Anatomy and Physiology: Resting Membrane Potential and Action Potential; Concentration Gradients Electrical, Chemical and Electrochemical Part One.

What is a resting membrane potential?

A fixed distribution of charge across a barrier

A neuron in its resting state has what distribution of positive and negative charge intracellularly and extracellularly?

Neurons have a higher quantity of negative charge intracellularly and a higher quantity of positive charge extracellularly

What events need to occur so that an action potential is generated at the axon hillock?

The graded action potentials generated at the dendrites and the cell body have to sum to an overall event of depolarization?

What is the absolute refractory period? What Ion Channel is inactive or closed during this period?

This is when an action potential is being generated and another one cannot be initiated regardless of the voltage applied to the membrane; During this period, the Na+ Sodium channels will remain inactivated or closed.

What is Hyperpolarization and why does it occur?

This is when pottassium continues to exit the cell and the interior membrane potential gets more negative than it was at its original resting state.

What is Saltatory Conduction?

Action potentials which travel along the axon yet get regenerated at the Nodes of Ranvier.

What is the difference between an electrical gradient and a concentration gradient?

Electrical Gradient- Ions which will move towards an area of opposite electrical charge; Concentration gradient- Ions which move from an area of higher concentration to an area of lower concentration.

What is the difference in the ion channels used in Action Potentials and Graded Potentials?

Graded Potentials utilize chemically gated ion channels; Action potentials utilized voltage gated channels.

What is the difference between graded and action potentials?

Graded potentials- they degrade with distance, react differently to magnitude of stimuli; They are short lived/ Action Potentials- They do not decay with distance; Used for long distance communication; They are an all or none event.

After the absolute refractory period, another action potential can be generated during the relative refractory period. What conditions allow for the regeneration of another action potential? What channel is open during this period?

If the stimulus is stronger another action potential can be generated; The applied stimulus during the relative refractory period needs to be greater than that initially applied to overcome threshold;K+ channels stay open.

What conditions allow for a greater conduction velocity?

More myelination results in a greater conduction velocity; Axons which are wider in diameter have a greater conduction velocity

During an action potential, which event follows depolarization?

Repolarization, at this point pottassium ions travel to the extracellular environment

What compensates for the sodium-pottassium leak channels and works to pump Sodium out and Pottassium in?

The Sodium-Pottassium Pump

When is the NA+ voltage gate's Activation gate open? When is it closed? Which gate closes shortly after the NA+ Voltage channel opens?

The activation gate will open during depolarization and will stay closed during periods of rest; When the NA+ Voltage channel opens, The Inactivation gate will close.

If the threshold potential is surpassed, an action potential is generated. What events occur at this phase which lead to depolarization? Does the membrane potential get more positive or negative?

The generation of an action potential leads to depolarization and the influx of sodium ions intracellularly; This brings the membrane potential closer to a positive value.

What two factors does the resting potential of a neuron depend upon?

The ratio of sodium and pottassium ions intracellularly and extracellularly; The pattern of leak channels to expell three sodium ions to the extracellular environment to every two pottassium ions permitted entry intracellularly.

What is the proportion of Sodium and Pottassium Ions in the intracellular and extracellular environments of a neuron?

There are more Sodium Ions extracellularly and more pottassium ions intracellularly

Action potentials are generated in response to what signal?

They are generated in response to graded potentials.

What is the mechanism of action of action potentials which occur in myelinated axons?

They are regenerated at the nodes of ranvier

What are the three conformational state a voltage gated Sodium channel can exist in ?

They can exist in an Closed, Open , Inactivated