Motor Control - 2 Flashcards
What are the structures involved in the high level of motor control?
Association neocortex and basal ganglion
What the structures involved in the middle level of motor control?
Motor cortex and cerebellum
What are the structures involved in low level of motor control?
Brain stem and spinal cord
What is the function of the high level of motor control?
Strategy - goal and movement strategy to best achieve this goal
What is the function of the middle level of motor control?
Tactics - sequence of spatiotemporal muscle contractions to achieve a goal smoothly
What is the function of the lower level of motor control?
Execution - activation of motor neuron and interneuron pools to generate goal directed movement
What do lateral pathways control?
Voluntary movements of distal muscles - direct cortical control
Includes the corticospinal and rubrospinal tracts
What do the ventromedial pathways control?
Posture and locomotion - brain stem control
Includes tectospinal, vestibulospinal, pontine and medullary reticulospinal
Where does the CST cross over?
Decussates at medulla/ spinal cord junction so right motor cortex controls left side and left motor cortex controls right side
Where does the corticospinal tract originate?
Longest tract
2/3 originates in areas 4 and 6 in frontal motor cortex and 1/3 is somatosensory
Where do CST axons synapse?
On ventral horn motor neurons and interneurons to control muscles voluntarily
Where does the RST start?
Is smaller and starts in red nucleus of midbrain and receives input from same cortical areas as CST
What happens if there is a lesion to CST and RST?
Fine movements of arms and hands are lost. Cant move shoulders, elbows, wrist and fingers
If CST alone - same deficits but reappear few months later
Describe CST axons controlling pools of spinal motor neurons
Large pyramidal neurons in motor cortex project via CST
Mono-synaptically excite pools of agonist motoneurons
Same pyramidal neurons branch and excite inhibitory interneurons - inhibit pool of antagonist motoneurons
What is the function of the vestibulospinal and tectospinal tracts?
VST - stabilise head and neck
TST - ensures eyes remain stable with the body
Where do pontine and medullary reticulospinal tracts originate?
In brain stem
Describe pontine and medullary reticulospinal tracts
Use sensory info about balance, body position and vision
Reflexly maintain balance and body position
Innervate trunk and antigravity in limbs
What can the motor cortex activate?
Spinal motoneurons directly
Also free spinal neurons from spinal reflexes by interactions with nuclei of ventromedial pathways
Describe upper motor neurons
In cortex and brainstem - innervate lower motor neurons in the spinal cord
LMN distribution is somatotopic
What do medial and lateral motor neurons control?
Medial -Axial and proximal limb muscles
Lateral - distal limb muscles
What are the origin and function of medial and lateral descending tracts?
Medial - from brainstem control pressure, balance, and orienting mechanisms
Lateral - from cortex control precise skilled voluntary movements
Where is the primary motor cortex and supplementary motor areas?
Area 4 is in the precentral gyrus
Area 6 - PMA and SMA lies rostrally
What is needed to plan movement by cerebral cortex?
Where body is in space
Where it wants to go
Devise a plan to get there
Describe the somatotopic map of motor cortex
Area 4 has somatotopic organisation of precentral gyrus
Area 6 neurons drive complex movements on either side of body
Area 6 has 2 maps - premotor areas and supplementary motor area
What does SMA innervate?
Supplementary motor area innervates distal motor units directly
What does PMA connect?
Premotor area connects reticulospinal neurons innervating proximal motor units
Why is the somatotopic map not precise?
Does not represent upper motor neurons causing individual muscle movements
Functional maps in cortex appear to map movements
What generates the mental image of body in space?
By somatosensory, proprioceptive and visual inputs to posterior parietal cortex - area 5 and 7
What is the function of the prefrontal and parietal cortex?
Where decisions are taken
Which actions/ movements to take and likely outcome
Where do axons o prefrontal and parietal cortex converge?
On area 6
Signals encoding actions are converted into how to carry this out
Describe decision making neurons in cortical PMA (area 6)
Big increase in PMA APs when there is instruction stimulus and these keep firing through action
PMA neurons fire APs one second before a movement occurs
When do specific neurons in area 6 fire?
When movement is made or imagined - rehearsed mentally
Or when others make the same movement
