Question 1

The major inhibitory neurotransmitter of the human brain is

Accepted Answer

GABA (gamma-aminobutyric acid) is the major inhibitory neurotransmitter of the human brain. It works by binding to specific receptors on the post-synaptic cell, which causes the opening of chloride channels and results in hyperpolarization of the cell, making it less likely to fire an action potential. This helps to dampen or inhibit neural activity and regulate excitability in the brain.

Question 2

Neurotransmitters affect postsynaptic cells by

Accepted Answer

All of these options are correct because neurotransmitters initiate signal transduction pathways, cause molecular changes such as gene expression, affect ion-channel proteins by either opening or closing them, and alter the permeability of cells to ions such as sodium, potassium, or chloride.

Question 3

Adjacent neurons with direct (non-neurotransmitter)action potential transfer are said to have electrical synapses, based on the presence of

Accepted Answer

Gap junctions are the structures found at the point of contact between adjacent neurons in an electrical synapse. These junctions allow for direct transfer of ions and small molecules between the two neurons, which is what enables the electrical signal to propagate from one neuron to the next. Tight junctions, leaky junctions, anchoring junctions, and desmosomes are all types of junctions found between cells, but they are not involved in the direct transfer of electrical signals.

Question 4

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 primarily found on the dendritic membrane of the postsynaptic neuron. This allows for the reception of chemical signals from a presynaptic neuron and subsequent transmission of electrical impulses down the axon hillock and along the axon.

Question 5

The activity of acetylcholine in a synapse is terminated by

Accepted Answer

Acetylcholine in a synapse is terminated by its degradation by a hydrolytic enzyme called acetylcholinesterase on the postsynaptic membrane.

Question 6

The heart rate decreases in response to the arrival of

Accepted Answer

Acetylcholine is released by the parasympathetic nervous system and causes the heart rate to decrease.

Answer: B 
 Epinephrine is released by the sympathetic nervous system and causes the heart rate to increase.

Answer: C 
 Endorphins are opioids that can cause a decrease in pain perception, but they do not directly affect heart rate.

Answer: D 
 Nitric oxide is involved in vasodilation, but does not directly affect heart rate.

Answer: E 
 GABA is an inhibitory neurotransmitter in the brain, but does not directly affect heart rate.

Question 7

Neurotransmitters categorized as inhibitory are expected to

Accepted Answer

Inhibitory neurotransmitters typically function by hyperpolarizing the membrane, making it more negative and thus less likely to fire an action potential. This is often achieved through mechanisms such as opening potassium channels (allowing K+ to exit the cell, making the inside more negative) or opening chloride channels (allowing Cl- to enter the cell, making the inside more negative), not by closing them.

Question 8

The major excitatory neurotransmitter of the human brain is

Accepted Answer

Glutamate is the major excitatory neurotransmitter in the brain and is involved in various cognitive functions such as learning and memory, as well as in the development and plasticity of neural circuits.

Other choices:
A) Acetylcholine is involved in various functions such as muscle control, attention, learning, and memory, but it is not the major excitatory neurotransmitter of the brain.
B) Epinephrine, also known as adrenaline, is a hormone secreted by the adrenal glands, and although it can act as a neurotransmitter in the peripheral nervous system, it is not a major neurotransmitter in the brain.
D) Nitric oxide is a gas neurotransmitter involved in various functions such as blood pressure regulation and immune response, but it is not a major excitatory neurotransmitter.
E) GABA (gamma-aminobutyric acid) is the major inhibitory neurotransmitter in the brain, counteracting the effects of glutamate and reducing neuronal excitability.

Question 9

Assume that a single IPSP has a negative magnitude of -0.5 mV at the axon hillock, and that a single EPSP has a positive magnitude of +0.5 mV. For a neuron with an initial membrane potential of -70 mV, the net effect of the simultaneous arrival of six IPSPs and two EPSPs would be to move the membrane potential to

Accepted Answer

The net effect is calculated by adding the effects of the IPSPs and EPSPs: (6 * -0.5 mV) + (2 * +0.5 mV) = -3 mV + 1 mV = -2 mV. Starting from -70 mV, the membrane potential moves to -72 mV.

Question 10

The primary neurotransmitter from the parasympathetic system that influences its autonomic targets is

Accepted Answer

The parasympathetic system primarily releases acetylcholine as its neurotransmitter, which slows down heart rate, increases digestion and salivation, and promotes rest and relaxation. Adenosine is not a primary neurotransmitter of the parasympathetic system, while norepinephrine and adrenaline are primarily released by the sympathetic system to prepare the body for fight or flight responses. Dopamine is involved in reward and motivation, but does not play a significant role in the autonomic nervous system.

Question 11

An example of ligand-gated ion channels is

Accepted Answer

Acetylcholine receptors at the neuromuscular junction are an example of ligand-gated ion channels, as they open in response to binding of the neurotransmitter acetylcholine.

Question 12

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 the portion of the neuron where action potentials are typically initiated. This is because it contains the highest concentration of voltage-gated ion channels, which are needed for the rapid depolarization required for an action potential to occur. While other membrane locations may contribute to the overall excitability of the neuron and the aggregation of synaptic inputs, the axon hillock is considered to be the primary "decision-making site" for action potential initiation.

Question 13

A chemical that affects neuronal function but is not stored in presynaptic vesicles is

Accepted Answer

Nitric oxide is a gas that is produced by neurons and diffuses out of the cell, rather than being stored in presynaptic vesicles. It is a signaling molecule that affects neuronal function. The other options (A, B, C, and E) are neurotransmitters that are stored in vesicles and released at the synapse to affect neuronal function.

Question 14

A neuropeptide that might function as a natural analgesic is

Accepted Answer

Endorphins are neuropeptides that bind to the same receptors as opioid drugs, and they are known to function as natural painkillers in the body. This makes them a good candidate for a natural analgesic. The other choices either have different functions or are not neuropeptides.

Question 15

When several IPSPs arrive at the axon hillock rapidly in sequence from a single dendritic location, hyperpolarizing the postsynaptic cell more and more and thus preventing an action potential, this is an example of

Accepted Answer

This is an example of temporal summation, where several IPSPs arrive at the axon hillock in rapid succession from a single dendritic location, leading to the summation of their hyperpolarizing effects on the postsynaptic cell. This can prevent the generation of an action potential. Spatial summation, on the other hand, is the summation of IPSPs and EPSPs from different dendritic locations, which can also affect the generation of an action potential. Tetanus refers to a sustained contraction of skeletal muscles due to rapidly repeated stimulation. The refractory state is the period during and after an action potential when the neuron is unable to generate another action potential. An action potential with an abnormally high peak of depolarization is not related to this scenario.

Question 16

An example of the action of metabotropic receptors is when

Accepted Answer

The answer of An example of the action of metabotropic...

Question 17

An amino acid that operates at inhibitory synapses in the brain is

Accepted Answer

GABA (gamma-aminobutyric acid) is an amino acid that operates at inhibitory synapses in the brain. It is the main inhibitory neurotransmitter in the central nervous system and helps to regulate neuronal excitability. The other options listed are not typically associated with inhibitory synapses in the brain.

Question 18

Ionotropic receptors are found at synapses operated via

Accepted Answer

Ionotropic receptors are ligand-gated ion channels, meaning that they open in response to a specific neurotransmitter binding to the receptor. This allows ions to flow through the channel, resulting in a rapid change in the membrane potential of the postsynaptic neuron.

Question 19

When several EPSPs arrive at the axon hillock from different dendritic locations, depolarizing the postsynaptic cell to threshold for an action potential, this is an example of

Accepted Answer

This is an example of spatial summation, where multiple inputs are added up at different locations on the dendrites to reach the threshold for an action potential. Temporal summation involves the addition of inputs that arrive at the same location on the dendrite at different times. Tetanus refers to a sustained contraction of a muscle due to rapid stimulation of motor neurons. The refractory state refers to a period of time after an action potential where the neuron cannot fire another action potential. An action potential with an abnormally high peak of depolarization does not accurately describe this situation.

Question 20

The botulinum toxin reduces the synaptic release of

Accepted Answer

Botulinum toxin inhibits the release of acetylcholine at the neuromuscular junction, leading to muscle paralysis.

Quiz 48: Neurons, Synapses, and Signaling