Motor cortex and motor control concepts

Primary motor cortex

Executes commands to motor neurons. Stimulation elicits simple movements of single joints. Organisation is somatotopic.

Pre-motor cortex

Planning of movement. Receives input from sensory areas for sensory guidance and spatial guidance of movement

Supplementary motor cortex

Sequencing of movement.Feeds correct motor instructions in correct sequence to the primary motor cortex.

Somatotopic organisation

- Areas of cortex correspond to areas of the body
- Densely innervated areas of body occupy large regions of cortex
- Left cortex represents right body and vice versa

Name the three classes of movement

Voluntary, reflexive and rhythmic

Voluntary movement

- Purposeful, goal-oriented movements that can be learnt and improved with practice. - Initiated at a cerebral cortex level.- Requires planning, programming and execution.
- E.g. complex actions: writing, speaking, preparing food

Reflexive movement

- Involuntary, rapid, stereotyped movements.
- Same response initiated by a stimulus each time in a health person
- E.g. Pupillary reflex of the oculomotor nerve

Rhythmic motor patterns

- Combination of voluntary and reflex responses
- Initiation and termination is voluntary; once initiated, movement is repetitive and reflexive.
- E.g. chewing, running

Central pattern generators (CPGs)

- Neuronal circuits that produce rhythmic motor patterns in the absence of sensory or descending inputs that carry specific timing information.
- E.g. Walking - involves alternating contraction/relaxation of flexors/extensors
- Initiated by the brainstem and modified by sensory input from PNS

Stepping pattern generators (SPGs)

Adaptable networks of spinal interneurons that activate lower motor neurons to elicit alternating flexion and extension of the lower limbs to AID walking.

Motor control

The ability to regulate or direct the mechanisms essential to movement. Relies heavily on sensory information from our external environment; proprioceptive, visual and vestibular information.

Name the three theories of motor control

Hierarchical model, Dynamic systems theory, Ecological model

Hierarchical model

- The CNS is organised in hierarchical levels such that the higher association areas are followed by the motor cortex, followed by the spinal levels of motor function.
- Limitations: can't explain reflexes in normal adults where lower levels dominate motor function e.g. stepping on something sharp

Dynamic systems theory

- Seeks to solve the 'degrees of freedom' problem.
- Degrees of freedom: There are multiple ways for humans to perform a movement in order to achieve the same goal: each joint can move in multiple planes of motion.
- Sees whole body as a mechanical system, with mass, subject to both external forces, such as gravity, and internal forces such as both inertial and movement-dependent forces

- Limitations: presumes the nervous system have a less important role than principles of body mechanics

Ecological model

Suggests motor control evolved to cope with the environment
- Limitations: less acknowledgement to structure/function of nervous system