Sense of Hearing and Balance ProfAmann The ear One of the sensory organs responsible for hearing and equilibrium. Internal ear External ear Middle ear 1- semicircular canal Auricle( pinna) 2- cochlea External ear canal 3- vestibular nerve 4- auditory nerve
1. Ear drum( tympanic membrane 2. Ear ossicles( malleus, incus, stapes) 3.Tympanic cavity 4. Auditory tube ( eustachian tube)
The External ear
Auricle( pinna) External acoustic meatus
-It collects the -It conducts vibration to ear sound waves and drum (tympanic membrane). protects the It contains ceruminous gland middle and inner that secrete ear wax ear. -it moved by the action of ear Mm. Auricular Cartilage
external Ear tube Cartilage The middle ear
Irregular space within the temporal bone filled with air.
Auditory ossicles Tympanic cavity طبلة االذن Ear drum Auditory tube & المطرقة tympanic membrane( -malleus) (eustachian tube) السندان Separates outer ear -incus - الركاب from middle ear - stapes - Barrier from foreign objects It convey the vibration from the external ear to the -Cone-shaped in internal ear. appearance, Vibrates in response to sound waves.
Conduction ◦ Conduct sound from the outer ear to the inner ear Protection ◦ Creates a barrier that protects the middle and inner areas from foreign objects ◦ Middle ear muscles may provide protection from loud sounds Transducer ◦ Converts acoustic energy to mechanical energy Amplifier ◦ Transformer action of the middle ear ◦ only about 1/1000 of the acoustic energy in air would be transmitted to the inner-ear fluids (about 30 dB hearing loss) MUSCLES OF MIDDLE EAR Tensor tympani Ms. : attached to the tympanic membrane.it Helps open Eustachian tube
Stapedius Ms. : attached to the stapes, Contracts in Response to Loud sounds, chewing, speaking; Facial (VIIth cranial) nerve.
there are four opening in the middle ear: 1-The oval window: Bet. Stapes and cochlea filled by base of stapes, Lead to internal ear.
2-The round window: Bet. Cochlea and tympanic cavity and covered by 2ry tympanic membrane, lead to internal ear
3-The opening of the auditory tube. The m.m. of the tympanic cavity continuous with that of the pharynx through the auditory tube.
4-The opening of ear canal through tympanic membrane.
Auditory (Eustachian) tube it connects tympanic cavity with pharynx
Two openings: •ostium pharyngeum tubae •ostium tympanicum tubae.
Function: • Equalizes pressure on both sides of tympanic membrane for optimal hearing. N.B. Normally closed except during yawning or swallowing Not a part of the hearing process
في الصعود على جبل او فى الطيارة فإن ضغط الهواء سيكون منخفضاً وهذا يجعل طبلة األذن تتوتر إلى الخارج، فإذا بلع اإلنسان ريقه فإن العضلة موترة شراع الحنك ) (tensor veli palatiniستتقلص وتسمح بالهواء بالهرب من األذن الوسطى، مما يعادل الضغط فيها ويرجع طبلة األذن إلى شكلها الطبيعي. فإذا نزل اإلنسان من الجبل فإن الهواء سيدخل من جديد.
إذا كنت مصاب بالزكام فإن القناة ستتورم وسيقل الهواء الداخل والخارج عبرها. لذلك فإن الهواء ال يستطيع أن يدخل: فربما تشعر بألم في أذنك وأحياناً إلى حد تمزق طبلة األذن.
تصريف المخاط من األذن الوسطى: إذا أصيب اإلنسان بالتهاب أو حساسية المجاري التنفسية العليا فممكن أن تتورم قناة أوستاكي وتتكاثر فيها البكتيريا، مما يسبب التهابات األذن.
ألم األذن أكثر شيوعاً في االطفال ألن قناة أوستاكي عندهم تكون أكثر أفقية وأضيق مما هي عند الكبار، مما يجعل حركة اإلفرازات عبر القناة أصعب مما هي في الكبار. The internal ear
menbranous labyrinth Osseous labyrinth Cochlear labyrinth 1-semicircular canal •Vestibular membrane 2- cochlea •Basilar membrane 3-vestibule Vestibular labyrinth •Utricle it contain perilymph •saccule
It contains endolymph Function of inner ear: Converts mechanical sound waves to neural impulses that can be recognized by the brain for ◦ Hearing ◦ Balance
The cochlea resembles a snail shell and spirals around a bony column (Snail-shaped organ with a series of fluid-filled tunnels) Snail shaped cavity within mastoid bone
The Perilymph: found between the osseous and membranous labyrinth. The Endolymph: found inside the membranous labyrinth. The acoustic nerve (vestibulocochlear N.) ( VIII) distributed within the membranous labyrinth Within the cochlea are three canals: ◦ Scala Vestibuli ◦ Scala Tympani ◦ Scala Media The end organ of hearing; contains stereocilia and hair cells. 8th Cranial Nerve or “Auditory Nerve” carries signals from cochlea to brain Fibers of the auditory nerve are present in the hair cells of the inner ear) from cochlea to brain through inner acoustic meatus). Auditory Cortex: Temporal lobe of the brain where sound is perceived and analyzed.
23 Sound waves reaching the ear are directed by the pinna to the external auditory meatus and then to the tympanic membrane. vibrate like a drum, and changing it into mechanical energy.
The malleus, connected to the tympanic membrane’s inner surface, passes on and amplifies vibrations via the incus and stapes to the oval window.
Vibrations of the oval window by the stapes sets the perilymph into a wave motion that travels through the membranous labryinth to the round window. The round window bulges into the middle ear and then back into the membranous labryinth , reversing the fluid wave movement and generate wave motion of the endolymph within the cochlear duct displacing the hair cells of the spiral organ.
The movement of the hair cells of the spiral organ (Organ of Corti) that present at cochlear tympanic membrane to develops a nerve impulse.The nerve impulse passes through the cochlear branch of the vestibulocochlear nerve (CNVIII) to the hearing centers in the brain.
Consists of three semi-circular canals Shares fluid with the cochlea Controls balance No part in hearing process Hair cells at the ampulla that conduct waves to vestibular branch of vestibulocochlear nerve.