Download Sensory_systems

Sensory systems
Chapter 16
Ear anatomy
• 3 major areas of ear:
1) outer ear
- pinna – directs sound waves toward auditory
canal
- external auditory canal – produces earwax
that prevents foreign particles from entering
- tympanic membrane (eardrum) – vibrates in
response to sound waves and sends signal to
middle ear
- separates outer and middle ear
Ear anatomy
2) middle ear
- oval window
- round window
- Eustachian tube – links middle ear to throat
- opens in response to swallowing or yawning
- equalizes pressure in middle ear cavity with air
pressure
- important for proper vibration of
eardrum
- ossicles – transmit vibration of eardrum to oval
window
- malleus, incus, and stapes
Ear anatomy
3) inner ear or labyrinth
- bony labyrinth
- vestibule
- cochlea
- semicircular canals
- membranous labyrinth – sacs and ducts
within the labyrinth
Inner ear
• Vestibule – central cavity of labyrinth
- 2 membranous sacs:
- saccule
- utricle
- important in maintaining balance
- respond to movement of head and change
in gravity
Inner ear
• Semicircular canals
- anterior and posterior at right angle
- lateral lies horizontally
- semicircular duct – communication with
utricle
- contains ampulla at one end
- maintain balance
Inner ear
• Cochlea (snail)
- cochlear duct
- organ of Corti – receptor region for hearing
- spiral lamina – divides cochlea into 3 regions
- scala vestibuli – next to oval window
- filled with perilymph
- scala media – cochlear duct
- fsAAilled with endolymph
- scala tympani – next to round window
- filled with perilymph
Inner ear
• Cochlea
- basilar membrane in cochlear duct
- supports organ of Corti
Properties of sound
• Sound is vibration that creates pressure
disturbance
- propagated by compression of molecules
- speed determined by medium
- sound wave is produced by a series of molecule
compressions and rarefactions (low pressure areas)
- moves outward in all directions
- energy transferred in direction of sound wave
and as the wave energy declines, sound disappears
Properties of sound
• Sine wave can be used to infer frequency and amplitude
- distance between 2 consecutive crests is wavelength
- wavelength constant for a particular tone
• Frequency – number of sine waves that pass a given
point in a given time
- smaller wavelengths have higher frequency
- human hearing is 20 – 20,000 Hz
- best between 1400 and 1500 Hz
- perceive frequency as pitch
- increased frequency means higher pitch
Properties of sound
• Amplitude – height of sound waves
- corresponds to intensity
- pressure differences between compressed and
rarefied areas
• Loudness – person’s interpretation of sound
intensity
Sound transmission in ear
• Signal for sound must reach the auditory cortex before
sound can occur
• Steps involved in sound transmission:
1) sound enters auditory canal and hits tympanic membrane
(eardrum)
2) tympanic membrane vibrates at the frequency of the
sound wave
3) vibration is passed to ossicles and sound is amplified
4) ossicle activity causes oval window to vibrate and fluid
in cochlea to move in waves
Sound transmission in ear
5) Basilar membrane swings up and down and round
window swings in and out
6) Basilar membrane vibrates
- if vibration occurs near the oval window then
high frequency
- if vibration occurs near the cochlear apex then
low frequency
- difference due to size of fibers
Sound transmission in ear
6) Movement of basilar membrane causes hair
cells in organ of Corti to bend
- if hair bends toward tallest hair, then get
depolarization
- neurotransmitter release
- cochlear fibers transmit impulses to brain
for auditory interpretation
- if hair cells bend away from tallest hair, then
hyperpolarization
From ear to brain
7) Impulses from organ of Corti travel to
cochlear nuclei of the medulla
8) From medulla impulses travel to superior
olivary nucleus then to the inferior colliculus
9) From inferior colliculus impulses go to
medial geniculate bodies in the thalamus and
then to auditory cortex
- inferior colliculus also sends impulses to
superior colliculus for reflex action
Hearing disorders
• Conduction deafness – sound cannot reach fluids of inner
ear
- earwax buildup
- ruptured eardrum
- middle ear inflammation (ear infection)
• Sensorineural deafness – damage to auditory structures in
brain
- loss of hearing receptors
- age
- sudden explosive loud noise
- prolonged exposure to high-intensity sounds
Hearing disorders
• Tinnitus – ringing or clicking sound in ears
- cochlear nerve degeneration
- middle or inner ear inflammation
- side effect from some medications