Spinal Cord and Pathways

Exam 3

tract name

often includes the location of the tract, where it begins and ends, and the direction of info flow

somatopy

point to point mapping of body regions - exhibited by spinal tracts

first order neurons

the primary afferent neurons, whose cell bodies are located in the ganglia and are unipolar

second order neurons

cell bodies lie in the dorsal horn or nedullary nuclei. axons cross over during their ascending pathway

third order neurons

located in the thalamus and conduct impulses to the somatosensory cortex

perception

a conscious awareness of the stimulus

ascending pathways

take in sensory input. consists of the anterior/ventral and lateral spinothalamic tracts, dorsal column medial lemniscus tract, and anterior/posterior spinocerebellar tracts

nonspecific ascending pathways

consists of the anterior/ventral spinothalamic tract and lateral spinothalamic tract

specific ascending pathways

consists of the dorsal column medial lemniscus pathways - fasciculus cuneatus and fasciculus gracilis

anterior spinothalamic tract

relays crude touch, pressure, tickle, and itch sensations to the thalamus

lateral spinothalamic tract

relays pain and temperature sensations to the thalamus

level of cord entry

both nonspecific ascending pathways decussate near to…

thalamic nucleus

second order neurons in nonspecific ascending pathways carry their impulses here in the contralateral hemisphere

somatosensory cortex

third order neurons of the nonspecific ascending pathways carry their information here from the thalamus

parallel pathways

the specific and nonspecific ascending pathways are considered…

dorsal column medial lemniscus pathway

precise transmission of inputs of a single type of receptor that can be localized on the body surface

fasciculus cuneatus

this part of the specific ascending pathway is associated with conscious proprioreception, fine and discriminative touch, and pressure in the upper body

fasciculus gracilis

this part of the specific ascending pathway is associated with conscious proprioreception, fine and discriminative touch, and pressure in the lower body

first order neurons

carry impulses to the medulla and synapse with second order neurons at the nucleus cuneatus or gracilis

second order neurons

decussate in the medulla, enter medial lemniscus on the contralteral side of cord and extend to thalamus

anterior and posterior spinocerebellar tracts

carry information from propioreceptors in the trunk and lower limbs to the cerebellum

first order neurons

synapse at level of entry to the cord

none

decussation in the posterior spinocerebellar tract

two

decussations in the anterior spinocerebellar tract

second order neurons

carry input to the cerebellum via the inferior cerebellar peduncle (for posterior spinocerebellar tract) or superior cerebellar peduncle (for anterior)

no

are there third order neurons present in the anterior/posterior spinocerebellar tracts?

upper and lower motor neurons

neurons types in somatic motor/descending pathways

upper motor neurons

the pyramidal cells of the motor cortex and other neurons in the subcortical motor nuclei

lower motor neurons

extend through peripheral nerves into skeletal muscles, cell bodies are in the ventral/anterior horn or cranial nerve nuclei

direct pathways

these tracts descend without synapsing from the pyramidal neurons to the spinal cord or CN nuclei and decussate in medulla or spinal cord level

direct pathways

consists of the lateral corticospinal tracts, anterior corticospinal tracts, and corticobulbar tracts

lateral corticospinal tracts

fibers of upper motor neurons decussate in the medullary pyramids and controls muscles of the extremities

anterior corticospinal tracts

ibers of upper motor neurons decussate at the level of exit from the cord and controls muscles of the neck & part of the trunk

corticobulbar tracts

upper motor neurons terminate in motor nuclei of CNs and lower motor neurons control precise voluntary movement of face and neck