nervous s, motor, lect3

8/14/2019 Nervous S, Motor, Lect3

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PERIPHERAL NERVOUS SYSTEM COMPONENTSFOR THE CONTROL OF MOVEMENT

It is important to appreciatethat even the simplesteven the simplest

reflex or voluntaryreflex or voluntary

movement requires themovement requires theinteraction of multipleinteraction of multiple

levels of the nervouslevels of the nervous

systemsystem


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MOTOR CONTROL SYSTEMMOTOR CONTROL SYSTEM

Alpha motor neurons are

the final common pathfinal common path formotor control.Peripheral sensory inputand spinal cord tract signalsthat descend from thebrainstem and cerebralcortex influence the motorinfluence the motor

neurons.neurons.The cerebellum and basalganglia contribute to motorcontrol by modifyingmodifying

brainstem and cortical


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ALPHA MOTOR NEURONS ARE THE FINAL COMMPATH

FOR MOTOR CONTROL

Motor neurons segregate into TWO MAJORTWO M

AJORCATEGORIESCATEGORIES, alpha and gamma.

Alpha motorAl

pha motor neurons innervate theEXTRAFUSALEXTRAFUSALmuscle fibers, which areresponsible for force generationforc

e generation.

Gamma motorGamma motor neurons innervate the

INTRAFUSALINTRAFUSALmuscle fibers, which arecomponents of the muscle spindlemuscle spindle.

An alpha motor neuron controls several musclefibers, 10 to 1,000, depending on the muscle.


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MOTOR UNIT STRUCTURE

A motor unit consists of an

alpha motor neuron and thegroup of extrafusal musclefibers it innervates.Functional characteristics,such as activation threshold,activation threshold,

twitch speed, twitch force,twitch speed, twitch force,

and resistance to fatigueand resistance to fatigue, aredetermined by the motorneuron.Low- and high thresholdLow- and high threshold

motor units are shown.motor units are shown.


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MOTOR UNITMOTOR UNIT

The term motor unit describes:

2. a motor neuron,

3. its axon, the branches of the axon,

4. the neuromuscular junction synapses the distal end of each axon branch,

5.and all of the extrafusal muscle fibersinnervated by that motor neuron.

When a motor neuron generates an actionpotential, all of its muscle fibers are

activated.


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AFFERENT MUSCLE INNERVATION PROVIDESFEEDBACK

FOR MOTOR CONTROL

The muscles, joints, and ligaments areinnervated with sensory receptors thatinform the central nervous system aboutbody position and muscle activity.

Skeletal muscles contain muscle spindles,

Golgi tendon organs, free nerve endings, asome Pacinian corpuscles.


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AFFERENT MUSCLE INNERVATION PROVIDES FEEDBAFOR MOTOR CONTROL .

Joints contain Ruffini endings and PacinianRuffini endings and Pacinian

corpuscles.corpuscles. Joint capsules contain nerve endings; ligament

contain Golgi tendon-like organs. Together, these are the proprioceptors,Together, these are the proprioceptors,

providing sensation from the deep somatproviding sensation from the deep somat

structures.structures. These sensations, which may not reach aconscious level, include the position of the limand the force and speed of muscle contractio

They provide the feedback that is necessary fothe control of movements.


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MUSCLE SPINDLES

Muscle spindles are sensory organs fouMuscle spindles are sensory organs fou

in almost all of the skeletal muscles.in almost all of the skeletal muscles.

They occur in greatest density in smallin small

musclesmuscles serving fine movements, such asthose of the hand, and in the deep muscle

of the neck.

The muscle spindle, named for its longnamed for its long

fusiform shapefusiform shape, is attached at both endsextrafusal muscle fibers.


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Muscle spindles provide information about

muscle lengthmuscle length and the velocity at whichmuscle is being stretched.

Golgi tendon organsGolgi tendon organs provide informationthe force being generated.

Spindles are located in the mass of the min parallel with the extrafusal muscle fiber

Golgi tendon organs are located at thejunction of the muscle and its tendons, in swith the muscle fibers


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GOLGI TENDON ORGANSGOLGI TENDON ORGANS

Golgi tendon organs (GTOs) are 1 mm long

slender receptors encapsulated within thetendons of the skeletal muscles.

The distal pole of a GTO is anchored in collagefibers of the tendon.

The proximal pole is attached to the ends of thextrafusal muscle fibers.

This arrangement places the GTO in series witthe extrafusal muscle fibers such thatcontractions of the muscle stretch the GTO.


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THE ROLE OF THE CEREBRAL CORTEXIN MOTOR CONTROL

The cerebral cortical areas concerned withmotor function exert the highest level ofmotor control.

All of these areas contribute fibers to thecorticospinal tract, the efferent motor

pathway from the cortex.


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SUPRASPINAL INFLUENCES ON MSUPRASPINAL INFLUENCES ON M

CONTROLCONTROL

Descending signals from thecervical spinal cord,cervical spinal cord,

brainstem, and cortexbrainstem, and cortex can

INFLUENCEINFLUENCE the rate of motorneuron firing and the recruitmenof additional motor neurons toincrease the speed and forcespeed and force

muscle contraction


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THE SPINAL CORD IN THE CONTROLOF MOVEMENT

Muscles interact extensively in the maintenan

posture and the production of coordinated mov Sensory feedback from muscles reaches moto

neurons of related muscles and, to a lesser demore distant muscles.

In addition to activating local circuits, muscles

joints transmit sensory information up the spinto higher centers.

This information is processed and can be relayto influence spinal cord circuits.


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THE BASAL GANGLIA AND MOTOR CO

The basal ganglia are a group ofsubcortical nuclei located primarily in tbase of the forebrain, with some in thediencephalon and upper brainstem.

Basal ganglia action influences the enti

motor system and plays a role in thepreparation and execution ofpreparation and execution of

coordinated movements.coordinated movements.


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ROLE OF THE BRAIN STEM INCONTROLLING MOTOR FUNCTION

The brain stem consists of themedulla, pons, andmesencephalon.

It contains motor and sensorynuclei that perform motor ansensory functions for the facand head regions

ROLE OF THE BRAIN STEM IN


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ROLE OF THE BRAIN STEM INCONTROLLING MOTOR FUNCTION

Special control functions, such asthe following:

1. Control of respiration2. Control of the cardiovascular system3. Partial control of gastrointestinal function4. Control of many stereotyped movements of the body

5. Control of equilibrium6. Control of eye movements

Finally, the brain stem serves as away station for command signalfrom higher neural centers.

nervous s, motor, lect3

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