SENSORY AND MOTOR SYSTEMS REFLEXES D C Mikulecky

SENSORY AND MOTOR SYSTEMS: REFLEXES D. C. Mikulecky Professor of Physiology

ADEQUATE STIMULUS • A SPECIFIC STIMULUS UNIQUE TO A SENSORY RECEPTOR • FOR EXAMPLE, PHOTORECEPTORS IN THE EYE RESPOND ONLY TO ELECTROMAGNETIC RADIATION

TYPES OF ENERGY TRANSDUCED

GRADED VS ALL OR NONE • A RECEPTOR’S RESPONSE TO A STIMULUS IS GRADED • IF THRESHOLD IS EXCEEDED, THE ACTION POTENTIAL RESULTING IS ALL OR NONE

SENSORY TRANSDUCTION ADEQUATE STIMULUS MEMBRANE CONDUCTANCE CHANGE GENERATOR POTENTIAL ACTION POTENTIAL

EXAMPLE: THE PACINIAN CORPUSCLE • PRESSURE RECEPTOR • PRESSURE DISTORTS THE CAPSULE, STRETCHING THE CELL MEMBRANE • SODIUM CHANNELS OPEN, DEPOLARIZING THE MEMBRANE • IF BEYOND THRESHOLD, ACTION POTENTIAL RESULTS

HOW IS THE INTENSITY OF THE STIMULUS ENCODED? • FREQUENCY CODING • POPULATION CODING

FREQUENCY CODING LIGHT PRESSURE LOW FREQUENCY MORE PRESSURE HIGHER FREQUENCY

POPULATION CODING LIGHT PRESSURE MORE PRESSURE

THE LABELED LINE CODE OF STIMULUS QUALITY NEOCORTEX LIMBIC CORTEX NOSE SMELL EYE VISION TONGUE TASTE EAR AUDITION SKIN SOMATIC THALAMUS BRAIN STEM SPINAL CORD

LOCALIZATION, DISTRIBUTION, AND ACUITY • CODING OF LOCATION DEPENDS ON RECEPTOR LOCATION • AREA COVERED BY RECEPTORS IN A SENSORY UNIT IS A RECEPTIVE FIELD • ACUITY DEPENDS ON THE DENSITY OF RECEPTORS

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 ORGANIZATION MOTOR CORTEX BRAIN STEM SPINAL CORD SKELETAL MUSCLE

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

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 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

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 TYPE IA SENSORY FIBER TYPE II SENSORY FIBER NUCLEAR CHAIN FIBER NUCLEAR BAG FIBER

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 STIMULATE RECORD Afferent Activity Muscle Force

THE ROLE OF GAMMA MOTOR NEURONS IN REGULATING MUSCLE SPINDLE RESPONSE STIMULATE RECORD Afferent Activity Muscle Force

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 EXTENSOR ACTIVATED FLEXOR INHIBITED SENSORY NEURON FROM MUSCLE SPINDLE DETECTS STRETCH SPINAL CORD

INVERSE MYOTACTIC REFLEX ARM EXTENDS WEIGHT RELEASED BICEPS & SYNERGYSTIC MUSCLE RELAXEDEXTENSOR 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 SENSORY SIGNAL TO SPINE VIA INTERNEURONS IPSILATERAL EXTENSORS INHIBITED IPSILATERAL FLEXORS CONTRACT-LEG LIFTS CONTRALATERAL EXTENSORS CONTRACT CONTRALATERAL FLEXORS INHIBITED- MAINTAIN BALANCE AND SUPPORT WEIGHT