Which of the following relays interneurons on anterior horn cell ?
Ans. is 'b' i.e., Coicospinal tractCoicospinal tract terminates on a-motor neuron (anterior or ventral horn cells) interneuron.PYRAMIDAL TRACT (COICOSPINAL TRACT)Coicospinal tract is the most impoant tract through which the motor coex controls the activity of the ventral horn cells (a-motor neurons) in the spinal cord. It is also called pyramidal tract because they form the pyramid of the medulla.The coicospinal tract originates about 30 percent from primary motor coex, 30 percent from premotor areas (premotor coex & supplementary motor area) and 40% from the somatosensory area. So, there are 40% sensory fibers in the coicospinal tract.After leaving the coex, it passes through the posterior limb of internal capsule and then downward through the brainstem, forming the pyramids of medulla. The majority (80%) of the pyramidal fibers then cross the lower medulla to the opposite side and descend as the lateral coicospinal tract and finally terminating principally on the interneuron in the intermediate region of gray matter. Some also terminate directly on the a-motor neuron, especially those concerned with skilled movement.A few fibers (20%) do not cross to the opposite in the medulla and descend ipsilaterally as anterior (ventral) coicospinal tract.The most impressive fibers in the pyramidal tract are a population of large (16 pm) myelinated fibers which originate from Giant pyramidal cells, called Betz cells, that are found only in primary motor coex. These fibers transmit the nerve impulses to the spinal cord at fastest speed. However, these fibers form only 3% of the total. The other 97% are mainly fibers smaller than 4 m in diameter that conduct background tonic signals to the motor areas of the cord.Coricospinal tract is concerned with voluntary activities of body- Voluntary control of movement is absolutely dependent on the activity of coicospinal fibers.
Muscle spindle
Coicospinal tract
Spinothalamic tract
Spinocerebellar tract