Overview of Motor Systems Flashcards
Somatotropic organization of muscles for Lower Motor Neurons
- Motor neurons for axial muscles are medial,
- Lateral for more distal muscles
- Flexor motor neurons are dorsal to extensor motor neurons
Motor Unit
-a motor neuron and all of the muscle fibers it innervates
Each muscle fiber receive contact from only one motor neuron; all muscle fibers in motor unit contract
What are the type of muscle fibers?
- Red fibers/ Type I (Slow oxidative fibers) – slow, sustained movements (Posture)
- Intermediate fibers/ Type IIA (Fast oxidative fibers) – intermediate in speed and fatigue (Walking)
- White fibers/ Type IIB (Fast glycolytic fibers) – fast, brief movements (Jumping ,Sprinting)
What are the types of motor units?
-Type S (Slow-twitch) motor unit -
Small amounts of force for extended time (red)
-Type FF (Fast-twitch, Fatigable) motor unit -
Large amounts of force for brief periods of time
-Type FR (Fast-twitch, fatigue-Resistant) motor unit-
Moderate amounts of force over moderate time
How are motor units recruited?
-Increasing numbers of motor neurons stimulate more motor units (and therefore, more muscle fibers) to contract
-Recruited in order of size
S then FR then FF
Temporal Summation
-when a muscle is stimulated more than once within a brief period, the successive twitches produced add to each other, so the overall response is greater than the twitch response to a single stimulus
-Muscle does not have time to completely relax between stimuli
If stimuli are given quickly enough, a smoothly fused contraction called tetanus results
Lower motor neurons are regulated by __________ . Upper Motor neurons synapse with ______ or ________.
-Supraspinal centers
-LMN
- Interneurons
(UMN located in cerebral cortex or braistem)
Function of the corticospinal tract
Mediate voluntary movements
Origin of corticospinal tract
- 1/2 from contralateral primary motor cortex
- 1/3 from contralateral frontal cortex (premotor and supplementary motor areas)
- From contralateral parietal cortex association areas
Parts of corticospinal tract
- Motor cortex, premotor cortex, association cortex, thalamus, basal ganglia, cerebellum,
- And a variety of brainstem nuclei (vestibular, reticular formation, superior colliculus)
How is a movement generated?
- Association cortex “decides” on a movement, premotor cortex devises plan for movement, and motor cortex executes
- Projected to spinal cord (lower motor neurons) to carry out the movement
- And basal ganglia/cerebellum for fine tuning
Know the pathway of lateral corticospinal tract
Refer to flow chart
Know the pathway of the anterior corticospinal tract
Refer to flow chart
What would occur if there was damage to the lateral corticospinal tract? anterior corticospinal tract?
-Inability to use fingers individually (Ex. Pincer grip)
-Does not result in obvious weakness
(Probably because of bilateral distribution of fibers from the contralateral tract)
What are some other descending tracts?
- Vestibulospinal tract – postural adjustments and head movements
- Reticulospinal / rubrospinal tracts – alternate routes of voluntary movement mediation
- Tectospinal tract – coordinating head movements and visual stimuli
UMN damage results in ____ paralysis while LMN damage results in _____ paralysis.
- Spastic
- Flaccid
