Brain control of Movement - Motor control Flashcards
Voluntary movement uses a functional hierarchy with 3 levels, what are these 3 levels?
What is the function of the high level of the functional hierarchy of voluntary movements?
strategy
What is the function of the middle level of the functional hierarchy of voluntary movements?
tactics
What is the function of the low level of the functional hierarchy of voluntary movements?
execution
What structures are involved in the high level of the functional hierarchy of voluntary movements?
Association neocortex
Basal ganglion
What structures are involved in the middle level of the functional hierarchy of voluntary movements?
Motor cortex
Cerebellum
What structures are involved in the low level of the functional hierarchy of voluntary movements?
Brain stem
Spinal cord
What does strategy mean in terms of voluntary movements?
The goal and the movement strategy to best achieve this goal
What does tactics mean in terms of voluntary movement?
The sequence of spatiotemporal muscle contractions to achieve a goal smoothly and accurately
What does exectution mean in terms of voluntary movements?
Activation of motor neuron and interneuron pools to generate goal-directed movement
How is the brain connected to the spinal cord?
Lateral pathways
Ventromedial pathways
What do lateral pathways of the spinal cord control?
Voluntary movements of distal muscles – direct cortical control
what are the four ventromedial pathways?
tectospinal tract
vestibulospinal tract
pontine spinal tract
medullary reticulospinal tract
what are the two lateral pathways?
corticospinal tract
rubrospinal tract
Lateral pathways of the spinal cord are under the control of what?
Direct cortical control
What do ventromedial pathways control?
Posture and locomotion
Ventromedial pathways of the spinal cord are under control by what?
brain stem control
What is the longest and largest tract of the spinal cord?
Corticospinal tract (CST), with about 1 million axons
Where does the corticospinal tract originate?
2/3 in areas 4 and 6 of the fontal motor cortex
Rest is somatosensory
Does the corticospinal tract decusscate? And if so, where does this occur?
Yes it does, at the medulla/spinal cord junction so the right motor cortex controls the left side and vice versa
Where do axons of the corticospinal tract synapse?
Ventral horn motor neurons and interneurons to control muscles voluntarily
Where does the rubrospinal tract originate?
Red nucleus of midbrain and receives inputs from same cortical areas as CSF (2/3 if areas 4 and 6 of frontal motor cortex, rest is somatosensory)
What do lesions of the corticospinal and rubrospinal tracts cause?
Fine movement of arms and hands lost
Cannot move shoulders, elbows, wrist and fingers independently
What happens if lesions only occur in the corticospinal tract and not both the corticospinal and rubrospinal tract?
Deficits are seen for a few months, then functions reappear as they are taken over by the rubrospinal tract
For the rubrospinal tract, what side of the brain controls what side of the body?
Decussates above between medulla and midbrain so controls contralateral half of body
What does strategy mean in terms of voluntary movements?
The goal and the movement strategy to best achieve this goal
What does tactics mean in terms of voluntary movement?
The sequence of spatiotemporal muscle contractions to achieve a goal smoothly and accurately
What does exectution mean in terms of voluntary movements?
Activation of motor neuron and interneuron pools to generate goal-directed movement
How is the brain connected to the spinal cord?
Lateral pathways
Ventromedial pathways
What do lateral pathways of the spinal cord control?
Voluntary movement of distal muscles
Lateral pathways of the spinal cord are under the control of what?
Direct cortical control
Ventromedial pathways of the spinal cord are under control by what?
Brain stem control
What do ventromedial pathways control?
Posture and locomotion
What are examples of lateral pathways?
Corticospinal tract
Rubrospinal tract
What are examples of vestromedial pathways?
Vestibulospinal tract
Tectospinal tract
Pontine reticulospinal tract
Medullary reticulospinal tract
What is the longest and largest tract of the spinal cord?
Corticospinal tract (CST), with about 1 million axons
Where does the corticospinal tract originate?
2/3 in areas 4 and 6 of the fontal motor cortex
Rest is somatosensory
Does the corticospinal tract decusscate? And if so, where does this occur?
Yes it does, at the medulla/spinal cord junction so the right motor cortex controls the left side and vice versa
Where do axons of the corticospinal tract synapse?
Ventral horn motor neurons and interneurons to control muscles voluntarily
Where does the rubrospinal tract originate?
Red nucleus of midbrain and receives inputs from same cortical areas as CSF (2/3 if areas 4 and 6 of frontal motor cortex, rest is somatosensory)
What do lesions of the corticospinal and rubrospinal tracts cause?
Fine movement of arms and hands lost
Cannot move shoulders, elbows, wrist and fingers independently
What happens if lesions only occur in the corticospinal tract and not both the corticospinal and rubrospinal tract?
Deficits are seen for a few months, then functions reappear as they are taken over by the rubrospinal tract
For the rubrospinal tract, what side of the brain controls what side of the body?
Decussates above between medulla and midbrain so controls contralateral half of body
What does the corticospinal tract control in the spinal cord?
Pools of motor neurons (monosynaptically excite pool of agonist motoneurons whilst via interneurons inhibit pools of antagonist motoneurons)
What projects via the corticospinal tract to pools of motoneurons in the spinal cord?
Large pyramidal neurons in motor cortex
What is the function of the vestibulospinal tract?
Stabilises head and neck
What is the function of the tectospinal tract?
Ensures eye reamins stable as the body moves
What does TST stand for?
Tectospinal tract
Where do the poutine and medullary reticulospinal tracts originate?
Brainstem
What are the functions of the poutine and medullary reticulospinal tracts?
Use sensory information about balance, body position and vision
Reflexly maintain balance and body position
Innervate trunk and antigravity muscles in limbs
What pathways does voluntary movement require input from?
Motor cortex via lateral pathways
What nuclei is found between the motor cortex and the spinal cord for vestromedial pathways?
Reticular nuclei
Superior colliculus and vestibular nuclei
What areas of the brain plana nd control precise voluntary movements?
Primary motor cortex and pre-motor areas
What do upper motor neurons target to form?
Lower motor neurons in the spinal cord to form circuits, some of which control reflexes such as stretch reflex
Where are upper motor neurons found?
Cortex
Brainstem
What can the distribution of lower motor neurons be described as?
Somatotopic
What does somatotopic mean?
Point-for-point correspondence of an area of the body to a specific point on the CNS
What do medial lower motor neurons control?
Axial and proximal muscles
What do lateral lower motor neurons control?
Distal limb muscles
What do white matter tracts differ in?
Origin and function
What do medial tracts from the brainstem down the spinal cord control?
Posture and balance and orienting mechanism
What do lateral tracts from the brainstem down the spinal cord control?
Skilled voluntary movement
Where are the upper motor neurons that are the beginning of lateral white matter of spinal cord?
cerebral cortex of contralateral si
Where are upper motor neurons that are the origin of anterior-medial white matter of spinal cord?
Brainstem
What Brodmann area is the primary motor cortex?
Area 4
Where is the primary motor cortex (what gyrus)?
Precentral gyrus
What does PMA stand for?
Pre-motor area
What does SMA stand for?
Supplementary motor area
What broddman area is the premotor and supplementary motor areas?
Areas 6
For movement, what does the cerebral cortex need to know?
Where the body is in space
Where it wants to go
Plan to get there
(these 3 things are functions of different areas of the cortex)
What are some examples of areas of the brain involved in planning and instructing voluntary movement?
Prefrontal cortex
Area 6 (SMA and PMA)
Area 4 (M1) Central sulvus
S1
Posterior parietal cortex (area 5 and area 7)
what does M1 stand for?
motot cortex
From medial to lateral, what body parts are arranged in the somatotopic organisation of the primary motor cortex?
Toes > legs up to shoulder > shoulder to fingers (little to thumb) > top of head to bottom of head > tongue then swallowing
What is an example of a physical display of the presents of somatotopic maps?
Epileptic seizures often ‘march’ across the body, beginning with abnormal fingers movements then hand, then arm, shoulder, finally face
What is used in epileptics to decide which brain areas to be spared surgically?
Penfield electrical stimulation
What does the SMA do?
Innervates distal motor units directly
What does the PMA do?
Connects with reticulospinal neurons innervating proximal motor neurons
how is penfeild electrical simulation carried out in epileptics?
Weak stimulation of area 4 caused twitch of specific contralateral muscles
Systematic probing of area 4 (primary motor cortex) revealed somatotopic organisation of precentral gyrus ……… like that in somatosensory areas of post-central gyrus.
Area 6 neurones drive complex movements on either side of the body
Explain the process of originating and coordinating body movements?
1) Mental image of body in space is generated by somatosensory, proprioceptive and visual inputs to posterior parietal cortex (areas 5 and 7)
2) Prefrontal and parietal cortex is where decisions are taken (such as which actions/movements to take and their likely outcome)
3) Axons from both converge on area 6, where signals encoding desirected actions are converted into how to carry this out
What Broddman areas are associated with the posterior parietal cortex?
Areas 5 and 7
For movement, do the neurons in are 6 or area 4 fire first?
Area 6 fire before area 4, because area 4 is for “doing it” by activating neurons of the CST and RST
Explain the process of neurons in the PMA (area 6) firing before movement?
1) Getting ready, few action potentials from PMA neurons
2) Get set, big increase in PMA action potentials
3) Go, PMA firing continues through actions, neurons in premotor area (PMA) fire action potentials one second before a movement occurs
How long is between the premotor area (PMA) firing an action potentials and a movement occuring?
1 second
What tells us that movement plans are rehearsed mentally?
Specific neurons in area 6 fire when movement is made and when movement is imagined
are somatotopic motor maps precise?
no
It does not represent upper motor neurones causing individual muscle movements
Microstimulate arm region of primary motor cortex (area 4) see movements that bring hands to mouth, or into central space:
To inspect, manipulate, or defend.
Functional maps in cortex appear to map movements – perhaps (in area 6) even the intention of a complete movement
Mental image of body in space - generated by somatosensory, proprioceptive & visual inputs to posterior parietal cortex (areas 5 and 7).
Prefrontal and parietal cortex - where decisions are taken -
which actions/movements to take and likely outcome
Axons from both converge on area 6. Here signals encoding
desired actions are converted into how to carry this out.
During practised voluntary finger movements, PET imaging shows blood flow increases in somatosensory, posterior parietal areas and prefrontal cortex (I.e. area 6 & area 4, so - all of the above).
BUT…….
if you only think about moving : only area 6 is active, area 4 is not: area 4 is for “doing it” (by activating CST and RST neurones).
(a) Get ready - in front of lights – just a few action potentials in premotor area (PMA) neurones.
(b) Get set – monkey shown “instruction stimulus” - the movement needed for a reward, so already planning it. Big increase in PMA action potential firing.
(c) Go - make the movement now, touch the trigger stimulus button. PMA firing continues through action.
PMA neurones fire action potentials one second before a movement occurs.
= decision making neurones in command centres.
Specific neurones in area 6 fire when movement is made or is imagined – rehearsed mentally
Also fire when others make the same movement: (this allows understanding of the actions or intentions of others) = ‘mirroring’
Perhaps same motor circuits plan our movements and allow us to understand the actions/goals of others
Perhaps mirror neurones underpin understanding of emotions and empathy – & may be wired/function differently in autism?
