Photoreceptors (and a few more)

What does the cornea do?

transfers light into eye

What does the iris do?

controls size of pupils

What do the pupils do?

determine how much light enters the eye

What do the ciliary muscles do?

control lens shape

What does the lens do?

focuses light onto the retina

How does the lens of the eye adjust for far vs near sight?

• Near object: light rays enters more spread out/diverging - bends light more in .

• Far object: light rays enters the eye more parallel, bends the light less.

What do rods do?

• black/white vision

• nocturnal vision

• sensitive to dim light

What do cones do?

• color vision

• more sensitive to bright light

  • intensity affects response

What range of light can humans see?

350 to 750 nm

Describe the process of phototransduction step by step

• light hits rhodopsin

• rhodopsin underoges conformational change in response to a wavelength of light

• transducin g-protein is activated

• trasducin activates cGMP phosphodiesterase

• cGMP phosphodiesterase converts cGMP to GMP, creating low levels of cGMP

• cGMP-gated Na⁺ channels into the cell close

• cell hyperpolarizes

• Glutamate release from photoreceptor decreases (stop inihbitting bipolar cells)

• bipolar cell activity alters

• Ganglion cells generate action potentials

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What molecule converts cGMP to GMP and why?

• phosphodiesterase

• low CGMP levels cause ligand-gated Na+ channels close so the cell hyperpolarizes and begins action potential

What molecule converts GMP back to cGMP?

guanylyl cyclase

When no light is present in a photoreceptor, what state are the ligand-gated Na+ channels in?

• open

• cGMP is high

• cell won’t hyperpolarize

What do photoreceptors release in light vs dark conditon?

• light - STOP inhibiting bipolar cells

• dark - inhibit bipolar cells; inhibitiroy neurons sent

What is the pathway from a rod photoreceptor to the optic nerve?

Rod photoreceptor → bipolar cell → ganglion cell → optic nerve

What do thermoreceptors respond to?

changes in temperature

What are the different types of thermoreceptors?

1. warm-senstive - activated when temp increases and capscain

2. cold sensitive - actived when temp decreases and menthol

3. nociceptors - painfully hot

What are nociceptors?

• register pain

• can detect various stimuli, including temp, pressure, and chemicals (polymodal)

What are electroreceptors and where are they found?

• detect electrical fields

• common in fish

What are magnetoreceptors commonly found in?

migratory animals