M8: Exciteable Cells

What is excitability in cells?

The ability of a cell to send and receive electrical signals across the plasma membrane.

Define concentration gradient.

The difference in concentration of a substance between two compartments.

What is the general equation for calculating concentration gradients?

Gradient = [Ion]OUT - [Ion]IN.

What happens when moving down a concentration gradient?

Moving from high to low concentration.

What are the key points about ion channels?

1. Channels allow passive transport only. 2. They are selective for specific ions.

What is membrane potential?

A form of potential energy created by a difference in charge between two environments.

What does the Nernst equation calculate?

The equilibrium potential for an ion.

What is the relationship between equilibrium potential and membrane potential?

Equilibrium potential is not the same as membrane potential; membrane potential depends on ion permeability.

What is a graded potential?

A transient change from resting membrane potential that decreases in intensity over time and distance.

What are the two types of graded potentials?

Depolarizing and repolarizing.

What is the significance of summation of graded potentials?

It determines whether the action potential threshold is met.

What characterizes an action potential?

A rapid depolarization followed by repolarization of the membrane.

What is the role of sodium (Na+) during the depolarization phase of an action potential?

Rapid sodium entry into the cell.

What occurs during the repolarization phase?

Potassium efflux accelerates, returning the membrane potential toward resting levels.

What are refractory periods?

Times during which a neuron cannot fire another action potential.

How does axon diameter affect action potential propagation?

Wider axons allow for faster action potential propagation.

What is the function of myelin in action potential propagation?

Acts as electrical insulation, speeding up conduction.

What is the difference between chemical and electrical synapses?

Chemical synapses use neurotransmitters, while electrical synapses allow current to spread passively across gap junctions.

What is the role of the axon terminal?

It relays messages to post-synaptic cells.

What is the significance of the Goldman-Hodgkin-Katz (GHK) equation?

It predicts membrane potential based on the contributions of multiple ions.

What happens to membrane potential when ion permeability increases?

Resting membrane potential moves toward that ion's equilibrium potential.

What is the absolute refractory period?

A period during which no new action potential can be initiated, regardless of stimulus strength.

What is hyperpolarization?

A phase where the membrane potential becomes more negative than the resting potential.

What is the role of the axon hillock?

It is the trigger zone where action potentials are generated.

What is the synaptic cleft?

The gap between pre-synaptic and post-synaptic cells filled with interstitial fluid.

What is the significance of ligand-gated channels?

They are primarily found in dendrites and respond to specific chemical signals.

What occurs during the after-hyperpolarization phase?

Potassium channels remain open, making it harder to reach threshold for a new action potential.

What is the role of neurotransmitters in synaptic transmission?

They transmit signals across the synaptic cleft from one neuron to another.

What is the effect of demyelinating diseases on action potential conduction?

They reduce or block conduction by allowing current to leak out of previously insulated regions.