Chapter 17: Special Senses (Hearing) Flashcards
the ability to perceive sounds
HEARING
the science that deals with the ears, nose,
pharynx (throat), and larynx (voice box)
and their disorders.
OTORHINOLARYNGOLOGY
consists of the auricle, external auditory canal, and
eardrum
EXTERNAL EAR
or pinna is a flap of elastic cartilage
shaped like the flared end of a trumpet and
covered by skin
Auricle
The rim of the auricle
HELIX
the inferior portion
LOBULE
o is a curved tube about 2.5 cm (1 in.) long
that lies in the temporal bone and leads to
the eardrum.
External Auditory Canal
or eardrum is a thin, semitransparent
partition between the external auditory
canal and middle ear.
Tympanic Membrane
usually periodic ear irrigation or removal of wax with
a blunt instrument by trained medical personnel.
Impacted Cerumen
a small, air-filled cavity in the petrous portion of the
temporal bone that is lined by epithelium
MIDDLE EAR
attaches to the internal surface of the
tympanic membrane. The head of the
malleus articulates with the body of the
incus.
Malleus
the middle bone in the series, articulates
with the head of the stapes
Incus
o fits into the oval window.
Stapes
supplied by the mandibular branch of the
trigeminal (V) nerve, limits movement and
increases tension on the eardrum to
prevent damage to the inner ear from loud
noises
Tensor Tympani Muscle
which is supplied by the facial (VII) nerve,
is the smallest skeletal muscle in the
human body.
Stapedius Muscle
abnormally sensitive hearing due
Hyperacusia
or pharyngotympanic tube, commonly
known as the eustachian tube.
o The auditory tube, which consists of both
bone and elastic cartilage, connects the
middle ear with the nasopharynx (superior
portion of the throat)
Auditory Tube
also called the labyrinth because of its complicated
series of canals
INTERNAL EAR
alternating high- and low-pressure regions
traveling in the same direction through
some medium (such as air)
Sound Waves
The auricle directs sound waves into the external
auditory canal.
(2) When sound waves strike the tympanic membrane,
the alternating waves of high and low pressure in the
air cause the tympanic membrane to vibrate back
and forth. The tympanic membrane vibrates slowly in
response to low-frequency (low-pitched) sounds and
rapidly in response to high-frequency (high-pitched)
sounds.
(3) The central area of the tympanic membrane
connects to the malleus, which vibrates along with
the tympanic membrane. This vibration is transmitted
from the malleus to the incus and then to the stapes.
(4) As the stapes moves back and forth, its oval-shaped
footplate, which is attached via a ligament to the
circumference of the oval window, vibrates in the
oval window.
(5) The movement of the stapes at the oval window sets
up fluid pressure waves in the perilymph of the
cochlea. As the oval window bulges inward, it pushes
on the perilymph of the scala vestibuli.
(6) Pressure waves are transmitted from the scala
vestibuli to the scala tympani and eventually to the
round window, causing it to bulge outward into the
middle ear.
(7) As the pressure waves deform the walls of the scalea
vestibuli and scala tympani, they also push the
vestibular membrane back and forth, creating
pressure waves in the endolymph inside the cochlear
duct.
(8) The pressure waves in the endolymph cause the
basilar membrane to vibrate, which moves the hair
cells of the spiral organ against the tectorial
membrane. This leads to bending of the stereocilia
and ultimately to the generation of nerve impulses in
first-order neurons in cochlear nerve fibers.
PHYSIOLOGY OF HEARING
The axons of these neurons form the
cochlear branch of the vestibulocochlear
(VIII) nerve
o These axons synapse with neurons in the
cochlear nuclei in the medulla oblongata.
COCHLEAR NUCLEI
Some of the axons from the cochlear nuclei
decussate (cross over) in the medulla,
ascend in a tract called the ___________ on the opposite side
lateral
lemniscus
terminate in the inferior colliculus of the
midbrain
Inferior Colliculus
Other axons from the cochlear nuclei end in
the ____________ of the pons.
superior olivary nucleus
From each inferior colliculus, axons extend
to the medical geniculate nucleus of the
thalamus
Medial Geniculate nucleus
Neurons in the thalamus, in turn, project
axons to the ________________ of the
cerebral cortex in the temporal lobe of the
cerebrum ) in the temporal lobe, where
conscious awareness of sound occurs
primary auditory area
The ear not only detects sound, but also changes in
equilibrium or balance.
Body movements that stimulate the receptors for
equilibrium include linear acceleration or
deceleration, such as when a car suddenly takes off
or stops; tilting the head forward or backward, as if to
say “yes”; and rotational (angular) acceleration or
deceleration, such as when a rollercoaster takes a
quick curve
EQUILIBRIUM
Attached to the inner walls of both the
utricle and the saccule is a small, thickened
region
Mascula
Two types of cells
Hair Cells (sensory receptor)
Supporting Cells
As in the cochlea, the stereocilia are
connected by tip links. Collectively, the
stereocilia and kinocilium
Hair bundle
Scattered among the hair cells are
columnar supporting cells that probably
secrete the thick, gelatinous, glycoprotein
layer
Otolithic membrane
A layer of dense calcium carbonate crystals
o extends over the entire surface of the
otolithic membrane.
Otoliths
The three semicircular ducts lie at right angles to one
another in three planes posterior semicircular ducts,
and the horizontal one is the lateral semicircular duct
SEMICIRCULAR DUCTS
The dilated portion of each duct
o contains a small elevation called the crista
Ampulla
Each crista consists of a group of hair cells
and supporting cells
Crista
The hair cells contain a kinocilium and
stereocilia (collectively known as a hair
bundle), and the stereocilia are
interconnected via tip links
Hair Cells
Covering the crista is a mass of gelatinous
material
Cupula
Covering the crista is a mass of gelatinous
material
Cupula
