Ascending Neural Pathways

Question 1

What are the 3 principal ascending tract systems of the spinal cord?

Answer 1

1. dorsal column - medial lemniscus
2. spinothalamic
3. spinocerebellar

Question 2

What tract carries information from the lower body extremities?

Answer 2

fasciculus gracilis (up to T6)

Question 3

Where does fasciculus cuneate carry information from?

Answer 3

upper body (from above T6)

Question 4

Where does the first order neuron/first afferent terminate?

Answer 4

the spinal cord or brainstem

Question 5

Where does the second order neuron project to?

Answer 5

the thalamus

Question 6

Where does the third order neuron project to?

Answer 6

primary sensory cortex

Question 7

What is the dorsal column - medial lemniscal pathway for?

Answer 7

MECHANICAL STIMULI

1. conscious proprioception
2. discriminative touch
3. vibration
4. pressure

Question 8

What fibres is the medial lemniscal pathway composed of?

Answer 8

large diameter, fast A-beta fibres

Question 9

In the dorsal columns, how do the 1st order neurons ascend?

Answer 9

ipsilaterally

Question 10

What are the steps in the medial lemniscal pathway?

Answer 10

1. 1st order neurons ascend dorsal colum
2. at gracile and cuneate nuclei, they synapse with 2nd order neurons
3. they then decussate and form medial lemniscus
4. project to VPL of thalamus

Question 11

What pathological process occurs when the brain is deprived of information about the position of the feet?

Answer 11

gait ataxia

Question 12

What can lesions in the cervical cord cause?

Answer 12

upper extremity ataxia

Question 13

What does paraesthesia usually result from?

Answer 13

ectopic discharge in damaged dorsal column axons

Question 14

What is the spinothalamic pathway for?

Answer 14

NOCICEPTIVE STIMULI

1. mech/chem/therm detection of coarse or non-discriminating touch
2. pain
3. temperature

Question 15

What sort of fibres are spinothalamic pathways composed of?

Answer 15

+ smaller diameter
+ A-delta or C fibres
+ no specialised sensory endings
+ myelinated fibres (quick to cross)

Question 16

What do A-delta fibres detect?

Answer 16

+ non-discriminative touch (strong stimuli that does not damage skin)
+ heat/cold
+ sharp pain

Question 17

What do C fibres detect?

Answer 17

+ dull, aching pain
+ itch (histamine sensitive)

+ thermal
+ mechanical

Question 18

What are the steps in the spinothalamic pathway?

Answer 18

1. 1st and 2nd order neurons synapse in dorsal horn
2. decussate then ascend lateral OR ventral tracts
3. synapse with 3rd order neurons at thalamus
4. project to sensory cortex

Question 19

What are the features of the spinothalamic LATERAL route?

Answer 19

+ mix of A-delta and C fibres
+ carries info about:
- pain/heat and cold (A-delta)
- dull pain/itch (C)

Question 20

What are the features of the spinothalamic VENTRAL/ANT. route?

Answer 20

only C fibres carrying info about coarse/non-discriminating touch via mechanosensitive fibres

Question 21

What are the 4 types of nociceptor?

Answer 21

+ polymdal
+ mechanical
+ chemical
+ thermal

Question 22

What are the features of pricking/stabbing pain?

Answer 22

+ fast
+ conducted along A-delta fibres
+ arrives first in CNS (fast conduction velocity)

Question 23

What are the features of burning/aching pain?

Answer 23

+ slower
+ conducted along C fibres
+ arrives later in CNS (slow conduction velocity)

Question 24

What is the role of substance P?

Answer 24

+ modulates the peripheral neuronal response to noxious stimuli

+ released from pain neurons when stimulated in fast succession

+ increase sensitivity to noxious stimuli

Question 25

What is referred pain?

Answer 25

+ signals of noxious and normal cutaneous stimuli enter spinal cord at same point

+ cross talk in dorsal horn between modalities common

+ signals from viscera picked up by ascending nerve fibres mapped cortically to dermis

Question 26

What is the role of the spinocerebellar pathway?

Answer 26

PROPRIOCEPTIVE INFO

takes info about body’s position and movements to cerebellum for integration (for control of posture and co-ordination of movement)

Question 27

What are the two principal routes for info in the spinocerebellar pathway?

Answer 27

+ ventral/anterior route

+ dorsal/posterior route

Question 28

Where is information carried from in the spinocerebellar pathway?

Answer 28

Dorsal route: from muscle spindles (muscle tension)

Ventral route: from golgi organs (proprioception) and touch receptors

Question 29

How many neurons does each pathway contain along its length (1st and 2nd order)

Answer 29

only 2 neurons

Question 30

Where are the 2nd order cell bodies located?

Answer 30

dorsal horn of spinal cord, and terminate in vermis of cerebellum

Question 31

How do dorsal tract neurons ascend?

Answer 31

ipsilaterally

Question 32

How do dorsal tract neurons enter the cerebellum?

Answer 32

via the inferior peduncle

Question 33

How do ventral tract neurons ascend?

Answer 33

contralaterally

Question 34

How do ventral tract neurons enter the cerebellum?

Answer 34

via the superior peduncle

Question 35

What is Friedreich’s ataxia

Answer 35

Inherited disease where spinocerebellar tract becomes increasingly ineffective

Question 36

What causes Friedreich’s ataxia

Answer 36

multiple repeats of gene for protein (Frataxin) responsible for iron metabolism in mitochondria

Question 37

What does Friedreich’s ataxia result in?

Answer 37

1. progressively uncoordinated arm and leg movements
2. wide based ‘reeling’ gait
3. intention tremor