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The Nervous System

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The Nervous System
Divisions of the Nervous System
Central Nervous System [CNS] = Spinal Cord
Brain
Peripheral Nervous System [PNS]= Spinal Nerves [31 pair]
Autonomic Nervous System [ANS]
Sympathetic Division
Parasympathetic Division
Cranial Nerves [12 pair]
Cells of the Nervous System
• Neurons are the
functional cell of the
system
• Have 3 basic parts to
them
Body [soma]
Axon
Dendrites
• Neuroglial [glial] are
the supporting cells of
the system. They are
smaller and more
plentiful than neurons.
In some areas, there
are 10x more
neuroglial cells than
neurons.
Neuroglial Cells
CNS astrocyte oligodendrocyte microglial ependymal
PNS satellite
Schwann
Myelin
80:20
Sheath – Phospholipid
: protein
fatty
covering
of axons
microglial
astrocyte
oligodendrocyte
Nerve Conduction
• Action Potential – generated by change in
membrane’s permeability which causes an
exchange of ions – caused by impulse
Resting state of cell – polarized
receiving stimulus – depolarized
returning to resting state - repolarized
At rest, inner environment has a higher concentration
of K, the outer environment has a high Na
concentration. The neuron’s cell membrane has active
Na/K gates. When an impulse comes in contact with
the membrane, it turns off the gate.[polarized]
Na rushes in, K leaves and the electrical impulse
passes through the cell body. [wave of depolarization]
After the electrical impulse leaves, the gates are turned
back on, and Na is pumped out - K reenters the cell
3 Na pumped out for every 2 K pumped in
[repolarization]
The Synapse
Gap between two cells
Information can �jump’ gap via a chemical [neurotransmitter]
or electrical signal.
Electrical synapses cross gap junctions, such as in cardiac and
smooth muscle.
Neurotransmitters are used in nervous system synapses. They
are released from the axon. Bouton / knobs / presynaptic
terminal
Neuromodulators – can influence an action potential
Meninges
• The CNS is covered in a protective
membrane
• Dura mater
• Arachnoid mater
– Subarachnoid space – Cerebral
Spinal Fluid
• Pia mater
The pia is on the surface of the CNS
and forms the filum terminale which
anchors the spinal cord onto the
sacrum/coccyx
The Spinal Cord
Extends from foramen magnum to
the 2nd or 3rd lumbar vertebrae
The uppermost portion is called the
medulla oblongata
The lowermost portion is called the
conus medullaris and gives rise to the
cauda equina
Spinal Cord Anatomy
• White matter –
myelinated axons
• Gray matter – cell
bodies
• Anterior – median
fissure
• Posterior – median
sulcus
• Central canal
• Commissure = connecting
nerve fibers from one side
to other
• Posterior horn- receives
sensory / afferent input
• Anterior horn – transmits
motor/efferent response
• Columns – pathways /
nerve tracts
Cross Section of Spinal Cord
Dermatomes
Each spinal nerve, except C1, has
a specific cutaneous sensory
distribution
Letters and numbers indicate the
spinal nerves that innervate a
given region
Reflexes
• Protective mechanism
• Automatic response to
a stimulus that occurs
without conscious
input
• Reflex vs reaction
The Brain
The brain can be divided
into 4 regions
• Brain Stem
– medulla oblongata
– pons
– midbrain
• Cerebellum
• Diencephalon
- thalamus
- hypothalamus
- pituitary/pineal glands
•Cerebrum
-lobes -> frontal, occipital,
temporal, parietal, prefrontal
-corpus callosum -> main
commissure
-ventricles - spaces where
CSF is produced/flows
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