The Nervous System

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The Nervous System
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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
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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.

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Neuroglial Cells
CNS astrocyte oligodendrocyte microglial ependymal
PNS satellite Schwann Myelin Sheath fatty covering of axons 8020 Phospholipid protein
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microglial
astrocyte
oligodendrocyte
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Nerve Conduction

• Action Potential generated by change in
  membranes permeability which causes an exchange
  of ions caused by impulse
• Resting state of cell polarized
• receiving stimulus depolarized
• returning to resting state - repolarized

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At rest, inner environment has a higher
concentration of K, the outer environment has a
high Na concentration. The neurons 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
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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. Neurotransmi
tters are used in nervous system synapses. They
are released from the axon. Bouton / knobs /
presynaptic terminal Neuromodulators can
influence an action potential
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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

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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
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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

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Cross Section of Spinal Cord
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Dermatomes
Each spinal nerve, except C1, has a specific
cutaneous sensory distribution Letters and
numbers indicate the spinal nerves that innervate
a given region
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Reflexes

• Protective mechanism
• Automatic response to a stimulus that occurs
  without conscious input
• Reflex vs reaction

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The Brain
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The brain can be divided into 4 regions

• Brain Stem
• medulla oblongata
• pons
• midbrain
• Cerebellum
• Diencephalon
• - thalamus
• - hypothalamus
• - pituitary/pineal glands

• Cerebrum
• -lobes -gt frontal, occipital, temporal, parietal,
  prefrontal
• -corpus callosum -gt main commissure
• -ventricles - spaces where CSF is produced/flows

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