4d: Communication And Signalling Flashcards
What is the resting membrane potential
The state where there is no net flow of ions across the membrane
What does the transmission of a nerve impulse require
Changes in the membrane potential of the neurone’s plasma membrane
What is depolarisation
A change in the membrane potential to a less negative value inside
if the change in membrane potential caused by depolarisation is big enough it may trigger an _________
Action potential
What is an action potential
Aa wave of electrical excitation (or wave of depolarisation) along a neurones’s plasma membrane
How do neurotransmitters initiate a response
By binding to their receptors at a synapse.
Neurotransmitter receptors are ligand gated channels
what happens after the binding of a neurotransmitter
Triggers the opening of a ligand gated ion channels at the synapse
Ion movement occurs and the depolarisation of the plasma membrane.
What causes depolarisation
Entry of sodium ions
What causes repolarisation
Exit of potassium ions
What happens if the membrane is depolarised past the threshold value
The opening of voltage-gated sodium channels is triggered, and sodium ions enter the cell down their electrochemical gradient.
It’s huge influx of sodium ions causes the cell to be much more negative and triggers the potassium gated channels to open, and the K+ can leave the cell.
What re-establishes the resting potential of a nerve cell after depolarisation?
Voltage gated potassium channels open to allow K+ to move out of cell
What is the area within the cell that detects light
The retina
The retina contains 2 types of photoreceptor cells, ______ and _________
Rods and cones
What are rods (photoreceptor)
Rods function in dim light but do not allow for colour perception.
Useful for vision in areas of low light intensity. Nocturnal animals have a greater proportion.
What are cones (photoreceptor)
Cones are responsible for colour vision and only function in bright light
Not as sensitive to light as rods. They are particularly sensitive to specific colours: green, red, blue and in some animals, UV.
In animals, what does retinal combine with to form the photoreceptors in the eye
Membrane protein opsin
In rod cells the retinal-opsin complex is called _________
Rhodopsin
In cone cells, different forms of opsin combine with retinal to…
Give different photoreceptor proteins, each with a maximal sensitivity to specific wavelengths: red, green, blue or UV
How does the retina respond to light
Retinal absorbs a photon of light and rhodopsin changes conformation to photoexcited rhodopsin.
A cascade of proteins amplifies the signal.
What does a photoexcited rhodopsin activate.
G-protein called transducin.
A single photoexcited rhodopsin activates hundred of molecules of G-protein
What does transducin activate
The enzyme phosphodiesterase (PDE).
Each activated G-protein only activates one molecule of PDE
What does phosphdiesterase (PDE) do.
Catalyses the hydrolysis of a molecule called cyclic GMP (cGMP). Each active PDE molecule breaks down thousands of cGMP molecules per second.
What does the reduction in cGMP concentration as the result of hydrolysis (catalysed by PDE) do.
It affects the function of ion channels in the membrane of rod cells.
Consequently, it results in the closure of ion channels in the membrane of the rod cells, which triggers nerve impulses in neurons in the retina.
Why are rod cells more sensitive than cone cells at low light intensities
A higher degree of amplification (in dim light)
