Three sensory neurons involved
First order neuron
conducts the nerve impulse from the receptor to the spinal cord or brain stem
If neuron origantes from face
travels through a crainal nerve to the brainstem.
If neuron originates from anywhere else
enters a spinal nerve and enter the spinal cord.
Second order neuron
conducts the impulse from the brainstem- spinal cord to the thalamus (ALWAYS ENDS IN THE THALAMUS)
Third order neuron
conducts nerve impulses from the thalamus to the primary somatosensory area.
Two general pathways that carry somatic sensory nerve impulses
Posterior column medial lemnisus pathway, Anterolateral/ spinothalamic pathway.
Posterior column medial lemnisus pathway
carries nerve impules for propioception touch, pressure, and vibration.
Two tracts within this pathway
Gracile fasciculus and cuneate faciculus
If it comes from the lower half of the body more towards the middle of the spinal cord (medial)
more lateral tract cames impulses from the upper half of the body.
pathway: first order neurons
Extends from the receptor enters one of the two tracts in the spinal cord and ends in the medula oblongota
pathway: seconds order neurons
extends from the medula oblongota and crosses over and extends up to the thalumus.
pathway: third order neuron
extends from the thalumus up to the primary somatosensory area of the cortex.
Anterolateral/ spinothalamic pathway
receive nerce impulses for pain temp tickle and itch
Lateral spinothalamic tract
carries impulses for pain and temp.
Anterior spinothalamatic tract
carries impulses for tickle and itch.
spinothalamic: first order neuron
extends from receptor- the grey mater of the spinal cord.
spinothalamic: sedond order neuron
extends from spinal cord and crosses over within- lateral/ anterior tract- thalamus.
spinothalamic: third order neuron
extends from the thalamus up to the primary somatosensory area.