Flashcards in Bales: Touch and Proprioception-Trunk and Limbs Deck (27):
Where do all primary afferent cell bodies from the trunk and limbs exist?
the dorsal root ganglion.
They enter the spinal cord at the dorsal horn
What does the gracile fasciculus consist of?
lower limb axons (below T6)
What does the cuneate fasciculus consist of?
Upper limb axons (above T6)
What is the somatotopy of the dorsal column?
fibers are added from medial to lateral:
lower limb (most medial)--> trunk--> upper limb --> neck
Where do the 1st order axons of touch and proprioception synapse? What happens here after the synapse? (DC-ML Pathway)
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
What is the somatotopy of the medial lemniscus at the level of the caudal medulla? (DC-ML Pathway)
feet ventral and the neck dorsal (like a little headless half-man standing on the pyramids)
What happens to the medial lemniscus at the medullopontine junction? (DC-ML Pathway)
it begins to shift--> ventral part swings laterally
*man slips on the inferior olivary nucleus
What does the medial lemniscus somatotopy look like mid-pons? (DC-ML Pathway)
horizontal (upper extremity=medial and lower extremity=lateral)
What is the somatotopy of the medial lemniscus at the midbrain? (DC-ML Pathway)
complete 180 from initial
headless half-man is now upside down
Where do the second order neurons of the ML synapse on the 3rd order neurons?(DC-ML Pathway)
in the ventral posterolateral thalamus (VPL) of the thalamus
Where do the 3rd order neurons of conscious proprioception and discriminatory touch (DC-ML pathway) go?
-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
What is the PLIC somatotopy for the DC-ML pathway fibers?
leg posterior, arm anterior
How is the primary somatosensory cortex somatotopically organized?
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)
What would produce a contralateral loss of descriminative touch and conscious proprioception from the limbs and trunk?
Lesions of the ML, VPL thalamus, PLIC, and medial and upper lateral postcentral gyrus (i.e., above internal arcuate fibers)
What would produce an ipsilateral loss of descriminative touch and conscious proprioception from the limbs and trunk?
Lesions of the dorsal column or gracile and cuneate nuclei (i.e., below internal arcuate fibers)
What is tabes dorsalis? What would result from it?
-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
What could a unilateral lesion of half of the spinal cord cause (in the DC-ML pathway)?
loss of discriminative touch and conscious proprioception ipsilaterally from the lesion level down (and other things in other pathways)
What are the 4 tracts that carry unconscious proprioception to the cerebellum for coordination? What is their purpose?
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.
What is the path of the dorsal spinocerebellar tract (DSCT)?
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)
Describe the path of the cuneocerebellar tract (CCT)
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
Describe the ventral spinocerebellar tract (VSCT)
-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
describe the rostral spinocerebellar tract (RSCT)
-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)
What do spinocerebellar lesions result in?
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!!
How is a spinocerebellar lesion masked in Brown-Sequard?
spinocerebellar lesions are masked clinically because a paralysed muscle can't be uncoordinated
What happens in Friedreich's ataxia?
dorsal column + DSCT + VSCT (among other things) degenerate, slowly robbing patient (usu children) of proprioception
What are the two SCTs of the lower limb?
Ventral and Dorsal
(the Velocity and Dance limb--> help remember)