cns 15

Systems regulating body balanceSystems regulating body balance

1. Senses from the environment

2. Summation and coordination of senses in the CNS

3. Motor commands to muscle regulation of body balance

1. Senses from the environment

2. Summation and coordination of senses in the CNS

3. Motor commands to muscle regulation of body balance

There are three components that regulate body balanceThere are three components that regulate body balance

CNS1- Cerebral cortex2- Brainstem 3- Cerebellum

2 -Vestibular

3 -Proprioceptive

1-Muscle commands

1-

2-

Systems regulating body balance

The Vestibular ApparatusThe Vestibular Apparatus

Componentsa. Three semicircular canals (SCCs)

Anterior Posterior Lateral

b. Utricle and Sacculec. Vestibular nerve and nuclei These organs contain the sensory hair receptors:

the maculae (for the utricle & saccule) and cristae (ampullae).

Componentsa. Three semicircular canals (SCCs)

Anterior Posterior Lateral

b. Utricle and Sacculec. Vestibular nerve and nuclei These organs contain the sensory hair receptors:

the maculae (for the utricle & saccule) and cristae (ampullae).

Anatomy of the vestibular labyrinthAnatomy of the vestibular labyrinthAnatomy of the vestibular labyrinthAnatomy of the vestibular labyrinth

Anterior

Lateral

Posterior

The Semicircular CanalsThe Semicircular Canals

1. Fluid filled

2. Each canal has a dilated end = Ampulla

3. The ampulla houses the sensory hair cells which are covered by a gelatinous material

a. Ampulla

b. Cristae = hair cells

c. Cupulae = gelatinous material

1. Fluid filled

2. Each canal has a dilated end = Ampulla

3. The ampulla houses the sensory hair cells which are covered by a gelatinous material

a. Ampulla

b. Cristae = hair cells

c. Cupulae = gelatinous material

Cupula

Cristae

Ampulla

Sensory cell (Hair cell)Sensory cell (Hair cell)

Kinocilium

Stereocilia

Stimulation

InhibitionAfferent vestibular nerve fibers

The Utricle and SacculeThe Utricle and Saccule

Present in the vestibule of the labyrinth Utricle is vertically oriented Saccule is horizontally oriented Sensory hair cells are embedded in the maculae

of the utricle and saccule Hair cells are covered by a membrane called

otolithic membrane

Present in the vestibule of the labyrinth Utricle is vertically oriented Saccule is horizontally oriented Sensory hair cells are embedded in the maculae

of the utricle and saccule Hair cells are covered by a membrane called

otolithic membrane

The vestibule of the labyrinthThe vestibule of the labyrinthThe vestibule of the labyrinthThe vestibule of the labyrinth

Otolithic membrane

Hair cell

Anatomy: Maculae of Utricle or SacculePhysiology: Linear acceleration of head

Types of Equilibrium

1. Static equilibrium: is concerned with the orientation of the body relative to the ground ( Linear acceleration)

2. Dynamic equilibrium is concerned with the maintenance of posture, especially in the head ( Rotational movement)

Rotational movement

Stimulus to the vestibular sensory organsStimulus to the vestibular sensory organs

=

MotionVelocity

Acceleration

Head acceleration in an angular fashion stimulates SCCs

Head acceleration in a linear fashion stimulates maculae in utricle and saccule

=

MotionVelocity

Acceleration

Head acceleration in an angular fashion stimulates SCCs

Head acceleration in a linear fashion stimulates maculae in utricle and saccule

Mechanism of Stimulation

Deflection of stereocilia towards kinocilium = Stimulation

Deflection of stereocilia away from kinocilium = Inhibition

Mechanism of Stimulation

Deflection of stereocilia towards kinocilium = Stimulation

Deflection of stereocilia away from kinocilium = Inhibition

Stimulus to the vestibular sensory organsStimulus to the vestibular sensory organs

Dynamic Equilibrium

The receptors for Dynamic equilibrium are the ampulla which is found in the semicircular canals.

In each ampulla is a small elevation called a crista. Each crista is made up of hair (receptor) cells and supporting cells, and covered by a jelly-like material known as the cupola. Movement of the cupola stimulates the hair cells

Ampulla

Dynamic Equilibrium

•The ampulla is responsible for the change in rotational movement, as continuous rotation does not stimulate the ampulla.

– when the head starts moving in a rotationally the endolymph in the semicircular ducts move in the direction opposite to the body’s direction deforming the crista in

the duct causes depolarization –If the body continues to rotate at a constant rate The

endolymph moves at the same direction and speed as the body and stop the movement of hair cells

Dynamic Equilibrium

•When we suddenly stop moving, the endolymph keeps on moving in the opposite direction hyperpolarization of the hair

cells that will tell the brain that we have stopped movement.

Otolithic membrane

Hair cell

Mechanism of Stimulation in Utricle & Saccule1- Linear acceleration of head or changes of head position 2- Shift of position of otolithic membrane3- Deflect stereocilia to or away from kinocilium4- Stimulation or inhibition

Linear Acceleration Stimuli

When the head starts or stops moving in a linear

acceleration otolothic membrane slides backward or forward over hair cells the hair cells will bend

When the hair bends towards the kinocilium the hair cell depolarize faster steam of impulse is sent to the brain

Linear Acceleration Stimuli

Nerve Action Potential

When the hair bends in the opposite direction the hair cells hyperpolarize Slower impulse generation

NOTE: It is important to understand that the maculae is responsible for the change in acceleration only. Because the hair cell can adapt it quickly

Static Equilibrium

The Maculae are responsible for linear acceleration forces.

The Maculae are in the Saccule : is responsible for

vertical acceleration Utricle: Is responsible for

horizontal acceleration

Saccule

Utricle

Maculae in Saccule & utricle

Connections of the vestibular sensory organsConnections of the vestibular sensory organs

Vestibulo-Ocular reflex (VOR) Vestibulo-Spinal reflex (VSR)

Vestibulo-Ocular reflex (VOR) Vestibulo-Spinal reflex (VSR)

Function of vestibular reflexesFunction of vestibular reflexes

The VOR stabilizes gaze during fast head movement

The VSR sends information regarding gravity and linear acceleration to body muscles

The VOR stabilizes gaze during fast head movement

The VSR sends information regarding gravity and linear acceleration to body muscles

Vestibulo-Ocular Reflex (VOR)

STIMULUS =Head movement

Efferent = oculomotor nervesEffector = Extra-ocular muscles

Sensory = Vestibular HC

Afferent = vestibular nerve

Center

Vestibulo-Spinal Reflex (VSR)STIMULUS =Gravity linear acceleration

Efferent = Spinal nervesEffector = Neck and body muscles

Sensory = Vestibular HC

Afferent = vestibular nerve

Center

The Visual System

The 2nd system that plays an important role in equilibrium is the visual system.

The effect of the visual system is best noticed when there is a conflict between the messages that reach the brain.

Motion sickness is a very common equilibrium disorder in which is due to sensory input mismatch. The main symptoms are: Nausea, dizziness, vomiting and pale appearance

Motion sickness

When a person reads while traveling, the visual inputs indicates that the body is fixed. But as the vehicle is moving the vestibular system detects movement and send impulses that

conflict with the visual system .The Brain receives conflicting information which will lead to motion sickness.

Vestibular EvaluationVestibular Evaluation Taking History

- Complaints- History of present illness

- Past medical history

Question the character of “Dizziness”(spinning, blurring of vision, loss of balance, light headedness,….)

Character of course of dizziness (onset, duration: sec/min/hrs/days, in attacks or

constant, position, alleviation, aggravation,…)

Taking History- Complaints- History of present illness

- Past medical history

Question the character of “Dizziness”(spinning, blurring of vision, loss of balance, light headedness,….)

Character of course of dizziness (onset, duration: sec/min/hrs/days, in attacks or

constant, position, alleviation, aggravation,…)

Vestibular evaluationVestibular evaluation

Associated symptoms1. otologic (tinnitus, fullness, otalgia, draining ear,

…)

2. Neurologic (headache, migraine, epilepsy, diplopia, tremors, …)

3. Psychiatric (anxiety, pallor, sweating, depression,…)

4. Cardiac (syncope, arrhythmias)

5. Medication side effects (ototoxic drugs)

Associated symptoms1. otologic (tinnitus, fullness, otalgia, draining ear,

…)

2. Neurologic (headache, migraine, epilepsy, diplopia, tremors, …)

3. Psychiatric (anxiety, pallor, sweating, depression,…)

4. Cardiac (syncope, arrhythmias)

5. Medication side effects (ototoxic drugs)

Physical examinationPhysical examination Standard ENT examination Examine VOR for presence of nystagmus Examine VSR by testing:

- Balance and gait

- Posture

- Coordination

- Fine motor skills

Standard ENT examination Examine VOR for presence of nystagmus Examine VSR by testing:

- Balance and gait

- Posture

- Coordination

- Fine motor skills

NystagmusNystagmus

Nystagmus = rhythmic involuntary oscillation of eyes with fast and slow phases

Examination of nystagmusExamination of nystagmus

Observe for eye movements in darkness or with Frenzel’s glasses

Observe for eye movements with eyes open for fixation suppression

Vestibular nystagmusVestibular nystagmus

Spontaneous Induced

Peripheral or Central

Spontaneous Induced

Peripheral or Central

Spontaneous nystagmusSpontaneous nystagmusPeripheral lesion

Examples:

1- Acute labyrinthitis

2- Vestibular neuronitis

3- Meniere’s disease

Usually unilateral Suppressed by visual fixation Associated otologic symptoms

Spontaneous nystagmusSpontaneous nystagmusCentral lesion

Not suppressed by

visual fixation Associated neurologic

symptoms

Induced nystagmusInduced nystagmus

Nystagmus induced by position change Nystagmus induced by caloric stimulation

Nystagmus induced by position change Nystagmus induced by caloric stimulation

Positional nystagmusPositional nystagmus

Normally not present

Induced by position

Evaluation: Hallpike maneuver

Peripheral or central

Characteristics: latent period, fatigable, +/- paroxysmal

Barany’s Caloric testingConceptBarany’s Caloric testingConcept Convection currents created

in the endolymph will move the cupula inwards or outwards

Convection currents are created in the endolymph by irrigating the external auditory canal by warm water and cold water to be below or above body temperature.

Caloric testing Procedure and recordingCaloric testing Procedure and recording

Postural Reflexes

Impossible to separate postural adjustments from voluntary movement

maintain body in up-right balanced position provide constant adjustments necessary to

maintain stable postural background for voluntary movement

adjustments include static reflexes (sustained contraction) & dynamic short term phasic reflexes (transient movements)

Postural Control (cont)

A major factor is variation of in threshold of spinal stretch reflexes

caused by changes in excitability of motor neurons & changes in rate of discharge in the gamma efferent neurons to muscle spindles

Posture

Represents overall position of the body & limbs relative to one another & their orientation in space

Postural adjustments are necessary for all motor tasks & need to be integrated with voluntary movement

Postural Adjustments Functions

support head & body against gravity maintain center of the body’s mass aligned &

balanced over base of support on the ground stabilize supporting parts of the body while others

are being moved Major mechanisms

anticipatory (feed forward)-predict disturbances modified by experience; improves with practice

compensatory (feedback) evoked by sensory events following loss of balance

Righting reflexes

Tonic neck reflexes

Vestibular placing reaction