Disease of Motor Units

Question 1

What are the most common symptoms in patients with neurological diseases?

Answer 1

Movement disorders, (they will have other symptoms also)

Question 2

What are the types of paralysis (when muscles don’t respond to command of the brain)

Answer 2

Monoplegia (one limb)

Hemiplegia (2 limbs)

Paraplegia (both bottom limbs)

Quadriplegia (all limbs)

** you cn also have these in Paresis (weakness not full paralysis)

Question 3

What types of muscle tone abnormalities can you get?

Answer 3

• *Hypertonia**:
  a) spasticity; stroke, ALS, MS
  b) rigidity (PD)

Question 4

What is Ataxia?

Answer 4

Incoordination of movement

• Decomposition of movement
• Dysmetria (finger nose test)

Question 5

What types of involunary movements/muscle contractions can you get?

Answer 5

• Muscle spasm
• Epileptic fit
• Tremor (at rest= PD, intention tremor = parkinsons)
• Dyskinesia (in PD after prolonged L-dopa)

Question 6

Draw the table that shows the general overview of

lesion type vs motor symptoms

Answer 6

Acute Chronic

Focal trauma or vasc. cause Brain Tumor

Diffuse Toxin or infection Degeneration

Question 7

Located in the __________. There are two types, a_______________and ____________________

-
-

Answer 7

Located in the spinal cord/brainstem. There are two types, alpha-motoneurons (directly control muscles) and gamma-motoneurons (influence muscle spindle fibres).

The a-motoneurons are the ‘final common path’ who get their inputs from

• Descending tracts (cortico-spinal, rubro-sinal, reticulospinal)
• Spinal (brainstem interneurons
• Peripheral receptors (1a afferent fibres from muscle spindles)

Question 8

Where are the different locations you can get a lesion in a ‘motor unit’ (cell body + axons + neuromuscular junctions + innervated muscle fibres)

Answer 8

Cell Body
Axons ‘axotomy’
Neuromuscular Junction
Muscle Fibres

Question 9

What is it when you get a lesion at the level of the muscle fibre?

Answer 9

A Myopathy.

1. Muscular Dystrophy
   2.

Question 10

Muscular Dystropy

Answer 10

A common form of myopathy.

• A group of inherited disorders which all have deficits in muscle proteins and progressive muscle wasting and weakness (w/o primary structutal abnormality in motoneurons/LMN, muscles not nerves!)
• Duchenne Muscular Dystrophy (DMD); most common MD in kids
• Myotonic Muscular Dystrophy (MMD): most common MD in adults,heart esp affected, get myotinia

Question 11

Myotonia?

Answer 11

Delayed relaxation of a muscle after a strong contraction.

Seen in MMD patients

Question 12

How do you get MMD?

Answer 12

Inherited Dominant gene.

Up to 2000 ‘triple’ CTG repeats in chromosome 19, coding for a protein kinase myotonin.

Question 13

What type of disease affects the NM junction?

Answer 13

Myasthenia Gravis!

• Muscle weaknes not wasting
• Can be generalised (lots of muscles affect.) or Ocular (eyes)
• Autoimmune Disease → fewer Ach receptors → lower EPP → less synaptic transmission
• If you looked at a biopsy the folds of tissue are much smaller.

Question 14

Can we treat the symptoms of Myasthenia Gravis?

Answer 14

Yes, by using endrophonium; an ACh esterase blocker.

More ACh present in the synaptic cleft → better muscle contraction

But this only works for ~30seconds so this is a diagnostic test more then anything!

**You can also detect antibodies against ACh in serum (~85% of patients)

Question 15

What is Botulism?

Answer 15

A type of food poisoning; with bacteria releaseing botulinum toxins under anaerobic condition.

1 micrograms kills an adult human if injected!

Question 16

How does Botulinum actually work?

Answer 16

Toxins blind the nerve terminals; are internalised by endocytosis and cause proteolysis of several membrane proteins involved in NT release.

This leads to muscle (both striated and smooth) paralysis due to les ACh, because the ANS is also affected.

Infant botulism was a massive concern due to contaminated milk products/honey: constipation, lethargy, weakness etc

Question 17

What is botox made out of and what is it used for?

Answer 17

Made from botulim, paralysis muscles → apparence of youth

• Severe neck spasms
• Strabismus
• Upper or lower limb spasticity
• Dystonias (involuntary movements)
• Hyperhydrosis (exessive sweating)
• urinary disorders (eg;overactive bladder)
• Migrane (by reducing facial tension)

Question 18

What happens with a lesion of the axons ‘Axotomy’, in terms of the abandoned peripheral part and the central nerve?

Answer 18

Proximal Part: stays relatively the same, a little chromatolysis

• Peripheral Part:* dramatic wallarian degeneration
• loss of the synaptic transmission (~24hrs)
• degeneration due to the loss of ‘axon survival factor’ NMNAT2 (within days)

**draw the injured lesion!!

Question 19

If an axon is injured can it regenerate?

Answer 19

Yes!

1. Axon regeneration occurs 1-2mm/day, due to lots of Schwann cells (that usually create myelin form a tunnel)
2. Re-innervation of muscles (if it reaches the body)
3. Re-myelination of axons (partial, and sometimes you get functional recovery)

**although Wallerian degeneration of axons can also occur in the CNS it’s NOT followed by regeneration!!!