Lecture 03 Tactile and Proprioceptive Pathways

Question 1

What is active touch?

Answer 1

2pt tactile discrimination; sterognosis(awareness of shape, size and texture); proprioception, vibratory sensations and weight perception

Conveyed via posterior column/medial lemniscal system

Question 2

What does the Ventral spinothalamic pathway convey?

Answer 2

light (passive) touch, crude tactile sensations and pressure

Question 3

Describe the primary neurons and their axons in the crude tactile pathway

Answer 3

Course through medial division of dorsal root
Enter posterior funiculus of spinal cord
Bifurcate and ascend 6-10 cord segments or descend
Terminate on 2dary neurons in ipsilateral nucleus proprius and intermediate gray

Question 4

What do the collaterals of the primary axons in the crude tactile pathway often participate in?

Answer 4

intersegmental spinal reflexes

Question 5

What are the receptors for the crude tactile pathway?

Answer 5

free nerve endings
peritrichial nerve endings
and merkel’s tactile disks

Question 6

Where are the secondary neurons in the crude tactile pathway?

Answer 6

in nucleus proprius

Question 7

Where do the secondary axons in the crude tactile pathway course?

Answer 7

cross in the anterior white commissure
decusate
and ascend to form ventral spinothalamic tract (VSTT)

Question 8

What forms the spinal lemniscus?

Answer 8

In the medulla the VSTT joins with the LSTT and the spinotectal fibers to form the spinal lemniscus

Question 9

Where does the spinal lemniscus terminate?

Answer 9

on tertiary neurons in the VPL (ventral posterior lateral) nucleus of the dorsal thalamus

Question 10

Where do tertiary axons from the VPL nucleus project to?

Answer 10

through the posterior limb of the internal capsule and corona radiata to the primary somesthetic cortex

Question 11

Whaat does unilateral lesions of the VSTT result in?

Answer 11

may be difficult to lose crude touch sensations, bc fibers ascend in both the posterior and anterolateral funiculi

Separation of info provides the system w a degree of bilaterality

Deficits may be masked if posterior column/medial lemniscal system is intact

Question 12

What does unilateral lesion of the spinal lemniscus result in?

Answer 12

contralateral hemianalgesia and thermal hemianesthesia

Loss of passive touch may be masked by intact posterior column/medial lemniscal system

Question 13

The sensory neurons from the upper extremity will form and ascend in what part of the spinal cord?

Answer 13

Fasiculus cuneatus

Question 14

Sensory information from the lower extremity will form and ascend in what part of the spinal cord?

Answer 14

fasiculus gracilis

Question 15

In the medulla, the primary axons in fasiculus cuneatus and fasiculus gracilis will terminate in what?

Answer 15

the corresponding nucleus gracilis and nucleus cuneatus

Question 16

some of the collaterals from the fasciculi gracilis and cuneatus are part of what reflex?

Answer 16

the myotatic reflex circuit when the fibers synapse directly upon alpha motor neurons

Question 17

What does the fasiculus gracilis convey?

Answer 17

proprioception, 2-pt tactile discrimination and vibratory sensation from the lowerr extremities and the body
(below T6)

Question 18

What does the fasiculus cuneatus convey?

Answer 18

Proprioception, 2-pt tactile discrimination and vibratory sensations from the upper extremities and body (down to T7)

Question 19

What do the secondary axons from the nucleus gracilis and cuneatus become ?

Answer 19

in the medulla they decussate as internal arcuate fibers and form the contralateral medial lemniscus

Question 20

What does the dorsal spinocerebellar tract convey?

Answer 20

precise coordination, postural adjustments and precise movements of individual mm of the lower limbs and body

Question 21

What does the ventral spinocerebellar tract convey?

Answer 21

gross postural adjustments and overall proprioception of the lower limb

Question 22

What does the cuneocerebellar tract convey?

Answer 22

direct arcuate fibers convey fine coordination, postural adjustments and precise movements of individual mm of the upper limbs and body

Question 23

What does the rostral spinocerebellar tract convey?

Answer 23

gross postural and limb proprioception from the upper limbs

Question 24

What are the neurological tests for tactile and proprioceptive pathways?

Answer 24

testing positions sense: bend finger
Testing vibratory sense: activated tuning fork on joint
Testing stereognosis and 2 pt: distinguish two blunt tips of paper clip as being separate on hand

Question 25

What results from complete unilateral lesions of the posterior columns?

Answer 25

ipsilateral loss of proprioception, 2-pt tactile discrimination and vibratory sensations below the level of the lesion

Question 26

What does a lesion of the fasiculus gracilis result in?

Answer 26

ipsilateral loss of proprioception, 2 pt tactile discrimination and vibratory sensations from the lower half of the body

Question 27

What do lesions of the fasiculus cuneatus result in?

Answer 27

ipsilateral loss of proprioception, 2 pt tactile discrimination and vibratory sensations from upper half of the body s

Question 28

What does unilateral lesions of the medial lemniscus result in?

Answer 28

loss of proprioception and 2 pt tactile discrimination and vibratory sensations on the opposite side of the body and limbs

Question 29

What is tabes dorsalis?

Answer 29

meningovascular inflammation of the blood vessels as they pierce through the pia at the junction of the dorsal rootlets and the posterior columns

Question 30

What are most frequently affected by tabes dorsalis?

Answer 30

lumbosacral nn and spinal cord segments

Question 31

When does tabes dorsalis occur?

Answer 31

during the tertiary (late) stage of syphilis and results in bilateral ischemic necrosis of the posterior columns

Question 32

What does tabes dorsalis result in?

Answer 32

bilateral ischemic necrosis of the posterior columns and the dorsal roots at this lvl

Question 33

What are the signs of tabes dorsalis?

Answer 33

pts complaint: lightning pains or rheumatic pains from the lower limbs for the last several years
atonic bladder and painless retention of urine
Locomotor ataxia: slapping feet
Positive romberg test
Argyll-Roberston pupils
Swollen distorted joints

Question 34

What is locomotor ataxia?

Answer 34

broad-based gait with slapping feet bc of loss of proprioception information from lower extremities, both for reflexes and ascending conscious and unconscious pathways, causes this gait

Vibratory sensations: pt stops feet to obtain tactile cues

Question 35

What is the Romberg test?

Answer 35

standing with feet together and arms extended in front. Pt will fall when eyes are closed: suggestive of posterior columns and/or cerebellum issues

Question 36

What is passive touch?

Answer 36

sensory modalities such as roughness, texture, form and localization
conveyed via ventral spinothalamic pathway
Crude tactile