Anatomy and physiology of the Inner ear, and Motion Sickness

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PREPERED BY Othman Abdikarim Othman1

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Amoud Medical school

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2. Motor Function of the brain

stem and cerebral cortex

WARM UP !!!!

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Table of

objectives

Introduction

Motion sickness

Reticular formation

Vestibular apparatus

Utricle and saccule

Semicircular canals

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Today’s Topic

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A wide image and texts

The brain stem is a complex extension

of the spinal cord which performs

sensory, motor and reflex function .

Besides containing centres that

regulate cardiovascular , respiratory

and gastrointestinal functions, the brain

stem plays major role in the control of

eye movement in the support the body

against the gravity.

Brain stem

Today’s Topic

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A wide image and texts

The reticular formation is a large

structure occupying the core of the

brain stem from caudal medulla to

the rostral midbrain. It consist of

areas of diffuse neurons of two

types : Sensory& Motor

Reticular Formation

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3 columns

Sensory neuron

Sensory neuron are greater in number and make

multiple connection with in the reticular formation it self.

Motor neurons

Motor neuron give rise to axons which divide into

ascending branches and descending branches.

The former( ascending branches) pass to the non-specific

thalamic nuclei, to the basal ganglia and to the cerebral

cortex via the thalamus . This is known as the Reticular

activating system , which plays a major rule in the control of

brain activity such as consciousness and alertness.

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The descending branches, however, pass

to the spinal cord to supply the anterior

motor neurons these are the lateral and

ventral reticulo-spinal tract. A number

of nuclei function in association with the

reticular formation of the brain stem.

These are :

Vestibular nuclei

Red nuclei

Substantia nigra

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Vestibular

apparatus

Dare to answer !!!

1. What are the three general

parts of the ear?

2. Which parts of ear contain

the sensory organs for

hearing and balance ?

3. Which structures make up

the inner ear or labyrinth?

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ANSWERS

1. The external ear, the middle

ear(tympanic cavity) and inner

ear( labyrinth)

2. The inner ear

3. Vestibule, cochlea and semi-

circular canals


The internal ear or labyrinth is situated in

the petrous part of the temporal bone,

medial to middle ear it consist of :

Bony labyrinth

Membranous labyrinth

The bony labyrinth consist of three parts

The vestibule

Semi-circular canal

Cochlea


Between the bony and membranous

labyrinths is a space filled with fluid,

the perilymph. Inside the

membernous labyrinth there is also

fluid, called the endolymph.

The cochlear duct is the sensory

organ for hearing while the utricle,

saccule and semicircular canals

contain receptors concerned with the

control of equilibrium or balance.

Cont….

The bony labyrinth is formed of the vestibule, a bony

cochlea and three bony semi-circular canals

The membranous labyrinth which consist of mainly

of the cochlear duct (membranous cochlea), three

membranous semi circular canals and two chambers :

Utericle and Saccule.

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In Shortcut

Inside the Bony Labyrinth ,there is bony spaces and

with it there is fluid called perilymph

With in the perilymph fluid there is floating membranous

structure called Membranous labyrinth.

With in the membranous labyrinth there is another fluid

called endolymph.

With in the endolymph fluid there is sensory

epithelium.

floating


Bony structure Membranous structure Sensory epithelium Function

1. Cochlea Cochlea Duct Organ of corti Hearing

2. Vestibule Saccule & Utericle Macule Balance

3. Semi-circular canals Semi-circular Duct Cristae Balance

Utricle & Saccule

Be with me !!!

Sensory epithelium of vestibular present on

the floor of utricle and the wall of saccule

and It is called maculae or otolithic.

Sensory information from two maculae

plus sensory information from sensory

epithelium of semi-circular canal(cristae)

they form Vestibular Nerve 18

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!!!

Otoconia

Sterocilia Tip links

KinociliumGELATINOUS LAYER

Calcium carbonate crystals

Each macule is formed of

columnar epithelial cells and

hair cells and is covered by

gelatinous layer(gel like

material) inside gelatinous

layer are numerous small

calcium carbonate

stones(otoliths)(otoconia)

The Otoliths/Otoconia lie on top of

hairs or process that project from the

apical ends of hair cells. Because of

their weight, otoliths will bend the hairs

in the direction of the pull of gravity

Small hairs: Stereocilia

Large hairs: Kinocilium

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CONTINUEUR

Attention

plz

Electron microscopy shows that very

fine filamentous attachments called tip

tinks connect the kinocilium to the

nearest stereocilium.

So when stereocilia bend towards

kenocilium tip links pull stereocillium

one by one this opens ion channels and

cell is depolarized.

Be happy

ppt is

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finish

When the sterocilia are bent in

opposite direction( away from

kinocilium) the pulling effect of the tip

links on the sterocilia is reduced and

ion channels closed and the cell

undergo hyperpolarized.


Semi-circular canals There are three semicircular canals on each

side The three canals are:

the horizontal semicircular canal (also

known as the lateral semicircular canal),

superior semicircular canal (also known as

the anterior semicircular canal),

and the posterior semicircular canal (also

known as the inferior semicircular canal).22

Semicircular canals: structure

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Each semicircular canal

opens at both ends into

the utricle one of this ends

is dilated to form an

ampulla which houses the

sensory epithelium called

crista

Contains Cilia of hair

cells project into

gelatinous cap called

cupula

Enlargement of

ampulla

Crista ampullaris

Semicircular

canals

Semicircular canals:

function24

The cristae of the semicircular canals

detect head rotation in any direction.

This movement is called Angular

acceleration.

Head rotation results in inertial

movement of endolymph in opposite

direction

Bends cupula which bends hair cells

B&B Figure 13-18

Semicircular canals: sensory transduction25

B&L Figure

Steriocilia maintain directionality on both sides of the head

Bending towards kinocilium opens ion channels

depolarization

Bending away from kinocilium closes ion channels

hyperpolarization

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Motion

sickness

Cont….

Motion sickness or kinetosis, also known as travel

sickness, is a condition in which there is a disagreement

exists between visually perceived movement and the

vestibular system 's sense of movement.

Dizziness, fatigue, and nausea are the most

common symptoms of motion sickness.

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What cause

it ?

Cont….

The most common hypothesis for the cause of motion sickness is that it functions as

a psychological defence mechanism against neurotoxins.

The area postrema in the brain is responsible for inducing vomiting when

poisons are detected, and for resolving conflicts between vision and balance.

When feeling motion but not seeing it (for example, in a ship with no

windows), the inner ear transmits to the brain that it senses motion, but

the eyes tell the brain that everything is still.

As a result of this Conflicts the brain will come to the conclusion that the

individual is hallucinating and further conclude that the hallucination is

due to poison ingestion. Then brain responds by inducing vomiting, to

clear the supposed toxin.

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Advice 4 pple who have motion sickness

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One common suggestion is to simply look out of the window of the moving

vehicle this helps to re-orient the inner sense of balance

Take Scopolamine as a prophylaxis during travelling b4 30 minutes

Thank You for Watching!

PREPERED BY: Othman Abdikarim

Othman)

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Health & Medicine

Anatomy and physiology of the Inner ear, and Motion Sickness