30. Biophysics of sensory organs Flashcards
What does the action potential code?
modality, intensity (strength), duration and locaization of the stimulus
Stevens’s law
Empirical relationship in psychophysics between an increased intensity of stimulus and the PERCIEVED magnitude increase in sensation. Power law.
Stevens law equation
psi = cst * (phi/phi0)^n
phi : background intensity
phi0 : absolute threshold intensity
n : constant specific for the type of sensation percieved
Weber Fechnar’s law
intensity of a sensation is proportional to the logarithm of the intensity of the stimulus causing it
W-F law equation
psi = cst * log (phi/phi0)
Frequency range at which auricle and canal are msot effective
2000-5000 Hz
Parts of the inner ear (4)
oval window, semilunar ducts, cochlea, auditory tube
How much is the stimulus amplified in the middle ear?
22x total, 17x because of surface difference with oval window, 1,3x because of lever action of ossicles
Sone scale
L = 1/16 * (J/J0)^0.3
How many phons is 1 sone?
1 sone = 40 phone
Combines sensitivity of receptors
10^-9 - 10^5 lux
Receptor that absorbs 1 photon
rhodopsin
What is the name of activated rhodopsin
metarhodopsin
What does metarhodopsin activate?
transducin (alpha subunit separated)
Which percentage of the visible spectrum does the red receptor absorb?
64%
Which percentage of the visible spectrum does the green receptor absorb?
32%
Which percentage of the visible spectrum does the blue receptor absorb?
2%
What are the 4 steps of signal transduction?
- Incoming stimulus
- Reception of stimulus (amplitude coding, adaptation) - receptor potential
- Generation of an action potential (constant amplitude, frequency coding)
- Activation of sensory areas in the brain
What do receptors transform?
sensed stimuli into membrane potential changes = receptor potential
What is the strength of the sensation proportional to?
to product of number of excited nerve fibers and he frequency of the action potential propagating through the fibers
What is sensory adaptation?
a decrease in the frequency of the action potential during constant exposure to the stimulus
What is the name of rapidly adapting receptors?
phasic adapting receptors
What is the name for slowly adapting receptors?
tonic adapting receptors
What is the amplitude of the oscillation at the stimulus threshold?
10^-11
What do the ossicles do?
amplify the signal (22x total at the end) and transmit it to oval window
How are the hair cells stimulated?
As the basilar membrane vibrates, it rubs the attached hair cells against the tectorial membrane
Which ions enter the cells to depolarize it?
potassium ions
What happens after the hair cells are depolarized?
Ca2+ channels open, Ca2+ enters hair cell, causes release of neurotransmitter in the synaptic cleft,
How are outer hair cells used as amplifiers?
amplify by refining sensitivity of chochlea to mechanical vibration = source of mechanical energy by elongating
What does the amplitude of the bekesy wave maximum depend on?
on loudness of stimulus
What is the name of the reaction that is the basis of light sensing?
photochemical reaction
What is the name of the receptor that absorbs 1 photon?
rhodobsin
What is the activated form of that rhodobsin?
metarodobsin
Which molecule does the receptor “cut” to activate?
transducin molecule
Which molecule is then activated by the separated subunit of transducin?
phosphodiesterase
