cns 15
TRANSCRIPT
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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
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CNS1- Cerebral cortex2- Brainstem 3- Cerebellum
2 -Vestibular
3 -Proprioceptive
1-Muscle commands
1-
2-
Systems regulating body balance
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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).
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Anatomy of the vestibular labyrinthAnatomy of the vestibular labyrinthAnatomy of the vestibular labyrinthAnatomy of the vestibular labyrinth
Anterior
Lateral
Posterior
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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
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Cupula
Cristae
Ampulla
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Sensory cell (Hair cell)Sensory cell (Hair cell)
Kinocilium
Stereocilia
Stimulation
InhibitionAfferent vestibular nerve fibers
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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
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The vestibule of the labyrinthThe vestibule of the labyrinthThe vestibule of the labyrinthThe vestibule of the labyrinth
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Otolithic membrane
Hair cell
Anatomy: Maculae of Utricle or SacculePhysiology: Linear acceleration of head
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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
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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)
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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
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Vestibulo-Ocular Reflex (VOR)
STIMULUS =Head movement
Efferent = oculomotor nervesEffector = Extra-ocular muscles
Sensory = Vestibular HC
Afferent = vestibular nerve
Center
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Vestibulo-Spinal Reflex (VSR)STIMULUS =Gravity linear acceleration
Efferent = Spinal nervesEffector = Neck and body muscles
Sensory = Vestibular HC
Afferent = vestibular nerve
Center
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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
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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.
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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,…)
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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)
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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
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NystagmusNystagmus
Nystagmus = rhythmic involuntary oscillation of eyes with fast and slow phases
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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
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Vestibular nystagmusVestibular nystagmus
Spontaneous Induced
Peripheral or Central
Spontaneous Induced
Peripheral or Central
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Spontaneous nystagmusSpontaneous nystagmusPeripheral lesion
Examples:
1- Acute labyrinthitis
2- Vestibular neuronitis
3- Meniere’s disease
Usually unilateral Suppressed by visual fixation Associated otologic symptoms
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Spontaneous nystagmusSpontaneous nystagmusCentral lesion
Not suppressed by
visual fixation Associated neurologic
symptoms
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Induced nystagmusInduced nystagmus
Nystagmus induced by position change Nystagmus induced by caloric stimulation
Nystagmus induced by position change Nystagmus induced by caloric stimulation
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Positional nystagmusPositional nystagmus
Normally not present
Induced by position
Evaluation: Hallpike maneuver
Peripheral or central
Characteristics: latent period, fatigable, +/- paroxysmal
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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.
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Caloric testing Procedure and recordingCaloric testing Procedure and recording
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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)
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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
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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
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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
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Righting reflexes
Tonic neck reflexes
Vestibular placing reaction
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