Action Potential + The Synapse

SBI4U - Howes

describe electrochemical impulses

neurons send messages using electrical charges (ions) — dissimilar solutions are separated by a membrane

label the steps in the graph

1) Polarized Membrane (resting potential)

2) Depolarization

3) Repolarization

4) Hyperpolarization and Refactory Period

Cells are polarized through ________ __________

active transport

A Na-K pump moves __ Na+ ____ of the cell for every __ K+ pumped ____ the cell: results in a net _____ of 1 positive charge inside

3 OUT, 2 INTO, loss

When a cell is ___________, the inside becomes ________ relative to the outside

polarized, NEGATIVE

A polarized membrane

stores energy by holding opposite charges apart

⚡ this membrane potential is called voltage

The resting potential of a cell is ____

-70mV

Depolarization of a cell generates an __________ __________, ie a ______ ___________

Action Potential, Nerve Impulse

How does a stimulus trigger depolarization?

• Stimulus causes an ↑ in membrane permeability to Na+

• Na+ rushes in and the cell becomes depolarized

Stimulus (give example)

any environmental factor that causes a change in the neuron’s environment

ex: physical pressure, temperature change, etc

What happens after an action potential is generated? What direction?

it moves as a wave of depolarization down the axon: starts from soma ➙ axon terminals

⇨ in vertebrates, it jumps between nodes of Ranvier

explain the “all or nothing” principle

neurons fire maximally or not at all — the stimulus needs to be above a critical intensity and duration

the critical intensity to stimulate a nerve fibre is called ___________ ________ (___mV)

Threshold Potential (-55 mV)

Repolarization

occurs because of ↑ membrane permeability to K+

🛏 the restoration of resting potential

Hyperpolarization

the cell undershoots its resting potential, this occurs because K+ channels are slow to close so the voltage dips below resting for a bit

Refactory Period

brief interval of time following the response of a membrane, during which it is incapable of a second response