Diseases of Motor Units

Question 1

Focal vs diffuse and acute vs chronic lesions for motor systems

OUTLINE don’t memorise

Answer 1

Acute Chronic

Focal Trauma/Vascular Brain tumour

Diffuse Toxin/Injection Degeneration

Question 2

Motoneuron locations

Motoneuron is a LMN

Answer 2

Brainstem and spinal cord

Question 3

Types of motoneurons

Answer 3

Alpha-extrafual

Gamma- intrafusal/ msucle spindles

Question 4

Inputs to motoneurons (alpha)

Answer 4

Corticospinal; rubro-spinal; reticulo spinal; vestibulo-spinal; 1a afferent

Question 5

Muscular Dystrophy, what is it and what does it cause

Childen vs adults

Answer 5

Inherited group of disorders that present due to a lack of muscle proteins.

Results in Muscle wasting and weakness.

Most common in children is DMD, dystrophin defect.

Most common in adults is myotonic MD, also show myotonia (delay of muscle to relax after contraction). Myotonin defect (expansion of CTG)

Question 6

Myasthenia Gravis

test?

Answer 6

Autoimmune, fewer ACh receptors, less EPP, less transmission.
Muscle weakness

Test: edrophonium blocks ACh esterase or test for antibodies in serum

Question 7

Botulism

Answer 7

A form of food poisoning, from clostridium botulinum.

Toxins are internalised and break down proteins involved in NT release, so less ACh released. Affects striated and smooth muscle

Question 8

Axotomy causes

Answer 8

Disc protrusion or plexus lesion

Causes distal Wallerian Degeneration
Proximal chromatolysis
Axon regenerates through debris

Question 9

Wallerian Degeneration

note can occur in CNS but no regeneration

Answer 9

• Loss of synaptic transmission
• Degeneration due to lack of axon survival factor NMNAT2
• Schwann cells can survive for axon regeneration and re-innervation