Ear Anatomy

The external ear The auricle is a paired structure that can be found on both sides of the head. It captures and directs sound waves to the external acoustic meatus. It is primarily cartilaginous, with the lobule being the only part that is not supported by cartilage. The helix is an outer curvature formed by the cartilaginous part of the auricle. The antihelix is a second innermost curvature that runs parallel to the helix. The antihelix is divided into two cura: inferoanterior and superoposterior crus. The concha is a hollow depression in the middle of the auricle. It continues as the external acoustic meatus into the skull. The concha is responsible for directing sound into the external acoustic meatus. The external acoustic meatus is a sigmoid-shaped tube that runs from the concha's deep part to the tympanic membrane. The external third's walls are made of cartilage, while the inner two-thirds are made of temporal bone. The external acoustic meatus does not travel in a straight line, but rather in an S-shaped curve, as shown below: It moves in a superoanterior direction at first. In then makes a slight turn to move superoposteriorly. It eventually runs in an inferoanterior direction. The external acoustic meatus is a sigmoid-shaped tube that runs from the concha's deep part to the tympanic membrane. The external third's walls are made of cartilage, while the inner two-thirds are made of temporal bone. A fibrocartilaginous ring connects the membrane to the surrounding temporal bone. The tympanic membrane's translucency allows structures within the middle ear to be seen during otoscopy. The handle of malleus attaches to the tympanic membrane on the inner surface of the membrane at a point known as the umbo of tympanic membrane. The malleus handle continues superiorly, and at its highest point, a small projection known as the malleus lateral process can be seen. The anterior and posterior malleolar folds are the parts of the tympanic membrane that move away from the lateral process. Branches of the external carotid artery supply the external ear: Auricular artery in the back. The surface temporal artery. The artery of the occipital bone. The artery of the maxilla (deep auricular branch). Numerous nerves innervate the auricle's skin with sensory information: Greater auricular nerve (cervical plexus branch) - innervates the auricular skin. The lesser occipital nerve (a branch of the cervical plexus) innervates the auricle skin. Auriculotemporal nerve (mandibular nerve branch) - innervates the skin of the auricle and the external auditory meatus. Facial and vagus nerve branches - innervates the deeper aspect of the auricle and the external auditory meatus When cleaning their ears, some people experience an involuntary cough, which is caused by stimulation of the vagus nerve's auricular branch (the vagus nerve is also responsible for the cough reflex). External ear lymphatic drainage goes to the superficial parotid, mastoid, upper deep cervical, and superficial cervical nodes. The middle ear The middle ear is divided into two sections: Tympanic cavity – located medially to the tympanic membrane. The auditory ossicles are three small bones known as the malleus, incus, and stapes. They send vibrations of sound through the middle ear. Epitympanic recess - a space above the tympanic cavity, next to the mastoid air cells. The malleus and incus extend partially into the epitympanic recess. Consider the middle ear to be a rectangular box with a roof and floor, medial and lateral walls, and anterior and posterior walls. A thin bone from the petrous part of the temporal bone forms the roof. It connects the middle cranial fossa to the middle ear. The floor, also known as the jugular wall, is a thin layer of bone that separates the middle ear from the internal jugular vein. The lateral wall of the epitympanic recess is made up of the tympanic membrane and the lateral wall of the epitympanic recess. The lateral wall of the internal ear forms the medial wall. It has a noticeable bulge caused by the facial nerve as it travels nearby. The anterior wall is a thin bony plate with two openings: one for the auditory tube and one for the tensor tympani muscle. It connects the internal carotid artery to the middle ear. The posterior wall (mastoid wall) is a bony partition that separates the tympanic cavity from the mastoid air cells. This partition has a hole in the middle that allows the two areas to communicate. The aditus to the mastoid antrum is the name given to this hole. The auditory ossicles - the malleus, incus, and stapes - are the bones of the middle ear. They form a chain that connects the tympanic membrane to the oval window of the internal ear. Sound vibrations move the tympanic membrane, which causes movement or oscillation in the auditory ossicles. This movement aids in the transmission of sound waves from the external ear's tympanic membrane to the internal ear's oval window. The malleus is the largest and most lateral of the ear bones, with the handle of malleus attaching to the tympanic membrane. The malleus head is located in the epitympanic recess, where it articulates with the incus, the next auditory ossicle. The incus bone is made up of a body and two limbs. The body articulates with the malleus, the short limb connects to the middle's posterior wall, and the long limb connects to the last of the ossicles, the stapes. The stapes is the human body's smallest bone. It connects the incus to the inner ear's oval window. It has a stirrup-shaped head, two limbs, and a base. The head connects to the incus, and the base connects to the oval window. Mastoid air cells are found behind the epitympanic recess. They are a collection of air-filled spaces in the temporal bone's mastoid process. The air cells are housed in a cavity known as the mastoid antrum. The aditus to mastoid antrum connects the mastoid antrum to the middle ear. When the pressure in the tympanic cavity is too low, the mastoid air cells act as an air "buffer system," releasing air into the cavity. The tensor tympani and stapedius muscles serve a protective function in the middle ear. They contract in response to loud noise, inhibiting malleus, incus, and stapes vibrations and reducing sound transmission to the inner ear. The acoustic reflex is the name given to this action. The tensor tympani originates from the auditory tube and attaches to the handle of malleus, pulling it medially when contracting. The tensor tympani nerve, a branch of the mandibular nerve, innervates it. The facial nerve innervates the stapedius muscle, which attaches to the stapes. The auditory tube (eustachian tube) is a bony and cartilaginous tube that connects the middle ear to the nasopharynx. It works by bringing the pressure in the middle ear in line with the pressure in the external auditory meatus. It extends from the middle ear's anterior wall in an anterior, medioinferior direction, opening onto the lateral wall of the nasopharynx. It creates a pathway for an upper respiratory infection to spread into the middle ear by connecting the two structures. The inner ear The inner ear is located in the petrous region of the temporal bone. It is located between the middle ear and the internal acoustic meatus, which are located laterally and medially. The inner ear is made up of two parts: the bony labyrinth and the membranous labyrinth. A bony labyrinth is a series of bony cavities located within the petrous part of the temporal bone. The cochlea, vestibule, and three semicircular canals make up the cochlea. Internally, all of these structures are lined with periosteum and contain a fluid called perilymph. The bony labyrinth is surrounded by the membraneous labyrinth. It is made up of the cochlear duct, semicircular ducts, utricle, and saccule. Endolymph is the fluid that fills the membranous labyrinth. The inner ear is located in the temporal bone's petrous region. It is situated laterally and medially between the middle ear and the internal acoustic meatus. The inner ear is divided into two sections: the bony and membranous labyrinths. A bony labyrinth is a collection of bony cavities in the petrous part of the temporal bone. The cochlea is made up of the cochlea, vestibule, and three semicircular canals. All of these structures are lined with periosteum and contain a fluid known as perilymph. The membraneous labyrinth surrounds the bony labyrinth. The cochlear duct, semicircular ducts, utricle, and saccule are all part of it. The fluid that fills the membranous labyrinth is known as endolymph. The inner ear has two membrane-covered openings into the middle ear. The oval window connects the middle ear to the vestibule, while the round window connects the middle ear to the scala tympani (part of the cochlear duct). The bony labyrinth is a collection of bony cavities located within the petrous part of the temporal bone. It is divided into three sections: the cochlea, the vestibule, and the three semicircular canals. The vestibule is located in the centre of the bony labyrinth. The oval window separates it from the middle ear, and it communicates anteriorly with the cochlea and posteriorly with the semicircular canals. The vestibule contains two parts of the membranous labyrinth: the saccule and the utricle. The cochlea duct of the membranous labyrinth - the auditory part of the inner ear - is housed in the cochlea. It twists around a central portion of bone known as the modiolus, forming a cone shape that points anterolaterally. Branches from the vestibulocochlear (VIII) nerve's cochlear portion can be found at the base of the modiolus. A ledge of bone known as the spiral lamina extends outwards from the modiolus and attaches to the cochlear duct, holding it in place. The presence of the cochlear duct results in the formation of two perilymph-filled chambers above and below: Scala vestibuli: Located above the cochlear duct. It is, as the name implies, continuous with the vestibule. The cochlear duct is located inferiorly to the scala tympani. It comes to an end at the round window. The semi-circular canals are anterior, lateral, and posterior. They contain the semicircular ducts that are in charge of balance (along with the utricle and saccule). The canals are superoposterior to the vestibule and at right angles to one another. They have a swelling at one end called an ampulla. The membranous labyrinth is a continuous network of endolymph-filled ducts. It is located within the bony labyrinth and is surrounded by perilymph. The cochlear duct, three semicircular ducts, the saccule, and the utricle comprise it. The cochlear duct is the organ of hearing located within the cochlea. The organs of balance are the semicircular ducts, saccule, and utricle (also known as the vestibular apparatus). The cochlear duct runs through the bony scaffolding of the cochlea. The spiral lamina holds it in place. The presence of the duct results in the formation of two canals above and below it, known as the scala vestibuli and scala tympani, respectively. A triangular shape can be described for the cochlear duct: The spiral ligament forms the lateral wall, which is formed by thickened periosteum. The roof is formed by the Reissner's membrane, which separates the cochlear duct from the scala vestibuli. The basilar membrane, which separates the cochlear duct from the scala tympani, forms the floor. The basilar membrane is home to the Organ of Corti's hearing epithelial cells. In the vestibule, there are two membranous sacs called the saccule and utricle. They are balance organs that detect movement or acceleration of the head in the vertical and horizontal planes. The larger of the two, the utricle, receives the three semicircular ducts. The cochlear duct enters the saccule, which is globular in shape. Endolymph drains into the endolymphatic duct from the saccule and utricle. The duct connects to the posterior aspect of the petrous part of the temporal bone via the vestibular aqueduct. The duct expands to form a sac in which endolymph can be secreted and absorbed. The semi-circular ducts share the same orientation as the semi-circular canals. The flow of endolymph within the ducts changes speed and/or direction when the head moves. Sensory receptors in the semicircular canals' ampullae detect this change and send signals to the brain, allowing balance to be processed.