Chapter 6

Organ of Corti

the part of the cochlea that converts sound into neural activity

Structure of the organ of Corti

Structure of the organ of Corti

Sensory cells, or hair cells
Framework of supporting cells
Terminations of the auditory nerve fibers
The basilar membrane is the base of the organ of Corti.

Neurotransmitter release in hair cells

Stereocilia are connected to each other by tip links—tiny fibers that open ion channels when the stereocilia bend, a depolarization of the hair cell occurs and neurotransmitter is released

Tonotopic mapping

internally arranged sound frequencies from low frequency to high frequency

Place coding

pitch is determined by the location of the activated hair cells

Temporal coding

encodes the frequency of auditory stimuli in the firing rate of auditory neurons

Conduction deafness

disorders of the outer or middle ear prevent sounds from reaching the cochlea

Sensorineural deafness

hair cells fail to respond to movement of the basilar membrane; no action potentials fired

Central deafness

damage to auditory brain areas, such as by stroke, tumors, or traumatic brain injury

Ampulla

enlarged chamber at the base of the canals; contains hair cells

Vomeronasal system

detects pheromones

Why olfactory neurons regenerate

neurons die and are replaced in adulthood, this regenerative capacity is most likely an adaptation to the hazardous environment that olfactory neurons inhabit

Ossicles

the malleus, incus, and stapes—connect the tympanic membrane (eardrum) to the oval window

Decibel system

A pure tone is a tone with a single frequency of vibration. Most sound is more complex; sound from a musical instrument contains:
•A fundamental—the basic frequency
•Harmonics—multiples of that frequency
•Amplitude, or intensity, measured in decibels (dB) and perceived as loudness
•Frequency, measured in number of cycles per second, or hertz (Hz), and perceived as pitch

Function of hair cells in auditory system

A sloping brush of stereocilia, tiny hairs, protrude from each hair cell.
•Stereocilia are connected to each other by tip links—tiny fibers that open ion channels when the stereocilia bend.
•A depolarization of the hair cell occurs and neurotransmitter is released.

Frequency of sound

Different parts of the basilar membrane respond to different frequencies:
•High frequency—have greatest effect at the base, where it is narrow and relatively stiff
•Low frequency—produce larger response near the apex, where it is wider and more flexible

Factors that shape the auditory cortex

The spiral-shaped cochlea of the inner ear converts vibrations into neural activity.The cochlea has three parallel canals:
•Scala vestibuli (vestibular canal)
•Scala media (middle canal)
•Scala tympani (tympanic canal) The round window is a membrane that separates the tympanic canal from the middle ear; it can bulge outward a bit.

Taste receptor location on tongue

Papillae on the tongue increase surface area.Three kinds of taste papillae:
•Circumvallate
•Foliate
•Fungiform
Taste buds, embedded in the papillae, extend microvilli into a pore where they can contact tastants.
All areas of the tongue detect all five tastes.

Function of the vestibular system

The sensory system that detects balance. It consists of several small inner-ear structures that adjoin the cochlea.

The basic tastes

Salty, Sour, Sweet, Bitter, Umami

How tastes are perceived by taste cells

Taste buds, embedded in the papillae, extend microvilli into a pore where they can contact tastants.
All areas of the tongue detect all five tastes.

Gustatory system

extends from the tongue, to brainstem nuclei, to the thalamus, and ultimately to the somatosensory cortex.

Anatomy of the vestibular system

Semicircular canals—three fluid-filled tubes, connected to the utricle and sacculeo Canals (tubes) are oriented in three planes of head movement:
Nodding (pitch, y-axis)
Shaking (yaw, z-axis)
Tilting (roll, x-axis)