Control of Body Movement and Posture

8/4/2019 Control of Body Movement and Posture

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CONTROL OF BODY

MOVEMENT AND POSTUREIntroduction

oCoordinated movement in a body is a complicatedprocess and involves nerves muscles and bones.


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The skeletal muscle contraction in the body is controlled through the motorunit which includes a single motor neuron and all the muscle fibres suppliedby it and all the motor neuron for a given muscle make up a motor neuron pool.


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When all the motor neuron in a pool get activated at one time leads to acoarse movement.Therefore the skeletal muscle activity depends ultimatelyupon the pattern and rate of discharge of motor neuron.

Inputs(information)to each spinal motor neuron end directly on alpha motorneurons which innervate the extrafusal muscle fibre which form the finalcommon pathway over which the neural control system coordinates theactivity of skeletal muscle fibres.

skeletal muscle contraction skeletal musclerelaxation

Therefore alpha motor neuron is the final common pathway serving bothAs integrating centreand efferent pathway.

Alphamotorneuron


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Many other inputs exert their effects via interneuronsor via gamma motorneurons which innervates the intrafusal muscle fibre.

ipsilateral inputs contralateral inputs

(from same side of (from opposite side of body)body)

Stretch reflex,tone crossed extensorAnd posture(muscle reflexSpindle)

Flexion reflex,noxious tendon reflexStimuli(skin)

Relax antagonist recurrent inhibition through(muscle spindle) renshaw cell

Tendon reflex

final common pathway

Major inputs to the cell body of a single spinal motor neuron

Spinal alpha

motor neuron


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Voluntary movement is planned within brain and the commands are sent tomuscles via descending pathways or motor pathways as follows:


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IN BRAIN AND SPINAL CORD

anterior descending pathway lateral pathways

concerned with the control of muscles concerned with the controlof trunk and proximal parts of limbs. of distal group of muscles.

control posture regulating system control fine,skilledfor postural adjustments and gross movements.movements.


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Levels of motorcontrol system

Highest level:The cerebral

cortex

Middle level:

subcorticalcenters

Brain stem andspinal cord

.levels of organization of neural system controlling body movement

Sensory motorcortex

1.Subcortical nuclei2.Brain stem.

Association cortex

Other brain areas

Spinal cord

Muscle fibres Receptors inmuscles,tendons,joints,

skin.

Motor neurons

Basal gangliacerebellum

Via descending pathway


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Cerebral cortex generate idea for voluntary movementand issue motor commands.

Subcortical centres i.e convert complex plans and

sensory motor cortex, ideas generated in cerebralCerebellum,basal ganglia, cortex into number of smallerSubcortical nuclei. motor programmes which

determines the pattern of neuralactivation required to performthe movement.

Brain stem and spinal cord major relay stationfor all motorcommands.smaller motor programmesgenerated at subcortical level

results into execution of movement.at this level.


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In this block diagram is shown that after the initial motor programme is

Implemented and the action has begun,those brain regions concerned withMotor control continue to receive a constant feedbackofupdatedinformationFrom the receptors in periphery in the form of peripheral sensory input aboutthe movements taking place.


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Body posture is controlled by brain and reflex mechanism. Reflex mechanisms are concerned with maintaining upright static postureand that of maintaining balance.

Postural reflexesThese are the group of reflexes which maintains body position andequilibrium either during rest or during movement by changing thedistribution of muscle tone in limbs and trunks.

Components of reflex arc in postural reflex: eyes

vestibular appratus

proprioceptors

alpha motor neuron

In the above flowchart afferent pathwaysare the inputs received fromEyes,the vestibular appratus and proprioceptors which are relayed to the

Higher integrating centre i.e brain stemand spinal cordwhich further resultsInto execution of motor task via efferent pathwayor motor pathway.

Afferent pathway

Integrating centre

Efferent pathway


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Postural reflex has two adjustment components:

Static reflexes phasic reflexes

It involves sustained contraction Involve transient movements onof musculature for upright base provided by the static reflexesbalanced position and maintain to the body.a stable possible background forvoluntary activity.

A major factor in control of posture is variation in the threshold of the spinalStretch reflex.this in turn is caused by:

1. Changes in excitability of motor neurons;and2. Changes in the rate of discharge in the gamma motor neuronsto muscle

spindles.

Gamma motor neurons activity is regulated to a large degree by descendingtracts from number of areas in the brain.


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Thus the sensitivity of muscle spindle and hence the threshold of spinalStretch reflex in various parts of the body can be adjusted and shifted toMeet the needs of postural control.

Postural reflexs are integrated at various levels in CNS from the spinal cordto cerebral cortex

Levels of integration Principle function

1. Spinal cord Control of spinal reflexes

2. medulla Regulation of heart,respiration and antigravityreflexes.

3. midbrain Regulation of rightning reflexes

4. midbrain,thalamus Regulation of locomotor reflexes

5. hypothalamus,limbic

system

Emotional functions

6. Cerebral cortex Initiates involuntary movements,emotions andmemory involved in conditioned reflexes


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Control of Body Movement and Posture

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