0827 - Anatomy and Physiology of the Ear Flashcards
What is sound? How is it measured?
A longitudinal waves of pressure variations in a medium (typically air or water). It can be measured by pressure change or particle displacement. Pressure (Pa) is usually measured for hearing. Expressed in decibels, which is Pa relative to 20 micropascals.
Describe the cochlea.
A hollow, pea-sized, spiral-shaped organ. Hollow and fluid-filled with hair cells.
What are the three components of the ear and their sub-components?
Outer ear - pinna to tympanic membrane
Middle ear - 3 ossicles (malleus, incus, stapes) in an air space vented by the eustachian tube.
Inner ear - Labyrinth (Cochlea and semicircular canals.)
Where does the stapes connect? where is the pressure relieved?
Stapes Connects at oval window. Waves of pressure go through cochlea and resonate at round window.
What is the purpose of the middle ear muscles?
Gain control - in loud noises, reduce the amount of gain from the tympanic membrane and ossicles, reducing stress on the hair cells.
Stapedius and tensor tympani.
How does the organ of Corti work?
Contains the hair cells, innervated by cochlear nerve. Has 3 rows of outer hair cells (pressure detection and gain control/amplification via hydraulic motion, more efferent) and one row of inner hair cells (displacement sensing, more afferent). Outer hair cells much more delicate and sensitive, and degenerate with age.
What is the difference between efferent and afferent nerve pathways to the ear? What is their function?
Inner hair cells are actually hearing receptors, with afferent axons. Outer hair cells are largely efferent and control the gain (sensitivity) of the system.
How does the structure of the ear assist with hearing?
Pinna serves to amplify sound, direct it toward the tympanic membrane, and allow some direction sensing.
Middle ear allows that sound to be transmitted to the cochlear under higher pressure/less movement.
Cochlea has sensitivity for different frequencies along its length (base high, apex low). The shear stress bends the stereocilia, opening a K+ channel, causing depolarisation (remembering endolymph is rich in K+). In turn, this opens a VGCC, leading to an AP and Glu release.
