PSY280: Lecture 2 Notes
1. Recognize the dual nature of light
a. Sensory systems can be thought of as being either near or far with
respect to detecting external stimuli
b. Vision is our dominant sensory system in humans, and takes up
about half of the brain for processing
i. It receives information at once and within long distances
c. The farthest object visible with the naked eye is M-31, which is
approximately 2.5 million light years away.
2. Describe the journey that light takes, from a distant star to your
a. Light travels through empty space at about 186,000 miles/sec.
b. At the atmosphere, some gets absorbed, some gets scattered.
c. The remaining light will eventually hit a surface, where it might be
reflected, absorbed, and transmitted. (or even refracted)
3. Explain the electromagnetic spectrum and recognize the portion visible to
a. The electromagnetic spectrum characterized electromagnetic
radiation by its wavelength.
b. People can only see part of the spectrum (i.e. the visible spectrum),
from ~400nm to 700nm.
4. Summarize what happens to light when it hits a white, black or transparent
a. Light got reflected, absorbed and transmitted respectively.
5. Label the major structures of the human eye
1 6. Apply concepts of accommodation to determine where an object will be
focused under different conditions
a. The lens actively refracts light by changing its shape to help focus
light on the retina.
b. Through accommodation, the eye changes its focus by making the
lens fatter when gaze is directed towards nearer objects.
c. For people with myopia, when an object is near, the light tends to
be focused farther back, so near objects vision is not a problem.
d. Hyperopia results in light being focused behind the retina. This is
also what happens with nearer objects.
e. Astigmatism is due to an irregularly shaped cornea.
7. Explain the distribution of ions before, during and after an action potential
a. Ion channels and ion transporters regulate the number of ions
inside and outside of the axon.
b. At rest, there are more negative ions inside, more positive ions
i. More Na outside
ii. More K inside
iii. Membrane potential at -70mV
c. With an action potential, Na ion channels open and Na rushes into
the axon, resulting in fewer positive ions outside.
i. Membrane potential at +40mV
d. The reversal of the membrane potential causes Na channels to
close, and K channels to open, letting K out.
i. Membrane potential drops
iii. REFRACTORY PERIOD + +
e. The sodium-potassium pump trade 3 Na for 2K , so the ions end
up in their original concentrations.
8. Describe the effects that different neurotransmitters have on the
movement of ions across the cell membrane, and how that relates to firing
a. Neurons usually produce and release only one kind of
i. Excitatory: Na channels open
ii. Inhibitory: K channels open
b. Neurons usually have receptors for multiple neurotransmitters.
i. The cell body will summate all the signals received via
c. Neurons fire in the absence of stimuli, called spontaneous activity.
2 i. This means that signals can involve either an