Question 1

How could you increase the magnitude of inhibitory postsynaptic potentials (IPSPs) generated at a synapse?

Accepted Answer

Increasing the K+ permeability would hyperpolarize the postsynaptic membrane, making it more difficult for that neuron to depolarize and fire an action potential. This is the mechanism by which IPSPs work, so increasing their magnitude would involve making it harder for the neuron to depolarize.

Answer A is incorrect because increasing Na+/K+ pump activity would not directly affect the postsynaptic membrane potential. Answer C is incorrect because increasing the influx of calcium would generally cause excitation, not inhibition. Answer D is incorrect because while the Na+/K+ pump and calcium influx can both indirectly affect postsynaptic potential, they do not directly influence the size of IPSPs.

Question 2

Which of the following manipulations would reduce the release of neurotransmitter from a presynaptic neuron terminal?
I. reduction in extracellular calcium ion concentration at the axon terminal
II. increase in extracellular sodium ion concentrations at the axon terminal
III. addition of tetrodotoxin to the extracellular fluid at the axon terminal

Accepted Answer

I. A reduction in extracellular calcium ion concentration at the axon terminal would lead to a decrease in the amount of calcium entering the neuron upon depolarization. Since calcium influx is crucial for the vesicles containing neurotransmitters to fuse with the presynaptic membrane and release their contents into the synaptic cleft, a decrease in calcium levels would reduce neurotransmitter release. II. An increase in extracellular sodium ion concentrations would not directly reduce neurotransmitter release; it might actually enhance depolarization of the neuron. III. Tetrodotoxin blocks sodium channels, preventing action potentials from occurring, which indirectly affects neurotransmitter release by inhibiting the initial depolarization needed for calcium influx, but this option is not included in the correct answer choice.

Question 3

Neurotransmitters can affect postsynaptic cells by ________.
I. initiating signal transduction pathways in the cells
II. causing molecular changes in the cells
III. affecting ion-channel proteins
IV. altering the permeability of the cells

Accepted Answer

Neurotransmitters can affect postsynaptic cells by initiating signal transduction pathways, causing molecular changes, affecting ion-channel proteins, and altering the permeability of the cells. All the options provided in the question are correct regarding the effects of neurotransmitters on postsynaptic cells.

Question 4

An example of ligand-gated ion channels is ________.

Accepted Answer

Acetylcholine receptors at the neuromuscular junction are an example of ligand-gated ion channels. When acetylcholine binds to these receptors, they open up and allow ions to flow through, triggering muscle contraction. The other answer choices do not involve ligand-gated ion channels.

Question 5

Which neurotransmitter excites muscle cells?

Accepted Answer

Acetylcholine is the neurotransmitter that stimulates muscle cells, causing them to contract. This process is known as excitation-contraction coupling. Epinephrine and endorphins can affect muscle function indirectly, but they do not directly excite muscle cells. Nitric oxide and GABA have inhibitory effects on muscle cells.

Question 6

Neurotransmitters categorized as inhibitory are expected to ________.

Accepted Answer

Inhibitory neurotransmitters typically function by hyperpolarizing the membrane, making the neuron less likely to fire an action potential. This is often achieved through mechanisms such as opening chloride channels or closing sodium channels, leading to an increase in the negative charge inside the cell.

Question 7

An important excitatory neurotransmitter in the central nervous system (CNS) is ________.

Accepted Answer

Glutamate is the most abundant excitatory neurotransmitter in the CNS, playing key roles in synaptic plasticity and memory formation. A, B, D, and E are all neurotransmitters but not primarily excitatory in nature.

Question 8

Receptors for neurotransmitters are of primary functional importance in assuring one-way synaptic transmission because they are mostly found on the ________.

Accepted Answer

Receptors for neurotransmitters are typically found on the postsynaptic membrane, which is the membrane of the target neuron that receives the signal transmitted from the presynaptic neuron. This ensures that the signal is transmitted in only one direction, from the presynaptic neuron to the postsynaptic neuron.

Question 9

What happens if the correct ligand binds to ligand-gated sodium channel in a post-synaptic neuron?

Accepted Answer

When the correct ligand binds to a ligand-gated sodium channel in a post-synaptic neuron, an excitatory post-synaptic potential (EPSP) occurs. This means that the membrane potential of the neuron becomes more positive, bringing the neuron closer to reaching its threshold for firing an action potential.

Question 10

In a synapse, what initiates the release of neurotransmitter?

Accepted Answer

The release of neurotransmitter is initiated when an action potential depolarizes the presynaptic membrane. This depolarization opens voltage-gated calcium channels, which allows calcium ions to enter the axon terminal and trigger the release of neurotransmitter into the synapse.

Question 11

Excitatory postsynaptic potentials (EPSPs) produced nearly simultaneously by different synapses on the same postsynaptic neuron can also add together, creating ________.

Accepted Answer

When EPSPs produced by different synapses on the same postsynaptic neuron add together, it creates a summation, which can lead to the initiation of an action potential if the threshold is reached. Interference, refractory state, and only action potentials are not accurate descriptions of this phenomenon.

Question 12

Muscle cells are stimulated by neurotransmitters released from the synaptic terminals of ________.

Accepted Answer

Muscle cells are stimulated by neurotransmitters released from the synaptic terminals of motor neuron axons. These neurotransmitters, such as acetylcholine, bind to receptors on the surface of the muscle cell membrane, triggering a series of cellular events that ultimately result in muscle contraction.

Question 13

Functionally, which cellular location is the neuron's "decision-making site" as to whether or not an action potential will be initiated?

Accepted Answer

The axon hillock is considered the "decision-making site" of the neuron. This is because it integrates the inputs from various dendrites and if the net input is large enough to reach threshold, an action potential will be initiated. The axonal membranes and presynaptic membranes are involved in the propagation and transmission of the action potential, but not in the initial decision to fire. The mitochondrial membranes are involved in cellular respiration and energy production, but not in the processing of neuronal information.

Question 14

Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal?

Accepted Answer

Depolarizing the presynaptic membrane causes voltage-gated calcium channels to open, allowing calcium ions to enter the axon terminal.

Question 15

Which neurotransmitter is involved in reducing perceptions of pain?

Accepted Answer

Endorphins are known to reduce the perception of pain and are released in response to pain and stress. Acetylcholine is involved in muscle contraction, EPinephrine is involved in the body's "fight or flight" response, Nitric oxide plays various roles in the body including regulating blood pressure, and GABA is mainly an inhibitory neurotransmitter involved in reducing neural activity.

Question 16

When two excitatory postsynaptic potentials (EPSPs) occur at a single synapse so rapidly in succession that the postsynaptic neuron's membrane potential has not returned to the resting potential before the second EPSP arrives, the EPSPs add together, producing ________.

Accepted Answer

When two EPSPs occur in rapid succession, they can summate, leading to a higher amplitude and longer duration of depolarization in the postsynaptic neuron. This is known as temporal summation. Therefore, the correct choice is A) summation.

Question 17

What is the space between the presynaptic and postsynaptic membranes?

Accepted Answer

The space between the presynaptic and postsynaptic membranes is called the synaptic cleft. This is where neurotransmitters are released by the presynaptic neuron and bind to receptors on the postsynaptic neuron.

Question 18

What happens if twice as many inhibitory postsynaptic potentials (IPSPs) as excitatory postsynaptic potentials (EPSPs) arrive at a postsynaptic neuron in close proximity?

Accepted Answer

If the inhibitory signals are twice as strong as the excitatory signals, they will cancel out the effect of the excitatory signals and prevent the threshold potential from being reached. This means that no action potential will be generated. This is known as spatial summation.

Question 19

The botulinum toxin, which causes botulism, reduces the synaptic release of ________.

Accepted Answer

Botulinum toxin reduces the synaptic release of acetylcholine, a neurotransmitter involved in muscle contraction. This results in paralysis, the main symptom of botulism.

Question 20

An important inhibitory neurotransmitter of the human brain is ________.

Accepted Answer

Gamma-aminobutyric acid (GABA) is the most important inhibitory neurotransmitter in the brain. It reduces neural activity, which plays an important role in mental health and relaxation. It is involved in various functions such as controlling anxiety, regulating muscle tone, and processing visual information.

Quiz 43: Animal Nervous Systems