Download Nervous System 1

Nervous System 1
Nervous system is conservative
Because of its role, the nervous system
is resistant to evolutionary change.
 Even if bones change shape, the nerves
innervating the muscles must still work.
 The system is therefore an ideal
comparative tool to help us understand
the evolution of vertebrates.
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Nervous system is conservative
It does not fossilize, but it does leave its
traces, particularly in the skull.
 Behavior, psychology, and physiology
are all tools we can use to help us
decipher the evolutionary and functional
history of vertebrates.
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Neurons and neuroglia
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Neurons
– Nerve cell body
– Nissl granules contribute to protein
synthesis.
– Multipolar – many filamentous processes
(brain and spinal cord)
– Bipolar (nose, eye, ear, and lateral line)
– Pseudounipolar (spinal nerves)
Neurons and neuroglia
Dendrites
 Axon
 Schwann Cells
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Neurons and neuroglia
Myelinn
 Axon cylinder
 Nodes of Ranvier
 Neurilemma
 Neuroglia
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Nerve Impulse and Synapse
There is a potential of 60mV across the
cell membrane.
 Maintained by imbalance of K and Na.
 Na outside of cell, K inside.
 Excitation is all or none
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Nerve Impulse and Synapse
Synapse
 Synaptic Knob
 Presynaptic vesicle
 Neurotransmitter

– Acetylcholine
– Noradrenalin
– Serotonin
– Dopamine
– Glutamic Acid
– ATP
– Nitric Oxide
Tracts, Nerves, and Ganglia
Tracts
 White Matter
 Grey Matter
 Neurilemma (around fiber)
 Perineurium (around fascicles)
 Epineurium
 Ganglia / Plexus
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Components
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CNS
PNS
Afferent – sensory
Efferent – motor
Association neurons
Somatic
Visceral
Autonomic system
Function and Structure: Reflex arcs and Association
neurons. Notice intersegmental nature of some
fibers.
Function and Structure
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Dorsal gray columns
Ventral gray
columns
Gray commisure
Dorsal funiculus
Ventral funiculus
Lateral funiculus
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Central pattern
generators
– Modified by brain,
but operate w/o brain
as well.
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Meninges
Evolution of the Spinal Cord
Gray matter – what happens to the
organization of white and gray matter in
lower and higher vertebrates?
 Amniotes – cervical and lumbar
enlargements.
 Birds – glycogen body in expanded
dorsal median sulcus of lumbar region.
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Evolution of Spinal Nerves

Amphioxus
– Paired dorsal spinal nerves, sensory and
motor components, and no ganglia. They
are intersegmental.

Lampreys
– Intersegmental like amphioxus, but some
cell bodies lie outside the cord.
– Segmental ventral spinal nerves that
contain only somatic motor fibers.
Evolution of Spinal Nerves

Fish and Amphibians
– Dorsal and ventral nerves of each segment
join outside the vertebral column, thus, one
spinal nerve per segment.
– Separate dorsal and ventral roots.
– Dorsal ramus – structures of epaxial origin.
– Vental ramus – structures of hypaxial
origin.
– Visceral ramus – structures derived from
hypomere.
– Nerve cell bodies are in dorsal root
ganglion.
Evolution of Spinal Nerves

Amniotes
– Dorsal and ventral roots of spinal nerves
join insdte the vertebral column.
– Each dorsal root joins at the same level as
the corresponding ventral root, rather than
posterior to it.
– Usually all visceral motor fibers exit from
the cord in the ventral root. So the shift is
complete – leaving the dorsal root with only
sensory neurons.
– Brachial and lumbosacral plexuses are
more complex.