University:
Kentucky State University
Course:
BIO 301 | Human Anatomy
Academic year:

2023
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425

Pages:

86
Author:

tretjinmtv

The Ear The ear consists of the external ear; the middle ear (tympanic cavity); and the internal ear (labyrinth), which contains the organs of hearing and balance. Sound is captured by the external ear Mechanical signals in the middle ear The internal ear converts the mechanical signals into electrical signals to transfer information to the brain The internal ear also contains receptors that detect motion and position External ear Middle ear Inner ear External Ear Auricle (pinna) ✓The auricle has a characteristic shape ✓It collects air vibrations ✓It consists of a thin plate of elastic cartilage covered by skin External auditory meatus ✓The external auditory meatus is a curved tube that leads from the auricle to the tympanic membrane ✓It conducts sound waves from the auricle to the tympanic membrane 1 7 5 6 5 9 2 8 10 11 12 3 4 1. Helix. 2. Crus of helix 3. Auricular tubercle. 4. Antihelix. 5. Crura of antihelix. 6. Triangular fossa. 7. Scaphoid fossa. 8. Concha of auricle. 9. Tragus. 10. Antitragus. 11. Intertragic notch. 12. Lobule of auricle. The cartilage of the auricle is arranged in a pattern of elevations and depressions Prominent ears (also known as ‘bat’ ears) are caused by the absence or inadequacy of an antihelical fold. Anotia is complete absence of the external ear, and is most likely caused by a developmental disturbance between the seventh and eighth gestational week. Nerve supply of the auricle Auriculotemporal nerve: upper part of the outer surface Lesser occipital nerve: the upper part of the inner surface Great auricular nerve: the lower part of both inner and outer surfaces Note that the Auricular branches of vagus and facial nerves supply deeper parts of the auricle !!!!The cough reflex via the vagus nerve The external auditory meatus ✓The framework of the outer third of the meatus is elastic cartilage, and the inner two thirds is bone ✓The meatus is lined by skin ✓The outer third is provided with hairs and sebaceous and ceruminous glands Ceruminous glands are modified sweat glands that secrete (along with the sebaceous glands) a yellowish brown wax (cerumen=earwax) The hairs and the wax provide a sticky barrier that prevents the entrance of foreign bodies Cerumen is produced in the outer third of the ear canal pH is acidic in normal healthy canals. Contains a bactericidal enzyme. Inner two thirds Bony Outer third Cartilagenous External acoustic meatus Opposite Outer third is directed upward and backward Move the mobile part to make meatus straight This straightens the ear canal and improves visualization. Inner two thirds are directed downward and forward Otoscopic examination of the tympanic membrane is facilitated by first straightening the external auditory meatus by gently pulling the auricle upward and backward in the adult In the adult the external meatus is about 1 in. (2.5 cm) long and is narrowest about 0.2 in. (5 mm) from the tympanic membrane The Tympanic membrane (ear drum) The inner surface of tympanic membrane is fixed to handle of Malleus Is a thin, fibrous membrane Is formed of: 1-Outer layer: Skin 2- Middle layer: Fibrous tissue 3-Inner layer: Mucous membrane ✓It is concave laterally ✓Umbo is a small depression produced by the tip of the handle of the malleus The membrane is obliquely placed, facing downward, forward, and laterally Remember that the middle fibrous layer is present in the major parts of the ear drum which called pars tensa However, this layer is absent in the upper part of the ear drum which is called pars flaccida (Shrapnell's membrane) (Rivinus’ ligament) The pars tensa and flaccida are separated from each other by two folds called the anterior and posterior malleolar folds Posterior malleolar fold Pars flaccida (thin and slack) Malleus (lateral process) Anterior malleolar fold Handle of malleus Pars tensa (Thick and taut) Umbo Cone of light The tympanic membrane is extremely sensitive to pain Otoscopic Examination Note The translucency of the tympanic membrane allows the structures within the middle ear to be observed during otoscopy. When the membrane is illuminated through an otoscope, the concavity produces a cone of light, which radiates anteriorly and inferiorly from the umbo Clinical application The tympanic membrane is a relatively thin connective tissue structure, and is susceptible to perforation (usually by trauma or infection). An infection of the middle ear (otitis media) causes pus and fluid to build up behind the tympanic membrane. This causes an increase in pressure within the middle ear, and eventually the eardrum can rupture. Cone of light ✓ The tympanic membrane is pearly white or light gray, and you can see through it. ✓ You can see the tiny bones of the middle ear pushing on the tympanic membrane. Left tympanic membrane Right tympanic membrane The cone of light is at the 5 o'clock position in the right ear and at the 7 o'clock position in the left ear. Lateral surface of tympanic membrane Handle of malleus Cone of light Note the tympanic membrane is translucent, concave laterally The antero-inferior quadrant of the ear drum is called the cone of light (because it reflects the light coming from the otoscope) Otitis media The light reflex on the tympanic membrane is dull or absent The tympanic membrane is red and bulging. You can often see amber liquid or bubbles behind the eardrum. Middle Ear (Tympanic Cavity) ➢Is an air-containing cavity in the petrous part of the temporal bone ➢Is lined with mucous membrane ➢It contains the auditory ossicles, whose function is to transmit the vibrations of the tympanic membrane (eardrum) to the inner ear The middle ear has ROOF FLOOR ANTERIOR WALL POSTERIOR WALL LATERAL WALL MEDIAL WALL Tympanic cavity (middle ear) is a narrow, oblique, slitlike cavity whose long axis lies approximately parallel to the plane of the tympanic membrane Walls of middle ear Roof Medial wall Posterior wall Anterior wall Floor Roof TEGMENTAL WALL Is formed by tegmen tympani (part of the petrous temporal bone) It separates the tympanic cavity from the meninges and the temporal lobe of the brain in the middle cranial fossa. Floor JUGULAR WALL It separates the tympanic cavity from the internal jugular vein Tegmen tympani Petrous bone Jugular foramen Anterior wall (carotid wall) Tensor tympani Auditory tube Internal carotid artery ➢Is formed below by a thin plate of bone that separates the tympanic cavity from the internal carotid artery ➢At the upper part of the anterior wall are the openings into two canals The lower and larger leads into the auditory tube The upper and smaller is the entrance into the canal for the tensor tympani muscle Opening of Eustachian tube into nasopharynx EUSTACHIAN TUBE: It connects the anterior wall of the tympanic cavity to the nasopharynx It serves to equalize air pressures in the tympanic cavity and the nasopharynx Its posterior inner third is bony Its anterior two thirds are cartilaginous Bony Cartilaginous Pharyngo-tympanic tube Auditory tube Eustachian tube Promontory is a rounded projection (results from the underlying first turn of the cochlea) Medial wall Labyrinth wall The horizontal part of the facial nerve arching above the promontory Oval window: Above and behind the promontory, oval shaped and closed by the base of the stapes (Fenestra vestibuli) The medial wall is formed by the lateral wall of the inner ear. Fenestra means window Tympanic plexus Round window: Below the posterior end of the promontory, round and closed by the secondary tympanic membrane (Fenestra cochleae) Promontory The base of stapes closes the oval window of the internal ear Cochlea Lateral wall Membranous wall Internal acoustic meatus 7th Brain stem 8th Stylomastoid foramen Aditus Pyramid Vertical part of Facial canal Chorda tympani Posterior wall Posterior wall Mastoid wall 1- Has in its upper part a large, irregular opening, the aditus to the mastoid 2-Below, a small conical projection, the pyramid, from its apex emerges the tendon of the stapedius muscle 3- The vertical part of the facial nerve Mastoid Antrum The mastoid antrum lies behind the middle ear in the petrous part of the temporal bone It communicates with the middle ear by the aditus The horizontal part of the facial nerve Stylomastoid foramen Infections and Otitis Media The meninges and the temporal lobe of the brain lie superiorly Into the mastoid antrum The posterior wall of the mastoid antrum is related to the sigmoid venous sinus. If the infection spreads in this direction, a (Meningitis and cerebral abscess in the temporal lobe) (Acute mastoiditis) Through the auditory tube from nasopharynx. (nasopharyngitis) thrombosis in the sigmoid sinus may take place Medial wall: A spread of the infection in this direction can cause a facial nerve palsy and labyrinthitis with vertigo Although rare, complications of OM are commonly encountered given its high prevalence. Complications of OM are classified as extracranial or intracranial. Brain abscess are commonly considered the second most common intracranial complication of OM after meningitis Groove for the sigmoid sinus CONTENTS OF THE MIDDLE EAR Malleus Incus . Stapes . A-3 Auditory Ossicles B-2 muscles C-2 nerves (tympanic plexus and chorda tympani) D-air - It contains the auditory ossicles, whose function is to transmit the vibrations of the tympanic membrane (eardrum) to the perilymph of the internal ear Ossicles 1-The malleus is the largest ossicle and possesses head, a neck, a long process or handle, an anterior process, and a lateral process. its head is rounded and articulates posteriorly with the incus The incus possesses: a large body and two processes: The body articulates with the head of the malleus. The long process articulates with the head of the stapes The stapes has a head, a neck, two limbs, and a base The head articulates with the long process of the incus. The neck is narrow and receives the insertion of the stapedius muscle. The two limbs diverge from the neck and are attached to the oval base which closes the oval window of the internal ear Malleus The handle is firmly attached to the medial surface of the tympanic membrane Handle of malleus Incus Stapes The base of stapes closes the oval window of the internal ear The Annular stapedial ligament is a ring of fibrous tissue that connects the base of the stapes to the oval window of the inner ear Calcification and hardening of the annular ligament of the stapes (Otosclerosis) is a common cause of adult deafness Muscles of middle ear Muscle Nerve supply Action Tensor tympani Mandibular division of trigeminal nerve Dampens down vibrations of tympanic membrane Stapedius Facial nerve Dampens down vibrations of stapes Tensor tympani muscle Stapedius muscle Anterior Tensor tympani muscle Stapedius muscle Anterior Chorda tympani Chorda tympani Anterior Posterior Chorda tympani The chorda tympani ✓It arises from the facial nerve just above the stylomastoid foramen ✓It enters the middle ear close to the posterior border of the tympanic membrane. ✓ It then runs forward over the tympanic membrane and crosses the root of the handle of the malleus ✓It leaves the middle ear through the petrotympanic fissure and enters the infratemporal fossa, where it joins the lingual nerve The chorda tympani contains: 1. Taste fibers from the mucous membrane covering the anterior two thirds of the tongue and the floor of the mouth. 2. Carries preganglionic parasympathetic fibers to the submandibular and sublingual glands via the submandibular ganglion The petrotympanic fissure is a fissure in the temporal bone The chorda tympani runs through the fissure to join with the lingual nerve in the infratemporal fossa The chorda tympani is a branch of the facial nerve The chorda tympani passes medial to the tympanic membrane and the handle of the malleus, and again enters the temporal bone. It exits the skull through the petrotympanic fissure and descends in the infratemporal fossa. Tympanic Nerve ➢The tympanic nerve arises from the glossopharyngeal nerve, just below the jugular foramen ➢It passes through the floor of the middle ear and onto the promontory ➢Here it splits into branches, which form the tympanic plexus. ➢The tympanic plexus supplies the lining of the middle ear and gives off: Lesser petrosal nerve It leaves the skull through the foramen ovale Carries preganglionic parasympathetic fibers to the parotid gland via the otic ganglion Lessor petrosal nerve Medial wall Tympanic nerve IJV Glossopharyngeal nerve Foramen ovale transmits: Mandibular nerve Accessory meningeal artery Lesser petrosal nerve Emissary vein MALE Cavernous sinus Foramen ovale Emissary vein Pterygoid venous plexus in Infratemporal fossa Inner Ear (labyrinth) Internal acoustic meatus Inner ear is situated in the petrous part of the temporal bone The inner ear is divided into: 1- Bony labyrinth 2- Membranous labyrinth Semicircular canals Vestibule Cochlea The vestibule, the central part of the bony labyrinth Semicircular canals Vestibule Cochlea Bony labyrinith Membranous labyrinith Semicircular ducts Saccule and utricle Cochlear duct The membranous labyrinth is lodged within the bony labyrinth It is filled with endolymph and surrounded by perilymph The cochlea (spiral chamber) resembles a snail shell Cochlear duct The duct of the cochlea lies within the bony cochlea Bony Cochlea Posterior semicircular canal Posterior semicircular duct Lodged within the canals are the semicircular ducts Superior semicircular canal Superior semicircular duct Lodged within the canals are the semicircular ducts Lateral semicircular canal Lateral semicircular duct Lodged within the canals are the semicircular ducts Bony ampullae Each canal has a swelling at one end called the ampulla Membranous ampullae Membranous ampullae are lodged in the bony ampullae Utricle Utricle and Saccule are lodged in the bony vestibule Saccule Utricle and Saccule are lodged in the bony vestibule Vestibulo-cochlear nerve Vestibular nerve Cochlear nerve Vestibule and semicircular canals The inner ear contains Sensory receptors for hearing and balance Mechanoreceptors/ Hair cells (Columnar cells) ✓ Two maculae of the utricle and saccule, ✓ Three cristae ampullares in the ampullae of each semicircular duct ✓The organ of Corti in the cochlear duct. Cochlea Vestibulo-cochlear nerve Vestibule Ampullae of semicircular canals Utricle Saccule Vestibular nerve carries impulses from the utricle, the saccule, and the ampullae of the semicircular ducts (contain the sensory receptors for balance) Cochlea Cochlear nerve carries impulses from organ of Corti in cochlea (contains the sensory receptors for hearing) Scala vestibuli (perilymph) Scala media (Cochlear duct) (endolymph) Section through cochlea Scala tympani (perilymph) ✓ The cochlear duct itself forms the middle compartment, or scala media, filled with endolymph. It is continuous with the saccule and ends at the apex of the cochlea. ✓The larger scala vestibuli contains perilymph and is separated from the scala media by the very thin vestibular membrane (Reissner membrane) ✓The scala tympani also contains perilymph and is separated from the scala media by the basilar membrane Middle ear Scala media Scala tympani Helicotrema Scala vestibuli The scalae tympani and vestibuli communicate with each other at the apex of the cochlea via the helicotrema 1: Scala vestibuli 2: Scala media (Cochlear duct) 3: Scala tympani Vestibular membrane (Reissner membrane) Basilar membrane 1 2 Modiolus 3 The cochlea is about 35 mm long and makes 2¾ turns around a bony core called the modiolus The organ of Corti, or spiral organ, where sound vibrations of different frequencies are detected, consists of hair cells and other epithelial structures supported by the basilar membrane Vestibular membrane (Reissner membrane) Scala vestibuli Scala media Tectorial membrane Spiral ganglion Basilar membrane Scala tympani Note: Cell Bodies of cochlear Nerve (CN VIII) located in the Modiolus (Spiral ganglion) Sensory receptor for hearing (organ of Corti) Section through cochlea (Scala media) Section through cochlea Organ of corti The auditory nerve (cochlear) carries the electrical signal to the brain, which turns it into a sound that we recognize and understand Dr. Heba Kalbouneh Tectorial membrane With the tectorial membrane removed, SEM shows the apical plate of the rat spiral organ through which rigid stereocilia bundles project into endolymph The auditory hair cells are located within the spiral organ of Corti on the basilar membrane in the cochlea of the inner ear Stereocilia (hair bundles ) protrude from the apical surface of the cell into the fluid-filled cochlear duct. K + channels open K + channels close The inner hair cells transform the sound vibrations in the fluids of the cochlea into electrical signals that are then relayed via the auditory nerve to the auditory brainstem and to the auditory cortex The deflection of the hair-cell stereocilia opens mechanically gated ion channels that allow positively charged ions (primarily potassium) to enter the cell. The influx of positive ions from the endolymph in the scala media depolarizes the cell, resulting in a receptor potential K+ K+ Damage to these hair cells results in decreased hearing sensitivity, and because the inner ear hair cells cannot regenerate, this damage is permanent K+ Note: hair cells detect movement Transmission of sound Problems of the vestibular system can result in vertigo, or dizziness, a sense of bodily rotation and lack of equilibrium. Spinning the body produces vertigo due to overstimulation of the cristae ampullares of the semicircular ducts. Overstimulation of the maculae of the utricle caused by repetitive changes in linear acceleration and directional changes can normally lead to motion sickness (sea sickness/ car sickness). Semicircular canal Semicircular duct Ampulla Utricle Saccule Crista Horizontal Macula Sensory receptors for balance Vestibule (saccule, utricle and semicircular ducts) Maculae : detect linear acceleration of the head (static balance) Cristae: detect angular acceleration of the head (kinetic balance) Vertical Macula Depolarization Hyperpolarization Gelatinous layer Bending of these stereocilia change membrane potential Columnar hair cells Supporting cells Sensory epithelium of saccule, utricle and semicircular ducts Foramen lacerum Facial nerve Internal acoustic meatus Horizontal part of facial canal Vertical part of facial canal N to stapedius Chorda tympani Stylomastoid foramen Stylohyoid Post belly of digastric Parotid gland Dr. Heba Kalbouneh Posterior auricular n

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