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A neuron’s nucleus is located in its _____. |
a. cell body |
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A nerve impulse moves toward a neuron’s cell body along ________. |
a. dendrites Dendrites conduct an impulse from a synapse toward the cell body |
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A nerve impulse moves away from a neuron’s cell body along ________. |
d. axon Axons conduct a nerve impulse away from the cell body |
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An impulse relayed along to myelinated axon "jumps" from ______ to _______. |
c. node of Ranvier / node of Ranvier In myelinated neurons the impulse jumps from node to node. |
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Axons insulated by a(n) ______ are able to conduct ipulses faster than those not so insulated. |
c. myelin sheath Myelin sheaths, formed when Schwann cells wrap around an axon, allow such neurons to conduct impulses more rapidly than unmyelinated axons. |
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What type of cell makes up the myelin sheath of a motor neuron? |
e. Schwann cells Myelin sheaths are formed when Schwann cells wrap around the axons of motor neurons |
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What part of a neuron relays signals from one neuron to another neuron or to an effector? |
c. synaptic terminal Synaptic terminals contain neurotransmitter molecules that relay the nerve impulse across a synapse |
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How neurons work |
Each neuron receives input from one or more cells. In response, the neuron may generate an electrical signal known as an action potential that travels down the length of the axon. |
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Resting Potential description |
Even without an action potential, the axon is a busy place, with many ions moving across its membrane. Much of this ion movement is driven by the sodium-potassium pump. Using energy from ATP, sodium potassium pumps actively transport sodium ions out of the cell and potassium ions in creating an uneven distribution of charge across the membrane. Some potassium channels are open all the time, allowing potassium ions to leave the cell. As a result of these ion movements, the inside of the cell is negative relative to the outside. This condition is called the resting potential |
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Action Potential description |
The membrane of an axon is also packed with gated ion channels that open and close during an action potential. At resting potential, the gated channels are closed. If a stimulus changes the distribution of charge across the membrane sufficiently, the gated sodium channels open. Movement of sodium ions across the membrane makes the inside of the cell more positive. This reversal of the charge distribution causes the gated sodium channels to close and the gated potassium channels to open. As potassium ions move out of the cell, the original charge difference is re-established across the membrane, closing the gated potassium channels. This sequence of events is called the action potential. The sodium-potassium pump restores the distribution of ions back to their levels at resting potential. |
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Conduction of an Action Potential description |
As the change in charge difference across the membrane spreads from open sodium channels, other sodium channels farther along the axon begin to open. The original sodium channels close and adjacent potassium channels open. As potassium ions move out of the cell, the original charge difference across the membrane is restored and then the potassium channels close. Meanwhile, new sodium channels open, followed by the opening of new potassium channels and the closing of sodium channels. In this manner, the action potential is propagated along the axon of the neuron, eventually reaching another cell. The information carried by this action potential will be processed with other information. |
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Which term describe the difference in electrical charge across a membrane? |
a. membrane potential |
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Resting neurons are most permeable to which of the following ions? |
a. K+ |
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True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane. |
False The potential energy of a membrane potential comes from the difference in electrical charge and from the concentration gradient of ions across a membrane |
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Which channel is mainly responsible for the resting potential of a neuron? |
d. Potassium leak channel K+ ions flow along their concentration gradient to maintain the resting potential of a neuron |
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Which term describes an electrical signal generated by neurons? |
d. action potential |
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Which channel maintains the concentration gradients of ions across a neuronal membrane? |
a. the sodium-potassium pump moving Na+ ions out and K+ ions in |
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What behavior is observed if the voltage across a neuronal membrane is set to -20mV? |
d. the sodium channel opens, and NA+ ions flow in |
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A neuron has a resting potential of about _____ mV. |
d. -70 |
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An action potential moves along a(n) ______. |
b. axon |
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At rest, which of these plays a role in establishing the charge differential across a neuron’s plasma membrane? |
d. the sodium-potassium pump moving the sodium ions out of the neuron and potassium ions into the neuron The net loss of positive ions establishes a charge differential across the plasma membrane. |
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The transmission first triggers the _________. |
b. opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron This is the first of the events listed here. As a result of the inward flux of sodium ions, that region of the neuron depolarizes. |
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A stimulus has opened the voltage-gated sodium channel in an area of a neuron’s plasma membrane. As a result, _______ rushes into the neuron and diffuses to adjacent areas; this in turn results in the ________ in the adjacent areas. |
c. sodium / opening of voltage-gated sodium channels |
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The synapse description |
Signals are passed from a sending neuron to a receiving neuron at a junction called a synapse. An action potential in the sending neuron travels down the axon until it reaches a synaptic terminal. The narrow gap between the synaptic terminal and the receiving neuron is called the synaptic cleft. |
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Neurotransmitters descrition |
The synaptic terminal of a sending neuron contains numerous vesicles filled with neurotransmitters, chemicals that carry information across the synaptic cleft. When an action potential reaches the synaptic terminals, the vesicles fuse with the plasma membrane of the sending neuron, releasing neurotransmitters into the synaptic cleft. The neurotransmitters affect the receiving neuron, changing the distribution of charge across its membrane. An action potential is propagated down an axon by the opening and closing of sodium and potassium channels. When an action potential arrives at the synaptic terminal, it causes the opening of calcium channels. Calcium ions enter the synaptic terminal through the calcium channels. Calcium ions bind to the vesicles containing neurotransmitters. This causes the vesicles to fuse with the plasma membrane of the sending neuron, releasing neurotransmitters into the synaptic cleft. The neurotransmitters diffuse across the synaptic cleft and bind to receptors in the plasma membrane of the receiving neuron. Neurotransmitters are quickly removed from the synaptic cleft, ending their effect on the receiving neuron |
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Effect of Multiple Synapses description |
A single neuron can receive signals from many sending neurons. Two sets of signals – excitatory and inhibitory cancel each other out and no action potential is generated. |
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Which structure is not part of a neuron? |
c. myelin sheath Myelin sheath is just a layer of Schwann cells wrapped around a neuron |
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Which of the following statements about action potential in a given neuron is false? |
d. they are propagated down the length of the denrite |
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True or false? Action potentials travel in only one direction down an axon because potassium channel in the neuron are refractory and cannot be activated for a shirt time after they open and close. |
False Action potentials travel in only one direction down an axon because sodium channels in the neuron are refractory |
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Which event triggers the creation of an action potential? |
d. the membrane depolarizes above the certain threshold potential |
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Which of the following terms describes how a neuronal membrane’s potential is altered in the presence of inhibitory signals? |
b. hyperpolarization Inhibitory signals hyperpolarize the membrane and make the membrane potential even more negative than normal. |
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Where is the neuron do action potentials begin? |
a. axon hillock |
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How is an action potential propagated down an axon after voltage-gated sodium channels open in a region of the neuron’s membrane? |
d. sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon |
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What are neurotransmitter receptors located? |
d. the postsynaptic membrane |
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Why are action potentials usually conducted in one direction? |
c. the brief refractory period reopening of voltage-gated Na+ channels |
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Temporal summation always involves ________. |
a. multiple inputs at a single synapse |
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Why is an action potential an all-or-none response to stimuli? |
a. because voltage-gated ion channels open when membrane potential passes a particular level |
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The plasma membrane of a neuron has voltage-gated sodium and potassium channels. What is the effect of membrane depolarization on these channels? |
a. membrane depolarization first opens sodium channels and then opens potassium channels |
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What happens when a resting neuron’s membrane depolarizes? |
b. the neuron’s membrane voltage becomes more positive |
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What causes the falling phase of the action potential? |
b. inactivation of voltage-gated sodium channels and the opening of voltage-gated potassium channels |
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Of these choices, neuronal communication between the brain and the muscles of the leg is best conceptualized as ________. |
a. electrical and chemical signaling |
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Identify the correct statement(s) about the resting membrane potential of a cell. |
a. potassium and sodium gradients are maintained by active transport in a resting mammalian neuron c. concentration gradients of potassium and sodium across the plasma membrane represent potential energy |
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If the membrane potential of a neuron decreases, the membrane potential _____. |
b. becomes less negative |
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