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MOTOR SYSTEMS
1. Components of Motor Systems
muscles, spinal cord, brain stem, motor cortex,premotor and supplemental areas of the cortex,
cerebellum and basal ganglia
Serial (hierarchical) organization
parallel organization
2. Muscles: controlled by nerves
A. General structure
A skeletal muscle is made up of muscle cells(muscle fibers)
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Supplementalarea
BasalgangliaCerebellum
Premotor
cortex
Thalamus
Motor
cortex
Brainstem
Gammamotor
neuron
Interneuron
Golgitendonorgan
Musclespindle
Alphamotorneuron
Muscle
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Multinucleate
extrafusal fibers and intrafusal fibers
B. Types and actions of skeletal muscle
muscle tendons
flexor extensor
synergistic and antagonistic
fast skeletal muscle slow skeletal muscle
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3. Motor neurons
A. E motor neuron
large diameter with axons of 12-20 Qmdiameter
innervating extrafusal fibers neuromuscular junctions
neurotransmitter: acetylcholine
receptor: nicotinic receptorsB. K motor neuron
small cells with axons of 1-8 Qm diameter
innervating intrafusal fibers
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4. Motor units
an individual motor neuron + all the musclefibers
small motor unit controls very fine movements
large motor unit responsible for grossmovements
frequency code of contractile force
population code of contractile force
5. The Spinal Cord in the Motor Response System
A. Interneurons
located dorsally at the base of the ventral horn
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receive inputs from sensory nerves and othermotor centers
act locally with the same spinal segment or
some send information to other spinal levels.
excitatory interneurons are associated with theactivation of synergistic muscles
inhibitory interneurons are associated with
suppressing the activation of antagonisticmuscles
B. Locomotor generators control walking movement
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C. Regulation of motor neuron activity by sensorysignals
muscle spindle (stretch receptor)
sensory neurons + intrafusal fibers
detect the length of the muscle and also
velocity of muscle contraction
innervated by gamma fibers, which regulate
the sensitivity of sensory nerves of themuscle spindles
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Golgi tendon organs transmit information about the force or
tension produced by the contraction of
the muscle
spinal cord reflexes stretch reflex
inverse myotatic reflex
flexor withdrawal reflex
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Stretch reflex
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Inverse myotatic reflex
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Flexor withdrawal reflex
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6. The Brain in the Motor Response System
A. The brain stem controls posture
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B. The motor cortex control reaching and fine
voluntary movements cells in the motor cortex are organized in a
somatotopic manner similar to that of the somatic
sensory cortex
pyramidal tract majority of fibers cross the midline of the body
C. The cerebellum: planning, coordination, and
postureD. The basal ganglia: planning of movement and
inhibition of motor tone
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7. Disorders of the Motor System
A. Lesions of the pyramidal tract: paralysis
upper-motor-neuron lesions
paralysis on the side of the body opposite the
side of the lesion increase in muscle tone
hyperactive reflexes
Babinski sign
lesions within the spinal cord
changes occur ipsilaterally
loss of strength
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loss of movement in muscle groups
loss of voluntary contracting force
Babinski sign
lower-motor-neuron lesions (spinal cord injuries)
injuries to the motor neurons rather than their
inputs
ipslateral hypoactive reflexes
paralysis to specific groups of muscles
flaccid muscles with prominent atrophy
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B. Lesions of the cerebellum
ipsilateral disturbancesl lack of limb coordination
Ataxia
action tremor