Special Senses: Ear (Hearing and Balance) Flashcards
The ear houses two senses:
Hearing and Equilibrium (balance)
Are involved in both hearing and the
detection of equilibrium,
Mechanoreceptors
The ear is divided into three areas
External (outer), middle, and internal (inner)
Involved only in collecting sound waves
External ear
→ The fleshy part on the outside of the head, primarily made of elastic cartilage covered with skin.
→ Its shape collects and directs sound towards the auditory canal.
Auricle (pinna)
A short, narrow chamber (~1inch long and 1/4 inch wide) carved into the temporal bone, lined with skin and ceruminous glands.
External acoustic meatus (auditory canal)
Protects the tympanic membrane
Cerumen (earwax)
→ A thin, semi-transparent membrane separating the external ear from the middle ear.
Tympanic membrane (eardrum)
Inner layer of the eardrum is made of
Simple cuboidal epithelium
Middle layer of the eardrum is made of
Connective tissue
Outer layer of the eardrum is made of
Stratified squamous epithelium
→ Air-filled mucosa-lined cavit within the temporal bone Involved only in the sense of hearing.
→ Located between tympanic membrane and oval window and round window
Middle ear cavity
→ Connects the middle ear to the throat, equalizing air pressure in the middle ear cavity so the eardrum can vibrate
→ Actions likes wallowing, yawning, or chewing can open the tube, relieving pressure on the tympanic membrane.
→ Equalizes pressure in the middle ear cavity so the eardrum can vibrate
Pharyngotympanic tube (Auditory tube)
These bones transmit vibrations from the tympanic membrane to the inner ear
Auditory ossicles
Vibrations travel from the…
Hammer to anvil to stirrup to oval window of inner ear
Houses sense organs for both hearing and balance, located within the bony labyrinth of the temporal bone.
Internal (inner) ear
Bony labyrinth (Osseous labyrinth) is divided into three regions:
Vestibule, cochlea, semicircular canals
Bony labyrinth is filled with
Perilymph
→ Resembles the bony labyrinth but is smiley and filled with endolymph (clear fluid).
Membranous labyrinth
The space between the bony labyrinth and the membranous labyrinth is filled with ______
perilymph
→ Similar to blood plasma; high sodium and low potassium concentration.
→ Supplies mechanical stimuli to the cochlea and vestibule
perilymph
→ Low sodium and high potassium concentration
→ Created from perilymph; essential for hearing and balance.
Endolymph
→ Located within the cochlear duct
→ Receptors = hair cells on the basilar membrane
→ Gel-like tectorial membrane is capable of bending hair cells
→ Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex in the temporal lobe
Spinal Organ of Corti
Where can the hair cells be found
Basilar membrane
→ Disturb the short, stiff fibers of the basilar membrane, stimulating receptor cells near the oval window.
→ Since high-pitched sounds have more energy, they can stimulate receptor cells close to the eardrum.
high pitched sounds
Since high-pitched sounds have more energy, they can stimulate receptor cells close to the
eardrum
The membranous labyrinth of the cochlea forms the cochlear duct, which is filled with
endolymph
Where are the hearing receptors housed?
Spinal organ of corti
Hearing receptors
hair cells
Above the cochlear duct, filled with
perilymph.
Scalar vestibuli
Below the cochlear duct, also filled with perilymph.
Scalar Tympani
The vestibular membrane borders
the
scala vestibuli
the basilar membrane borders the
scala tympani
pressure waves cause vibrations in the basilar membrane within the
spiral organ of Corti.
Once the hair cells are stimulated,
they send nerve impulses through the _____ to the auditory cortex in the temporal lobe of the brain.
cochlear nerve,
Equilibrium is the body’s ability to maintain balance and orientation in response to head movements.
Equilibrium
The receptors for equilibrium are located in the inner ear, collectively known as the
vestibular apparatus
Static equilibrium is monitored by the
Maculae
Dynamic equilibrium is monitored by the
Crista Ampullaris
→ are the receptors for static equilibrium, located within the vestibule’s membranes.
→ They report the position of the head concerning gravity when the body is at rest, Help us keep our head erect
Maculae
→ Information from the maculae is transmitted via the vestibular division of the ____________ to the cerebellum and the cerebral cortex of the brain.
vestibulocochlear nerve (Cranial Nerve VIII)
Are embedded in a gelatinous structure known as the otolithic membrane.
Hair cells
→ is studded with otoliths—tiny stones made of calcium carbonate that float in a gel around hair cells
→ Movements cause otoliths to roll and bend hair cells
Otolithic membrane
→ It serves as the receptor for dynamic equilibrium
→ Located in the ampulla ofeach semicircular
→ There are three semicircular canals, oriented in different planes
○ Transverse plane, coronal plane, sagittal plane
Crista Ampullaris
Each Crista Ampullaris consists of a ridge of epithelium with a curved gelatinous mass called the _____.
cupula
→ When the head moves in a rotational or angular motion, the endolymph within the semicircular canals moves, displacing the cupula.
→ The movement of the cupula bends the hair cells, stimulating them to send impulses through the vestibular nerve to the cerebellum, which helps maintain balance during motion.
Mechanism of dynamic equilibrium
→ When the head moves, the otoliths shift, causing the otolithic membrane to bend, which in turn bends the hair cells.
→ This bending stimulates the hair cells, sending impulses via the vestibular nerve to the brain.
Mechanism of static equilibrium
→ results when the transmission of sound vibrations through the external and middle ears is hindered
→ Causes:
○ Buildup of earwax
○ Fusion of ossicles
○ Ruptured eardrum
○ Inflammation of the middle ear
→ This can be temporary or permanent.
Conduction deafness
→ Occurs due to damage or degeneration of the receptor cells in the cochlea, the cochlear nerve, or neurons in the auditory cortex.
→ Often results from prolonged exposure to loud sounds.
→ Often results from prolonged exposure to loud sounds.
Sensorineural deafness
→ A disorder affecting the inner ear,
leading to progressive deafness and
vertigo (a severe spinning sensation). → The condition can cause extreme
discomfort and instability.
Meniere’s syndrome
