Chapter 11 - Fundamentals of the Nervous System

How do action potential propagation speeds compare in myelinated and unmyelinated axons?

Propagation is faster in myelinated axons.

Which of the following is NOT one of the basic functions of the nervous system?

Release hormones into the bloodstream to communicate with other cells in the body.

Which of the following peripheral nervous system (PNS) neuroglia form the myelin sheaths around larger nerve fibers in the PNS?

Schwann cells

Given your understanding of what happens to neurotransmitters after being released in the synapse, choose the intervention that would not benefit the given medical condition.

Stimulating proteins that contribute to the diffusion of neurotransmitters from the synapse can be used to oppose the addictive effects of cocaine on dopamine receptors.

Tetraethylammonium (TEA) blocks voltage-gated K+ channels such that K+ cannot pass even when the channels are open. However, TEA leaves K+ leakage channels largely unaffected. How would you expect the action potential to change if you treated a neuron with TEA?

The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time.

In a myelinated axon, how do the nodes of Ranvier differ from other segments of the same axon?

The nodes are more permeable to ions

Which of the following statements concerning inhibitory synapses (IPSPs) is correct?

The postsynaptic membrane becomes more permeable to potassium and chloride

During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?

The previous axonal segment is in the refractory period.

The myelin on myelinated neurons can be degraded or destroyed in diseases such as multiple sclerosis-a process called demyelination. If a myelinated neuron was affected by demyelination, how would this affect action potentials in that neuron?

The speed of action potential propagation would be slower.

Which of the following is not true of chemical synapses?

They transmit nerve impulses directly from one neuron to another

When an action potential arrives at the end of the axon terminal, a series of events take place that result in the release of neurotransmitter from the presynaptic axon. Select the answer that correctly describes the primary stimulus for vesicles to move toward the cell membrane and eventually release their contents.

Voltage-gated membrane channels open, and Ca+2 enters the cytoplasm, increasing intracellular calcium.

Parallel processing is to serial processing as __________.

a complex behavior like the withdrawal reflex is to a simple process like a simple reflex

The mechanism by which the neurotransmitter is returned to a presynaptic neuron's axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned?

acetylcholine

Caffeine's stimulatory effects result from blocking receptors for which neurotransmitter?

adenosine

What condition will increase the diffusion of molecules, such as neurotransmitters?

an increase in the amount of neurotransmitter exocytized by the presynaptic axon

trigger zone

area where nerve impulse is generated

During what part of the action potential do voltage-gated Na+ channels begin to inactivate (their inactivation gates close)?

at the end of the depolarization phase, as the membrane potential approaches its peak value

Where are action potentials regenerated as they propagate along a myelinated axon?

at the nodes of Ranvier

If the membrane of a postsynaptic dendrite is setting up a graded potential, what must have happened after neurotransmitter was released by the presynaptic terminal?

bound at postsynaptic receptors to open postsynaptic ion channels

Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.

chemically gated; postsynaptic

Match the term to its correct description: Serotonin __________.

is a "mood" transmitter, the target of Prozac to relieve depression

Match the term to its correct description: Norepinephrine __________.

is a neurotransmitter of postganglionic neurons in the sympathetic nervous system

Ependymal cells line many open cavities in the central nervous system (CNS). Ependymal cells have cilia on the side of the cell that face these openings. What is the most likely function of these ciliated cells?

movement and circulation of cerebrospinal fluid

Spatial summation occurs when __________.

multiple local potentials occur at different places on the same cell at the same time

Which of the following pairings does NOT fit? afferent neurons: sensory neurons motor neurons: efferent neurons. multipolar neurons: peripheral nervous system sensory neurons association neuron: functional classification

multipolar neurons: peripheral nervous system sensory neurons

When trying to think about your future career, and weigh the pros and cons of various choices, what type of circuit is likely involved?

parallel after-discharge circuit

secretory region

plasma membrane exhibits voltage-gated Ca2+ channels

conducting region

plasma membrane exhibits voltage-gated Na+ and K+ channels

Which of the following choices best represents synaptic transmission?

presynaptic axon to synapse to dendrite or postsynaptic cell body

In a synapse, neurotransmitters are stored in vesicles located in the __________.

presynaptic neuron

Which of the following defines integration?

processing and interpretation of sensory input and determining what should be done at each moment in the body

Match the word with its corresponding statement: G protein-linked receptors __________.

provide indirect synaptic responses that are complex, prolonged, and often diffuse as a result of the production of intracellular second-messenger molecules

axon terminal

release neurotransmitters into the extracellular space

The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.

saltatory conduction

Which of the following best characterizes depolarization?

small, consecutive steps of Na+ penetration into the axon along its length

What division of the nervous system is most specifically responsible for voluntary motor control?

somatic nervous system

Calcium has a great many roles in the body from providing structure to bones, stimulating muscle contraction, altering heart rate, influencing heart strength and stimulating hormone release. In a neuron, calcium's main role is __________.

stimulating the release of neurotransmitters

Match the term to its correct description: Numerous nerve impulses arriving at a synapse at closely timed intervals exert a cumulative effect.

temporal summation

Which is the main receptive portion of the neuron?

the dendrite

An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism?

the generation of local currents

As you start working out, you notice that your heart rate and breathing rate start to increase. Which division of your nervous system is generating this response? Be as specific as possible.

the sympathetic division of the autonomic nervous system

An action potential releases neurotransmitter from a neuron by opening which of the following channels?

voltage-gated Ca2+ channels

Which of the following events is NOT involved in the transfer of information across a chemical synapse?

Ions flow directly from one neuron to the next

During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels?

K+ channels close. Na+ channels go from an inactivated state to a closed state.

During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________.

K+ ions diffusing through voltage-gated channels

The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________.

K+ ions leaving the cell through voltage-gated channels

Predict the possible effect of a drug that totally blocks the neurotransmitter receptor on the postsynaptic membrane. For example, curare is a neurotoxin used by several South American cultures. The primary effect of curare is that acetylcholine, a major neuromuscular neurotransmitter, cannot bind at its receptor because curare is blocking it. Predict the possible effects of curare on the postsynaptic membrane and muscle.

Local graded potential and action potential transmission is blocked, and there is no response by the postsynaptic cell, the muscle.

Which statement best describes exocytosis?

Membrane organelles fuse with the membrane and release contents out of the cell.

The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?

Na+ (sodium)

During the action potential of a neuron, which ion is primarily crossing the membrane during the depolarization phase, and in which direction is the ion moving?

Na+ is entering the cell

receptive region

- receives stimuli - plasma membrane exhibits chemically gated ion channels

Drag and drop the descriptive labels of events into the correct sequence at the chemical synapse.

1. Action potential sweeps down presynaptic axon 2. Calcium channels open in axon terminal. 3. Synaptic vesicles fuse and exocytize neurotransmitter 4. Diffusion of neurotransmitter into extracellular fluid separating two neuron's membranes 5. Graded potential at postsynaptic membrane

Which of the following is true of axons? Neurons can have multiple axons but only one dendrite. A neuron can have only one axon, but the axon may have occasional branches along its length. Axons use chemically gated ion channels to generate graded potentials. Smaller (thinner) axons are more likely to bear myelin sheaths than larger (thicker) axons.

A neuron can have only one axon, but the axon may have occasional branches along its length.

Destruction of which of the neuroglial cell types leads to the disease multiple sclerosis (MS)?

A - The defects in nerve transmission associated with MS are caused by a loss of myelin within the CNS.

The graded potentials generated at __________ and are generated by __________ ion channels.

A; chemically gated

In which area of the neuron is an action potential initially generated?

C - axon hillock

Control of ion concentrations is a very important function controlled by the kidneys. A change in the concentration of what ions may directly affect the action shown in the figure?

Changes in the concentration of sodium, potassium, or chloride may affect a neuron's ability to make the "decisions" required in conscious thought

Which of the cell types shown is most associated with the production and flow of cerebrospinal fluid (CSF)? Glial cells of the central and peripheral nervous systems.

D - These cells line central cavities of the CNS and, in certain places, produce CSF. The cilia of these cells help circulate the CSF that nourishes and cushions the brain and spinal cord.

Which of the neuroglial cell types shown are found in the peripheral nervous system (PNS)? Glial cells of the central and peripheral nervous systems.

E - The cell shown in E wraps and insulates the soma of neurons within ganglia in the PNS.

Which of the following statement is false? Electrical synapses provide a complex means to allow areas of the brain to work independently. As the nervous system develops, chemical synapses replace some electrical synapses and become the vast majority of all synapses. Chemical synapses are like a lake that two neurons shout across. Just as shouting can be amplified or muted, chemical synapses can often be "muted" or "amplified" by pharmaceutical interaction. Electrical synapses are far more abundant in embryonic nervous tissue, where they permit exchange of guiding cues during early neuronal development so that neurons can connect properly with one another.

Electrical synapses provide a complex means to allow areas of the brain to work independently.

Na+ leaks through neuron membranes faster than K+ because of the properties of the non-gated leak channels.

False - K+ leak channels allow K+ to leak through the neuron membrane almost 25 times faster than Na+.

Arrange the parts in order, from left to right, of a successful direct depolarization path within one neuron.

dendrite cell body axon hillock axon presynaptic terminal

Which of the following circuit types is exemplified by impulses that travel from a single neuron of the brain, activate one hundred or more motor neurons in the spinal cord, and excite thousands of skeletal muscle fibers?

diverging circuits

Binding of the neurotransmitter to its receptor causes the membrane to __________.

either depolarize or hyperpolarize

Which of the following neurotransmitters acts as a natural opiate?

endorphins

Match the term to its correct description: Acetylcholine __________.

excites skeletal muscle

Match the term to its correct description: GABA __________.

generally inhibitory; found throughout CNS

Match the term to its correct description: Dopamine __________.

is a "feel good" transmitter; deficient in Parkinson's disease