Lecture 4 (Polished)

Who was Luigi Galvani and what did he discover?

Luigi Galvani showed that frog muscles twitch when nerves are connected with different metals, even after death. He concluded that living tissue contains its own electricity, rejecting the idea of "animal spirits." Simple explanation: He discovered biological electricity.

What experiment did Galvani perform with frog legs?

Galvani completed a circuit between a frog nerve and muscle using two metals, causing muscle contraction. He also used atmospheric electricity (lightning) to trigger contractions. Simple explanation: Circuits made muscles move.

What is electrophysiology?

Electrophysiology is the study of electrical properties of biological tissues. Galvani's work established this field. Simple explanation: Studying electricity in living systems.

How did Alessandro Volta challenge Galvani's conclusion?

Volta argued the electricity came from the metals, not the tissue. He showed that two different metals create a voltage difference. Simple explanation: Metals generate electricity.

What was Volta's lasting contribution?

Volta's work led to the invention of the first battery. Although he was right about metals, Galvani was correct that neurons use electrical signals. Simple explanation: He built the battery.

How does the nervous system transmit information over long distances?

The nervous system uses electrical signals called action potentials that travel along axons. These signals rely on membrane properties. Simple explanation: Electricity moves messages.

What is a reflex arc?

A reflex arc is a fast, automatic response pathway involving sensory input, spinal processing, and motor output. Simple explanation: A quick response loop.

What happens when you step on a tack?

Sensory neurons send signals to the spinal cord. One pathway goes to the brain for pain perception, while another activates motor neurons to withdraw the foot. Simple explanation: Feel pain and pull away.

Why are reflexes faster than conscious actions?

Reflexes are processed in the spinal cord without waiting for brain involvement. Simple explanation: Shorter pathway.

What generates electrical signals in neurons?

Electrical signals arise from ions dissolved in water that are separated by a lipid membrane. Simple explanation: Charged particles + barrier.

What is a polar molecule?

A polar molecule has uneven electron distribution, creating positive and negative ends. Water is a classic example. Simple explanation: Unequal charge.

What is a nonpolar molecule?

A nonpolar molecule has even electron distribution and no charge separation. Carbon dioxide is an example. Simple explanation: No charged ends.

What are hydration shells?

When salts dissolve, water molecules surround ions to keep them dissolved. This organized shell stabilizes ions in solution. Simple explanation: Water shields ions.

What does "like dissolves like" mean?

Polar molecules dissolve in water, while nonpolar molecules cluster together. This explains why oils avoid water. Simple explanation: Similar types mix.

What is the structure of a phospholipid?

A phospholipid has a hydrophilic (polar) head and hydrophobic (nonpolar) tails. Simple explanation: Water-loving head, water-fearing tails.

Why do phospholipids form a bilayer?

Heads face water inside and outside the cell, while tails pack inward away from water. This creates a stable barrier. Simple explanation: Self-assembling wall.

Why does the membrane block ions?

The membrane's hydrophobic core repels charged ions and water. Ions require channels to cross. Simple explanation: Charges can't pass through oil.

What is diffusion?

Diffusion is the movement of molecules from high to low concentration until equilibrium is reached. Simple explanation: Spreading out.

What is a concentration gradient?

A concentration gradient is a difference in ion concentration across the membrane. It drives diffusion. Simple explanation: Unequal distribution.

Why are ion channels necessary?

The lipid bilayer blocks ions, so channels provide selective pathways for diffusion. Simple explanation: Doors through the wall.

What is electrical potential difference (voltage)?

Voltage is stored energy caused by separation of charge. It represents the potential to do work. Simple explanation: Electrical pressure.

How does the water reservoir analogy explain voltage?

A pump lifts water to create stored energy. When released, water flows and does work—just like ions flowing down voltage. Simple explanation: Height equals energy.

What is electrical current (I)?

Current is the movement of electrical charge (ions). It is measured in amperes. Simple explanation: Flow of charge.

What is electrical conductance (g)?

Conductance is how easily charge moves across the membrane. More open channels increase conductance. Simple explanation: Openness.

What is electrical resistance (R)?

Resistance is the opposition to charge movement. It equals 1/g. Simple explanation: Blockage.

How do neurons increase current flow?

They open more ion channels, increasing conductance and lowering resistance. Simple explanation: Open more doors.

How is membrane potential measured?

A voltmeter uses one electrode inside the neuron and a reference electrode outside. Simple explanation: Compare inside to outside.

What is the resting membrane potential?

The inside of the neuron is negative relative to the outside at rest. Simple explanation: Inside is more negative.

Why does the membrane act like a capacitor?

Charge accumulates only at the membrane surfaces, storing energy. The bulk fluids remain neutral. Simple explanation: Charge storage.

What is ionic equilibrium?

Equilibrium occurs when diffusion and electrical forces on an ion are equal and opposite. Net movement stops. Simple explanation: Perfect balance.

Why does potassium want to leave the neuron?

K+ concentration is higher inside the cell, so diffusion pushes it out. Simple explanation: Crowded inside.

Why does potassium stop leaving the cell?

As K+ leaves, the inside becomes negative, pulling K+ back in. Forces eventually balance. Simple explanation: Pulled back.

What is the equilibrium potential for potassium (EK)?

EK is approximately −84 mV. At this voltage, K+ has no net movement. Simple explanation: Balance point.

What is the equilibrium potential for sodium (ENa)?

ENa is approximately +66 mV. Sodium strongly enters the neuron until balance is reached. Simple explanation: Na+ wants in.

What is ionic driving force?

Driving force equals Vm − Eion. It determines the direction and magnitude of ion movement. Simple explanation: How hard ions are pushed.

When is ionic current large?

When Vm is far from Eion, driving force is high and current is large. Simple explanation: Big difference, big flow.

When is ionic current small?

When Vm is close to Eion, driving force is low and current is minimal. Simple explanation: Near balance.

Why don't ion concentrations change much?

Only a tiny fraction of ions move to create large voltage changes. Simple explanation: Small movement, big effect.

What is the Nernst equation used for?

It calculates the equilibrium potential for an ion based on its concentration gradient. Simple explanation: Finds balance voltage.

What factors affect the Nernst equation?

Ion concentration ratio, temperature, ion charge, gas constant, and Faraday's constant. Simple explanation: Physics inputs.

What is the simplified Nernst equation at body temperature?

Eion ≈ 61.54 mV × log10([ion]in / [ion]out). Simple explanation: Easier calculation.

Why does ion charge matter in the Nernst equation?

The sign of the ion (z) determines the direction of the voltage. Negative ions flip the sign. Simple explanation: Charge changes polarity.

Why is the phospholipid bilayer essential for signaling?

It prevents free ion flow, allowing controlled electrical signaling. Simple explanation: Controlled barrier.

How do neurons control ion movement?

Selective ion channels regulate when and where ions cross the membrane. Simple explanation: Gated flow.

What forces govern ion movement?

Diffusion (chemical gradient) and electrical forces act together. Simple explanation: Push and pull.

When is equilibrium reached?

When diffusion and electrical forces cancel out, producing no net ion movement. Simple explanation: Balanced forces.