Nerve Function & Communication PT 2

Question 1

A chemical synapse involves a physical connection between the pre-synaptic neuron and the post-synaptic neuron.

True or False

Answer 1

False

Explanation

An electrical synapses involves a direct physical connection between the pre-synaptic and post-synaptic cells. A chemical synapse involves communication between the pre-synaptic cell and post-synaptic cell that involves the release of a neurotransmitter from the pre-synaptic cell and the binding of that transmitter on the post-synaptic cell.

Question 2

Which of the following voltage-gated ion channels will open when an action potential arrives at the terminal of the pre-synaptic neuron?

Voltage-gated Na+ channels

Voltage-gated Ca++ channels

Voltage-gated K+ channels

Answer 2

Voltage-gated Ca++ channels

Explanation

Voltage-gated Ca++ channels will open in response to depolarization of the axon terminal. Voltage-gated Na+ channels open in response to depolarization of the trigger zone, and voltage-gated K+ open in response to depolarization during an AP (at a slower rate as compared to Na+ channels).

Question 3

An influx of Ca++ into the cell causes which of the following events to occur?

Release of neurotransmitter from the pre-synaptic cell

The removal of the neurotransmitter from the synaptic cleft.

The depolarization of the axon terminal.

The binding of the neurotransmitter to the receptor.

Answer 3

Release of neurotransmitter from the pre-synaptic cell

Explanation

The influx of Ca++ into the pre-synaptic neuron will cause the synaptic vesicle to fuse to the cell membrane and the release of the neurotransmitter. The removal of a neurotransmitter from the cleft is accomplished by an enzyme that will break the transmitter down, or by active uptake mechanisms (transporter mediated). The depolarization of the axon terminal is due to an influx of Na+. The binding of a neurotransmitter to a receptor occurs because they have an affinity for each other.

Question 5

The binding of a neurotransmitter to a receptor causes a graded potential (EPSP or IPSP)

True

False

Answer 5

True

Explanation

The binding of a neurotransmitter to a receptor causes a graded potential (EPSP or IPSP). There will be one exception to this rule the neuromuscular junction of skeletal muscle - in the case the post-synaptic response will be depolarization of the muscle fiber (always excitatory). Will discuss when we discuss the motor system.

Question 5

Inhibitory neurotransmitters are transmitters that move the membrane potential toward hyper-polarization.

True or False

Answer 5

True

Explanation

Inhibitory neurotransmitters are transmitters that move the membrane potential toward hyper-polarization. The majority due so by opening ion channels that are selective for Cl- or K+. Excitatory neurotransmitters are transmitters that move the membrane potential toward depolarization. The majority due so by opening cation channels (e.g., Na+ or Ca++).

Question 5

Which of the following neurotransmitters is important for the activation of muscle contractions?

Serotonin

Acetylcholine

GABA

Glycine

Question 5

Which of the following neurotransmitters is considered the chief excitatory neurotransmitter of the brain?

GABA

Glutamate

Glycine

Dopamine

Answer 5

Glutamate

Explanation

Glutamate is considered the chief excitatory neurotransmitter of the brain. GABA is the chief inhibitory neurotransmitter of the brain. Glycine is considered the chief inhibitory neurotransmitter of the spinal cord and caudal BS. Dopamine can have both excitatory and inhibitory effects dependent on the receptor (as can NE, Serotonin, and ACh).

Question 5

An ionotropic receptor is a ligand-gated ion channel.

True or False

Answer 5

True

Explanation

Ionotropic receptors are ligand-gated ion channels that are selective for cations or anions.

Question 6

Which of the following receptors is involved in mediating complex biological responses such as gene expression?

Ionotropic receptor

Metabotropic receptor

Answer 6

Metabotropic receptor

Explanation

Metabotropic receptors are G-protein couple receptors that are capable of mediating complex biological response inside of the cell, including gene expression.

Question 6

Which of the following terms describes a drug that binds the main receptor binding site but doesn’t activate the receptor?

-Agonist
-Antagonist
- Positive allosteric modulator
- Negative allosteric modulator

Answer 6

Antagonist

Explanation

An antagonist is a drug that will bind the main binding site, but it doesn’t activate the receptor. In this way, it competes with the neurotransmitter and prevents activation of the receptor. An agonist is a drug that binds the main binding site and activates the receptor (functions in the same way as the neurotransmitter). A positive allosteric modulator is a drug that binds a regulatory site on the receptor that enhances the activity of the neurotransmitter. A negative allosteric modulator is a drug that binds a regulatory site on the receptor that decreased the activity of the neurotransmitter.

Question 6

Which of the following processes results in desensitization? Select all that apply.

• receptor up-regulation
• receptor down-regulation
• sequestering of receptors
• Strengthening the coupling of the receptor with the downstream signaling pathway.

Answer 6

receptor down-regulation and sequestering of receptors

Explanation

Desensitization is a reduced response to a neurotransmitter or agonist drug due to a decrease in the number of available receptors or decreased activity of the intracellular signaling pathways and ion channels. It can occur by uncoupling - reducing the receptor’s ability to activate downstream signaling pathways, by removing receptors from the cell membrane (sequestering) or by down-regulation (removing and destroying receptors to they are no longer available).