Ear Anatomy & Physiology Flashcards
what 3 regions is the ear divided into?
external, middle, and internal
what is the inner ear associated with?
vestibular sense (equilibrium)
the outer ear consists of?
auricle (pinna), external auditory canal (meatus), and the tympanic membrane
purpose of the external auditory canal?
lined with ceruminous glands that secrete cerumen (ear wax) that traps & removes debris before it reaches tympanic membrane; also lubricates and waterproofs canal and tympanic membrane
what is the tympanic membrane?
thin sheet of epithelium and connective tissue
purpose of tympanic membrane?
separates outer and middle ear regions; transmits energy of sound waves
what is the auricle (pinna)?
elastic cartilage with fleshy lobule covered with skin
purpose of the auricle (pinna)?
funnels sound waves into external auditory canal
purpose of the pharyngotympanic tube?
connects nasopharynx with middle ear; equalizes air pressure on both sides of tympanic membrane
what does the middle ear consist of?
pharyngotympanic tube and auditory ossicles
what are auditory ossicles?
bones within the middle ear, named by their shapes and connected to one another
list the auditory ossicles
malleus, incus, and stapes
purpose of the auditory ossicles?
link tympanic membrane to outer wall of inner ear; amplify and convert incoming sound waves in air into fluid movement
what skeletal muscles are attached to ossicles?
tensor tympani and stapedius muscle
purpose of tensor tympani muscle?
tightens tympanic membrane by pulling it medially
purpose of stapedius muscle?
reduces movement of ossicles as unit
what is reflexive in middle ear?
prevents damage from loud sounds by reducing movement of both the tympanic membrane and ossicles
what are the 3 parts of the inner ear?
cochlea, vestibule, and semicircular canals
what are labyrinths?
network of serpentine pathways
what types of labyrinths are in the inner ear?
bony and membranous
what is bony labyrinth?
open passageways that make up inner ear chamber
what is membranous labyrinth?
membranes that line bony labyrinth
what is endolymph?
within membranous labyrinth; potassium ion concentration is greater than sodium ion concentration; similar to intracellular fluid
what is perilymph?
between bony and membranous labyrinths; sodium ion concentration is greater than potassium ion concentration; similar to extracellular fluid
what is the purpose of labyrinths?
transduce sound waves and head movements into electrical signals
what does the vestibule contain?
membranous oval window and utricle & saccule
what is the purpose of the vestibule?
information about head tilting and linear movement
what is the utricle & saccule?
two parts of membranous labyrinth that contain receptor cells
what are semicircular canals?
three tubes of membranous labyrinth
list the semicircular ducts
anterior, posterior, and lateral
what is the purpose of the semicircular ducts?
detect rotational movement of head in any body plane
what is the ampulla?
enlarged bulb at base of each duct that contains receptor cells
what is the round window?
membrane-covered opening on the cochlea
what are the parts of the cochlea?
cochlear duct (scala media), scala vestibuli, scala tympani, and vestibular membrane, basilar membrane, and spiral organ (organ of Corti)
what separates the middle and inner ear?
cochlea
what is the cochlear duct (scala media)?
spiral-shaped segment of membranous labyrinth
what are the chambers of the cochlea?
scala vestibuli and scala tympani
what is the vestibular membrane?
epithelium; boundary between cochlear duct and scala vestibuli
what is the basilar membrane?
collagenous connective tissue
what is the purpose of the vestibular membrane?
separates endolymph from perilymph; maintains homeostasis of each fluid
what is the purpose of the basilar membrane?
separates cochlear duct and scala tympani; detects variations in sound pitch
what is the spiral organ (organ of Corti)?
within cochlear duct and supported by basilar membrane
what is the purpose of spiral organ (organ of Corti)?
contains receptor cells for hearing; converts sound waves into electrical impulses; allows for transfer of sound wave energy to region where vibrations can be transduced
what are sound waves?
generated by displacement of air molecules in response to moving object
pitch =
frequency
what is frequency measured in?
Hertz
what is the hearing range for a human?
between 20-20,000 Hertz
loudness =
amplitude
what is amplitude measured in?
decibels
what is pitch?
how many times object vibrates back and forth during certain period; determined by which area of basilar membrane vibrates
what is loudness?
difference between areas of high and low pressure; determined by how much basilar membrane vibrates
what is the transmission of sound?
auricle – auditory canal – tympanic membrane – vibration – ossicles – oval window – vibration of oval window – waves in fluid (mostly perilymph)
high frequency vibrations in the inner ear travel where?
shortcut through cochlear duct to reach scala tympani; cause endolymph and basilar membrane to vibrate
low frequency vibrations travel where?
further into the cochlea where basilar membrane is wider and more flexible
very low frequency sound waves travel where?
tip of the cochlea where scala vestibuli is connected to scala tympani at helicotrema (opening)
what part is essential for allowing fluid to move within the inner ear?
round window
what is the inner ear function?
oval window – perilymph of vestibule – scala vestibuli of cochlea – high or low vibrations
what are hair cells?
receptor cells within spiral organ that are grouped into inner and outer hair cells
what are inner hair cells?
form single row of cells and primarily responsible for detecting sound
what are outer hair cells?
three rows of cells
the action of sound with hair cells
vibration of basilar membrane causes hair cells to move at tectorial membrane – stereocilia bend as they bump into tectorial membrane – opens potassium ion channels to depolarize hair cell
the basilar membrane moves up toward the tectorial membrane, bending the stereocilia toward the tallest stereocilium – bending the stereocilia opens potassium channels that depolarize the hair cell – the depolarized hair cell releases neurotransmitters, triggering action potentials in the axon of the cochlear nerve
what is the tectorial membrane?
stiff structure that extends over hair cells
what is stereocilia?
microvilli; arranged from longest to shortest and flex at their junction with hair cell body
what is the auditory pathway?
action potentials propagate through axons of the cochlear portion of the vestibulocochlear nerve to the cochlear nuclei at the medulla-pons junction – axons from the cochlear nuclei synapse on the superior olivary nucleus in the pons – auditory stimuli are then sent to the inferior colliculus of the midbrain – the auditory stimuli are relayed to the medial geniculate nucleus of the thalamus – the thalamus stimulates neurons of the primary auditory cortex in the superior portion of the temporal lobe
what is the sense of equilibrium?
depends on input from the visual system, proprioceptors in muscles and joints, and vestibular system
what are the 2 types of equilibrium?
static and dynamic
what is static equilibrium?
maintaining balance when head is tilted but head and body are not moving
what is dynamic equilibrium?
maintaining balance when head or body is undergoing rotational or angular motions or linear acceleration
what is macula?
receptor cells for head position and movement
as stereocilia bend toward the kinocilium –
the hair cells depolarize and release more glutamate
as stereocilia bend away from the kinocilium –
the hair cells hyperpolarize and release less glutamate
when head turns –
the endolymph lags behind and moves in the opposite direction from the way the head turns; this pushes on the cupula, which depolarizes the hair cells and produces more glutamate
when head stops turning –
the endolymph continues to move in the same direction as the head was turned, which hyperpolarizes the hair cells and produces less glutamate
vestibular sensation pathway
action potentials propagate to the vestibular nuclei located at the medulla-pons junction – the vestibular nuclei relay the signals simultaneously to the following areas of the CNS: the thalamus and then the inferior parietal lobe, for conscious awareness of head position and movement
the cranial nerve nuclei, to coordinate eye movement in response to head movement
the cerebellum and spinal cord, to coordinate muscle movement that maintains balance in response to head movement
what is the vestibular system?
vestibule & semicircular canals; provide info about head position and movement
what are otoliths?
calcium carbonate crystals that increase membrane density
