L19 - Overview of central sensory and motor pathways - WIP

Question 1

Which direction are the tracts in which somatic efferents are carried by?

Answer 1

Somatic efferents are carried by descending tracts

Question 2

Which direction are the tracts in which somatic afferents are carried by?

Answer 2

Somatic afferents are carried by ascending tracts

Question 3

What is the name of the anatomical landmarks that separates the motor from the sensory brain?

Answer 3

Central sulcus - a distinctive narrow strip of depression in brain tissue

Question 4

After sensory information has been processed in the spinal cord, what is the movement to the cerebral cortex afterwards?

Answer 4

Spinal cord (dorsal horn) --> medulla --> thalamus --> cerebral cortex
(carried through ascending tracts)

Question 5

Where is the primary sensory cortex?

Answer 5

The post-central gyrus of the cortex

Question 6

What are the 2 categories of sensation that sensory signals give rise to?

Answer 6

1. Conscious sensation
   - Pain
   - Temp
   - Crude touch
   - arouses awareness
2. Non-conscious sensation
   - Tactile sensation
   - Pain
   - Muscle length
   - Tension
   - Joint position

Question 7

What is the primary (somato)sensory cortex responsible for?

Answer 7

• Processing somatic sensations; these sensations arise from receptors positioned throughout body

Question 8

What are ascending tracts?

Answer 8

Fibre tracts of the sensory system by which sensory info is conveyed to the brain (cerebral cortex) from the peripheral nerves

Question 9

Where are the different positions which the ascending tracts can be found?

Answer 9

1. Dorsal column (DC)
2. Lateral column - Lateral spinothalamic tract (LSTT)
3. Dorsal spinocerebellar tract (DST)

Question 10

What happens to the primary sensory neurone once it reaches the spinal cord?

Answer 10

On reaching spinal cord, a primary sensory neurone then divides

• 1 axonal process terminates in the dorsal horn of its respective spinal segment
• Another axonal process is sent to the dorsal horn of the spinal segment above
• Another axonal process is sent to the dorsal horn of the spinal segment below

Question 11

Which tract does the axonal segments travel in during the first stage of spinal sensation?

Answer 11

The axonal segments travelling to the spinal segments above and below travel in the POSTEROLATERAL TRACT OF LISSAUER

Question 12

What happens in the first stage of spinal sensation?

Answer 12

The first sensory neurone carries signals to the grey matter of the dorsal horn where it terminates

Question 13

What happens in the second stage of spinal sensation?

Answer 13

A 2nd order sensory neurone picks up the sensory signal before crossing the midline to travel in the spinal cord of the opposite side, where it ascends until it reaches the thalamus and where it terminates

Question 14

What happens in the third stage of spinal sensation?

Answer 14

Axons of 3rd order sensory neurones of the ventral posterolateral ascend further to terminate in the post-central gyrus of the cerebral cortex

Question 15

Where is sensory info from the right side of the body represented?

Answer 15

Sensory info from the right side of the body is represented and perceived by the left brain
- Sensory function is decussated

Question 16

How is pain and temp info carried to the cerebral cortex?

Answer 16

• Pain and temp info crosses the midline at the same neural level as its respective dermatome
• Pain and temp info carried on the contralateral spinal cord, medulla, thalamus and cortex

Question 17

How is proprioceptive and tactile info carried to the cerebral cortex?

Answer 17

• Proprioceptive and tactile info carried on the SAME side of the spinal cord as its origin
• This info remains ipsilateral until the level of the medulla where it decussates to the contralateral side
• It then travels in the contralateral medulla, pons, midbrain and thalamus before terminating in contralateral sensori-motor cortex

Question 18

What is syringomyelia?

Answer 18

Development of a fluid filled cyst (syrinx) within the spinal cord

Question 19

Describe the development of syringomyelia

Answer 19

1. Central cavitation of the central canal (at very early stage)
2. Cyst expands ventrally
3. Cyst expands into the ventral horn
4. Effective transection of spinal cord

Question 20

What would be a complication if the cyst in syringomyelia grows inferiorly?

Answer 20

If cyst grows inferiorly, it will cut sensations arising from pain systems –> bilateral loss of sensation

Question 21

Where is the primary motor cortex?

Answer 21

The pre-central gyrus of the cortex

Question 22

What is the journey of motor commands from the cerebral cortex to the spinal cord?

Answer 22

Carried by descending tracts

Cerebral cortex –> thalamus –> basal ganglia –> spinal cord (ventral horn)

Question 23

What are the different general classes of the decending tracts?

Answer 23

1. Cortical descending tracts

2. Non-cortical descending tracts

Question 24

Where are cortical descending tracts located?

Answer 24

• Originates in the motor areas of the cerebral cortex

- Primary motor cortex (in pre-central gyrus)

Question 25

Where are non-cortical descending tracts located?

Answer 25

• Originates in sub-cortical areas of the brain

- Midbrain, brainstem, pons and medulla

Question 26

What is the resting muscle tone for?

Answer 26

Maintenance of posture (minimal contraction)

Question 27

What is the displacement of joints for?

Answer 27

Movements (large forces may be required)