Tracts

Question 1

What are tracts?

Answer 1

Organised nerve fibres sharing common origins, terminations and functions which run between the spinal cord and the brain

Question 2

Define funiculi

Answer 2

Continuous area of white matter running the whole way down the spinal cord. Hold bundles of myelinated nerve fibres together (fascicles)

Question 3

Where does the spinal cord finish?

Answer 3

At the conus medularis - L1/L2. Below this is the cauda equina

Question 4

What type of matter is in the central part of the spinal cord?

Answer 4

Grey matter

Question 5

Where does motor info exit the spinal cord?

Answer 5

Ventral root

Question 6

Where does sensory info enter the spinal cord?

Answer 6

Cell body of the dorsal root ganglion

Question 7

What are the descending tracts split into?

Answer 7

Extrapyramidal and pyramidal

Question 8

What type of information do ascending/afferent tracts carry?

Answer 8

Carry impulses like pain, thermal, tactile, muscle and joint receptors to the brain and within spinal cord

Question 9

Where do descending tract originate?
What type of information do descending/efferent tracts carry?
Name the 2 main descending tracts.

Answer 9

Originate from the cerebral cortex and brain stem.
Carry impulses controlling movement, muscle tone,
spinal reflexes, spinal autonomic functions and
modulate sensory transmission.
• Pyramidal/ direct/ Corticospinal
• Extrapyramidal/ indirect

Question 10

Which is motor and which is sensory in descending/ascending tracts?

Answer 10

Descending = motor
Ascending = sensory

Question 11

What are the 3 areas of funiculi in the spinal cord?

Answer 11

Anterior, posterior funiculus and lateral funiculus

Question 12

Name the 6 ascending tracts

Answer 12

Spinocerebellar - posterior + anterior
Spinothalamic - lateral + anterior
Dorsal white columns - fasciculus cuneatus + fasciculus gracilis

Question 13

Name the function of

a) Spinocerebellar
b) spinothalamic
c) dorsal white columns

Answer 13

a) subconscious proprioception lower limb - ipsilateral
b) lateral: pain and temperature - contralateral
anterior: coarse touch - contralateral
c) Discriminative touch & conscious proprioception

Question 14

Describe the posterior spinocerebellar tract

Answer 14

Runs: through spinal cord
Terminates: at cerebellum
Carries: afferent subconscious proprioception from
muscles spindles, Golgi tendon organs, joint proprioceptors in lower limb (ipsilateral)
1st order neurons: bring afferent nerve impulses through dorsal root ganglion, dorsal root and then synapses with 2nd order neuron
2nd order: transmits it to posterior part of lateral funiculi which then goes up the spinal cord through medulla and pons and then cerebellum

Question 15

Describe the anterior spinocerebellar tract

Answer 15

Runs: through spinal cord
Terminates: at cerebellum
Carries: afferent subconscious proprioception from
muscles spindles, Golgi tendon organs, joint proprioceptors in lower limb (ipsilateral)
1st order neurons: bring afferent nerve impulses through dorsal root ganglion, dorsal root and then synapses with 2nd order neuron. Signal decassates (moves to opposite side of the spinal cord at which the movement occurred e.g. if movement occurred in left lower limb it would decasste to right hand side of spinal cord)
2nd order: transmits it to anterior part of lateral funiculi which then goes up the spinal cord through and pons (where it crosses back to the original side) and ends at cerebellum

Question 16

Describe the lateral spinothalamic tract

Answer 16

contralateral
Runs: from spinal cord
Terminates: thalamus
Carries: info on pain and temperature i.e. signals from nociceptors and thermoreceptors across the body
1st order: impulses come in via 1st order through dorsal root and into dorsal horn.
2nd order neuron: 1st order synapses to 2nd. Signal crosses over in the lateral funiculus and stays on this side travelling up the spinal cord to the thalamus
3rd order: before going to cerebral cortex 2nd order synaposes to 3rd order

Question 17

What part of the brain is the somatotopic representation of the body?

Answer 17

The somatosensory cortex on the post-central gyrus of the cerebral cortex

Question 18

Describe the anterior spinothalamic tract

Answer 18

(similar to lateral spinothalamic)
1st order: via dorsal root ganglion 1st order neurons carry coarse touch and pressure info to 2nd order neurons. A synapse occurs into 2nd order neurons
2nd order: bring impulse to anterior funiculi through medulla, pons and midbrain before synapsing in thalamus
3rd order: bring it to an area on the contralateral side of the somatosensory cortex

Question 19

Describe the type of information dorsal white columns relay

Answer 19

Fine discriminative touch
• Vibration
• Two point discrimination
• Conscious proprioception
• stereognosis

Question 20

Describe the pathway of fasciculus cuneatus

Answer 20

Terminates: somatosensory cortex
Carries: info from the upper limbs
1st oder: enters via posterior dorsal root and organises to lateral part of dorsal white column without synapsing. It ascends to the nuclei cuneatus in the medulla as a 1st order neuron
2nd order: 1st order synapses to 2nd and crosses over to opposite side of thalamus
3rd order: goes to somatosensory cortex

Question 21

Describe pathway of fasciculus gracilis

Answer 21

Carries: info from lower limbs/trunk enters spinal cord at dorsal root, dorsal horn.
1st order neurons: enter posterior horn via dorsal root and enters the medial aspect of posterior dorsal white column without synapsing. It ascends as a 1st order neuron to reach the nuclei gracilis in medulla and synapses to a 2nd order neuron
2nd order neuron: crosses over and travels to medial lemniscus tract, through pons and midbrain before synapsing at thalamus where it turns into a;
3rd order neuron goes to somatosensory cortex

Question 22

What areas of the dorsal white column is responsible for upper and lower limb?

Answer 22

Medial = lower limb
Lateral = upper limb

Question 23

How are the upper limb signals differentiated from lower limb signals in the medulla?

Answer 23

Medulla is split into 4 medullary nuclei - 2 nuclei gracilis (medial 2) and 2 nuclei cuneatus (outer/lateral 2).
Upper limb signals ascend to the nuclei cuneatus
Lower limb signals ascend to the nuclei gracilis

Question 24

Name the descending motor tracts

Answer 24

1. Pyramidal (direct)
   - corticospinal (lateral and anterior)
2. Extrapyramidal (indirect)
   - rubrospinal
   - tectospinal
   - retuculospinal
   - vestibulospinal
   - olivospinal

Question 25

Where do direct descending tracts come from?

Answer 25

Cortex

Question 26

Where do indirect descending tracts come from?

Answer 26

Brainstem

Question 27

What is Friedrich’s ataxia?

Answer 27

Degeneration of spinocerebellar tracts

Causes tremors difficulty in co-ordinating movement and damage to subconscious proprioception