Lecture 27: diseases of motor units Flashcards

1
Q

Frequent symptoms/neurological terms?

A

Paralysis - inable to conduct voluntary movements in a certain part

Paresis - weakness in a certain part but not full paralysis

Muscle tone abnormalities - (Hypertonia)

= spasicity(stroke, ALS, MS) or rigidity (PD)

Ataxia - (Incoordination)

= decomposition of movement or dysmetria

Involuntary movements

= Spasm, epileptic fit, tremor (at rest in PD or intention tremour in cerebellar ataxia), dyskinesia (PD after prolonged L-DOPA)

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2
Q

Acute v chronic

focal v diffuse?

A
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3
Q

A motor unit consists of?

A

Cell body and axon with a varying number of branches off the axon towards the endplates/neuromuscular junction and all the striated muscle fibres innervated by these braches.

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4
Q

Most common form of myopathy?

in Children?

A

Muscular dystrophy -(a familiar form of myopathy)

A group of inherited disorders characterised by deficits in muscle proteins and progressive muscle wasting and weakness (without primary structural abnormality in motorneurons)

In children most common is DMD - Duchenne MD where protein dystrophin has a mutation on its gene.

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5
Q

Most common MD in adults?

A
  • MMD - Myotonic MD
  • Onset usually in the 30s
  • Is a wasting and weakness of muscles (inc. the heart)
  • Myotonia: Delayed relaxation of a muscle after a strong contraction
  • Inherited (dominant): up to 2000 triple (CTG) repeats in chromosome 19 coding for protein kinase (Myotonin)
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6
Q

Myasthenia Gravis features?

A
  • Muscle weakness (without wasting)
  • Autoimmune disease
  • Fewer ACh receptors > dec end plate potential > dec transmission
  • Junctional folds become a lot smaller
  • May be generalised and/or ocular form
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7
Q

Diagnosis of Mysthenia Gravis?

A

Face appears droopy and then after an injection of endophonium (a blocker of ACh esterase) their face become a lot more normal looking for about 30sec-1min.

-Often pre-treated atropine to reduce gastro-intestinal and other side-effects.

detection of antibodies against ACh receptors in the serum (found in ≈ 85%)

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8
Q

Botilism features?

Mechanism of action?

Muscles affected and effects of this?

A

Food poisoning (by Clostridium botulinum)

Botulinum toxins produced under anaerobic conditions: 1 microgram can kill a human if injected

Muscle paralysis due to decreased ACh release by:

  1. Toxins bind to nerve terminals and are internalised by endocytosis
  2. Toxins cause proteolysis of several membrane proteins involved in neurotransmitter release (eg. SNAP-25 and Syntaxin)

Striated and Smooth muscle affected:

  • Disruptions also in the ANS (dry mouth, postural hypotension)
  • Infant botulism = constipation, lethargy, weakness, difficulty feeding, can progress to flaccid paralysis and resp arrest!
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9
Q

Other applications of botulinum toxins? (botox)

A
  • Severe neck spasms
  • Cross eyes
  • upper and lower limb spasticity
  • Dystonias
  • Hyperhydrosis
  • Gastrointestinal and urinary disorders
  • migrane
  • depression
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10
Q

Wallerian degeneration in peripheral nervous system?

A

Changes in distal part of the axon:

  • Loss of synaptic transmission (on electrical stimulation of the axon) within ≈24h
  • Progressie degeneration within days (due to the loss of the ‘axon survival factor’ NMAT2)
  • changes in the motorneuron cell body: Chromatolysis
  • Axon regeneration: 1-2mm /day facillitated by schwann cells > re-innervation of muscles > Re-myelination of axons (partial) > sometimes functional recovery to varied extent.
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11
Q

Wallerian degeneration in the CNS?

A

This will occur the same in the CNS but it is not followed by regeneration.

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12
Q

First symptoms patients present with when suffering from mysthenia gravis?

A

Muscle weakness that gets worse when they try and do simple tasks

Issues with day to day tasks like washing their hair and prolonged chewing.

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