Bales: Touch and Proprioception-Trunk and Limbs

Question 1

Where do all primary afferent cell bodies from the trunk and limbs exist?

Answer 1

the dorsal root ganglion.

They enter the spinal cord at the dorsal horn

Question 2

What does the gracile fasciculus consist of?

Answer 2

lower limb axons (below T6)

Question 3

What does the cuneate fasciculus consist of?

Answer 3

Upper limb axons (above T6)

Question 4

What is the somatotopy of the dorsal column?

Answer 4

fibers are added from medial to lateral:

lower limb (most medial)–> trunk–> upper limb –> neck

Question 5

Where do the 1st order axons of touch and proprioception synapse? What happens here after the synapse? (DC-ML Pathway)

Answer 5

in the caudal medulla at the corresponding nucleus

(fasciculus gracilis–> nucleus gracilis; fasciculus cuneatus–> nucleus cuneatus)

2nd order axons decussate as internal arcuate fibers –> gracile=ventral, cuneate=dorsal

–> form the vertical rectangular medial lemniscus adjacent to midline

Question 6

What is the somatotopy of the medial lemniscus at the level of the caudal medulla? (DC-ML Pathway)

Answer 6

feet ventral and the neck dorsal (like a little headless half-man standing on the pyramids)

Question 7

What happens to the medial lemniscus at the medullopontine junction? (DC-ML Pathway)

Answer 7

it begins to shift–> ventral part swings laterally

*man slips on the inferior olivary nucleus

Question 8

What does the medial lemniscus somatotopy look like mid-pons? (DC-ML Pathway)

Answer 8

horizontal (upper extremity=medial and lower extremity=lateral)

Question 9

What is the somatotopy of the medial lemniscus at the midbrain? (DC-ML Pathway)

Answer 9

complete 180 from initial

headless half-man is now upside down

Question 10

Where do the second order neurons of the ML synapse on the 3rd order neurons?(DC-ML Pathway)

Answer 10

in the ventral posterolateral thalamus (VPL) of the thalamus

Question 11

Where do the 3rd order neurons of conscious proprioception and discriminatory touch (DC-ML pathway) go?

Answer 11

• 3rd order axons of VPL thalamus enter posterior limb of internal capsule (PLIC)
• These thalamocortical fibers ascend in PLIC and corona radiata to terminate in appropriate parts of the sensory homunculus (somatorsensory cortex) of the postcentral gyrus

Question 12

What is the PLIC somatotopy for the DC-ML pathway fibers?

Answer 12

leg posterior, arm anterior

Question 13

How is the primary somatosensory cortex somatotopically organized?

Answer 13

foot, leg and thigh are medial and the trunk and upper limb are superolateral

(homunculus=standing on the cingulate gyrus in the longitudinal fissure bending over with the lateral aspect or its arms hanging down)

Question 14

What would produce a contralateral loss of descriminative touch and conscious proprioception from the limbs and trunk?

Answer 14

Lesions of the ML, VPL thalamus, PLIC, and medial and upper lateral postcentral gyrus (i.e., above internal arcuate fibers)

Question 15

What would produce an ipsilateral loss of descriminative touch and conscious proprioception from the limbs and trunk?

Answer 15

Lesions of the dorsal column or gracile and cuneate nuclei (i.e., below internal arcuate fibers)

Question 16

What is tabes dorsalis? What would result from it?

Answer 16

• slow, progressive degenerative spinal cord disease secondary to spirochete (syphilis) infection.
• dorsal column fibers preferentially degenerate BILATERALLY
• Loss of lower limb conscious proprioception –> positive Romberg sign ==> fall without the visual compensation
• can also lose knee jerk reflex

Question 17

What could a unilateral lesion of half of the spinal cord cause (in the DC-ML pathway)?

Answer 17

loss of discriminative touch and conscious proprioception ipsilaterally from the lesion level down (and other things in other pathways)

Question 18

What are the 4 tracts that carry unconscious proprioception to the cerebellum for coordination? What is their purpose?

Answer 18

1. from the lower limb: dorsal and ventral spinocerebellar tracts (D SCT and V SCT)

from the upper limb: cuneo- and rostral spinocerebellar tracts (CCT and RSCT)

• all=direct tracts to the cerebellum (no synapses)
• all originate ipsilaterally to the side of termination in the cerebellum (3 are uncrossed and 1 is double crossed (VSCT))
  2. their purpose is to coordinate skeletal mm actions to ensure smooth, accurate, appropriate movements.

Question 19

What is the path of the dorsal spinocerebellar tract (DSCT)?

Answer 19

primary afferent processed from the lower limb and lower trunk (up to C8) synapse on the second order cells in the dorsal nucleus (of clark) and collect ipsilaterally along the posterolateral surface of the spinal cord.

this ascends through the upper (rostral) medulla where it enters the cerebellum via the inferior cerebellar peduncle (ICP)

Question 20

Describe the path of the cuneocerebellar tract (CCT)

Answer 20

primary proprioceptor afferents from the arm, shoulder and neck (C8 and up) ascend ipsilaterally parallel to fasciculus cuneatus fibers in the dorsal column

synapse in the accessory (lateral, external) cuneate nucleus

*parallels DSCT to the ipsilateral cerebellum

Question 21

Describe the ventral spinocerebellar tract (VSCT)

Answer 21

• Primary afferents from lower limb (and up to T6) end along central lateral margin of spinal gray (spinal border cells - lamina VII)
• Spinal border cell axons decussate in ventral white commissure and collect in an anterolateral surface zone as ventral spinocerebellar tract (VSCT)
• ascend (on the contralateral side) to the superior cerebellar peduncle
• re-decussate again at the superior cerebellar peduncle (rostral pons) to end up on the cerebellum, ipsilateral to the origin

Question 22

describe the rostral spinocerebellar tract (RSCT)

Answer 22

• upper limb counterpart to VSCT
• originates in lamina VII
• ascends ipsilaterally, parallel to the spinocerebellar tracts
• C8 and up
• to the inferior cerebral peduncle (parallels the DSCT and CCT)

Question 23

What do spinocerebellar lesions result in?

Answer 23

Ataxia (uncoordination of movement).

the uncoordinated muscles are always on the SAME SIDE as the cell of origin of the sensory pathway

these lesions are usually more complex!!

Question 24

How is a spinocerebellar lesion masked in Brown-Sequard?

Answer 24

spinocerebellar lesions are masked clinically because a paralysed muscle can’t be uncoordinated

Question 25

What happens in Friedreich’s ataxia?

Answer 25

dorsal column + DSCT + VSCT (among other things) degenerate, slowly robbing patient (usu children) of proprioception

Question 26

What are the two SCTs of the lower limb?

Answer 26

Ventral and Dorsal

the Velocity and Dance limb–> help remember

Question 27

What are the 2 SCTs of the upper limb?

Answer 27

Rostral and Cuneo

Rubbing and Cursive limb