Chapter 3 Workbook Questions

Question 1

What events occur in the presynaptic terminal when an action potential reaches the presynaptic terminal?

Answer 1

The membrane of the presynaptic terminal depolarizes; voltage-gated calcium ion (Ca+2) channels open; Ca+2 influxes into the nerve terminal; synaptic vesicles move toward a release site in the membrane, fuse with the membrane, then rupture to release a neurotransmitter into the synaptic cleft.

Question 2

How does the binding of a neurotransmitter to a receptor result in the opening of a ligand-gated ion channel?

Answer 2

The associated membrane channel changes shape, allowing it to open

Question 3

What is a postsynaptic potential?

Answer 3

local change in ion concentration across the postsynaptic membrane.

Question 4

What is an excitatory postsynaptic potential (EPSP)?

Answer 4

local depolarization of a postsynaptic membrane from an influx of positively charged ions (Na and Ca)

Question 5

What is an inhibitory postsynaptic potential (IPSP)?

Answer 5

local hyperpolarization of a postsynaptic membrane from an influx of chloride ion (Cl–) or an efflux of potassium ion (K+).

Question 6

What happens when acetylcholine (ACh) binds to receptors associated with membrane channels on a muscle cell?

Answer 6

When ACh binds to the receptor, Na+ channels open and the influx of Na+ initiates a series of events that produce a mechanical contraction of the muscle cell

Question 7

What are the three types of synaptic connections between neurons?

Answer 7

1. axoaxonic (communication occurs at axon of postsynaptic neuron)
2. axodendritic (communication occurs at the dendrites)
3. axosomatic (communication occurs at cell body)

Question 8

What is the effect of presynaptic facilitation on the action potential produced by the second axon at an axoaxonic synapse?

Answer 8

The action potential is longer in duration, allowing increased Ca+2 into the second synaptic terminal, and more neurotransmitter vesicles than usual move to the cell membrane and rupture. The facilitated neuron releases more transmitter than normal.

Question 9

How are neurotransmitters removed from the synapse, allowing inactivation of ligand-gated channel receptors?

Answer 9

The three mechanisms of receptor inactivation are:

1. neurotransmitter diffusion away from the synaptic cleft
2. enzymatic degradation of the neurotransmitter in the synaptic cleft; or
3. neurotransmitter reuptake by the presynaptic axon terminal.

Question 10

What is a guanine nucleotide–binding protein (G-protein)–mediated receptor?

Answer 10

A receptor that has an associated G-protein. When the receptor is bound by a neurotransmitter, the G-protein is activated and may alter the opening of membrane ion channels or may produce long-lasting changes in the neuron.

Question 11

What is the first step in the sequence of action in the G protein?

Answer 11

Neurotransmitters bind with the receptor.

Question 12

What is the second step in the sequence of action in the G protein?

Answer 12

Receptor protein changes shape.

Question 13

What is the third step in the sequence of action in the G protein?

Answer 13

Alpha (α) chain separates to act as a cytoplasmic shuttle.

Question 14

What is the fourth step in the sequence of action in the G protein?

Answer 14

The α chain activates a target protein.

Question 15

The second messenger in a second messenger system is a(n):

A. G-protein

B. α chain of the G-protein

C. Enzyme inside the neuron that can trigger responses within the neuron

D. Neurotransmitter

E. Gene

Answer 15

C: The G-protein–mediated second-messenger system involves:

(1) binding of a neurotransmitter (first messenger) to a G-protein–associated membrane receptor
(2) activation of an effector enzyme (second messenger)
(3) increased levels of the second second messenger that elicits responses within the neuron.

Question 16

Second messengers may initiate the:

A. Opening of membrane ion channels

B. Activation of genes, causing increased synthesis of specific cellular products

C. Modulation of Ca+2 levels inside the cell

D. A, B, and C

E. None of the above

Answer 16

D: Second messengers activate responses inside the cell. In these cases, a single neurotransmitter might turn on a molecular pathway that ends with a change in gene expression, the opening of ion channels, and/or phosphorylation of a structural protein.

Question 17

Which one of the following can serve as the postsynaptic cell of a synapse?

A. Smooth muscle cell in an artery

B. Hepatocyte in the liver

C. Neuron in the thalamus

D. Muscle cell in the triceps

E. All of the above

Answer 17

E: A postsynaptic cell is any cell of an organ, gland, blood vessel, neuron, or muscle cell that synapses with a neuron.

Question 18

ACh receptor subtypes include:

A. Adrenergic and noradrenergic.

B. Nicotinic and muscarinic

C. Alpha and beta

D. Alpha and gamma

E. None of the above

Answer 18

B: Receptors that bind ACh fall into two categories: nicotinic and muscarinic. These receptors are distinguished by their ability to bind certain drugs. Nicotine, derived from tobacco, selectively activates the nicotinic receptors. Muscarine, a poison derived from mushrooms, activates only the muscarinic receptors.

Question 19

How does onabotulinumtoxinA (BOTOX) therapeutically produce paresis in overactive muscles?

A. Acts as an antagonist by binding to the ACh receptor on the postsynaptic membrane

B. Rapidly degrades ACh in the synaptic cleft

C. Facilitates the reuptake and sequestration of ACh into the presynaptic cell

D. Disrupts the protein structure of the muscle cell receptor, thus preventing ACh from binding

E. Inhibits the release of ACh from the presynaptic terminal at the neuromuscular junction.

Answer 19

E: Botulinum toxin is naturally produced by a family of bacteria and, when ingested, causes widespread paralysis by inhibiting the release of ACh at the neuromuscular junction. When small doses of BOTOX are therapeutically injected directly into an overactive muscle, the inhibition of ACh release reduces or prevents contraction of the injected muscle.

Question 20

N-methyl-D-aspartate (NMDA) receptors

A. Are involved in long-term potentiation

B. Bind glutamate

C. Have been implicated in pathologic changes in the nervous system

D. A, B, and C

E. None of the above

Answer 20

D: The ligand-gated ion channels that bind glutamate are alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), kainate, and NMDA receptors. The NMDA receptor is unique because glutamate must be bound to the receptor and, simultaneously, the membrane must depolarize to open the ion channel. Thus the NMDA receptor is both voltage and ligand-gated. Activation of an NMDA receptor causes the associated channel to open and close very slowly, resulting in prolonged ionic changes inside the postsynaptic neuron. This produces long-term potentiation (LTP), a prolonged increase in the size of the postsynaptic response to a given stimulus. Abnormal NMDA receptor activity has been implicated in epilepsy, chronic pain, Parkinson’s disease, stroke, and schizophrenia.

Question 21

Myasthenia gravis:

A. Is caused by the destruction of gamma-aminobutyric acid (GABA) receptors on the postsynaptic membrane of muscles

B. Results in the decreased release of ACh at the neuromuscular junction

C. Is an autoimmune disease that destroys ACh receptors on the postsynaptic membrane of muscles, thus interferes with ACh binding for repetitive muscle contractions

D. Is successfully treated with removal of the pituitary gland

E. All of the above

Answer 21

C: Myasthenia gravis is an autoimmune disease during which antibodies attack and destroy nicotinic receptors on muscle cells. Normal amounts of ACh are released into the cleft, but few receptors are available for binding, resulting in increasing weakness with repetitive muscle contractions.

Question 22

What local membrane potential is created when a Sodium (Na) channel opens on the postsynaptic membrane?

Answer 22

EPSP (Excitatory Postsynaptic Potential)

Question 23

What local membrane potential is created when a Calcium (Ca) channel opens on the postsynaptic membrane?

Answer 23

EPSP (Excitatory Postsynaptic Potential)

Question 24

What local membrane potential is created when a Chloride (Cl) channel opens on the postsynaptic membrane?

Answer 24

IPSP (Inhibitory Postsynaptic Potential)

Question 25

What local membrane potential is created when a Potassium (K) channel opens on the postsynaptic membrane?

Answer 25

IPSP (Inhibitory Postsynaptic Potential)

Question 26

What is the purpose of Neurotransmitters and neuromodulators?

Answer 26

chemicals that convey information among neurons

Question 27

Neurotransmitters are released by what type of neuron?

Answer 27

released by presynaptic neuron and acts directly on postsynaptic ion channels or activates proteins made inside the postsynaptic neuron

Question 28

Neuromodulators are released into what space?

Answer 28

released into extracellular fluid and adjust activity of many neurons.

Question 29

Neurotransmitters that effect the postsynaptic neuron directly are called what?

Answer 29

ionotropic

Question 30

Neurotransmitters that effect the postsynaptic neuron indirectly are called what?

Answer 30

metabotropic

Question 31

ionotropic neurotransmitters or neurotransmitters that act directly on the postsynaptic neuron are classified as what?

Answer 31

fast-acting: effects are extremely short lived (less than 1/1000 of a second)

Question 32

metabotropic neurotransmitters or neurotransmitters that act indirectly on the postsynaptic neuron are classified as what?

Answer 32

slow-acting: transmission takes 1/10 of a second to minutes

Question 33

How to slow-acting neurotransmitters regulate fast acting neurotransmitters?

Answer 33

1. control the amount of neurotransmitter released from presynaptic terminal
2. can influence the actions of fast-acting neurotransmitters on the postsynaptic membrane

Question 34

how long can a neuromodulators effects last?

Answer 34

minutes to days: neuromodulators cellular effects may take seconds to be initiated, but the changes they create can last from minutes to days

Question 35

What is the fifth step in the sequence of action in the G protein?

Answer 35

Membrane channels open, or intracellular target proteins are activated.