The Ear - Application

what are the three divisions of the ear

external ear, middle ear, inner ear

what is the function of the cartilage in the ear

what makes the ear flexible

what is the function of the auricle

• external, visible part of the ear

• supported by cartilage

• captures and directs sound waves into the external acoustic meatus

what is the role of the external acoustic meatus

• canal that extends medially towards the middle ear

what is the ceruminous glands

• distributed along the EAM secrete waxy substance (cerumen); protective function

where are the debris trapping hairs located

• in the external ear

what is the tympanic membrane

• colloquially referred to as the eardrum

• separates the external ear from the middle ear

• vibrates in response to sound waves

what is the function of the middle ear

• collects and amplifies sound waves

• transfers sound waves to the inner ear via the auditory ossicles

what are the auditory ossicles

• smallest bones in the body

• 3 bones in the middle ear

• connect the tymapnic membrane with the inner ear (oval window)

what are the functions of the muscles of the middle ear

• to dampen loud sound transmission through the middle ear

what is the eustachian tube

• aka the pharyngotympanic tube

• air filled passageway that connects the pharynx and middle ear

what is the function of the eustachian tube

• equalize pressure between the middle ear and the external environment

what what the pathologies of the eustachian tube

• microorganisms can travel from the pharynx into the middle ear, resulting in an ear infection (otis media)

what is the inner ear

• innermost compartment of the ear

• encased in temporal bone

• sensations of hearing and balance detected by receptors in the inner ear

• innervated by branches of CN VIII

what are the functions of the of the semi-circular canals & vestibule in the inner ear

• receptors detect sensations of gravity, linear acceleration, rotation (balance)

what is the organ of hearing

cochlea

what is the bony and membranous labyrinth

• bony outer wall of the inner ear fused with the temporal bone (bony labyrinth)

• contains fluid: perilymph, in which the membranous labyrinth is situated

what is the membranous labryinth

• series of fluid - filled chambers that contain the receptors for hearing and balance (equilibrium)

• filled with endolymph fluid

• surrounded by the bony labyrinth and perilymph

what is the vestibular system

• part of the inner ear that provides equilibrium sensations by detecting rotation, gravity and acceleration

• helps with balance & spatial orientation

• maintains stability and posture

what does the vestibular system consist of

1. semi-cicular canals

2. vestibule

what are the semi-circular canals

• 3 semi- circular canals

• detect rotational movement of the head across 3 different planes

what do the semi-circular canals contain

• contain sensory receptors (hair cells) that respond to rotational movement of the head

what are hair cells

• sensory receptors of the inner ear are called hair cells

• highly specialized mechanoreceptors sensitive to the distortion of their stereocilia

• detect equilibrium sensations in the vestibular system, and hearing in the cochlea

where are the hair cells embedded?

• sensory hair cells are embedded in gelatinous mass called the cupula; surrounded by endolymph

how do we sense rotational movement

• when the head rotates, movement of the endolymph pushes the cupula and distorts the stereocilia of the hair cells

• the receptors within each semi-circular duct respond to rotational movement of the head along 3 axes

which parts of the semi- circular canals sense the yes, no and tilting head to side movement

yes = anterior

lateral = no

posterior = tilting head to side

what is the purpose of the vestibule

contain sensory receptors that detect: gravity, linear acceleration

what is the macculae

clustered hair cells

what is the gelatinous mass

• where hair cells processes are embedded

• the surface of this mass contains densely packed otoconia

what is otoconia

on the surface of the gelatinous mass and is packed calcium carbonate crystals

how is the macula during resting/ normal position

in a normal upright position otoconia and gelatinous mass rest on top of the macula with their weight pressing down on hair cells

how is the macula in a tilted position

• the pull of gravity shifts the otoconia and the gelatinous mass, distorting the sensory hair cells, which send a signal to the CNS

where does CN VIII pass through

internal acoustic meatus

what are the three different parts of the cochlea

cochlear ducts (scala media), vestibular ducts (scala vestibuli) and tympanic duct (scala tympani)

which parts of the coclhea are surrounded by endolymph and perilymph

endolymph: cochlear duct

perilymph: vestibular duct, tympanic duct

where is the organ of corti located

• located in the cochlear duct

• converts sound waves into electrical signals that can be transmitted to the brain via CN VIII

what is the first step in the process of hearing

• the sound waves enter the External Acoustic Meatus (EAM) and cause vibration of the tympanic membrane

what is the second step in the process of hearing

• movement of the tympanic membrane vibrates the ossicles and amplifies sound

what is the oval window / function

• the stapes pushed against the oval window to transmit sound waves into the inner ear (opening is covered by a membrane)

• vibration cause movement of the fluid filled scala vestibuli and tympani

what is the round window

• allows fluid in the cochlea to move

• pressure is relieved at the round window

what is the third step in the process of hearing

• stapes pushed against oval window causing wave sin the perilymph

what is the fourth step in the process of hearing

• waves distort the cochlear duct and the organ of corti (basilar membrane)

what is the fifth step of the process of hearing

• vibration of the basilar membrane causes vibration of hair cells (stereocilia) against the tectorial membrane resulting in hair cell stimulation

what is the sixth step in the process of hearing

• this is where information concerning pitch, intensity is relayed to the CNS (temporal lobe) via CN VIII

what seals the scala tympani

sealed by the membrane of round windows

what is the membrane of round windows like/ why is it important?

membrane is flexible: prevents pressure build up and allows for movement of the basilar membrane

what detects pitch

• hair cells at the base of the cochlea detect high pitch sounds

• hair cells towards the top of the cochlea detect low pitch sounds

• the brain uses spatial information to determine pitch

what detects sound intensity

• louder sounds generate larger movements of the basilar membrane

• greater vibration amplitude causes greater bending of stereocilia

what is conductive hearing loss

• when sound waves cannot reach inner ear

• sound blocked by the external/ middle ear

what is sensorineural hearing loss

• pathology/ injury of the inner ear structures and/or auditory nerve pathway

• usually permanent but can be mild to total hearing loss