Somatosensory Pathways MCQs

Gate control theory is the mechanism behind Transcutaneous electrical nerve stimulation (TENS). This method uses electrodes to activate Aα and Aβ fibers in the vicinity of the injury. The relief is due to activation of innocuous cutaneous mechanoreceptors whose afferents emit collaterals that terminate in the dorsal horn. The activity of these cutaneous mechanosensitive afferents reduce the responsiveness of dorsal horn neurons to their input from nociceptive afferent terminals. This is called the gate-control mechanism of pain modulation.

Gate control theory is the mechanism behind Transcutaneous electrical nerve stimulation (TENS). This method uses electrodes to activate Aα and Aβ fibers in the vicinity of the injury. The relief is due to activation of innocuous cutaneous mechanoreceptors whose afferents emit collaterals that terminate in the dorsal horn. The activity of these cutaneous mechanosensitive afferents reduce the responsiveness of dorsal horn neurons to their input from nociceptive afferent terminals. This is called the gate-control mechanism of pain modulation.

Ans. is 'b' i.e., Medulla [Ref Quantitative Human physiology : An introduction p. 327] It has not been mentioned in any textbook. But according to the above mentioned reference nucleus fasciculatus is the other name of nucleus cuneatus. "The sensory fibers of dorsal column travel in tracts, fasciculus gracilis and fasciculus Cuneatus in the Cord and these fibers make synapses with second order neurons in the nucleus gracilis and the nucleus fasciculatus". — Quantitative Human physiology. Nucleus gracilis and nucleus fasciculus are found in the medulla.

Ventral posterior lateral (VPL) and ventral posteromedial nuclei (VPM) Transmit somatosensory information to sensory cortex Reference: Ganong, 25th edition page no.269

Gate control theory of pain: Proposed by Melzack and Wall Dorsal horn neuron receives collaterals from both the touch receptors and pain receptors. Simultaneous activation of innocuous touch receptors reduces the responsiveness of dorsal horn neurons to their input from pain receptor afferents It is also the basis behind transcutaneous electrical nerve stimulation (TENS) where in electrodes are used to activate Aα and Aβ fibers near the site of injury to relieve pain Reference: Ganong, 25th edition page no.172

Dorsal column pathway is the principal pathways for touch, vibration and proprioception. They primarily contain Aα and Aβ afferents They ascend ipsilaterally (same side) in dorsal column of spinal cord to medulla In medulla, they synapses with two important nuclei namely gracilis and cuneate nuclei . They cross the midline and ascend in the medial lemniscus to end in the contralateral ventral posterior lateral (VPL) nucleus Reference: Ganong, 25th edition page no.168

Primary somatosensory cortex Located in post central gyrus of the parietal lobe Brodmann's area - Areas 3,1,2 Reference: Ganong, 25th edition page no.168

Lips and thumb has got the maximum representation in somatosensory area Representations for trunk and back are small Reference: Ganong, 25th edition page no.169