MODULE 2 Hearing Process The human sense of hearing and balance is the ear. The ear contains receptors that are sensitive to sound vibrations in the air. The ears also contain receptors that are sensitive to vibrations, position and head movement. These receptor cells are found in the inner ear and each consists of hair cells with sterocilia. The ear is the sense of hearing, divided into several parts such as: outer, middle and inner ear. 1. Outer Ear => is the outermost part of the ear. Consist of : a. Ear leaf / Pinna / Auricle => is a cartilage leaf => function: captures sound waves and transmits them to the auditory canal external (a narrow passage about 2.5 cm long that stretches from the auricle to the tympanic membrane). b. Tympanic membrane (ear drum) => is the border of the outer and middle ear. Conical, lined with skin on the external surface, lined with mucosa on the internal surface. => has the appropriate tension, size and thickness for transmit sound waves mechanically. The parts: 1) The upper part or Pars Flaksid (shrapnell membrane), consists of 2 layers: (a) external: continuation of the ear epithelium (b) inside: ciliated cuboidal epithelium There is a part called atik. There is this placeauditus ad antrum in the form of a hole that connects the middle ear to the mastoid antrum. 2) The lower part or Pars tensa (membrane propria), consists of 3 layers: - middle: consists of cholangen fibers and a few elastin fibers The shadow of the lower protrusion of the malleus on the tympanic membrane is called the umbo. From the umbo, a downward light reflex (cone of light) begins, i.e 7 o'clock on the left tympanic membrane and 5 o'clock on the right tympanic membrane. In the tympanic membrane there are 2 fibers, circular and radial. These fibers are what cause the cone light reflex. If the light reflex is flat, then an abnormality in the eustachian tube is suspected. The tympanic membrane is divided into 4 quadrants to determine the location of the perforation: 1) top front; 2) top back; 3) bottom front; 4) lower back => where the myringotomy was performed 2. Middle Ear => located in the air-filled cavity in the petrous part (canalis facialis) of the temporal bone Consist of: a. Eustachian tube => connects the middle ear to the pharynx. => Normally this tube closes and opens when swallowing, chewing and yawning. => functions as a balance of air pressure on both sides of the tympanic membrane. If the tube opens => the sound will be muffled. b. Auditory ossicles (ossicles) => consists of 3 bones, namely: Malleus (hammer), Incus (anvill), Stapes (stirrup) => MIS. => functions as a conductor of vibrations from the tympanic membrane to the fenesta vestibuli c. Muscle => helps the body's compensatory mechanism to fight high-pitched sounds (sound dampening). 1) m stapedius => contracts => stapes becomes stiff => sound is reflected 2) m tensor tympani => tenses the eardrum => muffled sound 3. Inner ear => contains fluid and is located in the temporal bone. Consists of a labyrinth. Consists of A. Bone labyrinth=>the tortuous space contains perilymph (a fluid similar to cerebrospinal fluid). Consists of the vestibular, semicircular canals, and cochlea. a)Vestibular=>the central part of the bony labyrinth that connects the cochlea with the semicircular canals. b) Semicircular canals • The anterior (superior) and posterior semicircular nerves point in the vertical plane at each right angle. • Lateral semicircular S. => located horizontally a)Cochlea=>forms 2.5 turns around the bony nucleus, contains auditory receptors (N VIII branch = vestibulocochlear, blood vessels. The highest frequency is in the front. The septum divides the cochlea into 3 parts: 1. Cochlear duct (medial scale) => part of the membranous labyrinth connected to the saccule, filled with endolymph fluid. two parts of the bony labyrinth located above and below the scala media => scala vestibuli and scala tympani => contain perilymph fluid and continue to extend through the hole in the apex of the cochlea called the helicotrema. 2. Reissner's membrane (vestibular membrane) => separates the scala media from the scala vestibuli which is connected to the fenestra vestibuli. 3. Basilar membrane => separates the scala media from the scala tympani, connected to the cochlear fenestra. The organ of Corti scale => located on the basilar membrane, consists of receptors called hair cells and supporting cells. Hair cells do not have axons and synapse directly with the cochlear nerve endings. B.Membranous labyrinth=>a series of hollow tubes and sacs located within the bony labyrinth filled with endolymph fluid (a fluid similar to intracellular fluid). It is the beginning of 2 sacs (utriculus and sacculus) which are connected by the endolymph duct. Each duct contains receptors for static equilibrium (how the head is oriented in space depending on the force of gravity) and dynamic equilibrium (whether the head is moving or stationary, what speed and direction of movement). The utricle is connected to the semilunar duct. The saccule connects with the cochlear duct in the cochlea.