Ch. 12 AP1

A traveling wave of excitation is known as a(n) ______.

• local potential

• graded potential

• action potential

• nerve signal

• depolarizing signal

Answer explanation

A traveling wave of excitation in the nervous system is referred to as a nerve signal. This term encompasses the propagation of action potentials along neurons, which are essential for communication within the nervous system.

What would be the best explanation for why myelinated fibers conduct signals faster than unmyelinated fibers?

• There are no internodes in unmyelinated fibers

• There are more internodes in unmyelinated fibers

• Facilitated diffusion of sodium and potassium is faster in myelinated fibers

• Active transport of sodium and potassium is faster in myelinated fibers

• Diffusion of ions along the axoplasm is faster

Answer explanation

Myelinated fibers have segments called internodes that allow for faster ion diffusion along the axoplasm. This increases the speed of signal conduction compared to unmyelinated fibers, where ion movement is slower.

Norepinephrine is a monoamine

• True

• False

Answer explanation

Norepinephrine is classified as a monoamine neurotransmitter, which includes other compounds like dopamine and serotonin. Therefore, the statement is true.

Which neurotransmitter excites skeletal muscle and inhibits cardiac muscle?

• Norepinephrine

• Dopamine

• Histamine

• Acetylcholine

• B-endorphin

Answer explanation

Acetylcholine is the neurotransmitter that stimulates skeletal muscle contraction while inhibiting cardiac muscle activity, making it the correct choice for this question.

In the brain, neurons are more abundant than neuroglia.

• True

• False

Answer explanation

Neuroglia, or glial cells, outnumber neurons in the brain by a significant margin, providing support and protection. Therefore, the statement that neurons are more abundant than neuroglia is false.

Which of the following ions has the greatest influence on the resting membrane potential?

• Sodium

• Chloride

• Calcium

• Phosphate

• Potassium

Answer explanation

Potassium ions have the greatest influence on the resting membrane potential due to their high permeability across the cell membrane. The resting potential is primarily determined by the concentration gradient of potassium.

Most neurons have multiple dendrites.

• True

• False

Answer explanation

Most neurons indeed have multiple dendrites, which allow them to receive signals from various sources. This structure is essential for the complex communication within the nervous system, making the statement true.

All of the following are typical characteristics of neurotransmitters except ______.

• they are synthesized by a presynaptic neuron

• they are released in response to stimulation

• they are released into the bloodstream before reaching the postsynaptic cell

• they bind to specific receptors on the postsynaptic cell

• they alter the physiology of the postsynaptic cell

Answer explanation

Neurotransmitters are not released into the bloodstream; they act locally at synapses. The correct choice highlights that they directly affect postsynaptic cells without entering the bloodstream.

The respiratory center gathers information from a variety of sources in order to set the rate and depth of breathing. This is an example of what type of neural circuit?

• Convergent

• Divergent

• Reverberating

• Parallel after-discharge

Answer explanation

The respiratory center integrates signals from various sources, illustrating a convergent neural circuit where multiple inputs converge to influence a single output, in this case, the regulation of breathing rate and depth.

In a myelinated fiber, only the initial segment in the trigger zone has voltage-regulated channels.

• True

• False

Answer explanation

The statement is false because myelinated fibers have voltage-regulated channels not only in the initial segment but also at the nodes of Ranvier, where action potentials are propagated.