1.4dii - Initiation of a Nerve Impulse in Response to an Environmental Stimulus: The Vertebrate Eye Flashcards
The retina is…
the area within the eye that detects light
The retina contains…
2 types of photoreceptor cells: rods and cones
Rods function in…
dim light, but do not allow colour perception
Cones only function in…
bright light
Cones are responsible for…
colour vision
What forms the photoreceptors of the eye in animals?
the light-sensitive molecule retinal which is combined with a membrane protein opsin
What is rhodopsin?
the retinal-opsin complex in rod cells
Retinal absorbs…
a photon of light
Rhodopsin changes…
conformation to photoexcited rhodopsin
A cascade of proteins amplifies…
the signal
Photoexcited rhodopsin activates a G-protein called…
transducin
Transducin activates…
the enzyme phosphodiesterase (PDE)
A single photoexcited rhodopsin activates…
hundred of molecules of G-proteins
Each activated G-protein activates…
one molecule of PDE
Each activated G-protein activates…
one molecule of PDE
PDE catalyses the…
hydrolysis of a molecule called cyclic GMP (cGMP)
Each active PDE molecule…
breaks down thousands of cGMP molecules per second
The reduction in cGMP concentration as a result of its hydrolysis…
affects the function of ion channels in the membrane of rod cells, resulting in the closure of ion channels in the membrane of rod cells
The closure of ion channels in the membrane of rod cells triggers…
nerve impulses in the neurons in the retina
The reduction in cGMP concentration as a result of its hydrolysis…
affects the function of ion channels in the membrane of rod cells, resulting in the closure of ion channels in the membrane of rod cells
A very high degree of amplification results in…
rod cells being able to respond to low intensities of light
In cone cells, different forms of…
opsin combine with retinal to give different photo-receptor proteins
Each photo-receptor protein has…
a maximal sensitivity to specific wavelengths, red, blue, green and UV
