Physiology of posture movementand equilibrium

PHYSIOLOGY OF POSTURE,MOVEMENTAND PHYSIOLOGY OF POSTURE,MOVEMENTAND

EQUILIBRIUMEQUILIBRIUM

II

Emeritus Professor, The Emeritus Professor, The Tamilnadu Dr.M.G.R. University,Tamilnadu Dr.M.G.R. University,

Former HODFormer HODINSTITUTE OF NEUROLOGYINSTITUTE OF NEUROLOGY

MADRAS MEDICAL MADRAS MEDICAL COLLEGE,CHENNAICOLLEGE,CHENNAI

PROF.A.V.SRINIVASAN, MD, DM, PhD, F.A.A.N, F.I.A.N,

Control of Posture Control of Posture and Movementand Movement

Somatic motor activity Somatic motor activity depends on the pattern and depends on the pattern and rate of discharge of spinal rate of discharge of spinal

motor neurons. motor neurons. These neurons, the final These neurons, the final

common paths are bombarded common paths are bombarded from array of pathways.from array of pathways.

The inputs converging on the motor neurons subserve The inputs converging on the motor neurons subserve three semi distinct functions through the:three semi distinct functions through the:

1. Pyramidal System1. Pyramidal System ( ( corticospinal pathwayscorticospinal pathways))= they bring about voluntary activity = they bring about voluntary activity

FigFig. 12-1. 12-1

2.2. Extrapyramidal SystemExtrapyramidal System - they - they adjust adjust

body posture to provide stable body posture to provide stable

background for movement. background for movement. Concerned Concerned

with grosser movements and posturewith grosser movements and posture

3.Cerebellum3.Cerebellum – – coordinating and coordinating and smoothing movementssmoothing movements

Control of Axial and distal Control of Axial and distal MusclesMuscles

Medial or Ventral PathwaysMedial or Ventral Pathways and and neuronsneurons are concerned with control are concerned with control of of muscle of the trunkmuscle of the trunk andand proximal portions of the limbsproximal portions of the limbs

Lateral pathwaysLateral pathways are concerned are concerned with the control of muscles in thewith the control of muscles in the distal portions of the limbsdistal portions of the limbs

Axial musclesAxial muscles are concerned with are concerned with postural adjustment and gross postural adjustment and gross movementsmovements

Distal limb musclesDistal limb muscles are those are those that mediate fine, skilled that mediate fine, skilled movementsmovements

CORTICOSPINAL

TRACT

Anatomy and FunctionAnatomy and Function

The fibers that cross the midline in The fibers that cross the midline in the medullary pyramids and from the medullary pyramids and from the the lateral corticospinallateral corticospinal tracttract make make up about 80% of the fibers in the up about 80% of the fibers in the corticospinal pathway.corticospinal pathway.

20% of the fibers make up the 20% of the fibers make up the anterior or ventral, corticospinal anterior or ventral, corticospinal tracttract

The lateral corticospinal tract is The lateral corticospinal tract is concerned with skilled movements concerned with skilled movements

Cortical Motor AreasCortical Motor Areas

30% of the fibers making up the 30% of the fibers making up the corticospinal tracts come from corticospinal tracts come from the the motor cortexmotor cortex

30% comes from the 30% comes from the premotor premotor cortexcortex

40% from the parietal lobe 40% from the parietal lobe especially the especially the somatic sensory somatic sensory areaarea

The cortical representation of The cortical representation of each body part is each body part is proportionate in size to the proportionate in size to the skill skill with which the part is with which the part is used for fine, voluntary used for fine, voluntary movement. movement.

Effects of Section or Destruction Effects of Section or Destruction of Pyramidal Systemof Pyramidal System

A. Role in MovementA. Role in Movement Effects of Section or Destruction Effects of Section or Destruction

of the of the Lateral Corticospinal TractLateral Corticospinal Tract loss of ability to grasp small loss of ability to grasp small

objects between two fingers and objects between two fingers and to make isolated movements of to make isolated movements of the wristthe wrist

can still use the hand in a gross can still use the hand in a gross fashion and can stand and walk fashion and can stand and walk

These deficits are consistent with loss of These deficits are consistent with loss of control of distal musculature of the limbs , control of distal musculature of the limbs , which is concerned with fine skilled which is concerned with fine skilled movementsmovements

Lesions of Lesions of Ventral Corticospinal Ventral Corticospinal TractTract

produce produce axial muscle deficitsaxial muscle deficits that cause difficulty with that cause difficulty with balance, walking and climbingbalance, walking and climbing

B. Effects on Stretch ReflexesB. Effects on Stretch Reflexes

prolonged hypotonia and prolonged hypotonia and flacidity rather than spasticityflacidity rather than spasticity

Damage of the lateral Damage of the lateral corticospinal tract producescorticospinal tract produces

BabinskiBabinski sign:sign: dorsiflexion of dorsiflexion of the great toe and fanning of the the great toe and fanning of the other toes when the other toes when the

lateral aspect of the sole of the lateral aspect of the sole of the foot is scratchfoot is scratch

POSTURE-REGULATING POSTURE-REGULATING SYSTEMS ( Extrapyramidal SYSTEMS ( Extrapyramidal

Mechanisms)Mechanisms)

When the neural axis is When the neural axis is transected, the activities below transected, the activities below the section are cut off or the section are cut off or released from the “control of released from the “control of higher brain centers” and often higher brain centers” and often appear to be appear to be accentuatedaccentuated

Levels of IntegrationLevels of Integration

SPINAL INTEGRATIONSPINAL INTEGRATION

Spinal ShockSpinal Shock – results from – results from transection of the cervical spinal cordtransection of the cervical spinal cord

all spinal reflexes are depressedall spinal reflexes are depressed duration of the shock depends upon duration of the shock depends upon

the degree of encephalizationthe degree of encephalization

frogs and ratsfrogs and rats – lasts for minutes – lasts for minutes dogs and catsdogs and cats – lasts for 1-2 hours – lasts for 1-2 hours monkeysmonkeys – lasts for days – lasts for days humanshumans – minimum of 2 weeks – minimum of 2 weeks

The recovery of the reflex The recovery of the reflex excitability may be due to: excitability may be due to:

* development of denervation * development of denervation hypersensitivity to the mediators hypersensitivity to the mediators by the remaining spinal by the remaining spinal excitatory endings excitatory endings

* sprouting of collaterals from * sprouting of collaterals from existing neurons existing neurons

The first reflex response to appear as spinal The first reflex response to appear as spinal shock wares off isshock wares off is slight contraction of the slight contraction of the leg flexors and adductors in response to leg flexors and adductors in response to noxious stimulusnoxious stimulus

Responses of Chronic Spinal Responses of Chronic Spinal AnimalAnimal

* * Magnet reactionMagnet reaction (positive (positive supporting reaction)supporting reaction)

* Autonomic reflexes* Autonomic reflexes – reflex – reflex contraction of full bladder and rectumcontraction of full bladder and rectum

* Sexual reflexes* Sexual reflexes

* Mass reflex* Mass reflex - evacuation of bladder - evacuation of bladder and rectum, sweating, pallorand rectum, sweating, pallor

II. MEDULLARY COMPONENTS

Hindbrain and spinal cord are Hindbrain and spinal cord are isolated from the rest of the brain isolated from the rest of the brain by by transection of thetransection of the brainstem at brainstem at the superior border of the ponsthe superior border of the pons. . Procedure is called Procedure is called DecerebrationDecerebration

Decerebrate rigidity develops as Decerebrate rigidity develops as soon as the brainstem is transected soon as the brainstem is transected

It is found to be spastic due to It is found to be spastic due to

diffuse facilitation of stretch diffuse facilitation of stretch reflexesreflexes

Facilitation is due to two Facilitation is due to two factors:factors:

increased general excitability of increased general excitability of the motor neuron poolthe motor neuron pool

increase in the rate of discharge increase in the rate of discharge in the gamma efferent neuronsin the gamma efferent neurons

Characteristics of Characteristics of Decerebrate RigidityDecerebrate Rigidity

1. Decerebrate Posture – 1. Decerebrate Posture – “ Caricature of the normal standing position” “ Caricature of the normal standing position”

– neck and limbs extended, back arched, – neck and limbs extended, back arched, tail elevated. tail elevated.

2. Tonic Labyrinthine Reflexes2. Tonic Labyrinthine Reflexes

no righting reflexes are present, no righting reflexes are present, and the animal stays in position and the animal stays in position where they are putwhere they are put

rigidity in the limbs varies with rigidity in the limbs varies with positionposition

if the animal is placed on its back if the animal is placed on its back extension of all 4 limbs is maximalextension of all 4 limbs is maximal

as the animal is turned to either as the animal is turned to either side, rigidity decreasesside, rigidity decreases

when prone, the rigidity is minimalwhen prone, the rigidity is minimal

3. Tonic Neck Reflexes3. Tonic Neck ReflexesRigidity changes with head movementRigidity changes with head movement

head turned to one side limbs on that head turned to one side limbs on that side (jaw limb) become more rigidly side (jaw limb) become more rigidly extended, while the contralateral limb extended, while the contralateral limb become lessbecome less

flexion of the head causes flexion of the flexion of the head causes flexion of the forelimbs and extension of the hindlimbsforelimbs and extension of the hindlimbs

extension of the head causes flexion of extension of the head causes flexion of the hindlimbs and extension of the the hindlimbs and extension of the forelimbsforelimbs

III. MIDBRAIN COMPONENTSIII. MIDBRAIN COMPONENTS

Midbrain AnimalMidbrain Animal – produced by – produced by section of the neural axis at the section of the neural axis at the superior border of thesuperior border of the midbrainmidbrain

Chronic midbrain animalChronic midbrain animal can rise can rise to the standing position, walk, to the standing position, walk, and right themselvesand right themselves

Manifestations:Manifestations:

A. extensor rigidityA. extensor rigidity – when – when animals lies quietly on its backanimals lies quietly on its back

B. Righting reflexB. Righting reflex – to maintain the – to maintain the normal standing position and normal standing position and keep head uprightkeep head upright

1. head righting reflex1. head righting reflex 2. neck righting reflex2. neck righting reflex 3. body righting reflex3. body righting reflexC. grasp reflexC. grasp reflex

IV. CORTICAL COMPONENTSIV. CORTICAL COMPONENTS

DecorticationDecortication (removal of (removal of the cerebral cortex) produces the cerebral cortex) produces little motor deficit.little motor deficit.

Decorticate Animal Decorticate Animal

Effects of DecorticationEffects of Decortication

1. decorticate rigidity occurs only when 1. decorticate rigidity occurs only when animal is at restanimal is at rest

2. Placing and Hopping reactions are 2. Placing and Hopping reactions are disrupteddisrupted

Hopping movementsHopping movements – keep the limbs in – keep the limbs in position to support the body when position to support the body when animal animal

standing is pushed laterallystanding is pushed laterally

Placing reactionsPlacing reactions – place the foot firmly – place the foot firmly on the supporting surfaceon the supporting surface

EQUILIBRIUMEQUILIBRIUMBrainstem structures, axial Brainstem structures, axial extensor tone, equilibriumextensor tone, equilibrium

Lesions of the medial brainstem interrupting Lesions of the medial brainstem interrupting decending reticulospinal vestibulospinal, decending reticulospinal vestibulospinal, and tectospinal systems that innervate and tectospinal systems that innervate proximal and axial muscles result in severe proximal and axial muscles result in severe dysequilibrium. These brainstem efferents dysequilibrium. These brainstem efferents convey the output of networks involving the convey the output of networks involving the cerebellum (flocculonodular and anterior cerebellum (flocculonodular and anterior lobes), brainstem reticular and central lobes), brainstem reticular and central vestibular pathways, and descending inputs vestibular pathways, and descending inputs from the basal ganglia, thalamus, and from the basal ganglia, thalamus, and frontal and parietal lobes. The control of frontal and parietal lobes. The control of truncal posture in humans may be mediated truncal posture in humans may be mediated by similar networks.by similar networks.

HISTORY & COMMON SYMPTOMS HISTORY & COMMON SYMPTOMS OF GAIT DISTURBANCEOF GAIT DISTURBANCE

A detailed account of the walking difficulty and its evolution A detailed account of the walking difficulty and its evolution provide the first clues to the underlying diagnosis. When provide the first clues to the underlying diagnosis. When evaluating the history it is helpful to note the particular evaluating the history it is helpful to note the particular circumstances in which the walking difficulty occurs, the leg circumstances in which the walking difficulty occurs, the leg movements most affected, and any associated symptoms. movements most affected, and any associated symptoms. Because disorders at many levels of the peripheral and central Because disorders at many levels of the peripheral and central nervous systems give rise to difficulty waling, it is necessary nervous systems give rise to difficulty waling, it is necessary to consider whether the problem is caused by muscle to consider whether the problem is caused by muscle weakness, a defect of higher motor control, or imbalance due weakness, a defect of higher motor control, or imbalance due to cerebellar disease or proprioceptive sensory loss. Walking to cerebellar disease or proprioceptive sensory loss. Walking over uneven ground exacerbates most walking difficulties, over uneven ground exacerbates most walking difficulties, leading to tripping, stumbling, and falls. Aligamentous ankle leading to tripping, stumbling, and falls. Aligamentous ankle strain or even a bony fracture may result form tripping and strain or even a bony fracture may result form tripping and falling in this situation and may be presenting symptom of a falling in this situation and may be presenting symptom of a gait disorder. Fear of falling may lead to a variety of voluntary gait disorder. Fear of falling may lead to a variety of voluntary protective measures to minimize the risk of injury. In some protective measures to minimize the risk of injury. In some patients, particularly the elderly, compensatory strategies and patients, particularly the elderly, compensatory strategies and a fear of falling lead to a “cautious” gait that dominates the a fear of falling lead to a “cautious” gait that dominates the clinical picture.clinical picture.

WeaknessWeakness Weakness of the legs may be described in several ways. Weakness of the legs may be described in several ways.

Complaints of stiffness, heaviness, or “legs that do not do what Complaints of stiffness, heaviness, or “legs that do not do what they are told” may be the presenting symptoms of a spastic they are told” may be the presenting symptoms of a spastic paraparesis frequently report that they drag their legs to walk or paraparesis frequently report that they drag their legs to walk or that their legs suddenly give way, causing stumbling and falls.that their legs suddenly give way, causing stumbling and falls.

Weakness of certain muscle groups may be described as difficulty Weakness of certain muscle groups may be described as difficulty performing particular movements during the gait cycle,. Catching performing particular movements during the gait cycle,. Catching or Scraping the toe on the ground and a tendency to trip may be or Scraping the toe on the ground and a tendency to trip may be presenting symptom of hemiplegia (causing a spastic equinovarus presenting symptom of hemiplegia (causing a spastic equinovarus foot posture) of footdrop caused by weakness of ankle foot posture) of footdrop caused by weakness of ankle dorsiflexion. Weakness of knee extension presents with a dorsiflexion. Weakness of knee extension presents with a sensation that the legs will give way while standing or walking sensation that the legs will give way while standing or walking down stairs. Weakness of ankle plantar flexion intereres with the down stairs. Weakness of ankle plantar flexion intereres with the ability to stride forward, resulting in a shallow stepped gait. ability to stride forward, resulting in a shallow stepped gait. Weakness of certain movements may first become apparent in Weakness of certain movements may first become apparent in particular situations; for example, difficulty in climbing stairs or particular situations; for example, difficulty in climbing stairs or rising from a seated position is suggestive of proximal muscle rising from a seated position is suggestive of proximal muscle weakness, which is most commonly caused by a myopathy.weakness, which is most commonly caused by a myopathy.

CLINICAL EXAMINATION OF CLINICAL EXAMINATION OF POSTURE AND GAITPOSTURE AND GAIT

POSTUREPOSTURE Trunk posture (upright or stooped)Trunk posture (upright or stooped) Postural reflexes (“pull test”)Postural reflexes (“pull test”) Stance (narrow or wide based)Stance (narrow or wide based)

WALKINGWALKINGInitiation (start hesitation shuffling, magnetic feet) Initiation (start hesitation shuffling, magnetic feet)

SteppingStepping Rhythm (regular, irregularRhythm (regular, irregular Length (normal, short)Length (normal, short) Trajectory (shallow, high-setpping)Trajectory (shallow, high-setpping) SpeedSpeedAssociated trunk movement and arm swing.Associated trunk movement and arm swing.

Special maneuversSpecial maneuvers Heel-toe walkingHeel-toe walking Romberg’s testRomberg’s test Walking backward or runningWalking backward or running

FORMAL MOTOR AND SENSORY EXAMINATION (SUPINE)FORMAL MOTOR AND SENSORY EXAMINATION (SUPINE) Muscle bulk, tone, strengthMuscle bulk, tone, strength Voluntary movementVoluntary movement Trunk movement (rolling over, standing or sitting up) leg Trunk movement (rolling over, standing or sitting up) leg

movement when not standing or sitting up)movement when not standing or sitting up) Leg movement when not standingLeg movement when not standing Tendon reflexesTendon reflexes Sensation : ProprioceptionSensation : Proprioception Heel-to-shin testHeel-to-shin test

Musculoskeletal Examination Musculoskeletal Examination

Leg size and lengthLeg size and length Range of joint movement (especially Range of joint movement (especially

hip)hip)