Descending Motor Pathways Flashcards
What are the requirements for movement ?
- Goal or purpose,
- Activation of relevant movement
- Feedback of movement
- Refinement/correction of movement 5. Cessation on completion
Where in the brain is the motor cortex located ?
Anterior to central cortical sulcus, in the frontal love
How much of the frontal lobe does the motor cortex occupy ?
1/3 of it
What are the sub areas of the motor cortex ?
– 1° motor cortex
– Premotor area
– Supplementary motor area

What does most of the primary motor cortex control ?
> 1/2 1° motor cortex controls hands and muscles of speech
How many muscles does the excitation of a single motor neuron control ?
Excitation of a single mn ususally excites a specific movement – not one specific muscle.
I.e. A pattern of separate muscles are excited.
Which of the primary motor cortex or premotor area gives more complex patterns of movement ?
Nerve signals from premotor areas give more complex “patterns” of movement.
What is a special feature of contractions elicited by the Supplemental Motor Area ?
Contractions elicited are often bilateral eg grasping movements of both hands.
Does the Supplemental motor area work by itself ?
Usually functions together with premotor area.
What is the function of the supplemental motor area ?
Gives background movement onto which premotor and 1° motor cortex add finer control.
How do motor signals get transmitted from cortex to the spinal cord ?
Through the Corticospinal tract
What proportion of each motor area in the cortex does the Corticospinal tract originate from ?
30% 1°
30% premotor/ supplementary motor
40% somatosensory.
Describe the path of motor signals from the cortex to
Cortex –> pyramids of medulla –> (majority)cross in lower medullae –> lateral corticospinal tractse –> mainly terminate on interneurons
Those that do not cross pass ipsilaterally in ventral corticospinal tracts.
What pathways exist to transmit motor signals ? Are they for conscious or unconscious movements ?
Lateral Pathways = Conscious Movements
Ventromedial pathways = Unconscious Movements
How are the lateral, and ventromedial pathways controlled respectively ?
LATERAL PATHWAY
Principally controlled by the cerebral cortex via 2 corticospinal tracts.
VENTROMEDIAL PATHWAY
Principally controlled in the brainstem.
What do the lateral, and ventromedial pathways control respectively ?
LATERAL PATHWAY
General control of voluntary movement.
Mainly associated with control of distal muscles.
VENTROMEDIAL PATHWAY
Control of posture and rhythmic movements associated with locomotion and posture
Control axial and proximal muscles.
What is posture ?
Position of a body and its parts relative to each other. It is a compromise between balance and movement.
Which structure is involved in controlling/adjusting posture ?
-Controlled and driven by the brainstem (where the postural set is governed)
Describe the entire posture control mechanism, especially for both unexpected and expected movement.
Central command –> Limb Movement –> Postural Instability –> Postural Adjustment (FEEDBACK for unanticipated postural instability)
Central command –> Postural Adjustment (FEEDFORWARD for anticipated postural instability)
Explain how the terms postural set and compensation relate to posture.
Posture is adjusted predominantly by involuntary movement driven both predictively (postural set) and reactively (compensation).
Where is sensory information for posture control integrated from ?
- Muscle proprioceptors (detect changes in muscle length and or tension)
- Vestibular apparatus (Detect movements of the head relative to the Earths gravitational field, and give sense of balance)
- Visual inputs (detecting movements in visual field representing movement of the body)
Where is the sensory information for posture control integrated in ?
Brainstem
What are the important parts of the brainstem in the processing of information for posture control ?
- Reticular nuclei
* Vestibular nuclei (cranial nuclei for the vestibular nerve)
What are the principal effects of the Lateral vestibulospinal tract ?
- Facilitate extensor motor neurons and inhibit flexor motor neurones innervating the ipsilateral medial and axial muscles.
- Activates alpha and Gamma MNs which causes enhanced muscle spindle mediated stretch reflexes
- Overall effect is to increase the tone to the antigravity muscles
