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CHAPTER 9- Auditory System. Audition- the process associated with hearing Essential element of verbal communication Energy Transducer- converts acoustic.

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Presentation on theme: "CHAPTER 9- Auditory System. Audition- the process associated with hearing Essential element of verbal communication Energy Transducer- converts acoustic."— Presentation transcript:

1 CHAPTER 9- Auditory System

2 Audition- the process associated with hearing Essential element of verbal communication Energy Transducer- converts acoustic energy into electrochemical energy

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4 THREE BASIC COMPONENTS Pinna or Auricle- It serves as a collector of sound to be processed at deeper levels. It is primarily made of a cartilagenous framework External Auditory Meatus- ear canal. It is approximately 7 mm in diameter and 2.5 cm long. Tympanic Membrane- most medial portion of the EAM

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6 Outer 1/3 is lined with hairs and has cerumen- traps insects and dirt which protects the medial most point of the outer ear, the Tympanic Membrane Osseus Meatus- medial 2/3 of the canal surrounded by the temporal bone Isthmus- junction of the cartilaginous and bony framework of the ear canal.

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9 Tympanic Membrane- thin 3 layer sheet of tissue Fibrocartilaginous ring that fits into the tympanic sulcus, a groove in the temporal bone. The epithelial cover of the pinna continues into the EAM and is the outer layer of the TM Middle layer is fibrous tissue that provides structure Inner layer is the lining of the middle e ar TM is slightly concave oval structure with Umbo the most depressed portion of this concavity

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12 Occupied by three of the smallest bones of the body Ossicles- The bones of the ear Malleus Incus Stapes Tympanic Muscles Stapedius Tensor Tympani Landmarks of the Middle Ear Medial Wall Anterior Wall Posterior Wall and Floor

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17 Largest of the 3 bones- attaches to the TM

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19 Shaped like an anvil Intermediate communicating link of the ossicular chain The body of the incus articulates with the head of the malleus by means of the malleolar facet- saddle joint Malleus and Incus move as a unit upon movement of the TM

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21 Shaped like a stirrup Incus/Stapes articulation is a ball and socket joint

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23 Strategically placed ligaments suspend the ossicles from the walls of the middle ear cavity Anterior ligament of the malleus Superior ligament of the malleus Lateral ligament of the malleus Superior ligament of the incus Posterior ligament of the incus Annular ligament

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25 Stapedial Smallest striated muscle in the body Originates from the posterior wall Inserts into the posterior surface of the stapes Innervated by the facial nerve Contraction rotates the stapes posteriorly Stiffens the middle ear ossicles Reduces strength of the signal reaching the cochlea- protects from loud sounds

26 Tensor Tympani Originates from the anterior wall just superior to the eustachian tube Inserts into the upper manubrium malli Contraction pulls the malleus anteromedially Innervated by trigeminal nerve Stiffens the middle ear ossicles Reduces strength of the signal reaching the cochlea- protects from loud sounds

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31 Extends downward, forward and medially from the tympanic cavity to the nasopharynx Lateral part is bony (osseous) Medial part is cartilage and connective tissue It is normally closed to protect the middle ear It opens during yawning and swallowing Equalizes pressure between the middle ear and external pressure Drains the middle ear cavity

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35 Houses the vestibular system – needed for balance Houses the cochlea- needed for hearing Osseous-Bony Labyrinth Outer system Membranous Labyrinth Internal system

36 A series of ducts and cavities Lie within the petrous portion of the Temporal bone Vestibule Semicircular Canals Coiled Cochlea

37 Oval window is within the lateral wall of the vestibule Vestibular Aqueduct is in the medial wall Vestibule is the space between the entrance to the cochlea and the semicircular canals It houses 3 prominent recesses Spherical- vestibular nerve passes through Cochlear- communicates between the vestibule and the basal end of the cochlear duct Elliptical-communicates between the utricle and the ampullae

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39 House the sense organs for the movement of the body in space Near the opening to the vestibule in each canal is an enlargement that houses the ampulla A series of three rings attached to a ball ( the vestibule) Anterior (anterior, vertical, superior) Posterior (posterior vertical) Horizontal (lateral)

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41 Anterior Vertical Canal Senses movement of your head as it moves toward your shoulde r Posterior Vertical Canal Sense movement if you move your head to nod “yes” Lateral horizontal Canal Helps your brain differentiate rotatory movement toward the left vs. right- shaking your head “no”

42 Utricle and Saccule Mediating the sense of acceleration of your head in space, such as in sudden movement or falling

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44 Looks like a coiled snail shell Modiolus- core of the labyrinth which is a finely perforated bone Fibers of the VIII vestibulocochlear nerve pass through these perforations

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46 Cochlear Duct- Scala Media houses the sensory organ for hearing Divided into two incomplete chambers by the Osseous spiral lamina which is an incomplete bony shelf protruding from the modiolus Scala vestibuli Scala Tympani

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48 Osseous spiral lamina becomes progressively smaller approaching the apex Space between it and the opposite wall of the labyrinth increases The apex where the two chambers formed by the incomplete lamina become hooklike which forms the helicotrema which is the region where the scala tympani and scala vestibuli will communicate

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50 Round Window provides communication between the scala tympani and the middle ear space Oval window permits communication between the scala vestibuli and the middle ear space Perilymph fluid fills the scala vestibuli and the scala tympani

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52 A fluid-filled sac that rests within the cavity of the osseous labyrinth- filled with endolymph fluid Vestibular system- Houses the vestibular organ Membranous labyrinth is in each ampulla, saccule and utricle

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54 Each ampulla houses a crista ampularis which is the sense organ for movement Houses the vestibular organ Ampulla- expanded region of the semicircular canals Utricle and Saccule- houses the otolithic organs of the vestibular system Communicate via the endolymphatic duct

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56 Cochlear duct forms a small portion of the membranous labyrinth Fluid in cochlear duct is endolymph Cochlear Duct- membranous labyrinth within the Cochlea Called the Scala Media-Resides between the scala vestibuli and scala tympani Houses the sensory apparatus for hearing

57 Reissner’s Membrane Divides the Scala vestibuli from the Scala Media Ceiling of the Organ of Corti Basilar Membrane Divides the Scala Media from the Scala tmpani Organ of Corti sits on it Floor of the Organ of Corti Tectorial Membrane Semitransparent and gelatinous-like Overlays hair cells- outer hair cells are embedded

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59 Cochlear Duct Organ of Corti has four rows of hair cells resting on a bed of Deiters’ cells for support Tunnel of Corti- separates 3 rows of outer hair cells from the single row of inner hair cells

60 Outer Hair Cells Three rows- approximately 12,000 Broadens to four rows at the apical end At the surface of each hair cell, forms a “W” or “V” pattern Shaped like a test tube Inner Hair Cells Modiolar side of the tunnel of Corti 3500 Hair cells Form a single row stretching from base to apex Upper surface of each hair cell forms a slight “U” pattern Shaped like a test tube or gourd

61 Each inner hair cell is connected to as many as 10 VIII vestibulocochlear nerve fibers referred to as “many-to-one” innervation Each outer hair cell shares its innervation with 10 other outer hair cells, all being innervated by the same VIII nerve fiber (one to many

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