Chapter 2 - Basic Principles of Sensory Physiology Flashcards
1- In what order do we see in the perceptual process?
-In focus (step 2): light reflected and focused to create image of tree on retina
-In dim light (step 3): receptors (cones and rods) transform light into electricity
-In fine details (step 4): signals travel in a network of neurons
see image
2- Describe the electromagnetic spectrum.
Shorter (tighter) wavelength = bigger energy
Bigger wavelength (wider) = smaller energy
Order from shorter wavelength (bigger energy) to bigger wavelength (smaller energy):
-Gamma rays (0.0001 nm)… like space telescope
-X-Rays
-Ultra-violet
-Visible light (from around 400nm (purple) to 750nm (red))
-infrared (like snakes seeing prey in dark…heat)
-radio waves (radar(1cm), tv, fm (1m), am (100m))
3- Know the different parts of the eye and the order energy goes through it.
4- Where are rod and cone cells located? What is the blind spot?
Rods: periphery of retina. From 0 to around 160,000 per square mm. Depends on angle. See graph.
Cones: Fovea (0 degrees) = center of retina. Around 150,000 per square mm.
Blind spot= where the optic nerve starts. There are no receptors. Brain fills in with surrounding details.
5- Describe the two photoreceptor cells diseases?? (slide 8)
? see textbook
cones problem: can’t see center
rod problem: can’t see periphery
6- Explain accommodation.
a) Object is far. Eye is relaxed. Light is focused on the retina.
b) Object is near. Eye is relaxed. The focus point is pushed back behind the retina. How to fix this?
c) Accommodation. The lens gets thicker? This brings the focus point forward and onto the retina.
But if myopia?
When object is far and the eye is relaxed, the focus point is in front the retina instead of on it. We use a corrective lens to bring the focus point back onto the retina.
7- Describe myopia, hyperopia and presbyopia. Associate them with pictures.
Myopia (nearsightedness):
Trouble seeing distant objects
-Refractive myopia:
* Cornea and lens overbend the light
-Axial myopia:
* Eyeball is too long
Hyperopia (farsightedness):
Trouble seeing near objects
* Focus point beyond the retina
* Eyeball too short
Presbyopia:
* Trouble seeing near objects due to aging
* Lens becomes more rigid with age
8- Explain transduction.
Molecules rearrange structure?
Ex: molecule in the dark. vs. retinal isomerized by light.
??
9- Describe the steps of an experimentation of dark adaptation.
- Subject looks at a small fixation point while paying attention to a flashing test light that is off to the side
- While still in the light, the subject turns a knob that adjusts the intensity of the flashing light until it can just barely be seen.
- Sensitivity
- Minimal amount of energy necessary to just barely see the light
(sensitivity = 1/threshold) - Light adapted sensitivity
- Sensitivity measured in the light
- Measured when eyes are adapted to light
- Because room light are on the intensity of flashing test light has to be high to be seen
- Therefore, at the beginning of the experiment:
- Threshold is high and sensitivity is low.
- Once sensitivity to the test light is determined:
- Room lights (adapting lights) are turned off (subject is in the dark).
- Subjects continue to adjust the intensity of the test light until it can
barely be seen (sensitivity in the dark) - As the subject becomes more sensitive to the light:
- The subject must decrease the intensity of the light for it to be just barely visible.
10- Explain the dark adaptation curve graph.
Dark adaptation curve:
* Function relating
sensitivity to light to
time in the dark
* As adaptation
proceeds subjects
become more sensitive
to the light
Explain with graph and textbook!
11- Explain spectral sensitivity.
?
rod=more sensitive to left side of spectrum (blues)
cones=more sensitive to right side of spectrum (green yellow red)
12- Explain the pigment absorption spectra.
rods in between short and medium
short, rods, medium, long wl
13- Explain how to record electrical signals in neurons and explain action potentials.
Small electrodes are used to record from single neurons.
* Recording electrode is inside the nerve fiber.
* Reference electrode is outside the fiber.
* Difference in charge between them is −70 mV
* This negative charge of the neuron relative to its
surroundings is the resting potential
Action Potential
* This signal is called the action potential and lasts about 1 millisecond (ms, 1/1,000 second).
* When neurons are “firing,” the neuron has action potential.
* These signals can be recorded on a computer.
Action potentials:
* Show propagated response.
* Remain the same size regardless of stimulus intensity.
* Increase in rate to increase in stimulus intensity.
* Have a refractory period of 1 ms – upper firing rate is 500 to 800 impulses per
second.
* Show spontaneous activity that occurs without stimulation.
Chemical Basis of Action Potentials Neurons are surrounded by a solution
containing ions.
* Ions carry an electrical charge.
* Sodium ions (Na+): positive charge
* Chlorine ions (Cl−): negative charge
* Potassium ions (K+): positive charge
* Electrical signals are generated when such ions cross the membranes of neurons. Membranes have selective permeability.
Synapse is the small space between neurons.
Neurotransmitters are:
* Released by the presynaptic neuron from vesicles.
* Received by the postsynaptic neuron on receptor sites.
* Matched, like a key to a lock, into specific receptor sites.
* Used as triggers for voltage change in the postsynaptic neuron.
Excitatory transmitters cause
depolarization.
* Neuron becomes more positive.
* Increases the likelihood of an action potential.
Inhibitory transmitters cause
hyperpolarization.
* Neuron becomes more negative.
* Decreases the likelihood of an action potential.
14- Explain convergence.
15- Explain acuity.
