Lecture 3 Motor

8/9/2019 Lecture 3 Motor

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Lecture 3 Sensory/Motor

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

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Lecture 3 Motor