Motor Control and Diseases 1

Question 1

Differentiate between upper and lower motor neurons.

Answer 1

Lower motor neurons = spinal motor neurons
located in the spinal cord
are responsible for conveying motor signals from the spinal cord to muscles, causing them to contract
Each muscle fibre receives input from a single lower motor neuron
Each lower motor neuron innervates the fibres of just one muscle

Neurons in the brain that control motor function are upper motor neurons
located in the brain and spinal cord
are responsible for initiating and modulating voluntary movements

Question 2

Recall that motor neurons also exhibit somatotopy.

Answer 2

Motor cortex is also somatotopically mapped

They are organised in a spatial manner within the nervous system according to the body part they control

Lower body represented medially, upper body laterally

Somatotopy in the motor cortex reflects the location of the upper motor neurons that innervate lower motor neurons in the spinal cord

Question 3

Recall the mechanism by which movement planning/anticipation is achieved

Answer 3

Achieved through the coordination of multiple brain regions, including the primary motor cortex, the premotor cortex, and the supplementary motor area. These regions work together to generate a motor plan, which is a sequence of commands that specify the muscle contractions needed to produce a particular movement.

Postural control is integrated with voluntary movement and is part of movement planning/anticipation

Question 4

Note the consequences of motor neuron degeneration

Answer 4

E.g. Motor neuron disease, AKA, ALS
-Muscle atrophy and sclerosis of the lateral spinal cord (which is the mark of the degeneration of axons in the CST
-Can affect upper and lower motor neurons
-Lower motor neuron disease - muscle paresis or paralysis, loss of muscle tone due to loss of stretch reflexes, leading to severe muscle atrophy, patients usually die from lung dysfunction due to atrophy of intercostal muscles
-Upper motor neuron disease - muscle weakness, spasticity due to increased muscle tone due to failure of modulation of stretch reflex, hyperactive reflexes, loss of fine voluntary movement, patients die from loss of input to bulbar muscles via the corticobulbar tract

Excitotoxicity is one possible cause of the neurons degeneration, overstimulation by glutamate leads to neuronal cell death

Motor neuron degeneration is almost always fatal