Photoreception and Chemoreception Flashcards
What are the Three Types of Photoreceptor Arrangements Found in Animals?
- Eye-spots/cups (Ocelli)
- Compound Eyes
- Single Lens (Camera) Eyes)
What are Eye-spots/cups (Ocelli)?
The simplest eye (e.g. flatworms, insects, mollusks). They do not form an image, consists of less than a 100 photoreceptors lining a cup or pit with a layer of pigmented cells stopping light from penetrating in the other direction. The stimulus/signal goes straight to the CNS.
What are Compound Eyes?
Found in insects, crustaceans, and molluscs, they are composed of visual units (ommatidia) that each sample a small part of the visual field (mosaic). Photopigment = rhodospin, located in the microvilli in the centre. Extremely efficient in detecting movement.
What are Single Lens/Camera Eyes?
The most advanced eyes, found in vertebrates and some molluscs/snails/annelids. Light is transmitted through pupil (regulates light) to retina located at the back of the eye, the light is captured by photoreceptors and have photo-transduction capability (converts into electrical signals). Image formed upside down, corrected in the CNS.
What are the Three Layers of Cells in the Retina?
- Rods and Cones (deepest against sclera)
- Bipolar Cells (interneurons between 1 & 3, transparent, responsible for 30% of input to 3)
- Ganglion Cells (sends axon out of eye into optic nerve, sends final signal to brain, transparent).
What are Amacrine Cells?
Interneurons in the retina, responsible for 70% of input to retinal ganglion cells. Centre for lateral integration and regulation.
What are Horizontal Cells?
In the retina, forms synapses with the rods and cones, centre for lateral integration and regulation.
What are Rods?
Retina cells that are sensitive to low intensity light (used mostly at night), do not discriminate colours, outer segment contains pigment/photoreceptors; no axons.
Do humans have more rods or cones?
Rodes.
What are Cones?
Retina cells that require more light for stimulation, detect colour, outer segment contains pigment/photoreceptors. No axons.
What is Retinal?
A chromophore vitamin A derivative that absorbs energy from light; same in rods and cones, a visual pigment.
What is Opsin?
G-protein coupled receptors that convert photons of light into an electrical signal.
What is the Opsin in Rods?
Rhodopsin.
What is the Opsin in Cones?
Photopsin.
How do Retinal and Opsins work in humans?
The two visual compounds are bonded together, cone pigments are composed of 1 retinal and 3 opsins. Each opsin determines wavelength absorbed (red, blue, green).
Colour vision depends on the __ _ __ of the __ __ __.
Ration of stimulation of the various cone types.
What does hyperpolarization stop and therefore cause (in Rods and Cones)?
Stops glutamate release and is interpreted as a visual image. Glutamate is an inhibitory neurotransmitter.
What does Retina transform into upon absorbing photons?
Cis formation to trans formation, which activates glutamate.
What happens with no light?
Sodium channels open - depolarization - as glutamate is released from the cell.
What happens with light?
Sodium channels close, causing hyperpolarization and stopping glutamate from being released.
What direction does photo input move?
In the opposite direction of the direction of light, which is why bipolar and ganglion cells are transparent.
What is Chemoreception?
Chemicals from environment influence a receptor protein in the membrane of sensory receptors; two types, olfaction and taste. Or an internal sensory receptor responds to some chemical property of bodily fluids. Most diverse sensory system.
What does taste rely on?
Near contact chemoreception.
How many types of taste do humans have?
5; salt, sour, bitter, sweet, umami (meaty)
What does Olfaction rely on?
Distant chemoreception.
