BIOL 2410 - Quiz 3

Is negative, except when there is a change in membrane permeability to ions
Explanation: The membrane potential of most cells is negative at all times. This is because the cell membrane is made up of a phospholipid bilayer that is impermeable to most ions. The only ions that can pass through the cell membrane are sodium ions (Na+), potassium ions (K+), and chloride ions (Cl-). These ions are able to pass through the cell membrane because they are small and have a charge that is opposite to the charge of the cell membrane.The cell membrane is negatively charged on the inside and positively charged on the outside. This creates a potential difference across the cell membrane. The inside of the cell is negative with respect to the outside of the cell. This potential difference is called the membrane potential.The membrane potential is determined by the concentration of ions on either side of the cell membrane and the permeability of the cell membrane to those ions. The concentration of ions inside the cell is usually different from the concentration of ions outside the cell. This difference in concentration creates a concentration gradient. The concentration gradient is the driving force for the movement of ions across the cell membrane.The permeability of the cell membrane to an ion is a measure of the ease with which that ion can pass through the cell membrane. The cell membrane is more permeable to some ions than others. For example, the cell membrane is more permeable to potassium ions (K+) than it is to sodium ions (Na+).The membrane potential is the result of the movement of ions across the cell membrane. Ions will move from an area of high concentration to an area of low concentration. This movement of ions creates an electrical current across the cell membrane. The magnitude of the membrane potential is determined by the balance of ionic currents across the cell membrane.

Most membranes are 40 times more permeable to K+ than to Na+

Depolarization
Explanation: The membrane potential is said to be depolarized when it moves towards the threshold potential, in this case +30 mV. This can be caused by the flow of either an excitatory or inhibitory post-synaptic potential (EPSP or IPSP) across the membrane. If the depolarization is strong enough, it will reach the threshold potential and an action potential will be generated.Hyperpolarization is the opposite of depolarization and results in the membrane potential moving further away from threshold. This can be caused by the flow of an IPSP across the membrane.

Gated
Explanation: Gated channels are membrane protein pores that can be opened and closed in response to a variety of stimuli, including changes in voltage, ligand binding, or changes in pressure. These proteins play important roles in a variety of cellular processes, including cell signaling, ion transport, and cell-cell communication.

Dendrite
Explanation: The part of the neuron that receives most of the incoming signals is the dendrite. The dendrite is a long, thin, branching structure that extends from the cell body. It is covered with a large number of small projections called dendritic spines. These spines increase the surface area of the dendrite and allow it to receive signals from a large number of other neurons.

The rising phase of an action potential
Explanation: If the axonal permeability to sodium were to suddenly increase, it would cause the rising phase of an action potential to become more pronounced. This would in turn lead to more rapid depolarization and repolarization of the axon membrane. Additionally, it would cause the action potential to propagate more rapidly down the length of the axon.

Synapse
Explanation: The region where the axon terminal meets its target cell is called the synapse. This is the point at which the electrical signal from the axon is converted into a chemical signal, which is then transmitted to the next cell.

Schwann cells and oligodendrocytes
Explanation: Myelin is a type of insulation that helps to protect nerve cells and helps to improve the speed of communication between nerve cells. Myelin is produced by a type of cell called an oligodendrocyte in the central nervous system, and by a type of cell called a Schwann cell in the peripheral nervous system.

61/z × log [ion]out / [ion]in
Explanation: The Nernst equation is used to calculate the voltage across a cell membrane. The equation is:E = E0 - (RT/zF) * log[ion]out/[ion]inwhere E0 is the standard electrode potential, RT is the gas constant, z is the charge of the ion, and F is the Faraday constant.The equation can be rearranged to solve for [ion]out/[ion]in:[ion]out/[ion]in = e-(E-E0)/(RT/zF)where e is the natural logarithm.Thus, the correctly written Nernst equation is:E = E0 - (RT/zF) * log[ion]out/[ion]in

Potassium
Explanation: The answer is more than one of the answers is correct. The reason for this is that the cell is constantly bombarded with various ions and molecules from the outside environment. In order to maintain a balance, the cell must actively transport ions and molecules across the cell membrane. This process is called active transport.Active transport requires the cell to expend energy in order to move ions and molecules against their concentration gradient. This means that the concentration of ions and molecules inside the cell is typically higher than the concentration outside the cell. The ions and molecules that are most often actively transported into the cell include calcium, chloride, potassium, and sodium.

Na+ flow into the cell only
Explanation:The answer is more than one of the answers is correct. The reason for this is that the cell is constantly bombarded with various ions and molecules from the outside environment. In order to maintain a balance, the cell must actively transport ions and molecules across the cell membrane. This process is called active transport.Active transport requires the cell to expend energy in order to move ions and molecules against their concentration gradient. This means that the concentration of ions and molecules inside the cell is typically higher than the concentration outside the cell. The ions and molecules that are most often actively transported into the cell include calcium, chloride, potassium, and sodium.

K+ flow out of the cell only
Explanation: The falling phase of the action potential is due primarily to Na+ flow out of the cell and K+ flow into the cell.

Activation gate opened at rest & Inactivation gate closed at rest
Explanation: The activation gate should be open at rest, while the inactivation gate should be closed. The activation gate should close during depolarization, while the inactivation gate should open.

the Na+ and K+ ions that moved in/out of the cell must move back to their original compartments.
Explanation: A second action potential cannot occur until the Na+ and K+ ions that moved during the first action potential have moved back to their original compartments. Additionally, the Na+ inactivation gate must open and the Na+ activation gate must close.

Requires ATP to function
Explanation: The sodium-potassium exchange pump is a protein that sits in the cell membrane and helps to regulate the concentrations of sodium and potassium ions inside and outside the cell. During repolarization, the pump transports potassium ions out of the cell and sodium ions into the cell. This helps to maintain the ion gradients across the cell membrane and prevents the cell from becoming overloaded with potassium ions. The pump requires ATP to function and must re-establish ion concentrations after each action potential.

all stimuli great enough to bring the membrane to threshold will produce action potentials of identical magnitude.
Explanation: The all-or-none principle states that all stimuli great enough to bring the membrane to threshold will produce action potentials of identical magnitude. The greater the magnitude of the stimuli, the greater the intensity of the action potential.

bind to Na+ channels and inactivate them and prevent depolarization by blocking Na+ entry into the cell.
Explanation: Some neurotoxins work essentially the same way as some local anesthetics by binding to Na+ channels and inactivating them. This prevents depolarization by blocking Na+ entry into the cell. In addition, some neurotoxins can also inactivate the enzyme that destroys the neurotransmitter, which amplifies the effect of the toxin.

Relative refractory period
Explanation: The absolute refractory period is the period of time during which an excitable membrane cannot respond to any stimulus, regardless of how great the stimulus is. The relative refractory period is the period of time during which an excitable membrane can respond again, but only if the stimulus is greater than the initial stimulus. The resting membrane potential is the potential difference between the inside and outside of a cell when the cell is not being stimulated. The excessive period is the period of time during which an excitable membrane can respond to any stimulus, regardless of how great the stimulus is.

Will start at that point and travel in both directions in the axon
Explanation: If a stimulating electrode is placed in the middle of a resting axon and an above-threshold voltage is applied to the electrode, action potentials will start at that point and travel in both directions in the axon. This is because when an action potential is generated, it will travel down the length of the axon until it reaches the axon terminal. At the same time, the action potential will also travel back up the axon toward the cell body.

Myelin and increasing the temperature
Explanation: Conduction speed is enhanced by myelin and increasing the temperature. Myelin is a lipid-rich substance that forms a sheath around certain axons. This sheath acts as an insulator, preventing the electrical impulses from leaking out. As a result, the impulses are able to travel faster along the axon. Increasing the temperature also helps to increase the conduction speed, as the electrical impulses move more quickly at higher temperatures.