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Physiology 3120 Lecture Notes - Amacrine Cell, Ganglion Cell, Axon Terminal

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indigoweasel955

26 Nov 2011

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Western University

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Course

Physiology 3120

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Document Summary

The visual system: cell types in the retina. Amacrine cells: functional characteristics of the rod & cone systems. Sensitive to faint light (single photon: due to higher photopigment & convergence. Concentrated in the fovea: most sensitive part of the eye, must constantly move the eye to focus objects of interest on the fovea. Greater acuity (less convergence: flow diagram of the steps in the retina by which light is transduced to action potentials. Sodium channels open, so inward sodium current. Hyperpolarization of rods & cones proportional to amount of light. On = increase in aps; off = decrease in aps. Off surround mediated by inhibitory ( sign-changing ) interneurons around the on centre (see neuro 26: major feature of information processing by the retina. Retinal ganglion cells don"t respond to light per se, but contrast in light shone on the retina. First step of processing in visual system.

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Related Questions

Image intensifiers used in night-vision devices create a bright image from dim light by letting the light first fall on a photocathode. Electrons emitted by the photoelectric effect are accelerated and then strike a phosphorescent screen, causing it to glow more brightly than the original scene. Recent devices are sensitive to wavelengths as long as 900 nm, in the infrared.

Part A. If the threshold wavelength is 900nm, what is the work function of the photocathode?

Part B. If light of wavelength 600nm strikes such a photocathode, what will be the maximum kinetic energy, in eV, of the emitted electrons?

ceruleanmacaw325

To derive the formulas for the major characteristics of motion as functions of time for a horizontal spring oscillator and to practice using the obtained formulas by answering some basic questions.

A block of mass is attached to a spring whose spring constant is . The other end of the spring is fixed so that when the spring is unstretched, the mass is located at $x=0$ . . Assume that the +xdirection is to the right.

The mass is now pulled to the right a distance beyond the equilibrium position and released, at time $t=0$ , with zero initial velocity.

Assume that the vertical forces acting on the block balance each other and that the tension of the spring is, in effect, the only force affecting the motion of the block. Therefore, the system will undergo simple harmonic motion. For such a system, the equation of motion is

$a(t)=-\frac{k}{m}x(t)$ ,

and its solution, which provides the equation for , is

$x(t)=A\cos\left(\sqrt{\frac{k}{m}}t\right)$ .

Find the velocity

of the block as a function of time.

Express your answer in terms of some or all of the variables:

The emergence of line spectra from a gas when a current passesthrough it was an observed phenomenon waiting for an explanation inthe early 20th century. The atomic line spectra coming fromelements such as hydrogen had been analyzed since the late 19thcentury. By studying the wavelength of the emerging radiation ofhydrogen, experimenters found (often by trial and error) that thewavelengths in those spectra were described by the formula

\frac{1}{\lambda} = R \left( \frac{1}{n_1^2} - \frac{1}{n_2^2}\right),
where R is known as the Rydberg constant. It has a value of R =1.097 \times 10^{7}\; \rm m^{-1}. The variables n_1 and n_2 areinteger numbers (n_1 = 1,2,3,4,\dots). As experiments continued,scientists began to see more and more characteristic lines emergingfrom the hydrogen spectrum. Each of them corresponded to awavelength predicted by this formula with some integer values forn_1 and n_2.

In 1913, Niels Bohr provided an explanation for the observationsmade in experiments by proposing that each electron in an atom hadonly certain allowable energy levels. Furthermore, he postulatedthat when an electron changed its energy level, it must emit orabsorb a single photon with the energy equal to the energydifference between the two levels.

With this interpretation, the variables n_1 and n_2 acquired newsignificance. Bohr's model predicted that n_2 was the initialenergy state of the atom (n_initial) and that n_1 was the finalstate of the atom (n_final). A photon with the predicted wavelengthwas created when an atom made a transition from its initial energystate to a lower final energy state. The equation now read

\frac{1}{\lambda} = R \left( \frac{1}{n_{\rm final}^2} -\frac{1}{n_{\rm initial}^2} \right).
Bohr's model also predicted that a photon of the appropriatewavelength (given by the same formula) could promote an atom from alower energy level to a higher one.

In this problem, we explore the photon characteristics necessaryfor transitions between energy levels in hydrogen and singlyionized {\rm He}^+, whose energy levels are accurately predicted bythe Bohr model.
What is the change in energy DeltaE of the hydrogen atom as theelectron makes the transition from the n=3 energy level to the n=1energy level?
Express your answer numerically in electron volts.

b. When an atom makes a transition from a higher energy level to alower one, a photon is released. What is the wavelength of thephoton that is emitted from the atom during the transition from n=3to n=1?
Express your answer numerically in angstroms.

c.

When the hydrogen atom makes the transition from the n=2 to the n=1energy level, it emits a photon. This photon can be absorbed by toa singly ionized helium atom ({\rm He}^+) in its second energylevel (n_{\rm initial} = 2), causing it to move to a higher energylevel. To what final energy level number n_final can the photonpromote the helium ion?

Note that {\rm He}^+ has two protons in its nucleus and a singleelectron.
Express your answer as an integer.

Please answer fully, Thank you
a.