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The Ear

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Kristi Bui

on 13 June 2014

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Transcript of The Ear

The Ear
The Ear
The ear is an organ that deals primarily with the systems of:
Hearing (
Balance (
Hair cells with stereocilia (sensory receptors) are important within both systems.
Stereocilia are long microvilli, sensitive to mechanical stimulation.
Fetal Development
The ear begins to develop on the twenty-second day of the embryonic development.
The three primary sections of the ear originate from the ectoderm, endoderm and mesoderm.
inner ear
is the first to develop.
Originates from the ectoderm.
A group of sensory cells known as a
is in charge of forming the
, which in turn will connect to the
cochlear duct
Fetal Development
middle ear
forms next, originating from the endoderm.
The outer ear is the last to form.
It originates from the mesoderm, and is fully expanded by the eigteenth week of development.
The part of the outer ear closest to the neck situates first and then moves slowly up to the point where is is level with the eyes.

One out of one thousand children suffer from deafness due to maldevelopment of the inner ear.
Middle ear defects occur due to head and neck development issues.
Malformation of the pinna is a common outer ear defect.
These defects are typically caused by Trisomy 18 (also known as Edwards Syndrome).
The syndrome has a very high mortality rate, although survivors who live past the age of 5 can recieve surgery for treatment.
Four Big Ideas
How do the functions of the ear and brain, from fetal state to working state now, correlate to the Four Big Ideas explored in AP Biology?

shaped so that sound waves bounce off of it into the auditory canal in unique ways to distinguish sources of sounds, known as
Sound Localization
The Outer Ear
The Middle Ear
1. The process of evolution drives the diversity and
unity of life.
2. Biological systems utilize free energy and
molecular building blocks to grow, to reproduce and to
maintain dynamic homeostasis.
Parts of the Ear
The Outer Ear:
the external part of the ear filled with air that contains the
auditory canal
The Inner Ear:
the interal section of the ear filled with fluid that contains the
semicircular canals
, and the
2. Sound waves strike the
tympanic membrane
, causing it to vibrate.

The Middle Ear:
the middle section of the ear filled with air that contains the
tympanic membrane
round windows

1. Sound waves enter the auditory canal through the
, traveling by the vibration of molecules.
3. The pressure from the vibrations of the tympanic membrane passes onto the
(hammer), where it is passed to the
(anvil), which is then passed to the
Pressure is multiplied 20x as it passes from one bone to another.
4. The stapes strikes the membrane of the oval window which vibrates.
5. Pressure is the passed to fluid within the cochlea.
Parts of the Cochlea
The cochlea contains the
vestibular canal
cochlear canal
, and
tympanic canal
The Inner Ear
The vestibular and tympanic canals contain perilymph, which is like cerebrospinal fluid.
The cochlear canal contains endolymph, which is like tissue fluid.
Organ of Corti: Hair cells with stereocilia imbedded within the tectorial membrane (gelatinous material).
Basilar Membrane:
lower wall of the cochlear canal.
Connected to the
(auditory nerve).
11. Nerve impulses reaches auditory cortex of cerebral cortex.
6. The stapes strikes the oval window membrane, causing the perilymph in the inner ear to move.
7. Pressure waves from the fluid movement move from the vestibular canal to the tympanic canal across the basilar membrane.
8. The round window membrane bulges.
9. Basilar membrane moves up and down.
10. Stereocilia bend, opening ion channels with the TMHS protein and sending nerve impulses through cochlear nerve.
Elements of Sound
Which pitch we hear depends on which region of the
basilar membrane
that vibrates and the area of the brain that is stimulated.
The region of the basilar membrane which vibrates sends nerve impulses to different parts of the auditory cortex.
of the Organ of Corti reponds to low pitches.
of the Organ of Corti responds to higher pitches.
Volume perception is based on the amplitude of the sound waves.
Kristi Bui, Bhavya Bhushan, Katherine Griffin
In Physics
: Sound is a vibration that travels as audible waves through mediums (ex. air, water).
In application to Biology
: Sound is recepted and percieved by the auditory system including the ear and the brain.
Humans can percieve frequencies from 20Hz to 20000Hz.
The ability to percieve higher frequencies deterioriates as aging occurs.
How does sound travel
in our body?
What is sound?
3. Living systems store, retrieve, transmit and
respond to information essential to life processes.
4. Biological systems interact, and these systems
and their interactions possess complex properties.
Works Cited
Rotational Equilibrium:
1. Endolymph within canal displaces cupula

3 Semiciruclar Canals
Each responds to movement in different planes of space
Base of Canals
: ampulla
: gelatinous material with stereocilia imbedded in its hair cells

rotational and angular movement
How does the brain interpret and utilize
sounds heard?
2. The sterocilia bend and send impulses through the vestibular nerve.
Impulses change as position of the fluid changes
3. Brain responds to these impulses through a motor output- adjusting the bodies position in order to maintain homeostasis
Gravitational Equilibirum:
straight line movement of the head

Calcium carbonate granuales called Otholiths rest on this membrane.
Takes place in the utricle and the saccule, membranous sacs located in the vestibule
Both sacs contain Otholitic Membrane: gelatinous membrane with stereocilia embedded
The biggest stereocilia is called the kinocilium
The utricle is more sensitive to horizontal movement
Difference in signals show which way the head is moving
When the head moves in a straight line the otholiths are displaced and the otholitic membrane sags, bending the stereocilia
The saccule is more sensitive to vertical movements
Stereocilia move towards the kinocilium: nerve impulses increase in the vestibular nerve
Stereocilia move away from kinocillium: nerve impulses decrease in vestibular nerve
When the head is upside down: there are no nerve impulses in the vestibular nerve
The Inner Ear
in relation to the ear
Louder noise is a result of the fluid exerting more pressure, causing the basilar membrane to vibrate more.
Infants - Recognition of Sounds
Infants are highly complex in their capability of recognizing and processing sound.
“Labeling” is a strategy used by many parents to teach their infants how to speak. By “labeling” a certain object with a particular sound, the brain of the infant associates that sound with the object.
By hearing the sound being repeatedly associated with that particular object, the brain will interpret that the sound correlates to the object.
Thus, the brain will utilize the sound to help them recognize objects.
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