Motor systems Flashcards
Describe the somatotopic organization of BA 4
The motor cortex is arranged with neurons to the lower extremity at the midline, and the face laterally. The hand takes up the middle third of motor cortex.
What are the different types of motor units?
S: small, red fibers, slow twitch, small force, fatigue resistant
FR: white fibers, fast twitch, moderate force, fatigue resistant
FF: white fibers, fast twitch, large force, fatiguable
What are lower motor neurons?
Neurons of the brainstem and spinal cord, arranged into columns
Describe the somatotopic organization of lower motor neurons within the grey matter
Neurons to axial muscles are medial and distal muscles lateral. Flexor muscles are dorsal and extensor muscles are ventral.
What is the size principle of LMNs?
LMNs are recruited in order of size and force:
S –> FR –> FF
What are upper motor neurons?
Corticospinal and corticobulbar neurons
What brain structure does the CST pass through?
The CST passes through the posterior limb of the internal capsule between the thalamus and the lentiform complex
Describe the somatotopic organization of the CST within the midbrain
Nerves to the upper extremity are medial, to the lower extremity are lateral
What clinical feature distinguishes central lesions from upper and lower motor neuron lesions?
Weakness is not present from central lesions, but is present in UMN and LMN lesions
Which motor cranial nerves do not receive direct corticobulbar innervation?
The CN for extraocular muscles: III, IV, and VI
Which motor CN’s are innervated primarily by the contralateral CST?
V
VII (completely contralateral in lower face)
XII
Which motor CN’s are innervated by both sides of the CST?
VII (upper face)
IX
X
