Module 4 Flashcards
(34 cards)
What types of ion channels are required for the conduction of an action potential?
Voltage gated Na+ and K+ channels, as well as the leak channels that help set the resting membrane potential.
What are voltage gated Na+ and K+ channels activated by?
Depolarization
What occurs during the rising phase (depolarization) of an action potential?
- Depolarizing stimuli open voltage gated Na+ channels at -55mV which allow Na+ to travel down the electrochemical gradient.
- At +30mV, the Na+ channels inactivate.
What occurs during the falling phase (repolarization) of an action potential?
Voltage gated K+ also open in response to depolarization, but do so more slowly than Na+ channels, causing delayed efflux.
What occurs during the after-hyperpolarization phase (undershoot) of an action potential?
- Voltage gated K+ channels do not immediately close when reaching -70mV, causing membrane potential to dip below the resting membrane potential.
- leak channels bring the membrane potential back to -70mV.
How do voltage gated Na+ channels suddenly close at the peak of an action potential?
Na+ channels contain two gates: an activation gate and an inactivation gate.
Absolute refractory period vs relative refractory period
Absolute refractory period: a second action potential cannot be initiated (1-2ms)
Relative refractory period: a second action potential can be initiated but requires a larger than normal stimulus (2-5ms)
What is the purpose of a refractory period?
It ensures that an action potential travels in one direction and limits the rate at which signals can be transmitted down a neuron.
How are action potentials conducted? (6 steps)
- graded potential enters the trigger zone
- voltage gated Na+ channels open, and Na+ enters the axon
- positive charge spreads along the adjacent sections of the axon by local current flow
- local current flow causes a new section of the membrane to depolarize
- loss of K+ repolarizes the membrane
- the refractory period prevents backward conduction
What two physical parameters determine the velocity of action potentials in mammalian neurons?
- the diameter of the axon: larger diameter will offer less internal resistance to current flow, and more ions will flow in a given time, bringing adjacent regions to threshold faster.
- the resistance of the axon membrane to ion leakage: current will spread to adjacent sections more rapidly if it is not lost via leak channels.
Where do neurons communicate?
Neurons communicate at synapses: presynaptic cell (neuron) to postsynaptic cell (neuron, muscle, target cell)
How many synapses can a postsynaptic neuron contain?
Up to 150 000 synapses on its dendrites, soma, and even on the axon and axon terminals.
What do the majority of neurons in the nervous system use for cell-to-cell communication?
Chemical signals.
What is a neurocrine? What are the three types?
A neurocrine is a chemical substance released from neurons and used for cell-to-cell communication.
The three types are: neurotransmitters, neuromodulators, and neurohormones.
What is a neurotransmitter? What does it do?
A neurotransmitter is a chemical that is released, acts on a postsynaptic cell in close vicinity, and causes a rapid response in the postsynaptic cell.
What is a neuromodulator? What does it do?
A neuromodulator is a chemical that is released, acts on a postsynaptic cell in close vicinity, and causes a slow response in the postsynaptic cell.
Where are neurohormones secreted? What do they do?
Neurohormones are secreted into the bloodstream and act on targets throughout the body.
What are the two categories of neurocrine receptors?
Ionotropic receptors (ligand gated ion channels) and metabotropic receptors (G-protein coupled receptors).
What happens when ligands bind to ionotropic receptors?
Ligand binding to ionotropic receptors causes conformational changes leading to the opening of a channel.
Mediates a fast postsynaptic responses.
What happens when ligands bind to metabotropic receptors?
Ligand binding to metabotropic receptors leads to a g-protein mediated cellular response: interacting directly with ion channels or activate membrane bound enzymes.
Where are large peptide neurotransmitters produced and packaged?
Produced and packaged into vesicles at the soma and then transported (fast axonal transport).
Where are small neurotransmitters synthesized and packaged?
Synthesized and packaged at the axon terminal (empty vesicles transported from the soma or recycled vesicles).
How are enzymes for synthesis brought to the terminal?
Via slow axonal transport.
How are neurotransmitters released?
Release occurs via Ca^2+ mediated exocytosis.
