Action potentials

• action potentials are all or nothing, meaning that the neuron will either fire or not fire
• what is ohms law

  current = potential/ resistance
• the resting membrane potential is -70mV
• How do currents flow differently in wires and axons?

  Wires: Electrons flow in the wire. Axons: Ions flow in and out of the axon membrane in wave
• A cell has a resting membrane potential, what is it?


  -70mv
• Potassium K+ ions are attracted to the inside of the cell at rest, hence there are more k+ inside the cell at rest
• What is an ion channel?

  Channels through a cell membrane to allow specific ions to pass through
• The chemical gradient balances with the electrical gradient

  
• what is an equilibrium potential?

  potential across membrane when there is no flow of an ion. it depends on the ion
• What are the equlibrium potentials of potassium, sodium and chlorine?

  Potassium: -80mV Sodium: +62mV Chlorine: -65mV
• The resting potential of neurons is near to potassium's equilibrium potential, why?


  there are more potassium channels open at rest than any other ion
• If permeability of a membrane to an ion increases, the membrane potential will move towards that ions equilibrium
• what does a na+/k- atpase do?

  pump na out of and k into the cell to restore concentration gradients
• where does the most atp get used in neurons?

  the atpase pump for na and k
• what is depolarisation?


  a positive increase in membrane potential
• what is hyperpolarisation?


  a decrease in membrane potential
• which is faster an action potential or synaptic chemical signals?

  action potential
• what 2 ways can ion channels be opened?

  Voltage-gated and ligand-gated (binding neurotransmitters etc)
• action potentials move across axons by transient depolarisation opening voltage gated ion channels
• the axon hillock must reach a threshold potential to initiate an action potential
• stages of action potential

  1. resting- threshold reached
  2. depolarisation- sodium channels open
  3. repolarisation- sodium inactivation gate closes/potassium leaves now positive inside of cell
  4. hyperpolarisation- as potassium leaves cell
  5. resting- inactivation opens, pump restores concentration gradient
• relatively few ions actually move during action potentials, gradient barely changes if they get pumped back
• what is an absolute refractory period?

  Period of time after an action potential when a neuron cannot generate another action potential.
• what is a relative refractory period?

  some sodium channels open so very string stimuli can generate action potentials
• what is action potential propagation?

  The action potential moving down the axon aka the movement
• why can the action potential travel in only one direction?

  the inactivation gate on the sodium channels is closed for the absolute refractory period after firing a signal
• why is the speed of ap propagation so variable?

  1. resistance- slower if leakier
  2. capacitance- ease of changing membrane potential- how much charge
• what affects how far depolarisation can go down the axon

  1. membrane resistance- leaky = less far
  2. diameter- conduct faster if bigger diameter
• what are myelin sheaths?

  insulation for the axon causes the ap to jump between nodes of ranvier to travel faster and with less ion flow
• synaptic neuron

  A) terminal bouton

  B) synaptic vesicles

  
• what channels are there in the synapse?


  calcium ions ca+ that are voltage gated
• when the calcium ions go into the cell, vesicles fuse to the membrane releasing neurotransmitters into the synaptic cleft
• what type of gated ion channels are in the post synaptic membrane?

  ligand
• what is the main excitatory neurotransmitter?

  Glutamate
• when the glutamate opens the ion channels in the post synaptic neuron, what is generated?

  excitatory post-synaptic potential (EPSP) that adds towards the threshold for action potential firing
• why do only sodium ions move through the ampa receptor and not potassium ions?

  tho its a cation channel, the potassium ions are near their equilibrium potential inside the cell
• explain the NMDA receptor and how its different to ampa

  it has a magnesium ion in the channel that only moves when the rmp depolarises- adds a voltage gate to a ligand gated channel
• what does the nmda ion channels also let through?

  calcium- useful for associative learning
• name the 3 types of glutamate receptors

  ampa, nmda, metabotropic
• what are the two ways epsp can create a ap as one does not provide enough volatge?


  temporal-multiple bursts in rapid succession from one synapse

  spatial- multiple synapses producing one epsp to reach threshold-poly