(1) MASTERING A&P

T or F : Efferent nerve fibers may be described as motor nerve fibers.

true

The plasma membrane is much more permeable to K+ than to Na+. Why? - There are many more voltage-gated K+ channels than voltage-gated Na+ channels. - Ligand-gated cation channels favor a greater influx of Na+ than K+. - There are many more K+ leak channels than Na+ leak channels in the plasma membrane. - The Na+-K+ pumps transport more K+ into cells than Na+ out of cells

- There are many more K+ leak channels than Na+ leak channels in the plasma membrane. [More leak channels translates into more leakiness. Thus the outward flux of K+ is greater than the inward flux of Na+]

What opens first in response to a threshold stimulus? - Voltage-gated K+ channels - Voltage-gated Na+ channels - Ligand-gated Cl- channels - Ligand-gated cation channels

- voltage-gated Na+ channels [The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm]

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference? -Threshold potential -Resting membrane potential (RMP) -Action potential -Positive membrane potential

-Resting membrane potential

What event triggers the generation of an action potential? -The membrane potential must return to its resting value of -70 mV from the hyperpolarized value of -80 mV. -The membrane potential must depolarize from the resting voltage of -70 mV to its peak value of +30 mV. -The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV. -The membrane potential must hyperpolarize from the resting voltage of -70 mV to the more negative value of -80 mV

-The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV. [This is the minimum value required to open enough voltage-gated Na+ channels so that depolarization is irreversible]

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors. -The presence of concentration gradients and leak channels -The presence of concentration gradients and Na+-K+ pumps -The presence of concentration gradients and voltage-gated channels -The presence of a resting membrane potential and leak channels

-The presence of concentration gradients and leak channels [The concentration gradient and the large number of K+ leak channels allow for rather robust K+ diffusion out of a cell. In contrast, the concentration gradient and the relatively few Na+ leak channels allow for much less Na+ diffusion into a cell]

Which of the following is not true of graded potentials? -They can be called postsynaptic potentials. -They are short-lived. -They increase amplitude as they move away from the stimulus point. -They can form on receptor endings.

-They increase amplitude as they move away from the stimulus point

What triggers the release of phosphate from the Na+-K+ pump? -hydrolysis of ATP -binding of K+ ions to the pump -release of Na+ ions from the pump -release of K+ ions from the pump

-binding of K+ ions to the pumpAs [K+ ions bind to the pump, the pump's phosphate is released and the pump changes shape to open inward. After this shape change, the K+ ions are released into the cytoplasm. Note that despite the details of protein phosphorylation and phosphate release; in the end, the overall chemical reaction is pretty straightforward. To power one cycle of the pump, one ATP molecule is hydrolyzed to one ADP molecule and one (free) phosphate ion]

Which component has a role in the postsynaptic cell during synaptic activity? -axon terminal -Vesicles filled with neurotransmitter -calcium channels -chemically gated channels

-chemically gated channels [Neurotransmitter binds to receptors on the postsynaptic cell. These chemically gated channels open, allowing the transfer of the "signal" from a presynaptic neuron to the postsynaptic cell]

What type of conduction takes place in unmyelinated axons? -Continuous conduction -Synaptic transmission -Saltatory conduction -Electrical conduction

-continuous conduction [An action potential is conducted continuously along an unmyelinated axon from its initial segment to the axon terminals. The term continuous refers to the fact that the action potential is regenerated when voltage-gated Na+‎ channels open in every consecutive segment of the axon, not at nodes of Ranvier]

Which neurotransmitter(s) is/are the body's natural pain killer? -substance P -acetylcholine -endorphins -norepinephrine

-endorphins

A vesicle fuses with the plasma membrane and releases its contents to the extracellular fluid. This statement describes _____. -exocytosis -simple diffusion -facilitated diffusion -active transport -endocytosis

-exocytosis [The term exocytosis literally means "out of the cell."]

Which of the following types of glial cells produce the myelin sheaths that insulate the neural fibers in the CNS? -Oligodendrocytes -Ependymal cells -Microglia -Astrocytes

-oligodendrocytes

The sodium-potassium pump uses ATP to move sodium and potassium ions across the plasma membrane. This statement describes _____. -secondary active transport -simple diffusion -facilitated diffusion -exocytosis -primary active transport

-primary active transport [The sodium-potassium pump is activated by ATP. This activation allows the pump to transport sodium and potassium ions against their gradients]

The sodium-potassium pump uses ATP to move sodium and potassium ions across the plasma membrane. This statement describes _____.

-primary active transport [The sodium-potassium pump is activated by ATP. This activation allows the pump to transport sodium and potassium ions against their gradients.]

Which of the following best describes how phosphorylation affects the Na+-K+ pump? -Phosphorylation causes the unloading of K+ ions from the pump. -Phosphorylation causes the pump to change shape. -Phosphorylation allows Na+ ions to bind to the pump. -Phosphorylation allows ATP to bind to the pump.

Phosphorylation causes the pump to change shape. [Before being phosphorylated, the pump's opening faces the cytoplasm, which allows cytoplasmic Na+ to bind. After phosphorylation, the pump changes shape such that its opening faces the extracellular fluid. Phosphorylation is a common cellular mechanism for altering the activity, shape, or function of a protein]

What is the function of the myelin sheath? The myelin sheath decreases the resistance of the axonal membrane to the flow of charge. The myelin sheath increases the insulation along the entire length of the axon. The myelin sheath decreases the speed of action potential conduction from the initial segment to the axon terminals. The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

T or F: The nodes of Ranvier are found only on myelinated, peripheral neuron processes.

false

That part of the nervous system that is voluntary and conducts impulses from the CNS to the skeletal muscles is the ________ nervous system.

somatic

Which of the following would not diffuse through the plasma membrane by means of simple diffusion? -A lipid soluble molecule -Water -Glucose -A small, non-charged molecule

glucose

The period after an initial stimulus when a neuron is not sensitive to another stimulus is the ________. -depolarization -absolute refractory period -resting period -repolarization

-absolute refractory period

Which of the following is an excitatory neurotransmitter secreted by motor neurons innervating skeletal muscle? -cholinesterase -acetylcholine -norepinephrine -gamma aminobutyric acid

-acetylcholine

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization? - Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open. - Activation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open. - Inactivation gates of voltage-gated Na+‎ channels close, while inactivation gates of voltage-gated K+‎ channels open. - Activation gates of voltage-gated Na+‎ channels close, while inactivation gates of voltage-gated K+‎ channels open.

- Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open. [Closing of voltage-gated channels is time dependent. Typically, the inactivation gates of voltage-gated Na+‎ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+‎ channels open]

What is the first change to occur in response to a threshold stimulus? - Voltage-gated Na+ channels change shape, and their inactivation gates close. - Voltage-gated K+ channels change shape, and their activation gates open. - Voltage-gated Na+ channels change shape, and their activation gates open. - Voltage-gated Ca2+ channels change shape, and their activation gates open

- Voltage-gated Na+ channels change shape, and their activation gates open. [The activation gates of voltage-gated Na+ channels open very rapidly in response to threshold stimuli. The activation gates of voltage-gated K+ channels are comparatively slow to open]

What is the role of calcium in synaptic activity? -Calcium degrades neurotransmitter in the synaptic cleft. -Calcium influx into the synaptic terminal causes vesicle fusion. -Calcium diffuses across the synaptic cleft and binds to receptors on the postsynaptic neuron. -Calcium influx into the axon causes an action potential to propagate into the synaptic terminal.

-Calcium influx into the synaptic terminal causes vesicle fusion. [When an action potential reaches the synaptic terminal, voltage-gated channels open and calcium enters the cell. Calcium causes vesicles to fuse with the presynaptic membrane and release neurotransmitter into the synaptic cleft]

Which of the following is the conducting region of the neuron? -Neurofibrils -Dendrites -Ganglia -Axon

-axon

What is the direct role of neurotransmitter at a chemical synapse? -Neurotransmitter causes calcium to flood into the presynaptic cell. -Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane. -Neurotransmitter causes vesicles to fuse with the presynaptic membrane. -Neurotransmitter causes a graded potential in the postsynaptic cell.

-Neurotransmitter binds to receptors on the postsynaptic cell membrane and allows ions to diffuse across the membrane. [Neurotransmitter leaves the presynaptic neuron by exocytosis and binds receptors on the postsynaptic cell membrane, opening the channels. When ions enter the postsynaptic cell, a graded potential takes place]

What characterizes repolarization, the second phase of the action potential? -As the membrane repolarizes to a negative value, it goes beyond the resting state to a value of -80 mV. -Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV. -Once the membrane depolarizes to a threshold value of approximately -55 mV, it repolarizes to its resting value of -70 mV. -Before the membrane has a chance to reach a positive voltage, it repolarizes to its negative resting value of approximately -70 mV

-Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV. [The plasma membrane was depolarized to a positive value at the peak of the first phase of the action potential. Thus, it must repolarize back to a negative value]

What sort of Ca2+ concentrations are maintained by the calcium pump? -The Ca2+ concentration is higher in the extracellular fluid than in the cytoplasm. -The Ca2+ concentration is about the same in the cytoplasm as it is in the extracellular fluid. -The Ca2+ concentration is higher in the cytoplasm than in the extracellular fluid.

-The Ca2+ concentration is higher in the extracellular fluid than in the cytoplasm. [Near constant ejection of Ca2+ by this pump helps keep intracellular levels very low in most cells]

Most cancer cells have a lower intracellular ATP concentration compared to normal cells. How would you expect this to affect the Na+-K+ pump in cancer cells? -The Na+-K+ pump would work slower. -The Na+-K+ pump would work faster. -The Na+-K+ pump would not work at all. -So long as the concentrations of Na+ and K+ are normal, the Na+-K+ pump would work normally.

-The Na+-K+ pump would work slower. [The Na+-K+ pump uses intracellular ATP to operate. The lower ATP concentration in cancer cells would tend to decrease the pump's activity]

Why does regeneration of the action potential occur in one direction, rather than in two directions? -The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential. -The activation gates of voltage-gated K+‎ channels open in the node, or segment, that has just depolarized. -The inactivation gates of voltage-gated K+‎ channels close in the node, or segment, that has just fired an action potential. -The activation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just depolarized

-The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential. [At the peak of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+‎ channels become absolutely refractory to another depolarizing stimulus]

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you? -The outside surface of the plasma membrane is much more negatively charged than the inside surface. -The inside surface of the plasma membrane is much more negatively charged than the outside surface. -The inside surface of the plasma membrane is much more positively charged than the outside surface. -There is no electrical potential difference between the inside and the outside surfaces of the plasma membrane.

-The inside surface of the plasma membrane is much more negatively charged than the outside surface. [The inside surface of the plasma membrane accumulates more negative charge because of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+]

What characterizes depolarization, the first phase of the action potential? -The membrane potential changes to a much more negative value. -The membrane potential reaches a threshold value and returns to the resting state. -The membrane potential changes to a less negative (but not a positive) value. -The membrane potential changes from a negative value to a positive value

-The membrane potential changes from a negative value to a positive value [The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to a positive value]

Which of the following allows us to consciously control our skeletal muscles? -The involuntary nervous system -The parasympathetic division of the autonomic nervous system -The sympathetic division of the autonomic nervous system -The somatic nervous system

-The somatic nervous system

What type of channel on the postsynaptic membrane binds neurotransmitter? -a leakage channel -a voltage-gated channel -a chemically gated channel -a mechanically gated channel

-a chemically gated channel -Chemically gated channels bind a specific chemical, which causes the channel to open. At chemical synapses, neurotransmitter molecules are released by the presynaptic neuron and bind to chemically gated channels on the postsynaptic cell membrane. The opening of these channels allows ions to diffuse across the membrane, causing a graded potential in the postsynaptic cell]

A postsynaptic cell can be a neuron, a muscle cell, or a secretory cell. What is an example of a presynaptic cell? -a neuron -a secretory cell -a Schwann cell -a muscle cell

-a neuron [A neuron is the only type of presynaptic cell. Neurons release neurotransmitters, effectively changing an electrical signal or action potential into a chemical signal that can communicate across the synaptic cleft to the postsynaptic cell]

An action potential is self-regenerating because __________. -depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment -repolarizing currents established by the efflux of K+‎ flow down the axon and trigger an action potential at the next segment -repolarizing currents established by the efflux of Na+‎ flow down the axon and trigger an action potential at the next segment -depolarizing currents established by the influx of K+‎ flow down the axon and trigger an action potential at the next segment

-depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment [The Na+‎ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold]

Neurotransmitter is released from presynaptic neurons through what mechanism? -pinocytosis -exocytosis -phagocytosis -endocytosis

-exocytosis

The majority of water molecules moving across plasma membranes by osmosis do so via a process that is most similar to ____. -co transport -facilitated diffusion -active transport -simple diffusion -a process that requires energy from the cell

-facilitated diffusion

Some transport processes use transport proteins in the plasma membrane, but do not require ATP. This type of transport is known as _____. -endocytosis -exocytosis -facilitated diffusion -active transport -simple diffusion

-facilitated diffusion [Facilitated diffusion is a passive transport process during which molecules move down their concentration gradients through transport proteins]

What sort of ion distributions are established and maintained by Na+-K+ pump activity? -high Na+ concentration in the extracellular fluid; high K+ concentration in the cytoplasm -high Na+ and K+ concentrations in the extracellular fluid -high Na+ concentration in the cytoplasm; high K+ concentration in the extracellular fluid -high Na+ and K+ concentrations in the cytoplasm

-high Na+ concentration in the extracellular fluid; high K+ [The Na+-K+ pump moves Na+ ions from the cytoplasm to the extracellular fluid while moving K+ ions in the opposite direction. This creates/maintains a higher concentration of Na+ in the extracellular fluid, and a higher concentration of K+ in cytoplasm. These concentration gradients are important in all cells. In excitable cells such as neurons and muscle fibers, these concentration gradients are used to generate electrical signals]

What is the energy source used by the Na+-K+ pump during its normal operation? -movement of ATP across the plasma membrane -movement of Na+ ions across the plasma membrane -movement of K+ ions across the plasma membrane -hydrolysis of ATP

-hydrolysis of ATP [Hydrolysis of ATP leads to phosphorylation of the pump. This leads to shape changes in the pump that ultimately transport Na+ and K+ against their respective concentration gradients. Without ATP hydrolysis, the pump cannot actively transport Na+ and K+]

Where do most action potentials originate? -Initial segment -Cell body -Axon terminal -Nodes of Ranvier

-initial segment [The first part of the axon is known as the initial segment. The initial segment is adjacent to the tapered end of the cell body, known as the axon hillock]

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, ___________. -ion channels in the plasma membrane of the receiving neuron open. -ion channels in the plasma membrane of the sending neuron open. -the receiving neuron becomes more positive inside. -the receiving neuron becomes more negative inside. -vesicles in the synaptic terminal fuse to the plasma membrane of the sending neuron.

-ion channels in the plasma membrane of the receiving neuron open.

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel? - Ligand-gated channels - Leak channels - Sodium-potassium ATPases - Voltage-gated channels

-leak channels

A primary active transport process is one in which __________. -the plasma membrane folds inward to form a vesicle containing extracellular material -molecules pass directly through the phospholipid bilayer of the plasma membrane -molecules move through transport proteins that have been activated by ATP -molecules move across the plasma membrane without an input of energy -an intracellular vesicle fuses with the plasma membrane and releases its contents to the extracellular fluid

-molecules move through transport proteins that have been activated by ATP [Primary active transporters, such as the sodium-potassium ATPase (or pump), are activated when ATP is hydrolyzed. This activation allows for the transport of solutes across the plasma membrane against concentration gradients]

Which of the following types of neurons carries impulses away from the CNS? -motor -sensory -afferent -association

-motor

A molecule that carries information across a synaptic cleft is a ___________. -receiving neuron. -neurotransmitter. -sending neuron. -synaptic cleft. -synapse.

-neurotransmitter

The substance released at axon terminals to propagate a nervous impulse is called a(n) ________. -cholinesterase -biogenic amine -ion -neurotransmitter

-neurotransmitter

Which of the following are gaps found along a myelin sheath? -Nodes of Ranvier -Axolemma -Telodendria -Neurilemma

-nodes of ranvier

Which of the following PNS neuroglia help to form myelin sheaths around larger nerve fibers in the PNS? -Satellite cells -Oligodendrocytes -Schwann cells -Astrocytes

-schwann cells

The small space between the sending neuron and the receiving neuron is the _________. -synaptic cleft. -calcium channel. -vesicle. -synaptic terminal. -neurotransmitter.

-synaptic cleft

What event initiates ATP attachment to the Na+-K+ pump, leading to the pump's phosphorylation? -the release of K+ ions from the pump -the binding of Na+ ions to the pump -the release of Na+ ions from the pump -the pump changing shape, opening toward the extracellular fluid

-the binding of Na+ ions to the pump [Na+ ions loading into the pump triggers the docking of ATP which initiates enzymatic activity of the pump. This causes ATP hydrolysis, and ultimately, phosphorylation of the pump]

When calcium ions enter the synaptic terminal, __________. -they cause an action potential in the sending neuron. -they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron. -the inside of the receiving neuron becomes more negative. -the inside of the receiving neuron becomes more positive. -neurotransmitter molecules are quickly removed from the synaptic cleft.

-they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.

Which of the following best describes why cells need active transport mechanisms? -to move solutes across the plasma membrane -to move solutes against their concentration gradients -to move solutes down their concentration gradients -to move solutes that cannot be transported by facilitated diffusion

-to move solutes against their concentration gradients [Active transport allows the cell to move solutes against their concentration gradient. This cannot be accomplished by passive processes such as simple diffusion or facilitated diffusion. The importance of active transport is evident in the amount of energy cells dedicated to these processes. For example, the Na+-K+ pump can use up to 40 percent of the ATP produced by a resting cell]

T or F: Myelination of the nerve fibers in the central nervous system is the job of the oligodendrocyte.

true