SENSORY AND MOTOR SYSTEMS: REFLEXES
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Transcript of SENSORY AND MOTOR SYSTEMS: REFLEXES
SENSORY AND MOTOR SYSTEMS: REFLEXES
D. C. MikuleckyProfessor 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 HANDLEDMECHANORECEPTORSTOUCH,PRESSURE,PAIN
MECHANICAL: PRESSURE ORPHYSICAL DISPLACEMENT
THERMORECEPTORS HEAT OR COLDCHEMORECEPTORS:TASTE AND SMELL
CHEMICAL
PHOTORECEPTORS VISIBLE LIGHTNOCIOCEPTORS: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
MEMBRANECONDUCTANCE
CHANGE
GENERATORPOTENTIAL
ACTIONPOTENTIAL
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 CODINGLIGHT PRESSURE
LOW FREQUENCY
MORE PRESSURE
HIGHERFREQUENCY
POPULATION CODING
LIGHT PRESSURE
MORE PRESSURE
NEOCORTEX
THALAMUS
LIMBICCORTEX
BRAINSTEM
SPINALCORD
NOSE
EYE
TONGUE
EAR
SKIN
SMELL
VISION
TASTE
AUDITION
SOMATIC
THE LABELED LINE CODE OF STIMULUS QUALITY
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 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
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