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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