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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

Gracile fasciclus

If it comes from the lower half of the body more towards the middle of the spinal cord (medial)

Cuneate fraciculus

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.

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