The Peripheral Nervous System Flashcards
What are dorsal root ganglia and what are their features?
Groups of sensory neurone cell bodies
Associated with spinal dorsal roots
Have no dendrites
Pseudounipolar cells
Where do postganglionic cell bodies lie and how are they arranged?
Lie in Autonomic ganglia
Either arranged in rows paravertebrally (sympathetic NS) or closer to internal organs (parasympathetic NS)
How are bundles of axons arranged?
Bundles of individual axons = Fascicles
Bundles of fascicles = Nerves
How are axons packaged to prevent damage by movement?
Endoneurium - loose connective tissue wrapping individual axons and their associated Schwann cells
Perineurium - dense connective tissue wrapping fascicles (groups of axons)
Epineurium - loose connective tissue surrounding the whole nerve
Features of unmyelinated axons?
Usually small diameter
Clothed in cytoplasm of Schwann cells (neurolemma)
Slow conduction speed by continuous conduction (1m/s)
Features of myelinated axons?
Large diameter
Clothed in succession of tightly wrapping Schwann cells (wrapping forces loss of cytoplasm so sheath of cell membranes is formed)
Fast conduction speed by saltatory conduction (120m/s)
Process of saltatory conduction?
Depolarisation of axon only occurs at nodes of Ranvier
No Na+ channels in membrane of insulating Schwann cells so depolarisation cannot occur
So depolarisation “jumps” between adjacent nodes of Ranvier
Features of sensory neurones in PNS?
Autonomic and somatic neurones are the same
Receptors on skin/viscera trigger action potential when stimulated
Impulses travel via dorsal root ganglion to CNS
Features of motor neurones in PNS? There are differences.
Somatic - soma in CNS, impulses travel along ventral root through spinal nerve to appropriate skeletal muscle to trigger contraction
Autonomic - Preganglionic neurone in CNS, impulse travels along axon where is synapses at autonomic ganglion with postganglionic neurone, impulse then carried to appropriate target
Stages of ANS sensory and motor transmission?
Sensory - Periphery of body to dorsal root ganglion to dorsal horn of grey matter
Motor - From ventral horn of grey matter to preganglionic neurone to autonomic ganglion to postganglionic neurone
Stages of SNS sensory and motor transmission?
Sensory - Periphery of body to dorsal root ganglion to dorsal horn of grey matter
Motor - Ventral horn of grey matter via the ventral root
Spinal nerve formed where and from what?
Intervertebral foramen
From junction of dorsal and ventral roots
What do spinal nerves divide into and what do these innervate?
Dorsal and ventral rami
Dorsal rami innervate muscle and skin of the back
Ventral rami innervate muscles and skin of the rest of body
What is a dermatome?
An area of skin innervated by a particular spinal nerve
What is a myotome?
An area of muscle innervated by a particular spinal nerve
Where are spinal nerves recombined to form peripheral nerves?
At a point called a plexus
Which spinal nerves innervate the upper limbs and how?
C5-T1
Ventral rami innervate upper limbs through the BRACHIAL plexus
Which spinal nerves innervate the lower limbs and how?
L2-S2
Ventral rami innervate the lower limbs through the LUMBOSACRAL plexus
Peripheral nerve changes after compression injury?
Compression injury breaks continuity of axoplasm so no action potentials can be propagated.
Distal part of nerve degenerates but proximal stump remains intact, macrophages phagocytose axonal/myelin debris.
Growth of axonal sprouts from proximal stump guided by scaffold of proliferating Schwann cells.
First axonal sprout makes contact with target organ, growth/myelination occurs.
Nodes of Ranvier in regenerated axon will be closer together than initially (slower transmission)
What is and what are the 2 types of peripheral neuropathy?
Progressive degeneration of peripheral nerves
Segmental demyelination - Schwann cells die so slower continuous conduction replaces saltatory conduction in regions without Schwann cells
Axonal degeneration - Leads to complete conduction block
What can be used to diagnose peripheral nerve disorders?
Conduction velocity - can determine is a peripheral neuropathy is present and what type
Nerve biopsy - can be used to study pathogenesis of the disease
