2. Practice Short Answer Question: Briefly describe the role of dorsal root neur

Question

2. Practice Short Answer Question: Briefly describe the role of dorsal root neurons in somatosensation (e.g. Fig. 16-3). In your answer be sure to describe: (1) Where the dorsal roots are located and where the neurites (axons and dendrites) of these neurons project to, (2) Where each bifurcation of dorsal root neurons forms a synapse, and (3) What the physiological consequence would be if each of these bifurcations were damaged. LO: Briefly describe the sequence of synapses in the somatosensory pathway from receptors to the brain, and state what the consequences of damage would be at each site.

Explanation / Answer

There are two roots which emerge from spinal cord. First one is dorsal or posterior root of spinal nerve and second one is ventral or anterior root. Dorsal root emerges directly from spinal cord and traveles to the dorsal root ganglion. The dorsal root neurons innervate the deep muscles of the back which maintain motor control, such as the erector spinae and also a horizontal strip of skin for sensory function.

The dorsal root ganglion consist the cell bodies of sensory neurons which carry information from the periphery to the spinal cord. These neurons are pseudounipolar and have an axon-like process that bifurcates into two branches. One branch goes toward the periphery and the other branch goes toward the grey matter of the spinal cord. Fibers going toward the periphery leave the ganglion through the spinal nerve, where they run combindingly with motor fibers. Fibers going to the spinal cord travel through the dorsal root.

The axons of dorsal root neurons which goes to the grey matter of spinal cord connect through interneurons instead of synapses. The axon of motor neurons present in grey matters of spinal cord comes out through the ventral root.

Somatosensory function: The lateral portion of the dorsal root contains partially myelinated and unmyelinated fibres of small diameter. These transfer pain and temperature sensation. These fibers cross via the anterior white commissure to constitute the anterolateral system in the lateral funiculus.

The medial division of the dorsal root consist of myelinated fibres of larger diameter. These carry information of discriminative touch, pressure, vibration, and conscious proprioception originating from spinal levels.

If bifurcation of dorsal root of a spinal nerve were damaged it would lead to numbness in certain areas of the body.

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