Download CHAPTER NINE: THE NERVOUS SYSTEM

CHAPTER NINE: THE NERVOUS SYSTEM (Part 1 of 3)
I. Nervous System Introduction
A. Functions of the Nervous System
a. Sensory input- ________________ gathered
by sensory receptors about internal and
external changes
b. ______________- interpretation of sensory
input
c. Motor output- activation of
______________ (muscles & glands)
produces a response
B. Divisions of the Nervous System
a. Central Nervous System (_____)
i. ___________ and spinal cord
ii. Integration and command center
b. Peripheral nervous system (_____)
i. Paired ____________ and cranial nerves
carry messages to and from the CNS
C. Peripheral Nervous System
a. Functions
i. Sensory (___________) division
1. Somatic afferent fibers- convey
impulses from skin, skeletal muscles,
and joints
2. Visceral afferent fibers- convey
impulses from visceral organs
ii. Motor (___________) division
1. Transmits impulses from the CNS to
effector organs
2. Somatic (___________) nervous
system
a. Conscious control of skeletal
muscles
3. Autonomic (___________) nervous
system (ANS)
a. Visceral motor nerve fibers
b. Regulated smooth muscle,
cardiac muscle, and glands
c. Functional divisions
i. Sympathetic
ii. Parasympathetic
D. Histology of nervous system
a. Two cell types
i. ___________ - excitable cells that
transmit electrical signals
1. Characteristics
a. Long lived, amitotic, high
metabolic rate, electrical
signaling and cell-to-cell
interactions during development
2. Parts of a neuron
a. ___________ - biosynthetic
center of a neuron, network of
neurofibrils (neurofilaments)
i. Axon hillock- cone shaped
area where the axon arises
ii. Clusters of cell bodies in the
____ are called nuclei, and in
the PNS are called ganglia
b. Processes- bundles are classed
tracts (CNS) and nerves (PNS)
i. Dendrites
1. Short, tapering and
diffusely branched
2. Receptive (input) region
of the neuron
3. Convey electrical signals
__________ the cell body
ii. Axons
1. One long axon per cell
body
2. Long axons are called
nerve _______
3. Knoblike axon terminals
a. Secretory region of
the neuron
b. Release neurotransmitters to excite
or inhibit other cells
4. Conducting region of the
neuron, generates and
transmits nerve impulses
___________ from the
cell body
5. Unmyelinated axons are
thin nerve fibers and one
Schwann cell can
incompletely enclose 15
or more unmyelinated
axons
CHAPTER NINE: THE NERVOUS SYSTEM (Part 1 of 3)
3. Structural classifications of neurons
a. ___________ - 1 axon and
several dendrites (most
abundant)
b. Bipolar- 1 axon and 1 dendrite
(_______)
c. ___________ (pseudounipolar)single, short process that has
two branches
i. Peripheral process- most
distal branch
ii. Central process- branch
entering the CNS
4. Functional classification of neurons
a. Sensory (___________)transmit impulses from sensory
receptors toward the CNS
b. Motor (___________)- carries
impulses from the CNS to
effectors
c. Interneurons (association
neurons)- Shuttle signals
through CNS pathways
ii. Neuroglia (glial cells)- supporting cells
1. ___________ (CNS)
a. Most abundant, versatile, and
highly branched glial cells
b. Cling to neurons, synaptic
endings, and capillaries
c. Support and brace neurons
d. Determine capillary permeability
e. Guide migration of young
neurons
f. Control chemical environment
g. Information processing in the
brain
2. ___________ (CNS)
a. Migrate toward injured neurons
b. Phagocytize microorganisms and
neuronal debris
3. ___________ cells (CNS)
a. May be ciliated
b. Line the central cavities of the
brain and spinal column
c. Separate the CNS interstitial
fluid from the cerebrospinal fluid
in the cavities
4. ___________ (CNS)
a. Branched cells
b. Processes wrap CNS nerve fibers,
forming insulating myelin
sheaths
i. Myelin sheath- concentric
________ of Schwann cell
membrane
ii. Neurilemmal- peripheral
bulge of Schwann cell
cytoplasm
iii. Nodes of Ranvier-myelin
sheath gaps between
Schwann cells, sites where
axon collaterals can emerge
iv. CNS
1. Formed by processes of
oligodendrocytes, Nodes
of Ranvier not present, no
___________, thinnest
fibers are unmyelinated
v. _______ matter
1. Dense collections of
myelinated fibers
vi. _______ matter
1. Mostly neuron cell bodies
and unmyelinated fibers
5. ___________ cells (PNS)
a. Surround neuron cell bodies in
the PNS
6. ___________ cells (PNS)
a. Surround peripheral nerve fibers
and form myelin sheaths
b. Vital to regeneration of
damaged peripheral nerve fibers
CHAPTER NINE: THE NERVOUS SYSTEM (Part 1 of 3)
E. Membrane potentials
a. Role of membrane ion channels
i. Proteins serve as membrane ion
channels
ii. Two main types of channels
1. Leakage (___________) channelsalways open
2. ___________ channels
a. Three types
i. Chemical gated (ligand-gated)
channels- open with binding
of a specific neurotransmitter
ii. ________-gated channelsopen and close in response to
changes in membrane
potentials
iii. Mechanically gated channelopen and close in response to
physical deformation of
receptors
b. When gated channels are
_______
i. Ions diffuse quickly across the
membrane along their
electrochemical gradients
1. Chemical gradients go
from high to low
2. Electrical gradients go
from low to high
ii. Ion flow creates an electrical
current and voltage changes
across the membrane
b. Resting membrane potential
i. Potential difference across the
membrane of a resting cell
1. Approximately -_______ in neurons
ii. Generated by
1. Differences in ____ (intracellular
fluid) and ____ (extracellular fluid)
2. Differential permeability of the
plasma membrane
iii. Differences in ionic makeup
1. ICF has _______ concentration of
Na+ and Cl- than ECF
2. ICF has _______ concentration of K+
and negatively charged proteins (A-)
than ECF
iv. Sodium-potassium pump stabilizes the
resting membrane potential by
maintaining the concentration gradients
for Na+ and K+
c. Membrane potentials act as signals
i. Changes when concentrations of
_______ across the membrane change
and permeability of membrane to ions
changes
ii. Signals used to receive, ___________,
and send information
iii. Two types of signals
1. Graded potentials- incoming shortdistance signals
a. ___________
i. Reduction in membrane
potential
ii. Inside of the membrane
becomes less negative than
the resting potential
iii. Increases the probability of
producing a nerve impulse
b. ___________
i. An increase in membrane
potential
ii. Inside of the membrane
becomes more negative than
the resting potential
iii. Reduces the probability of
producing a nerve impulse
c. Occur when a stimulus causes
gated ion channels to open
d. Decrease in magnitude with
distance as ions flow and diffuse
through leakage channels
2. __________________ - longdistance signals of axons
a. Brief reversal of membrane
potential with an amplitude of
~100mV
b. Occur in muscle cells and axons
of neurons
c. Does not decrease in magnitude
over distance
F. Nerve Fiber Classification
a. Group ___ fibers
i. Large diameter, myelinated somatic
sensory and motor fibers
b. Group ___ fibers
i. Intermediate diameter, lightly
myelinated ANS fibers
CHAPTER NINE: THE NERVOUS SYSTEM (Part 1 of 3)
c. Group ___ fibers
i. Smallest diameter, unmyelinated ANS
fibers
G. The Synapse
a. A ___________ that mediated information
transfer form one neuron to another
neuron or an effector cell
b. Presynaptic neuron- conducts impulses
___________ the synapse
c. Postsynaptic neuron- transmits impulses
________ from the synapse
d. Types of synapses
i. Axodendritic- between the axon of one
neuron and the ___________ of another
ii. Axosomatic- between the axon of one
neuron and the _______ of another
iii. Less common
1. Axoaxonic (axon to axon)
2. Dendrodendritic (dendrite to
dendrite)
3. Dendrosomatic (dendrite to soma)
e. Electrical ___________
i. Less common than chemical synapses
ii. Neurons are electrically coupled (joined
by gap junctions)
iii. Communication is very _________ and
may be unidirectional or bidirectional
iv. Important in embryonic nervous tissue
and some brain regions
f. Chemical synapses
i. Specialized in the ___________ of
neurotransmitters
ii. Composed of two parts
1. ________ terminal of the
presynaptic neuron
2. ___________ region on the
postsynaptic neuron
g. Synaptic cleft
i. Fluid-filled space separating the
presynaptic and postsynaptic neurons
ii. Prevents nerve impulses from
___________ passing from one neuron
to the next
iii. Transmission across the synaptic cleft
1. Is a chemical event that involves the
release, ___________, and binding
of neurotransmitters that ensures
unidirectional communication
between neurons
H. Neurotransmitters and their receptors
a. Most neurons make two or more
neurotransmitters, which are released at
different stimulation frequencies
b. _____ or more neurotransmitters have
been identified
c. Classified by ___________ Structure and by
Function
i. Acetylcholine (Ach)
1. Released at neuromuscular
___________ and some ANS
neurons
2. Synthesized by enzyme choline
acetyltransferase
3. Degraded by the ___________
acetylcholinesterase (AChE)
ii. Biogenic amines include
1. Catecholamines
a. ___________, norepinephrine
(NE), and epinephrine
2. Indolamines
a. Serotonin and hisamine
3. Broadly distributed in the
___________
4. Play roles in ___________ behaviors
and the biological clock
iii. Amino acids
1. GABA (Gamma-aminobutyric acid)
2. Glycine
3. ___________
4. Glutamate
iv. Peptides (neuropeptides)
1. Substance P
a. Mediator of _______ signals
2. Endorphins
a. Act as natural opiates; ________
pain perception
3. Gut-brain peptides
a. Somatostatin and
cholecystokinin
v. Purines such as ATP
1. Act in both the CNS and PNS
2. Provoke ________ sensation
vi. Gases and lipids
1. Nitric oxide (NO)
a. Involved in _________ and
memory
2. Carbon monoxide (CO)
a. Regulator of cGMP in the brain
CHAPTER NINE: THE NERVOUS SYSTEM (Part 1 of 3)
I.
3. Endocannabinoids
a. Lipid soluble and involved in
learning and _________
d. Direct action
i. Neurotransmitter binds to channellinked receptor and opens ion channels
ii. Promotes ___________ responses
1. Ach and amino acids
e. Indirect action
i. Neurotransmitter binds to a G-proteinlinked receptor and acts through an
intracellular second messenger
ii. Promotes long –lasting effects
1. Biogenic amines, neuropeptides, and
dissolved gases
f. Types of ___________ receptors
i. Channel-linked receptors
ii. G protein-linked receptors
Basic concepts of neural integration
a. Neuronal pools ___________ incoming
information and forward the processes
information to other destinations
b. Simple neuronal pool
i. Single presynaptic fiber branches and
synapses with ___________ neurons in
the pool
ii. Discharge zone- neurons most
___________ associated with the
incoming fiber
iii. Facilitated zone- neurons ___________
away from incoming fiber
c. Types of circuits in neuronal pools
i. ___________ circuit
1. One incoming fiber stimulated an
ever-increasing number of fibers,
often amplifying circuits
2. May affect a single pathway or
several
3. Common in both sensory and motor
systems
ii. ___________ circuit
1. Opposite of diverging circuits; strong
stimulation or inhibition
2. Also common in sensory and motor
systems
iii. Reverberating (___________) circuit
1. Chain of neurons containing
collateral synapses with previous
neurons in the chain
iv. Parallel after-discharge circuit
1. Incoming fiber stimulates several
neurons in parallel arrays to
stimulate a common output cell
d. Neural processing
i. Serial processing
1. Input travels along one pathway to a
___________ destination
2. Works in all-or-none manner to
produce a specific response
3. Ex. reflexes
ii. Parallel processing
1. Input travels along ___________
pathways
2. Important in higher-level mental
functioning
3. Ex. Smell reminds you of an odor and
associated experience
J. Developmental aspects of neurons
a. Originates from the neural ________ and
neural _________ formed from ectoderm
b. Neural tube becomes the CNS
c. Cell ___________
i. About 2/3 of neurons die before birth
ii. Death results in cells that fail to make
functional synaptic contacts
iii. Many cells also die due to ___________
(programmed cell death) during
development
K. Multiple Sclerosis (MS)
a. An autoimmune disease that mainly affects
__________ adults
b. Myelin sheaths in the CNS become
nonfunctional scleroses
c. Shunting and short-circuiting of nerve
__________ occurs, impulse condition
slows and eventually ceases
d. Symptoms: visual disturbances,
___________, loss of muscular control,
speech disturbances, and urinary
incontinence.
CHAPTER NINE: THE NERVOUS SYSTEM (Part 1 of 3)