THE
NERVOUS
SYSTEM:
THE EAR
EMILY TORRES
ARIANA SOTO
PER: 5
SENSE OF HEARING
• The Ear enables us to be able to:
- hear sound waves
- have sense of equilibrium
• The Ear is composed of the:
- Outer (External) Ear
- Middle Ear
- Inner (Internal) Ear
OUTER (EXTERNAL)
EAR
• The Outer Ear consists of these
structures:
- Auricle (Pinna)
- External Auditory Canal
- Tympanic membrane
• The opening before the temporal bone,
there are hairs that guard the canal and
skin that contains ceruminous glands.
- Ceruminous glands secrete
cerumen (wax)
- wax helps keep foreign particles
out
MIDDLE EAR
• The middle ear consists
of these structures:
- tympanic membrane
- auditory ossicles:
i. Malleus
ii. Incus
iii. Stapes
- oval window
- tensor tympani
- stapedius
MALLEUS, INCUS, &
STAPES
•
These three bones connect the tympanic
membrane and inner (internal) ear by tiny
ligaments
•
Malleus
- vibrates at the same time as
tympanic membrane, then causing the
incus to vibrate
•
Incus
- vibrates and sends the vibrations on
to the stapes
•
Stapes
- vibrates and sends a fluid into the
inner ear through the oval window
TENSOR TYMPANI &
STAPEDIUS
• Tensor tympani
- connected to the wall of the auditory tube
- pulls malleus inward when contracted
• Stapedius
- pulls the stapes outward
• These involuntary actions are part of the
effectors in the tympanic reflex
TYMPANIC REFLEX
• Occurs in about 1/10th of a second after a loud sound in
order to protect the hearing receptors from possible
damage from a loud external noise
- also occurs when a person is simply talking or
singing
AUDITORY TUBE & EAR
PRESSURE ADJUSTMENT
• Connects each middle ear
to the nasopharynx
• Helps provide equal air
pressure on each side of
the tympanic membrane
EAR INFECTIONS
• Infection of the middle ear
• Most common ear infection
is otitis media and is
usually a result from:
- common cold
- flu
- allergies
- sinus infection
INNER (INTERNAL)
EAR
• Structures include;
• Cochlea
• Semicircular canals
• Vestibule
COCHLEA
• Fluid filled snail-like structure
that contains the receptor organ
for hearing
Spiral organ of Corti
• Divided into 3 chambers
• Contains hair cells
• 2 types of fluid
• Perilymph
• Endolymph
COCHLEA CHAMBERS
• Scala Vestibuli• Perilymph (provides
cushioning support, similar
to interstitial fluid)
• Scala Media• Endolymph
• Organ of Corti
• Scala Tympani• Perilymph (provides
cushioning support, similar
to interstitial fluid)
ORGAN OF CORTI
• Found on basilar
membrane in the scala
media chamber
• Sensory organ of
hearing
• Sound sensitive hair
cells
• Pressure change
causes hair cells to
bend and stimulate a
nerve signal which is
carried to the brain
• This is how sound
can be recognized
SEMICIRCULAR
CANAL
• Body’s balance organ
• 3 canals (superior,
horizontal, and posterior)
filled with endolymph
that are each responsible
for detecting motion on a
different plane
• Sense head
rotations/movement
VESTIBULE
• Senses movement
• Holds 2 sacs of fluid
•  the ultricle & the saccule
• Hair cells
• Macula
• Known as gravity receptors
EQUILIBRIUM
• State of balance
• Condition in which contending forces are equal
• 2 types:
• Static
• Dynamic
STATIC EQUILIBRIUM
• Occurs when the body is motionless or moving in a
straight line
• Maintains stability and posture
• Entrance of inner ear is the Vestibule
• Vestibule contains 2 sacs of fluid (Ultricle & Saccule)
• The maculae of the ultricle and saccule are the gravity
receptors that respond to linear acceleration, deceleration,
and position in space
• Otoliths are calcium carbonate particles found in the fluid
• When your head moves, the otoliths bursh against the hair
cells that line the utricle & saccule
• Sends message to brain
STATIC EQUILIBRIUM
DIAGRAM
DYNAMIC
EQUILIBRIUM
• Occurs when the body is moving in a rotational or angular
direction (spinning)
• Detects motion
• Sense of balance is interpreted in the Semicircular Canals
• Ampullae, the organs of dynamic equilibrium, are located
at the base of each semicircular canal
• A gelatinous cupula is found in the ampullae
•
•
Hair cells found on the cupula respond to movement
When head rotates, endolymph moves and flows into the
ampulla and causes the cupula to bend which triggers the
hair cells to send messages to the brain
DYNAMIC EQUILIBRIUM
DIAGRAM
SOUND COLLECTION & PATHWAY
THROUGH THE EAR CANAL
• The Auricle (Pinna)
- collects sound waves in the air,
then sends them into the auditory
canal
• The Auditory Canal
- once sound waves enter here and
pass to the end of the canal, they
alter pressure on the tympanic
membrane
• The Tympanic Membrane
- moves back and forth due to sound
waves, which then makes the
vibrations
MALLEUS, INCUS, &
STAPES (OSSICLES)
•
These three bones connect the tympanic
membrane and inner (internal) ear by tiny
ligaments
•
Malleus
- vibrates at the same time as
tympanic membrane, then causing the
incus to vibrate
•
Incus
- vibrates and sends the vibrations on
to the stapes
•
Stapes
- vibrates and sends fluid into the
inner ear through the oval window
(CONTINUED)
•
The Oval Window
- is an opening that transmits pressure
waves of sound into the cochlea
•
The Round Window
-waves move to the round window and
it releases pressure caused by the
vibrations of the stapes in the oval
window
•
The Cochlea
- sound waves make fluid in cochlea
move and trigger the hair cells to move
as well. The hair cells located on the
organ of corti separate the sound
waves according to their frequencies
(CONTINUED)
• The Auditory Nerve
- hair cells cause an electrical
signal to travel through the
auditory nerve and to your
brain
• The Brain
- the brain responds to these
separate frequencies and
makes a complete sound from
them
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•
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•
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•
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•
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n.d. Web. 30 Apr. 2015.
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