Question

1. Describe the structural characteristics of the spinal cord and their functions in the control of voluntary movement 2. Distinguish between the ascending and descending tracts of the CNS and describe their functions in the control of voluntary movement. 3. Describe a motor unit and its function in the control of voluntary movement. Discuss how the motor unit is involved in the generation of muscular force.

Answer 1

Ans 1...Structure of spinal cord

Spinal cord is the continuity of medulaa oblangta of brain.it extends up to L2 vertebra where it terminates into filum terminale that attaches to Sacram and a network of nerves called the cauda equana.

From a single spinal cord segment arises the anterior spinal nerves which carry motor fibres and posterior spinal nerves which carry sensory nerve.

Coming to voluntary control.spinal cord has tracts in it from peripheral nerves sensroy sensations are relayed in sensory tracts like spimothmic and spinocerebellar and then it is processed in brain and then motor tracts like corticospinal tracts carry motor sensation which relay in the motor nuclei in the spinal cord and then through the anterior spinal nerves it goes to muscle and action of muscles take place

Ans 2..Ascending tracts...They carry sensory sensation to the brain via the spinal.cord for example

Touch,temperature,pain sensations are carried by spinothalamic tracts

Vibration are carried by posterior column

Two point discrimination by spinocerebeller tracts

Whereas descending tracts carry motor sensations to the motor nuclei of spinal cord.for example the corticospinal tracts

Corticospinal tracts crosses to opposite side at the medula

Posterior column do not cross to opposite side

Ans 3...Motor unit is defined as the muscle with its nerve supply.

Motor nerve cary sensations from brain for contraction of muscles .At the motor end plate it release neurotransmitters like acetylcholine which causes contraction of muCles.

Mechanism of generation of force of contraction of muscle is by Calcium ion .The shifting of actin filament of muscle cell over myosin filament is ultimately causes contraction of muscles.