Question

In charge of the body's touch, proprioception, and vibration.

Options:
a) Posterior root ganglions have bipolar neurons that relay signals to the posterior column to synapse with cuneate (arm)/gracile (leg) fasiculi.
b) These fibers ascend rostrally towards their respective nuclei in the medulla and synapse with their respective nuclei, decussate to the contralateral side and continue as the medial lemniscus towards the VPL of the thalamus.
c) There they synapse to the final 3rd order neuron which leaves the VPL and ascends as the posterior limb of the internal capsule to their respective places in the cortex.
Clinical:
- Damage to posterior column fibers on one side of the spinal cord results in ipsilateral loss of vibration, proprioception, and discriminative touch below the level of the lesion.
- Lesion rostral to the decussation such as the medial lemniscus will result in contralateral losses that include the entire body besides the head

Answer 1

The dorsal column-medial lemniscal pathway processes touch, proprioception, and vibration sensations through a three-neuron relay, which starts with the dorsal root ganglion cells. Segregated into the fasciculus gracilis and cuneatus based on body region, axons ascend to the medulla, cross over at the medial lemniscus, and finally reach the postcentral gyrus of the cortex for conscious sensory perception. Lesions in this pathway lead to ipsilateral or contralateral sensory deficits depending on whether they occur below or above the medullary decussation.

Step-by-step explanation:

The dorsal column-medial lemniscal pathway is responsible for transmitting sensory information related to touch, proprioception, and vibration. It involves a well-defined three-neuron chain. The first-order neurons are the dorsal root ganglion cells, which transmit signals from the periphery to the dorsal columns in the spinal cord. As these axons ascend, they segregate into two fasciculi: the fasciculus gracilis, containing fibers from the lower body and legs, and the fasciculus cuneatus, containing fibers from the upper body and arms.

These axons terminate and synapse in the medulla oblongata at their respective nuclei, the nucleus gracilis or nucleus cuneatus. The second-order neurons decussate (cross over) to the opposite side, forming the medial lemniscus. This bundle ascends to the thalamus, where it synapses with third-order neurons. These neurons then project to the postcentral gyrus of the cerebral cortex, completing the sensory relay for conscious perception.

Clinical significance lies in the fact that damage at different levels of this pathway can lead to distinct sensory deficits. A lesion in the dorsal columns or below the decussation can cause ipsilateral loss of proprioception and discriminative touch. In contrast, damage above the decussation, such as in the medial lemniscus, will result in contralateral losses, excluding the face since cranial nerves innervate it.