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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• "Sense of Balance." Flashcards. N.p., n.d. Web. 30 Apr. 2015.

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