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Describe the anatomy of the ears, Eustachian tubes and pharynx Week 30 1. Understand the terminology used to describe the gross anatomy of the ear and upper air passages viz. nose pharynx & larynx 2. Identify the constituent parts and major internal features of the upper respiratory tract including the nose, nasopharynx, oropharynx, laryngopharynx, and larynx. Ear see LO 3 Nose the part of the respiratory tract superior to the hard palate and contains the peripheral organ of smell external nose o consists of bone (paired nasal and maxillae), hyaline cartilage and fibro-fatty tissue external nares (nostrils) the skin extends into the vestibules of the nose (entrance) where it has a variable number of stiff hairs (vibrissae) Nasal Cavity paired cavities separated by midline nasal septum inter nares = choanae – open posteriorly into nasopharynx nasal choncae dividethe nasal cavity into 4 passages: o spehnoethmoidal recess (receives opening of sphenoidal sinus) o superior meatus o middle meatus o inferior meatus choncae produce turbulence which: warms humidifies filters air Paranasal air sinuses air filled extensions of respiratory part of nasal cavity frontal, ethmoid, sphenoid, maxilla (Pneumatic bones) lighten skull and contribute to vocal resonance Pharynx: About 15cm long, the pharynx extends from base of skull to the inferior border of the cricoid cartilage anteriorly and the inferior border of C6 posteriorly. The superior pharynx receives the posterior openings of the choanae. located posterior to the nasal and oral cavities and the larynx. conducts food to the oesophagus, and air to the larynx and lungs. Divided into three parts: Nasopharynx: Posterior to the nose and superior to soft palate pharyngeal tonsil in mucous membrane of roof and posterior wall Pharyngeal openings of the auditory tubes (eustachian tube). Oropharynx: Posterior to mouth soft palate – superior border of epiglottis palatine tonsils in the interval between palatoglossal and palatopharyngeal arches Opens into the oral cavity anteriorly via the fauces (the area at the back of the oral cavity bounded by the palatine tonsils and their enclosing palatoglossal & palatopharyngeal mucosal folds). Contains the lingual tonsil located on the posterior surface of the base of the tongue. Laryngopharynx: Posterior to the larynx superior border of epiglottis to inferior border of cricoid cartilage (C6) Larynx: anterior to laryngopharynx extends from C4-C6 and in adult males is around 5cm in length. In females and children it is shorter. The hyoid is at the level of C3. The framework of the larynx is made up of cartilages and associated ligaments and membranes. The larynx is the organ of voice production. It consists of a framework of cartilages and elastic membranes housing the vocal folds and the muscles which control the position and tension of these elements. The larynx consists of 9 cartilages that are joined by various ligaments and membranes. Three of the cartilages are single (thyroid, cricoid and epiglottis) and three are paired (arytenoids, corniculate and cuneiform). The position of the larynx is seen anteriorly by the ‘Adam's apple’ which is formed by the thyroid cartilage of the larynx. It serves as an external indication of the level of the fifth cervical vertebra. 3. Describe the anatomical subdivisions of the ear. The External Ear: The external ear is composed of a fleshy cartilaginous (elastic) flap called the auricle, which surrounds the external acoustic meautus (EAM) The auricle provides protection for the opening of the ear and funnels sound into the external auditory canal. It is made up of cartilage covered with skin The external acoustic meautus: S-shaped passageway that passes through the tympanic part of the temporal bone and ends at the tympanic membrane (ear drum). tympanic membrane is a thin semi-transparent sheet that also signifies the limit of the external ear. The external ear’s nerve supply is by the auriculo-temporal nerve (CN V) and great auricular nerve from C2. Lymph from the external ear is drained to the parotid, mastoid and jugular lymph nodes. The lateral portion is cartilagenous with thick skin that is continuous with skin of auricle. The skin contains ceruminous and sebaceous glands which produce cerumen (ear wax). The medial portion is bony and very thin skin lies directly over the bone and is continuous with external layer of the tympanic membrane. Tympanic membrane: thin oval, semitransparent membrane at the medial end of the external auditory canal. It is roughly 1cm in diameter and conical in shape, with the concave aspect facing the auditory canal. The apex is supported medially by the malleus. The shallow, cone-like central depression’s peak = umbo (remember umbrella) When viewed with otoscope, bright reflection (= Cone of light) radiates anteroinferiorly from umbo Divided into two parts: Flaccid part = Thin part of tympanic membrane superior to the lateral process of the malleus lacks the radial and circular fibres of the rest of the membrane. Tense part = Rest of tympanic membrane. The Middle Ear: The middle ear is in the petrous part of the temporal bone. air filled cavity separated from the external auditory canal by the tympanic membrane. includes: o tympanic cavity, which is the space directly internal to the tympanic membrane o epitympanic recess, which is the space superior to the tympanic membrane. Posterosuperiorly, the tympanic cavity connects with the mastoid air cells via the mastoid antrum. middle ear is separated from the brain only by a thin piece of bone in the roof of the tympanic cavity called the tegmen tympani (infection in the middle ear can spread through this bone and penetrate into the brain). The middle ear communicates with the nasopharynx via the auditory tube or Eustachian tube. The auditory tube is about 4cm long and has two different sections: o section near the middle ear is supported by cartilage, o section near the nasopharynx is funnel shaped and broader. Auditory tube functions to equalize pressure on either side of the tympanic membrane. middle ear also communicates with the mastoid air cells via numerous tiny connections. The middle ear is connected to the inner ear via the oval and round window. The middle ear contains the auditory ossicles (malleus, incus and stapes). The ossicles increase the force x10 but decrease the amplitude of sound vibrations transmitted from the tympanic membrane. Two muscles, the stapedius and tensor tympani, attach to the stapes and malleus respectively and contract to dampen vibrations. The middle ear’s nervous supply comes from the facial (CNVII), glossopharyngeal (CN IX) and vagus (CN X). Walls of the tympanic cavity: Tegmental roof Floor (jugular wall) Lateral (membranous) wall Medial (labyrinthine) wall Anterior (carotid) wall Posterior (mastoid) wall Thin plate of bone, tegmen tympani. Seperates the tympanic cavity from the cranial cavity. Layer of bone separating tympanic cavity from the internal jugular vein. Mostly by tympanic membrane; superiorly it is formed by bony wall of epitympanic recess Separates tympanic cavity from the inner ear. Separates tympanic cavity from the carotid canal and the internal carotid artery. Has opening in superior part – the aditus to the mastoid antrum – connecting tympanic cavity to mastoid cells. The Inner Ear: The vestibulcochlear apparatis is responsible for the sense of equilibrium made up of a system of spaces in the petrous temporal bone – bony labyrinth containg perilymph filling these spaces is a closed system of membrane bound sacs and tubules – membranous labyrinth containing endolymph both fluids carry sounds waves to end organs for hearing and balancing Bony labyrinth composed of 3 parts: cochlea, vestibule and semicircular canals 4. Identify and describe the arrangement and function of the ear ossicles within the middle ear. The Auditory Ossicles: The auditory ossicles are three tiny bones in the middle ear. They connect the tympanic membrane to the oval window of the inner ear. The three bones articulate via synovial joints. transmit and amplify sound-induced vin=brations of TM to inner ear Malleus (hammer): The most lateral of the three bones. Head (rounded superior part) lies in epitympanic recess (upper portion of the tympanic cavity above the tympanic membrane and articulates with the incus. Neck lies against the flaccid part of the tympanic membraneTM . The Handle is embedded in the tympanic membrane and it functions as a lever. Tendon of tensor tympani muscle inserts into the handle near the neck. It responds to or sound by tensing or relaxing respectively to change the transmittance of sound. Incus (anvil): The middle ossicle bone. Body lies in the epitympanic recess Articulates with the head of the stapes. Long limb articulates with stapes. Short limb connected by ligament to posterior wall of the tympanic cavity. attaches the malleus to the stapes (stirrup). The base of the stapes is bound to a ligamentous sheet that spans the oval window, an opening in the bone that surrounds the inner ear. Stapes (stirrup): Has head and base united by two limbs. Head articulates with the incus. Base is bound to the ligamentous sheet that spans the oval window on the medial wall of the tympanic cavity. The oval membrane is considerably smaller than the tympanic membrane so the vibratory force of the stapes is increased by ~10x over that of the tympanic membrane. The stapedius muscle restrains the stapes. Muscles associated with the ossicles: Two muscles dampen (resist movement) of ossicles; one also dampens the vibration of the tympanic membrane. Tensor tympani: Inserts into the handle of the malleus. Pulls handle medially, tensing the tympanic membrane and decreases the amplitude of oscillations. It therefore prevents inner ear damage when exposed to loud sounds. Supplied by the mandibular branch of the trigeminal nerve. Stapedius: Inserts into the neck of the stapes. Pulls stapes posteriorly, tilting its base in the oval window. Tightens the annular ligament and reduces the oscillatory range. Supplied by a branch of the facial nerve. 5. Describe the inter-connections and relationships of the middle ear to the mastoid air cells, and the anatomical basis of infections spreading from the pharynx to the middle ear and mastoid sinuses. the middle ear (tympanic cavity) has a roof, floor and 4 walls as described above A section of the mastoid process of the temporal bone of the cranium shows it to be hollowed out into a number of spaces, the mastoid cells Mastoid Antrum Cavity in mastoid process Separated from middle cranial fossa by tegmen tympani Floor of antrum has several apertures that communicate with mastoid cells Middle ear is connected to mastoid air cells via mastoid antrum Antrum + mastoid cells are lined by mucus membrane continuous with lining of middle ear Related to canal for facial nerve ANATOMICAL BASIS OF INFECTIONS SPREADING FROM PHARYNX TO MIDDLE EAR + MASTOID SINUSES Infection of pharynx may spread to middle ear via pharyngotympanic (Eustachian) tube Infection of middle ear may spread to mastoid sinuses via mastoid antrum = Mastoiditis Main risk = Spread of infection to brain via facial nerve