Bio Exam 4 Extra Credit Study Guide

What causes the striated patterns seen in skeletal muscle?

aligned borders of sarcomeres

What would happen if a skeletal muscle is deprived of adequate supplies of ATP?

the muscle enters a state where actin and myosin are unable to separate (ATP binds to end of myosin--causes to unbind. Seized up)

During the course of muscle contraction the potential energy stored in ATP is transferred to potential energy stored in _____.

the myosin head (The hydrolysis of ATP causes the myosin head to change position, storing energy that will be used to contract the muscle.)

During muscle contraction, the cross-bridge detaches when ____.

the myosin head binds to an ATP molecule

An action potential from a motor neuron arriving triggers a series of events leading to muscle contraction. Of the following four events, which occurs after the others?

the myosin-binding sites on actin are exposed (1: release of acetylcholine, 2: depolarization of muscle cells, 3: release of Ca2+ from the sarcoplasmic reticulum)

Of these events, the first to occur when a motor neuron stops sending an impulse to a muscle is _____.

the pumping of calcium ions out of the cytoplasm and back into the sarcoplasmic reticulum

What is the best indicator of the strength of a signal in a neuron?

the rate at which action potentials are produced

A neuron has a resting potential of about _____ millivolts.

-70

The following are events in the transmission of a signal at a chemical synapse. 1.Neurotransmitter binds with receptors associated with the postsynaptic membrane. 2.Calcium ions rush into neuron's cytoplasm. 3.An action potential depolarizes the membrane of the presynaptic axon terminal. 4.The ligand-gated ion channels open. 5.The synaptic vesicles release neurotransmitter into the synaptic cleft. Which sequence of events is correct?

3 → 2 → 5 → 1 → 4

For the following five events, which is the correct sequence that describes the excitation and contraction of a skeletal muscle fiber? 1. Tropomyosin shifts, exposing the myosin-binding sites on actin. 2. Calcium is released from the sarcoplasmic reticulum and binds to the troponin complex. 3. An action potential is propagated down the transverse tubules. 4. Cycles of myosin cross-bridge formation and breakdown cause the thin filaments to slide toward the center of the sarcomere. 5. An action potential in a motor neuron causes the axon to release acetylcholine, which triggers an action potential in a muscle fiber.

5 → 3 → 2 → 1 → 4

Which of the following describes the ion channels of a resting neuron?

The channels are open or closed depending on their type, and are specific as to which ion can traverse them.

Myosin heads have binding sites for _____.

ATP and actin

In multiple sclerosis, the myelin sheaths around the axons of the brain and spinal cord are damaged and demyelination results. How does multiple sclerosis manifest at the level of the action potential?

Action potentials move more slowly along the axon.

Which of the following statements about the stimulation of muscle cells is true?

An action potential in a muscle cell ultimately results in the release of calcium ions into the cell. (An action potential causes T tubules to depolarize, which stimulates the sarcoplasmic reticulum to release calcium ions into the muscle cell.)

Why is an action potential an all-or-none response to stimuli?

Because voltage-gated ion channels open when membrane potential passes a particular level (If a depolarization shifts the membrane potential sufficiently, the result is a massive change in membrane voltage, called an action potential. Unlike graded potentials, action potentials are an all-or-none response. Action potentials arise because some ion channels in neurons are voltage-gated ion channels, opening or closing when the membrane potential passes a particular level. If a depolarization opens voltage-gated sodium channels, the resulting flow of Na+ into the neuron results in further depolarization. Because the sodium channels are voltage gated, an increased depolarization causes more sodium channels to open, leading to a greater flow of current. The result is a process of positive feedback that triggers a very rapid opening of all voltage-gated sodium channels and the marked change in membrane potential that defines an action potential.)

Identify the role(s) of ATP in muscle contraction.

Binds to myosin to break an actin-myosin cross-bridge Provides the energy to convert myosin to a form that forms a cross-bridge with actin

True or false? Myofibrils are the alternating light-dark units that produce the banded appearance of muscle fibers.

False (Sarcomeres are the alternating light-dark units that produce the banded appearance of myofibrils, which are the strands that make up each muscle fiber.)

What causes the falling phase of the action potential?

Inactivation of voltage-gated sodium channels and the opening of voltage-gated potassium channels (Voltage-gated sodium channels inactivate soon after opening, halting Na+ inflow, and most voltage-gated potassium channels open, causing a rapid outflow of K+. Both events combine to cause the falling phase of the action potential.)

A patient is hospitalized with muscle spasms caused by failure of back muscles to relax after contraction. Which of the following would most likely help the back muscles relax?

Inject a drug that induces tropomyosin and troponin to bind to the myosin-binding sites on actin. (Ca--contaction, depolarization--contraction)

How does cardiac muscle differ from the other types of muscle?

It contains branched cells.

The activity of the sodium-potassium pump results in the movement of which ions across the plasma membrane?

It pumps sodium ions out of the cell and potassium ions into the cell.

Which of these ions is more abundant in the interior of a resting neuron than in the fluid surrounding the neuron?

K+

In a neuron, when voltage-gated K+ ion channels are open...

K+ ions flow out of the cell and the membrane becomes hyperpolarized

The plasma membrane of a neuron has voltage-gated sodium and potassium channels. What is the effect of membrane depolarization on these channels?

Membrane depolarization first opens sodium channels and then opens potassium channels. (Membrane depolarization opens both types of channels, but they respond independently and sequentially. Sodium channels open first, initiating the action potential. As the action potential proceeds, the sodium channels become inactivated and remain inactivated until after the membrane returns to the resting potential and the channels close. Potassium channels open more slowly than sodium channels but remain open and functional throughout the action potential.)

The venom of some cobras contains a mixture of substances that have a variety of physiological effects. One substance in the venom works by preventing acetylcholine from binding to muscle receptors. Which of the following describes the effect of the venom on the prey of the cobra?

Muscle contractions are prevented, causing paralysis.

Which molecules form the thick filaments of sarcomeres?

Myosin

Which of the following interactions is the molecular basis of muscle contraction?

Myosin and thin filaments.

In a neuron, when voltage-gated Na+ ion channels are open...

Na+ ions flow into the cell and the membrane becomes depolarized

A diamond-back rattlesnake (Crotalus atrox) alerts enemies to its presence with a rattle−−a set of modified scales at the tip of its tail. Complete the paragraph about the roles of gated ion channels in initiating and moving a signal along the nerve from the snake's head to its tail and then to the muscle that shakes the rattle. Match the words in the left column to the appropriate blanks in the sentences on the right.

Nerve impulses called action potentials are propagated along axons by voltage-gated channels. The opening of sodium channels initiates the action potential, whereas the inactivation of sodium channels and opening of potassium channels returns the membrane potential toward the resting potential. Signaling across synapses of the vertebrate neuromuscular junction, where axon terminals transmit signals that cause muscle contraction, is mediated by ligand-gated channels.

Why are action potentials conducted usually in one direction along an axon?

The brief refractory period prevents reopening of voltage-gated sodium channels.

Identify the correct statement(s) about the resting membrane potential of a cell.

Potassium (K+) and sodium (Na+) gradients are maintained by active transport in a resting mammalian neuron. Concentration gradients of potassium (K+) and sodium (Na+) across the plasma membrane represent potential energy. (All living cells have a resting membrane potential, caused by ions that are unequally distributed between the interior of cells and the fluid that surrounds them. In mammalian neurons, the concentration of K+ is highest inside the cell, whereas the concentration of Na+ is highest outside. Na+ and K+ gradients are maintained by sodium-potassium pumps in the plasma membrane. These ion pumps use the energy of ATP hydrolysis to actively transport Na+ out of the cell and K+ into the cell. The concentration gradients of K+ and Na+ across the plasma membrane represent a chemical form of potential energy.)

Which muscle type is involved in the function of the digestive tract and blood vessels?

Smooth.

A researcher uses the chemical inhibitor cyanide to reduce ATP production in a neuron. What would be one effect of preventing ATP production?

The "resting" distribution of potassium and sodium ions would be altered.

Which of the following best explains the observation that a resting neuron membrane, while highly permeable to potassium ions, is not at the equilibrium potential for potassium?

The membrane is also slightly permeable to sodium ions.

If you experimentally increase the concentration of K+ inside a cell while maintaining other ion concentrations as they were, what would happen to the cell's membrane potential?

The membrane potential would become less negative.

If you experimentally increase the concentration of Na+ outside a cell while maintaining other ion concentrations as they were, what would happen to the cell's membrane potential?

The membrane potential would become more negative.

Which step constitutes the power stroke of muscle contraction?

The phosphate ion is released, and the myosin head moves back to its original position. (The power stroke occurs when the myosin head pivots, causing the actin filament to slide past the myosin filaments.)

Acetylcholine released into the junction between a motor neuron and a skeletal muscle binds to a sodium/potassium channel and opens it. This is an example of ________.

a ligand-gated channel

Which of these causes the release of neurotransmitter molecules?

an action potential reaching the end of the axon (When an action potential reaches the end of an axon, vesicles fuse with the plasma membrane and release neurotransmitter into the synaptic cleft.)

During the contraction of a vertebrate skeletal muscle fiber, calcium ions ____.

are released through passive transport from the sarcoplasmic reticulum to the cytosol

An action potential moves along a(n) _____.

axon (An axon is the only portion of a neuron capable of generating an action potential.)

A nerve is a collection of ________.

axons

If the membrane potential of a neuron decreases, the membrane potential _____.

becomes less negative. (The membrane potential measures the difference in the electrical potential (voltage) across the neuron's plasma membrane. When the membrane potential of a neuron decreases, the negative value of the electrical potential across the plasma membrane is reduced and the membrane potential becomes more positive)

The release of _____ ions from the sarcoplasmic reticulum is required for skeletal muscle contraction.

calcium (Calcium ions interact with proteins on the thin filament, resulting in the exposure of the myosin-binding sites on the actin.)

According to the sliding filament model, binding sites on actin open when ____.

calcium ion levels rise

Muscle relaxation occurs when ____.

calcium ions are actively transported into the sarcoplasmic reticulum

The information-receiving section of a neuron is its __________.

cell body and dendrites (Together with the cell body, the dendrites receive signals from other neurons.)

Of these choices, neuronal communication between the brain and the muscles of the leg is best conceptualized as __________.

electrical and chemical signaling (A neuron propagates action potentials as a consequence of ion movements across its membranes (the electrical part), but it also requires chemical signaling at its synapses, via neurotransmitters, to be able to function properly.)

After a hurricane damages a coral reef, some sea anemones are broken apart. Several pieces from one anemone regenerate lost body parts and grow and develop into three complete anemones. Which type of reproduction is represented in this example?

fragmentation

The simultaneous arrival of a graded depolarization and a graded hyperpolarization of equal but opposite magnitude at a particular location on the dendritic membrane is likely to __________.

have no effect, since the depolarization and hyperpolarization will cancel each other out (Grade potentials are summable, so a depolarization and a hyperpolarization can offset each other to make it appear that there were no changes in membrane potential at that location.)

Which of the following is expected in a neuron that is receiving input through tens of thousands of synapses?

highly branched dendrites

Neurotransmitters categorized as inhibitory are expected to ________.

hyperpolarize the membrane

Some neurotransmitters are categorized as inhibitory, and they would be expected to ____.

hyperpolarize the membrane

In which of the following locations would we expect to find the release of neurotransmitter molecules?

in a chemical synapse

In exocytosis, dissolved materials move from fluid

in vesicles to fluid outside of cells. (In exocytosis, the fusion of vesicles with the plasma membrane releases vesicle contents outside of the cell.)

What type of neurons is responsible for the interpretation of sensory input?

interneurons

Gated ion channels

ion channels that open or close in response to stimuli (When gated ion channels are open, they enable ions to diffuse across a membrane. These channels open and close in response to stimuli and are often found at the cell surface.)

Many aphid species switch between asexual and sexual reproduction. Which of the following is only used during sexual reproduction?

meiosis

Action potentials move along axons ________.

more rapidly in myelinated than in unmyelinated axons

Which of the following generates the force of contraction of skeletal muscle cells?

myosin heads bind to actin and transition from a high-energy to a low-energy state (#1: Myosin head binds to actin filament. #2: when ATP binds to myosin and undergoes hydrolysis--it is putting in a high energy state. Then when it binds to actin, it moves to a low energy state)

The transmission first triggers the _____.

opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron (As a result of the inward flux of sodium ions, that region of the neuron depolarizes.)

You feel something touch your arm, think it might be a fly, and you extend your arm to scare it away. In which order is the information about the touch processed?

sensory input, integration, and motor output

A stimulus has opened the voltage-gated sodium channels in an area of a neuron's plasma membrane. As a result, _____ rushes into the neuron and diffuses to adjacent areas; this in turn results in the _____ in the adjacent areas.

sodium ... opening of voltage-gated sodium channels

The space between an axon of one neuron and the dendrite of another neuron is called a(n) _____.

synaptic cleft

Neurons store neurotransmitter molecules in vesicles located within _____.

synaptic terminals

A neuron just beginning an action potential is said to undergo a depolarization phase, meaning __________.

the cell is highly polarized at rest and becomes less so during the initial phase of the action potential (The inward movement of sodium ions, with their positive charges, makes the inside of the neuron suddenly less negative, relative to the cytosol, than it was at rest.)

The muscles of a recently deceased human can remain in a contracted state, termed rigor mortis, for several hours. What prevents the muscles from relaxing soon after death?

the depletion of ATP required to break actin-myosin bonds

At rest, which of these plays a role in establishing the charge differential across a neuron's plasma membrane?

the sodium-potassium pump moving sodium ions out of the neuron and potassium ions into the neuron (The sodium-potassium pump moves more sodium ions out of the cell than potassium ions into the cell; this net loss of positive ions establishes a charge differential across the plasma membrane.)

Myosin heads bind to _____, which they then pull and cause to slide toward the center of the sarcomere.

thin filaments (Myosin heads bind to thin filaments, release their bound ADP and phosphate, and bend, sliding the thin filaments toward the center of the sarcomere.)

In relaxed muscle, the myosin-binding site on actin is blocked by ____.

tropomyosin

The sodium-potassium pump in the plasma membrane of cells

uses chemical energy to generate chemical gradients. (The sodium-potassium pump uses energy released in ATP hydrolysis to transport both Na+Na+ and K+K+ against their concentration gradients. Three Na+Na+ ions are moved out of the cell for every two K+K+ ions that are pumped in.)

After the depolarization phase of an action potential, the resting potential is restored by ________.

voltage-gated potassium channels opening and sodium channels inactivating