University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

399

Pages:

32
Author:

Kenley Davila

The Ear Sound is the audible vibration of air molecules created as a vibrating object pushes air molecules. The vibrating object could be the string of a guitar, a tire spinning on asphalt, the vocal cords of a bird… The normal Tympanic Membrane is shiny, translucent and pearlescent pink/grey. A “cone of light” should be prominent at 7 o'clock in the left ear and 5 o'clock in the right. Dilated blood vessels such as those shown do not necessarily indicate Otits Media. This vascular dilation often occurs following crying, coughing or a even a hard sneeze. Normal Tympanum as viewed with a pneumatic otoscope 16- 16-38 Acute Otitis Media 16-39 Acute Otitis Media 16-40 Ventillation Tube Traumatic perforation from a blow to the head 16-41 16-42 Subtotal Perforation Middle Ear • Air-filled cavity in temporal bone • Contains: – ear ossicles • malleus • incus • stapes – auditory tube (eustachian tube) connects middle ear and nasopharynx • equalizes air pressure on tympanic membrane – tensor tympani muscle attaches to the malleus and contracts in response to potentially damaging volume Inner Ear • Inner Ear is composed of a network of membranes called the “Membranous Labyrinth” located in petrous portion of temporal bone • Membranes make up the cochlea, vestibule, semicircular canals (semicircular ducts) • Membranes are filled with endolymph and surrounded by perilymph (similar to cerebrospinal fluid) Inner Ear • Membranous Labyrinth - tubes of thin epithelia that line bony tunnels are filled with endolymph (similar to intracellular fluid) and surrounded by perilymph (similar to cerebrospinal fluid) Organs and Innervation of the Inner Ear • Vestibular branch of Cranial Nerve VIII innervates vestibule and semicircular canals • Cochlear branch of Cranial Nerve VIII innervates the cochlea 16 Sound Conduction Through the Ear The Organ of Corti is a strip of sensitive “hair cells” on the basilar membrane in the cochlea. Cochlea • Cochlear Duct (scala media) contains endolymph and sensory hair cells anchored to the basilar membrane. • Vibrations of ossicles are carried by perilymph in canals surrounding the cochlear duct that make the basilar membrane vibrate. Sound Wave Transduction Through the Ear • Vibration of the tympanum, ossicles and oval window send shock waves into the cochlear fluid that vibrates the basilar membrane supporting the hair cells. Vibrations are dampened by the secondary tympanic membrane of the round window. 16 Basilar Membrane Frequency Response The basilar membrane is tuned for frequencies in the range of 20-20,000 Hertz - 16-55 Hair Cells of the Cochlea • Stereocilia of hair cells bump into the gelatinous tectorial membrane as the basilar membrane vibrates. • Inner Hair Cells are for hearing. • Outer Hair Cells adjust the tectorial membrane to increase precision of perception of specific frequencies. 16-56 Cochlear Hair Cells on the Basilar Membrane This audiogram has been filled in with illustrations to show where common sounds and parts of speech fit in. Frequency, or tone pitch is measured on the x-axis (horizontal axis) and sound intensity, or loudness is measured on the y-axis (vertical axis) in decibels (dB). The purple shaded area on the audiogram shows the pitch and loudness where most common speech sounds occur. An “s” sound is high in pitch, yet quiet, whereas the “u” sound is lower in pitch but louder. 16-58 A typical audiogram comparing normal and impaired hearing. The dip or notch at 4 kHz as shown, or at 6 kHz, is a symptom of noise-induced hearing loss. Scanning electron micrographs of the normal (a) and damaged (b) cochlear sensory epithelium Ryan A F PNAS 2000;97:6939-6940 Left - An undamaged mouse organ of Corti, showing rows of inner and outer hair cells. Right – A damaged mouse organ of Corti showing significant loss of sensory hair cells Cochlear Implant Vestibule: Saccule and Utricle • Vestiblue provides a sense of position relative to gravity. • Saccule and Utricle are the two sensory pouches of the Vestibule. • Stereocilia of hair cells are buried in a gelatinous membrane. • The membrane contains otoliths (crystals of calcium carbonate) that add density to the membrane and enhance the sense of gravity. • Changes in position of the head are sensed as the otolithic membrane is pulled by gravity. Saccule and Utricle • With the head erect, stimulation is minimal, but when the head is tilted, weight of membrane bends the stereocilia (static equilibrium) • When head is tilted down, or during acceleration, weight of otolithic membrane bends the stereocilia down and activates the hair cells (one type of dynamic equilibrium). Semicircular Canals (Ducts) Each semicircular canal has a crista ampularis that is a tuft of hair cells buried in a cupula (a mound of gelatinous membrane). Crista Ampullaris and Head Rotation Head rotation causes endolymph circulation that pushes the cupula and the hairs of the hair cells in the direction of the motion providing a sense of acceleration or deceleration.