Overview of Motor Systems Flashcards
What do LMNs innervate?
Skeletal Muscle
What do the medial LMNs innervate?
Axial/Trunk Muscles
What do the lateral LMNs innervate?
Distal Limb Muscles
What do the dorsal LMNs innervate?
Flexor Muscles
What do the ventral LMNs innervate?
Extensor Muscles
What neurotransmitter do LMNs use?
Acetylcholine
What are the types of motor units?
S-Unit
FR-Unit
FF-Unit
Describe the S-Unit.
Slow twitch fibers that are fatigue resistant
Describe the FR-Unit.
Fast twitch fibers that are fatigue resistant
Describe the FF-Unit.
Fast twitch fast fatiguing fibers that have high force
What are the red muscle fibers?
S-Unit
What are the white muscle fibers?
FF-Unit and FR-Unit
What are the descending pathways of the LMNs?
Corticospinal tract
Vestibulospinal tract
Reticulospinal tract
Tectospinal tract
Describe the corticospinal tract.
All of it is excitatory and uses glutamate as the NT
Describe the tectospinal tract.
It supplies the reflex turning of head to visual/auditory stimuli
What are the higher cortical centers and their functions?
– Association cortex – “decide” that a movement is needed
– Supplementary motor area – planning/learning complex movements
– Premotor cortex – devise a “plan” for the movement
– Motor cortex – issues “commands” to motor neurons
What are Betz cells?
They are large neurons in the motor cortex
and invoked in most leg movements with some hand too
What are the contributions to the corticospinal tract?
50% from the primary motor cortex
Adjacent Frontal motor and Parietal areas contribute the rest of the CST fibers
Where does the CST project to?
– spinal cord and brainstem
– collaterals (direct and indirect) to basal ganglia, thalamus, reticular formation, sensory nuclei
What part of the internal capsule does the CST pass through?
Posterior Limb
What is the main distinction in an UMN and LMN lesion in the face on CN VII?
UMN of CN VII are bilateral, however, the LMN are unilateral. Thus, the main distinction between an UMN and LMN lesion is that in the former, there is hemiplegia of the contralateral mid- and lower-face, whereas in the latter, there is complete hemiplegia of the ipsilateral face.
Where do UMNs for cranial nerve nuclei descend?
Anterior to the corticospinal tract
What nerves receive no direct corticobulbar innervation?
CN 3, 4, 6. So specific collections of neurons in the brainstem control the movements of them.
What makes up large MNs? Small MNs?
Large MN - FF-Unit
Small MN - S-Unit
What are the parts of the internal capsule?
Anterior Limb
Genu
Posterior Limb
Describe LMN Syndrome.
Muscles become weak and atrophic. Sometimes twitches in the muscles may develop as well.
Caused as a result of damaged anterior horn cells.
Describe UMN Syndrome.
Damaged UMNs, often caused by stroke. Muscles become stiffened and atrophic after time, but no twitches develop.
Damage to what systems will not result in weakness?
Cerebellum
Association Cortex
Basal Ganglia
