Download Nervous System Chapter 7

Nervous System Chapter 7
Functions of Nervous System
1. Uses millions of sensory
receptors to monitor changes
in/out of body.
2. Processes and decides what to
do at each moment.
3. Effects a response by activating
muscles or glands
Structural classification of nervous
system
1. Central nervous system – brain,
spinal cord- interpret incoming
sensory information and issue
instructions. (CNS)
2. Peripheral nervous system –
nerves that extend from brain
and spinal cord. (PNS)
Functional classification – concerning
only w/PNS two subdivisions
1. Sensory, afferent division –
nerves that carry impulses to
CNS from sensory receptors.
2. Motor, efferent division –
nerves that carry impulses away
from the CNS to organs, muscles
and glands.
a. Somatic nervous system –
voluntary nervous system,
allows control of skeletal
muscles.
b. Autonomic nervous system
– involuntary nervous system
– such as activity of smooth
and cardiac muscles and
glands
1. sympathetic
2. parasympathetic
Nervous Tissue: structure and
function
Two types of cells: supporting
cells and neurons
1. supporting cells in CNS –
neuroglia
a. astrocytes – star shaped –
many projection connected to
nerve cells anchoring it to
blood capillaries. (Protect
brain from substances in
blood.)
b. Microglia – spider like –
phagocytes – dispose of debris.
c. Ependymal cells – line
cavities of brain and spinal
cord. Their cilia beat and move
cerebrospinal fluid.
d. Oligodendrocytes – wrap
around nerve fibers producing
fat insulating coverings called
myelin sheaths.
2. Supporting cells in PNS – two
major varieties:
a. schwann cells – form myelin
sheaths around nerve fibers that
extend from CNS.
b. Satellite cells – act as
generally protective,
cushioning cells.
Difference between neuroglia and
neurons
1. neuroglia not able to transmit
nerve impulses. Neurons
transmit impulses .
2. neuroglia never lose ability to
divide, neurons do.
3. Neurons – nerve cells
a. cell body – contains nucleus
b. Process or fiber – one or
more extending from cell body.
1. axon – generate nerve
impulses and conduct
them away from cell body.
2. Dendrites – conduct
impulses toward cell body
 may have hundreds of
dendrites but only one
axon.
3. axonal terminals –
thousands of endings on
the axon.
4. Neurotransmitter –
released by axonal
terminals into extracellular
space when impulse
reaches terminal.
5. Synaptic cleft – tiny gap
between neurons.
6. Synapse – junction
between neurons.
 neurons do not touch each
other. (synaptic cleft is
between them.)
7. myelin – whitish fatty
material, protects and
insulates fibers, increasing
transmission rate of nerve
impulses.
8. Schwann cells – wrap
around axon forming
myelin sheath.
9. Neurilemma – part of
schwann cell external to
myelin sheath.
10. Node of Ranvier – gaps
between schwann cells.
11. Ganglia – collection of
cell bodies.
12. Tracts – nerves running
through CNS.
13. White matter – dense
collection of myelinated
fibers.
14. Gray matter –
unmyelinated fibers.
Functional Classification – grouped
according to the direction the nerve
impulse is traveling relative to the
CNS. There are three types: 1.
Sensory 2. motor 3. association
neurons.
1. Sensory (afferent) – carry
impulses toward the central
nervous system. Cell bodies of
these are always found in
ganglion outside the CNS.
a. Sensory receptors –
dendrite endings of the
neuron are associated with
special receptors. 1.
Complex receptors of
special sense organs. 2.
cutaneous sense organs –
found in skin (pain
receptors – bare dendrite
endings – most numerous)
3.proprioceptors – in
muscles and tendonsconstantly advise the
brain on your movement
2. Motor – (efferent) – carry
impulses away from the CNS.
The cell bodies of the motor
neurons are always found in the
CNS.
3. Association Neurons –(
interneurons) – They connect the
motor and sensory neurons.
Their cell bodies are always
located in the CNS.
Structural Classification – based on
the number of processes extending
form the cell body. 1. Multipolar –
several processes; most common, all
motor and association neurons.
2. bipolar neurons – two processes –
an axon and a dendrite.
3.
Unipolar – single process from the
cell body.
Physiology Nerve Impulses
Two major functions:
1. irritability – respond to
stimulus and convert to impulse.
2. Conductivity – ability to
transmit the impulse to other
neurons and muscles and glands.
Irritability
1. plasma membrane of resting
neuron is polarized. (fewer ions
+ inside neuron than in fluid
around). K+ (potassium) –
major ion inside, Na + (sodium)
major ion outside.
 When inside neuron is
negative and outside is +,
the neuron is inactive.
2. neuron is stimulated (light,
touch, etc.)
3. “sodium gates” in membrane of
neuron open.
4. Sodium rushes into neuron.
5. Polarity changes- inside is now
more +, outside is less +.
(depolarization)
6. This activates neuron to
transmit nerve impulses (action
potential).
7. Impulse always runs entire
length of axon. (never part way)
8. K+ rush out into tissue fluid.
Restores cell to polarized
condition (repolarization)
 repolarization must occur
before another impulse can
be conducted.
Conductivity
1. action potential reaches axonal
endings.
2. Axon terminal releases a
neurotransmitter chemical.
3. Diffuses across synapse and
binds to receptors on another
neuron.
4. When enough neurotransmitter
is released the process described
in 1-8 under irritability will
occur.
Central Nervous System
Brain – 4 major sections
1. cerebral hemisphere
2. diencephalon
3. brain stem
4. cerebellum
Regions of cerebral hemisphere to
know:
1. parietal lobe – somatic (body)
sensory area. – left side of
sensory cortex receives impulses
from right side of body.
2. occipital lobe – visual area
3. temporal lobe – auditory area,
olfactory area.
4. frontal lobe – primary motor
area. (mouth, face, hands)
- Broca’s area – involved in
ability to speak
- Higher intellectual reasoning
– anterior part of frontal lobe.
- Speech area – junction of
temporal, parietal, and
occipital lobe.
- Language comprehension –
also in frontal lobe
5. Cerebral cortex- outermost gray
matter of cerebrum
6. Corpus callosum- deeper
cerebral white matter. Connects
the cerebral hemisphere.
7. Basal nuclei- buried deep
within white matter; islands of
gray matter- help regulate
voluntary muscle activity
Diencephalon- interbrain- sits on
the top of brain stem; enclosed by
cerebral hemisphere. Major
structures are: thalamus,
hypothalamus, epithalmus.
*Thalamus- relay station for
sensory impulses passing upward
to the sensory cortex.
*Hypothalamus- makes up
floor of Diencephalon. Plays a
role in the regulation of body
temperature, metabolism and H2O
balance thirst and appetiteregulates pituitary gland.
*Epithalamus- forms roof of 3rd
ventricle- important parts: pineal
body, choroid plexus. Choroid
plexus- forms cerebral spinal fluid.
Brain stem- includes- midbrain,
pons, and medulla oblongataprovides pathway for ascending
and descending tracts- control vital
activities such as breathing and
blood pressure.
*Midbrain- contains cerebral
aqueduct which connects 3rd and
4th ventricle.
*Pons- rounded structures- area
that controls breathing.
*Medulla Oblongata- most
inferior part of brain stem- controls
functions such as heart rate, blood
pressure, breathing, swallowing,
vomiting.
Protection of the Central Nervous
System
Meninges- protective covering in
CNS
1. dura mater- outermost layer –
double layered where it surrounds
the brain.
2. Arachnoid mater – weblike middle
layer – creates subarachnoid space –
fills with cerebrospinal fluid.
3. Pia mater – inner most layer –
clings tightly to brain and spinal
cord.
- arachnoid villi – protrude
through the dura mater.
Specialized projections out of
the arachnoid membrane.
- Cerebrospinal fluid – similar
to plasma formed from blood
by choroid plexuses. –
provides a watery cushion.
Pathway of Cerebrospinal fluid
through the brain – from two lateral
ventricles (cerebral hemispheres) into
3rd ventricle, then through the cerebral
aqueduct of the midbrain to the 4th
ventricle. Some fluid reaching the 4th
ventricle continues down central canal
of spinal cord. – most moves from 4th
ventricle into subarachnoid space.
Spinal fluid then returns to blood
through dural sinuses.
Spinal Cord - about 17 inches long,
glistening white, continuation of the
brain stem.
- Provides a two way pathway
to and from the brain
- It is enclosed in the vertebral
column
- Extends from the foramen
magnum to the 1st or 2nd
lumbar vertebrae.
- It is protected by meninges.
- The meningeal coverings
extend past the 2nd lumbar
vertebrae. This is a good area
to remove CSF if needed for
testing.
- 31 pairs of spinal nerves arise
from the cord
- the lowest spinal nerves travel
to the end of the vertebral
column before they exit.
- Cauda equina – collection of
spinal nerves at the inferior
end of the vertebral canal
(looks like horses tail). Pg
218
- Spinal cord has gray matter
and white matter.
- Gray matter is in the inner
part (shaped like a butterfly)
* dorsal (posterior) horns –
two posterior projections of
the butterfly shape. They
contain association neurons or
interneurons. * Ventral
(anterior) horns – two anterior
projections of the butterfly
shape. They contain the cell
bodies of the motor neuron of
the somatic (voluntary)
nervous system. This gray
matter region surrounds the
central canal which contains
CSF. Coming off of the spinal
cord are the dorsal root and
the ventral root. The dorsal
root has an enlarged area
called the dorsal root
ganglion. The cell bodies of
the sensory neurons are found
in the dorsal root ganglion.
The dorsal and the ventral
root fuse to form the spinal
nerves.