The somatosensory

Question 1

What motor neurons are in the brainstem?

Answer 1

Upper motor neurons

Question 2

What is the Fritsch and Hitzig experiment?

Answer 2

Electrically stimulated the cortex (anterior)
- Elicited contraction of the contralateral body muscles
- Region is now known as the motor cortex

Question 3

How is the motor cortex mapped?

Answer 3

Somatotopically
- Lower body is represented medially
- Upper body is mediated laterally
- The proportions reflect the density of innovation

Question 4

What motor neurons are in the spinal cord?

Answer 4

Lower motor neurons

Question 5

What movement do axial muscles provide?

Answer 5

Trunk movement

Question 6

What movement do proximal muscles provide?

Answer 6

Shoulder, elbow, pelvis and knee

Question 7

What movement do distal muscles provide?

Answer 7

Hands, feet, digits

Question 8

What do lower motor neurons in the ventral horn innervate?

Answer 8

Striated muscle via neuromuscular junctions

Question 9

What is the motor unit?

Answer 9

The motor neuron and all the muscle fibres it innervates

Question 10

What is the motor neuron pool?

Answer 10

All the motor neurons that innervate a single muscle

Question 11

How are motor pools organised?

Answer 11

Grouped in rod shaped clusters within the spinal cord extending over several vertebral segments
- Grouped together with all the motor neurons that innervate a particular muscle

Question 12

What would allow you to trace motor neurons to the spinal cord?

Answer 12

Retrograde labelling

Question 13

How is a motor pool organised?

Answer 13

Somatotopic
- Organisation reflects the organisation of the body
- Both medio-laterally and rostro-caudally

Question 14

How do upper motor neurons project axons to lower motor neurons?

Answer 14

Via the descending tracts

Question 15

What is the lateral pathway in control of voluntary movement ?

Answer 15

Corticospinal tracts

Question 16

Where do the axons of the CST reside?

Answer 16

Layer 5 of the motor cortex

Question 17

What are the main inputs into the motor cortex?

Answer 17

Stellate cells in layer 4

Question 18

Where are the main outputs for the motor cortex?

Answer 18

Layers 4, 5 and 6

Question 19

What are axons of the corticospinal tract derived from?

Answer 19

Large pyramidal cells

Question 20

Function of motor cortex upper motor neurons

Answer 20

Primarily concerned with fine voluntary control of distal structures

Question 21

Function of brain stem upper motor neurons

Answer 21

Project to medial motor pools
- Concerned with postural movements

Question 22

How do axons of the corticospinal tract project?

Answer 22

Cross the midline in the pyramidal decussation in the medulla
- Project laterally in the spinal cord to synapse on laterally located lower motor neurons
- Lower motor neuron circuits control distal muscles

Question 23

Where do outputs for the upper body originate?

Answer 23

From the lateral motor cortex

Question 24

Where do outputs for the lower body originate?

Answer 24

Medial motor cortex

Question 25

How do axons of the brainstem project?

Answer 25

- Ipsilaterally in vestibulospinal and reticulospinal tracts - Medially in the spinal cord - Synapse on medially lower motor neuron circuits that control axial muscles

Question 26

What is the function of the ventromedial pathway?

Answer 26

Control posture

Question 27

How does the ventromedial pathway project?

Answer 27

Mainly ipsilaterally and medially

Question 28

Function of the vestibulospinal tract

Answer 28

Head balance and turning

Question 29

Function of the tectospinal tract

Answer 29

Orienting response

Question 30

Function of the reticulospinal tracts

Answer 30

Control antigravity reflexes

Question 31

How does the body compensate forces?

Answer 31

There is anticipatory 'feedforward' mechanism - Posture is adjusted by anticipating the movement

Question 32

What is the function of premotor area 6?

Answer 32

Movement anticipation - Activates an indirect projection to axial muscles via reticular formation

Question 33

What is the function of motor area 4?

Answer 33

Movement initiation - Activation of voluntary movement direct to spinal cord via the corticospinal tract

Question 34

What does activity in the PMA preceed?

Answer 34

Activity in area 4 and coincides with movement planning/anticipation

Question 35

Where is the anticipation circuit?

Answer 35

From the motor cortex to the brainstem nuclei

Question 36

Describe motor neuron disease

Answer 36

Degenerative disease - Muscular atrophy and sclerosis of the lateral spinal cord - 3 years is a typical timecourse

Question 37

Describe lower motor neuron disease

Answer 37

- Muscle paresis or paralysis - Loss of stretch reflexes - Severe muscle atrophy - Patients usually die from lung dysfunction

Question 38

Describe upper motor neuron disease

Answer 38

- Muscle weakness - Spasticity due to increased muscle tone (failure of modulation of stretch reflex) - Hyperactive reflexes - Loss of fine voluntary movement - Patients usually die from loss of input of the bulbar muscles via the corticobulbar tract

Question 39

What causes neurons to degenerate in MND?

Answer 39

- Excitoxicity, glutamate overstimulation causes neuronal cell death

Question 40

What drug can alleviate MND?

Answer 40

Riluzole - Blocks glutamate release