Unit 3: ascending tracts

Question 1

what are the ascending tracts?

Answer 1

neural pathways by which sensory info from peripheral nerves is transmitted to cerebral cortex

Question 2

what stimulus do meissner’s corpuscles detect?

Answer 2

fine touch and pressure

Question 3

what stimulus do pacinian corpuscles detect?

Answer 3

vibration

Question 4

what stimulus do free nerve endings detect?

Answer 4

pain and temperature

Question 5

what stimulus do ruffini endings detect?

Answer 5

skin stretch, shear stress, deformation in joints

Question 6

what stimulus do merkel’s endings detect?

Answer 6

crude touch (discriminative) and pressure

Question 7

what stimulus do hair follicles detect?

Answer 7

light touch (fine touch/ non-discriminative)

Question 8

what are the two conscious tracts?

Answer 8

dorsal column medial leminiscus pathway

anterolateral system

Question 9

which pathway is initiated by fine touch, vibration and proprioception?

Answer 9

dorsal column medial leminiscus pathway

Question 10

how many neurones are involved in the dorsal column medial leminiscus pathway?

Answer 10

3 - first, second, third order

Question 11

what are the two types of first order neurones in the dorsal column pathway?

Answer 11

upper limb (t6 and above) travel in fasciculus cuneatus and synapse in nucleus cuneatus in the medulla oblongata (lateral)
lower limb (below t6) travel in fasciculus gracilis and synpase in nucleus gracilis in the medulla oblongata (medial)

Question 12

what do the second order neurones do in the dorsal column pathway?

Answer 12

carry information from the medulla oblongata to the ventral posterolateral nucleus in the thalamus
internal arcuate fibres decussate in the medulla and ascend the medial leminiscus to the thalamus

Question 13

what is the medial leminiscus?

Answer 13

decussation of the internal arcuate fibres

Question 14

what do the third order neurones do in the dorsal column pathway?

Answer 14

ascend from ventral posterolateral nucleus through the internal capsule to the sensory cortex

Question 15

what are the two tracts of the anterolateral system?

Answer 15

anterior spinothalamic: crude touch

lateral spinothalamic: pain and temperature

Question 16

what do the first order neurones do in the anterolateral system?

Answer 16

neurones arise from sensory receptors and enter spinal cord ascending 1-2 vertebral levels and synapse onto tip of dorsal horn = substantia gelatinosa

Question 17

what do the second order neurones do in the anterolateral system?

Answer 17

fibres decussate in the spinal cord through the anterior white commissure and ascend the medulla synapsing onto the ventral posterolateral nucleus of the thalamus

Question 18

what do the third order neurones do in the anterolateral system?

Answer 18

fibres ascend from the ventral posterolateral nucleus of the thalamus, through the internal capsule to the primary sensory cortex

Question 19

what is brown sequard syndrome? what is its effect on the dorsal column and spinothalamic tracts?

Answer 19

hemisection of spinal cord (one-sided lesion)
dorsal column = ipsilateral sensory loss of fine touch, vibration and proprioception
spinothalamic = contralateral sensory loss of crude touch, pain and temperature

Question 20

what are the unconscious tracts and what is their function?

Answer 20

spinocerebellar tracts - transmits information about propioception

Question 21

what are the two type of spinocerebellar tracts?

Answer 21

dorsal - carries information from upper limb to ipsilateral cerebellum
ventral - carries information from lower limb to ipsilateral cerebellum

Question 22

explain the two neurone pathway of the dorsal spinocerebellar tract

Answer 22

1) fibres enter spinal cord from dorsal root ganglion and synapse at thoracic nucleus
2) fibres ascend medulla along dorsal lateral funiculus and connects to cerebellum at inferior cerebellar peduncle

Question 23

explain the two neurone pathway of ventral spinocerebellar tract

Answer 23

1) fibres synapse onto dorsal horn cells in lumbral/ sacral segments
2) fibres immediately decussate and ascend to midbrain along ventral aspect of lateral funiculus, then descends to superior peduncle decussating at the midline

Question 24

what is the effect on the spinocerebellar tracts if there is a lesion in spnal cord?

Answer 24

ipsilateral loss of muscle coordination - spastic paralysis

accompanied by damage to descending motor tracts - muscle weakness/ paralysis