Question

1. Describe the three sensory pathways and their function. In your description, please be sure to describe where these pathways cross over.

Answer 1

Three sensory pathwy include :-

Posterior column -medial lemniscal (DCML) pathway

• It conveys proprioception , vibration sense and fine discriminative touch.
• It decussate at the level of internal arcuate fibers at the level of lower medulla.
• 1st order neuron run on the same side and synapses with secondorder neuron in the dorsal column nuclei.
• 2nd order neuron integrates the input and their axons cross to the opposite side .These ascend through medial lemniscus.
• Further integration in the thalamus and 3 order neuron projects to the cortex.

Anterior spinothalamic tract

• It is situated in the marginal part of the anterior funiculus.A beta fibres carry sensory information pertaining to crude touch from the skin.
• After entering spinal cord first order neuron synapses .
• The second order neurons decussate via the anterior white commissure.
• These second order neuron ascend synapsing in VPL (ventroposterolateral) nucleus of thalamus.

Spinoreticular tract

• Originates in laminae IV-VIII
• Contains uncrossed fibers that end in medullary reticular formation
• Crossed and uncrossed fibers that terminate in pontine reticular formation.
• Forms part of the ascending reticular activating system.
• These neurons decussate to the opposite side (anterolateral), and travel up the spinal column
• Involved in arousing consciousness in the reticular activating system through cutaneous stimulation.