Biophysics Of The Sensory System

Front 1

218. What is the definition of visible light?

Back 1

The range of electromagnetic radiation observable by the human eye (approximately 400-750 nm).

Front 2

219. What is the wavelength range of ultraviolet radiation?

Back 2

10 nm - 400 nm

Front 3

220. What is the wavelength range of infrared radiation?

Back 3

750 nm - 1 mm

Front 4

221. Which physical characteristics of the eye lens are changed during accommodation?

Back 4

The shape (radius of curvature) and the refractive index of the lens. In the case of humans the former is dominant.

Front 5

222. Give the definition and unit of diopter.

Back 5

D (diopter) = 1/f
where f is the focal length of the lens.
Unit: 1/m.

Front 6

223. What is the resolution of an eye?

Back 6

The smallest visual angle at which the images of two points can be distinguished.

Front 7

224. What is the physical and biological limit of the resolution of an eye?

Back 7

Physical: The separation between the two points to be distinguished should not be less than the wavelength of the illuminating light.
Biological: Images of the two points to be distinguished have to be on different photoreceptors, and there has to be an unstimulated receptor between them.

Front 8

225. What does it mean that photons are only triggers for photoreceptors?

Back 8

The energy of photons is used by the receptors for inducing chemical (signal transducing) processes.

Front 9

226. Which receptor cells of the retina are responsible for color vision and vision under dim conditions?

Back 9

color vision: cones;
vision under dim conditions: rods.

Front 10

227. What is monochromatic light?

Back 10

Light is monochromatic if its spectrum consists of a single wavelength only.

Front 11

228. What is the principle of Young-Helmholtz theory?

Back 11

The phsyiological basis of color vision is the existence of 3 different color sensitive receptors (the cones) with different photopigments which are able to make a distinction between red, green and blue colors.

Front 12

229. What is ERG?

Back 12

Electrotinogram: it records the potential charges of the retina as a whole during stimulation with light.

Front 13

230. Give the frequency range of sound waves audible by a normal human ear.

Back 13

16 Hz - 16000 Hz

Front 14

231. What is ultrasound?

Back 14

Sounds whose frequency is between 16000 and 10^10 Hz.

Front 15

232. What is infrasound?

Back 15

Sound with a frequency less than 16 Hz.

Front 16

233. Give the definition and unit of sound intensity.

Back 16

The energy carried by a sound wave perpendicularly through unit cross-sectional area per unit time. Its unit is Watt/m^2

Front 17

234. What is the threshold intensity of hearing? Give its value.

Back 17

Threshold intensity hearing is the minimal intensity of the 1000 Hz sinusoidal sound audible by a normal human ear. Its value is about 10^-12 Watt/m^2

Front 18

235. How does the intensity of sensation (loudness) change as a function of the intensity of the stimulus?

Back 18

Sensation is proportional to the logarithm of the relative intensity of the stimulus.

Front 19

236. What is the advantage of the phon scale compared to the bel and decibel scales?

Back 19

When using the phon scale the intensities of both the reference and actual sound intensities are converted to the intensities of the corresponding 1000 Hz sound, i.e. the reference is the threshold intensity of the 1000 Hz sound (10^-12 Watt/m^2), the actual intensity is the intensity of the 1000 Hz sound inducing the same sensation of loudness as the sound under investigation. Therefore, the threshold of hearing is 0 phon for every frequency.

Front 20

237. Give the Weber-Fechner law.

Back 20

sensation =
(const)(lg)
(actual stimulus intensity)/reference stimulus intensity

Front 21

238. A sound with intensity "I" and v=2000 Hz frequency is given by a sound generator. What is the loudness according to the phon scale?

Back 21

L=(10)(lg)((I1000/Io)) (phon)
where L is the loudness in phons;
I1000 is the intensity of the 1000 Hz sound which causes the same sensation of loudness as the given 2000 Hz sound with intensity "I";
Io is the threshold intensity of hearing for the 1000 Hz sound (10^-12 Watt/m^2).

Front 22

239. What relations are plotted by isophonic curves?

Back 22

The sound intensities producing the same sensation of loudness are plotted against the sound frequency.

Front 23

240. Give the threshold values of hearing according to the phon scale for sounds whose frequences are 1000 Hz and 2000 Hz, respectively.

Back 23

0 phon, the threshold of hearing is the same (0 phon) for any frequency.

Front 24

241. What is the basis of the son scale?

Back 24

Sensation can be more precisely described by the power of the relative stimulus intensity with a fractional exponent.

Hson=(1/16)((I/Iref))^0.3
where Hson is the loudness in son, and I and Iref are the stimulus intensity in question and the reference stimulus intensity, respectively.

Front 25

242. What is the mechanism of hearing by means of air conduction(also called ossicular conduction)?

Back 25

The vibration reaches the inner ear through auditory meatuses and the system of the tympanic membrane and auditory ossicles.

Front 26

243. What is the mechanism of hearing by means of bone conduction?

Back 26

The vibration reaches the inner ear directly through the cranial bones.

Front 27

244. What are the physical principles giving rise to an increased pressure on the foot plate of the stapes compared to the pressure of the original sound?

Back 27

1. the cross-sectional area of the ear drum is much larger than that of the stapes foot plate;
2. lever-like functioning of auditory ossicles.