M4.3 Electrical Properties of Membranes

What is resting membrane potential?

The baseline electrical charge across the membrane (~ -70 mV) — Think of it as the “battery at rest.”

What maintains resting potential?

K+ leak channels — Mnemonic: “Potassium leaks keep it steady.”

What happens during depolarization?

Na+ channels open

What happens during repolarization?

K+ channels open

What is hyperpolarization?

Membrane potential drops below resting (~ -80 mV) — Like “overshooting the reset.”

What triggers an action potential?

Stimulus crossing threshold (~ -55 mV) — “Threshold = trigger point.”

What is the peak voltage of depolarization?

+40 mV — Mnemonic: “Positive peak at forty.”

What prevents backward spread of action potential?

Refractory period (Na+ channels inactivated) — “Refractory = rest required.”

What is the refractory period?

Time when Na+ channels cannot reopen — Like a “cooldown timer.”

What is saltatory conduction?

Action potentials jump between nodes of Ranvier — “Saltare = to leap.”

Why is saltatory conduction faster?

Myelin insulation forces signals to jump — “Myelin = speed boost.”

What are voltage-gated channels?

Ion channels that open/close with voltage changes — “Voltage = gatekeeper.”

What are the three states of Na+ channels?

Closed

What ion flows in during depolarization?

Na+ — Sodium makes inside positive.

What ion flows out during repolarization?

K+ — Potassium restores negativity.

What is the role of delayed K+ channels?

Open after Na+ inactivation to repolarize — “Delay = reset.”

What is the trigger zone?

Initial site of action potential (axon hillock) — “Hillock = launch pad.”

What is conduction zone?

Axon where impulse travels — “Highway for signals.”

What is output zone?

Axon terminals releasing neurotransmitters — “Output = message sent.”

What do local anesthetics block?

Voltage-gated Na+ channels — Prevent nerve firing (Novocaine).

What do tetrodotoxins block?

Na+ channels — Found in puffer fish

What do conotoxins block?

Voltage-gated Ca2+ channels — Cone snail venom

What is Ziconotide (Prialt)?

Drug from conotoxin

What is a chemical synapse?

Junction where neurotransmitters transfer signals — “Chemical handshake.”

What ion triggers neurotransmitter release?

Ca2+ entering presynaptic terminal — “Calcium = release signal.”

What do excitatory neurotransmitters do?

Open Na+ channels

What do inhibitory neurotransmitters do?

Open Cl- or K+ channels

What enzyme breaks down acetylcholine?

Acetylcholinesterase — “Erase acetylcholine.”

What neurotransmitter activates muscle contraction?

Acetylcholine — “Ach = action.”

What ion causes muscle contraction?

Ca2+ release from sarcoplasmic reticulum — “Calcium = contraction.”

What is dopamine’s role?

Regulates movement

What disease involves dopamine neuron loss?

Parkinson’s disease — Leads to motor deficits.

What is serotonin’s role?

Mood regulation

What is GABA’s role?

Inhibitory neurotransmitter

What is glutamate’s role?

Excitatory neurotransmitter

What are endorphins?

Natural painkillers

What do SSRIs like Prozac do?

Block serotonin reuptake

What does Ritalin do?

Blocks dopamine reuptake — More dopamine available.

What does Adderall do?

Increases dopamine release into synapse — “Amp up dopamine.”

What do drugs of abuse target?

Brain’s dopamine reward pathways — “Hijack pleasure center.”

What happens with cocaine use?

Exaggerated dopamine release

What is addiction?

Compulsive use despite harm

What happens to dopamine receptors in addiction?

Brain reduces receptors or dopamine production — “Tolerance = fewer signals.”

Can the brain recover from addiction?

Yes

What is the neuromuscular junction?

Synapse between motor neuron and muscle — “Nerve-to-muscle bridge.”

What sequence activates muscle contraction?

Ach release → Na+ influx → Ca2+ release → contraction — “Ach → Na → Ca → contract.”

What is the role of myelin?

Insulates axons

What are nodes of Ranvier?

Gaps in myelin where action potentials regenerate — “Nodes = recharge points.”

What is the difference between excitatory and inhibitory signals?

Excitatory depolarizes

What is the difference between ligand-gated and voltage-gated channels?

Ligand-gated open with chemical binding

What is the difference between resting and action potential?

Resting = stable negative charge