ascending neural pathways

Question 1

what are the three ascending ascending pathways of sensory information?

Answer 1

1. dorsal column/medial lemniscus pathway
2. spinothalamic pathway
3. spinocerebellar pathway

Question 2

which dorsal column/medial lemniscus pathway carries information from the upper limb?

Answer 2

fasciculus cuneatus

Question 3

which dorsal column/medial lemniscus pathway carries information from the lower limb?

Answer 3

fasciculus gracilis

Question 4

what type of modal information is carried by the dorsal column pathway? (4)

Answer 4

• conscious proprioception (i.e. where your limbs are when your walking etc)
• discriminative touch (two point discrimination)
• vibration
• pressure

Question 5

what type of sensory fibres are the dorsal columns composed of?

Answer 5

AB fibres (fast, large diameter fibres) (30-70m/s conduction velocity, 5-12um diameter)

Question 6

where does the primary afferent neurone of the medial lemniscus pathway enter from and synapse?

Answer 6

primary afferent neurone enters the dorsal column of spinal cord, synapses on second order neurone in the brain stem (either gracile or cuneate nuclei)

Question 7

which vertebrae does the fasciculus cuneatus pathway start above?

Answer 7

T6

Question 8

where does the second order neurone of the medial lemniscus pathway originate and synapse?

Answer 8

comes from the gracile or cuneate nuclei in the brain stem, ascends CONTRALETERALLY as the medial lemniscus and synapses in the ventral posterolateral lobe of the thalamus (VPL)

Question 9

where does the third order neurone of the medial lemniscus pathway originate and synapse?

Answer 9

originates in the VPL region of the thalamus and projects to corresponding are of the somatosensory cortex

Question 10

what pathological processes can develop from a lesion in the medial lemniscus pathway BELOW T6?

Answer 10

gait ataxia (brain is deprived of info about feet)

Question 11

what symptoms does dorsal column disease cause and what is the cause of this disease?

Answer 11

causes paraesthesias in the extremities (i.e. tingling, crawling, numbness, deadness in fingers and toes)
caused by ectopic discharge in damaged dorsal column axons

Question 12

how can dorsal column function be tested?

Answer 12

by testing proprioception in fingers and toes or testing vibration sense with tuning fork

Question 13

what does the spinothalamic pathway detect primarily?

Answer 13

PAIN - nociception

Question 14

what types of pain does the spinothalamic pathway detect? (3)

Answer 14

1. mechanical pain (coarse pain and sharp pain)
2. thermal pain (e.g. extreme cold or heat)
3. chemical pain (e.g. histamine-sensitive fibres, noxious chemicals)

Question 15

what type of sensation do Aδ fibres detect?

Answer 15

• non-descriminative touch (but is high pressure sensitive)
• hot/cold pain
• sharp pricking pain - precise location of pain

Question 16

what do C fibres detect?

Answer 16

• dull aching pain (non-descrimitivae pain)

- itch sensitive (histamine sensitive)

Question 17

where do the first order neurones of the spinothalmic pathway originate and synapse?

Answer 17

enter the dorsal horn of spinal cord where they synapse with the second order neurone

Question 18

where do the second order neurons of the spinothalamic pathway originate and synapse?

Answer 18

organist in dorsal horn and cross immediately to contra-lateral side of spinal cord “QUICK TO CROSS”; ascend in either lateral spinothalmic route or anterior route depending on fibre type; and project to thalamus (VPL region)

Question 19

where do the third order neurons of the spinothalamic pathway originate and synapse?

Answer 19

originate in VPL region of thalamus and project to somatosensory cortex of brain (Aδ project tp somatosensory cortex to give more precise info about location of pain whereas C fibres do not)

Question 20

what is the lateral spinothalmic route made up of?

Answer 20

C and Aδ fibres:
pain
temperature
dull pain and itch

Question 21

what is the ventral anterior spinothalmic rate made up of?

Answer 21

C fibres only:

corse, non discriminating touch

Question 22

what happens when there is lesions in the spinothalamic tract?

Answer 22

patients have decreased perception of pain on the contraletral side of their body

Question 23

what substance is used in peripheral nerve endings to modulate pain

Answer 23

substance P

Question 24

which chemical do chilli peppers contain which mimic tissue damage?

Answer 24

capsaicin - stimulates Trp1 receptors

can be used to treat chronic pain

Question 25

how does referred pain work?

Answer 25

signals of noxious signals from viscera synapse with normal cutaneous fibres in the dorsal horn on the same ascending nerve fibres.
information from the viscera is then mapped on the somatosensory cortex

Question 26

what type of sensory information does the spinocerebellar pathway carry?

Answer 26

UNCONCSIOUS information from:
muscle spindles
golgi tendon organs
touch receptors

Question 27

how many neurons is the spinocerebellar pathway composed of and where do these end up?

Answer 27

only 2 neurone pathway

end in the vermis of the cerebellum

Question 28

how do dorsal tract neurons ascend and which peduncle of the cerebellum do they enter?

Answer 28

ipsilaterally and enter via the inferior peduncle

Question 29

how do ventral tract neurone ascend and which peduncle do they enter the cerebellum?

Answer 29

contraleterally and via the superior peduncle

Question 30

what is Friedrich’s ataxia cause by?

Answer 30

inherited disease where the spinocerebellar tract becomes increasingly ineffective