Ascending sensory tracts

Question 1

What does the spinothalamic pathway relay impulses for?

Answer 1

Pain, thermal, tickle, itch, crude touch and pressure

Question 2

What does the posterior column medial lemniscus transmit impulses for?

Answer 2

Conscious proprioception, and most tactile sensations

Question 3

What does the spinocerebellar tract relay impulses for?

Answer 3

Unconscious proprioception

Question 4

Describe the pathway for PCML

Answer 4

Impulses travel from receptor cells which are usually encapsulated, to the posterior horn of spinal cord, past the cell body in dorsal root ganglia. Axons continue up the posterior column of spinal cord (lower body = gracile, upper = cuneate). At the medulla these axons synapse. The second order neuron crossed over in the medulla to for the medial lemniscus at the gracile/cuneate nucleus. The axons travel up brainstem and synapse at the thalamus (central posterolateral nucleus). 3rd order neuron travels up posterior limb of internal capsule, axon synapse in the primary sensory cortex

Question 5

Describe the pathway for the spinothalamic pathway

Answer 5

Receptors are usually free nerve endings. The first point of contact between 1st and 2nd order neuron is in the spinal cord. The 2nd order neuron axon crosses side and continues towards the brainstem via lateral (pain/temp) or anterior (tickle/itch/crude touch). 2nd order terminates in the thalamus. 3rd order projects to the primary somatosensory area of cerebral cortex.

Question 6

Why does the spinocerebellar tract only have 2 order neurons?

Answer 6

Because the sensation is not consciously perceived so doesn’t go any further than the cerebellum