Biol Lecture Exam 4

What is the resting membrane potential for most neurons?

-70 mV

Place the events that occur during excitation-contraction coupling in the correct order from left to right

1. AP propagates along sarcolemma 2. AP travels down T tubules to triads 3. Voltage-sensitive proteins open Ca2+ channels 4. Sarcoplasmic reticulum releases Ca2+ 5. Ca2+ levels in sarcoplasm increase

Arrange the steps of the contraction cycle in the correct order from left to right.

1. Calcium ions arrive within the zone of overlap. 2. Calcium ions bind to troponin. Active sites on actin are exposed. 3. The myosin heads bind to active sites on actin. 4. The myosin head pivots (power stroke). ADP and P are released. 5. ATP binds to the myosin head. 6. The free myosin head "recocks." ADP and P are released.

Place the events involved in the propagation of an action potential in the correct order of occurrence from left to right.

1. Local current flows to axon segment 2. Axon segment depolarized to threshold 3. Voltage-gated Na+channels open 4. Influx of Na+ 5. AP regenerated inadjacent axon segment

Place the steps that occur during a single cross bridge cycle in the correct order from left to right.

1. The activated myosin head binds to actin,forming a cross bridge. 2. ADP is released and myosin slides the thin filament toward the center of the sarcomere. 3. ATP binds to the myosin head and detaches it from actin. 4. ATP is hydrolyzed to ADP and Pi and the energy released re-cocks the myosin head.

Place the events involved in generation of an action potential in the correct order of occurrence from left to right.

1. Threshold stimulus Na+ channels open 2. Na+ influx Depolarization 3. Na+ channels close K+ channels open 4. K+ efflux Repolarization 5. Hyperpolarization K+ channels close

What is the magnitude (amplitude) of an action potential?

100 mV

The Na-K ion exchange pump actively transports

3 intracellular sodium ions for 2 extracellular potassium ions.

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?

A myosin head bound to actin

A triad is composed of a T-tubule and two adjacent terminal cisternae of the sarcoplasmic reticulum. How are these components connected?

A series of proteins that control calcium release.

Which statement is true regarding the resting potential?

A typical neuron has a resting potential of approximately -70 mV.

A two-second duration of isometric tetanic contraction is supported by which energy source alone?

ATP

The muscle tissue in the meat would probably not become stiff after death if it still had enough

ATP

Which of the following molecules is NOT thought to accumulate during muscle fatigue?

ATP

After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?

ATP binds to the myosin head.

Describe the all-or-none principle

All stimuli that bring the membrane to threshold will generate identical action potentials.

What causes the release of calcium ions into the sarcoplasm from the terminal cisterns?

An action potential traveling along the t tubule

How is an action potential propagated along an axon?

An influx of sodium ions from the current action potential depolarizes the adjacent area.

________ neurons are short, with a cell body between dendrite and axon, and occur in special sense organs.

Bipolar

The cross bridge cycle starts when _________.

Ca2+ from the sarcoplasmic reticulum binds to troponin

Which of the following is responsible for muscle relaxation?

Calcium ions are removed from the sarcoplasm by active transport.

Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?

Calcium ions are stored in the sarcoplasmic reticulum.

What event initiates the contraction cycle?

Calcium ions arrive within the zone of overlap.

What specific event triggers the uncovering of the myosin binding site on actin?

Calcium ions bind to troponin and change its shape.

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?

Calcium ions.

Which of the following occurs during the relaxation phase of a muscle twitch?

Calcium levels are falling in the sarcomeres.

Excitation of the sarcolemma is coupled or linked to the contraction of a skeletal muscle fiber. What specific event initiates the contraction?

Calcium release from the sarcoplasmic reticulum initiates the contraction.

________ channels open or close in response to binding specific molecules.

Chemically gated

contrast fast fibers with slow fibers in terms of diameter, glycogen reserves, myoglobin content, and relative abundance of mitochondria.

Compared with slow fibers, fast fibers have a larger diameter, larger glycogen reserves, less myoglobin, and relatively fewer mitochondria.

Compare concentric and eccentric contractions.

Concentric contractions occur when the muscle tension exceeds the load, and the muscle shortens. Eccentric contractions occur when the muscle tension is less than the load, and the muscle elongates.

Which of the following situations delay the development of muscle fatigue the longest?

Consistent interruptions of muscle stimulation

When does cross bridge cycling end?

Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.

Rank the sequence of events in excitation-contraction coupling from first to last. Do not overlap any events.

Depolarization of the junctional folds triggers an action potential. Action potential travels along the sarcolemma. Action potential along the T tubules opens calcium channels. Calcium ions flood the sarcoplasm. Calcium ions bind to troponin. Troponinchangesshape. Tropomyosin moves off of actin binding sites. Myosin heads form cross bridges with actin.

Compare the absolute refractory period with the relative refractory period.

During the absolute refractory period the membrane cannot respond to further stimulation. During the relative refractory period the membrane can respond only to a larger-than-normal stimulus.

Which of the following is correct regarding muscle fatigue and recovery?

During the recovery period, lactate can be recycled back to pyruvate.

Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. The term excitation refers to which step in the process?

Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.

Which of the following is NOT a role of ATP in muscle contraction?

Exposing myosin binding sites on actin

Which of the following statements is/are not true regarding human muscles?

Fast fibers are high in myoglobin.

Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products?

Glycolysis

Define graded potential.

Graded potential is a temporary, localized change in the potential of a cell.

Which of the following is defined as a graded hyperpolarization of the postsynaptic membrane?

IPSP

Which statement regarding information processing is true?

Information is relayed in the form of action potentials.

Where do most action potentials originate?

Initial segment

________ monitor the internal environment.

Interoceptors

Which of the following processes produces 36 ATP?

Krebs cycle and oxidative phosphorylation

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel?

Leak channels

________ channels open or close in response to physical distortion of the membrane surface.

Mechanically gated

Define membrane potential

Membrane potential is the unequal charge distribution between the inner and outer surfaces of the plasma membrane.

Neurons and ________ have electrically excitable membranes that propagate action potentials.

Muscle Cells

Define muscle hypertrophy and muscle atrophy.

Muscle hypertrophy is an increase in the size of the muscle cells and muscle atrophy is a decrease in the size of the muscle cells.

What chemical changes most likely happen during aging to make meat regain its tenderness?

Myofilaments decompose and break down

In an undisturbed cell, which of the following can diffuse through leak channels?

Na+ and K+

What prevents the Na+ and K+ gradients from dissipating?

Na+-K+ ATPase (the pump)

Clusters of RER and free ribosomes in neurons are called

Nissl bodies

The tiny gaps between adjacent Schwann cells are called

Nodes

What characterizes repolarization, the second phase of the action potential?

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV. Submit

Define oxygen debt (excess postexercise oxygen consumption)

Oxygen debt is the amount of oxygen intake required to produce the ATP needed to restore the body after strenuous activity.

What produces the brief hyperpolarization during the action potential?

Potassium ions continue to leave the cell until all the potassium channels have closed.

__________ monitor the position and movement of skeletal muscles and joints.

Proprioceptors

The "rest and recovery" period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________.

Pyruvic acid is converted back to lactic acid.

Prior to the death of the cow that the meat came from, the living skeletal muscle cells used energy (hydrolyzed ATP) in order to

Reactivate myosin heads

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?

Resting membrane potential (RMP)

Define resting membrane potential.

Resting membrane potential is the membrane potential of an unstimulated cell.

What structure is the functional unit of contraction in a skeletal muscle fiber?

Sarcomere

Which glial cells are found only in the PNS?

Schwann cells

Which description is correct?

Spatial summation involves multiple synapses that are active simultaneously.

Axons terminate in a series of fine extensions known as

Telodendria

Why does the action potential only move away from the cell body?

The areas that have had the action potential are refractory to a new action potential.

What is the first step in Wallerian degeneration?

The axon and myelin degenerate and fragment.

Puffer fish poison blocks voltage-gated sodium channels like a cork. What effect would this neurotoxin have on the function of neurons?

The axon would be unable to generate action potentials.

What determines the frequency of action potential generation?

The degree of sustained depolarization at the axon hillock determines the frequency of action potentials.

How does the myosin head obtain the energy required for activation?

The energy comes from the hydrolysis of ATP.

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane is much more negatively charged than the outside surface.

What characterizes depolarization, the first phase of the action potential?

The membrane potential changes from a negative value to a positive value.

What event triggers the generation of an action potential?

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

During anaerobic glycolysis, which of the following does not occur?

The mitochondria are required.

What is the result when the zone of overlap is reduced to zero?

The muscle fiber cannot produce any active tension.

Which of the following would occur in a resting membrane after a stimulus is applied?

The opening of sodium channels will cause depolarization.

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

What is the relationship between myelin and the propagation speed of action potentials?

The presence of myelin increases the propagation speed of action potentials.

Which of the following statements about the action potential is false?

The rapid depolarization phase is caused by the entry of potassium ions.

Which occurs in a muscle at moderate levels of activity?

The skeletal muscle relies primarily on the aerobic metabolism of pyruvate to generate ATP.

Which occurs during an eccentric contraction?

The tension developed is less than the load, causing the muscle to lengthen while it is contracted.

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

Which is not true of voltage-gated sodium channels?

They have both an activation gate and an inactivation gate that work dependent of each other.

Why are CNS neurons that are lost to injury or disease seldom replaced?

They lack centrioles

The minimum stimulus required to trigger an action potential is known as the

Threshold

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated?

Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels Submit

What is the first change to occur in response to a threshold stimulus?

Voltage-gated Na+ channels change shape, and their activation gates open.

Regions of the CNS with an abundance of myelinated axons constitute the ________ matter.

White

Can a skeletal muscle contract without shortening? Why or why not?

Yes, because muscles can still contract during an isometric contraction when the muscle tension is equal to the load.

Tetanus is most likely to result from which condition?

a deep puncture wound, such as that from a nail

The velocity of the action potential is fastest in which of the following axons?

a small myelinated axon

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

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?

acetylcholine (ACh)

A myosin head binds to which molecule to form a cross bridge?

actin

Which phase of the contraction cycle directly requires that calcium ions bind to troponin?

active-site exposure

Creatine phosphate

acts as an energy reserve in muscle tissue.

Oligodendrocytes:

are the myelin-producing glial cells in the CNS.

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?

arrival of an action potential

Motor units are activated on a rotating basis to reduce fatigue. What is this mechanism called?

asynchronous motor unit summation

Which part(s) of the neuron can conduct an action potential?

axon and telodendria

Where in the neuron is an action potential initially generated?

axon hillock

Which neuronal structure contains neurofibrils, neurotubules, small vesicles, lysosomes, mitochondria, and various enzymes?

axoplasm

What causes the myosin head to disconnect from actin?

binding of ATP

Name the structural components of a typical neuron.

cell body, axon, and dendrites

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

chemically gated; postsynaptic

Which of the following is matched correctly?

complete tetanus - fused tetanus

Functions of astrocytes include all of the following except

conducting action potentials.

During which phase of a muscle twitch do cross-bridge interactions occur?

contraction phase

What is the type of chemical reaction used to rebuild ADP into ATP?

dehydration synthesis

A shift of the resting transmembrane potential toward 0 mV is called

depolarization

Conduction of an action potential along the sarcolemma depends upon ___________.

diffusion of sodium ions through voltage-gated channels

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

either depolarize or hyperpolarize

Which glial cells form an epithelium that lines a fluid-filled passageway within the spinal cord and brain?

ependymal cells

During muscle fatigue, the ____________ decreases.

force of contraction

During the Cori cycle, in the liver,

glucose is produced from lactate.

In saltatory propagation, a local current produces a(n) __________.

graded depolarization

Regions of the CNS where neuron cell bodies dominate constitute the ________ matter.

grey

In a typical undisturbed cell, the extracellular fluid (ECF) contains high concentrations of sodium ions and chloride ions, whereas the cytosol contains __________.

high concentrations of potassium ions and negatively charged proteins

Chemically gated channels:

include receptors that bind ACh at the neuromuscular junction.

Muscular force can be adjusted to match increased loads by

increasing the frequency of action potentials in motor neurons.

Polio __________.

is a viral disease that attacks motor neurons in the spinal cord and brain

The smallest neuroglia of the CNS that act as phagocytes are the

microglia

During activities requiring aerobic endurance,

most of the muscle's energy is produced in mitochondria.

The most common neurons in the CNS, including the motor neurons that control skeletal muscles, are __________.

multipolar neurons

Continuous propagation __________.

occurs along unmyelinated axons

Rigor mortis __________.

occurs as the sarcoplasmic reticulum deteriorates, releasing calcium ions

Voltage-gated sodium channels are __________.

open at -60 mV

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

presynaptic neuron

The smooth but steady increase in muscular tension that is produced by increasing the number of active motor units is called __________.

recruitment

Extensive damage to oligodendrocytes in the CNS could result in

reduced speed of nerve impulses.

Which phase of a muscle twitch is eliminated in complete tetanus?

relaxation phase

What causes the power stroke?

release of ADP and Pi

Glial cells that surround the neurons in ganglia are

satellite cells

Which division of the PNS brings information to the CNS?

sensory

Hyperpolarization results from __________.

slow closing of voltage-gated K+ channels

The ________ nervous system controls the skeletal muscles.

somatic

Which nervous system component controls skeletal muscle contractions?

somatic nervous system

The buildup of depolarization when EPSPs arrive at several places on the neuron is called ________ summation.

spatial

If the chemically gated sodium channels in the postsynaptic membrane were completely blocked,

synaptic transmission would fail.

In neuromuscular junctions (NMJs):

the cytoplasm of the synaptic terminal contains vesicles filled with molecules of acetylcholine.

The repolarization phase of an action potential results from __________.

the opening of voltage-gated K+ channels

What is name given to the regularly spaced infoldings of the sarcolemma?

transverse or T tubules

The binding of calcium to which molecule causes the myosin binding sites to be exposed?

troponin

Most sensory neurons of the PNS are of which type?

unipolar neurons

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

voltage-gated Ca2+ channels

Which type of membrane channels are found in axons?

voltage-gated Na+ and K+ channels

The depolarization phase of an action potential results from the opening of which channels?

voltage-gated Na+ channels

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?

voltage-gated calcium channels

The generation of an action potential in a neuron requires the presence what type of membrane channels?

voltage-gated channels

Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?

white fast twitch fibers