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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 RECEPTOR TYPE ENERGY HANDLED MECHANORECEPTORS MECHANICAL: PRESSURE OR TOUCH,PRESSURE,PAIN PHYSICAL DISPLACEMENT THERMORECEPTORS HEAT OR COLD CHEMORECEPTORS: CHEMICAL TASTE AND SMELL PHOTORECEPTORS VISIBLE LIGHT NOCIOCEPTORS: PAIN TISSUE DAMAGE 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 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 RECORD Afferent Activity Muscle Force THE ROLE OF GAMMA MOTOR NEURONS IN REGULATING MUSCLE SPINDLE RESPONSE STIMULATE RECORD 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