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What is the Brain?
• Billions of nerve cells
What is the Brain?
• Thousands of connections where one
neuron may interact (communicate) with
other neurons.
As many as 10,000 connections
40+ neurochemicals ( neurotransmitters)
Overarching Principles of Brain
function
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Hierarchically organized
Redundant control
Inhibition
Automaticity
• Conscious vs Unconscious processes
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Planes of orientation
Confusing terms (Particularly where
the CNS makes its’ 90 degree bend)
• Anterior-Posterior/Rostral-Caudal
• Dorsal-ventral/ Superior-inferior
Dorsal fins
The basic unit of the nervous
system
Myelin gives a whitish appearance
because its adipose content
Shwann cells
myelinate the PNS
Oligodendrocytes myelinate the CNS
White matter and gray matter
reflect organization
Staining for myelin in the brain
coronal section
Myelin Staining in the Spinal cord
Horizontal plane
Dorsal
ventral
Organizational schemes always have
shortcomings:
The PNS can not be truly separated from the CNS
To consider the PNS we first must consider
the spinal cord
The vertebral column
Each vertebra houses a spinal cord
segment
Midsaggital view
Each segment is similar: Central
gray and surrounding white matter
Central gray:
Dorsal = sensory
Ventral = motor
Each segment gives rise to nerve
pairs: i.e. The PNS
31 peripheral nerve pairs
Each nerve pair contains
thousands of incoming and
outgoing axons
The PNS:All neural tissue outside of the cranium
and vertebral column ( with one exception)
Major divisions of the PNS
motor output to skeletal muscles
And somatosensory input
The somatic division of the PNS gives rise to segmental
organiztion: Dermatomes and myotomes
The autonomic division
The other subdivision of the PNSthe ANS
The sympathetic chain
Sympathetic activation may be
magnified by adrenal gland
Some functional differences between
the somatic branch and the ANS
THE CNS
Exception- The cranial nerves