Ascending Pathway

Question 1

What is a tract

Answer 1

White matter pathway connecting two distinct regions of grey matter, stimulus travels in one direction

Question 2

What is an ascending tract

Answer 2

White matter pathway transmitting sensory info from peripheral nerves to cerebral cortex

Question 3

Types of Ascending tracts

Answer 3

Conscious tracts:
Dorsal columns medial lemiscus
Anterolateral spinothalamic

Subconscious
Spinocerebellar

Question 4

What are the modalities of DCML

Answer 4

Fine touch
2PD
Proprioception
Vibration

Question 5

Describe the pathway

Answer 5

1. FON enter spinal cord at dorsal root
2. FON ascend spinal cord in dorsal column on ipsilateral side
3. FON from LL ascend medially, in fasciculus gracilis. FON from UL ascend laterally, in fasciculus cuneatus
4. FON synapse with SON at nucleus gracilis/cuneatus in medulla
5. SON decussate to contralateral side at medulla
6. SON ascend to Thalamus in medial lemiscus
7. SON synapse with TON in Thalamus
8. TON project from thalamus to somatosensory cortex

Question 6

What are the modalities of spinothalamic tract

Answer 6

Pain
Temperature
Crude touch

Question 7

Describe the pathway

Answer 7

1. FON enters the spinal cord in dorsal root
2. FON synapses with SON in dorsal horn of spinal cord
3. SON decussates in spinal cord
4. SON ascends spinal cord in anterolateral spinothalamic tract
5. LL SON located laterally, UL SON located medially
6. SON synapses with TON in Thalamus
7. TON projects from Thalamus to somatosensory Cortex

Question 8

How might a central grey matter lesion present?

Answer 8

Loss of pain + temp at/below level of lesion
Bilaterally (because lesion is central)
First affecting cervical + thoracic regions (fibres located medially)
Sparing of lumbosacral fibres (located laterally)

Question 9

How might hemisection of left spinal cord at T10 present?

Answer 9

Loss of proprioception/2PD/fine touch in left side below umbilicus and entire leg (DCML)

Loss of temp/pain in right side below umbilicus and entire leg (STT)

Band of cutaneous anaesthesia at umbilicus (fibres both tracts affected at site of entry)

Question 10

Why might there be loss of pain sensation not at but below level of lesion?

Answer 10

FON for pain ascend 1-2 levels before synapsing with SON

Question 11

What is involved in pain transmission

Answer 11

A fibres (mechanoreceptors, myelinated and narrow receptor field) 
C fibres (unmyelinated and large receptor field)

Question 12

What does gating mean

Answer 12

Degree of freedom of synaptic transmission from one neurone to next

Question 13

Why does rubbing sore area help relieve pain

Answer 13

Applying pressure causes stimulation of mechanoreceptors of A fibres
A fibres project inhibitory enkephalinergic interneurones to SON of C pain fibres
Inhibitory interneurones inhibit transmission of nociceptive impulse from C fibres to its SON

Question 14

Describe Descending control of pain

Answer 14

1. There is release of tonic inhibition of PAG by hypothalamus
2. PAG stimulates MRN
3. Signals transmitted down raphespinal fibres
4. Raphespinal fibres release serotonin that activates inhibitory interneurones
5. Inhibitory interneurones release enkephalins - inhibit pain transmission between C fibre and SON

Question 15

When might descending control of pain occur

Answer 15

Life threatening situations:

Hypothalamus releases tonal inhibition of PAG where pain is price for escape