30. Biophysics of sensory organs

Question 1

What does the action potential code?

Answer 1

modality, intensity (strength), duration and locaization of the stimulus

Question 2

Stevens’s law

Answer 2

Empirical relationship in psychophysics between an increased intensity of stimulus and the PERCIEVED magnitude increase in sensation. Power law.

Question 3

Stevens law equation

Answer 3

psi = cst * (phi/phi0)^n
phi : background intensity
phi0 : absolute threshold intensity
n : constant specific for the type of sensation percieved

Question 4

Weber Fechnar’s law

Answer 4

intensity of a sensation is proportional to the logarithm of the intensity of the stimulus causing it

Question 5

W-F law equation

Answer 5

psi = cst * log (phi/phi0)

Question 6

Frequency range at which auricle and canal are msot effective

Answer 6

2000-5000 Hz

Question 7

Parts of the inner ear (4)

Answer 7

oval window, semilunar ducts, cochlea, auditory tube

Question 8

How much is the stimulus amplified in the middle ear?

Answer 8

22x total, 17x because of surface difference with oval window, 1,3x because of lever action of ossicles

Question 9

Sone scale

Answer 9

L = 1/16 * (J/J0)^0.3

Question 10

How many phons is 1 sone?

Answer 10

1 sone = 40 phone

Question 11

Combines sensitivity of receptors

Answer 11

10^-9 - 10^5 lux

Question 12

Receptor that absorbs 1 photon

Answer 12

rhodopsin

Question 13

What is the name of activated rhodopsin

Answer 13

metarhodopsin

Question 14

What does metarhodopsin activate?

Answer 14

transducin (alpha subunit separated)

Question 15

Which percentage of the visible spectrum does the red receptor absorb?

Answer 15

64%

Question 16

Which percentage of the visible spectrum does the green receptor absorb?

Answer 16

32%

Question 17

Which percentage of the visible spectrum does the blue receptor absorb?

Answer 17

2%

Question 18

What are the 4 steps of signal transduction?

Answer 18

1. Incoming stimulus
2. Reception of stimulus (amplitude coding, adaptation) - receptor potential
3. Generation of an action potential (constant amplitude, frequency coding)
4. Activation of sensory areas in the brain

Question 19

What do receptors transform?

Answer 19

sensed stimuli into membrane potential changes = receptor potential

Question 20

What is the strength of the sensation proportional to?

Answer 20

to product of number of excited nerve fibers and he frequency of the action potential propagating through the fibers

Question 21

What is sensory adaptation?

Answer 21

a decrease in the frequency of the action potential during constant exposure to the stimulus

Question 22

What is the name of rapidly adapting receptors?

Answer 22

phasic adapting receptors

Question 23

What is the name for slowly adapting receptors?

Answer 23

tonic adapting receptors

Question 24

What is the amplitude of the oscillation at the stimulus threshold?

Answer 24

10^-11

Question 25

What do the ossicles do?

Answer 25

amplify the signal (22x total at the end) and transmit it to oval window

Question 26

How are the hair cells stimulated?

Answer 26

As the basilar membrane vibrates, it rubs the attached hair cells against the tectorial membrane

Question 27

Which ions enter the cells to depolarize it?

Answer 27

potassium ions

Question 28

What happens after the hair cells are depolarized?

Answer 28

Ca2+ channels open, Ca2+ enters hair cell, causes release of neurotransmitter in the synaptic cleft,

Question 29

How are outer hair cells used as amplifiers?

Answer 29

amplify by refining sensitivity of chochlea to mechanical vibration = source of mechanical energy by elongating

Question 30

What does the amplitude of the bekesy wave maximum depend on?

Answer 30

on loudness of stimulus

Question 31

What is the name of the reaction that is the basis of light sensing?

Answer 31

photochemical reaction

Question 32

What is the name of the receptor that absorbs 1 photon?

Answer 32

rhodobsin

Question 33

What is the activated form of that rhodobsin?

Answer 33

metarodobsin

Question 34

Which molecule does the receptor “cut” to activate?

Answer 34

transducin molecule

Question 35

Which molecule is then activated by the separated subunit of transducin?

Answer 35

phosphodiesterase