Which of the following relays via interneurons on anterior horn cell -
Ans. is 'b- i.e., Corticospinal tracto Corticospinal tract terminates on a-motor neuron (anterior or ventral horn cells) via intemeuron.PYRAMIDAL TRACT tCORTICOSPIN AL TRACT)o Corticospinal tract is the most important tract through which the motor cortex 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.o The corticospinal tract originates about 30 percent from primary motor cortex, 30 percent from premotor areas (premotor cortex & supplementary motor area) and 40% from the somatosensory area. So, there are 40% sensory fibers in the corticospinal tract.o After leaving the cortex, 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 corticospinal 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.o A few fibers (20%) do not cross to the opposite in the medulla and descend ipsilaterally as anterior (ventral) corticospinal tract.o 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 cortex. 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.o Coricaspinal tract is concerned with voluntary activities of body -Voluntary control of movement is absolutely dependent on the activity of corticospinal fibers.
Muscle spindle
Corticospinal tract
Spinothalamic tract
Spinocerebellar tract
Neural Tracts