MOTOR SYSTEMS: SPINAL
CORD
D. C. MIKULECKY
PROFESSOR OF PHYSIOLOGY
AND
FACULTY MENTORING PROGRAM
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
MUSCLES AND NERVES
SKELETAL MUSCLE
THE MOTOR UNIT
THE CODING OF CONTRACTILE FORCE
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
SKELETAL MUSCLE:
ANTAGONISTIC ARRANGEMENT
ALL MUSCLES ATTACHED TO BONE AT
BOTH ENDS (ORIGIN AND INSERTION)
USUALLY ARRANGED IN ANTOGONISTIC
PAIRS (FLEXORS AND EXTENSORS)
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 CODING OF
CONTRACTILE FORCE
FREQUENCY CODING: HIGHER
FREQUENCY OF INCOMING ACTION
POTENTIALS GENERATES MORE FORCE
POPULATION CODING: MORE UNITS
RECRUITED TO GET MORE FORCE
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
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
THE INVERSE MYOTACTIC
REFLEX
DETECTION OF EXCESS WEIGHT BY
GOGLI TENDON ORGAN
INHIBIT FLEXOR (BICEPS)
ACTIVATE EXTENSOR
INVERSE MYOTACTIC REFLEX
WEIGHT
TOO
HEAVY
ARM FLEXED
BICEPS & SYNERGYSTIC MUSCLE
CONTRACTED EXTENSOR RELAXED
TENDON STRETCHED
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