Lecture 6 Audition, Vestibular Sense, Chemical Senses

Front 1

What are the two parts of the outer ear?

Back 1

Pinna and ear canal

Front 2

What does the pinna do?

Back 2

-captures sound, focuses and enhances sound in speech range (2k-5k Hz)

Front 3

What is the purpose of the middle ear?

Back 3

concentrates sound energy and transmits it from external environment to cochlea

Front 4

What are the parts of the middle ear?

Back 4

a. Tympanic membrane
b. Ossicles: malleus, incus, stapes (or hammer, anvil, stirrup)
c. Oval window
d. Regulation of vibration intensity: tensor tympani and stapedius

Front 5

What are the parts of the inner ear?

Back 5

a. Cochlea--three canals: tympanic, vestibular, middle
b. Round window to relieve pressure on incompressible fluid filling these canals
c. Basilar membrane
d. Organ of Corti

Front 6

What are the names of the three ossicles?

Back 6

malleus, incus, stapes

Front 7

What parts of the middle ear are responsible for regulating vibration intensity?

Back 7

tensor tympani and stapedius

Front 8

What are the three canals of the cochlea?

Back 8

tympanic, vestibular, middle

Front 9

What is the round window used for?

Back 9

relieve pressure on incompressible fluid filling these canals

Front 10

What is the basilar membrane used for?

Back 10

vibrates at different places for different frequencies

Front 11

What is the organ of coti?

Back 11

Sound transducer

Front 12

How does the organ of coti work?

Back 12

1) Basilar membrane vibrates
2) Inner hair cells and outer hair cells (about 12000 total) extend stereocilia into indentations in tectorial membrane and move when basilar membrane vibrates
3) Tip links on stereocilia open K+ gates, which depolarize cells cause influx of Ca+2 at base of cell 4. Most sound information carried by inner hair cells
5. Outer hair cells modulate and "tune" response of inner hair cells by changing distance of tectorial membrane from tip of IHC's --longer when hyperpolarized
—shorter when depolarized
--effect is to amplify or dampen basilar membrane motion

Front 13

How does the ear analyze incoming sounds?

Back 13

1. Sound waves cause waves in cochlear fluid
2. Shape and thickness of basilar membrane performs a physical Fourier analysis
3. Tuning curves of individual auditory nerve cells

Front 14

What are sources of sounds emitted by the ear?

Back 14

Evoked Otoacoustic emissions—triggered by external stimulation and seem to be part of normal sharpening of sound perception by cochlea itself

Spontaneous otoacoustic emissions--not perceived by the person, but are associated with more sensitive hearing

Front 15

What is the path from the ear to the brain?

Back 15

1. Inner and some outer hair cells synapse on cells of auditory nerve
2. Auditory nerve branches, goes to dorsal and ventral cochlear nuclei.
3. Several paths from cochlear nuclei:
--one set to superior olivary nuclei—from both ears--first binaural interaction
--other sets to inferior colliculi, then to medial geniculate nucleus of thalamus
4. Then to primary auditory cortex
5. And other auditory analysis systems for complex sounds or speech

Front 16

What are the theories of pitch discrimination?

Back 16

Place Theory
Volley Theory

Front 17

What is Place theory in terms of pitch discrimination?

Back 17

perception depends on where on the basilar membrane the maximal displacement occurs

Front 18

What is Volley theory in terms of pitch discrimination?

Back 18

perception depends on frequency and pattern of neural firing (phase locking)

Front 19

What is the real story of pitch discrimination?

Back 19

Place Theory above 1.5 kHz; Volley Theorymostly below 1.5 kHz, but up to 4kHz

Front 20

What are ways we localize sound?

Back 20

1. Monaural detection: loudness of sound
2. Binaural detection

Front 21

How do we localize sounds using both ears?

Back 21

a. Intensity differences for high frequency sounds
b. Latency differences (onset and phase disparity) for low-frequency sounds
c. As before, it's really duplex (both)
d. Most done in the superior olivary nucleus
e. And some spectral filtering by the pinna

Front 22

How / Where do we perceive complex sounds?

Back 22

1. Dorsal stream (parietal lobe): spatial location="where"
2. Ventral stream (temporal lobe): complex analysis="what"
3. Musical training enlarges Heschl's gyrus

Front 23

What are the three types of deafness

Back 23

1. Conduction deafness
2. Sensorineural deafness
3. Central deafness

Front 24

Define Conduction deafness

Back 24

problem is in the outer or middle ear, so sound never reaches the cochlea

Front 25

Define Sensorineural deafness

Back 25

problem is in the cochlea or the auditory nerve fibers (too much rock music)

Front 26

Define Central deafness

Back 26

problem is in the cortex, in comprehending sound; examples: word deafness, cortical deafness (loss of projections from medial geniculate--get reflexes and body responses, but no experience of hearing)

Front 27

What does the Vestibular sense do?

Back 27

motion/acceleration detection

Front 28

How does the vestibular sense work?

Back 28

1. Semicircular canals, oriented at right angles, filled with fluid
2. Connected by utricle to the saccule
3. Ampullae at junction between canal and utricle contain hair cells with cilia embedded in a gelatinous layer called the cupula; otoliths increase sensitivity.
4. Acceleration in any direction causes hair cells to bend and start a generator potential.
5. Receptors in utricle and saccule respond to static position of head

Front 29

What are the brain pathways for the vestibular sense?

Back 29

1. Fibers from receptors synapse in vestibular nuclei, while another set go to the cerebellum
2. Pathway complicated from there--to motor nuclei of eye muscles, thalamus and cortex

Front 30

What is the theory of Motion Sickness?

Back 30

1. Sensory conflict theory

Front 31

What are the two taste receptor cell types?

Back 31

a. Papillae
b. Taste buds

Front 32

Describe papillae

Back 32

fungiform around top edge (one taste bud per), foliate on sides of back, circumvallate on top of back of tongue

Front 33

Describe taste buds

Back 33

multiple receptor cells in various stages of development

Front 34

What are the five basic tastes?

Back 34

Salty
Sour
Sweet
Bitter
Umami

Front 35

What are the details of the salty taste?

Back 35

chemical salts, usually Na+ going through Na+ channels

Front 36

What are the details of the sour taste?

Back 36

chemical acids, i.e., H+ ions present -H+ blocks K+ channels so ion cannot get out

Front 37

What are the details of the sweet taste?

Back 37

saccharides, but that is not all
--second messenger G proteins: gustducins —coupled T1R2 +T1R3 receptors

Front 38

What are the details of the bitter taste?

Back 38

many different types
--Also gustducin second messengers
--25 types of T2R receptors, so pattern is the key

Front 39

What are the details of the umami taste?

Back 39

—"meaty" taste
--glutamate receptors
--amino acid receptors: T1R1+T1R3

Front 40

What are the pathways for taste?

Back 40

Initially to medulla, then to posterior medial nucleus of thalamus, then to somatosensory cortex

Front 41

What is the physiology of the olfactory sense?

Back 41

a. Olfactory epithelium with receptors, supporting cells and basal cells that will become receptor cells
b. Apical dendrite of receptor cells ends in a dendritic knob with cilia embedded in mucosal layer of epithelium
c. Connections to olfactory bulb are in glomeruli
d. Turbinates direct airflow to the receptor areas

Front 42

How is olfactory transduction accomplished?

Back 42

Transduction is another second messenger/G protein exercise
--Each odor seems to have its own receptor type, but all seem to use same Golf protein

Front 43

How many genes are involved in olfactory senses?

Back 43

Mice have 1000 different receptor proteins, humans have 900 genes but only 350 are expressed

Front 44

What are the olfactory pathways to the brain?

Back 44

a. Axons of olfactory receptors are very small and unmyelinated; pass through cribiform plate to synapse on mitral cells in olfactory bulb
b. One path goes through amygdala to hypothalamus, then to orbitofrontal cortex
c. Another path goes through prepyriform cortex (on tip of temporal lobe near amygdala), then to medial dorsal thalamus then orbitofrontal cortex
4. Note unique aspect: both pathways reach cortex without synapsing in thalamus; and both pass through limbic system on the way there.

Front 45

What is the Vomeronasal system

Back 45

specialized for pheromones
--human system is vestigial, and genes that encode the receptors are nonfunctional (but something works at least a little in humans)