MCAT Biology : Systems Biology and Tissue Types
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Example Question #81 : Systems Biology And Tissue Types
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
A scientist is studying the nerve cell depicted in the above figure. He notices that proteins like 1, 2, and 3 are only located a certain regions along the length of the axon. What are these regions most likely to be called?
Nissl bodies
Synaptic clefts
Dendrites
Nodes of Ranvier
Axon hillocks
Nodes of Ranvier
The proteins responsible for allowing ionic flow into and out of axons are most likely to be found at Nodes of Ranvier, where there is no myelin and ions can move freely. Action potentials travel via saltatory conduction, meaning that the ion channels are only stimulated a certain points on the membrane. The majority of the impulse is conducted through the interior of the axon without further external stimulation.
Example Question #82 : Systems Biology And Tissue Types
In saltatory conduction displayed by neurons containing myelinated axons, ion flow takes place at which region of the axon?
Ion flow does not take place during saltatory conduction
Schwann cells
Myelinated portion of the axon
Nodes of Ranvier
Nodes of Ranvier
Saltatory conduction is defined as the method by which action potentials are propagated along axons in myelinated neurons. The method by which they do this is by the generation of action potentials at each node of Ranvier. The only places along the myelinated axon that display ion flow are the nodes of Ranvier. The myelinated portions do not display ion flow, allowing the electrical stimulus to rapidly jump down the axon from one node to the next rather than slowly flow down the full axon length.
Schwann cells are types of cell that make up the myelin coated sheath for select neurons.
Example Question #81 : Systems Biology And Tissue Types
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
A scientist shows that the protein labeled "1" has a voltage gate, as well as an inactivation gate, while proteins 2 and 3 lack this dual gate architecture. What ion is most likely to be controlled by protein 1?
Chloride
Calcium
Sodium
Potassium
Magnesium
Sodium
Sodium channels have an inactivation gate, as well as a voltage gate. This allows the sodium channels to be turned off, even while voltage changes persist, thereby facilitating repolarization. This dual gate structure also causes the refractory period.
Example Question #81 : Systems Biology And Tissue Types
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
The protein labeled "2" in the diagram facilitates repolarization following the peak of an action potential. What ion is most likely to be controlled by this protein channel?
Sodium
Magnesium
Calcium
Chloride
Potassium
Potassium
Potassium is the major species that repolarizes a neuron following depolarization. After sodium has entered the cell to create depolarization, repolarization is driven by potassium ion efflux.
Example Question #97 : Biology
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
Before any of the voltage-sensitive channels in a neuron open in response to adjacent depolarization, what is true of the the resting membrane potential?
It is closest to the sodium equilibrium potential, because of the presence of potassium leak channels.
It is closest to the sodium equilibrium potential, because of the presence of sodium leak channels.
It is closest to the potassium equilibrium potential, because of the presence of sodium leak channels.
It is closest to the potassium equillibrium potential, because of the presence of potassium leak channels.
It is exactly midway between the sodium and potassium equilibrium potentials.
It is closest to the potassium equillibrium potential, because of the presence of potassium leak channels.
The presence of potassium leak channels in the membrane allows potassium to drive the resting cell membrane potential nearer to its equilibrium potential than to sodium's.
The equilibrium potential is the electric potential that would exaclty balance the competing forces of concentration and electrical gradients. High potassium concentration in the cytosol drives potassium out of leak channels in the membrane, toward the extracellular space, but the inside develops a negative charge as a result. When this negative charge pulling positive potassium ions back in is enough to exactly cancel the concentration forces pushing potassium out, the equilibrium potential has been reached.
Example Question #91 : Biology
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
The protein labeled "3" is an active transport pump that restores the normal balance of sodium and potassium every time an action potential travels through the region of the axon. What is this pump most likely to transport?
Three sodium out of the cell and two potassium into the cell
Two sodium out of the cell and two potassium into the cell
Three sodium into the cell and two potassium out of the cell
Two sodium into the cell and three potassium out of the cell
Two sodium out of the cell and three potassium into the cell
Three sodium out of the cell and two potassium into the cell
The sodium-potassium pump, or Na/K ATPase, is what restores ionic concentrations back to normal after an action potential. This pump is electrogenic, and active, using ATP to pump three sodium out of the cell, and two potassium into the cell. Along wtih the potassium leak channels, this keeps the potassium concentration in a cell high, and sodium concentration low.
Example Question #11 : Action Potentials And Synapse Biology
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
The refractory period is the period of time after action potential that a neuron is unable to "refire" if another stimulus is present.
If protein 1 is a voltage-gated sodium channel, protein 2 is a voltage-gated potassium channel, and protein 3 is a leak channel, which channel contributes most to the absolute refractory period?
Protein 1, due to its inactivation gate
Potassium channel, because its lacks an activation gate
Protein 3, due to its lack of an inactivation gate
Protein 2, due to its activation gate
Leak channel, due to its inactivation gate
Protein 1, due to its inactivation gate
The sodium channel being inactivated, via its inactivation gate, prevents a stimulus from initiating an action potential immediately after a previous stimulus.
During the absolute refractory period, this is a fact regardless of how strong the stimulus is. During the relative refractory period the neuron can be stimulated, but only by a very large stimulus.
Example Question #100 : Biology
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
The cell body associated with the axon in Figure 1 is actively taking in electrical inputs from neighboring cells. Which of the following properties is the major difference between post-synaptic potentials from neighboring neurons and pre-synaptic action potentials?
Post-synaptic potentials are driven by calcium depolarization; action potentials are driven by sodium depolorization
Post-synaptic potentials are "all-or-nothing;" action potentials are graded
Post-synaptic potentials are always excitatory; action potentials are always inhibitory
Post-synaptic potentials are graded; action potentials are "all-or-nothing"
Post-synaptic potentials are always inhibitory; action potentials are always excitatory
Post-synaptic potentials are graded; action potentials are "all-or-nothing"
Post-synaptic potentials are graded, while action potentials are "all-or-nothing". This means that the farther from the point of integration in a nerve cell an electrical input enters, the weaker its corresponding post-synaptic potential will be when it reaches the distant integration site.
In this way, post-synaptic potentials can be summed as a function of intensity and distance, while action potentials are always the same amplitude no matter from how far they travel.
Example Question #101 : Biology
The heart contains autorhythmic cells, which can generate an action potential on their own. These cells then spread the action potential throughout the heart, resulting in a contraction. Which of the following mechanisms is an explanation for why these cells can spontaneously generate action potentials?
These cells have no resting potential
Specialized channels allow sodium to enter the cell, which leads to depolarization
Specialized channels allow sodium to exit the cell, which leads to depolarization
These cells do not have sodium-potassium pumps, which allows for quicker depolarization
Specialized channels allow sodium to enter the cell, which leads to depolarization
Remember that an action potential starts with the diffusion of sodium into the cell. As more sodium enters the cell, more voltage gated sodium channels open up. This leads to depolarization of the cell. With a steady diffusion of sodium into the cell, the threshold stimulus will eventually be attained, and an action potential will be generated. It is the steady diffusion of sodium into the autorhythmic cells which results in an action potential.
Example Question #122 : Mcat Biological Sciences
In humans, nerve impulses are transmitted with the coordinated action of sodium and potassium ion channels. These channels open in a specific sequence, to allow for membrane potential changes to take place in a directional manner along the length of an axon.
Figure 1 depicts a single phospholipid layer of a cell membrane, and three transmembrane channels important to action potential propagation.
A dendrite carries an electrical signal to the nerve cell body associated with the axon in Figure 1. If this signal is inhibitory (an inhibitory post synaptic potential), which of the following is likely true of the impact of this signal on the cell?
It will hyperpolarize the cell, and make it less difficult to fire
It will hyperpolarize the cell, and make it more difficult to fire
It will depolarize the cell, and make it less difficult to fire
It will depolarize the cell, and make it more difficult to fire
It will not change the cell membrane potential, but will make it more difficult to fire
It will hyperpolarize the cell, and make it more difficult to fire
An inhibitory post synaptic potential (IPSP) drives the post synaptic cell membrane toward hyperpolarization, and thus away from the threshold necessary to fire an action potential. As a result, the axon requires more stimuli in order to fire an action potential.
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