16 Flashcards
Action potential
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.
Threshold potential
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.
Sequence of potential changes
EXPLAIN PICTURE
Events in the membrane leading to potential changes
- Stimulus
- Depolarization
- Membrane Repolarization
- Hyperpolarization
- Resting state
Synaptic transmission of action potentials
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.
Perception of light
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.