Peripheral Neurology Flashcards
What are the three most important disorders of the peripheral nervous system?
Guillain-Barre syndrome
Length dependent neuropathy
Mysathenia Gravis
What is the peripheral nervous system?
All neurons that are not in the brain and spinal cord
- nerve roots -> nerve plexus -> peripheral nerves -> neuromuscular junction -> muscle
What is the function of the peripheral nervous system?
Sensory input into the CNS
- pain, temperature, light touch, proprioception
Motor output to the muscles
Innervation of the viscera
- autonomic innervation of abdominal and thoracic viscera (Gut, CV system, breathing)
Where does sensory and motor information enter and exit the spinal cord?
Incoming sensory information enters via the posterior (dorsal) root
Motor information exits the cord via the anterior (ventral) root
What is the name of collections of nerve cell bodies in the PNS vs the CNS?
PNS - ganglia
CNS - nuclei
Describe the relationship of axons, endoneurium, perineurium and epineurium to each other.
Axons are bundled together in little sheaths called the endoneurium.
Lots of axon containing endoneurium bundles are bundles together within sheaths called the perinerium
These perineurum covered bundles are in turn grouped together within epineurium sheaths, and are called nerves
What are the possible nerves and their associated fibre types in the PNS?
Large (myelinated) fibres - motor nerves - proprioception, vibration and light touch (dorsal column) Thinly myelinated fibres - light touch - pain and temperature (spinothalamic) Small (unmyelinated) fibres - light touch - pain and temperature
Describe the pysiology of a neuromuscular junction.
An action potential arrives along the axon
This causes voltage gated calcium channels to open
The resulting calcium influx causes release of neurotransmitter filled vesicles, which fuse with the cell membrane
ACh is released into the synaptic cleft and binds to receptors, causing ion channels to open
ACh binds to postsynaptic receptors on the muscle, causing a sodium influx which depolarises the cell
This causes voltage gated calcium channels to open in the muscle, allowing an influx of calcium
Calcium influx stimulates muscle contraction
How does a neuropathy of the peripheral motor fibres present clinically?
Weakness
Muscle atrophy
How does a neuropathy of the peripheral sensory fibres present clinically?
Large myelinated fibres - sensory ataxia - loss of vibration sense - numbness and tingling Small (thinly myelinated/unmyelinated) fibres - impaired pin prick/ temperature - painful burning - numbness and tingling
How does a neuropathy of the peripheral autonomic fibres present clinically?
Postural hypotension Erectile dysfunction GI disturbance - constipation Abnormal sweating
What is the most common type of peripheral neuropathy?
Length-dependent axonal neuropathy
- so the pathology is within the axon of the nerve itselg
How is length-dependent axonal neuropathy length dependent?
Because whatever the toxic cause of the condition it, the longest nerves in the body are exposed to it the most
What is length-dependent axonal neuropathy?
A symmetrical, slowly progressive destruction of the longest nerves in the body
- so symptoms begin in the toes and feet
What are the signs and symptoms of length-dependent axonal neuropathy?
Burning pain/tingling
in the toes/feet (depending on which nerve are affected)
- slowly spreads up the legs
- starts affecting the hands once the symptoms reach the knee
Tends to affect the thinly/unmyelinated fibres
- no significant sensory ataxia
- little/no weakness
