MOTOR SYSTEMS: SPINAL CORD

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MOTOR SYSTEMS SPINAL CORD

• D. C. MIKULECKY
• PROFESSOR OF PHYSIOLOGY
• AND
• FACULTY MENTORING PROGRAM

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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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MUSCLES AND NERVES

• SKELETAL MUSCLE
• THE MOTOR UNIT
• THE CODING OF CONTRACTILE FORCE

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SKELETAL MUSCLE ANATOMICAL FEATURES

• EXTRAFUSAL FIBERS MULTINUCLEATE CELLS WHICH ARE
  THE MAIN CONTRACTILE ELEMENTS
• INTRAFUSAL FIBERS SENSING AND CONTROL OF THE
  CONTRACTING MUSCLE
• MUSCLE MANY PARALLEL FIBERS

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SKELETAL MUSCLE ANTAGONISTIC ARRANGEMENT

• ALL MUSCLES ATTACHED TO BONE AT BOTH ENDS (ORIGIN
  AND INSERTION)
• USUALLY ARRANGED IN ANTOGONISTIC PAIRS (FLEXORS
  AND EXTENSORS)

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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 CODING OF CONTRACTILE FORCE

• FREQUENCY CODING HIGHER FREQUENCY OF INCOMING
  ACTION POTENTIALS GENERATES MORE FORCE
• POPULATION CODING MORE UNITS RECRUITED TO GET
  MORE FORCE

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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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THE INVERSE MYOTACTIC REFLEX

• DETECTION OF EXCESS WEIGHT BY GOGLI TENDON ORGAN
• INHIBIT FLEXOR (BICEPS)
• ACTIVATE EXTENSOR

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INVERSE MYOTACTIC REFLEX
WEIGHT TOO HEAVY
ARM FLEXED
BICEPS SYNERGYSTIC MUSCLE CONTRACTED EXTENSOR
RELAXED TENDON STRETCHED
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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