CONTROL OF MUSCLE MOVEMENT

D. C. MIKULECKYDEPARTMENT OF PHYSIOLOGY

SPINAL CORDDORSAL HORN GREY

MATTER

DORSAL

VENTRALSPINAL NERVE

DORSALROOTGANGLION

VENTRALHORN

WHITEMATTER

LATERAL

SEGMENTAL STRUCTURE OF SPINAL NERVES

DERMATOMES

THE THALAMUS IN SOMATIC SENSATION

DORSAL COLUMN

MEDULLA

MEDIALLEMNISCUS

SENSORYNEOCORTEX

DORSAL COLUMNNUCLEI

SOMATOTOPIC ORGANIZATION OF THE SENSORY CORTEX

GENERAL FEATURES OF THE MOTOR SYSTEM

• HIERARCHICAL ORGANIZATION

• VS

• PARALLEL ORGANIZATION

HIERARCHICAL ORGANIZATION

MOTOR CORTEX

CEREBELLUM AND BASAL GANGLIA

BRAIN STEM

SPINAL CORD

SKELETAL MUSCLE

PARALLEL ORGANIZATIONMOTOR CORTEX

SKELETAL MUSCLE

BRAIN STEM

SPINAL CORD

THE MOTOR UNIT

• A SINGLE MOTOR NEURON AND ALL THE MUSCLES IT INNERVATES

• THE FUNCTIONAL UNIT OF THE MOTOR SYSTEM

• CORRESPONDS TO THE SENSORY UNIT/RECEPTIVE FIELD RELATIONSHIP

• SIZE OF MOTOR UNIT DETERMINES FINENESS OF MOTOR RESPOSE

SOMATOTOPIC ORGANIZATION OF THE MOTOR CORTEX

CORTICAL AREAS INVOVED IN MOTOR CONTROL

THE MOTOR RESPONSE SYSTEM: SPINAL LEVEL

• THE ORGANIZATION OF MOTOR NERVES IN THE SPINAL COLUMN

• THE ROLE OF INTERNEURONS• THE ROLE OF LOCOMOTOR

GENERATORS

THE ORGANIZATION OF MOTOR NERVES IN THE SPINAL COLUMN

• DORSAL AREA OF VENTRAL HORN: FLEXOR MOVEMENTS

• VENTRAL AREA OF VENTRAL HORN: EXTENSOR MOVEMENTS

• DORSOLATERAL AREA OF VENTRAL HORN: INNERVATE EXTREMITIES

• VENTROMEDIAL REGION: AXIAL MUSCLES TO MAINTAIN POSTURE

LOCATION OF CELL BODIES FOR EXTENSORS AND FLEXORS

FLEXORS

EXTENSORS

THE ROLE OF INTERNEURONS

• LOCATED IN THE INTER MEDIATE ZONE OF THE SPINAL CORD

• LATERAL SIDE NEURONS SYNAPSE IPSILATERALLY (TO DISTAL LIMB MUSCLES)

• MIDLINE NEURONS SYNAPSE BOTH SIDES (MUSCLES FOR POSTURE) ALPHA MOTOR NEURONS:EXCITE SYNERGISTIC AND INHIBIT ANTAGONISTIC

THE ROLE OF LOCOMOTOR GENERATORS

• RHYTHMIC ACTION OF ALTERANATING FLEXION AND EXTENSION INVOVED IN WALKING MOVEMENTS (CHICKEN WITH ITS HEAD CUT OFF)

• SPINAL TRANSECTED ANIMALS CAN WALK ON TREADMILL

• UNDER CONTROL OF LOCOMOTOR COMMAND CENTER IN THE BRAIN STEM

SENSORY FIBERS IN THE MUSCLE

• THE MUSCLE SPINDLE AS LENGTH DETECTOR

• GOGLI TENDON ORGANS: TENSION RECEPTORS

THE MUSCLE SPINDLE AS LENGTH DETECTOR(SENSORY FIBERS)

• TYPE Ia NERVE FIBERS: TRANSMIT INFORMATION ABOUT LENGTH AND VELOCITY TO THE CNS

• TYPE II NERVE FIBERS:TRANSMIT INFORMATION ABOUT MUSCLE LENGTH TO CNS

•

TWO TYPES OF INTRAFUSAL FIBERS

NUCLEARCHAIN FIBER

NUCLEARBAGFIBER

TYPE IISENSORYFIBER

TYPE IASENSORYFIBER

TWO TYPES OF MOTOR NEURON

• ALPHA MOTOR NEURON: INNERVATES EXTRAFUSAL FIBER

• GAMMA MOTOR NEURON: INNERVATES INTRAFUSAL FIBERS

STRETCHING AN INTRAFUSAL FIBER SENDS SIGNALS TO CNS

THE ROLE OF GAMMA MOTOR NEURONS IN REGULATING MUSCLE SPINDLE RESPONSE

RECORD

RECORD

STIMULATE

Afferent Activity

Muscle Force

THE ROLE OF GAMMA MOTOR NEURONS IN REGULATING MUSCLE SPINDLE RESPONSE

RECORD

RECORD

STIMULATE

Afferent Activity

Muscle Force

STIMULATE

GOGLI TENDON ORGANS: TENSION RECEPTORS

• IN SERIES WITH EXTRAFUSAL FIBERS

• TRANSMITS INFORMATION ABOUT FORCE OR TENSION TO CNS

• FREQUENCCY CODING

SPINAL REFLEXES

• THE STRETCH REFLEX

• THE INVERSE MYOTACTIC REFLEX

• THE FLEXOR WITHDRAWAL REFLEX

THE STRETCH REFLEX (KNEE JERK REFLEX)

• TAP PATELLAR TENDON BELOW KNEE

• SENSORY SIGNALS FROM MUSCLE SPINDLE INDICATE FLEXION OF LEG

• FLEXOR IS INHIBITED• EXTENSOR ACTIVATED• LEG EXTENDS

KNEE JERK REFLEX

SPINALCORD

SENSORY NEURON FROMMUSCLE SPINDLE DETECTSSTRETCH

FLEXOR INHIBITED

EXTENSORACTIVATED

INVERSE MYOTACTIC REFLEX

ARM EXTENDS

WEIGHTRELEASED

BICEPS & SYNERGYSTIC MUSCLERELAXEDEXTENSOR CONTRACTED

THE FLEXOR WITHDRAWAL REFLEX

• PAINFUL STIMULUS DETECTED• IPSILATERAL EXTENSORS INHIBITED• IPSILATERAL EXTENSORS EXCITED• LIMB IS WITHDRAWN• IF INVOLVING ONE FOOT WHILE

STANDING, CONTRALATERAL SIDE EXTENSORS ACTIVATED AND FLEXORS INHIBITED TO SUPPORT GREATER WEIGHT

FLEXOR WITHDRAWAL REFLEX

STEPON TACK

SENSORYSIGNAL TO SPINE

VIAINTERNEURONS

IPSILATERAL EXTENSORS INHIBITEDIPSILATERAL FLEXORS CONTRACT-LEG LIFTSCONTRALATERAL EXTENSORS CONTRACTCONTRALATERAL FLEXORS INHIBITED- MAINTAIN BALANCE AND SUPPORT WEIGHT