SENSORY AND MOTOR SYSTEMS: REFLEXES

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SENSORY AND MOTOR SYSTEMS REFLEXES

• D. C. Mikulecky
• Professor of Physiology

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ADEQUATE STIMULUS

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

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TYPES OF ENERGY TRANSDUCED
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GRADED VS ALL OR NONE

• A RECEPTORS RESPONSE TO A STIMULUS IS GRADED
• IF THRESHOLD IS EXCEEDED, THE ACTION POTENTIAL
  RESULTING IS ALL OR NONE

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SENSORY TRANSDUCTION
ADEQUATE STIMULUS
MEMBRANE CONDUCTANCE CHANGE
GENERATOR POTENTIAL
ACTION POTENTIAL
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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

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HOW IS THE INTENSITY OF THE STIMULUS ENCODED?

• FREQUENCY CODING
• POPULATION CODING

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FREQUENCY CODING
LIGHT PRESSURE
LOW FREQUENCY
MORE PRESSURE
HIGHER FREQUENCY
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POPULATION CODING
LIGHT PRESSURE
MORE PRESSURE
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THE LABELED LINE CODE OF STIMULUS QUALITY
NEOCORTEX
LIMBIC CORTEX
NOSE
SMELL
THALAMUS
EYE
VISION
TASTE
TONGUE
BRAIN STEM
EAR
AUDITION
SKIN
SOMATIC
SPINAL CORD
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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

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GENERAL FEATURES OF THE MOTOR SYSTEM

• HIERARCHICAL ORGANIZATION
• VS
• PARALLEL ORGANIZATION

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HIERARCHICAL ORGANIZATION
MOTOR CORTEX

CEREBELLUM AND BASAL GANGLIA
BRAIN STEM
SPINAL CORD
SKELETAL MUSCLE
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PARALLEL ORGANIZATION
MOTOR CORTEX
BRAIN STEM

SPINAL CORD
SKELETAL MUSCLE
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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

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THE MOTOR RESPONSE SYSTEM SPINAL LEVEL

• THE ORGANIZATION OF MOTOR NERVES IN THE SPINAL
  COLUMN
• THE ROLE OF INTERNEURONS
• THE ROLE OF LOCOMOTOR GENERATORS

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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

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LOCATION OF CELL BODIES FOR EXTENSORS AND FLEXORS
FLEXORS

EXTENSORS
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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 NEURONSEXCITE SYNERGISTIC
  AND INHIBIT ANTAGONISTIC

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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

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SENSORY FIBERS IN THE MUSCLE

• THE MUSCLE SPINDLE AS LENGTH DETECTOR
• GOGLI TENDON ORGANS TENSION RECEPTORS

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THE MUSCLE SPINDLE AS LENGTH DETECTOR(SENSORY
FIBERS)

• TYPE Ia NERVE FIBERS TRANSMIT INFORMATION ABOUT
  LENGTH AND VELOCITY TO THE CNS
• TYPE II NERVE FIBERSTRANSMIT INFORMATION ABOUT
  MUSCLE LENGTH TO CNS

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TWO TYPES OF INTRAFUSAL FIBERS
TYPE IA SENSORY FIBER
TYPE II SENSORY FIBER
NUCLEAR CHAIN FIBER
NUCLEAR BAG FIBER
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TWO TYPES OF MOTOR NEURON

• ALPHA MOTOR NEURON INNERVATES EXTRAFUSAL FIBER
• GAMMA MOTOR NEURON INNERVATES INTRAFUSAL FIBERS

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STRETCHING AN INTRAFUSAL FIBER SENDS SIGNALS TO
CNS
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THE ROLE OF GAMMA MOTOR NEURONS IN REGULATING
MUSCLE SPINDLE RESPONSE
STIMULATE
RECORD
RECORD
Afferent Activity
Muscle Force
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THE ROLE OF GAMMA MOTOR NEURONS IN REGULATING
MUSCLE SPINDLE RESPONSE
RECORD
RECORD
STIMULATE
Afferent Activity
Muscle Force
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GOGLI TENDON ORGANS TENSION RECEPTORS

• IN SERIES WITH EXTRAFUSAL FIBERS
• TRANSMITS INFORMATION ABOUT FORCE OR TENSION TO
  CNS
• FREQUENCCY CODING

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SPINAL REFLEXES

• THE STRETCH REFLEX
• THE INVERSE MYOTACTIC REFLEX
• THE FLEXOR WITHDRAWAL REFLEX

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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

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KNEE JERK REFLEX
EXTENSOR ACTIVATED
SENSORY NEURON FROM MUSCLE SPINDLE
DETECTS STRETCH
SPINAL CORD
FLEXOR INHIBITED
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INVERSE MYOTACTIC REFLEX
ARM EXTENDS
BICEPS SYNERGYSTIC MUSCLE RELAXEDEXTENSOR
CONTRACTED
WEIGHT RELEASED
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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

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FLEXOR WITHDRAWAL REFLEX
SENSORY SIGNAL TO SPINE
STEPON TACK
VIA INTERNEURONS
IPSILATERAL EXTENSORS INHIBITED IPSILATERAL
FLEXORS CONTRACT-LEG LIFTS CONTRALATERAL
EXTENSORS CONTRACT CONTRALATERAL FLEXORS
INHIBITED- MAINTAIN BALANCE AND SUPPORT WEIGHT