Motor System

http://www.rci.rutgers.edu/~aglass/M&ASyllabus.htm

Question How do you teach a one-armed

man to clap?

Two Kinds Motor Movements Reflexes Voluntary Motor Movements

(Actions)

Two Kinds Motor Movements Reflexes

Simplest reflex arc involves sensory neuron and motor neuron which causes muscle contraction

Voluntary Motor Movements (Actions)

Reflex Arc

Two Kinds Motor Movements Reflexes

Reflex arc Other reflexes may involve

complicated movements generated by central pattern generators in spinal cord.

Hormonal response May become conditioned to novel inputs.

Voluntary Motor Movements (Actions)

Involuntary movement: may be a single ballistic movement(eye blink) or a motor sequence if a central pattern

generatorin the spinal cord is activated (infant swim reflex)

Unconditionedinnate fast responseto unconditioned

stimulus

Conditionedinnate fast responseto (novel) stimulusroutinely preceding

unconditionedStimulus

(Rescorla-Wagnermodel)

Reflexes

Avoid

eye blink

Maintain

vestibular-ocular

pupil dilation

musclecontractionspindles,tendons,

joints, skin

Approach

ear pricking

salivate

None

goosebumps

Functions of Unconditioned Reflexes

Two Kinds Motor Movements Reflexes Voluntary Motor Movements

(Actions)

Voluntary Movements Require

Perception of target Awareness of location of movable

body part Ability to aim movement of body part Ability to detect errors and re-adjust,

(use feedback) Ability to use feedback to control

movement of body part

Motor System for Voluntary Movements (Actions) When a familiar voluntary action is

performed: Planning: a representation of a body-part

posture or sequence of postures is retrieved Cortical areas

Parietal cortex Premotor and supplementary motor cortex

Performance: muscle movements are initiated to move the body-part(s) into the represented posture(s)

Cortical Motor System

Planning An Action Parietal cortex

Neurons respond to both visual and tactual inputs

Input used in activating and selecting among plans

Premotor and supplementary motor cortex Activation and selection of plans Mirror neurons respond when the same

action is performed or observed

Planning A GraspFour steps in planning a grasping action. Representations of grasping hand postures are retrieved from memory (top panel). The hand posture providing the closest fit to the target is selected (second panel). Representations of arm extensions are retrieved from memory (third panel). The arm extension providing the best fit with the grasp posture and its location is selected (bottom panel).

Hierarchical Organization

Complex patterns of movements can be built up hierarchically by combining posture plans into a single motor program. Advantage of large program: speed.

Constructing A Motor Program (Povel & Collard, 1982)

0

1

2

3

4

5

6

1 2 3 4 5 6

Position in Sequence

Late

ncy

(mean r

ank)

imrrmimrrmii

Motor System for Voluntary Movements (Actions)

Planning Performance

Motor cortex and basal ganglia aim and initiate body movement

Cerebellum programs muscle movements

Cortical Motor System

Basal Ganglia

Motor & Somatosensory Maps

Damage: Motor and Somatosensory Cortex Damage to motor cortex (map)

causes hemiplegia, normal voluntary movement of body part corresponding to map damage is not possible.

If limb is severed a phantom limb results because the body map is unchanged.

Execution: Motor subsystems Locomotion

Motor cortex Manipulation

Motor cortex Vocalization

Broca’s area Visual Fixation and tracking

Frontal eye fields

Motor System for Voluntary Movements (Actions)

Planning Parietal cortex Premotor and supplementary motor

cortex Performance

Motor cortex and basal ganglia aim and initiate body movement

Cerebellum programs muscle movements

Cerebellum A motor program produces smooth

movements by specifying a precisely timed sequence of muscle contractions.

Vestibulocerebellum contains reflexes for maintaining balance and coordinating eye movements (vestibular-ocular reflex).

Spinocerebellum & neocerebellum turn motor plans into motor programs.

Motor system is heterarchical and redundant Redundant sources of plans

Premotor (external) Supplementary Motor (internal)

Redundant sources of limb information Visual Kinesthetic

Redundant ways of executing and controlling limb movements Motor cortex Basal Ganglia Cerebellum