The medial lemniscus terminates and synapses in the ventral posterolateral (VPL) nucleus of the thalamus the somatotopy is preserved. The medial lemniscus travels through the brainstem with a preserved somatotopic arrangement where its ventral fibers arise from the nucleus gracilis and its dorsal fibers arise from the nucleus cuneatus. The internal arcuate fibers on the contralateral side of the medulla will come together to form the medial lemniscus. The internal arcuate fibers are axons that emerge ventrally from the dorsal column nuclei, course ventromedially through the medullary tegmentum, and ultimately cross the midline. This is where the DCML pathway decussates. Both the nucleus cuneatus and nucleus gracilis represent the second-order neuron of the DCML pathway. The nucleus cuneatus, which receives axons from the fasciculus cuneatus, is located laterally to the nucleus gracilis, which receives axons from the fasciculus gracilis. Similarly to the fasciculus gracilis, the fasciculus cuneatus terminates and synapses at the nucleus cuneatus, which is in the caudal medulla. Thus, it is located at spinal level T6 and above. On the other hand, the fasciculus cuneatus carries sensory information associated with the DCML pathway from the upper extremities. It is medial relative to the fasciculus cuneatus and travels the length of the spinal cord. The fasciculus gracilis carries sensory information associated with the DCML pathway from the lower extremities and terminates and synapses at the nucleus gracilis in the caudal medulla. However, most of the central axonal process will leave the dorsal horn gray matter without synapsing and enter the dorsal funiculus to help constitute either the fasciculus gracilis or the fasciculus cuneatus. Once in the spinal cord, the central axonal process gives off small collateral branches that will terminate in the spinal gray matter to facilitate spinal reflexes. Īfter receiving the sensory input from the periphery via the mechanoreceptor and conscious receptors, the central (proximal) axons of the dorsal root ganglia enter the spinal cord through the medial dorsal root entry zone. These sensory organs detect changes in muscle length and contraction and contribute to fine motor control and the relay of axial position information to the nervous system. Receptors of conscious proprioception include muscle spindles and Golgi tendon organs. Pacinian corpuscles have pressure sense and vibration sense. Free nerve endings on hair follicles also transmit information about fine touch. Meissner corpuscles transmit information about fine touch and two-point discrimination. Tactile mechanoreceptors include Meissner corpuscles, free nerve endings on hair follicles, and Pacinian corpuscles. These receptors classify into two types: tactile mechanoreceptors and conscious proprioception. The peripheral (distal) axons receive various signal inputs from the skin via the receptors associated with the DCML pathway. The pseudounipolar neurons contain peripheral (distal) and central (proximal) axonal processes. The cell body of the dorsal root ganglia, which is composed of pseudounipolar neurons, characterizes the first-order neuron of the pathway. There are three orders of neurons involved in this pathway that orchestrate signal transmission from the skin and joints to the cerebral cortex. The primary function of the dorsal column medial lemniscus (DCML) pathway is to convey sensory information regarding fine touch, two-point discrimination, conscious proprioception, and vibration sensations to the postcentral gyrus in the cerebral cortex from our skin and joints, excluding the head.
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