Lecture: 11 Head and neck Dr. Omar Riadh
15-11-2017
Middle ear continue:-
Lateral wall:- formed by tympanic membrane which is oval translucent membrane separates the external meatus from the middle ear cavity, it is composed of fibrous layer covered externally by skin and internally by mucous membrane, it slopes obliquely downwards, forwards and medially. The lateral surface is concave while the medial surface is convex and the point of maximum convexity is called the umbo which is maintained by the handle of malleus.
Medial wall:- (labyrinthine wall) contains a bulge of bone called the promontory which is formed by the first turns of the cochlea and above the promontory is the oval window (fenestra vestibuli) closed by the base of stapes and below the promontory is the round window (fenestra cochleae) which is closed by membrane. The facial nerve and lateral semicircular canal enclosed in the bone produce parallel bulge superiorly.
Anterior wall:- (carotid wall) the lower part of anterior wall is formed by bone which separates the middle ear from the carotid canal and it is perforated by the caroticotympanic nerve (branch from sympathetic plexus around the internal carotid artery) to the tympanic plexus. Also in the anterior wall there are two opening separate by a shelf of bone, the upper opening is for tensor tympani muscle where its tendon passes to the handle of malleus, while the lower opening is for the auditory tube which connects the middle ear cavity to the nasopharynx. The auditory tube passes downwards, medial wards and forwards, the upper part of the tube is bony and it is about 1.5cm, while the lower part is cartilaginous and it is about 2.5cm long. The tube is lined with mucous membrane.
Posterior wall:- contains an opening called the aditus which leads to mastoid antrum, the antrum is the largest and most superior cavity of the mastoid air sinus, its lined by mucous membrane, below the aditus there is a small projection called the pyramid and from the pyramid tendon of stapedius muscle passes to stapes, lateral to the pyramid is the orifice of chorda tympani nerve.
Cranial portion of facial nerve:-
It emerges from the inferior border of pons. It has two roots:-
Motor root supplies all the muscles of facial expression.
Nervous intermedius which contains:-
Special sensation (taste fibers) to anterior 2/3 of the tongue.
General sensation from external acoustic meatus.
Parasympathetic for submandibular, sublingual, lacrimal, nasal and palatine glands.
Both roots pass with vestibulocochlear nerve through the internal acoustic meatus. At the lateral wall of internal acoustic meatus both roots unit forming geniculate ganglia. Near the geniculate ganglia, the greater petrosal nerve emerges at the greater petrosal hiatus in the middle cranial fossa. Then the facial nerve enters a complex bony canal till it reaches the stylomastoid foramen. It gives branch to stapedius muscle and chorda tympani nerve, the chorda tympani arises 5mm proximal to stylomastoid foramen, it turns upward and enters the tympanic cavity at the posterior border of tympanic membrane, it passes forward over the medial surface of tympanic membrane and leaves the cavity at the anterior border of the tympanic membrane through the petrotympanic fissure,
Tympanic plexus:-
Formed by:-
Tympanic branch of glossopharyngeal nerve.
Caroticotympanic branch from internal carotid sympathetic plexus.
Small branch of facial nerve from geniculate ganglia.
This plexus supplies mucous membrane of middle ear cavity.
The nose:-
Composed of external nose and nasal cavity.
the external nose:- which is prominent part of the face has anterior orifice called the nostril which lined with skin at its beginning and contain hairs called the vibrissae. The external nose composed of upper part (bony) and lower cartilaginous part, the skin over the bony part is movable while the skin over the cartilaginous part is firmly adheres to the cartilage. The bony part formed of nasal bones, frontal process of maxilla and nasal part of frontal bone.
The cartilaginous part formed of five cartilage one septal, two lateral and two alar cartilage.
Nerve supply of external nose:- by branches from trigeminal nerve (infratrochlear, infraorbital and external nasal nerves).
Blood supply of external nose:- by facial artery and infraorbital artery.
Nasal cavity:- is the first part of respiratory system. It extends from the nostril anteriorly to the choanae (posterior nasal aperture)posteriorly. It divided by nasal septum into two cavities which are mostly not equal. each cavity has roof, floor and lateral wall.
Roof:- from in front backward it is formed of nasal cartilage, nasal bone, frontal bone, cribriform plate of ethmoidal bone and sphenoid bone.
floor:- is formed of palatine process of maxilla and horizontal plate of palatine bone and these two bones forming the hard palate.
Lateral wall:- is marked by three projection called superior, middle and inferior conchae or turbinates. The area below each conchae is referred to as meatus which contain the orifices of paranasal sinuses.
the superior and middle conchae are processes of ethmoidal bone, while the inferior conchae is independent bone.
Sphenoethmoidal recess:- small recess lies above the superior conchae and in front the body of sphenoid bone. It receives the opening of sphenoidal air sinus.
Superior meatus:- lies below the superior conchae. It receives the opening of posterior ethmoidal sinus.
Middle meatus:- lies below the middle conchae, in this meatus there is a semilunar groove called hiatus semilunaris which receives the orifice of maxillary sinus which open in its posterior part, also receives the anterior ethmoidal sinus which open in its anterior part. Also near the anterior end of middle meatus the frontal sinus opens. Above the hiatus semilunaris there is a round prominence (bulla ethmoidalis) caused by bulging of underlying middle ethmoidal air sinus which opens in its upper border.
Inferior meatus:- is place between the inferior conchae and the floor of nasal cavity. It receives the orifice of nasolacrimal duct.
Nasal septum (medial wall):- is osteocartilaginous portion covered by mucous membrane. The upper part is formed by perpendicular plate of ethmoid, crest of nasal bone and crest of sphenoid bone. The lower part is formed by vomer bone, nasal crest of maxilla and crest of palatine bone. Anteriorly the septum composed of cartilage.
The vestibule:- is a dilated area inside the nostril bounded by the medial and lateral portion of alar cartilage. It is lined by skin with hair follicles.
Paranasal sinuses:-
Are cavities found inside the maxilla, frontal, sphenoid and ethmoid bones. It is lined by mucoperiosteum and filled with air, they communicate with the nasal cavity through relatively small aperture. The function of these sinuses are to act as resonator to voice and also to reduce the weight of skull.
Maxillary sinus:-
It is pyramid in shape with the base directed towards the lateral wall of the nose and the apex in the zygomatic process of maxilla. The roof is formed by the floor of the orbit, while the floor is formed by the alveolar process. It opens in the middle meatus of the nose through hiatus semilunaris. The mucous membrane of the sinus is supplies by the superior alveolar and infraorbital nerves.
Frontal sinus:-
Two in number within the frontal bone separate from each other by bony septum. Each sinus is roughly triangular in shape and extends upward above the medial part of the roof of the orbit and it is opens in the middle meatus. It is supplied by the supraorbital nerve.
Sphenoid sinus:-
Two in number lies within the body of sphenoid bone, each sinus opens into sphenoethmoidal recess above the superior conchae and it is supplied by posterior ethmoidal nerve.
Ethmoidal sinus:-
Presents within the ethmoidal bone, between the nose and orbit, it is divided into three groups which are anterior, middle and posterior ethmoidal sinus.
The posterior ethmoidal sinus opens in the superior meatus.
The middle ethmoidal sinus opens in the bulla ethmoidalis.
The anterior ethmoidal sinus opens in the hiatus semilunaris.
They all supplied by anterior and posterior ethmoidal nerve.