Neuro 7 - PNS Flashcards
What nerves is the PNS composed of?
Spinal nerves - 31
Cranial nerves - 12
so 43 pairs of nerves
What is the difference in firing between the somatic motor nervous system and the autonomic motor nervous system?
somatic - no firing at rest
ACh
autonomic - baseline firing
ACh and/or NA
What are rami ? (singular ramus)
They are lateral branches of the spinal nerve
Carry both motor and sensory fibers
They are formed after dorsal + ventral roots merge.
Dorsal rami will innervate the back, ventral the rest of the body including the limbs
What is the equivalent of astrocytes in the PNS?
Satellite cells
Describe the packaging of nerve axons into larger structures.
Axons are packaged into fascicles and the fascicles are packaged into nerves.
What are the three layers of connective tissue found in nerves?
Endoneurium - wraps around individual axons
Perineurium - wraps around fascicles (bundle of neurons)
Epineurium - wraps around nerves
REMEMBER: unmyelinated axons also have Schwann cells wrapped around them, the difference is that they only have one layer of membrane around them and one Schwann cell can accommodate many axons
Describe the arrangement of autonomic motor neurons.
Autonomic motor neurons have a preganglionic neuron and a postganglionic neuron with an autonomic ganglion in the middle. The location of the autonomic ganglion varies depending on whether it is sympathetic (in sympathetic chain) or parasympathetic (in the periphery).
What is a nerve plexus?
Network of intersecting spinal nerves. Brachial, cervical, lumbar, sacral, celiac and coccygeal plexuses. Nerves after plexus is peripheral.
What spinal nerves make up the brachial plexus?
C5-T1
What are dermatomes?
Areas of skin supplied by a single sensory spinal nerve
What are myotomes? Explain the distribution in the upper and lower extremities?
The muscle that a spinal nerve innervates
C1/C2: neck flexion/extension
T1: finger abduction
L3: knee extension
S2: knee flexion
What are the nerves called that are leaving the plexus?
Peripheral nerves
Describe the differences in the dermatomes of spinal nerves and peripheral nerves.
Spinal nerves = stripy
Peripheral nerves = patchy
Describe the process of regeneration following peripheral nerve injury
With compression injuries, the axoplasm is separated but the endoneurium is still in tact. The axon distal to the compression (further away from the cell body) degenerated - macrophages invade and phagocytose the cell debris. Axons sprouts then grow down the endoneurium. There is competition between the axonal sprouts to reach the target organ. When the first axon sprout reaches the target cell, the other axon sprouts regress. The axon then widens and a myelin sheath forms. The only difference is that the internodal distance is reduced so the conduction speed is reduced.
What could happen if the damage to the neuron is so severe that there are no guidance cues at all for the axonal sprouts?
A neuroma (thickening) could form which is very painful and needs to be surgically removed.
