A & P Ch 9 Muscles and Muscle Tissue
A more negative RMP would result.
Cl− is a common, negatively charged extracellular ion. Predict the effect on the RMP if many Cl− gated channels are suddenly opened.
Fast (glycolytic), fatigue-resistant fibers
Contain abundant amounts of glycogen.
tone Muscle tone is a state of partial, sustained contraction in a muscle that results from tetanic contraction of about 10% of the muscle fibers on a rotating basis.
Continued mild or partial contraction of a muscle that keeps it healthy and ready to respond is known as muscle __________.
Bundles of axons are called tracts in the CNS and nerves in the PNS
Difference between tracts and nerves
Myosin head form cross bridge with actin
First step in the sequence of cross bridge cycling is
What would happen if acetylcholine was not removed from the synaptic cleft?
Multiple action potentials would occur in the muscle fiber.
Myosin head is re-energized
fifth step in the sequence of cross bridge cycle
calcium ion concentration decreases below the threshold
seventh step in the sequence of cross bridge cycle
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
troponin
both the electrical and chemical gradients
During depolarization, which gradient(s) move(s) Na+ into the cell?
1) Glycogen is synthesized from glucose molecules. 2) Oxygen rebinds to myoglobin. 3) ATP is used to rephosphorylate creatine into creatine phosphate.
"rest and recovery" period, where the muscle restores depleted reserves, includes
Which of the following statements describes a critical event that occurs at the neuromuscular junction? 1) When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal. 2) Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein. 3) Acetylcholine is released by axon terminals of the motor neuron. 4) Acetylcholine is released and moves across the synaptic cleft bound to a transport protein.
3) Acetylcholine is released by axon terminals of the motor neuron. this is a critical even that occurs at the nueromuscular junction.
A band.
5. The myosin filaments are located in the
Voltage-gated Ca2+ channels
An action potential releases neurotransmitter from a neuron by opening which of the following channels?
The myosin filaments are located in the
A band
eccentric muscle contraction
A contraction in which the muscle lengthens as it contracts
motor unit
A group of muscle fibers innervated by a single neuron is called a
action potential
A long-distance electrical signal transmitted along an axon. Also called a nerve impulse.
motor unit
A motor neuron along with all the muscle fibers it supplies is called a(n) __________.
What is a cross bridge?
A myosin head bound to actin
Slow (oxidative), fatigue-resistant fibers
A relatively high percentage are found in successful marathon runners
Z discs
A sarcomere is the distance between two
motor neurons
A single nerve cell that extends from the brain or spinal cord to a muscle or gland and carries movement instructions to muscle.
Acetylcholine receptors
A type of chemically-gated ion channel located on the junctional folds of the neuromuscular junction.
storing energy that will be transferred to ADP to resynthesize
ATP Creatine phosphate functions in the muscle cell by ________.
Slow (oxidative), fatigue-resistant fibers
Abundant in muscles used to maintain posture.
Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?
Acetylcholine is degraded by acetylcholinesterase.
Chemically gated Na+-K+ channels
Acetylcholine receptors are best characterized as what type of channel?
acetylcholinesterase breaks apart the ACh
After nervous stimulation stops, what prevents ACh in the synaptic cleft from continuing to stimulate contraction?
contractility ---> does not refer to the ability to receive and respond responsiveness --> yes irritability --> yes excitability --> yes
All of the following terms refer to the ability to receive and respond to a stimulus EXCEPT __________. contractility responsiveness irritability excitability
Na+ permeability
Although it plays a role, it is not a primary determinant of the resting membrane potential
the generation of local currents
An action potential in one segment of axon causes adjacent sections of axon membrane to reach threshold through what mechanism?
depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment
An action potential is self-regenerating because __________.
glycolysis
An anaerobic metabolic pathway that results in the production of two net ATPs per glucose plus two pyruvic acid molecules is ________.
Epimysium (fascia)
An entire skeletal muscle is surrounded by __________.
produce movement through contractile force
Approximately 80% of a muscle fiber's volume are the myofibrils. This characteristic reflects muscles ability to ________.
Dendrites
Are chemically gated
The muscle tissues would never be able to relax.
Based on what you know of the relationship between the thick and the thin filaments, what would happen if a disorder existed that caused a person to produce no tropomyosin?
either depolarize or hyperpolarize
Binding of the neurotransmitter to its receptor causes the membrane to __________.
A type of graded potential
Both EPSP and IPSP
A band.
Both actin and myosin are found in the______
Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium ions.
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.
Neuron
Cell of the nervous system specialized to generate and transmit electrical signals or action potentials.
Neurotransmitters
Chemical messengers usually released from synaptic vesicles in neuron axon terminals that communicate with target cells.
Slow (oxidative), fatigue-resistant fibers
Depends on oxygen delivery and aerobic mechanisms.
The previous axonal segment is in the refractory period.
During action potential propagation in an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction? a) The extracellular sodium concentration is too low around the previous axonal segment for an action potential to be (re)generated. b) Positive charges only move in one direction after they enter the cell. c) New action potential generation near the soma repels previously generated action potentials, causing them to always propagate away from the soma. d) The previous axonal segment is in the refractory period.
Na+ is entering the cell. During the depolarization phase of the action potential, open Na+ channels allow Na+ ions to diffuse into the cell. This inward movement of positive charge makes the membrane potential more positive (less negative). The depolarization phase is a positive feedback cycle where open Na+ channels cause depolarization, which in turn causes more voltage-gated Na+ channels to open.
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? a) K+ is exiting the cell. b) Na+ is exiting the cell. c) K+ is entering the cell. d) Na+ is entering the cell.
K+ channels close. Na+ channels go from an inactivated state to a closed state.
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? a) K+ channels close. Leakage channels open. b) K+ channels open. Na+ channels inactivate. c) K+ channels close. Na+ channels go from an inactivated state to a closed state. d) K+ channels close. Na+ channels open.
The sarcoplasmic reticulum releases calcium.
During the phase of excitation-contraction coupling of skeletal muscle, what occurs immediately after the action potential spreads down the T tubule?
decreases in length
During the sliding filament mechanism of sarcomere shortening length the H ZONE
A BAND has no change in length
During the sliding filament mechanism of sarcomere shortening length the length of A BAND
I BAND decreases in length or distance
During the sliding filament mechanism of sarcomere shortening length the length of I BAND
Z DISC decreases in length or distance
During the sliding filament mechanism of sarcomere shortening length the length the distance between Z DISC
The thick and Thin filament have no change in length or distance
During the sliding filament mechanism of sarcomere shortening length the of thick and thin filament
May produce an action potential and the Membrane potential becomes more positive
EPSP
neuromuscular junction As a rule, each muscle fiber has only one neuromuscular junction. The axon of each motor neuron divides as it enters the muscle, and each of these axonal endings forms a branching neuromuscular junction with a single muscle fiber.
Each skeletal muscle fiber is controlled by a neuron at a single __________.
When does cross bridge cycling end?
Ends when sufficient calcium has been actively transported back into the sarcopasmic reitculum to allow calcium to unbind from troponin
The term excitation refers to which step in the Excitation-contraction coupling process
Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
More Positive: Triple the number of Na+ leak channels --Double the concentration of K+ outside the cell More Negative: Double the number of K+ leak channels -- Decrease the concentration of Na+ outside the cell Largely unchanged: Double the number of closed channels for K+ -- Double the size of the cell, without adding channels
For each of the following, indicate whether the condition will cause the membrane potential to become more positive, more negative, or largely unchanged when compared to the normal physiological resting membrane potential.
cross bridge detach from actin binding sites
Forth Step in the sequence of cross bridge cycle
Properly controlled skeletal muscle contractions produced by changing the frequency of stimulation and the strength of stimulation .
Graded muscle responses are:
Fast (oxidative), fatigue-resistant fibers
Have very fast-acting myosin ATPases and depend upon aerobic metabolism during contraction.
The bonds between the globular heads of thick filaments (myosin) and the globular protein actin are responsible for the formation of cross bridges between the thick and thin filaments.
How are cross bridges formed?
The inward diffusion of sodium ions, through acetylcholine receptors, depolarizes the sarcolemma. Potassium also diffuses through acetylcholine receptors, but less potassium diffuses than sodium, and the outward movement of potassium is not depolarizing.rize the sarcolemma?
How does sodium depolarize the sarcolemma?
through phosphorylation by: Creatine phosphate anaerobic glycolysis Aerobic respiration
How is ATP replenished?
An action potential in the motor neuron causes ACh to be released into the synaptic cleft. Binding of ACh to sarcolemma receptors initiates graded potentials
How is an action potential generated at the neuromuscular junction (NMJ) is converted to excitation in the muscle fiber?
slow closing of voltage-gated K+ channels
Hyperpolarization results from __________. A. fast closing of voltage-gated K+ channels B. slow closing of voltage-gated K+ channels C. slow closing of voltage-gated Na+ channels
The resting membrane potential would become less negative (more positive).
Hypothetically, what would be the most immediate effect of doubling the number of Na+ leakage channels in the plasma membrane?
Influx of negative ions and Membrane potential moves away from threshold
IPSP
b. Ca++ binds to troponin. d. Troponin removes tropomyosin from G actin. f. Myosin binds to actin. a. Myosin generates a power stroke. e. The sarcomere shortens. c. ATP recharges the myosin head.
Identify the correct sequence of the following events. a. Myosin generates a power stroke. b. Ca++ binds to troponin. c. ATP recharges the myosin head. d. Troponin removes tropomyosin from G actin. e. The sarcomere shortens. f. Myosin binds to actin.
ACh released; binds to receptors on sarcolemma
Identify the step in the phases leading to muscle fiber contraction indicated by "A."
motor neuron stimulates muscle fiber
Identify the step in the phases leading to muscle fiber contraction indicated by "B."
Local depolarization (end plate potential) ignites AP in sarcolemma
Identify the step in the phases leading to muscle fiber contraction indicated by "C."
Excitation-contraction coupling occurs
Identify the step in the phases leading to muscle fiber contraction indicated by "D."
The muscle length will not change during contraction
If a muscle is applied to a load that exceeds the muscle's maximum tension, __________.
the receiving neuron is less likely to generate an action potential.
If a signal from a sending neuron makes the receiving neuron more negative inside
the electrical gradient for K+ and the concentration gradient for K+
Imagine you changed the concentration of K+ outside a neuron such that the resting membrane potential changed to -80 mV (from the normal resting value of -70 mV). What have you changed?
decreased synthesis of muscle proteins and/or increased breakdown of muscle proteins
In a bedridden patient recovering from a badly fractured femur, disuse atrophy in the thigh muscles is caused by _________.
acetylcholine (ACh)
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
varicosities
In smooth muscle, neurotransmitter is released
Myosin
In the sliding filament model of muscle contraction, the myofilaments slide over each other, resulting in the overlapping of actin and __________.
Graded potentials originating in the dendrites and cell body are integrated (summated) at the axon hillock (C). Membrane potentials above threshold at the hillock will open voltage-gated Na+ channels found in the "trigger zone," producing an action potential that proceeds down the axon.
In which area of the neuron is the action potential generated?
During the period of relaxation, Ca2+ is transported by active transport into the SR. Decreased Ca2+ concentrations in the sarcoplasm leads to detachment of cross bridges and, consequently, decreased contractile force.
In which phase would the net movement of Ca2+ INTO the sarcoplasmic reticulum (SR) be greatest?
Propagation of the action potential
Increased positive charge inside sarcolemma changes permeability of adjacent areas, opening voltage-regulated Na+ channels
chemical gated channels
Ion channel stimulated to open by binding with a chemical ligand.
voltage-gated ion channels
Ion channel that is stimulated to open or close by changes in voltage across the plasma membrane.
out; in
Let's consider a scenario in which the resting membrane potential changes from −70 mV to +70 mV, but the concentrations of all ions in the intracellular and extracellular fluids are unchanged. Predict how this change in membrane potential affects the movement of Na+. The electrical gradient for Na+ would tend to move Na+ __________ while the chemical gradient for Na+ would tend to move Na+ __________.
Synaptic vesicles are
Membranous organelles containing neurotransmitter substances; found within the axon terminals of neurons.
What level of structural organization does the actin and myosin in a sarcomere of a muscle fiber represent?
Molecular
Almost all interneurons are multipolar
Most interneurons are confined within the CNS. They make up over 99% of the neurons of the body, including most of those in the CNS.
isometric contraction
Muscle contraction in which the muscle fibers produce increased tension although the muscle neither shortens nor lengthens is called __________.
isometric contraction
Muscle contracts but there is no movement, muscle stays the same length
sarcomeres
Myofibrils are composed of repeating contractile elements called __________.
BMD (2,3-butanedione 2-monoximime) inhibits myosin, such that ATP can bind to myosin but myosin is unable to hydrolyze the bound ATP. What effect would BMD have on the cross bridge cycle?
Myosin heads would remain detached, unable to cock.
voltage-gated sodium channels.
Outside the junctional folds, the sarcolemma contains
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes?
Release of acetylcholine from the synaptic vesicles
between 2 and 3
Rigor mortis occurs when there is a lack of ATP. Where would it happen?
power stroke moves thin filament
Second step in the sequence of cross bridge cycle
Sodium channels are open and potassium channels are closed
Select the correct description of the voltage-gated ion channels for a region of sarcolemma that is undergoing depolarization.
1. Threshold stimulates Na+ channels to open 2) Na+ influx depolarization 3) Na+ channels close and K+ channels open 4) K+ efflux repolarization 5) Hyperpolarization K+channels close
Sequence of Returning to resting state
Red fibers, the smallest of the fiber types.
Slow (oxidative), fatigue-resistant fibers
mitochondria, cytoskeletal elements, membrane components used to renew the axon plasma membrane, and enzymes needed to synthesize certain neurotransmitter
Substances moved in the anterograde direction include
neuromuscular junction (NMJ)
Synapse or junction between a motor neuron and skeletal muscle fiber.
Calcium entry into the axon terminal triggers which of the following events?
Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine via exocytosis
The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time. open Na+ channels inevitably inactivate regardless of whether K+ channels open or not. This means that the depolarization phase of the action potential stops on its own. Once Na+ channels inactivate, the membrane potential is set by other open channels. If voltage-gated K+ channels are blocked by TEA, then the membrane will be (slowly) set, by leakage channels, to the resting membrane potential.
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 fail. Once the voltage reached threshold, it would return to the resting membrane potential. The membrane would depolarize as usual but then stay at that depolarized voltage (about +30 mV). The action potential would depolarize as usual, but the repolarization phase would take longer, causing the action potential to be more broad in time. The membrane would depolarize and repolarize as usual, but no hyperpolarization beyond (more negative to) the resting membrane potential would occur.
Na+ is pumped out of the cell and K+ is pumped into the cell.
The Na+-K+ pump actively transports both sodium and potassium ions across the membrane to compensate for their constant leakage. In which direction is each ion pumped?
Sarcomere
The __________ shorten(s) during muscle contraction
I band
The __________contains only the actin filaments.
Peristalsis
The alternating contraction and relaxation of opposing layers of smooth muscle is referred to as __________.
Na+ and Cl-
The concentrations of which two ions are highest outside the cell.
Tendon
The connective tissue that covers structure A is continuous with which of the following?
Sarcomere
The contractile, or functional, unit of a muscle fiber is __________.
sarcomere, which is the smallest contractile unit of a skeletal muscle fiber.
The functional unit of contraction in a skeletal muscle fiber is the __________.
Na+ (sodium ions)
The diffusion of what ion, across the neuronal membrane, is responsible for the local currents that depolarize regions of the axon to threshold?
axon terminal
The enlarged, distal end of an axon; contains a neurotransmitter substance within synaptic vesicles.
an increase in intracellular calcium ion levels
The final "go" signal for skeletal muscle contraction is __________.
junctional folds of sarcolemma
The folded portion of the sarcolemma in close contact with the synaptic ending of the axon terminal.
Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?
The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
troponin; calcium ions
The interaction between which protein and ion initiates muscle coupling?
voltage-gated calcium channels
The membrane of the axon terminal contains
Depolarize
The membrane potential is becoming more positive than the resting membrane potential.
Hyperpolarize
The membrane potential is more negative than the resting membrane potential.
Repolarize
The membrane potential is moving from a more positive value toward resting membrane potential.
K+, Na+
The membranes of neurons at rest are very permeable to _____ but only slightly permeable to _____.
aerobic respiration
The most efficient means of producing ATP for muscle contraction is __________.
moves 3 Na+ to the ECF and 2 K+ to the cytoplasm
The operation of the Na+−K+ ATPase pump __________.
There are many more K+ leak channels than Na+ leak channels in the plasma membrane.
The plasma membrane is much more permeable to K+ than to Na+. Why?
K+ permeability
The primary determinant of the resting membrane potential
repolarization phase
The refractory period in which the muscle will NOT contract if stimulated occurs during __________ of the muscle cell.
sarcomere
The region of a myofibril between two successive Z discs; it primarily consists of thin and thick myofilaments.
K+ ions leaving the cell through voltage-gated channels The opening of voltage-gated K+ channels allows K+ ions to exit the cell, repolarizing the membrane. In other words, the exit of K+ ions makes the membrane potential more negative. K+ also exits through leakage channels during this phase because leakage channels are always active. However, most of the membrane permeability to K+ during this phase is due to voltage-gated channels. Voltage-gated K+ channels make the action potential more brief than it would otherwise be if only leakage channels were available to repolarize the membrane.
The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________. a) Na+ ions leaving the cell through voltage-gated channels b) K+ ions leaving the cell through voltage-gated channels c) Na+ ions transported out of the cell by the Na+-K+ pump d) K+ ions entering the cell through voltage-gated channels
The presence of concentration gradients and leak channels
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.
Action Potential (AP)
The sequence of electrical changes that occurs along the sarcolemma when a muscle fiber is stimulated is known as the __________.
actin and myosin sliding past each other and partially overlapping
The sliding filament model of contraction involves ________.
1 and 7
The smallest contractile unit within skeletal muscle would correspond to the distance between which two points in the figure?
synaptic cleft (synapse)
The space between the axon terminal and the membrane of the target cell.
Myosin
The thicker filaments are the __________ filaments.
Actin
The thin myofilaments of skeletal muscle are composed chiefly of __________.
Skeletal muscle
muscle that has peripherally located nuclei and has rapid and forceful contractions.
ATP attaches to myosin head
Third step in the sequence of cross bridge cycle
How does troponin facilitate cross bridge formation?
Troponin controls the position of tropomyosin on the thin filament, enabling myosin heads to bind to the active sites on actin.
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.
organs in the ventral body cavity to the CNS.
Visceral sensory (afferent) fibers carry information from the
The first part, the electrical gradient, is a consequence of the membrane potential. For negative membrane potential values, positively-charged ions (like K+ and Na+) tend to enter the cell. The second part, the concentration gradient, is the tendency of ions to diffuse from a region of high concentration to a region of low concentration. The electrochemical gradient determines the net movement of ions across the plasma membrane.
What are the two parts of an ion's electrochemical gradient
calmodulin
What binds calcium ions in a smooth muscle, causing contraction?
Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open.
What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization? a) Activation gates of voltage-gated Na+ channels close, while inactivation gates of voltage-gated K+ channels open. b) Activation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open. c) Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open. d) Inactivation gates of voltage-gated Na+ channels close, while inactivation gates of voltage-gated K+ channels open.
b) the membrane potential changes from a negative value to a positive value.
What characterizes depolarization, the first phase of the action potential? a) The membrane potential changes to a less negative (but not a positive) value. b) The membrane potential changes from a negative value to a positive value. c) The membrane potential reaches a threshold value and returns to the resting state. d) The membrane potential changes to a much more negative value.
d) Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
What characterizes repolarization, the second phase of the action potential? a) As the membrane repolarizes to a negative value, it goes beyond the resting state to a value of -80 mV. b) Before the membrane has a chance to reach a positive voltage, it repolarizes to its negative resting value of approximately -70 mV. c) Once the membrane depolarizes to a threshold value of approximately -55 mV, it repolarizes to its resting value of -70 mV. d) Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.
they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.
What effect do calcium ions have when they enter the synaptic terminal
action potential propagating down the T tubule
What event most directly triggers the release of calcium from the terminal cisternae?
The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
What event triggers the generation of an action potential? a) The membrane potential must hyperpolarize from the resting voltage of -70 mV to the more negative value of -80 mV. b) The membrane potential must return to its resting value of -70 mV from the hyperpolarized value of -80 mV. c) The membrane potential must depolarize from the resting voltage of -70 mV to its peak value of +30 mV. d) The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.
In the sliding filament model, during contraction, actin and myosin filaments overlap to a greater degree, shortening the muscle fiber.
What happens in the sliding filament model?
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.
What is an example of a presynaptic cell?
calcium influx into the sarcoplasm after death
What is the cause of rigor mortis?
the sum of the electrical and concentration gradients for that ion
What is the electrochemical gradient of an ion?
b) Voltage-gated Na+ channels change shape, and their activation gates open.
What is the first change to occur in response to a threshold stimulus? a) Voltage-gated Ca2+ channels change shape, and their activation gates open. b) Voltage-gated Na+ channels change shape, and their activation gates open. c) Voltage-gated Na+ channels change shape, and their inactivation gates close. d) Voltage-gated K+ channels change shape, and their activation gates open.
Ca2+ combines with troponin, causing troponin to change shape which removes the blocking action of tropomyosin, allowing cross bridges to form.
What is the ion released from the terminal cisternae that combines with troponin and removes the blocking action of tropomyosin, resulting in the formation of cross bridges?
maintaining the concentration gradients for Na+ and K+ across the cell membrane
What is the major role of the Na+-K+ pump in maintaining the resting membrane potential?
Calcium influx into the synaptic terminal causes vesicle fusion.
What is the role of calcium in synaptic activity?
dehydration synthesis
What is the type of chemical reaction used to rebuild ADP into ATP?
voltage-gated Na+ channels open rapidly
What opens first in response to a threshold stimulus? a) Voltage-gated Na+ channels b) Ligand-gated cation channels c) Ligand-gated Cl- channels d) Voltage-gated K+ channels
motor end plate (neuromuscular junction)
What part of the sarcolemma contains acetylcholine receptors?
Na+/K+ ATPase pump
What prevents the Na+ and K+ gradients from dissipating?
acetylcholine receptors in the motor end plate
What protein would be most associated with the characteristics of excitability?
elastic (titin) filaments
What protein would be most associated with the characteristics of extensibility?
motor neuron
What structure most directly stimulates a skeletal muscle fiber to contract?
The muscle would remain in a contracted state because of an inability to break actin-myosin cross bridges.
What would occur if a contracting muscle became totally depleted of ATP?
refractory period
When a muscle is unable to respond to stimuli temporarily, it is in which of the following periods?
the release of acetylcholine from the motor neuron
When an action potential arrives at the neuromuscular junction, the most immediate result is __________.
ion channels in the plasma membrane of the receiving neuron open.
When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,
at the nodes of Ranvier
Where are action potentials regenerated as they propagate along a myelinated axon?
initial segment (axon hillock)
Where do most action potentials originate?
ACh binds to receptors in the junctional folds.
Which of the following best describes how ACh changes the ion permeability of the sarcolemma?
terminal cisterna, transverse tubule, and terminal cisterna The triad refers to a set of three membranous channels and is formed by a single transverse tubule and two terminal cisternae, which are elements of the sarcoplasmic reticulum.
Which of the following best describes the composition of the structure known as a triad in a skeletal muscle fiber?
B
Which of the following corresponds to a single fascicle?
Calcium does NOT bind to myosin heads. Increase of hemoglobin concentration in muscle fibers is not a process that occurs during muscle contraction.
Which of the following does NOT occur during skeletal muscle contraction?
1) Exposing myosin binding sites on actin. Calcium ions, not ATP, are responsible for exposure of the myosin binding sites on actin. During excitation-contraction coupling, calcium ions released from the terminal cisterns of the sarcoplasmic reticulum flood into the sarcoplasm. Calcium ions bind to troponin, which changes its conformation to slide tropomyosin away from the myosin binding sites.
Which of the following is NOT a role of ATP in muscle contraction? 1) Exposing myosin binding sites on actin 2) Energizing the power stroke of the cross bridge 3) Transporting calcium ions into the sarcoplasmic reticulum 4) Detaching the cross bridge from actin
myasthenia gravis
Which of the following is an autoimmune disease that destroys acetylcholine receptors?
Muscle cells have myoglobin; most other cells do not.
Which of the following is present in muscle cells but absent in most other cell types?
Which of the following is responsible for muscle relaxation? 4) Calcium ions are removed from the sarcoplasm by active transport.
Which of the following is responsible for muscle relaxation? 1)ATP binds to the myosin head to cause cross bridge detachment. 2) Sodium ions enter into the sarcoplasm through voltage-gated channels. 3) Calcium ions are released from the terminal cisterns during depolarization of the T tubule. 4) Calcium ions are removed from the sarcoplasm by active transport.
K+ ions can diffuse across the membrane more easily than Na+ ions.
Which of the following is the clearest example of a neuronal membrane's selective permeability?
Krebs cycle and oxidative phosphorylation
Which of the following processes produces 36 ATP?
this is not correct. --> During contraction, thin filaments slide past thick filaments so that actin and myosin filaments do not overlap. actin and myosin filaments DO overlap.
Which of the following statements is FALSE?
The membrane potential of the postsynaptic membrane changes.
Which of the following statements most accurately describes the effect caused by binding of the neurotransmitter postsynaptic membrane
Glycolysis
Which process produces molecules of ATP and has two pyruvic acid molecules as end products?
muscle fiber
Which term best identifies a muscle cell?
fast glycolytic fibers
Which type of skeletal muscle contains abundant quantities of glycogen?
The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential.
Why does regeneration of the action potential occur in one direction, rather than in two directions?
Serotonin
a "mood" transmitter and drugs that block its uptake relieve anxiety and depression
muscle twitch
a brief, maximum contraction of a muscle in response to a stimulus.
Myasthenia gravis is a disease resulting from an autoimmune attack on the ACh receptors of the motor end plate. Binding of antibodies to the ACh receptors results in generalized muscle weakness that progresses as more ACh receptors are destroyed. Which of the following medications would help alleviate the muscle weakness?
a drug that binds to and inactivates acetylcholinesterase (neostigmine)
temporal summation
a rapidly firing presynaptic neuron that causes EPSPs that are close in time.
relative refractory period
a stronger than usual stimulus is necessary to initiate an action potential
A myosin head binds to which molecule to form a cross bridge?
actin
diverging circuit
are 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.
Endorphins
are peptides with inhibitory, opiate-like actions
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
arrival of an action potential
What causes the myosin head to disconnect from actin?
binding ATP
Sarcomeres are functional units of ________ muscle.
cardiac and skeletal only
Calcium ions
cause these vesicles to release acetylcholine into the synaptic cleft through exocytosis
concentric isotonic contraction
contraction in which the muscle shortens
somatic sensory fibers
convey impulses from skin, skeletal muscles, and joints to CNS
1) motor neuron action potential, 2) neurotransmitter release, 3)muscle cell action potential, 4)release of calcium ions from SR, 5)ATP-driven power stroke, 6)sliding of myofilaments
correct sequence of events for muscle contractions
smooth muscle
depends on the calcium-calmodulin system to regulate contraction
end plate potential (EPP)
depolarization of a membrane region by a sodium influx
Muscle cells do not initiate nerve impulses.
do muscle cells initiate nerve impulses?
Myosin binding sites are covered
eight step in the sequence of cross bridge cycle
1) AP propagates along sarcolemma 2) AP travels down T tubeules to triads 3) Voltage-sensitive proteins open Ca+ channels 4) Sarcoplasmic reticulum releases Ca2+ 5) Ca2+ levels in sarcoplasm increase
events that occur during excitation-contraction coupling
Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.
extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber
fast glycolytic muscle fiber
fatigues quickly: provide short periods of intense strenght (good for moving furniture)
Action Potential (AP)
is the result of a predictable sequence of electrical changes that occurs along the length of the sarcolemma.
GABA
inhibitory neurotransmitter
Dopamine
is a "feel good" transmitter that is deficient in Parkinson's disease.
Norepinephrine
is the neurotransmitter used by postganglionic neurons in the sympathetic nervous system.
Cardiac muscle
muscle that has branching fibers and is striated and involuntary.
fast oxidative muscle fiber
moderately fatigue resistant
myosin heads and globular actin
myosin heads and globular actin
Acetylcholine
neurotransmitter chemical released at the ends of nerve cells
Rigor mortis occurs because ________.
no ATP is available to release attached actin and myosin molecules
Inhibitory Post-Synaptic Potentials (IPSPs)
occur when Cl- enters the cell and K+ leaves the cell. Thus, changes in the electrochemical gradient, brought about changes in the concentration of Cl- or K+ may effect the abilities of neurons to communicate.
action potential arrives at axon terminal of motor neuron step
one Neurotransmitter action
temporal summation
refers to a rapidly firing presynaptic neuron that causes EPSPs that are close in time.
1) Ca2+ enters the axon terminal 2) Synaptic vesicles release ACh 3) ACh binds to ACh receptors 4) Ligand-gated cation channels open 5) Na+ enters and K+ exits 6) Membrane potential is less negative
place in the correct order of occurrence the events that occur at the neuromuscular junction after the action potential reaches the axon terminal.
isotonic contraction
produces uniform tension in a muscle
What causes the power stroke during the cross bridge cycle?
release of ADP and Pi
Which of the following events triggers the subsequent steps of excitation-contraction coupling?
release of acetylcholine from axon terminals at the neuromuscular junction. Release of acetylcholine from axon terminals at the neuromuscular junction is an event that precedes excitation-contraction coupling. Binding of acetylcholine to receptors in the motor end plate triggers an action potential that propagates along the sarcolemma and into the cell interior via T tubules.
skeletal muscle
relies on the calcium-troponin system to regulate contraction.
ACh receptors are found mainly in the __________.
sarcolemma. The sarcolemma contains ACh receptors. The opening of these ACh receptors depolarizes the muscle fiber, which leads to the generation of a muscle action potential.
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 in adjacent axon segment
sequence of events that occur during continuous propagation.
1) action potential arrives synaptic terminal 2) calcium channels ions enter the synaptic terminal 3) vesicles containing neurotransmitters fuse with the plasma membrane of the sending neuron 4) neurotransmitters diffuse across the synaptic plate 5) the neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, causing ion channels to open
sequence of events that occurs at a synapse. Reset
1) a neural signal at the presynaptic cell, 2) the release of neurotransmitter, 3) the creation of a graded potential in the postsynaptic cell, 4) degradation of the neurotransmitters. Neurotransmitters transfer information between a neuron and a postsynaptic cell. This process gets a "message" across a physical separation much like sending a text to your friend who is across town.
sequence of synaptic activity
similarities: The placement of the channel protein relative to the membrane The polarity of the substances they transport across the membrane The stimulus that triggers opening differences: The direction of ion movement through the channel The inactivation mechanism
similarities or differences between voltage-gated K+ channels and voltage-gated Na+ channels.
calcium ions pumped into the sarcoplamic recticulum
sixth step in the sequence of cross bridge cycle
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
sodium enters the cell through voltage gated sodium channels and causes depolarization. A small amount of potassium also leaves the motor end plate (junctional folds of the sarcolemma).
Acetylcholine
stimulates skeletal muscle.
Tetanic contraction
sustained and forceful contraction that results from high-frequency stimulation from the nervous system.
Contractility
the ability of a muscle to shorten forcibly when adequately stimulated.
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels
refractory period
the time following an action potential during which a new action potential cannot be initiated
Visceral sensory fibers
transmit impulses from the visceral organs (organs within the ventral body cavity)
The force of muscle contraction is controlled by multiple motor unit summation or recruitment.
true
isometric contraction
type of contraction that maintains posture
slow oxidative muscle fiber
type of muscle fiber that is most resistant to fatigue: slow speed of contraction & utilize aerobic glycolysis; they are fatigue resistant
Smooth muscle fibers
type of muscle that is small and spindle-shaped.
Resting Membrane Potential (RMP)
unequal distribution of charge creates a voltage across the plasma membrane is -70mV
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels
Transmission of the action potential along the T tubules of the triads causes the voltage-sensitive tubule proteins of the sarcoplasmic reticulum to change shape, releasing calcium into the cytosol.
what causes the release of calcium into cytosol?
Calcium influx into the cell after death promotes the formation of myosin cross bridges and stiffening of muscles after death.
what happens in rigor mortis
Peristalsis occurs in the digestive tract
where does peristalsis occur?
Dendrites
where one would find short-distance signals called graded potentials that travel toward the cell body
Na+ (sodium ions)
which ion is mainly responsible for depolarizing the sarcolemma?
voltage-gated calcium channels
will open in response to an action potential, allowing calcium ions to diffuse into the cell.
