ইমু..., EAR Definition - It is an organ of hearing and equilibrium. Parts of the ear –External.Middle.Inner ear.External ear – External ear consist of auricle External acoustic meatus.Auricle or, Pinna – It is a shell like projection from the side of the ear which collects sound vibration from the external environment. Features – it consists of Lateral surface. – it is irregular in shape and consists of elevation and depression.Helix – It is the prominent outer rim of the auricle.Antihelix – It is another prominent margin situated in front and parallel to the helix.Scaphoid fossa – Narrow area between the helix and Antihelix.Tragus – A smaller elevation guarding the depression of the concha.Anti-tragus – A triangular elevation opposite to the tragus and separated from the tragus by inter-tragic notch.Medial surface or, cranial surface.Lobule of the ear – It is mass fibro-fatty tissue covered by skin situated below the level of the anti-tragus. Structure:- Consist of Cartilage - Cartilage is elastic type and absent in lobule.Muscles and ligaments.Fibro fatty tissue covered by skin. N.S: (Sensory):Upper 2/3rd of the lateral surface: Auriculo temporal nerve by the mandibular nerve.Upper 2/3rd of the medial surface: lesser occipital nerve.Lower 1/3 of the both lateral and medial surface: Greater auricular nerve.Root of auricle auricular branch. of vagus nerve.External acoustic meatus: It is a canal forming part of the external ear which is responsible for conduction of sound wave from concha to the tympanic membrane. Extension - Concha to the tympanic membrane. Shape: S shaped. Length: 26 mm. Parts:according to structure:Cartilaginous part (lat 1/.3rd) - elastic cartilage in nature and continuous with the cartilage of the auricle.Bony part (medial 2/3rd) Formation – Mainly – Tympanic plate of the temporal bone. – Anterior wall, floor and lower ½ of the posterior wall. Partly – Squamous part of the temporal bone.According to direction:Pars externa (directed - upward, forward and medially)Pars intermedia(directed - upward, backward and medially)Pars interna (directed - downwards, forwards and medially) Lining epithelium – Keratinized stratified sq. epithelium with numerous sebaceous and ceruminous gland. These ceruminous glands are the modified sweat gland which secrets secret ear wax or cerumen which prevent the entry of foreign particles, it also maintain a warm humid weather for proper vibration of the tympanic membrane. Artery supply of the external acoustic meatus–Auricular branch of the superfiscial temporal artery, maxillary artery,Posterior auricular artery branch of the external carotid artery. Venous drainage of the external acoustic meatus – Drains into external jogular and maxillary vein. Nerve supply of the external acoustic meatus – Anterior part - Auricular branch of the temporal nerve branch of the mandibular division of the trigeminal nerve. Posterior part - Auricular branch of the vagus nerve. Development of external acoustic meatus – Dorsal part of the 1st branchial cleft.Tympanic membrane – It is a oval shaped, semi-transparent cuticulo-muco-fibrous partition between the external auditory meatus and middle air cavity. Another name - Air drum. Colour - Pearly grey in colour. Position - Obliquely placed making an angle of 55 degree with the floor of the external auditory meatus. Direction - Directed downwards, forwards and laterally. Surface - It consists of 2 surfaces –Lateral surface – Is concave.Medial surface – is convex. The maximum point of the convexity is called Umbo. The Umbo is point of rupture of the tympanic membrane. Subdivision of the tympanic membrane – The tympanic membrane is divided into 2 parts by 2 maleolar folds. The parts are –Pars flaccida –It is the part above the maleolar fold.It is thin and lax.Intermediate fibrous tissue is absent.It is also known as Sharpnell’s memebrane.Pars Tensa.Pars tensa is tense due to attachment of the handle of the maleus.It presents all 3 layers including the middle fibrous layer. Structure of the tympanic membrane – The tympanic membrane consist of 3 layers. Which are from inside to outside -Outer Skin – Lined by keratinized stratified squamous epithelium without hair follicles and sweat and sebaceous glands.Middle fibrous layer – This layer consist of outer radiating and inner circular fibers. In the pars tensa this layer contain handle of the maleus and Chorda-tympanic nerve. In the pars flaccida this layer contains fibro-fatty tissue.Inner mucous layer – Covered by mucous membrane which is lined by simple columnar epithelium (Cilliated). Artery supply of the tympanic membrane – Lateral surface - Deep auricular artery branch of the maxillary artery. Medial surface - Anterior tympanic artery branch of the maxillary artery. Venous drainage of the tympanic membrane – Lateral surface - External jogular vein. Medial surface - Pterygoid venous plexus. Nerve supply of the tympanic membrane – Lateral surface - Auriculo temporal nerve branch of the mandibular nerve. Medial surface - Tympanic branch of the glossopharyngeal nerve. Development of the tympanic membrane –Cuticular part – From the ectoderm of the dorsal end of the 1st branchial cleft.Fibrous part – Mesoderm surrounding branchial arches.Inner mucous part – Tubo-tympanic reces of the 1st and 2nd pharyngeal pouches. Cone of light – During otoscopic examination antero-inferior part of the tympanic membrane reflect more light and is known as the cone of light. Function of the tympanic membrane – Transmission of vibration of the sound from the external acoustic meatus to the middle ear cavity.Middle Ear cavity – Definition – It is an irregular space within the Petrous part of the temporal bone which is functionally concerned with transmission of vibration from the tympanic membrane to the internal ear. Location – Within the Petrous part of the temporal bone. Measurement – Vertical - 15 mm. Anterior-posterior - 15mm Boundary of the Middle ear cavity –Roof – Tegmen tympani of the temporal bone.Floor – Jogular fossa that lies on the inferior surface of the Petrous part of the temporal bone. Anterior wall –Canal for tensor tympani.Canal for auditory tube.Posterior wall of the carotid canalPosterior wall –Adidus to mastoid antrum.Pyramidal eminence.Vertical part of the facial canal.Medial wall –Oblique part of the facial canal.Promontory.Fenestra vestibullae.Fenestra cochlea.Lateral wall – Tympanic membrane. Content –Air.3 ossicles –Maleus.Incus.Stapes.2 muscles –Tensor tympani.Stapedius.Nerves –Chorda tympanic nerve.Tympanic plexus.Blood vessels - which supply the middle ear cavity. Ear ossicles –Maleus.Incus. Stapes. Incuddo-stapedial joint – Ball & socket variety of the Synovial joint. It is the smallest ball & socket joint of the body. Largest is hip joint. Muscles of the middle ear cavity –Tensor tympani – Supplied by the main trunk of the mandibular nerve. It makes the tympanic membrane tense.Stapedius – Supplied by the facial nerve. Draws the stapes laterally. Parts of the middle ear cavity – The tympanic cavity consist of 3 parts divided by the tympanic membrane Epitympanum – Part above the level of the tympanic membrane.Mesotympanum – Part opposite the tympanic membrane.Hypotympanum – Part below the level of the tympanic membrane. Features of the medial wall of the middle ear cavity – Formation - Formed by the bony labyrinth of the internal ear. Promontory – It is rounded bony elevation due to 1st turn of the cochlea of the internal ear. Fenestra vestibullae – It is a oval shaped gap which communicates with between the middle ear and vestibule of the internal ear. It is situated above and behind the promontory and usually closed by the foot plate of the stapes. Fenestra cochlea – It is a rounded gap which communicates between the middle ear cavity and the cochlea of the internal ear. Features of the lateral wall of the tympanic cavity presents –Tympanic membrane.Anterior and posterior canaliculi for the chorda-tympanic nerve.Ptero-tympanic fissure.Epitympanum. Features of the posterior wall of the tympanic cavity –Aditus of the mastoid antrum.Fossa indicus.Pyramid.Vertical part of the facial nerve canal.Posterior canaliculus for the chorda tympanic nerve. Communication of the middle ear cavity – Anteriorly - With Nasopharynx through the auditory tube. Posteriorly - With the mastoid antrum through the aditus. Medially - With the internal ear by Fenestra vestibullae & Fenestra cochlea. Artery supply of the middle ear cavity –Anterior tympanic artery branch of the maxillary artery.Superior tympanic artery branch of the middle meningeal artery.Tympanic branch of the internal carotid artery. Venous drainage of the middle ear cavity – Vein draining the middle ear drains into superior petrosal sinus. Nerve supply of the middle ear cavity – Tympanic plexus. Development of the middle ear cavity – 1st branchial cleft. Function of the middle ear cavity –It transmits air/ sound wave/ from the external ear to the internal ear.It increases the intensity of the sound wave.Internal Ear Parts – It consist of 2 parts –Outer bony labyrinth.Inner membranous labyrinth. Location of the internal ear – Within the Petrous part of the temporal bone.Bony labyrinth – Situation - within the petrous part of the temporal bone. Parts –Cochlea.Vestibule.2 semi-circular canals. Cochlea – Shape – Conical and resembles the shell of a snail. Extension – Apex (Copula) is directed towards the tympanic cavity and base lies at the internal acoustic meatus. Parts –Modiolus – a central pillar or, axis.Cochlear canal –arranged spirally- Turns – 2 ¾ (Two and three forth) Length – 35 mm long. Content – peri-lymph. Copula - Apex of the cochlea is called copula. Vestibule – Shape - Oval. (Bilaterally compressed) Situation - Oval bony cavity situated in-between the cochlea and 3 semi-circular canals which contain saccule and utricle. Content - Membranous saccule and utricle. Semi-circular canal – Number - 3 in number.Anterior.Posterior.Lateral. Composition - Bony canals. Length - 15-20 mm. Peri-lymph - it is a fluid that lies in-between the bony labyrinth and membranous labyrinth. Composition - It is homologous with the Extra cellular fluid but contains more sodium and less potassium than the ECF. Source - This fluid comes from the surrounding blood vessels, sheath around the Vestibulo-cochlear nerve and CSF.Membranous labyrinth – Situation - Within the bony labyrinth. Parts –Cochlear duct.Saccule and utricle.3 semi-circular ducts. Cochlear duct – Location - Within the cochlea. Content - Spiral organ of cortiEndo-lymph.SPIRAL ORGAN OF CORTI:Definition – It is the specialized receptor for hearing composed of number of cells and membrane.Structure: Consist of –Inner and outer rod cells.Inner and outer hair cells.Supporting cells- Dieter’s cells Hensen’s cells.Membrana tectoria - It is the acelluler protein rich gelatinous membrane over the hair cells. It is attached to the vestibular lip and other end is free.Inner tunnel ( tunnel of corti): Definition - Space between the inner and outer rode cells is called inner tunnel Content - cortilymph.Outer tunnel: Definition - U Shaped Space between the Hensen’s cells and Dieter’s cells is called outer tunnel. Shape - U Shaped. Content - cortilymph.Space of nuel: Definition - U space in-between the outer rode cells and the inner most row of outer hair cells is called space of nuel Content - cortilymph.Blood Supply of the organ of corti – It is Avascular and get nutrition from cortilymph.Nerve supply of the spiral organ of corti – Cochlear nerve.Function of the spiral organ of corti –: Acts as hearing receptor.ENDOLYMPH Situation – Situated within the membranous labyrinth Composition – Composition is homologous that it Intra Cellular Fluid (but here k+ is more, but Na+ is less). Synthesis – This fluid is synthesized by stria vestibularis.SAECULE AND UTRICLE: Location - Within Vestibule. Content - Macula. Function - Concerned with equilibrium.Macula – Definition – It is the special sense organ which acts as static balance receptor stimulated by gravitational change. Structure – Consist of type: I & II hair cells and supporting cells rest on the basal lamina and covered by otolithic membrane, which contain ca crystals.(In the form of Calcium carbonate). Function:Maintain static equilibrium and linear acceleration.When saccule is stimulated there head goes laterally.When utricle is stimulated their head goes forward and backwards.Semicircular ducts: Number – 3 in number ant, post and lat, Content – contain crista ampullaris.Ampullaris: Definition – it is a specialized sense receptor organ located within the ampulla of the semicircular duct. Structure – Consist of hair cells, supporting cells which rest on a basement membrane and covered by 3 cone shaped gelatinous mass called cupula. Function: maintain kinetic, equilibrium and angular acceleration.
Posted on: Mon, 22 Jul 2013 08:48:23 +0000
Trending Topics
Recently Viewed Topics
© 2015