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8 Cards in this Set
- Front
- Back
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External ear: Auricle |
Function: selective reinforcement of the ways sounds of the most important frequencies in human life, and amplification of 10 Db. - Helix - Antihelix - Concha - Tragus - Antitragus - Lobule |
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External ear: External acoustic meatus |
The external hear canal is 2.5 cm long and it is composed of a cartilaginous portion in the lateral 1/3 and a bony portion I the medial 2/3. It is quite similar to an S and of you want to performance good otoscopy you should drown upward and posteriorly the auricle to bring the ring and the fibrous cartilaginous portion in the same axis with the bony portion. It extends from the deepest part of the concha to the tympanic membrane. Anteriorly it borders with the temporomandibular joint and with the parotid gland. It is important because an infection or a tumor of the parotid gland may spread toward the external ear canal and vice-versa. Another important aspect is that there are some fissures in the cartilaginous portion which are called Santorini fissures which allow a more flexibility of the cartilaginous portion. but are also a way for the spread of the infections. The posterior wall of the external ear canal is the anterior wall of the mastoid process. An infection of the mastoid leads to a swelling of the posterosuperior portion of the external ear canal. Superiorly we have the temporal bone and beyond it there is the middle cranial fossa. Inferiorly there is the parotid gland. The external ear canal works as an amplifier. It amplifies wave sounds with frequencies between 2000-4000 Hz. All the external structures do not present the subcutaneous layer; it is important because a skin change of the external structures leads to a direct change of the perichondrium and periosteum. |
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External ear: tympanic membrane |
The tympanic membrane is 10mm long and 8 mm large. We can identify two portions: the pars tensa and pars flaccida. - The pars tensa is the stiff, vibrating portion of the tympanic membrane. It is possible to identify 3 layers of the pars tensa: the external epidermal layer, the middle ear layer and the layer in between, called the lamina propria, composed of circular and radial fibers at the external portion they form the annulus which anchors the tympanic membrane to the temporal bone. - Superiorly we have the pars flaccida without annulus and lamina propria and due to this anatomical element the pars flaccida is the first portion affected during middle ear disventilation disorder. Functions: it is mechanical linked to the ossicular chain. They compose the sound conducting system. It gaiters sound like the membrane of a microphone. It provides sonic shedding of the round window membrane. Some ways that directly impact the round window can lead to hearing loss of about 35Db. |
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Middle ear: tympanic cavity |
It is is like a room: - Superiorly we have the tegmen tympani. - Inferiorly the wall borders with the jugular bulb. - Anteriorly there is the carotid artery and the orifice of the Eustachian tube and tensor tympani muscle. - Posteriorly there is the aditus to the mastoid antrum. - Laterally there is the tympanic membrane. - Medially we find the promontory, the basal turn of the cochlea. The promontory separates the oval window from the round window and medially we can observe the facial nerve. |
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Middle ear: epitympanum, mesotympanum, hypotympanum |
- Epitympanum: the head of the malleus with the incus. I remind you that in the epitympanum there is a very thin wall of bone and beyond it there is the middle cranial fossa. - Mesotympanum consists of two parts: anterior mesotympanum in which there is the eustachian tube orifice and posteriorly the stapes with the long process of the incus. - The hypotympanum is the floor and borders with the bulge of the jugular vein |
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Middle ear: ossicular chain |
The ossicles are the smallest bones of our body. - Malleus: head, neck, lateral process, anterior process, handle. The lateral process and handle are the ones which form the vertical visible portion at the level of the tympanic membrane. - Incus: Body, short limb, long limb. - Stapes: head, anterior and posterior limbs, base. Function: it is like an impedance transformer. What is the meaning? We know that the air and the other fluid (endolymph, perilymph) have a different resistance. If some ways directly impact the fluid we have a reflection of more than 99% of the energy. The tympanic ossicular system works in other to avoid the reflection of this energy. It works as a second type lever and it provides a 90 times sound wave amplification. |
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Inner ear: Bony labyrinth |
Inner ear is developed in continuum with the otic capsule. The otic capsule is the strongest bone of our body. If there is a fracture of the otic capsule we can't observe a healing of this fracture. It is filled with endolymph. - Vestibule: it is the central part of the bony labyrinth and contains the oval window in its lateral wall. - Semicircular canals: anterior, posterior, lateral. They have an ampulla and are positioned at right angles between each other. - Cochlea: a bony structure twisting around a central column of bone (the modiolus). Circling around the modiolus, and held in a central position by its attachment to the lamina of the modiolus, is the cochlear duct, which is a component of the membranous labyrinth. The cochlear duct creates two canals: the scala vestibuli and the scala tympani. The scala tympani is separated from the middle ear by the round window. |
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Inner ear: Membranous labyrinth |
A continuous system of ducts and sacs which is filled with endolymph and separated from the periosteum that covers the walls of the bony labyrinth by perilymph. In the membranous labyrinth we can identify the basal membrane which supports the organ of Corti. It is comprised between the spiral lamina and the external wall of the cochlea. The innervation is provided by the 8th nerve, the cochlear nerve. An important element to remember is the tonotopic organisation of the sound. The tonotopic organisation of the pressure wave: a high-frequency pressure waves stimulate the cells at the basal level, instead low-frequency waves stimulate the cells at the apex. Some waves travel in the oval window, up to scala vestibuli, come down to the scala tympani and out of the round window. Organ of Corti is composed of inner hair cells and outer hair cells. The real cell receptors are the inner ear cells that transduce the relative movement between the basilar and tectorial membrane into nerve impulses. The take home message is that three structures can be identified: sound conducting system, transducer system, and the nerve conducting system. The sound conducting system is composed of: external ear, middle ear and labyrinthic fluids. The transducer system is composed of the organ of Corti. The nerve conducting system is composed of the cochlear nerve. |
