Sensory Lecture


Hearing


Fig. 10-17
Outer, middle and inner ear
Ear structure
pinna, eardrum=tympanic membrane, ossicles, cochlea, part of nerve VIII = cochlear nerve
hammer, anvil, stirrup=malleus, incus, stapes - to match impedance of air -> fluid
Eustachian tube
oval window is "inner ear drum"
20:1 "amplification" tympanic to oval
cochlea near vestibular apparatus

Fig. 10-18
Sound waves
waves of compressions and rarefactions of air (must have medium) described by sine wave
Frequency Hz cycles per sec
vibration - 20 - 20,000 Hz, above which is ultrasound

Fig. 10-19
Pressure in the perilymph

Fig. 10.22
Frequency discrimination
Vibration of basilar membrane is mapped by tonotopy
fluid vibration at oval window through helicotrema
released at round window
Frequency discrimination is mapped at high frequencies this way
Frequency discrimination very good - 2 Hz at 1000 Hz
Georg von Bekesy's data pertaining to Helmholtz's place (resonance) theory
1961 Nobel "physical mechanism of stimulation within the coclea"

Taste (Gustation)

Fig. 10-15
Histology and model of the taste cell
generally, channel or G-protein linked receptor ultimately increasing calcium somehow for synapse
note receptor does not have axon

Fig. 10-16
Transduction in the taste cell
salt - amiloride blocked Na+ channel opens (depolarization)
sour - pH sensitive K+ channel closes (depolarization)
also amiloride blocked Na+ channel
sweet - G-protein linked cAMP close K+ channel - depolarize
umami (glutamate) - and amino acids, channels as well as G-protein cascade
Note, here is the TRP (transient receptor potential) channel again
bitter -G-protein cascade involving PLC or quinine sensitive K+ channel
"gusducin" (like "transducin" for vision) is term for heterotrimeric G protein

Smell (Olfaction)

Fig. 10-14(a&b)
Anatomy of olfaction
Anatomy of olfactory epithelium.
Note: the receptors are neurons
Receptors turn over (this is unusual), as noted by dividing stem cell and developing (immature) receptor, since cells are very exposed (to dry air, pathogens, etc.). New cells must establish connections.
There are also sustaining cells

G-protein coupled receptor is very variable (there may be thousands, meaning that olfactory receptors contribute predominantly to diversity of G-protein-coupled receptors) and has specific variable regions.

In the early 1990's, olfactory receptors were found to be G protein coupled receptors, and there are lots of olfactory receptors; Richard Axel and Linda B. Buch won the 2004 Nobel prize for this work. I see from my alumni magazine that Axel was class of 67 at my college (Columbia College) while I was class of 69. He kept working there (at the med school) and joins 70 from Columbia to get the Nobel Prize, 19 in Physiology and Medicine. I followed the link suggested by by my alumni magazine and found this.

Recent work
G. Barnes, S. O'Donnell, F. Mancia, X Sun, A. Nemes, M. Mendelsohn, and R. Axel, Odorant Receptors on axon termini in the brain, Science, 304, 1468, 2004
Each cell expresses only one type of receptor.
Seemingly randomly arranged on olfactory epithelium.
Axons of axons with same receptors converge at glomeruli.
The same receptors are used in axon guidance.

Quiz and exam questions from 2005 relating to this outline and lab

In the 1800s, Helmholtz proposed a "place theory," confirmed and modified in the Nobel prize work of Bekesy. Place - in what specific structure? To explain what? (2 points)

place along basilar membrane for frequency discrimination

If two tones near 1000 Hz give 5 beats per second when presented simultaneously to one ear, what will you notice if they are presented sequentially to one ear?

one will be clearly a higher pitch than the other

How many primary taste qualities are mediated on the tongue?

sweet sour salty bitter umami

Axel and Buck won the 2004 Nobel prize for showing that what kind of molecules are responsible for the richness of olfactory perception?

G protein coupled receptors

Define ultrasound.

higher frequency than human limit (20,000 Hz)

Binaural beats (two slightly different low frequencies played to the two different ears), if you could hear them, pertain to what theory of frequency discrimination?

frequency telephone theory of Rutherford

Describe the function of the G protein-coupled receptor in olfaction

The chemical receptors for the odorant ligands, there are many (1,000)

When your ear was put to the tuning fork and speaker we heard beats, what exactly are
these beats?

constructive and destructive interference of sound waves

Is a non-taster for PTC a homozygote or heterozygote?

homozygous

What is the ligand for umami receptors?

glutamate

Waves are measured in cycles per second, but what are the units of frequency?

Hz


What is the snail like structure in the ear called?

cochlea

The Malleus, Incus, and Stapes are collectively referred at as what?

ossicles

What number cranial "nerve" is the olfactory bulb?

One

What type of receptor are all olfactory receptors?

G protein linked receptors

What number cranial nerve is the auditory nerve?

8

Where is the synapse of a gustatory receptor?

right in the cell, no axon

What type of molecule is the salt receptor?

channel

Name the five tastes mediated on the tongue.

salt sour sweet bitter umami

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