Function Of The Motor System

Question 0

Bulbar motor neurones

Answer 0

Those of the cranial nerves that are motor neurones

Question 1

Spinal motor neurones

Answer 1

Alpha motor neurones, leave through the ventral horn
Directly trigger the generation of force by muscles
One motor neurone and all the motor fibres it innervates-> motor unit
All the motor units in a muscle-> motor neurone pool
3 inputs-> interneurone, sensory from muscle spindles (reflex) and upper motor neurones
UMN synapse in specific positions->
Later al to medial-> peripheral to central
Flexors are always more posterior

Question 2

Types of cerebral cortex

Answer 2

Cell bodies of neurones are always arranged in layers
Neocortex is outside bit-> only in higher intelligence mammals
2-3cm think
Six layers
Supragranular -> layers I-III
Primary origin and termination of intra cortical connections
Highly developed in humans
Permits communication between cortex and other regions
Granular part-> layer IV
Receives thalamic connections
Most prominent in the sensory corticol areas
Infragranular part-> layers V and VI
Primarily connects the cerebral cortex with subcortical regions
Most developed in motor areas
Layer V-> pyramidal neurones-> project to basal ganglia, brain stem and spinal cord
Layer VI-> primarily to thalamus

Question 3

Pyramidal cells

Answer 3

Low action potential
Rapid conduction
Only about 10% of upper motor neurones
In the motor cortex only-> Betz cells-> send axons directly to lower motor neurones

Question 4

Motor cortex

Answer 4

Primary motor cortex-> area 4 on the pre central gyrus -> where most of the motor nerve axons originate from -> somatotrophic organisation
Area 6-> higher motor control
-> lateral area 6-> pre motor area-> learned and skilled movement
-> medial area 6-> supplementary motor area
-> damage here causes spasticity
Areas 23 and 24-> cingulate motor area-> damage here causes loss of voluntary movement

Question 5

Motor action

Answer 5

Information processing that the brain must perform to initiate a voluntary movement
1) to select an appropriate response to the situation from predetermined repertoire
2) to plan the movement in physical terms-> sequence of muscle contractions
3) to actually execute the movement
Ready-> partial and fronts lobes+ brain centres that control levels of attention and alertness (association areas)
Set-> supplementary and pre motor areas
Go-> primary motor cortex

Question 6

Pyramidal system

Answer 6

Most axons descend in the lateral column of the spinal cord
Chiefly innervates dorsolateral LMN's
For voluntary/ planned movements
Corticobulbar tract-> cranial LMN 
Corticospinal tract-> spinal LMNs

Question 7

Corticospinal tract

Answer 7

Triangular cross section
Originates in neocortex
2/3 or axons originate in areas 4 and 6, rest somatosensory
Decussate (80%) in medulla apart from a small number of fibres -> right motor cortex controls left side of body
Few that remain ipsilateral become contra lateral when required-> white anterior commisure

Question 8

Capsula interna

Answer 8

Area of white matter in the brain that separates the caudate nucleus and the thalamus
Contains ascending and descending axons between cerebral cortex and medulla
Separates caudate nucleus and thalamus (medial) from putamen and globus pallidus
V shaped when cut horizontally
Anterior limb-> frontopontine, thalamocortical
Genu-> Corticobulbar fibres-> cortex to brain stem
Posterior limb-> corticospinal fibres, sensory fibres, som Corticobulbar, retro and sublenticular part

Question 9

Blood supply to capsula interna and effects of vascular lesions

Answer 9

Middle cerebral artery via two branches->
-> lateral striate arteries-> anterior limb, genuinely and posterior limb
-> anterior choroidal artery-> inferior and posterior internal capsules
Small subcortical infarcts in deep penetrating arteries, don’t have many collaterals-> most commonly pure motor stroke-> hemiparesis with pyramidal signs

Question 10

Motor system disorders

Answer 10

Upper motor neurone-> transaction of corticospinal tract or disease or cortical cells of origin -> paresis with pyramidal signs-> extended spastic paresis, hyperflexia and excitability, babinski positve
Lower motor neuron-> damage to motor neurone-> flaccid paresis, hypotonia, hyporeflexia, atrophy, fasciculations and fibrilations

Question 11

Descending spinal tracts and their input to motor neurones

Answer 11

Cerebral cortex-> corticospinal and Corticobulbar
Vestibular nuclei-> lateral nucleus in medulla with info from vestibular labyrinth-> activates antigravity muscles
Reticulo spinal tract->postural control
-pontine part-> antigravity reflexes, extenders of lower limb
-medullary part -> opposes pontine-> flexors of lower limb