DC-ML Pathway

Question 1

First order neuron in DCML

Answer 1

. Cell body in DRG

. Pseudounipolar neuron w/ peripheral (distal) and central (proximal) axonal processes

Question 2

Peripheral receptors assoc. w/ this system

Answer 2

. Tactile mechanorecepotrs (Meissner’s, free n. Endings on hair, pacinian corpuscles)
. Conscious proprioception (muscle spindles, golgi tendon organs)

Question 3

Peripheral axonal process

Answer 3

. From peripheral receptor to cell body in BRG

. Large, heavily myelinated: types 1a, 1b, or II

Question 4

Central axonal process

Answer 4

. Rom cell body of DRG to dorsal horn of spinal cord
. Fibers enter spinal cord through medial dorsal root entry zone
. Once in spinal cord, the process gives off small collateral branches that terminate in spinal gray matter to facilitate spinal reflexes
. Main axon leaves dorsal horn w/o synapsing and enters dorsal funiculus to form fasciculus gracilis or cuneatus

Question 5

Faciculus gracilis

Answer 5

. Located at all spinal cord levels
. Med. to cuneatus
. Carries sensory info from lower 1/2 of body
. Terminate in nucleus gracilis in caudal medulla

Question 6

Fasciculus cuneatus

Answer 6

. On in T6 and above
. Lat. to gracilis
. Carries sensory info from upper 1/2 of body
. Terminate in nucleus cuneatus in caudal medulla

Question 7

Somatotopic arrangement of tracts

Answer 7

. Most inf. Levels of spinal cord entering dorsal columns at each successive spinal level will position themselves lat. to fibers already in the dorsal columns
. Fibers of sacral spinal levels most med. and cervical spinal levels most lat. in dorsal columns
. Organization persists throughout entire course of ascending pathway

Question 8

Second order neuron

Answer 8

. Dorsal volume nuclei (cuneatus and gracilis)
. NG corresponds to gracile tubercle in dorsal medulla
. NC correspond to cuneatus tubercle on dorsal medulla
. Axons of dorsal column nuclei neurons are large caliber and heavily myelinated

Question 9

Internal arcuate fibers

Answer 9

. Axons emerge ventrally from dorsal column nuclei and coarse ventromed. Through medullary tegmentum
. Cross midline
. Point where this sensory system decussates
. Very distinctive arching course through medullary tegmentum

Question 10

Medial lemniscus

Answer 10

. Internal arcuate fibers coalesce on contralateral side of medulla just dorsal to pyramidal tracts as a dorsal-ventrally oriented band of fibers
. Somatotopically arranged so that ventral fibers are from NG and dorsal fibers are from NC
. Travel up brainstem and fibers synapse on 3rd order neurons in thalamus

Question 11

3rd order neuron

Answer 11

. Located in ventral posterolateral nucleus of thalamus
. Axons project lat. out of thalamus, course through post. Limb of internal capsule and terminate in cortex
.

Question 12

Unconscious proprioception

Answer 12

. Conveyed to cerebellum through spinocerebellar tracts
. Dorsospinocerebellar tract projects through inf. Cerebellar peduncle
. Ventral spinocerebellar tract projects through sup. Cerebellar peduncle