Lecture 12; Motor Control + movement disorders

Question 1

Describe how the motor system does not act alone;

Answer 1

The motor system controls movement together with sensory systems

(feedback)

Question 2

Give an example of how the sensory system acts with with the motor system?

Answer 2

Feedback i.e did that movement actually happen? - propioceptors and visual system say so

Thus allowing planned movement

Question 3

How can motor function be affected by sensory loss?

Answer 3

Disoders can develop when the sensory system is effected

Question 4

What are the types of LMNs?

Answer 4

Alpha and gamma

Question 5

What is the motor unit?

Answer 5

Alpha motor neuron
Synapse
Muscle fibre it innervates

Question 6

Where do motor neurons located?

Answer 6

• Brain
• Anterior Ventral Horns
• 12 cranial nerves

Question 7

What are the alpha motor neurons also known as?

Answer 7

The final common pathway

• convergence of inhibitory and excitatory synapses (final output message to muscles)

Question 8

What to lower motor neurons recieve synpatic inputs from?

Answer 8

-Descending tracts
 cortico-spinal(pyr.) 
 rubro-spinal
 vestibulo-spinal
 reticulo-spinal
-Spinal (brainstem) interneurons
-Peripheral receptors (Group Iaafferent fibres from muscle spindles)

Question 9

What are the types of frequent symptoms of movement disorders?

Answer 9

• Paralysis
• Hypertonia
• Ataxia

Question 10

What are abnormal involuntary movements?

Answer 10

Epileptic fit

Tremor in PD

Question 11

What are the possible locations of lesions in motor units?

Answer 11

• Cell bodies
• Muscle fibre
• Motor end plates(myopathies)
• Axon

Question 12

What is the most common form of myopathy?

Answer 12

muscular dystrophy

Question 13

What is muscular dystrophy?

Answer 13

A group of inheriteddisorders characterized by deficits in muscle proteins and progressivemuscle wasting and weakness (withoutprimary structural abnormality in motoneurons)

Question 14

What is the most common form of muscular dystrophy in children?

Answer 14

Duchennemuscular dystrophy (DMD)

Question 15

What is the most common form of muscular dystrophy in adults?

Answer 15

Myotonic muscular dystrophy

Question 16

What is myotonia?

Answer 16

Myotonia: delayedrelaxation of amuscle after a strong contraction

Question 17

What happens in myotonia?

Answer 17

Wasting and weaknessof muscles

Question 18

What is the cause of myotonia?

Answer 18

Up to 2000’triple’ (CTG) repeats in chromosome19 coding for a protein kinase myotonin

Question 19

What is myasthenia gravis?

Answer 19

• Muscle weaking without wasting

•Autoimmune disease
•Fewer ACh binding sites
EPPs (decreased)
Synaptic transmission (decreased)

Question 20

What is botulism?

Answer 20

Food poisoning (Clostridium botulinum)Botulinum toxinsproduced under anaerobic conditions;1 μg kills an adult human if injected

Death by muscle paralysis

Question 21

What is the effect of botulism toxins?

Answer 21

Muscle paralysis due to ACh release

Question 22

Where does botulism toxin bind?

Answer 22

Toxins bind to nerve terminals, are internalized by endocytosis,and cause proteolysisof several membrane proteins involvedin vesicle ‘docking’ and neurotransmitter release(e.g. SNAP-25and Syntaxin)

Question 23

What types of muscles do botulism toxin effect?

Answer 23

•Striated and smooth muscles affected

Disruptions in the autonomic nervous system (dry mouth, posturalhypotension, severe constipation

Question 24

What happens in infant botulism?

Answer 24

Infant botulism (honey, contaminated milk products)Constipation, lethargy, weakness, difficulty in feeding, can progress to flaccid paralysis and respiratory arrest

Question 25

What else can the botulism toxin be used for?

Answer 25

• Severe neck spams
• Striabismus
• Upper and lower body spasticity
• Dystonias
• Hyperhydrosis
• GI and urinary disorders
• Migraine
• Depression

Question 26

What is wallerian degeneration?

Answer 26

Trauma to the distal part of axon.

• loss of synaptic transmission (on electrical stimulation of the axon) within ~ 24 hrs
• degeneration within days (due to the loss of the ‘axon survival factor’ NMNAT2, secreted by cell body)

Question 27

What else can happen when distal axons are damaged?

Answer 27

Axon regeneration(1-2 mm / day), 
facilitated by arrays of Schwann cells  

Re-innervationof muscles

Re-myelinationof axons (partial)

; in some cases functional recovery

Note: Wallerian (did these experiments)

Question 28

Describe how the axon regrowth occurs;

Answer 28

• NMNAT2 synthesised by cell body
• Histological changes occur to the cell body too (chromotolysis (after axon cut)
• Ribosomes shift distally to dendrites
• New growth cone forms expands and tries to reach target, but relies on surviving undamaged schwann cells to to secrete something and direct growth

(doesnt happen to unmyelonated axons)