Motor Control I Flashcards
a
central sulcus
b
primary somatosensory cortex
c
posterior parietal cortex
d
primary motor cortex
e
supplementary motor cortex
f
premotor cortex
g
prefrontal cortex
Motor Control is a functional hierarchy with how many levels?
3 levels
What are the 3 levels of motor control, their function and the strucutres involved?
High - Strategy - Association neocortex, basal ganglion
Middle - Tactics - Motor cortex, cerebellum
Low - Execution - Brain stem, spinal cord
How is the brain connected to the spinal cord?
lateral pathways
ventromedial pathways
What is the function of the lateral pathwyas and what controls it?
control voluntary movements of distal muscles
under direct cortical control
What is the function of the ventromedial pathway and what controls it?
control posture and locomotion
under brain stem control
What 2 tracts make up the lateral pathways?
Cortocospinal tract (CST)
rubrospinal tract (RST)
Where does the CST originate?
2/3 of CST originates in areas 4 and 6 of the frontal motor cortex – the rest is somatosensory
What happens at the medulla/spinal cord junction in the CST?
at medulla/spinal cord junction, the CST crosses over (decussates)
the right motor cortex controls the left side and the left motor cortex controls the right side
Where do CST axons synapse?
CST axons synapse on ventral horn motor neurones and interneurones to control muscles voluntarily
Where does the RST start and where does it recieve its inputs from?
starts in the red nucleus of midbrain and receives inputs from same cortical areas as the CST
What are the effects of lesions on CST and RST?
Lesion to CST and RST - fine movements of arms and hands are lost. Can’t move shoulders, elbows, wrist and fingers independently
Lesion to CST alone – same deficits seen, but after a few months functions reappear as functions been taken over by RST - but if you then get a lesion on RST – lose restored functions
What are the two lateral pathways that control voluntary movements?
CST and RST
How do corticospinal tract axons control pools of spinal motor neurons?
They monosynaptically excite pools of agonist motoneurones
The same pyramidal neurones branch and via interneurons inhibit pools of antagonist motoneurones
Large pyramidal neurones in _________ project via CST
motor cortex
What are the two ventromedial pathways control posture and locomotion?
Vestibulospinal and Tectospinal tracts
WHat is the function of the vestibulospinal tracts (VST)?
VST stabilizes head and neck
left pathway
What is the function of the tectospinal tracts?
TST ensures eyes remain stable as body moves
right pathway
Where do the vetromedial pathways originate?
in the brain stem
What information does the vetromedial pathways use?
Use sensory information about balance, body position and vision
How are voluntary movements carried out?
voluntary movements such as throwing require inputs from motor cortex via lateral pathways
Can the motor cortex activate spinal motorneurons directly?
yes
Can the motor cortex stop reflexes?
motor cortex can also free spinal neurones from reflex control - by interactions with the nuclei of the ventromedial pathways
What pathway reflexly maintains balance and body position?
ventromedial pathways
What is used to plan and control precise voluntary movements?
Primary motor cortex and pre-motor areas
What are the targets of upper motor neurons?
Upper motor neurons in cortex and brainstem target lower motor neurons in the spinal cord. Some form circuits that control reflexes such as the stretch reflex and withdrawal reflex
Lower motor neurone distribution is somatotopic - what does this mean?
Somatotopy is the point-for-point correspondence of an area of the body to a specific point on the central nervous system. Typically, the area of the body corresponds to a point on the primary somatosensory cortex
What is the difference between medial and laterla LMN in what they control?
Medial ones control axial and proximal limb muscles, lateral ones innervate distal limb muscles
What do medial tracts form the brainstem control and what do the lateral tracts from the cortex control?
medial tracts from brainstem control posture balance and orienting mechanisms
lateral tracts from cortex control precise skilled voluntary movements
Study this picture showing the origins, destinations and functions of upper and lower motor neurones
Where are the human primary motor cortex and premotor areas?
The primary motor cortex (area 4 or M1) is in the precentral gyrus
premotor and supplementary motor areas (PMA, SMA - area 6)
Planning oof movement is done by the cerebral cortex, what do we need to know in order to make movement?
- where the body is in space
- where it wants to go
- and select a plan to get there
This image shows the somatotopic organisation in primary motor cortex (M1 : area 4)
Are the homunculus similar in motor and sensory cortex?
yes
What would weak stimulation of specific areas of area 4 cause?
twitch of specific contralateral muscles
Does the precentral gyrus also have somatotopic organisation?
primary motor cortex revealed somatotopic organisation of precentral gyrus like that in somatosensory areas of post central gyrus
What does area 6 of the cortex do and how is it organised?
Area 6 neurones drive complex movements on either side of the body
They are also somatotopically organised
How many motor maps does area 6 have?
2
one is in the premotor area - PMA and one is in the supplementary motor area - SMA
What is the function ofthe SMA and PMA?
SMA innervates distal motor units directly
PMA connects with reticulospinal neurones innervating proximal motor units
An image showing the areas of cortex involved in planning and instructing voluntary movement
Is the somatotopic motor map is precise?
No
it does not represent upper motor neurones causing individual muscle movements
What do functional maps in the cortex map?
functional maps in cortex appear to map movements - perhaps (in area 6) even the intention of a complete movement
Purposeful movements of contralateral arm and hand during microstimulation - example
Microstimulation in specific area of primary motor cortex (area 4) elicits:
(A) coordinated movements of hand and mouth or
(B) movements that bring hands into central space to inspect/manipulate objects
(Blue crosses show start, lines are the movement, red dots the end point)
What is used to create a mental image of the bosy in space?
mental image of body in space is generated by somatosensory, proprioceptive and visual inputs to posterior parietal cortex (areas 5 and 7).
Where are decisions taken?
prefrontal and parietal cortex is where decisions are taken - which actions/movements to take and their likely outcome
What does area 6 do?
signals encoding desired actions are converted into how to carry this out
What areas of your brain do you use when thinking about a movement, not carrying it out?
if you only think about movements: area 6 is active, area 4 is not
area 4 is for “doing it”- by activating neurones of the CST and RST
What does the PMA do before an action is carried out
Thinks about how it is done
Neurones in the premotor area (PMA) fire action potentials one second before a movement occurs
They are decision making neurones in command centres
What are PMA mirrior neurones?
PMA “mirror neurones” fire when self or others perform specific actions
specific neurones in area 6 fire when movement is made and when movement is imagined – rehearsed mentally
they also fire when others make the same specific movement: this allows understanding of the actions or intentions of others
perhaps the same motor circuits plan our movements and allow us to understand the actions/goals of others
