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REVISIT ANATOMY OF EAR LEARNING OBJECTIVES • At the end of this class the student should be able to, • Discuss the division of ear in parts. • Understand the parts of external ear. • Understand the parts of middle ear. • Understand the parts of internal ear. • Consists of auricle or pinna and external acoustic meatus. THE EXTERNAL EAR • • • • • PINNA: Crumpled plate of elastic cartilage covered by skin. LOBULE: Lower part and soft part of ear, consists of connective tissue covered by skin. CONCHA: Is large depression which leads in to external acoustic meatus. INTRINSIC MUSCLES:Which can alter the shape of ear. EXTERNAL MUSCLES: Move ear (are rudumentary in human). PINNA cont. • • • • Blood supply: Posterior auricular artery and superior temporal artery. Lymphatic drainage: Preauricular and posterior auricular and superficial temporal lymph nodes. Nerve supply: • • • Upper two third of lateral surfaceauriculotemporal nerve and lower one thirds by greater auricular nerve. Medial surface upper two third by lesser occipital nerve and lower one third by greater auricle nerve. Root of auricle by is supplied by branches of facial nerve. EXTERNAL ACOUSTIC MEATUS • • • • • • Conducts sound waves. “S” shaped. About 3cm in length. It is straightened for examination by pulling upwards backwards and slightly laterally. Anterior wall and floor are longer than posterior wall and roof. Medial third is bony and lateral two thirds is cartilaginous. EXTERNAL ACOUSTIC MEATUS • BONY PART: • • • • “C” shaped in cross section. • Cartilaginous part: • • • Also “C” shaped in section gap is filled by fibrous tissue. Lined by thin skin firmly adherent to periosteum. Anteriorly formed by tympanic part of temporal bone. Posterosuperior part is formed by squamous temporal bone. Skin is adherent to the perichondrium. Contains sebaceous gland and ceruminous glands (modified sweat glands). EXTERNAL ACOUSTIC MEATUS • • • • • Blood supply: Outer part by superficial temporal and posterior auricular arteries. Inner part by deep auricular branch of maxillary artery. Lymphatic drainage: Preauricular, postauricular and superficial cervical lymph nodes. Nerve supply: Anterior half by auriculotemporal nerve and posterior half by auricular branch of vagus. THE MIDDLE EAR • • • • • Middle ear or Tympanic cavity is about 15 mm in anteroposterior and vertical diameter. Shape of a biconcave lens. The lateral wall:Is largely occupied by the tympanic membrane. Tympanic membrane extends upwards for 10 mm from the floor and also bulges inwards. Above the membrane the temporal bone is hollowed out into the epitympanic recess. THE TYMPANIC MEMBRANE • • • • • • • Thin fibrous structure. Circular. 1cm in diameter. Covered externally: By thin layer of stratified squamous epithelium (consists of collagen fibers). Lies obliquely at 55 degree with the external acoustic meatus.Facing downward forward and laterally. Concave towards the meatus. At the depth of the concavity is a small depression, the umbo. • Cone of light (is at anteroinferior quadrant). THE TYMPANIC MEMBRANE • • • • The handle of the malleus is firmly attached to the inner surface of membrane. From the lateral process of the malleus two thickened fibrous folds (mallear folds) diverge up to the margins of the tympanic bone between them is pars flaccidasharpnell’s membrane. (crossed internally by the chorda tympani). Pars tensa. (It is held tensa by the inward pull of the tensor tympanic muscles). The tympanic membrane is thickened at its circumference and slotted into a groove in the tympanic plate. THE TYMPANIC MEMBRANE • BLOOD SUPPLY: Deep auricular artery from maxillary artery on the meatal side and stylomastoid artery from posterior auricular artery on the mucosal surface forms a circular anastomosis with the anterior tympanic branch of the maxillary artery round the margin of the membrane • NERVE SUPPLY: on the meatal surface: auriculotemporal nerve supplemented by the vagus and on the mucosal surface: Tympanic branch of the glossopharyngeal nerve via the tympanic plexus. THE MEDIAL WALL OF THE TYMPANIC CAVITY • • Is also lateral wall of the internal ear. The promontory (first turn of the cochlea and indented with fine grooves by the tympanic plexus. Above it is a horizontal ridge for the canal for the facial nerve, and immediately above that is the (horizontal) bulge due to the lateral semicircular canal. • • Above and behind the promontory is the oval window the fenestra vestibuli (closed in life by the foot piece of the stapes). Below and behind the promontory is the round window the fenestra cochleae closed in life by the fibrous secondary tympanic membrane. THE ROOF OF THE TYMPANIC CAVITY • Tegmen tympani (petrous bone that roofs also the canal for the tensor tympanic and the tympanic antrum. • • • THE FLOOROF THE TYMPANIC CAVITY Is a thin plate of bone above the jugular fossa. At the anterior end is the internal opening of the tympanic canaliculus. (for tympanic branch of the glossopharyngeal nerve). THE ANTERIOR WALL OF THE TYMPANIC CAVITY • • • • • Shortend by approximation of roof and floor. It is perforated by the opening of two canals. Lower is the bony part of the auditory tube. Upper is the canal for the tensor tympani muscle. Lower part of this wall forms the posterior wall of the carotid canal (perforated by tympanic branches of the internal carotid artery and sympathetic fibers from the internal carotid plexus) THE POSTERIOR WALL OF THE TYMPANIC CAVITY Is deficient above, where there is an aperture, the aditus, which lead back in to the tympanic antrum. • • Below the aditus a hollow cone, the pyramid, projects in to the tympanic cavity. Apex is perforated by the tendon of stapedius. TYMPANIC ANTRUM • • • • • • • • • • • • • Small, circular, air filled space, situated in the posterior part of the petrous part of the temporal bone.1 cm in size, is of adult size at birth. Superiorly. Tegmen tympani. Beyond it is temporal lobe of cerebrum. Inferiorly. Mastoid process with mastoid air cells. Anteriorly. Communicates with epitympanic recess through aditus. Posteriorly. Separated from sigmoid sinus by thin plate of bone. Medially. Petrous temporal bone. Laterally. Squamous temporal bone. Relation with suprameatal triangle). CONTENTS OF MIDDLE EAR CAVITY 1. Ossicles– malleus, incus, stapes • 2. Muscles – tensor tympani, stapedius • 3. Vessels and nerves – chorda tympani and tympanic plexus of ear. • FUNCTIONS OF MIDDLE EAR CAVITY • • Narrow, oblique, slit like, air containing cavity in the petrous part of temporal bone. Transmit the vibrations of tympanic membrane to the perilymph of internal ear. OSSICLES 1. MALLEUS • • • The malleus or hammer is a hammer-shaped bone Connected with the incus and is attached to the inner surface of the tympanic membrane It transmits the sound vibrations from the eardrum to the incus. 2. INCUS • • • The incus or anvil is the anvil-shaped small bone. It connects the malleus to the stapes The incus transmits sound vibrations from the malleus to the stapes. MUSCLES STAPEDIUS • • • The stapedius is the smallest skeletal muscle in the human body. At just over one millimeter in length, its purpose is to stabilize the smallest bone in the body, the stapes. The stapedius emerges from a pinpoint foramen in the apex of the pyramidal eminence (a hollow, coneshaped prominence in the posterior wall of the tympanic cavity), and inserts into the neck of the stapes. Innervated by the nerve to stapedius, a branch of cranial nerve VII, the facial nerve. MUSCLES TENSOR TYMPANI • • • • The larger of the two muscles of the tympanic cavity, is contained in the bony canal above the osseous portion of the auditory tube. Its role is to dampen sounds, such as those produced from chewing. It arises from the cartilaginous portion of the auditory tube and the adjoining part of the great wing of the sphenoid Inserted into the handle (manubrium) of the malleus, near its root. AUDITORY TUBE • • • • • • Is the channel through which the tympanic cavity communicates with the nasal part of the pharynx. 35 mm long (in adults). Extends from the anterior wall of the middle ear to the lateral wall of the nasopharynx. Has two parts Osseous part Cartilagenous part ARTERIES OF MIDDLE EAR Anterior tympanic branch (maxillary artery) • • • • • Superior tympani (middle meningeal artery) and petrosal branch Posterior tympani (posterior auricular artery) Inferior tympanic (ascending Ph artery) Tympanic branch from artery of pterygoid canal.Coticotympanic from I.C artery VEINS AND LYMPH NODES OF MIDDLE EAR CAVITY Pterygoid plexus of veins which drain into superior petrosal sinus. • • LYMPH NODES:Periauricular and retro pharyngeal nodes NERVE SUPPLYTympanic branch of glossopharyngeal nerve (tympanic plexus). Superior and inferior corticotympanic nerves from the sympathetic plexus around internal carotid artery. INTERNAL EAR • All these structures are in the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially. PARTS OF INTERNAL EAR INTERNAL EAR CONSISTS OF: • Bony labyrinth – – • Vestibule, Three semicircular canals – Cochlea Membranous labyrinth. – – – Semicircular ducts Cochlear duct Two sacs (utricle and saccule). • These bony cavities are lined with periosteum and contain a clear fluid the perilymph. • The membranous spaces are filled with endolymph. FUNCTION OF INTERNAL EAR • • The internal ear converts the mechanical signals received from the middle ear, which start as sound captured by the external ear, into electrical signals to transfer information to the brain. The internal ear also contains receptors that detect motion and position. INTERNAL EAR • • • • The structures in the internal ear convey information to the brain about balance and hearing: Cochlear duct is the organ of hearing Semicircular ducts, utricle, and saccule are the organs of balance. The nerve responsible for these functions is the vestibulocochlear nerve [VIII], which divides into vestibular (balance) and cochlear (hearing) parts after entering the internal acoustic meatus. BONY LABYRINTH Vestibule: • • • • It is the central part of the bony labyrinth. contains the oval window in its lateral wall It communicates anteriorly with the cochlea and posterosuperiorly with the semicircular canals. A narrow canal (the vestibular aqueduct) leaves the vestibule, and passes through the temporal bone to open on the posterior surface of the petrous part of the temporal bone. BONY LABYRINTH Semicircular Canals • • • Projecting in a posterosuperior direction from the vestibule are three in number – Anterior (superior) vertical – Posterior (vertical) – Lateral (horizontal) Each of these canals forms two-thirds of a circle connected at both ends to the vestibule and with one end dilated to form the ampulla. The canals are oriented so that each canal is at right angles to the other two. BONY LABYRINTH COCHLEA • • • It is a bony structure that twists on itself two and onehalf to two and three-quarter times around a central column of bone (the modiolus). This arrangement produces a cone-shaped structure with a base of cochlea that faces posteromedially and an apex that faces anterolaterally. This positions the wide base of the modiolus near the internal acoustic meatus, where it is entered by branches of the cochlear part of the vestibulocochlear nerve [VIII]. BONY LABYRINTH LAMINA OF MODIOLUS, OR SPIRAL LAMINA). • • • Circling around the modiolus, and held in a central position by its attachment to the lamina of modiolus, is the cochlear duct, which is a component of the membranous labyrinth. Cochlear duct creates 2 canals – Scalavestibuli – Continuous with the vestibule – Scala tympani – Separated from the middle ear by the secondary tympanic membrane covering the round window They extend throughout the cochlea and are continuous with each other at the apex through a narrow slit (the helicotrema) . COCHLEAR AQUEDUCT • • Near the round window is a small channel (the cochlear canaliculus), which passes through the temporal bone and opens on its inferior surface into the posterior cranial fossa. This provides a connection between the perilymph-containing cochlea and the subarachnoid space. MEMBRANOUS LABYRINTH • • • • • • It is a continuous system of ducts and sacs within the bony labyrinth. It is filled with endolymph and separated from the periosteum that covers the walls of the bony labyrinth by perilymph. Consisting of Two sacs (the utricle and the saccule) and Four ducts (the three semicircular ducts and the cochlear duct). The general organization of the parts of the membranous labyrinth places: ORGANS OF BALANCE • • • 5 of the 6 components of the membranous labyrinth are concerned with balance. These are the: Two sacs (the utricle and the saccule) Three ducts (anterior, posterior, and lateral semicircular ducts). Utricle • • The utricle is the larger of the two sacs. It is oval, elongated and irregular in shape and is in the posterosuperior part of the vestibule of the bony labyrinth. Three semicircular ducts empty into the utricle. Saccule • • The saccule is a smaller, rounded sac lying in the anteroinferior part of the vestibule of the bony labyrinth. The cochlear duct empties into it. The utriculosaccular duct establishes continuity between all components of the membranous labyrinth and connects the utricle and saccule ORGANS OF BALANCE • • • Branching from utricosaccular duct is the endolymphatic duct, which enters the vestibular aqueduct (a channel through the temporal bone) to emerge onto the posterior surface of the petrous part of the temporal bone in the posterior cranial fossa. Here the endolymphatic duct expands into the endolymphatic sac, which is an extradural pouch. Each semicircular duct is similar in shape, including a dilated end forming the ampulla, to its complementary bony semicircular canal, only much smaller. SENSORY RECEPTORS • • • • • • Functionally, sensory receptors for balance are organized into unique structures and in each of the components of the vestibular apparatus. In the utricle and saccule this sense organ is the macula of utricle and macula of saccule, Ampulla of each of the three semicircular ducts it is the crista. Utricle responds to centrifugal and vertical acceleration, Saccule responds to linear acceleration. Receptors in the three semicircular ducts respond to movement in any direction. ORGAN OF HEARING • • Triangular-shaped cochlear duct has: An outer wall against the bony cochlea consisting of thickened, epithelial-lined periosteum (the spiral ligament). • Roof (vestibular surface membrane) which separates the endolymph in the cochlear duct from the perilymph in the scalavestibuli and consists of a membrane with a connective tissue core lined on either side with epithelium; • Floor, which separates the endolymph in the cochlear duct from the perilymph in the scala tympani and consists of the free edge of the lamina of modiolus, and a membrane (basilar membrane) extending from this free edge of the lamina of modiolus to an extension of the spiral ligament covering the outer wall of the cochlea. VESSELS • • • • • Arterial supply to the internal ear is divided between vessels supplying the bony labyrinth and the membranous labyrinth. Bony labyrinth is supplied by the same arteries that supply the surrounding temporal bone-these include Anterior tympanic branch from the maxillary artery stylomastoid branch from the posterior auricular artery Petrosal branch from the middle meningeal artery. MEMBRANOUS LABYRINTH • LABYRINTHINE ARTERY, which either arises from the anterior inferior cerebellar artery or is a direct branch of the basilar arterywhatever its origin, it enters the internal acoustic meatus with the facial [VII] and glossopharyngeal [IX] nerves and eventually divides into INNERVATION • • • The vestibulocochlear nerve [VIII] carries special afferent fibers for hearing (the cochlear component) and balance (the vestibular component). It enters the lateral surface of the brainstem, between the pons and medulla, after exiting the temporal bone through the internal acoustic meatus and crossing the posterior cranial fossa. Inside the temporal bone, at the distal end of the internal acoustic meatus, the vestibulocochlear nerve divides to form: the cochlear nerve, and the vestibular nerve. • INNERVATION • • • • The vestibular nerve enlarges to form the vestibular ganglion, before dividing into superior and inferior parts, which distribute to the three semicircular ducts and the utricle and saccule. The cochlear nerve enters the base of the cochlea and passes upwards through the modiolus. The ganglion cells of the cochlear nerve are in the spiral ganglion at the base of the lamina of modiolus as it winds around the modiolus. Branches of the cochlear nerve pass through the lamina of modiolus to innervate the receptors in the spiral organ. THE END