptic cleft) where they excite or inhibit neurons or target organs
25
two neurons connected by a synapse
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axon terminal of a pre-synaptic neuron
presynaptic membrane
synaptic cleft
post-synaptic membrane
post-synaptic dendrite of post-synaptic neuron
```
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synapses
elaborate nerve cell junctions
synaptic vesicles in nerve terminus are membrane-bound sacs containing neurotransmitter chemicals that transmit messages across the synapse
mitochondria abundant in axon terminals to provide energy for the secretion of neurotransmitters
synaptic cleft: separates the plasma membrane of the two neurons
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synaptic vesicles
membrane-bound sacs containing neurotransmitter chemicals that transmit messages across the synapse
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synaptic cleft
separates the plasma membrane of the two neurons
29
signals typically pass through a synapse in _____
one direction
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presynaptic neuron
conducts signal toward synapse
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postsynaptic neuron
transmits electrical signal away from a synapse
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structural classification of neurons
multipolar: >2 processes; interneurons and and motor neurons
bipolar: 2 processes; special sensory
unipolar (pseudounipolar): 1 process; sensory
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multipolar neurons
have >2 processes
typically have many processes extending from the cell body with multiple dendrites and one axon
make up >90% of the neurons in the body
interneurons and motor neurons
most are interneurons (association neurons) that conduct impulses within the CNS
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interneurons
association neurons
conduct impulses within the CNS
multipolar
35
bipolar neurons
have two processes that extend from opposite sides of the cell body; one is a fused dendrite and the other is an axon
rare
found in some special sensory organs eg the inner ear, olfactory epithelium of the nose, retina of the eye
36
unipolar neurons
one short, single process near the cell body
single process divides into two branches: axon extends to the CNS (central process) and dendritic axon extends peripherally to sensory receptors (peripheral process)
most start as bipolar neurons during development and are called pseudounipolar
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central process
branch of the single process of a unipolar neuron
| axon extends to the CNS
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peripheral process
branch of the single process of a unipolar neuron
| dendritic axon extends peripherally to sensory receptors
39
where are unipolar neurons found?
found in sensory ganglia of the PNS, where they function as sensory neurons
common in dorsal root sensory ganglia along spinal cord and the sensory ganglia of cranial nerves
cell bodies are in ganglia outside of CNS
40
functional classifications of neurons
according to direction that the nerve impulse travels relative to the CNS
sensory neurons
motor neurons
interneurons
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sensory neurons
afferent neurons
transmit nerve impulses toward the CNS
virtually all are unipolar neurons
special sensory neurons are bipolar neurons
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motor neurons
efferent neurons
transmit nerve impulses away from the CNS to effector organs which create motor output
mostly multipolar neurons
form junctions with effector cells, causing muscles to contract and glands to secrete
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cell body location of motor neurons
cell bodies of skeletal muscle are mostly found in the CNS
| cell bodies for involuntary motor control of autonomic nervous system are typically found in ganglia of PNS
44
interneurons
association neurons
confined to the CNS
mostly multipolar
lie between motor and sensory neurons - integrate sensory input and motor output
may be a single neuron connecting sensory and motor neurons or one of a chain of CNS neurons
link into chains that form complex neuronal pathways
show great diversity in size and branching patterns
interneurons make up 99.98% of neurons in the body
45
interneurons are mostly ____
multipolar
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function of neurons
integrate sensory input and motor output
| lie between motor and sensory neurons
47
most neurons in the body are ____
interneurons
| multipolar
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characteristics of neurons
1. extreme longevity: can live and function for a lifetime
2. most do not have the ability to undergo mitotic cell division - most fetal neurons lose their ability to undergo mitosis, however neural stem cells which can divide are located in some areas of the CNS
3. high metabolic rate: require abundant oxygen and glucose; neurons die after five minutes without oxygen
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most neurons do not have the ability to undergo mitotic division
most fetal neurons lose their ability to undergo mitosis
| however, neural stem cells which can divide are located in some areas of the CNS
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neurons have a ____ metabolic rate
high
require abundant oxygen and glucose
neurons die after five minutes without oxygen
51
neuroglial cells
supporting cells
cover nonsynaptic regions of neurons, insulating the neurons and keeping the electrical activities of adjacent neurons from interfering with each other
six types of supporting cells: four in the CNS, two in the PNS
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CNS neuroglial types
astrocytes - most common CNS type
oligodendrocytes - have processes that form myelin sheaths around CNS nerve fibers
microglial cells - defensive types
ependymal cells - line cerebral fluid filled cavities
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PNS neuroglial types
satellite cells - surround nerve cell bodies within ganglia
| Schwann cells - form myelin sheaths and surround axons
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neuroglial cells in the CNS
non-nervous supporting cells
smaller than neurons
glial cells have branching processes and a central cell body
outnumber neurons 10 to 1
make up half mass of the brain
can divide in mitotic division throughout life (most neurons are not able to do this)
55
half of the mass of the brain is made up of ____
neuroglial cells in the CNS
56
ependymal cells
CNS neuroglial cells
form a simple epithelium that lines the central cavity of the spinal cord and brain
fairly permeable layer between the cerebral spinal fluid and the tissue fluid that bathes the cells of the CNS
bear cilia which help circulate CSF
57
microglia
CNS neuroglial cells
smallest and least abundant glial cells
elongated cell bodies with cell processes with many pointed projections
phagocytes: the macrophages of the CNS
migrate to and engulf dead neuron or invading microorganisms
appear to support maturation of synaptic clefts
derived from blood cells called monocytes which migrate to the CNS during embryonic and fetal stages
58
the macrophages of the CNS are _____
microglia
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functions of microglia
migrate to and engulf dead neurons or invading microorganisms
appear to support maturation of synaptic clefts
60
_____ are derived from monocytes
microglia
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astrocytes: structure
neuroglial cells of the CNS
most abundant glial cell type
have radiating processes with bulbous ends which cling to neurons and/or capillaries
extract blood sugar from capillaries for energy
62
astrocytes: function
monitor neuron release of neurotransmitters
regulate neurotransmitter levels by increasing uptake in regions of high neuronal activity
signal increased blood flow through capillaries in active regions of the brain
take up and release ions to influence ionic environment around neurons
propagate calcium signals that may be involved in memory
help synapses form in developing neural tissue
produce molecules necessary for neural development (eg BDTF)o
63
oligodendrocytes
have fewer branches than astrocytes
line up in small groups and wrap their cell processes around the thicker axons in the CNS
produce insulating coverings called myelin sheaths
a single oligodendrocytes may have multiple processes that coil around and myelinate several different axons
64
myelin sheaths are produced by _____
oligodendrocytes in CNS
| Schwann cells in PNS
65
multiple sclerosis
immune system attacks the myelin around axons in the CNS
varies widely in intensity among those affected
more women than men are affected
when men are affected, disease develops quicker and is more devastating
66
myelin sheaths
produced by oligodendrocytes in CNS and Schwann cells in PNS
surround thicker axons
segmented structures composed of the lipoprotein myelin
each segment of myelin consists of the plasma membrane of a supporting cell rolled in concentric layers around the axon
form an insulating layer that prevents leakage of electrical current from the axon
increase the speed of impulse conduction
67
neuroglia in the PNS
satellite cells - surround neuron cell bodies within ganglia
| Schwann cells - surround axons in the PNS and form myelin sheaths around many of these axons
68
myelin sheaths in the PNS
formed by Schwann cells in the PNS
each Schwann cell wraps around the axon in concentric layer to produce a tightly packed coil of membranes
Schwann cells develop during fetal period and in the first year of post-natal life
neurilemma (sheaths of Schwann cells) - outermost nucleated cytoplasmic layer of Schwann cells external to myelin sheath layers
nodes of Ranvier (myelin sheath gaps) - gaps along axon between adjacent Schwann cells
69
nodes of Ranvier
in myelinated axons, nerve impulses do not travel along the myelin-covered regions of the axonal membrane
instead, nerve impulses jump from the membrane of one myelin sheath gap to the next, which speeds impulse conduction
70
axons in the PNS
PNS has both thick and thin axons
thick axons are myelinated
thin axons are unmyelinated and conduct impulses more slowly
71
Schwann cells in the PNS: thin axons
unmyelinated
conduct impulses more slowly
Schwann cells surround thin axons but do not wrap around in concentric rings and do not form sheaths
a single Schwann cell can surround multiple unmyelinated thin axons
thin axons are found in: portions of the autonomic nervous system and in some sensory fibers
72
where are thin unmyelinated axons found?
portions of the autonomic nervous system and in some sensory fibers
73
nerves
cable-like structures in the PNS
consists of numerous parallel axons wrapped in connective tissue
nerves can contain both myelinated and unmyelinated sensory and motor nerve fibers (axons)
74
nerve fascicles
groups of axons bound into bundles by a connective tissue wrapping within a nerve (perineurium)
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endoneurium
layer of delicate loose connective tissue covering the Schwann cells surrounding the axons
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perineurium
connective tissue wrapping nerve fascicles
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epineurium
tough fibrous sheath of dense irregular connective tissue that surrounds nerve
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gray matter in the spinal CNS
surrounds hollow central cavities of the CNS
forms butterfly-shaped region in the spinal cord
site where neuron cell bodies are clustered
dorsal half contains central bodies of interneurons
ventral half contains cell bodies of motor neurons
primarily composed of neuronal cell bodies, dendrites, short unmyelinated axons of interneurons, and neuroglia
79
gray matter is primarily composed of:
neuronal cell bodies
dendrites
short unmyelinated axons of interneurons
neuroglia
80
gray vs. white matter in the CNS
gray matter is rich in neuronal cell bodies
white matter lacks neuronal cell bodies
gray matter consists mainly of unmyelinated axons
white matter consists mainly of myelinated axons
81
_____ matter is rich in neuronal cell bodies
gray matter
82
____ matter consists mainly of myelinated axons
white matter
83
white matter in the CNS
myelin around the myelinated axons gives white matter its color
composed of bundles of many myelinated axons
tracts - bundles of axons passing between specific regions of the CNS
most of these axons either ascend from the spinal cord to the brain or descend from the brain to the spinal cord
white matter tracts connect various gray matter areas in the CNS to each other
84
white matter tracts
bundles of axons passing between specific regions of the CNS
| connect various gray matter areas in the CNS to each other
85
PNS and CNS interrelationships
the CNS and PNS are functionally interrelated
PNS is composed of axons of sensory (afferent) and motor (efferent) neurons bundled together as nerves
nerves of the PNS function as information pathways to and from body periphery
afferent PNS fibers respond to sensory stimuli
efferent PNS fibers transmit motor stimuli from CNS to muscles and glands
86
interneurons in the CNS
gray matter interneurons: receive and process sensory information, direct information to specific CNS regions, initiate appropriate motor response
white matter interneurons: transport information (sensory and motor) from one area of the CNS to another
87
reflex arcs
simple chains of neurons
explain our simplest reflex behaviors
responsible for reflexes which are defined as rapid involuntary motor responses to stimuli
responses can be somatic (skeletal muscle) or visceral (smooth muscle, cardiac muscle, or glands)
88
5 essential components to reflex arc
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receptor
sensory neuron
integration center
motor neuron
effector
```
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essential components to reflex arc
1. receptor - at terminal of sensory nerve is where stimulus acts
2. sensory neurons - transmits afferent impulses to the CNS
3. integration center - consists of one or more synapses in the gray matter of the CNS
4. motor neuron - conducts efferent impulses from integration center to an effector
5. effector - muscle or gland cell that responds to efferent impulses by contracting or secreting
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integration center
in the simplest reflex arcs - integration center is a single synapse (monosynaptic) between a sensory neuron and a motor neuron
in more complex reflex arcs - integration center involves multiple (two or more) synapses, polysynaptic
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monosynaptic reflexes
simplest of all reflexes with a sensory neuron and a motor neuron
one synapse, one sensory neuron, one motor neuron
no interneuron
very fast
stretch reflexes: include "knee jerk" reflex and reflexes which help maintain equilibrium and upright posture
stretch reflexes are fastest of all body reflexes
92
polysynaptic reflexes
more common type of reflex
one or more interneurons are part of the reflex pathway between sensory and motor neurons
most of the simple polysynaptic reflex arcs (such as a withdrawal reflex in response to a pricked finger) have one interneuron between sensory and motor neurons and therefore have two synapses and three neurons
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example of monosynaptic reflex
knee jerk
94
example of polysynaptic reflex
withdrawal reflex in response to a pricked finger
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neuronal circuit
diverging circuits
converging circuits
reverberating circuits
96
diverging circuits
one presynaptic neuron synapses with multiple other neurons (divergence)
example: stretch of a muscle stimulates numerous sensory neurons which synapse with 100-150 neurons in the spinal cord gray matter
some are motor neurons that directly innervate the stretch muscle and stimulate contraction
others are interneurons that act to inhibit the activity of the antagonistic muscle group
still others are interneurons that project sensory information to the brain
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diverging circuits: neuron types
motor neurons - directly innervate the stretch muscle and stimulate contraction
interneurons - inhibit activity of the antagonistic muscle group
other interneurons - project sensory information to the brain
98
converging circuits
many neurons synapse on a single postsynaptic neuron )(convergence) and a single motor neuron may receive both excitatory and inhibitory messages
99
reverberating circuit
one neuron in the circuit receives feedback from another neuron in the same circuit
a branch off the axon of one neuron circles back and synapses with a previous neuron in the circuit
involved in control of rhythmic activities, eg breathing
100
what type of circuit is involved in breathing?
reverberating circuit
101
what type of circuit is involved in stretching?
diverging circuit
102
serial processing
neurons pass a signal to a specific destination in sequence (in series) along a single pathway from one neuron to the next
examples: a reflex arc or long chain of interneurons carrying a sensory signal to the brain
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parallel processing
-a single sensory stimulus results in multiple perceptions
information from a single neuron is sent along two or more parallel pathways allowing a single sensory stimulus to result in multiple perceptions
-allows brain to rapidly evaluate stimuli and enables information to be processed and integrated along multiple pathways
104
parallel processing: example
when you see a dog approaching, there are multiple processing pathways triggered in parallel by the sensory visual stimulus including evaluation of shape, color, spatial location, movement, as well as memory from past experiences with dogs
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parallel processing: withdrawal reflex
withdrawal reflex: a painful stimulus triggers nerve impulses in a sensory neuron, which initiate the spinal withdrawal reflex
parallel processing: simultaneously, nerve impulses travel in an axon branch that extends into the spinal white matter and extends as an ascending pathway to the brain
106
parallel processing: integration in gray matter and voluntary motor response
integration in gray matter: multiple interneurons process the nerve impulses to localize the stimulus, identify its source, and plan a response
voluntary motor response: a voluntary (non-reflexive) motor response is initiated in the cerebral gray matter and is transmitted down a descending fiber in the white matter to stimulate somatic motor neurons, eg to run cold water over a burned finger
