NB8-7 - Peripheral Nervous System Disorders and DLA Flashcards
Describe how conduction velocity for a motor nerve is determined.
Proximal (further from the recorder and distal (closer to the recorder) electrical stimulators are placed over the same nerve and a recorder is placed on a muscle for that nerve. The nerve is stimulated with one, then the other stimulator and the time it takes for the muscle to twitch is recorded. To control for NMJ transmission time and muscle deploarization time, the time and distance difference between the two stimulators is used in the calculation of velocity. Refer to image
Describe how conduction velocity for a sensory nerve is determined.
Stimulator is placed on a region and two recorders are placed at different points along the nerve that senses for that region. Conduction velocity is calculated in the same way as it is for motor neurons. Refer to image
What is the average nerve conduction velocity?
55-60 m/s
D
What are positive and negative manifestations?
Positive Manifestations - an excess or distortion of normal functions
Negative Manifestations - total loss or diminution of normal function
What are the positive and negative manifestations of a peripheral nerve disease? Explain the underlying causes of these manifestations.
- Positive Manifestations
- Fasciculations caused by unpredictable activity in pathological motor units
- Paresthesias possibly caused by ephaptic coupling between adjacent hyperexcitable pathological sensory neurons
- Brief periods of pain caused by nerve compression
- Negative Manifestations
- Loss of or diminshed muscle strength
- Loss of or diminshed tendon reflexes
- Autonomic nervous deficites (ie - anhidrosis)
- Impaired sensations
Why doesn’t nerve regeneration occur in the CNS?
Unlike schwann cells in the PNS, oligodendrocytes do not release nerve growth factor to guide regenerating axonal sprouts. Also, astrocytes multiply in regions of trauma and form a gliotic scar that mechanically impedes sprouting axons.
Describe how a regenerating motor neuron knows where to contact a muscle. Also, how does the muscle know where to put the new end plate?
Different laminin isoforms exist in the synaptic basal lamina, laminin 11, and the extrasynaptic basal lamina, laminin 2. Association of these laminins guide a regenerating axon towards a motor end plate. Most of the time, the axon just happens to contact the muscle at the old NMJ. When the refenerating axon contacts the muscle basal lamina, it differentiates into a nerve terminal.
What is the acute peripheral neuropathy we need to know? Describe its etiology, symptoms, diagnosis, and treatments.
Guillian-Barre Syndrome is an auto-immune reaction that causes demyelination of peripheral axons. It typically occurs about 2-3 weeks after a GI or respiratory infection and rapidly ascends causing motor and sensory loss.
It is diagnosed via a nerve conduction study and LP (elevated protein in CSF)
Treated with immune globulin, plasma exchange, and ventilatory support
What are the chronic peripheral neuropathies we need to know?
- Leprosy (hansen Disease)
- Lead Poisoning
- Alcoholic Peripheral Neuropathy
- Diabetes Mellitus
Describe the etiology, symptoms, and treatments of leprosy
Leprosy (Hansen Disease) is a chronic bacterial infection that affects the skin and peripheral nerves causing profound loss of pain/temp sensation. Usually presents as a painless skin patch acccompanied by loss of sensation, wastins, and muscle weakness. Treatment with antibiotics
Describe the neuropathies that Lead Poisoning can cause.
Lead Poisoning can cause motor neuropathies in adults and encephalopathies in children. Virtually no sensory symptoms. Presents with bilateral focal weakness and wasting of extensor muscles of fingers, wrist, and arms.
Why does alcohol consumption cause a peripheral neuropathy and how does this neuropathy usually present? How does this neuropathy affect nerve conduction velocity?
Over consumption of alcohol leads to peripheral neuropathy because alcohol has neurotoxic effects. The neuropathy presents with bilateral sensory loss from the foot and progresses up. Motor losses follow.
No effect on nerve conduction velocity
Why does diabetes mellitus cause peripheral neuropathies? How does this type of neuropathy present?
Chronic diabetes is known to have a degenerative effect on blood vessel, beginning with the smallest. This is thought to be the reason that diabetes also leads to defects in the myelination of peripheral nerves. Usually presents with a loss of pain/temp sensation in the hands and feet and progresses up. Because of the loss of pain sensation, the feet often get injured which leads to an infection that quickly spreads because of a lack of blood flow to the region.
A
