5- Motor System Flashcards
Where are the cell bodies of lower motor neurones found?
The ventral horn of the cord and in cranial nerve nuclei (oculomotor, trochlear, trigeminal motor)
What signs can be seen in muscles supplied by damaged lower motor neurones?
Weakness, areflexia, wasting, hypotonia, fasiculation
Why do muscles supplied by damaged lower neurones show fasiculation?
Up-regulation of muscle nicotinic ACh receptors to try to compensate for denervation
Where are upper motor neurones found?
Primary motor cortex
Is the net effect of UMNs (upper motor neurones) on LMNs excitatory or inhibitory?
Net inhibitory effect
What is the route of upper motor neurones as they travel through the brain and spinal cord from the motor cortex to synapse on the lower motor neurones?
Motor cortex -> corona radiata -> internal capsule -> cerebral peduncle -> pons -> medullary pyramids -> decussate on of the pyramids -> lateral corticospinal tract
How does the action of neurones in the lateral corticospinal tract compare to those in the ventral corticospinal tract?
Lateral supplies distal musculature of limb and is involved in fine motor control, whereas ventral supplies more proximal musculature of the limbs
What happens to the motor fibres which do not decussate at the decussation of the pyramids?
Some join the ventral corticospinal tract, others join the lateral corticospinal tract on the same side
Why do UMN lesions involving the face spare the forehead?
The superior part of the facial motor nucleus receives UMNs from both hemispheres whereas the part supplying the lower face only receives a contralateral UMN input
When UMNs are damaged what signs are seen in the body parts supplied by them?
Weakness, hypertonic, hyperreflexia, extensor plantar reflexes
What is spinal shock?
Immediately following a UMN lesion (for a few days) there is flaccid paralysis with areflexia before normal signs are seen
Between which structures is anterior limb of the internal capsule?
Caudate nucleus and lentiform nucleus
Between which structures can the posterior limb of the internal capsule be found?
Thalamus and lentiform nucleus
What are the two sections of lentiform nucleus?
Globus pallidus and putamen
UMNs that supply facial structures form which tract and where is this found in the internal capsule?
Corticonuclear/corticobulbar tract located at the genu of internal capsule
How are the UMNs of upper and lower limbs arranged once they enter the internal capsule?
Upper limbs more anteriorly, lower limbs more posteriorly
