Action Potentials Flashcards Preview

-Resting membrane potential of -40 - -90mV

 - [Na] is higher outside the cell, [K] is higher inside the cell

 - cell membrane is super permeable to [K] due to potassium leakage channels

 - maintains gradients through K/Na pumps, ATP-ase pumps 3 Na out, 2 K in

-Gate-m (activation gate) is normally closed, but opens when the cell becomes positive

-Gate-h (deactivation gate) is normally open, but closes when the cell becomes very positive

States:

1) Deactivated: closed, @resting potential

2) Activated: open when threshold is reached

3) Inactivated: closed as neuron depolarizes and h-gate swings shut

-The n-gate is normally closed, but opens when the cell is depolarized

0) A triggering depolarizes the cell body

 - usually the result of neurotransmitter-gated ion channels

1) Depolarization: cell becomes less polar

 - threshold is reached, and V-gated Na channels open

2) Repolarization: brings cells back to resting potential

 - inactivation of sodium channels via closing of h-gate

 - K channels open, K flows outside cell

3) Hyperpolarization

 - K channels lag, staying open a bit past resting potential

 - fixed by Na/K pumps

• Cations
  • Potassium, K (inside)
  • Sodium, Na (outside)
  • Calcium, Ca (outside)
• Anions
  • Chloride, Cl (outside)
  • Organic Anions, OA (inside)
    • the membrane is impermeable to OA's

• Equilibrium occurs at around -70mV, with the chemical gradient pushing it outside and the electrical gradient retaining it inside

• Resting membrane potential is the dominant force for the movement of chloride, so at resting potential (-60mV) there is a low intracellular concentration of Cl
• Chloride-Potassium Symporter uses the gradient-based diffusion of potassium to move chloride out of the cell

• Sodium/Calcium Exchanger uses the gradient-driven diffusion of sodium into the cell to expell calcium
• The equilibrium potential of calcium is ~+120mV, but permeability of calcium is VERY low

1. Activity-dependent: excitatory input leads to action potentials. Large, sustained input leads to a train of action potentials
2. Steady-firing neurons: differences in leakage channels leads to rythmic firing of action potentials, excitatory input --> increased frequency, inhibitory input --> decreased frequency
3. Steady-firing burst neurons: fire bursts of action potentials at steady frequency, input changes both frequency and number of action potentials per burst

• Steady firing neurons can relay both excitatory and inhibitory information

1. AP travels down axon and depolarizes the axon terminal, opening V-gated calcium channels
2. Calcium activates Synaptotagmin (vesicle protein)
3. Synaptotagmin binds and activates Complexin (vesicle protein that prevents vesicle fusion in deactivated state)
4. Activated Complexin promotes SNARE-formation, leading to vesicle fusion and neurotransmitter release

• Direct: mainly ligand-gated ion channels, which can be either excitatory or inhibitory depending on which ion they are permeable to.
• Plasticity: indirect, the activated receptor sets off a cascade that can lead to the insertion or removal of receptors into the membrane (up and down-regulation, respectively)

1. Chemical Synapse: has a gap in between the terminals, and uses receptors to pass signal.
2. Electrical Synapse: uses gap junctions to directly pass ions into the post-synaptic neuron

1. Ionotropic: ligand-gated ion channels
2. Metabotropic: NT binding leads to activation of secondary messengers

• the effects are slower than ionotropic receptors, but can be bigger, more widespread, and last longer

1. Diffusion (passive)
2. Enzymatic: enzymes break down NT in synapse
3. Pre-Synaptic Reuptake Pumps
4. Astrocyte Endfeet: pump NT out of synapse and into astrocyte

Synaptic: changes in synapses or in response to input

• Presynaptic: changes in the amount of NT released (more=potentiation, less=depression)
• Postsynaptic: change in receptors

Structural: occurs on the level of entire cells

• Changes in the number of either presynaptic terminals or postsynaptic dendrites