Excitable cells 7: Motor nervous system and diseases

Question 1

Where are alpha-motor neurons located?

- controlled at which levels?

Answer 1

Ventral horn of spinal cord and hindbrain

• controlled at:
• spinal cord
• descending pathways from upper motor neurons in brain

Question 2

Name and describe the 2 main descending pathways of alpha motor neurons
- mention function

Answer 2

Ventromedial

• upper MN are in brain stem
• controls posture and locomotion

Lateral

• upper MN are in motor cortex
• controls voluntary movement of distal muscles

Question 3

Describe the pathway and function of the corticospinal tract (CST)

Answer 3

Main human lateral pathway

• motor cortex
• thalamus
• base of cerebral peduncle (midbrain)
• medulla
• pyramidal decussation
• corticospinal tract
• > lower motor neurone
• > peripheral nerve
• > muscle

Controls voluntary movement of distal muscles

Question 4

What does the conduction block in or death of lower motor neurons result in? What diseases can cause this?

Answer 4

Results in paralysis
caused by
- Spinal muscular atrophy
- Amyotrophic Lateral Sclerosis

Question 5

Which cells aid with cortical control of voluntary movement? Describe cells and pathway

Answer 5

Betz cells

• huge but few in number
• Originate in pre-central gyrus = primary motor cortex

Pathway
Betz cell ‘upper neuron’
-> pryamidal tract = corticospinal tract
-> ventral horn cell ‘lower neuron’

Question 6

Two important pathways for cortical control of upper Motor neurons?

Answer 6

Basal ganglia:
Frontal cortex -> basal ganglia -> thalamus -> motor cortex

Cerebellum:
Multiple cortical regions -> pons -> cerebellum -> thalamus -> motor cortex

Question 7

Example of diseases associated with

• death of basal ganglia neurons
• death of cerebellar neurons

Answer 7

Parkinson’s, Huntington’s disease
(death of basal ganglia neurons)
Spinocerebellar ataxias
(death of cerebellar neurons)

• movement disorders

Question 8

Two general types of neural lesion/dysfunction

Answer 8

• White matter (WM)/ interrupted axonal conduction;

- Grey matter (GM)/ death of neurons (post-mitotic cells; irreplaceable)

Question 9

Syndromes affecting either white matter and/or grey matter

Answer 9

• Injury - penetrating or blunt, to head, spine, limb
• Stroke - ischaemic or haemorrhagic
• Infection – meningitis, encephalitis
• Neural tumour – astrocytoma is most common

Question 10

Diseases primarily affecting white matter

Answer 10

• Multiple sclerosis – CNS inflammatory demyelination
• Paraplegias – distal degeneration of spinal cord tracts
• Neuropathies – distal degeneration and/or demyelination of peripheral nerve

Question 11

Diseases primarily affecting grey matter

Answer 11

• Motor neuron diseases – amyotrophic lateral sclerosis, spinomuscular atrophy
• Cerebellar diseases – spinocerebellar ataxias
• Basal ganglia diseases – Huntington’s, Parkinson’s (movement disorders)
• Temporal/frontal lobe diseases – Alzheimer’s, frontotemporal lobe dementias