Motor System

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 generator in the spinal cord is activated (infant swim reflex) Unconditioned innate fast response to unconditioned stimulus Conditioned innate fast response to (novel) stimulus routinely preceding unconditioned Stimulus (Rescorla-Wagner model) Reflexes

Avoid eye blink Maintain vestibular- ocular pupil dilation muscle contraction spindles, tendons, joints, skin Approach ear pricking salivate None goose bumps 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 Grasp Four 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)

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