Anatomy and physiology of the Inner ear

1. Welcome to the Presentation
PREPERED BY Othman Abdikarim Othman 1
One Column
Amoud Medical school
Let’s Begin Now!

2. 2. Motor Function of the brain
stem and cerebral cortex

3. 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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5. Today’s Topic
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 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

6. Today’s Topic
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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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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

10. 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

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 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

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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.

14. 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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16.  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

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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

18. 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
Kinocilium
GELATINOUS 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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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.

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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.
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22. 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

23. 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

24. 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

25. Semicircular canals: sensory transduction
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 Steriocilia maintain directionality on both sides of the head
 Bending towards kinocilium  opens ion channels 
depolarization
 Bending away from kinocilium  closes ion channels 
hyperpolarization

26. 
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Motion
sickness

27. 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 ?

29. 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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30. 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

31. Thank You for Watching!
PREPERED BY: Othman Abdikarim
Othman
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That is all