Ascending Pathways, Descending Pathways, and Reflexes

dorsal column system

touch and proprioception

spinothalamic tract

pain and temperature

first order neuron

detects a stimulus and transmits a signal to the spinal cord or brainstem

second order neuron

Interneuron

Cell body in dorsal horn of spinal cord or medullary nuclei

Axons extend to thalamus or cerebellum

third order neuron

carries the signal the rest of the way to the cerebral cortex

descending tracts

carry motor commands to spinal cord

lateral corticospinal tract

cross over in medulla

anterior corticospinal tract

muscle of trunk, ipsilateral

Reflex Arc

A relatively direct connection between a sensory neuron and a motor neuron that allows an extremely rapid response to a stimulus, often without conscious brain involvement.