9.1 Somatosensory Tracts 2

Question 1

What types of sensation are carried in the anterolateral system?

Answer 1

Crude touch

Thermal sensation

Nociception

Tickling

Question 2

What is the direct pathway of the ALS from primary neuron to thalamus?

Answer 2

Primary neurons (may travel up or down 3 vertebral levels) then synapse in lamina I.

They then decusate (forming the anterior white commisure) and travel up the anterolateral system.

They synapse again at the ventral posterolateral nucleus of the spinal cord.

Question 3

What is the indirect pathway of the ALS from primary neuron to thalamus?

Answer 3

Primary neurons (may travel up or down 3 vertebral levels) then synapse in lamina II or III.

They then decusate (forming the anterior white commisure) and travel up the anterolateral system.

They then synapse on the “reticular system of the spinal cord / brain stem reticular formation”.

Neurons in the reticular formation then project to the medial thalamic nuclei.

Question 4

How are the fibers in the ALS somatotopically arranged?

Answer 4

Opposite to the PCML pathway. The lower levels are posterolateral, and the upper levels get added anteromedially.

(Upper levels are medial, lower levels are lateral)

Question 5

What are Aδ nerve fibers responsible for?

What are C fibers responsible for?

Answer 5

Aδ nerve fibers are responsible for acute “sharp” pain.

C fibers are for dull chronic pain.

Question 6

What is the function of the spinohypothalamic fibers?

Answer 6

Nocioceptive and somatosensory issues that associates with the hypothalamus for memory formation and interpretation of pain.

Question 7

How will damage to the arterial vasocorona present?

Answer 7

As spotty damage to multiple regions, with gaps in between.

Question 8

What is dissociated sensory loss, and what might cause it?

Answer 8

Dissociated sensory loss is where one afferent tract (say PCML, for example) is compressed, but another one (say, ALS) is not. This leads to damage to one modality, but not the other.

Question 9

What is Brown-Sequard?

Answer 9

Hemisection of the spinal cord, causing contralateral loss of thermal and pain sensation, and ipsilateral loss of discriminatory sensory, vibratory, and proprioceptive input below the lesion.