Equilibrium I

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Equilibrium I II

• Prof.Lammers
• Unit 8/ Week 5-6

R.E.B, Equilibrium. 4medstudents.com 2003
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Systems involved in Equilibrium

• The main systems that are involved in equilibrium
  are

Cerebellum
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Vestibular System

• The vestibular apparatus is located in the inner
  ear and comprises of 3 semi-circular canals and
  vestibule which contain these sensor organs
• The utricle
• The saccule
• 3 ampulla
• These organs contain the sensory hair receptors
• the maculae (for the utricle saccule)
• and cristae (ampullae).

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Types of Equilibrium

• Static equilibrium is concerned with the
  orientation of the body relative to the ground (
  Linear acceleration)
• Dynamic equilibrium is concerned with the
  maintenance of posture, especially in the head (
  Rotational movement)

Rotational movement
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1. Static Equilibrium

• Receptors for static Equilibrium are the maculae.
• Each maculae conations supporting cells and
  scattered receptors called hair cells
• Each of the hair cells has a major process
  called a kinocilium and several smaller
  stereocilia. Lying over the supporting and hair
  cells is a gelatin-like otolithic membrane. This
  membrane slides over the hair cells and
  stimulates them when the head is moved.

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1- Supporting cells 4- Membrane
otolithique 2- Hair cell
5- nerve fibers 3- Cilia
6- Otolithes
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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

Maculae in Saccule utricle
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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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Linear Acceleration Stimuli

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

• 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
Nerve Action Potential
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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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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
  bodys 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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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

• Ex. of motion sickness
• When we read 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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Propreceptive system

• Nerve endings that respond to muscle and tendon
  stretch are called propreceptors (ex. Muscle
  spindle). They send signals to the brain, giving
  it information about the posture of the body.
• The proprioceptors are available in the muscles,
  ligaments, tendons, and joints. It which they can
  detect the initiation and termination of body
  movement.
• Note In a sitting situation the system that is
  responsible for equilibrium in the PRORIORECEPTOR