Vision
In this lesson, we’ll examine vision from visual pathways all the way to phototransduction, the process that allows us to detect light.
1) Start with these videos:
2) Read these articles to delve a little deeper into some of the topics from the videos:
Know Your Brain - Retina
Know Your Brain - Primary Visual Cortex
3) Watch this video to learn about how our eyes convert light into signals our brain can understand:
4) Watch this video to learn about color blindness, a common visual defect:
5) Finally, answer these questions to test your understanding:
1. These retinal cells carry visual information out of the eye, forming the optic nerve in the process:
- A. photoreceptor cells
- B. bipolar cells
- C. ganglion cells
- D. amacrine cells
Show Answer
Correct answer: C
The ganglion cells of the retina receive signals from other retinal neurons and their axons bundle together to form the optic nerve, which carries visual information from the brain.
2. Which of the following cell types provides direct input to bipolar cells in the retina?
- A. ganglion cells
- B. optic nerve fibers
- C. radial glia
- D. photoreceptors
Show Answer
Correct answer: D
Photoreceptors (rods and cones) synapse directly onto bipolar cells, initiating the flow of visual information that will eventually reach the brain and form a visual scene.
3. Why is the primary visual cortex sometimes referred to as the "striate cortex?
- A. its neurons fire in a striped pattern when exposed to visual stimuli
- B. myelinated axons runs along calcarine sulcus, creating a striped appearance
- C. it receives input from the retina in the form of stripe-like wave patterns
- D. the optic tract forms a stripe as it enters the cortex
Show Answer
Correct answer: B
The primary visual cortex is found in the occipital lobe, surrounding and extending into a sulcus called the calcarine sulcus. A large band of myelinated axons runs along the edges of the calcarine sulcus, giving the primary visual cortex a striped appearance. Because of this, it is sometimes called the striate cortex.
4. Which of the following best describes what happens during phototransduction in a rod cell when it is exposed to light?
- A. sodium channels open, causing depolarization and increased glutamate release
- B. sodium channels close, causing hyperpolarization and decreased glutamate release
- C. potassium channels close, causing depolarization and increased glutamate release
- D. calcium channels open, causing hyperpolarization and decreased glutamate release
Show Answer
Correct answer: B
Phototransduction works in a counterintuitive way compared to most neural signaling, where stimulation opens channels, depolarizes the cell, and increases neurotransmitter release. In photoreceptors, light lowers cGMP levels, which closes sodium channels. This hyperpolarizes the cell and reduces glutamate release. That drop in glutamate is the signal that light is present.
5. Color blindness (aka color vision deficiency), is much more common in males (up to 8% of males) than females (up to .5% of females). What is the main reason for this?
- A. males are more likely to engage in risky behavior (e.g., smoking, drinking)
- B. most types of color blindness are linked to mutations on the X chromosome
- C. females are culturally taught to recognize nuances in color from an early age
- D. males have lower serotonin levels, and this is a risk factor for color blindness
Show Answer
Correct answer: B
The genetic mutations that commonly lead to color blindness are frequently found on the X chromosome. Because females have two X chromosomes, if there is a mutation on an X chromosome gene in a female, it is more likely to be balanced out by a "healthy" gene on the other X chromosome. In males, however, a mutation on an X chromosome gene is more likely to have an influence due to a lack of another X chromosome and thus a lack of a "healthy" gene to counteract the mutation.
