Human Physiolgy Exam 2

What are lipid rafts and what purpose do they serve?

Lipid rafts are small, specialized regions of the cell membrane that contain high concentrations of cholesterol and certain lipids and proteins.

What determines how easily a molecule can get through the membrane?

• Size: Smaller molecules usually cross more easily than larger molecules.

• Polarity: Nonpolar molecules cross more easily than polar molecules.

• Charge: Charged molecules have a very difficult time crossing the membrane.

• Lipid solubility: Molecules that dissolve in lipids can pass through the membrane more easily.

Order most permiable to least permiable molecules.

Hydrophobic molecules

Small uncharged polar molecules

Large uncharged polar molecules

Ions

Are there any molecules that can cross without transport proteins?

Yes, some small and nonpolar molecules can cross directly through the phospholipid bilayer by simple diffusion

Review figure of the synthetic membrane

Why do ions have so much trouble making it across the bilayer?

• They carry an electrical charge.

• The inside of the phospholipid bilayer is hydrophobic (water-repelling).

• Ions interact strongly with water, so entering the membrane’s oily interior is energetically unfavorable.

What are the different types of transport proteins that can be found in the membrane?

• Channel Proteins: Allow specific ions or molecules to move across the membrane down their concentration or electrochemical gradient.

• Carrier Proteins: Bind to a specific molecule and change shape to move it across the membrane. They can perform facilitated diffusion or active transport.

• Pump:Use energy, often from ATP, to move substances against their concentration or electrochemical gradients

What are ion channels used for? Can they be gated? Are they selective, or can anything pass through? How fast can ions travel through these channels (quicker or slower than other transport proteins)?

• Ion channels are membrane proteins that allow specific ions to cross the cell membrane.

• Ion channels can be gated

  • Voltage-gated: Open or close in response to changes in membrane voltage.

  • Ligand-gated: Open when a specific chemical messenger binds to them.

  • Mechanically gated: Open in response to physical pressure, stretching, or vibration.

• Ion channels are selective

• Ion channels are much faster than other transport proteins

What happens during passive transport?

Movement of substances across a cell membrane without the cell using energy (ATP). Includes Simple diffusion, facilitated diffusion through channel or carrier proteins, and osmosis

What are gradients?

A concentration gradient occurs when a substance has different concentrations in two places.

For example, if there are many oxygen molecules outside a cell and fewer inside, oxygen tends to move from outside to inside.

For passive transport are solutes moving along their concentration gradient or against?

Solutes move down (along) their concentration gradient, from an area of higher concentration to an area of lower concentration.

What is an electrochemical gradient?

An electrochemical gradient combines two gradients:

• Chemical gradient: The difference in an ion's concentration across the membrane.

• Electrical gradient: The difference in electrical charge across the membrane.

Electrical gradients only apply to which molecules?

Electrical gradients affect ions.

What is active transport?

Active transport moves substances across a membrane against their concentration gradient or, for ions, against their electrochemical gradient. This requires energy, either directly or indirectly.

How do primary active transport and secondary active transport differ from each other?

Primary active transport

Uses energy directly from a source such as ATP to move substances against their gradients.

Secondary active transport

Uses energy stored in an ion's electrochemical gradient to move another substance against its gradient. It does not directly use ATP at the transporting protein.

What is coupled transport?

Coupled transport occurs when the movement of one substance is linked to the movement of another substance through a transport protein.

One substance moves down its gradient, releasing usable energy that drives the other substance against its gradient.

What types of transporters are GLUT, the Na+/K+ pump, and the Na+/glucose symporter? What do they do?

GLUT: Carrier protein; facilitated diffusion. Moves glucose down its concentration gradient without using ATP directly.

Na+/K+: Pump; primary active transport. Uses ATP directly to move 3 Na⁺ out of the cell and 2 K⁺ into the cell against their gradients.

Na+/glucose symporter: Cotransporter; secondary active transport; symport. Uses Na⁺ moving down its electrochemical gradient to move glucose against its concentration gradient. Both move in the same direction.

Na+/K+ pumps are important. How are sodium and potassium moved across the plasma membrane?

1. Three Na⁺ ions bind to the pump inside the cell.

2. The pump uses energy from one ATP molecule, causing it to change shape.

3. The pump releases the 3 Na⁺ ions outside the cell.

4. Two K⁺ ions bind to the pump outside the cell.

5. The pump changes back to its original shape and releases the 2 K⁺ ions inside the cell.

What do Na+/K+ pumps do for the cell? (Hint: think about cell volume and active transport)

Maintains cell volume: This helps prevent excess solute accumulation inside the cell, which could cause water to enter by osmosis and make the cell swell.

Maintains ion gradients: It keeps Na⁺ concentration low inside the cell and K⁺ concentration high inside the cell.

Uses active transport: It uses energy from ATP to move both ions against their electrochemical gradients.

What is digoxin?

Digoxin is a medication used to treat certain heart conditions, especially heart failure

How does Digoxin work? It is a toxin, so isn’t that bad?

Digoxin inhibits the sodium-potassium pump (Na⁺/K⁺-ATPase). The Na⁺/Ca²⁺ exchanger removes less Ca²⁺. More Ca²⁺ makes the heart contract more forcefully.

Too much digoxin is bad, but the right amount is very beneficial.

There were different examples of transport given in class. How is glucose transported across intestinal epithelial cells?

Glucose enters through sodium-glucose symporter with Na⁺ by secondary active transport and exits into the blood through GLUT2 by facilitated diffusion. Na⁺/K⁺-ATPase maintains the Na⁺ gradient.

It is important that glucose moves from the intestinal lumen into the epithelial cell and then out of the cell into the blood. What makes sure glucose is moving in this direction?

Na+ gradient maintained by the Na⁺/K⁺-ATPase

What are the intracellular and extracellular concentrations of Na+ and K+? How low are intracellular calcium levels are kept?

• Na⁺: Low inside (~10–15 mM), high outside (~145 mM).

• K⁺: High inside (~140 mM), low outside (~4–5 mM).

• Cytosolic Ca²⁺ is kept very low, around 100 nM (0.0001 mM), compared with extracellular Ca²⁺ at roughly 1–2 mM.

Who was Alessandro Giuseppe Antonio Anastasio Volta? Only the name Volta needs to be remembered.

Was an Italian physicist, chemist, and a pioneer of electricity and power, who is credited as the inventor of the electrical battery and the first to isolate methane.

What did Luigi Galvani believe? Did Volta and Galvani agree about animal electricity?

Galvani believed in animal electricity, that animals produce their own electricity, which causes muscles to contract and nerves to function.

No. Galvani believed electricity originated within the animal itself, while Volta believed the electricity came from contact between two different metals.

What did Volta invent? What was the big take away from his invention?

Volta invented the first electric battery. He proved electricity could be generated chemically. Volta's invention led to the development of the field of electrochemistry

Giovanni Aldini was the nephew of Luigi Galvani and a big supporter of animal electricity. What did he do?

Performed public demonstrations using electricity on the bodies of dead animals and executed humans, causing their muscles to twitch and contract.

He supported Galvani’s theory of animal electricity, believing electricity could activate muscles and potentially restore life.

What are leak channels? Why are they important?

Leak channels are proteins in the cell membrane that let ions move in and out without using energy. K⁺ leak channels help maintain the resting membrane potential.

What are fixed intracellular anions and what role do they play?

They are negatively charged molecules inside the cell that cannot easily leave. They help make the inside of the cell more negative.

Why does the thickness of the plasma membrane matter?

ts thinness allows a small separation of charges to create a voltage difference across the membrane.

How many of the cell’s total K+ ions are needed to establish the resting membrane

potential?

Only a tiny amount of K⁺ needs to move. Most K⁺ stays inside the cell.

What can you calculate with the Nernst equation?

Cell potentional

Do you know what the terms are for a membrane at rest vs when it changes?

Resting, Depolarization, repolarization and hyperpolarization

• Resting: The cell's normal voltage.

• Depolarization: The inside becomes less negative.

• Repolarization: The voltage returns toward resting.

• Hyperpolarization: The inside becomes more negative than at rest.

Which cells are the main excitable cells in the body?

Neurons and muscle cells can create electrical signals called action potentials.

Label the parts of a neuron

Dendrites, Soma(cell body), Nucleus, Axon Hillock, Myelin shieth, Axon, Axon terminal

Why are neurons called “terminally differentiated”?

Mature neurons are highly specialized and usually cannot divide to make new neurons.

Describe the difference between a local potential and an action potential?

• Local potential: A small change in membrane voltage that varies in strength and gets weaker as it spreads.

• Action potential: A rapid electrical signal that follows an all-or-nothing rule and travels along the cell membrane without getting weaker.

Which ion channels cause different membrane voltage changes?

Depolarization, Repolarization, Hyperpolarization, resting potential

• Depolarization: Voltage-gated Na⁺ channels open, allowing Na⁺ to enter.

• Repolarization: Na⁺ channels inactivate and voltage-gated K⁺ channels open, allowing K⁺ to leave.

• Hyperpolarization: K⁺ channels stay open a little longer, allowing extra K⁺ to leave.

• Resting potential: Mainly maintained by K⁺ leak channels and the Na⁺/K⁺ pump.

Where are there ligand gated ion channels?

hey are common on dendrites and cell bodies of neurons, where chemical messengers bind to them.

Where are there a lot of voltage-gated sodium channels (VGNCs)? VGKCs?

Sodium VG channels are concentrated at the axon hillock and initial segment of neurons, where action potentials usually begin, and along the axon.

Potassium VG channels are found along the axon, where they help repolarize the membrane after an action potential.

Why are action potentials an all-or-nothing event?

If the membrane reaches the threshold, a full action potential occurs. If it does not reach the threshold, no action potential occurs.

Why are action potentials an example of a positive feedback loop?

Na⁺ channels open, allowing Na⁺ to enter and depolarize the membrane. This opens even more Na⁺ channels, causing more Na⁺ to enter.

How can ion channels be selective?

Ion channels have specific sizes, shapes, and electrical charges that allow certain ions to pass through more easily than others.

What is the sphere of hydration and selectivity filter?

The hydration sphere is the layer of water molecules that surrounds an ion in an aqueous environment.

The selectivity filter is a narrow part of an ion channel that allows certain ions through while blocking others

What organism was studied that helped us understand action potentials?

The loligo’s giant squid axon was studied because its large size made it easier to study electrical signals in neurons.

What is the action potential threshold?

The threshold is the voltage needed to trigger an action potential, usually around −55 mV.

Do all voltage-gated sodium channels have to open to trigger an action potential?

No. Enough Na⁺ channels must open to reach the threshold and trigger an action potential.

What happens 1-2ms after voltage-gated sodium channels open? Why would this be important?

Na⁺ channels inactivate, stopping Na⁺ from entering. This helps end depolarization and allows repolarization to begin.

What is repolarization?

Repolarization is when the membrane voltage returns toward its resting level, mainly because K⁺ leaves the cell.

What is a refractory period?

he refractory period is the time after an action potential when the neuron cannot easily fire another one.

Difference between absolute and relative refractory periods? Why are refractory periods necessary?

• Absolute: No second action potential can occur, no matter how strong the stimulus.

• Relative: Another action potential can occur, but a stronger-than-normal stimulus is needed.

They help action potentials travel in one direction and prevent neurons from firing too rapidly.

What is hyperkalemia? How does that impact action potentials and recovery?

Hyperkalemia means high levels of K⁺ in the blood.

• Action potentials: High extracellular K⁺ makes the resting membrane potential less negative, which can make cells more excitable at first.

• Recovery: If K⁺ stays too high, Na⁺ channels can become inactivated, making it harder for cells to fire action potentials and recover normally.

How do local anesthetics work? Where do they come from?

Local anesthetics block voltage-gated Na⁺ channels, preventing nerves from sending pain signals to the brain.

They come from natural sources or are made synthetically in laboratories. Many modern local anesthetics are synthetic. Come from cocaine

What does tetrodotoxin (TTX) do? Where does TTX come from?

TTX blocks voltage-gated Na⁺ channels, preventing action potentials and nerve signals from traveling.

It is found in animals such as pufferfish and is produced by certain bacteria associated with these animals.