4 - Disorders of the Motor Unit Flashcards
Name some diseases that effect alpha lower motor neurons?
Spinal muscular atrophy, amylotrophic lateral sclerosis (also affects UMN), poliomyelitis, and tetanus.
Name some diseases that effect peripheral nerves?
Charcot-Marie Tooth and Guilian-Barre syndrome.
Name a neurological disease that impacts the neuromuscular junction?
Myasthenia gravis
Name a neurological disease that effects the muscle?
Duchenne’s muscular dystrophy (or any muscular dystrophy).
A 17 yo notices that for the last week she has worsening difficulty walking as well as numbness and tingling. Today she can’t walk. She has flaccid tone and areflexia peripherally, and has no atrophy, no fasiculations and no loss of sensory patterns. She has weakness in her legs and hips. What type of neuron does her injury involve?
Lower (peripheral) motor neuron. We can deduce this because we know that peripheral nerve lesions can result in hypotonia (flaccid tone in this girl) and hyporeflexia (no reflexes in her). She has guillain barré syndrome.
What are the symptoms of a central (upper motor neuron) lesion? What type of symptoms do these usually yield?
Hypertonia Hyperreflexia No (or mild) atrophy No fasciculation Central sensory pattern Seizures and cognitive abnormalities Tend to yield positive signs.
What are the symptoms of a peripheral (lower motor neuron) lesion? What type of symptoms do these usually yield?
Hypotonia Hyporeflexia Significant atrophy Fasciculations Peripheral sensory patterns Tend to yield negative signs
The cell body of lower motor neurons are located where?
In the spinal cord.
What are the components of a motor unit?
Alpha lower motor neuron will its cell body in the ventral horn of the spinal cord (LMN) whose axon forms the peripheral nerve. NMJ Muscle.
A 17 yo notices that for the last week she has worsening difficulty walking as well as numbness and tingling. Today she can’t walk. She has flaccid tone and areflexia peripherally, and has no atrophy, no fasiculations and no loss of sensory patterns. She has weakness in her legs and hips. Is her injury congenital or acquired?
Since her symptoms only began last week, we can safely assume that her disease is acquired. We also know that this is a lower motor neuron injury because of her decreased tone and decreased reflexes.
A 17 yo notices that for the last week she has worsening difficulty walking as well as numbness and tingling. Today she can’t walk. She has flaccid tone and areflexia peripherally, and has no atrophy, no fasiculations and no loss of sensory patterns. She has weakness in her legs and hips. Is her injury congenital or acquired?
Since her symptoms only began last week, we can safely assume that her disease is acquired. We also know that this is a lower motor neuron injury because of her decreased tone and decreased reflexes. She has guillain-barré syndrome.
What is guillain-barré syndrome? What is it caused by and where is it localized?
Peripheral neuropathy that occurs during an autoimmune attack against ones nerves. Predominantly proximal inflammation located outside of the spinal canal. Penetration of the spinal canal results in increased proteins in CSF.
What are symptoms of Guillain-Barré Syndrome? What does this disease usually occur?
Areflexia, ascending weakrness, respiratory weakness, symptoms peak at 2-3 weeks. Usually occurs post-infection.
What is the mechanism of destruction of Guillain-barré syndrome?
The body attacks its own myelin and slwos down the conduction of the AP; if it’s too slow, it stops early because the potential can’t cross a Node of Ranvier if its too large.
How is guillain-barré treated? What is the recovery time?
Immunosuppression with IV Ig (NOT steroids) Recovery is prolonged: 80-90% recovery at 1 yr. Slow because axon regrowth is approx 1mm/day
For the past 6 years a 17 yo girl has had progressive ascending weakness as well as numbness and tingling in her feet and legs. She is flaccid in her lower legs and areflexia in her legs. She has atrophy of her feet and lower leg muscles and sensory loss in both legs below the knee. She is weak in her lets to her feet. She has no fasciculations. What type of neuron is causing her symptoms? What is the source of her illness? What is her most likely diagnosis?
This is a congenital lower (peripheral) motor neuron problem. It’s probably congenital because she’s had it for 6 yrs. It’s a lower (peripheral) motor neuron problem because she has hypotonia (flaccid lower legs), areflexia of her legs, and atrophy of her feet and legs. She also has peripheral sensory loss. Charcot-Marie Tooth Peripheral Neuropathy.
What are symptoms of Charcot Marie Tooth? What is this caused by? What is the treatment?
A genetic peripheral neuropathy characterized by distal progressive sensory loss, distal progressive weakness, and “charcot foot” with a high arch. Numerous genes involved, variable age of onset, sensory neuron involvement. No treatment.
A 3 mo girl is noticed that for the last month she has had some decreased movements mostly in her legs. She is having problems breathing. She has flaccid tone, areflexia, no atrophy, tongue fasciculations, and no sensory loss. She is weak throughout her body and can’t lift her extremities against gravity. What type of neuron is causing her symptoms? What is the source of her illness? What is her most likely diagnosis?
Congenital lower (peripheral) motor neuron disease - spinal muscular atrophy. Congenital because she’s too young to have an acquired injury. Peripheral LMN because she has flaccid tone and areflexia.
What are symptoms of spinal muscular atrophy?
This is an alpha lower motor neuron disease that causers weakness (lower extremities more than upper), fasciculations, and muscle atrophy (with time).
A 7yo boy notices that for the past 6 mo he has had m\fluctuating weakness. He complains of his eyes drooping in the day but is better in the morning. His weakness is worse after activities. He has normal tone, reflexes, no atrophy, no fasciculations, and no sensory loss. He has fatiguable weakness and droopy eyes. What type of neuron is causing her symptoms? What is his most likely diagnosis?
He has an acquired lower motor neuron disease - myasthenia gravis.
What occurs biologically in myathenia gravis?
Affects nicotinic acetylcholine receptors and may also affect other parts of the NMJ. Ach depletion (synthesis in cell body and transport along axon takes time).
What occurs to the NMJ over time in pts with myastenia gravis?
Antibodies on the Ach receptors cause flattening of the junction and blocking of the receptors. Over time you can get fixed weakness because of this change in architecture.
A 7 yo boy notives that for the past 5 yrs he’s had progressive walking difficulties and often tip toe walks. His maternal uncle died in his 20s in a wheelchair. He has hyporeflexia in his legs, weakness in his legs (hips more than ankles) and very large calves. He has no atrophy, normal tone, and no sensory loss. What type of neuron is causing his symptoms? What is the source of his illness? What is his most likely diagnosis?
Congenital lower motor neuron disease: muscular dystrophy. Congenital because this has been occurring for five years. Peripheral because of hyporeflexia.
Muscular membrane dystrophy
What are symptoms of muscular dystrophy?
Progressive weakness, muscle degeneration due to instability of the membrane, and has involvement of the heart, brain, and skin.
