Motor Overview Flashcards
Define voluntary behaviour.
The physical manifestation of an individual’s intention to act on the environment, usually to achieve a goal immediately or at some point in the future.
Define sensorimotor transformation.
The brain transforms a goal into motor commands in order to realise that goal.
Give an example of sensorimotor transformation.
Taking a sip of coffee requires the brain to convert visual information about the coffee cup and somatic information about the current position and motion of your arm and hand into a pattern of muscle contractions that moves your hand to the cup, grasps it, and then lifts it to your mouth.
Name the three theoretical models for neural basis of voluntary behaviour/movement.
Traditional.
Dynamic causal model.
Optimal feedback control.
Describe the traditional model of voluntary behaviour/movement.
A linear process of perception to cognition to action. Uses representations of the external world to execute pre-planned sequences of movement. Any disruptions would result in failure in the execution.
Describe the dynamic causal model of voluntary behaviour/movement.
Uses the premise that the functional architecture of motor control circuits evolved to generate movements. Circuit adaptability allows for real-time adjustments but is most useful for repetitive movements.
Describe the optimal feedback control model of voluntary behaviour/movement.
Combines visual feedback with proprioceptive input to execute movement that achieves the goal. Uses real-time feedback to execute real-time adjustments.
What are the three key processes involved in the dynamic causal model of voluntary behaviour/movement?
State estimation.
Task selection.
Control policy.
Explain the process of state estimation.
Involves forward internal models that use efference copies of motor commands and external sensory feedback to provide the best estimate of the present state of the body and the environment.
Explain the process of task selection.
Involves the neural processes by which the brain chooses a behavioural goal in the current context and what motor action(s) might best attain that goal.
Explain the process of control policy.
Provides the set of rules and computations that establish how to generate the motor commands to attain the behavioural goal given the present state of the body and the environment.
Describe Brodmann’s area 6.
It is divided into 5 or 6 functional areas involved in different aspects of the planning and control of motor actions of different parts of the body.
Where are the arm-control regions in Brodmann’s area 6?
Dorsal premotor cortex (PMd) and predorsal premotor cortex (pre-PMd) in the caudal and rostral parts of the dorsal convexity of lateral area 6.
Where are the hand-control regions in Brodmann’s area 6?
Ventral premotor cortex (PMv) in the ventral convexity of area 6.
Where are the supplementary motor areas in Brodmann’s area 6?
Split into the supplementary motor area proper (SMA) which is caudal and the presupplementary motor area (pre-SMA) which is rostral.
Where is the primary motor cortex (M1) located?
Brodmann’s area 4.
Where is the primary somatosensory cortex (S-I) located?
Anterior postcentral gyrus.
What is the role of the S-I?
Processes cutaneous and muscle mechanoreceptor signals from the periphery and transmits that information to other parietal and precentral cortical regions.
What is the pyramidal tract?
A key descending pathway for voluntary control.
Where does the pyramidal tract originate?
In the cortical layer V in a number of precentral (M1, SMA, PMd, PMv and cingulate motor areas) and parietal areas.
Where do the axons of the pyramidal tract travel to?
Axons terminate in brainstem motor structures (corticobulbar tract).
Axons project down to the spinal cord (corticospinal tract).
What does CST stand for?
Corticospinal tract.
Describe the lateral CST.
Axons originate in one hemisphere and decussate at the pyramid in the caudal medulla. They then project to the spinal cord.
Describe the ventral CST.
A small portion of axons do not decussate.
In mammals, where do many CST axons terminate?
Terminate only on spinal interneurons and exert their influence on voluntary movement indirectly through spinal interneuronal and reflex pathways.
In monkeys, where do CST axons from postcentral and parietal areas terminate?
Interneurons in the dorsal horn.
What are corticomotoneuronal cells?
M1 neurons with direct monosynaptic projections to spinal motor neurons.
What is the role of the parietal lobe in sensory processing for motor action?
Receives somatosensory inputs about body posture and movement from S-I. Reciprocally interconnected with precentral cortical motor areas to provide the precentral cortex with signals for the sensory guidance of movement and to receive efference copies of motor commands from those same precentral areas.
What does electrical stimulation of the supplementary motor cortex (SMC) below the threshold for movement initiation lead to?
Evokes an introspective sense of an urge to move that does not arise during M1 stimulation.
What may be evidence that neural activity in the SMC is involved in forming the intention to move, not just in executing movement?
Recordings of slow cortical potentials at the surface of the skull during the execution of self-paced movements show that the initial potential arises in the frontal cortex as much as 0.8-1.0 secs before the onset of movement. (Readiness potential.)
