The neuron will produce an action potential only if the depolarization exceeds what level?
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The membrane of a neuron is specialized to: keep all types of intercellular chemicals from moving out of the neuron. control the exchange of chemicals between the inside and outside of the cell. The membrane of a neuron is composed of ___ with ___ embedded in them. carbohydrates; purines What is the difference in voltage called that typically exists between the inside and the outside of a neuron? concentration gradient The resting potential is mainly the result of: negatively charged proteins inside the
cell negatively charged proteins inside the cell What is the approximate resting potential of the inside of a neuron's membrane, relative to the outside? -70 millivolts The selectivity of a neuron membrane is analogous to: the blood-brain barrier When the neuronal membrane is at rest, the potassium channels: permit potassium
ions to pass quickly and easily. permit potassium ions to pass slowly. When the neuronal membrane is at rest, the sodium channels: permit sodium ions to
pass quickly and easily Which of the following describes selective permeability? Ions can only travel in certain directions across the membrane. Only certain molecules are allowed to cross the membrane freely. When a neuron's membrane is at rest, the concentration gradient tends to move sodium ____ the cell and the electrical gradient tends to move it ___ the cell. into, into When a neuron's membrane is at rest, the concentration gradient tends to move potassium ___ the cell and the electrical gradient tends to move it ___ the cell. into, into The sodium-potassium pump repeatedly transports ___ sodium ions out of the cell while drawing ___ potassium ions into it. three; two Electrical gradients lead to what kind of movements? the general movement of ions into the neuron the movement of ions to areas having the opposite electrical charges What is meant by the term "concentration gradient" with respect to neurons? Sodium is more concentrated in the dendrites and potassium in the
axon. Sodium and potassium ions are more concentrated on opposite sides of the membrane. Concentration gradients lead to what kind of movements? the general movement of ions into the neuron the movement of ions to areas of their lowest concentrations The concentration gradient for potassium tends to: draw potassium into the cell. push potassium out of the cell. When the neuron is at rest, what is responsible for moving potassium ions OUT of the cell? a concentration gradient When the neuron is at rest, what is responsible for moving potassium ions into the cell? concentration gradient both the sodium-potassium pump and electrical gradient When a membrane is at rest, what attracts sodium ions to the inside of the cell? an electrical gradient both an electrical gradient and a concentration gradient When the neuron is at rest, what is responsible for moving sodium ions out of the cell? a concentration gradient the sodium-potassium pump Which of the following is an advantage of having a resting potential? The toxic effects of sodium are minimized inside the cell. The cell is prepared to respond quickly to a stimulus. Ordinarily, stimulation of a neuron takes place: through hyper polarization. What is the result if a stimulus shifts the potential inside a neuron from the resting potential to a more negative potential? Hyperpolarization What is the result if a stimulus shifts the potential inside a neuron from the resting potential to a potential slightly closer to zero? hyperpolarization The neuron will produce an action potential only if the depolarization exceeds what level? the threshold of excitation the threshold of excitation What tends to open the sodium gates across a neuron's membrane? hyperpolarization of the
membrane depolarization of the membrane Stimulus A depolarizes a neuron just barely above the threshold. Stimulus B depolarizes a neuron to 10 mV beyond threshold. What can we expect to happen? Stimulus B will produce an action potential that is conducted at a faster speed than A. Stimulus A and stimulus B will produce the same response in the neurons. Which of the following actions would depolarize a neuron? decreasing membrane permeability to calcium increasing membrane permeability to sodium The action potential of a neuron depends mostly on what movement of ions? sodium ions entering the cell sodium ions entering the cell In the normal course of an action potential: sodium channel remain open for long periods of time sodium remains much more concentrated outside than inside the neuron When the potential across a membrane reaches threshold, the sodium channels: open to let the sodium enter the cell rapidly open to let the sodium enter the cell rapidly During the entire course of events from the start of an action potential until the membrane returns to its resting potential, what is the net movement of ions? sodium in, potassium in A drug that blocks the sodium gates of a neuron's membrane would: decrease the threshold block the action potential After the peak of an action potential, what prevents sodium ions from continuing to enter the cell? There is no longer a concentration gradient for sodium The sodium gates in the membrane close Just after the peak of the action potential, what movement of ions restores the membrane to approximately the resting potential? Sodium ions enter the cell Potassium ions leave the cell A drug that decreases the flow of potassium through the potassium gates of the membrane would: block action potentials slow the return of the membrane to its resting potential Local anesthetic drugs attach to the sodium channels of the membrane, which: allows sodium ions to
enter and stop action potential prevent sodium ions from entering and stopping action potential Which of the following represents the all-or-none law? Every depolarization produces an action potential The size of the action potential is independent of the strength of the stimulus that initiated it The presence of an all-or-none law suggests that neurons can only convey different messages by changing their: rate or pattern of action potentials rate or pattern of action potentials The primary feature of a neuron that prevents the action potential from traveling back from where it just passed is the: concentration gradient Which feature of a neuron limits the number of action potentials it can produce per second? the threshold A neuron's sodium gates are firmly closed and the membrane cannot produce an action potential during: the absolute refractory period the absolute refractory period Where do most action potentials begin? in the dendrites What happens once an action potential starts? It is conducted the rest of the way as an electrical current. It is regenerated at other point along the axon. The presence of myelin and the diameter of the axon: affect the strength and frequency of the stimulus affect the speed of an action potential In a myelinated axon, where are sodium gates abundant? in the areas covered my myelin To what does saltatory conduction refer? the production of an action potential by the movement of sodium
ions the transmission of an impulse along a myelinated axon What disease is related to the destruction of myelin sheaths? multiple sclerosis In what way is a myelinated axon that has lost its myelin (through disease) different from an axon that was never myelinated? It has a smaller diameter. It lacks sodium gates along parts of its surface. A local neuron: has an axon approximately a meter long is a small neuron with no axon or a very short one What is the maximum voltage of depolarization during action potential?Action potentials are triggered when an initial depolarization reaches threshold. This threshold potential varies, but generally is about 15 millivolts above the cell's resting membrane potential, occurring when the inward sodium current exceeds the outward potassium current.
What are the three levels of depolarization?The action potential has three main stages: depolarization, repolarization, and hyperpolarization. Depolarization is caused when positively charged sodium ions rush into a neuron with the opening of voltage-gated sodium channels.
Which action would depolarize a neuron?When at rest, the neuron initially has a negative membrane potential. At the beginning of an action potential, voltage-gated sodium channels open, allowing sodium ions to enter the cell. This causes the cell to become positively charged compared to the outside of the cell. This process is called depolarization.
What occurs when depolarization is less than the cells threshold?If the resting potential decreases to less than the threshold potential, depolarization results, repolarization cannot occur, and the cell is no longer excitable.
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