Excitable cells 7: Motor nervous system and diseases Flashcards
Where are alpha-motor neurons located?
- controlled at which levels?
Ventral horn of spinal cord and hindbrain
- controlled at:
- spinal cord
- descending pathways from upper motor neurons in brain
Name and describe the 2 main descending pathways of alpha motor neurons
- mention function
Ventromedial
- upper MN are in brain stem
- controls posture and locomotion
Lateral
- upper MN are in motor cortex
- controls voluntary movement of distal muscles
Describe the pathway and function of the corticospinal tract (CST)
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
What does the conduction block in or death of lower motor neurons result in? What diseases can cause this?
Results in paralysis
caused by
- Spinal muscular atrophy
- Amyotrophic Lateral Sclerosis
Which cells aid with cortical control of voluntary movement? Describe cells and pathway
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’
Two important pathways for cortical control of upper Motor neurons?
Basal ganglia:
Frontal cortex -> basal ganglia -> thalamus -> motor cortex
Cerebellum:
Multiple cortical regions -> pons -> cerebellum -> thalamus -> motor cortex
Example of diseases associated with
- death of basal ganglia neurons
- death of cerebellar neurons
Parkinson’s, Huntington’s disease
(death of basal ganglia neurons)
Spinocerebellar ataxias
(death of cerebellar neurons)
- movement disorders
Two general types of neural lesion/dysfunction
- White matter (WM)/ interrupted axonal conduction;
- Grey matter (GM)/ death of neurons (post-mitotic cells; irreplaceable)
Syndromes affecting either white matter and/or grey matter
- Injury - penetrating or blunt, to head, spine, limb
- Stroke - ischaemic or haemorrhagic
- Infection – meningitis, encephalitis
- Neural tumour – astrocytoma is most common
Diseases primarily affecting white matter
- Multiple sclerosis – CNS inflammatory demyelination
- Paraplegias – distal degeneration of spinal cord tracts
- Neuropathies – distal degeneration and/or demyelination of peripheral nerve
Diseases primarily affecting grey matter
- 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