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why are motor system organized?

basic patterns of movement can take place automatically and modifications of movement can occur with little or no conscious thought.
Allows brain to be directed to more important goals. Cerebellum helps to make motor movements automatic.


Hierarchial organization of motor system

1. Organized by the central pattern generators in the spinal cord that control the relative timing of the output.

2. Central pattern generators are subject to control from “projection regions”:
a. Brainstem
b. Motor cortex

3. Above these central regions areas providing volitional intent:
a. Premotor cortical area
b. Supplemental cortical area.


Where in the pathway from the periphery to the cortex could these dynamic changes take place?

1. DRG – No map no changes
2. Nucleus gracilis & nucleus cutaneatus – Map changes
3. Thalamus (VPL/VPM) – Map changes
4. Cortex – Map changes


function of rubrospinal tract

The rubrospinal tract and the lateral corticospinal tract comprise the ventrolateral system.
This lateral pathway initiates and maintains fine, detailed movements of the distal limbs.


the ruprospinal tract maintains tone in

flexor muscle groups


The sources of the ventrolateral system are the

cortex and the red nucleus in the brain stem.


The red nucleus receives input from

1. branches of the corticospinal axons
2. branches of the paravermal region of the cerebellum.


What are central pattern generations

central pattern generators generate the intrinsic rhythmicity for coordinated movement through these command centers for movement intrinsic to the spinal cord.

Allow for limbs to alternate when walking.


CPG's are located

in the spinal cord


CPGs considt of

flexor and extendor motor neuon to fire out of phase with each other.

One CPG for each leg


CPG's allow for

alteration of arm and leg swinging when walking


Midbrain Locomotor Region (MLR):

a region of the brainstem that tonically activates the cord. It is located somewhere beneath and close to the inferior colliculus.


ventromedial system is responsible for

posture control and many axial muscles on both sides need to work in concert.


The medial musculature and is made up of inputs from the:

1. vestibular nuclei
2. reticular formation
3. superior colliculus


medial musculature: vestibular nuclei

1. gets direct input from the vestibular apparatus
2. maintain balance


medial musculature: reticular formation

1. receive input from the MLR (mesencephalic motor region)
2. helps initiate movement.


medial musculature: superior colliculus

1. receives direct input from the retina and from the visual cortex
2. important for eye movements
3. Involved in control of neck muscles associated with head and eye movements.


CPGs are

consciously controlled by a region in the brainstem between the inferior colliculus and the superior colliculus called the mesencephalic locomotor region.


Describe the somatotopic organization of the primary motor cortex.

Primary motor cortex is organized like a homonculus.

But different than somatosensory homunculus.

Rather than individual muscles, joints and simple movements are grouped in the premotor cortex and SMA.


Specify the signaling that is involved in the flexor withdrawal reflex and the crossed extensor reflex (consider only the spinal cord and the periphery, i.e. not higher centers).

The idea is that if you step on a nail, you will activate your flexors to remove your foot, and inhibit your extensors so that it is easier to lift your leg, and they simultaneously work the opposite way on flexors and extensors in your other leg to help you balance.

This is all triggered by the Aδ fibers than the spinal cord. To coordinate movement with the other leg, interneurons exist as well.