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Question 1

Action potential

Answer 1

Short-lasting changes of electric membrane potential with a consistent profile in response to stimuli. Occurs in excitable cells and tissues (nerve, muscle, gland, cells in organs of perception) able to change their potential in response to a stimulus.

The mechanisms of generation of action potentials have been clarified by measurements with microelectrodes on isolated giant axons from squids.

Question 2

Threshold potential

Answer 2

The critical level to which a membrane potential must be depolarized to initiate an action potential. The threshold potential for most excitable cells is about 15 mV less negative than the resting membrane potential. In a nerve, if the membrane potential decreases from -70 mV to -55 mV the cell fires an action potential which propagates along the axon.

Question 3

Sequence of potential changes

Answer 3

EXPLAIN PICTURE

Question 4

Events in the membrane leading to potential changes

Answer 4

1. Stimulus
2. Depolarization
3. Membrane Repolarization
4. Hyperpolarization
5. Resting state

Question 5

Synaptic transmission of action potentials

Answer 5

Pre-synaptic membrane: Са2+-channels opening upon polarization

Са2+ions enter the cytosol initiating fusion of neurotransmitter vesicles

Acetylcholine is released in the interstitial fluid

Na+-channels of the postsynaptic membrane open (ligand-gated) and allows Na+ diffuses into the cytosol - depolarization

Acetylcholinesterase in the post-synaptic membrane recycles Ach by transporting it back through the pre-synaptic membrane by endocytosis.

Question 6

Perception of light

Answer 6

the eye receives monochromatic light – the visual perception depends on the wavelength and the radiant flux density of the light (brightness). Viewing in dark light is regulated by the rod photoreceptor cells (extremely numerous). In twilight viewing, cone photoreceptor cells also aid vision. In day time, only cones regulate vision (rhodopsin pigment sensitive to colour). The photoreceptor cells are located in the retina of the eye, and are stimulated by light – the retina then sends nerve signals (via action potentials) to the optic nerve which transmits them to the brain interpreting them as visual images.