Regional Anatomy II Week 8 SU22 PDF

Week 8 Ear Auditory Transduction Ear Three parts 1. 2. 3. External Middle Internal/inner External Ear Consists of auricle (pinna) and external acoustic/auditory meatus. Auricle - made up of elastic cartilage covered with skin ● ● ● ● ● ● Helix - rim of auricle (resembles beginning of a spira...

Week 8 Ear Auditory Transduction Ear Three parts 1. 2. 3. External Middle Internal/inner External Ear Consists of auricle (pinna) and external acoustic/auditory meatus. Auricle - made up of elastic cartilage covered with skin ● ● ● ● ● ● Helix - rim of auricle (resembles beginning of a spiral) Anti-helix - curved eminence anterior to the helix Concha - most depressed area of auricle, anterior to antihelix Tragus - small prominence that overhangs entrance to external acoustic meatus Anti-tragus - small tubercle posterior to tragus Lobule - non-cartilaginous part of auricle (consists of loose connective tissue and fat covered with skin) External Ear External acoustic/auditory meatus ● ● ● ● ● Curved, blind-ended canal that conducts sound waves from the auricle to the tympanic membrane Can be straightened for examination by pulling auricle upward and backwards Lateral part has cartilaginous walls (the cartilage is continuous with that of the auricle) Medial part has no bony walls (squamous and tympanic parts of temporal bone) Lined by skin (continuous with skin of auricle) Tympanic Membrane ● ● ● ● ● Thin membrane located at the medial end of the EAM, it forms the boundary between the external and middle ear. Concave laterally at the umbo, which is the most drawn in part of the membrane Handle and lateral process of malleus are firmly attached to its inner surface and can be seen on otoscopic examination When the membrane is illuminated, its concavity produces a cone of light that radiates from the umbo Covered with thin skin externally and mucous membrane of the tympanic cavity internally.There is a fibrous tissue (tense part) that is deficient superiorly (flaccid part) Clinical Considerations Ear infections and glue ear Tinnitus Clinical Considerations Ear infection ● Aka otitis media; an infection of the ear that can either be viral or bacteria ○ ● ● Can occur in any of the three parts of the earl Can be chronic or acute ○ ● Can develop from infected or enlarged adenoids blocking drainage from the eustachian tube ~80% of children develop an acute ear infection at some point ○ ● Bacteria - Streptococcus pneumoniae or haemophilus influenzae Infants who are bottle fed have a higher incidence of ear infection Symptoms of infection may include: ○ ○ ○ ○ Pain and/or/discomfort inside the ear Feeling of pressure inside the ear Pus-like drainage Hearing loss Clinical Considerations Glue ear ● Aka, otitis media with effusion, or serous otitis media. Occurs where the middle ear fills with fluid ○ ○ ○ ● ● May cause an ear infection Can cause temporary hearing loss More common in children, the most common cause of hearing impairment in children Can clear up on its own after ~3 months Not to be confused with adhesive otitis, which is a condition where the tympanic membrane is retracted and becomes stuck in the middle ear space ○ A form of chronic otitis media Clinical Considerations Tinnitus ● ● Ringing of the ears that affects 10-15% of the population Causes may include: ○ ○ ○ ○ ○ ○ ○ Sensorineural hearing loss/cochlear damage Ototoxic drugs, i.e. aspirin Ear infections Head injury or brain tumor Anxiety or depression Vit. B12 deficiency Meniere’s disease Middle Ear Middle Ear Tympanic cavity ● ● Small, air-containing cavity in petrous part of temporal bone Contains auditory ossicles (malleus, incus, and stapes) that transmit vibrations from tympanic membrane to internal ear Walls ● ● ● ● Roof - thin, bony plate that separates tympanic cavity from middle cranial fossa Floor - thin bony plate that separates tympanic cavity from the IJV Anterior wall - separates tympanic cavity from internal carotid artery. Two openings lead into auditory tube and a canal for the tensor tympani muscle Posterior wall - has an irregular opening which communicates tympanic cavity with mastoid antrum. This antrum communicates inferior and posterior with mastoid air cells Middle Ear Tympanic Cavity ● ● ● Posterior wall (cont.) -pyramidal eminence houses the stapedius muscle. The tendon of the stapedius emerges through the small opening at the tip of the pyramidal eminence and inserts into the stapes Lateral wall - formed mostly by tympanic membrane Medial wall - separates the middle ear from the internal ear. ○ Promontory - rounded elevation produced by underlying 1st turn of chochlea Middle Ear There are three auditory ossicles 1. Malleus a. b. 2. Incus a. b. 3. Articulates with body of incus Receives insertion of tensor tympani muscle Articulates with head of stapes Articulates with head of malleus Stapes a. b. c. Head articulates with the incus Neck receives insertion of stapedius muscle Base attached to margins of oval window Middle Ear ● Movements of ossicles are modified and dampened by protective action of two small muscles ○ ○ Tensor tympani Stapedius Middle Ear ● Tensor tympani ○ ○ ○ Inserts into handle of malleus Innervated by mandibular nerve Action - draws handle of malleus and tympanic membrane medially to dampen the vibrations of tympanic membrane Middle Ear ● Stapedius ○ ○ ○ Located within pyramidal eminence of posterior tympanic cavity and inserts into stapes Innervated by facial nerve (nerve to stapedius branch) Action - Tilts stapes and dampens its vibrations Eustachian Tube ● ● ● ● ● ● Aka pharyngotympanic tube Canal that communicates nasopharynx with tympanic cavity and allows for equalization of pressure on both sides of tympanic membrane Begins in anterior wall of tympanic cavity and ends in lateral wall of nasopharynx Posterior ⅓ (close to tympanic cavity) has bony walls Anterior ⅔ (close to pharynx) has cartilaginous walls Contraction of tensor veli palatini (swallowing, yawning) helps open lumen of auditory tube Internal Ear ● ● Bony labyrinth - series of cavities within petrous portion of temporal bone Membranous labyrinth - series of membranous sacs and ducts contained within bony labyrinth Internal Ear Bony labyrinth ● ● ● Contains clear fluid (perilymph) that circulates through the sacula vestibula and sacula tempani. Perilymph composition is similar to intracellular fluid Three semicircular canals (anterior, posterior, and lateral) are perpendicular to each other and open into posterior part of vestibule. Each canal has a swelling at one end called the ampulla Cochlea resembles a snail shell and consists of central pillar (modiolus) around which a bony tube makes approximately 2 ½ turns. The central channel, called the cochlear duct, contains circulating endolymph. It is compositionally CSF and is connected to the subarachnoid space through the perilymphatic duct Bony labyrinth within the temporal bone 1. 2. 3. Vestibule (central part) Cochlea (anterior to vestibule) Semicircular canals (posterior to vestibule) Internal Ear Membranous labyrinth ● ● ● The channels created by bony labyrinth and are filled with perilymph Central canal is filled with endolymph Main channels include: ○ ○ ○ Utricle and saccule (lie within vestibule of bony labyrinth) 3 semicircular ducts (lie within 3 semicircular canals) Cochlear ducts (lies within body cochlea) Posterior: Lateral head flexion Anterior: Flexion/extension Lateral: Left/right todation Utricle: Sensitive to horizontal acceleration Saccule: Sensitive to vertical acceleration Internal Ear Membranous labyrinth summary: 1. 2. 3. 4. 5. Utricle and saccule are otoliths that contain specialized receptors (maculae) sensitive to the position of the head with respect to gravity and linear acceleration Ampulla of each semicircular duct contains a specialized receptor (crista ampullaris) sensitive to angular acceleration Cochlear duct contains a specialized hearing receptor called the spiral organ/organ of Corti Maculae and cristae ampullares are innervated by the vestibular part of CNVIII Spiral organ is innervated by cochlear part of CNVIII