Chapter 4 part 2

Question 1

Voltage-activated ion channels

Answer 1

Ion channels that open or close in response to changes in the level of the membrane potential.

Question 2

Absolute refractory period

Answer 2

The brief period of about 1 to 2 milliseconds after the initiation of an action potential during which it is impossible to elicit a second one.

Question 3

Relative refractory period

Answer 3

The period that follows the absolute refractory period, during which it is possible to fire the neuron again but only by applying higher-than-normal levels of stimulation. The end of the relative refractory period is the point at which the amount of stimulation necessary to fire a neuron returns to baseline.

Question 4

The refractory period is responsible for two important characteristics of neural activity: ____________

Answer 4

First, it is responsible for the fact that action potentials normally travel along axons in only one direction. Because the portions of an axon over which an action potential has just traveled are left momentarily refractory, an action potential cannot be reversed.

Second, the refractory period is responsible for the fact that the rate of neural firing is related to the intensity of the stimulation.

Question 5

The conduction of action potentials along an axon is _______.

Answer 5

Nondecremental

This means that action potentials do not grow weaker as they travel along the axon membrane.

Question 6

Action potentials are conducted more _______ than postsynaptic potentials (EPSP’s and IPSP’s).

Answer 6

slowly

Question 7

Saltatory conduction

Answer 7

The transmission of action potentials in myelinated axons.

Saltare means to skip or jump.

Question 8

Exocytosis

Answer 8

The process of neurotransmitter release.

Question 9

Neuropeptides

Answer 9

Short amino acid chains comprising between 3 and 36 amino acids; in effect, they are short proteins.

Large neurotransmitters are all neuropeptides.

Question 10

Dendritic spines

Answer 10

Nodes of various shapes that are located on the surfaces of many dendrites.

Question 11

Coexistence

Answer 11

When a neuron contains two neurotransmitters.

Question 12

Receptor

Answer 12

A protein that contains binding sites for only particular neurotransmitters; thus, a neurotransmitter can influence only those cells that have receptors for it.

Question 13

Ligand

Answer 13

Any molecule that binds to another.

A neurotransmitter is said to be a ligand of its receptor.

Question 14

Ionotropic receptors

Answer 14

Associated with ligand-activated ion channels.

When a neurotransmitter molecule binds to an ionotropic receptor, the associated ion channel usually opens or closes immediately, thereby inducing an immediate postsynaptic potential.

Question 15

Metabotropic receptors

Answer 15

Associated with signal proteins and G proteins (guanosine-triphosphate-sensitive proteins).

More prevalent than ionotropic receptors, and their effects are slower to develop, longer lasting, more diffuse, and more varied.

There are many different types of metabotropic receptors, but each is attached to a serpentine signal protein that winds its way back and forth through the cell membrane seven times.

Attached to a portion of the signal protein outside the neuron; the G protein is attached to a portion of the signal protein inside the neuron.

Question 16

Autoreceptor

Answer 16

Metabotropic receptors that have two unconventional characteristics:

they bind to their neuron’s own neurotransmitter molecules;

and they are located on the presynaptic, rather than the postsynaptic, membrane.

Their usual function is to monitor the number of neurotransmitter molecules in the synapse, to reduce levels when high and increase when low.