The Peripheral Nervous System Flashcards
What is the morphology of somatic sensory neurons?
Pseudounipolar - they do not have any dendrites
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
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 or parasympathetic.
Which roots do motor and sensory nerves go out of?
Motor = ventral Sensory = dorsal
Where do autonomic sensory neurons have their cell bodies?
In the dorsal root ganglion
What is a myotome?
The muscle that a spinal nerve innervates
What spinal nerves make up the brachial plexus?
C5-T1
What are the nerves called that are leaving the brachial plexus?
Peripheral nerves
Describe the differences in the dermatomes of spinal nerves and peripheral nerves.
Spinal nerves = stripey
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 could form which is very painful and needs to be surgically removed.
What are the two types of peripheral neuropathy? Describe them.
Segmental Demyelination - loss of a Schwann cell hear and there. This will not kill the cell but it will slow down the action potential.
Axonal Degeneration - once you already have degeneration of an axon, the myelin also degenerates and you get a conduction block
What are two techniques of diagnosing peripheral neuropathy?
Conduction velocity
Nerve biopsy
