Motor System And Corticospinal Tract Flashcards
What is unique about the facial motor nucleus in the medulla?
What significance does this have?
It is split in two, with the upper half supplying the forehead having a bilateral nerve innervation. The lower half has only contralateral innervation. As such, in a stroke, the forehead is spared.
What type of innervation do the trigeminal motor nucleus and the nucleus ambiguous have?
Bilateral nerve innervation
What does the lateral corticospinal tract mainly supply?
Distal extremities - finer movement.
What does the ventral corticospinal tract supply?
Proximal limb (girdles). The fibres here have not yet decussated.
Where is the corticonuclear pathway found?
What does it contain?
Midbrain.
Lower motor neurones associated with the cranial nerves.
In what order is the body represented in the corticospinal tract?
Upper limbs found more medial,
Lower limbs found more lateral.
Trunk intermediate.
What does the corticospinal tract primarily control?
Precise voluntary movement (very interesting!)
Describe the structures an upper motor neurone will pass through, starting from the cerebral cortex
Cortex - corona radiata - internal capsule - cerebral peduncle (brainstem) - medullary pyramids (decussation) - synapses at level of motor innervation.
What does the internal capsule contain?
Descending upper motor neurones,
Ascending third order sensory neurones.
Upper motor neurones supplying the face are found where in the internal capsule?
The genu (bend)
Where are the majority of the descending upper motor neurones located within the internal capsule?
Posterior limb
Which area of the internal capsule contains ascending third order neurones?
Superior thalamic radiation.
What signs are commonly seen in lower motor neurone lesions?
Hypotonia, Hyporeflexia, Flaccid paralysis, Fasciculation, Atrophy.
What are common upper motor neurone signs?
Spinal shock, Hypertonia, Rigid paralysis (spasticity), Hyperreflexia, Disus atrophy (less pronounced).
What is spinal shock?
When deprived of an input, lower motor neurones tend to send reduced signals, leading to originally lower motor neurone signs in upper motor neurone pathology.
What causes fasciculation in lower motor neurone lesions?
Upregulation of acetylcholine muscle fibres leading to involuntary contractions.
Why does spasticity often present in the arm as a flexed elbow, flexed wrist and flexed fingers?
Excitatory and inhibitory pathways destroyed, as such a lack of inhibition (which is stronger at rest in a healthy example) results in increased action potentials and hypertonia/contraction. Flexors are stronger than extensors in the upper limb.
What is the corona radiata?
Point at which fibres of the corticospinal tract begin to converge before entering the internal capsule,
In lacunar strokes, why are the face and upper limb afected equally?
Lacunar arteries actually innervate both facial and upper motor nerves relatovely equally, despite medical textbooks suggesting otherwise.
What is the babinski reflex?
Stroking the bottom of the foot should lead to flexion of the toes, but here leads to extension. Linked to underlying nervous system pathologies (eg ALS, stroke)
What is descending inhibition on spinal reflexes?
In a reflex arc, the afferent neurone may also send excitatory signals to the inhibitory interneurones of antagonistic muscles, resulting in an effect only in the desired muscle.
