Lecture 12; Motor Control + movement disorders Flashcards
Describe how the motor system does not act alone;
The motor system controls movement together with sensory systems
(feedback)
Give an example of how the sensory system acts with with the motor system?
Feedback i.e did that movement actually happen? - propioceptors and visual system say so
Thus allowing planned movement
How can motor function be affected by sensory loss?
Disoders can develop when the sensory system is effected
What are the types of LMNs?
Alpha and gamma
What is the motor unit?
Alpha motor neuron
Synapse
Muscle fibre it innervates
Where do motor neurons located?
- Brain
- Anterior Ventral Horns
- 12 cranial nerves
What are the alpha motor neurons also known as?
The final common pathway
- convergence of inhibitory and excitatory synapses (final output message to muscles)
What to lower motor neurons recieve synpatic inputs from?
-Descending tracts cortico-spinal(pyr.) rubro-spinal vestibulo-spinal reticulo-spinal -Spinal (brainstem) interneurons -Peripheral receptors (Group Iaafferent fibres from muscle spindles)
What are the types of frequent symptoms of movement disorders?
- Paralysis
- Hypertonia
- Ataxia
What are abnormal involuntary movements?
Epileptic fit
Tremor in PD
What are the possible locations of lesions in motor units?
- Cell bodies
- Muscle fibre
- Motor end plates(myopathies)
- Axon
What is the most common form of myopathy?
muscular dystrophy
What is muscular dystrophy?
A group of inheriteddisorders characterized by deficits in muscle proteins and progressivemuscle wasting and weakness (withoutprimary structural abnormality in motoneurons)
What is the most common form of muscular dystrophy in children?
Duchennemuscular dystrophy (DMD)
What is the most common form of muscular dystrophy in adults?
Myotonic muscular dystrophy
What is myotonia?
Myotonia: delayedrelaxation of amuscle after a strong contraction
What happens in myotonia?
Wasting and weaknessof muscles
What is the cause of myotonia?
Up to 2000’triple’ (CTG) repeats in chromosome19 coding for a protein kinase myotonin
What is myasthenia gravis?
- Muscle weaking without wasting
•Autoimmune disease
•Fewer ACh binding sites
EPPs (decreased)
Synaptic transmission (decreased)
What is botulism?
Food poisoning (Clostridium botulinum)Botulinum toxinsproduced under anaerobic conditions;1 μg kills an adult human if injected
Death by muscle paralysis
What is the effect of botulism toxins?
Muscle paralysis due to ACh release
Where does botulism toxin bind?
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)
What types of muscles do botulism toxin effect?
•Striated and smooth muscles affected
Disruptions in the autonomic nervous system (dry mouth, posturalhypotension, severe constipation
What happens in infant botulism?
Infant botulism (honey, contaminated milk products)Constipation, lethargy, weakness, difficulty in feeding, can progress to flaccid paralysis and respiratory arrest
What else can the botulism toxin be used for?
- Severe neck spams
- Striabismus
- Upper and lower body spasticity
- Dystonias
- Hyperhydrosis
- GI and urinary disorders
- Migraine
- Depression
What is wallerian degeneration?
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)
What else can happen when distal axons are damaged?
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)
Describe how the axon regrowth occurs;
- 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)
