Download Nervous System

Nervous System
Chapters 8 and 9
MIT Neuropathology Pics
Homeostasis Review
Variables:
 Set Point:
 Normal Range:
 Sensor: Detects change in internal
env’t. (sensory receptor)
 Regulatory Center: CNS- brain
 Effector: muscle cell, gland cell or
specialized cell
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System Functions
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Sensory Input: Sensory receptors within
the skin and internal organs respond to
internal and external stimuli by generating
nerve impulses that travel to the brain and
spinal cord.
Integration: The brain and spinal cord
sum up the impulses received from all
over the body and send out nerve
impulses.
Motor Output: The impulses from the
brain and spinal cord go to the effectors,
which are muscles and glands.
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Nervous Tissue
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All nervous tissue is composed of only two
types of cells: Nerve cells (neurons) and
supporting cells (neuroglia).
Neurons vary in appearance, but all have
1) cell body, 2) dendrite, and 3) axon.
Neurolemmocyte (Schwann cell):
specialized neuroglial cell of the PNS that
creates myelin.
Types of Neurons
Motor: impulses from CNS to
muscles or glands (mostly
multipolar).
 Sensory: impulses from sensory
receptors to the CNS (many are
unipolar).
 Interneurons: impulses conducted
within the CNS (often multipolar).
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Motor Neuron
Sensory Neuron
Interneuron
CNS
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Gray matter: cell bodies and short
nonmyelinated fibers.
White matter: contains myelinated axons
that run together in bundles called tracts.
Meninges: membranes covering the brain
and spinal cord. (dura mater (outermost),
arachinod, pia mater (innermost)).
The subarachinod area is full of
cerebrospinal fluid.
CNS: Spinal Cord
Extends from the base of the brain
through the foramen magnum of the
cranium.
 It is protected by the vertebral
column and is located in the
vertebral foramen.
 The spinal cord ends at L1.
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CNS: Spinal Cord Anatomy
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Central canal with gray matter surrounded by
white matter.
The central canal contains cerebrospinal fluid.
Portions of sensory and motor neurons reside in
the gray matter as do interneurons. The
posterior root of a spinal nerve enters here and
the anterior root (containing motor fibers) exits
the gray matter.
Spinal nerves are created by the joining of these
two roots (part of PNS).
White matter is made of ascending and
descending tracts that take data to and from the
brain. Because these tracts cross just after they
enter or exit the brain, the right side of the brain
controls the left side of the body and the left side
of the brain controls the right side of the body.
CNS: Spinal Cord Function
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Communication between the Brain and the
PNS.
Example: hand touched sensory fibers
generate nerve impulses  passes
through sensory neurons  spinal cord 
ascending tract  brain.
Center for reflex arcs. A stimulus causes
sensory receptors to generate nerve
impulses through sensory nerves these go
to interneurons that integrate the data
and respond.
CNS - Brain
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The brain is organized in ventricles. The
Cerebrum is in the two lateral ventricles,
the diencephalon is in the third ventricle,
and the brain stem is in the fourth
ventricle.
Cerebrum: largest portion; last to receive
sensory input and integrate it before
commanding voluntary motor response;
coordinates other areas of the brain; and
carries out higher thought processes,
memory, language, speech, and learning.
More Brain
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Diencephalon: hypothalamus, thalamus
and the pineal gland. Thalamus receives
all sensory input except smell. This area
integrates this information and sends it to
the appropriate area of the cerebrum.
Cerebellum: Receives sensory input from
the eyes, ears, joints, and muscles about
the position of body parts. It also receives
information from the cerebral cortex as to
where those parts should be located.
Therefore it plays a role in posture,
balance, and coordination.
Even More Brain
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Brain stem: contains the midbrain, the
pons, and the medulla oblongata.
Midbrain – relay station for tracts
Pons – contains bundles of axons traveling
between the cerebellum and the rest of
the CNS.
Medulla Oblongata - contains a lot of
reflex centers for controlling heartbeat,
breathing, and vasoconstriction.
PNS
Composed of neurons and ganglia.
Ganglia are swellings associated with
nerves that contain collections of cell
bodies.
 Somatic division: serves the skin,
skeleton, and tendons.
 Autonomic division: regulates the
activity of cardiac and smooth
muscles and glands.
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Types of PNS Nerves
Cranial: 12 pairs; many belong to
the somatic division; includes the
vagus nerve which has branches to
most of the internal organs.
 Spinal: 31 pairs; associated with the
3 regions of the vertebral column;
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Somatic Division
Most actions are voluntary which
means they originate in the cerebral
cortex.
 Others are reflexes: cranial (blinking)
and spinal reflexes (hand on stove).
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Autonomic Division
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Sympathetic: most arise from the lower
thoracic or lumbar region. Highly involved
in the fight or flight reflex.
Parasympathetic: Craniosacral; promotes
all the internal responses we associated
with a relaxed state.
Commonalities: 1) they function
automatically and usually involuntary, 2)
they innervate all internal organs, and 3)
they utilize 2 motor neurons and 1
ganglion for each impulse.
Nerve Impulses
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Resting Potential: membrane is polarized (outside
+ inside -). The sodium potassium pumps are
responsible for setting this up.
Action Potential: 1) depolarization (inside +); 2)
repolarization (inside -).
If an axon is myelinated, the action potentials are
stimulated between the nodes of Ranvier (faster
potential) in non-myelinated it stimulates another
part of the axomembrane.
All or None event. One way from cell body to
axion terminal.
Transmission
Every axon terminates in an axon
terminal. All of these lie close to a
dendrite or the cell body of another
neuron.
 Pre-synaptic and Postsynaptic region.
Between them is the Synaptic cleft.
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Transmission
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Transmission is carried out by molecules
called neurotransmitters. These are
stored in vesicles in the axon terminals.
Impulse reaches terminal  opens calcium
channels  Calcium enters the terminal 
vesicles move toward membrane for
exocytosis neurotransmitters are
released and diffuse through synaptic cleft
neurotransmitters bind with receptors on
postsynaptic membrane.
Depending on the neurotransmitter and
receptor the response will be excitation or
inhibition.
Integration
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Neurons can have many dendrites and can
synapse with many other neurons.
An excitatory NT produces a potential
change called a signal. The signal drives
the polarity of a neuron closer to an action
potential. An inhibitory NT does the
opposite.
Integration is the summing up of all of the
excitatory and inhibitory signals. Which
ever side wins determines if an Action
Potential will be transmitted.