action potentials

https://youtu.be/OZG8M_ldA1M?si=dleqEm9vPosvSapq

IMPULSES (AKA: ACTION POTENTIALS)

ELECTROCHEMICAL SIGNALS CAUSED BY THE MOVEMENT OF IONS ACROSS THE MEMBRANE

Resting Potential

WHEN NEURONS ARE NOT SENDING A MESSAGE THEY STILL HAVE AN ELECTRICAL CHARGE DIFFERENCE ACROSS THEIR CELL MEMBRANE (~ -70 MV)

Na/K Pump

-MAINTAINS RESTING POTENTIAL

-ACTIVELY PUMPS 2 POTASSIUM IONS IN & 3 SODIUM IONS OUT

THIS CAUSES AN OVERALL NEGATIVE CHARGE ON THE INSIDE & POSITIVE CHARGE ON THE OUTSIDE. (POLAR)

Why a 3 for 2 exchange?

-Builds up a difference in charge & concentration of ions

-Builds up POTENTIAL for movement down a concentration gradient

How is the message transmitted?

1. A stimulus causes local depolarization of the membrane.

2. If the depolarization is strong enough and the threshold is reached, the Action Potential will trigger.

3. The local depolarization causes more of the membrane to depolarize. The signal travels the length of the neuron.

4. The membrane repolarizes and gets ready for a new action potential.

What is the progression of a message?

-The stimulus must cause the depolarization to be significant enough that it reaches the threshold.

-It is an all or nothing response

-All impulses are the same strength regardless of the strength of the stimulus

until when does AP continue?

AP continues down the axon until it reaches the AXON TERMINAL

Acetylcholine

excites skeletal muscle

Epinephrine (adrenaline) & norepinephrine

fight or flight response

Dopamine

widespread in brain

affects sleep, mood, attention & learning

lack of dopamine associated with Parkinson’s disease excessive dopamine linked to schizophrenia

Saltatory Conduction

-ACTION POTENTIALS “JUMP” FROM NODE TO NODE OF MYELINATED AXONS

-THIS IS BECAUSE NA+ CHANNELS CANNOT OPEN WHEN WRAPPED IN MYELIN

-INCREASES THE SPEED OF THE NERVE IMPULSE