Membrane Transport Mechanisms Quiz

Membrane Transport

• Lateral Diffusion: Molecules move from side to side within a membrane layer.
• Rotation: Molecules rotate within the membrane layer.
• Swing: Molecules move from side to side within the membrane layer.
• Flexion: The contraction of molecules within the membrane layer.
• Transverse Diffusion (Flip-Flop): Molecules move from one half of a phospholipid monolayer to the other.

Membrane Transport Mechanisms

• Simple Diffusion: Fat-soluble molecules pass directly through the phospholipid bilayer.
• Carrier-mediated Facilitated Diffusion: The movement of a molecule is facilitated through a carrier protein that is specific to that molecule. The carrier protein changes shape to move the molecule across the membrane.
• Channel-mediated Facilitated Diffusion: Molecules move through a channel protein. The channel protein is often selective for size and charge, thus not all molecules can pass through.
• Osmosis: Water diffusion across a membrane, following the concentration gradient.

Fick's First Law

• Flux (J) is the number of atoms passing through a plane of unit area per unit time.
• Fick's first law describes the rate at which atoms, ions, particles, or other species diffuse in a material.
• The rate of diffusion is proportional to the concentration gradient.

Osmosis and Tonicity

• Water moves across a semipermeable membrane from an area of low solute concentration (hypo-osmotic) to an area of high solute concentration (hyper-osmotic) in an attempt to equalize solute concentrations.

• Isotonic: Solutions have the same solute concentration. Net water movement is zero.

• Hypertonic: Solution with higher solute concentration than the inside of the cell. Water moves out of the cell, causing shrinkage (crenation).

• Hypotonic: Solution with lower solute concentration than the inside of the cell. Water moves into the cell, causing swelling (lysis).

Active Transport

• Active processes use energy (ATP) to move substances against a concentration gradient.
• Primary active transport directly uses ATP to transport the substance.
• Examples of primary active transport include: the sodium-potassium pump (3Na+ out, 2K+ in).
• Secondary active transport uses an existing electrochemical gradient to move substances against their concentration gradient.

Ion Channels

• Mechanically gated (ion) channel: Integral membrane protein that opens and closes in response to a stimulus (e.g., touch, vibration, pressure, stretch).
• Voltage-gated (ion) channel: Opens or closes in response to changes in the membrane potential.
• Ligand-gated (ion) channel: Opens or closes in response to a specific signaling molecule (ligand).
• Signal-gated (ion) channel: Responds to intracellular signaling.

Action Potentials

• Changes in membrane potential that propagate along nerve and muscle cell membranes.
• Excitatory postsynaptic potentials (EPSPs): depolarizations leading to a greater likelihood that a neuron will fire.
• Inhibitory postsynaptic potentials (IPSPs): hyperpolarizations leading to a decrease in that likelihood.

Action Potentials in Skeletal Muscle

• Action potentials are electrochemical signals that spread across the sarcolemma of skeletal muscles, initiating muscle contraction.
• The action potential propagation depends on the movement/flow of Na+ ions into and K+ ions out of the muscle cell.

Nerst Equation and Goldman Equation (Simplified)

• The Nerst equation calculates the equilibrium potential for a single ion.
• The Goldman equation takes into consideration multiple ions to calculate the resting membrane potential of a cell.

Nerve-Muscle Transmission

• Acetylcholine is released from the axon terminal and binds to receptors on the sarcolemma.
• This initiates an action potential that travels down the T-tubules to trigger the release of Ca2+ from the sarcoplasmic reticulum.
• Calcium ions bind to troponin, leading to muscle contraction.
• Acetylcholinesterase removes acetylcholine from the synaptic cleft to stop contraction.

Types of Summation

• Spatial Summation: Simultaneous stimulation by several presynaptic neurons.
• Temporal Summation: High-frequency stimulation by a single presynaptic neuron.

Electrocardiography (ECG)

• ECG recording of electrical activity of the heart.
• Used to diagnose heart conditions.

EMG (Electromyography)

• Records electrical activity of skeletal muscles.
• Used to diagnose muscle and nerve disorders.