Motor Behavior

Control

I.  Overview

Motor Behavior – Study of the  psychological and physiological processes that affect motor performance

   Motor Control

   Motor Learning

   Motor Development

   

II.  Motor Control - Neurobiology

A.  Central Nervous System:  Brain and spinal cord

1.  Motor neurons – efferent (away from CNS)

2.  Sensory neurons – afferent (toward CNS)

3.  Association neurons – connectors/integrators

 

 B.  Cerebrum

1.  About 80% of the brain, right and left sides connected by corpus callosum, divided into five lobes

Frontal lobe – contains the motor cortex

Parietal lobe – contains the sensory cortex

Temporal lobe – contains auditory centers

Occipital lobe – contains vision centers

Insula – memory and integration center

2.  Cerebral cortex – outer layer (~3mm) of the cerebrum

 

C.  Motor Cortex

1.  Mapping of areas – “homunculus”

Initially done on anesthetized dog

Later experiments done on humans during brain surgery with local anesthesia (Penfield and Rasmussen, 1950)

2.  Parts of body needing fine motor control (hands, tongue) occupy greater brain area

 

D.  Basal Ganglia

1.  Basal Ganglia – a group of neural centers located deep in the cerebrum

   Help control voluntary movements

Movement organization

Scale and amplitude of movement

Perceptual-motor integration

2.  Destruction of the connection between the substantia nigra and the caudate nucleus causes Parkinson’s disease

Insufficient dopamine production

Resting tremor, difficulty initiating voluntary movements

 

E.  Cerebellum

1.  Part of the “hindbrain” – well developed in non-mammalian species

2.  Second largest structure of brain (to cerebrum), contains ~30 billion neurons

3.  Receives input from proprioceptors (joint, tendon, and muscle sensory neurons)

4.  Coordinates with basal ganglia and motor cortex to coordinate movement

5.  Damage results in ataxia, characterized by erorrs in speed, force, and direction of movement

 

F.  Peripheral Nervous System

1.  Neurons outside the CNS

Motor neurons that innervate muscles

Sensory neurons that carry messages from muscles and tendons (stretch sensors, pain sensors etc.)

2.  Example:  Knee-jerk reflex

   Patellar tendon is stretched

   Detected by sensory neuron

   Communicates with motor neuron (in spinal cord)

   Quadruceps muscles contract

 

III.  Motor Control Theories

A.  Open vs. Closed Loop Movement Control

1.  Closed-loop control:  sensory feedback information is used ‘on the fly’ to control movements

Advantages:  Good for novel situations, good for accuracy, flexibility

Disadvantages:  Slows down movement

2.  Open-loop control:  movements are pre-programmed

Advantages:  Good for speed

Disadvantages:  Less flexible, potentially less accurate

 

B.  Speed-Accuracy trade-off

As the speed of a movement increases, the accuracy decreases

 

C.  Fitt’s Law or Index of Difficulty

The larger the target or the closer the target, the easier the task (think of throwing darts)