Chapter 12.3 and 12.4 Flashcards
Graded potentials occur when a neurotransmitter is released into the synapse between two neurons and binds a ligand-gated ion channels.
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Graded potentials occur when a neurotransmitter is released into the synapse and binds to ligand-gated ion channels on the postsynaptic neuron. This binding causes the ion channels to open, leading to a localized change in membrane potential, which is known as a graded potential.
Graded potentials may occur on a neuron cell body, dendrites or axons.
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Graded potentials primarily occur on the dendrites and cell body of a neuron, not on the axons. Axons are typically associated with action potentials.
Action potentials occur only in axons of neurons and in muscle fibers.
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Action potentials typically occur in the axons of neurons and in muscle fibers. In neurons, action potentials propagate along the axon to transmit signals over long distances, while in muscle fibers, they lead to muscle contraction.
For an action potential to be generated, depolarizations must reach threshold.
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For an action potential to be generated, the depolarization of the neuron’s membrane must reach a certain threshold level. If this threshold is not reached, an action potential will not occur.
The unidirectional flow of an action potential is due to the delay in K+ channels closing until they are “reset” by hyperpolarization.
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The unidirectional flow of an action potential is primarily due to the refractory period, which consists of the absolute and relative refractory periods. During the absolute refractory period, Na+ channels are inactivated and cannot reopen immediately, preventing the action potential from traveling backward. Hyperpolarization, caused by K+ channels remaining open longer, contributes to the relative refractory period but is not the main reason for the unidirectional flow.
Which of the following statements about graded potentials is not true?
A) Graded potentials can occur in a variety of intensities unlike action potential which are of one size only.
B) Graded potentials are short, localized impulses.
C) Graded potentials always initiate action potentials.
D) Graded potentials can occur in the neuron soma (cell body) or in dendrites.
C) Graded potentials always initiate action potentials.
This statement is not true. Graded potentials do not always initiate action potentials; they only do so if they are strong enough to reach the threshold at the axon hillock. If the threshold is not reached, an action potential will not be generated.
Which of the following statements about action potentials is false?
A) Action potentials (A.P.’s) are initiated by local changes in membrane current (graded potential) and the associated influx of ions through voltage gated Na+ channels.
B) During an A.P. repolarization is due to the closing of Na+ channels and opening of K+ channels, causing the cytoplasmic side of the membrane to become more negative once again.
C) A.P.’s are self-sustaining - once begun they will continue all along the length of an axon.
D) The absolute refractory period is key in the one-way transmission of A.P.’s down the axon.
E) All are true statements
E) All are true statements
Put the events of the generation of an action potential in the correct order:
A)
1. An A.P. arrives at the pre-synaptic neuron terminal
2. Neurotransmitters are released and diffuse across the synaptic cleft to the post-synaptic terminal
3. Na+ influx causes a localized membrane depolarization (graded potential)
4. Neurotransmitters bind to receptors and open ion channels
5. If the depolarization is strong enough, voltage gated Na+ channels in the axon hillock open
6. An action potential is generated and moves down the neuron
B)
1. An A.P. arrives at the pre-synaptic neuron terminal
2. Neurotransmitters bind to receptors and open ion channels
3. If the depolarization is strong enough, voltage gated Na+ channels in the axon hillock open
4. Na+ influx causes a localized membrane depolarization (graded potential)
5. Neurotransmitters are released and diffuse across the synaptic cleft to the post-synaptic terminal
6. An action potential is generated and moves down the neuron
C)
1. An A.P. arrives at the pre-synaptic neuron terminal
2. Neurotransmitters are released and diffuse across the synaptic cleft to the post-synaptic terminal
3. Neurotransmitters bind to receptors and open ion channels
4. Na+ influx causes a localized membrane depolarization (graded potential)
5. If the depolarization is strong enough, voltage gated Na+ channels in the axon hillock open
6. An action potential is generated and moves down the neuron
C)
1. An A.P. arrives at the pre-synaptic neuron terminal
2. Neurotransmitters are released and diffuse across the synaptic cleft to the post-synaptic terminal
3. Neurotransmitters bind to receptors and open ion channels
4. Na+ influx causes a localized membrane depolarization (graded potential)
5. If the depolarization is strong enough, voltage gated Na+ channels in the axon hillock open
6. An action potential is generated and moves down the neuron
An action potential will travel fastest along which type of axon?
A) A non-myelinated axon
B) A myelinated axon
B) A myelinated axon
Action potentials travel fastest along myelinated axons due to the process of saltatory conduction, where the action potential jumps from one Node of Ranvier to the next, increasing the speed of transmission.
Most synapses are electrical synapses.
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Most synapses are chemical synapses, where neurotransmitters are released to transmit signals between neurons. Electrical synapses are less common and involve direct electrical connections between neurons through gap junctions.
The arrival of a neurotransmitter at the post-synaptic neuron cell membrane causes an excitatory or inhibitory event (a graded potential).
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The arrival of a neurotransmitter at the post-synaptic neuron cell membrane can cause either an excitatory or inhibitory event, which results in a graded potential.
Action potentials are initiated by IPSPs (inhibitory postsynaptic potentials) and inhibited by EPSPs (excitatory postsynaptic potentials)
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Action potentials are initiated by excitatory postsynaptic potentials (EPSPs) and inhibited by inhibitory postsynaptic potentials (IPSPs). EPSPs depolarize the membrane and bring it closer to the threshold for firing an action potential, while IPSPs hyperpolarize the membrane, making it less likely to reach the threshold.
The brain’s main inhibitory neurotransmitter is GABA (gamma-aminobutyric acid).
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The brain’s main inhibitory neurotransmitter is gamma-aminobutyric acid (GABA).
Neurotransmitters can have both excitatory and inhibitory effects.
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Neurotransmitters can have both excitatory and inhibitory effects, depending on the type of receptors they bind to on the post-synaptic neuron and the context within the nervous system.
Which of the following statements about excitatory post-synaptic potentials (EPSP) is not true?
A) An EPSP is a local depolarization of the post-synaptic membrane caused by the flow of positively charged ions into the cell.
B) An EPSP makes the neuron more likely to initiate an action potential.
C) An EPSP causes primarily Na+ to move into the cell.
D) Neurons may receive many EPSPs at the same time.
E) All are true statements
E) All are true statements
Which of the following statements about inhibitory post-synaptic potentials (IPSP) is not true?
A) An IPSP is a local hyperpolarization of the post-synaptic membrane caused by the flow of positively charged ions out of the cell or negatively charged ions into the cell.
B) An IPSP makes the neuron less likely to initiate an action potential.
C) An IPSP causes primarily Ca++ to move into the cell.
D) Neurons may receive many IPSPs at the same time.
E) All are true statements
C) An IPSP causes primarily Ca++ to move into the cell.
This statement is not true. An IPSP typically involves the movement of K+ ions out of the cell or Cl- ions into the cell, leading to hyperpolarization of the post-synaptic membrane, not the movement of Ca++ ions into the cell.
If a neuron is stimulated simultaneously by many axon terminals at the same time, this would be an example of _______ summation.
A) Spatial
B) Temporal
A) Spatial
When a neuron is stimulated simultaneously by many axon terminals at different locations on its dendrites or cell body, this is an example of spatial summation.
Which of the following statements about neurotransmitters is false?
A) Some neurotransmitters can be either excitatory or inhibitory depending upon the receptor.
B) Acetylcholine is an excitatory neurotransmitter secreted by motor neurons innervating skeletal muscle.
C) Endorphins are a class of primarily inhibitory neurotransmitters that act as natural pain killers.
D) Most neurons produce only one type of neurotransmitter.
E) Direct acting neurotransmitters bind to and open ion channels.
D) Most neurons produce only one type of neurotransmitter.
This statement is false. Many neurons can produce and release more than one type of neurotransmitter.
Graded potentials vary in magnitude depending on the strength of the stimulus.
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Explanation: Graded potentials are not all-or-none responses like action potentials; their magnitude varies based on the strength and duration of the stimulus.
Which type of ion channel is primarily involved in generating an action potential?
A) Ligand-gated ion channels
B) Voltage-gated ion channels
C) Mechanically-gated ion channels
D) Leak channels
B) Voltage-gated ion channels
Explanation: Voltage-gated ion channels are crucial for the initiation and propagation of action potentials.
Hyperpolarization of the neuronal membrane is due to the opening of which type of channels?
A) Na+ channels
B) Ca2+ channels
C) K+ channels
D) Cl- channels
C) K+ channels and D) Cl- channels
Explanation: Hyperpolarization occurs due to the efflux of K+ ions or the influx of Cl- ions, making the inside of the membrane more negative.
The refractory period in neurons ensures that:
A) Action potentials can travel in both directions
B) Action potentials are unidirectional
C) Graded potentials can summate
D) Neurotransmitter release is inhibited
B) Action potentials are unidirectional
Explanation: The refractory period prevents the action potential from traveling backward, ensuring unidirectional flow.
Which of the following statements about synaptic transmission is true?
A) Electrical synapses use neurotransmitters to transmit signals.
B) Chemical synapses involve direct flow of ions between neurons.
C) Electrical synapses allow faster transmission compared to chemical synapses.
D) Chemical synapses do not require neurotransmitter receptors.
C) Electrical synapses allow faster transmission compared to chemical synapses.
Explanation: Electrical synapses provide rapid communication through direct electrical connections, whereas chemical synapses rely on neurotransmitter release and receptor binding.
What type of glial cell is responsible for myelinating axons in the central nervous system?
A) Schwann cells
B) Astrocytes
C) Microglia
D) Oligodendrocytes
D) Oligodendrocytes
Explanation: Oligodendrocytes are the glial cells that form myelin sheaths around axons in the central nervous system.
In a neuron, the region where an action potential is initiated is called the:
A) Dendrite
B) Soma
C) Axon hillock
D) Synaptic terminal
C) Axon hillock
Explanation: The axon hillock is the region where graded potentials summate to initiate an action potential if the threshold is reached.
Which neurotransmitter is primarily associated with the ‘fight or flight’ response?
A) Dopamine
B) Serotonin
C) Acetylcholine
D) Norepinephrine
D) Norepinephrine
Explanation: Norepinephrine is involved in the ‘fight or flight’ response, increasing alertness and energy levels.
Temporal summation occurs when:
A) Multiple neurons release neurotransmitters simultaneously
B) A single neuron releases neurotransmitters in rapid succession
C) Action potentials decrease in amplitude over time
D) Neurotransmitter reuptake is inhibited
B) A single neuron releases neurotransmitters in rapid succession
Explanation: Temporal summation is the additive effect of multiple excitatory signals from a single neuron over a short period of time.
Which structure in a neuron is responsible for receiving incoming signals?
A) Axon
B) Soma
C) Dendrites
D) Synaptic terminal
C) Dendrites
Explanation: Dendrites are the branched projections of a neuron that receive signals from other neurons and convey them to the soma.
What is the main function of the Na+/K+ pump in neurons?
A) To generate action potentials
B) To maintain the resting membrane potential
C) To release neurotransmitters
D) To facilitate synaptic transmission
B) To maintain the resting membrane potential
Explanation: The Na+/K+ pump helps maintain the resting membrane potential by actively transporting Na+ out of the cell and K+ into the cell.
The period during which a neuron cannot initiate another action potential, no matter how strong the stimulus, is called the:
A) Absolute refractory period
B) Relative refractory period
C) Resting period
D) Depolarization period
A) Absolute refractory period
Explanation: During the absolute refractory period, Na+ channels are inactivated, preventing the initiation of another action potential.
Which of the following ions is primarily responsible for the depolarization phase of an action potential?
A) K+
B) Na+
C) Cl-
D) Ca2+
B) Na+
Explanation: The influx of Na+ ions through voltage-gated Na+ channels is responsible for the depolarization phase of an action potential.
Inhibitory post-synaptic potentials (IPSPs) are typically associated with the influx of which ion?
A) Na+
B) K+
C) Cl-
D) Ca2+
C) Cl-
Explanation: IPSPs often involve the influx of Cl- ions, which hyperpolarize the post-synaptic membrane and make it less likely to generate an action potential.
Which neurotransmitter is involved in both learning and memory and is found in the central and peripheral nervous systems?
A) Dopamine
B) Glutamate
C) GABA
D) Acetylcholine
D) Acetylcholine
Explanation: Acetylcholine plays a crucial role in learning and memory and is involved in neuromuscular junctions in the peripheral nervous system.
What is the main excitatory neurotransmitter in the central nervous system?
A) GABA
B) Glutamate
C) Serotonin
D) Dopamine
B) Glutamate
Explanation: Glutamate is the main excitatory neurotransmitter in the central nervous system, involved in cognitive functions such as learning and memory.
The release of neurotransmitters into the synaptic cleft is triggered by the influx of which ion?
A) Na+
B) K+
C) Cl-
D) Ca2+
D) Ca2+
Explanation: The influx of Ca2+ ions into the synaptic terminal triggers the release of neurotransmitters into the synaptic cleft.
Which part of the neuron contains the nucleus and is responsible for the metabolic activities of the cell?
A) Axon
B) Soma
C) Dendrites
D) Synaptic terminal
B) Soma
Explanation: The soma, or cell body, contains the nucleus and is responsible for the neuron’s metabolic activities and maintenance.
The process by which neurotransmitters are cleared from the synaptic cleft includes all of the following except:
A) Reuptake into the presynaptic neuron
B) Enzymatic degradation
C) Diffusion away from the synaptic cleft
D) Conversion into ions
D) Conversion into ions
Explanation: Neurotransmitters are cleared from the synaptic cleft by reuptake, enzymatic degradation, or diffusion, but not by conversion into ions.
