4. Sensory tracts dysfunction

Question 1

What is sensory tract?

Answer 1

Ascending tacts, somatosensory pathway/system. Sensory info. from peripheral nerves transmit to cerebral cortex.

Question 2

Tracts

Answer 2

Divides into

1) Conscious tracts:
- Dorsal column-medial lemniscal pathway (DCMLP)
- Anterolateral system or spinothalamic tract (ALS)
2) Unconscious tracts:
- Post./dorsal spinocerebellar tract
- Cuneocerebellar tract
- Ant. spinocerebellar tract
- Rostral spinocerebellar tract

Question 3

DCMLP

Answer 3

Responsible for tactile sensation (fine touch & vibration) & proprioception

Pathway:
1st order neurons: Rcpts or nerve endings from periphery to spinal cord through dorsal horn & synpase
–> neurons from upper limbs through fasciculus cuneatus, lower through fasciculus gracilis
–> travels via dorsal column: Upper limbs synapse in medulla, cuneate nucleus, lower in gracile nucleus: 2nd order neurons
–> decussate in medulla
–> travels through medial lemniscus
–> travels to thalamus (ventral posterolateral nucleus) and synapse: 3rd order neurons
–> internal capsule & terminate in sensory cortex

Question 4

DCMLP dysfunction

Answer 4

A few tactile fibres travel w/ALS.
Lesions in spinal cord => below, ipsilateral.
Vit. B12 def., tabes dorsalis (neurosyphilis), Brown-Sequard syndrome

% vibration, position sensation & fine touch

• Loss of stereognosis
• 2-point discrimination

Question 5

ALS

Answer 5

Divides into:

1) Anterior spinothalamic tract: Responsible for crude touch & pressure
2) Lateral spinothalamic tact: Pain & temp.

Pathway:
1st order neurons: Rcpts or nerve endings from periphery to spinal cord through dorsal ganglion
–> at lissauer’s fasciculus they ascend obliquely 1-2 levels and synapse at substantia gelatinosa (nucleus proprius): 2nd order neurons:
–> decussate to lat. or ant. spinothalamic tract
–> ascend to thalamus and synapse: 3rd order neurons
–> travel from ventral posterolateral nucleus of thalamus to internal capsule and terminate in prim. sensory cortex

Question 6

ALS dysfunction

Answer 6

Lesions in spinal cord => below lesion, contralateral
Brown-Sequard syndrome

% pain, temp.

Question 7

Spinocerebellar tracts

Answer 7

Unconscious proprioceptive info. to coordinate and refine motor movements.

Info. from lower limbs
=> doral horn –> post. spinocerebellar tract –> (ipsilateral) inf. cerebellar peduncle
=> dorsal horn, decussate –> ant. spinocerebellar tract –> (ipsilateral) sup. cerebellar peduncle, decussate

Info. from upper limbs
=> (ipsilateral) cuneo cerebellar tract
=> (ipsilateral) rostral spinocerebellar tract

Question 8

Spinocerebellar tracts dysfunction

Answer 8

Below lesion, at spinal cord, ipsilateral loss of mus. coordination (except ant. spinocerebellar tract: contralateral) –> dystaxia

Question 9

Neurological examination

Answer 9

Romberg’s test

• Feet together, eyes closed => swaying occurs –> problem w/sensory pathway
• Ataxia but neg. Romberg’s –> problems in cerebellum