Actions and Motor Control Flashcards
What is the process during an action?
Hundreds of muscle fibres must contract in a correct sequence and the correct amount of force
What does understanding motor control help with?
Can lead to improvements in treatment of people affected by movement disorders, can lead to improvements in human/object interfaces
What are the ways we study motor control?
Behavioural, muscle physiology, single unit electrophysiology, neuroimaging
How do we behaviourally study motor control?
Using video or electronic recording equipment to record the position of body parts in space and time.
What can behavioural methods measure?
Speed, accuracy and kinematics
What are the strengths of behavioural methods of studying motor control?
Allows us to systematically investigate the output of the action system
What are the limitations of behavioural methods of studying motor control?
Not a direct measurement of brain activity
What does muscle physiology record?
Records the activity of individual muscles or muscle fibers during action
What are the strengths of muscle physiology?
Allows an understanding of how muscles operate
What are the limitations of muscle physiology?
Not a direct measurement of brain activity
What do they do in single unit electrophysiology?
They implant electrodes in the brain and record activity of individual neurones
What does single unit electrophysiology record?
A number of neurones and measure their activity in real time
What are the strengths of single unit electrophysiology?
Allows for excellent spatial and temporal resolution at the level of a single neurone
What are the limitations of a single unit electrophysiology?
Cannot examine more than a miniscule percentage of the neurone at any one time
What neuroimagery is used in motor control?
fMRI and EEG
What are the strengths of neuroimaging?
Allows for a direct measure of activity in the human brain
What are the limitations of neuroimaging?
Recording equipment can restrict movement. Can be hard to localise processing in space or time.
How do muscles attach to the skeleton?
At the origin and insertion
What are muscles?
A collection of multiple muscle fibers
What do muscle spindles and Golgi tendon organs provide in muscles?
Proprioceptive information from the muscle
How are muscle spindles and la axons specialised?
For detection of changes of muscle length
How are muscles organised?
Antagonistic pairs with extensors extending the join and flexors contracting the joint
What causes muscle contraction?
Motor neurones release neurotransmitters at the neuromuscular junction
What is the process at the neuromuscular junction?
Acetylcholine binds to the ionotropic receptors causing depolarisation.
Voltage gated ion channels open.
Rapid depolarisation allows an in-flow of calcium.
Calcium inside causes actin and myosin proteins to interact.
Acetylcholinesterase removed the neurotransmitter to end the contraction.
What are the three components of motor behaviour?
Motor control, motor learning, motor development
What is motor control?
An area of study stressing primarily the principles of human skilled movements generated at the behavioural level of analysis
What is motor learning?
A set of internal processes associated with practice or experience leading to permanent changes in the capability of motor skill
What is motor development?
A field of study concerning the changes in motor behaviour occurring as a result of growth, maturation and experience
What is the hierarchy of motor control system?
Non-primary motor cortex, primary motor cortex, brainstem, spinal cord, the muscle of the body
What does the non-primary motor cortex do?
It is an additional source of motor commands
What does the primary motor cortex do?
Initiates the motor commands
What does the brainstem do?
Integrate motor commands from higher levels of the brain and transmits them to the spinal cord
What does the spinal cord do?
Crucial for controlling body movement, transfers input to motor neurones, locomotion, central pattern generator
What is the central pattern generator?
Neural circuitry responsible for generating rhythmic pattern of behaviour such as walking
What are reflexes?
Simple automatic movements coordinated by the spinal cord
What do proprioceptors do in reflexes?
Detect a stretch and trigger a motor response to counteract the stretch
What do cranial motor nuclei of the brainstem do?
Send axons directly to innervate muscles of the head and neck
What is the pathway from brain to control movement?
The brain–>spinal cord–> to control muscles
What is the pyramidal system?
How neuronal cell bodies i the cerebral cortex and their axons that pass through the brainstem to form the pyramidal tract of the spinal cord
What occurs in the medulla in the pyramidal system?
Decussation the pyramidal tract from the right hemisphere crossing the midline to innervate the left spinal cord and vice versa
What does motor output come from?
The motor cortex (primary and non-primary motor cortices)
How does motor output project for movement?
Projects through pyramidal tract to the spinal cord where it synapses with peripheral motor neurones
What is the other pathway for control of movement?
Extrapyramidal system
What occurs the extrapyramidal system when controlling movement?
The other pathways run parallel from cortex, basal ganglia and cerebellum via the brainstem and spinal cord. They run outside the pyramidal tract.
What are the motor control systems in the cortex?
Primary motor cortex, premotor cortex, supplementary motor cortex
What is the source of pyramidal tract neurones?
Primary motor cortex
What does the primary motor cortex do?
Planning, control and execution of voluntary movements
What does the premotor cortex do?
Important in motor coordination
What do lesions in the premotor cortex do?
Impairments in stability of stance, gait and hand coordination
What does supplementary motor cortex do?
Conception and initiation of movement
What do lesions in the supplementary motor cortex do?
Deficits in voluntary movement or speech
Where is the primary motor cortex?
In the frontal lobe and anterior to the central sulcus
What does TMS do?
Temporarily disrupts brain activity in healthy humans using a magnetic coil. Causes temporary virtual lesions and the effects can last from msec to miute
What do areas with more motor control look like in homunculus?
They look larger
What are the controversies with the primary motor cortex?
It can be debated whether muscles or movements are represented in M1, newer research with longer stimulation suggests that the map can be more complex than homunculus, longer stimulus evokes complete movements
What is mirror neurones?
Neurones that are active when performing an action or when observing another individual perform a similar action
What is the basal ganglia?
A group of subcortical forebrain nuclei
What is the 2 structures of the basal ganglia?
Striatum and globus palludus
What is the components of the striatum?
Caudate nuclei and putamen
What does the basal ganglia do in motor control system?
Modulate patterns of motor activity
What does the cerebellum do in motor control system?
Control neural programs fro the execution of skilled movements and motor learning
Where does the basal ganglia project to?
Areas involved in motor control, cognition and judgement
What matter structure are in basal ganglia?
Grey matter structure deep in white matter
What does the basal ganglia initiate and maintain?
Activity in the cortex
What other areas are functionally connected to the basal ganglia?
The subthalamic nucleus and substantia nigra
What is a disease of the basal ganglia?
Parkinson’s disease
What are the symptoms of Parkinson’s disease?
Resting tremors in limbs, muscle rigidity, akinesia, stooped posture, shuffling gait, excessive sweating
What is Parkinson’s disease caused by?
Progressive destruction of the dopaminergic neurones of the substantia nigra
What is the cerebellum important for?
Motor coordination and fine tuned motor control
What does injury to the cerebellum do?
Results in impairments to the coordination, accuracy and timing of movement
What does the cerebellum send to the brain and spinal cord?
Excitatory connections
What does the cerebellum combine?
Sensory and motor information to predict where an object will be at some future point in time
Where does forward modelling occur?
In the cerebellum
What is forward modelling?
When you are trying to touch a moving object and you will miss an object if you steer your hand to its current location
What is a closed loop system?
A system that is trying to maximise accuracy
Where else does the cerebellum send projections to and what does it influence?
Frontal lobe
Influences cognition, emotion, motivation and judgement
What can EEGs measure?
A readiness potential
What is the Libet task procedure?
PPs asked to take note of the time of a clock when they decided to press a button
What were the findings from the Libet task?
The intent to move occurred 200msec before the movement but the readiness potential rises earlier
What occurs during muscle contraction?
- Ca2+ binds to troponin
- Tropomyosin shifts position and myosin binding sites on the actin are exposed
- Myosin head bind actin
- Myosin heads pivot
- ATP binds to each myosin head and disengages from actin
What is the somatic motor system?
How the smooth muscle lines the digestive tract, arteries and innervated by nerve fibres from the ANS
What are the 3 musculatures in the somatic motor system?
Axial, proximal and distal
What does the axial musculature do?
Maintains posture
What does the proximal musculature do?
Locomotion
What does the distal musculature do?
Manipulation of objects through the hands
How will the central nervous system control muscle contraction?
By varying the firing rate of the motor neurones and recruiting additioning synergistic motor units
What are the types of motor units?
Slow fibers, fast fibers
What are the two subtypes of fast fibres?
Fast fatigable and fatigue resistant
What are the characterisitcs of slow fibres?
Darker, more mitochondria, enzymes specialised for oxidative energy metabolism, slow to contract, sustains contraction for long periods of time without fatigue
What are characteristics of fast fibres?
Pale, less mitochondria, anaerobic metabolism, contracts fast and powerfully, fatigues more,
What are characteristics of fast fatigable fibres?
Strongests and fastest contraction, quick exhaustion when stimulated at high frequency
What are characteristics of fatigue resistant fibres?
Moderately strong and fast contractions, resistant to fatigue
What are muscle fibres enclosed by?
The sarcolemma
What are myofibrils?
Structures in the muscle fibre that contract in response to the action potential going down the sarcolemma
What are the two different pathways for how the brain communicates with the motor neurones of the spinal cord?
The lateral column of the spinal cord and the ventromedial column
What is the lateral column of the spinal cord involved in?
The voluntary movement of the distal musculature
What is the ventromedial column of the spinal cord involved in?
Control of posture and locomotion
