Motor Control Flashcards
What are the observable signs of decreased quality of movement?
Paralysis, Weakness
Stiffness
Increased reactivity
Ticks, Twitches and Jerks
Fibrillations and fasciculations
Loss of coordination and smoothness
Loss of the effectiveness of movements
What is a “sign”, in relation to disorders of motor control?
Observable or measurable motor abnormalities, the presence of abnormalities, or the absence of normal motor actions.
What is a symptom, in relation to disorders of motor control?
Problems of motor function reported by patients Syndromes: associated or clustered signs and symptoms
Where are motor neuron cell bodies located?
Brainstem (cranial motor neurons) and spinal cord
Why are motor neurons able to produce 1:1 transmission?
Highly myelinated axons
Large synapse spread across muscle fibres
Ruffled post-synaptic membrane for increased SA
Where do motor neurons sit in the spinal cord?
Ventral horn
What are motor columns?
The topographically organised motor neurons in the spinal cord that belong to one muscle.
They tend to be organised into a pool in the ventral spinal cord, spanning multiple segments.

What is a motor unit?
All muscle fibres innervated by a single alpha motor neuron.
What is Henneman’s size principle?
The smallest motor neurons are recruited first, then gradually larger motor units are recruited with the largest being recruited last.
This ensures low force contractions are initially made and large force contractions made last, allowing fine movements to take place.

What types of muscle fibres are recruited first?
Slow fatiguing, because they’re active for all movements, whereas larger motor units are recruited only in large force movements, and therefore are fast fatiguing.
What is myasthenia gravis?
Autoimmune disease whereby the action of the NAChR is blocked.
ACh therefore can’t get to the receptor, blocking contractions.
What happens to muscles if they are un-innervated?
Fibrillations, fasciculations and eventually atrophy and degeneration.
What are fibrillations?
Tiny contraction cause by activity of a single muscle cell - can be due to hypersensitivity, increased AChR expression (including extra-junctional).
What are fasciculations?
Groups of muscle fibres contracting involuntarily, probably a motor unit synaptically activating due to spontaneous activation of a degenerating MN/axon.
Can be measured on surface (cf. fibrillations - need extracellular electrode).
What will happen to a muscle if it is denervated for a long time?
Atrophy and degeneration.
Atrophy can occur in catabolic states (diabetes, Cushing’s disease) but complete denervation will lead progressively to irreversible muscle loss.
When is the only time muscles are naturally inactive?
During REM sleep
What causes involuntary muscle activation?
Lower motor neurons connected to muscle spindles and Golgi tendon organs.
What does the muscle spindle do?
Sensory axons sit within the intrafusal muscle fibres and send signals back to the spinal cord to report on length of the muscle.
What is the Golgi tendon organ?
The Golgi tendon organ is embedded within the collagen matrix of the tendon with nerves that respond to how much force is experienced in the muscle.
What are the signs and symptoms of low motor neuron lesions?
Weakness or paralysis
Decreased superficial reflexes
Hypoactive deep reflexes
Decreased tone
Fasciculations and fibrillations
Severe muscle atrophy
Where can the monosynaptic reflex pathway be tested?
Anywhere there’s an exposed tendon.
This allows elucidation of where the lesion is in the spinal cord.
What is an upper motor neuron?
Any neuron that controls the excitability of lower motor neurons.
What is most of the input to the lower motor neurons via?
Local interneurons
What are the 2 main pathways by which axons get from the brain to the spinal cord?
Ventromedial and lateral pathways.





























