CHAPTER 2: Basic Principles of Sensory Physiology

Question 1

What are the four types of visual disorders discussed in Chapter 2?

Answer 1

1. Myopia is nearsightedness
   
   • Axial myopia (the eyeball is too short)
   • refractive myopia -> The lens is too thick, so the light converges differently
2. Hyperopia is farsightedness
   
   • the lens is too thin
3. Astigmatism
4. Presbyopia
   
   • farsightedness due to old age
   • the lens become more rigid

Question 2

What is resting potential and how is it related to action potentials in neurons?

Answer 2

The resting potential is the amount of voltage in the neuron when it is inactive. Sodium is 10x more concentrated on the outside than the inside at resting potential
Potassium is 20x more concentrated on the inside than the outside at resting potential

Question 3

What are the basic properties of action potentials?

Answer 3

When sodium ions enter the neuron, the voltage of the neuron increases to about 40 mV, causing the potassium channels to open, so the voltage hyperpolarizes and becomes more negative than -70 mV. 1000 action potentials/s is the maximum rate at which they are able to fire at.

Question 4

What are two types of refractory periods?

Answer 4

1. Absolute Refractory Period occurs when the sodium channels close and there is no possibility of an action potential being fired
2. Relative Refractory Period occurs when sodium channels are starting to open again, and action potentials can fire, but it is unlikely

Question 5

What are excitatory and inhibitory transmitters?

Answer 5

Excitatory transmitters: more likely to increase the likelihood of action potentials firing -> Glutamate is an example of a transmitter that increases the voltage of a neuron.
Inhibitory transmitters: more likely to decrease the likelihood of action potentials firing -> GABBA is an example of a transmitter than decreases the voltage of a neuron.

Question 6

Sparse, Specificity, and Population Coding

Answer 6

Sparse coding: only one neuron is associated with a specific stimulus -> idea of a grandmother neuron (very unlikely)
Specificity coding: a group of neurons are associated with specific stimulus, but not all
Population coding: a large group of neurons are associated with with the specific stimulus in the environment, and neurons within the group respond to different aspects of the environment -> this is considered the most likely method of coding