[0:43]Good morning, everyone. This is Dr. Adel Bondok, Professor of Anatomy and Neuroscience, Mansoura University, Egypt. Today, I will talk about the anatomy of the ear. The ear is divided into three parts. External ear, middle ear, and internal ear. The external ear is divided into three parts: the auricle, the external auditory meatus, and the tympanic membrane. Regarding the middle ear, I will talk about the boundaries, the contents, and Eustachian tube. This tube. Regarding the inner ear or internal ear, actually, it is membrane, membranous part inside a bony part. So I will talk about the bony labyrinth and the membranous labyrinth. Start by the external ear. As I mentioned, external ear is formed of auricle, external auditory meatus, and tympanic membrane. Regarding the auricle, the skeleton of the auricle is formed of elastic cartilage covered by skin. And the auricle is formed of five parts.
[2:30]This part is called helix. And this part is called anti-helix. And this anti-helix terminates by anti-tragus. Then this part is called concha. This depression, which leads to the external auditory meatus, concha. And this part is called the tragus. And this part is the lobule of the ear or lobule of the auricle.
[3:10]Regarding the nerve supply of the auricle, I will talk about the outer surface and the inner surface. The outer surface is the lateral surface, and the inner surface is the medial surface. The outer surface is supplied by four nerves. The upper part above the tragus supplied by the auriculotemporal nerve branch from the mandibular nerve. The lower part below the tragus this part supplied by the great auricular nerve, and the great auricular nerve arises from C2 and C3.
[4:00]The red triangles, the concha is supplied by the auricular branch of the vagus, that is why slapping the auricle might lead to cardiac arrest due to stimulation of the vagus nerve. The blue circles, okay, this area supplied by the facial nerve, the posterior auricular branch of the facial nerve. Therefore, the outer surface of the auricle is supplied by four nerves. The upper part by the auriculotemporal nerve. The lower part by the great auricular nerve. The concha is supplied by the vagus, auricular branch of the vagus, and this area is supplied by the facial nerve. Regarding the inner surface or the medial surface, the upper part is supplied by the lesser occipital nerve, which arises from C2. And the lower part is supplied by the great auricular nerve. So actually, the great auricular nerve supplies the lower part of the auricle outer surface and inner surface. Regarding the arterial supply, three arteries. This is the first one, anterior auricular artery. And this anterior auricular artery is a branch from the superficial temporal artery. And then posterior auricular artery and occipital artery. So the three arteries supplying the auricle, anterior auricular, posterior auricular, and occipital arteries.
[5:43]Anterior auricular from the superficial temporal artery, posterior auricular and occipital from the external carotid artery. Then the external auditory meatus. The external auditory meatus is about 2.5 cm in length, one inch long.
[6:08]The external auditory meatus is not straight, it is S-shaped, that is why during the examination of the tympanic membrane, you have to straighten the external auditory meatus by pulling the auricle upward and backward. The external auditory meatus is formed of two parts. Cartilaginous part and bony part. So two parts. Cartilaginous part: outer 1/3, contains glands that secrete wax. For self-cleaning of the ear. The inner 2/3 is bony part. So the external auditory meatus, cartilaginous part 1/3, bony part 2/3. Regarding the nerve supply of the external auditory meatus, very similar to the auricle. Auriculotemporal nerve and auricular branch of the vagus. Regarding the arterial supply, very similar to the auricle. Anterior auricular artery from the superficial temporal artery, posterior auricular artery from the external carotid, and deep auricular artery from the maxillary artery. Then we talk about the tympanic membrane. This tympanic membrane. I will talk about the layers, the parts, the umbo, and the cone of light. Regarding the tympanic membrane, it is formed of three parts. The outer layer, three layers. The outer layer is fibrous layer, and actually formed by the skin of the external auditory meatus. The middle layer is fibrous, and the inner layer is mucous membrane of the tympanic, tympanic cavity of the middle ear. Okay? So the tympanic membrane is formed of three layers. Outer fibrous layer or skin, inner mucous membrane, and in the middle fibrous layer. Tympanic membrane is formed of two parts, smaller part, and larger part. The smaller part is called pars flaccida. This pars flaccida doesn't have fibrous layer or very small amount of fibrous tissue. The larger part is called pars tensa, and it is tense because it is, it contains fibrous tissue. The pars flaccida and the pars tensa are separated by two ligaments, anterior malleolar ligament and posterior malleolar ligament or anterior malleolar fold and posterior malleolar fold. Okay? So pars flaccida is the upper 1/6, and pars tensa is the lower 5/6. Regarding the umbo, umbo actually is a depression in the center of the tympanic membrane. This depression is produced by is produced by the handle of malleus. This is the handle of the malleus. The cone of light is actually a reflection of light from the doctor's mirror. This is the tympanic membrane, outer layer skin, inner layer mucous membrane, and middle layer fibrous layer, and never clean your ear with ear swab because it might perforate the tympanic membrane. This is ruptured tympanic membrane and this is normal tympanic membrane, pars flaccida, pars tensa. This is handle of the malleus. This is the umbo, and this is the cone of light.
[10:15]Then the third part is the tympanic membrane. Okay, we'll talk about the nerve supply and arterial supply. Nerve supply of the tympanic membrane. We have to talk about the outer surface and inner surface. The outer surface is similar to the external auditory meatus. Auriculotemporal nerve from the mandibular nerve, and auricular branch of the vagus. The inner surface is supplied by the same nerve supplying the middle ear. So tympanic branch of the IX nerve. Arterial supply from the external ear and from the middle ear. First part of the maxillary artery. Outer surface: deep auricular artery and inner surface: anterior tympanic artery.
[11:37]Now, the middle ear. The middle ear is a box-like structure. And this box has six walls. It has roof, floor, anterior wall and posterior wall, and lateral wall and medial wall. The roof of the middle ear is part of is a plate of bone called Tegmen Tympani. This Tegmen Tympani separates the middle ear cavity from the cranial cavity. Therefore, in otitis media, infection can extend to the cranial cavity through the Tegmen Tympani. The floor, this floor is related to the jugular foramen and it is called jugular wall related to the internal jugular vein. The lateral wall is related to the external ear. So it is the tympanic membrane. Lateral wall tympanic membrane. And the medial wall is related to the inner ear or internal ear. It has four features. In the middle part of the cochlea, it is called promontory of the cochlea. Above the promontory oval window, and this oval window is closed by the footplate of the stapes. And below the promontory another window is called round window. It is closed by secondary tympanic membrane. And in the upper part, horizontal part of the facial canal or horizontal part of the facial nerve. So the medial wall contains four features: promontory of the cochlea, above the promontory of the cochlea, oval window, below the promontory round window, and horizontal part of the facial canal or horizontal part of the facial nerve. Then the anterior wall. The anterior wall contains three openings. T, T, N.
[13:59]Tendon, tube and nerve. The tendon tensor tympani muscle, the tube Eustachian tube, and the nerve is the exit of the chorda tympani nerve. So the anterior wall has three openings. One for tensor tympani, one for the Eustachian tube, and one for the chorda tympani. The posterior wall has also three openings. One for tendon, one for tube, and one for nerve. The tube, okay, the tendon is the stapedius muscle.
[14:44]The tube is the mastoid antrum. And the nerve is the entrance of the chorda tympani nerve. And the vertical part of the facial canal or vertical part of the facial nerve. So anterior wall has an opening for a muscle, tensor tympani. The posterior wall has an opening for another muscle, stapedius. The anterior wall has an opening for tube, Eustachian tube. The posterior wall has an opening for the mastoid antrum. The anterior wall has an opening for the exit of the chorda tympani. The posterior wall has an opening for the entrance of the chorda tympani. And the vertical part of the facial canal. Therefore, the facial nerve is related to the medial wall and the posterior wall. That's why in otitis media, inflammation can extend to the facial nerve causing facial paralysis.
[15:50]Again, this is the middle ear, six walls: roof, floor, lateral wall, medial wall, anterior wall, and posterior wall. The roof is Tegmen Tympani separating the middle ear from the cranial cavity. The floor is the jugular wall related to the internal jugular vein. The lateral wall is the tympanic membrane. The medial wall is the inner ear related to four structures: promontory of the cochlea in the middle. Above the promontory oval window, closed by the footplate of the stapes. Below the promontory another window, round window, closed by secondary tympanic membrane. And in the upper part, horizontal plate, horizontal part of the facial canal. Then the anterior wall. Tendon, tube, and nerve. The tendon is the tensor tympani muscle. The tube is the Eustachian tube. And the nerve is the chorda tympani. The posterior wall has another three openings. Tendon, tube, and nerve. The tendon is the stapedius muscle. The tube is the mastoid antrum. And the nerve is the chorda tympani.
[19:30]And the vertical part of the facial canal or vertical part of the facial canal. Okay, this is the lateral wall. This is the middle ear. Okay? This is the lateral wall tympanic membrane separating the middle ear from the external auditory meatus. This is the medial wall. Very nice medial wall. Here this projection, promontory of the cochlea. Above the promontory, this window is the oval window. It is closed by the footplate of the stapes. And below the promontory another window, it is the round window, closed by secondary tympanic membrane. Promontory, oval window, and round window.
[25:52]Then we talk about the Eustachian tube. How long the Eustachian tube is? It is about 4 cm or it is exactly 36 mm long.
[26:08]It is similar to the external auditory meatus in that it is formed of cartilaginous part and bony part. But the cartilaginous part is longer than the bony part. Cartilaginous part anterior 2/3, bony part posterior 1/3. This Eustachian tube connects the nasopharynx with the middle ear cavity. So actually ventilation of the middle ear is done by the Eustachian tube here coming from the nasopharynx. And also infection from this area can extend to the middle ear through the Eustachian tube. It is supplied by the tympanic branch of the glossopharyngeal nerve. It has two functions. First function is ventilation of the middle ear. Second function, it equalizes air pressure on each side of the tympanic membrane.
[27:07]Therefore, closure of the Eustachian tube will lead to pain in the middle ear. And this pain is due to difference in pressure between external ear and middle ear.
[27:39]And finally, we'll talk about the inner ear or internal ear. It's formed of bony part and membranous part. Membranous part inside the bony part. So bony labyrinth and membranous labyrinth.
[28:06]So bony labyrinth is filled with perilymph. And the membranous part is filled with endolymph. Bony labyrinth is formed of three parts: the cochlea, the vestibule, and semicircular canals, superior, posterior, and lateral.
[29:10]Regarding the membranous part, it is also formed of three parts: cochlear duct inside the cochlea. And this cochlear duct contains the receptors for hearing, which is organ of Corti. This is the cochlear nerve going to organ of Corti. So the cochlear duct is present inside the cochlea. It contains organ of Corti, receptors for hearing. Second part is the utricle and saccule inside the vestibule. And they contain another receptors called macula, and these receptors are receptors for balance or equilibrium. Macula.
[30:18]Utricle and saccule contain macula are present inside the vestibule. Then inside the semicircular canals we have semicircular ducts. And these semicircular ducts contain crista ampullaris, another receptors for balance or equilibrium. So the receptors in the inner ear are present in the membranous labyrinth.
[30:43]In the cochlear duct organ of Corti for hearing. In the utricle and saccule macula for balance, and in the semicircular canals crista ampullaris for balance.
[31:10]And thank you very much. Good luck and have a nice day.
