Neurophysiology

When the cell is at rest, which ions are most highly concentrated inside of the cell, and which ones are most highly concentrated outside of the cell?

Na+ (Sodium)- 10x greater outside the cell

K+ (Potassium)- 20x greater inside the cell

Cl- (Chlorine)- greater outside

A-(Anion) – greater inside

How is the membrane potential maintained?

Selective Permeability- Equilibrium Potential (potassium moves across the membrane because of the channels are not closed so they follow their concentration gradient

Sodium Potassium Pump: moves 3 sodiums out for every 2 potassium in, helps to maintain resting state

Understand the forces working on the ions (electrical gradient and concentration gradient).

Electrical Gradient: different overall charge inside versus outside

Concentration Gradient: different number of ions inside versus outside

What is a voltage-gated channel? Where are they?

It is a channel that is specifically for certain elements such as sodium, potassium, or calcium voltage gated channels. These channels are selective and only open for their particular element. They open or close in response to change in the voltage of the local membrane potential. They are found on the cell membrane (body) of the neurons. 

Understand the steps of the action potential, and how one leads to the next. How is an action potential started and propagated? What ion enters first? Through what type of channel does it enter? What forces drive it inside? Why does that channel close? What channel opens next? What ion moves thru that? What forces drive that ion? Etc etc.

1. 0. Neurotransmitters bind to receptors on the neuron
2. 1. If the axon hillock depolarizes to -40mV (threshold)
3. 2. Voltage-gated sodium channels open
4. 3. Sodium rushes into the cell
5. 4. Cell become depolarized  (super positive)
6. 5. Voltage gated potassium channels open (to let it out)
7. 6. Voltage Gated Sodium channels close (to keep it in)
8. 7. Potassium rushes out of the cell (becoming more negative (equilibrium))
9. 8. Cell become  hyperpolarized (very negative (less than -60mV))
   10. 9. Voltage-gated potassium channels close
   11. 10. That part of the membrane returns to resting potential (-60mV)
   12. 11. Sodium then diffuses through the myelin  to the next Node of Ranvier (exposed part of the axon) (this continues till the last node on the axon)
   13. 12. The action Potential open voltage-gated calcium channels in membrane of terminal
   14. 13. Calcium triggers Neurotransmitters release via specialized proteins
   15. 14. Neurotransmitters bind to receptors in postsynaptic membrane
   16. 15. Ions move into or out of the postsynaptic cell
   17. 16. Local voltage changes in the postsynaptic cell (Synaptic Potential)
   18. 17. Synapse cause local changes in the postsynaptic membrane potential (Either Excitatory Postsynaptic Potential or Inhibitory Postsynaptic Potential)
   19. 18. Dendritic receptors bind to neurotransmitters from other neurons 

Then it all Repeats

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With regard to those last 2 terms, What voltage is resting potential? What voltage is threshold? Where must threshold be reached for an action potential to occur?

• i. Resting Potential (-60mV) 
• ii. Threshold (-40 mV)
• iii. In the Node of Ranvier, the threshold must be reached for an AP to occur.
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• What is the sodium/potassium pump? What purpose does it serve?

The Sodium Potassium Pump helps maintain the equilibrium and moves 3 sodiums out for every 2  Potassiums.

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What is the purpose of myelin? What happens at the nodes of Ranvier? What is saltatory conduction?

Myelin is there so that there is a break between action potentials firing. It allows a buffer between these AP’s and would cause ap’s to constantly fire all along the axon without a break and therefore it would slow down the flow of information. There are diseases where myelin is not present and can cause major deficits.

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What are the 2 factors that determine the speed of the action potential?

Whether or not there is myelin other than this action potentials  speed and size cannot change. The rate can change though.

Myelination and diameter

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What does it mean that an action potential is all or none and that a synaptic potential is graded?

Action Potentials either happen or they do not. They must reach a voltage of a specific positive charge in order for the AP to occur, but once it is reached there is no going back.

Synaptic Potential happens in the post synaptic cell at the dendrites. These are a smaller, more localized change in voltage during either hyperpolarization (negative) or de polarization (positive). The graded part just means there is a change is electrical potential either positive or negative.

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What is the role of calcium in neurotransmitter release?

The calcium gets enters the axon terminal through calcium channels in the membrane. It then trigger the Neurotransmitters release via specialized proteins.

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Describe, compare and contrast spatial summation and temporal summation.

Spatial Summation is when the  neuron gets 3 separate inputs from the dendrites (causes EPSP). These potentials are not enough to reach the threshold for action potentials. So, we summate the information about these potential until -40mV is reached and then SAP is carried out. Summating across space.

Temporal Summation is the summation of post synaptic potentials that reach the neuron/axon hillock at different times.

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Define ionotropic receptor and ligand-gated channel.

Ionotropic receptor: A receptor protein containing an ion channel that opens and ions go through

Ligand-Gated Channel: same as an ionotropic receptor, a channel that opens up and lets ions go through, key is the gate is acetylcholine