Special senses- 3 Flashcards
Each ear consists of three parts:
The external ear
The middle ear
The inner ear
Hearing
neural perception of sound energy
neural perception of sound energy
the identification of the sounds and their localization.
traveling vibrations of air
Sound waves
Sound is characterized by its
pitch (tone), intensity (loudness), and timbre (quality)
The pitch, or tone, of a sound is determined by
the frequency of vibrations.
The greater the frequency of vibration
the higher the pitch
The intensity, or loudness, of a sound depends on the
amplitude of the sound waves
Within the hearing range, the greater the amplitude
the louder the sound
The timbre, or quality, of a sound depends on
its overtones
The specialized receptor cells for sound are located in
the fluid filled inner ear
The external ear consists of:
The pinna (ear) The external auditory meatus (ear canal) Tympanic membrane (eardrum).
vibrates when struck by sound waves
tympanic membrane
causes the eardrum to bow inward and outward in unison with the wave’s frequency,
A sound wave
For the membrane to be free to move as sound waves strike it
the resting air pressure on both sides of the tympanic membrane must be equal.
connects the middle ear to the pharynx
The eustachian (auditory) tube
The middle ear
transfers the vibrating movements of the tympanic membrane to the fluid of the inner ear.
This transfer of the vibrating movements is facilitated by
a movable chain of three small bones, or ossicles (the malleus, incus, and stapes).
the malleus
[The first bone]
- Is attached to the tympanic membrane
the stapes
[the last bone]
- attached to the oval window
–> the entrance into the fluid-filled cochlea.
Transmits the frequency of movement from the tympanic membrane to the oval window.
The resulting pressure on the oval window with each vibration produces
wavelike movements in the inner ear fluid at the same frequency as the original sound waves.
The snail-shaped cochlea
[Inner ear]
the “hearing” portion of the inner ear, is a coiled tubular system lying deep within the temporal bone
The cochlea is divided throughout most of its length into three fluid-filled longitudinal compartments.
the sense organ for hearing.
Organ of Corti
Pitch and Timbre discrimination
- Depends on the shape and properties of
the basilar membrane - Different regions of the basilar membrane
naturally vibrate maximally at different
frequencies - A sound wave of a particular frequency
travels to the region of the basilar
membrane that naturally responds
maximally to that frequency - Each hair cell is “tuned” to an optimal
sound frequency, determined by its
location on the organ of Corti. - Overtones of varying frequencies cause
many points along the basilar membrane to vibrate simultaneously but less intensely than the fundamental tone, enabling the CNS to distinguish the timbre of the sound (timbre discrimination).
Intensity (loudness) discrimination
- Depends on the amplitude of vibration.
- As sound waves originating from louder
sound sources strike the eardrum, they
cause it to vibrate more vigorously but at
the same frequency as a softer sound of the
same pitch. - The greater tympanic membrane deflection
translates into greater basilar membrane
movement in the region of peak
responsiveness, causing greater bending of
the hairs in this region. - The CNS interprets this greater hair
bending as a louder sound. - Thus, pitch discrimination depends on
“where” the basilar membrane maximally
vibrates and loudness discrimination
depends on “how much” this place vibrates.
Intensity (loudness) discrimination
- Depends on the amplitude of vibration.
- As sound waves originating from louder
sound sources strike the eardrum, they
cause it to vibrate more vigorously but at
the same frequency as a softer sound of the
same pitch. - The greater tympanic membrane deflection
translates into greater basilar membrane
movement in the region of peak
responsiveness, causing greater bending of
the hairs in this region. - The CNS interprets this greater hair
bending as a louder sound. - Thus, pitch discrimination depends on
“where” the basilar membrane maximally
vibrates and loudness discrimination
depends on “how much” this place vibrates.
Loss of hearing, or deafness, may be
temporary or permanent,
partial or complete.
Deafness is classified into two types
- Conductive deafness
- Sensorineural deafness
Depending on the part of the hearing mechanism that fails to function adequately.
Conductive deafness
Occurs when sound waves are not adequately conducted through the external and middle portions of the ear.
Possible causes of conductive deafness
- Physical blockage of the ear canal with
earwax - Rupture of the eardrum
- Middle ear infections with accompanying
fluid accumulation - Restriction of ossicular movement because
of bony adhesions.
Sensorineural Deafness
sound waves are transmitted to the inner ear, but they are not translated into nerve signals that are interpreted by the brain as sound sensations.
In Sensorineural Deafness, the defect can lie
- In the organ of Corti,
- In the auditory nerves
- rarely, in the ascending auditory pathways
or auditory cortex
Hearing Aids
- Are helpful in conductive deafness but are
less beneficial for sensorineural deafness. - These devices increase the intensity of
airborne sounds and may modify the sound
spectrum and tailor it to the person’s
particular pattern of hearing loss at higher
or lower frequencies. - For the sound to be perceived the receptor
cell–neural pathway system must still be
intact
Is the sense of body orientation and motion.
Equilibrium
The vestibular apparatus consists of two sets of structures lying within a tunneled-out region of the temporal bone near the cochlea:
The semi-circular canals
The otolith organs.
The vestibular apparatus
detects changes in position and motion of the head
The semi-circular canals
detect rotational or angular acceleration or deceleration of the head, such as when turning the head, starting or stopping spinning, or somersaulting.
The otolith organs
provide information about the position of the head relative to gravity and detect changes in the rate of linear motion
Collects and transfers sound waves to middle ear
external ear
Collects sound waves and channels them down the ear canal; contributes to sound localization
Pinna (ear)
Tunnel from the exterior through to the temporal bone, to the tympanic membrane
Directs sound waves to the tympanic membrane
External auditory meatus ( ear canal)
House sensory system for hearing
Cochlea (inner ear
Thin membrane at the entrance of the cochlea, separates the middle ear from the scala vestibule
Vibrates in unison with the movement of the stapes, to which it is attached; oval window movement sets cochlear perilymph in motion
Oval window
Contains perilymph that is set in motion by oval window movement, driven by the oscillation of middle ear bones
Scala vestibuli
Lower compartment of the cochlea
Contains perilymph that is continuous with the scala vestibuli
Scala tympani
Contains endolymph, houses the basement membrane
Cochlear duct ( scala media)
Forms floor of the cochlear duct
Vibrates in unison with perilymph movements; bears the organ of corti
Basil membrane
Contains hair cells, the receptors for sound; inner hair cells undergo receptor potentials when their hairs are bent as a result of fluid movement in the cochlea
Organ of corti
Stationary membrane that overhangs the organ of corti and contracts the surface hairs of the receptor hair cells
Tectorial membrane
Thin membrane that separates the scala tympani from the middle ear.
Vibrates in unison with the perilymph to dissipate pressure in the cochlea; does not contribute to sound reception
ROund window
Detects changes in head position away from vertical and horizontally directed linear acceleration and declaration
Utricle
Detects changes in head position away from horizontal and vertically directed linear acceleration and declaration
Saccule
