Pearson Review Muscle Physiology Flashcards
Which of the following is/are mechanism(s) to end neural transmission at the neuromuscular junction?
ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE).
ACh binds to ACh receptors.
ACh is taken up by the axon terminal via endocytosis.
ACh diffuses away from the synaptic cleft.
ACh is broken down into acetic acid and choline by the enzyme acetylcholinesterase (AChE).
ACh diffuses away from the synaptic cleft.
The cross bridge cycle starts when _________.
Ca2+ from the sarcoplasmic reticulum binds to troponin.
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
What structure is the functional unit of contraction in a skeletal muscle fiber?
The sarcomere
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.
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.
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of ATP.
What specific event triggers the uncovering of the myosin-binding site on actin?
Calcium ions bind to troponin and change its shape
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.
The narrow space between the axon terminal and the motor end plate is called the:
synaptic cleft
Stimulation of acetylcholine (ACh) receptors by ACh will primarily result in
sodium ions entering the muscle fiber.
The end-plate potential is:
a depolarization caused by sodium ion movement into the cytosol.
The neurons of patients with multiple sclerosis are unable to transmit action potentials down the axon. How will that affect skeletal muscle stimulation?
The muscle will not be stimulated and, therefore will not contract
The active ingredient of Botox, botulinum toxin, blocks the release of ACh from the axon terminal. An overdose of Botox will most likely result in:
Muscle paralysis at the site of injection.
Excitation-contraction coupling is a series of events that occur after the events of the neuromuscular junction have transpired. Which step in the process does the term excitation refer to?
Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
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.
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.
What is name given to the regularly spaced infoldings of the sarcolemma?
transverse or T tubules
What is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers?
Calcium ions
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.
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes?
Release of acetylcholine from the synaptic vesicles
What structure most directly stimulates a skeletal muscle fiber to contract?
Motor neuron
: membranous sac located in the axon terminal that contains neurotransmitter.
Synaptic Vesicle
the space between the axon terminal and junctional folds.
Synaptic Cleft
a type of chemically-gated ion channel located on the junctional folds of the muscle fiber.
Acetylcholine Receptor
a type of voltage-gated ion channel located on the axon terminal.
Calcium Channel
neurotransmitter that stimulates skeletal muscle contraction.
Acetylcholine
: a type of voltage-gated ion channel located on the sarcolemma of the muscle fiber.
Sodium Channel
enzyme located in the synaptic cleft that breaks down acetylcholine.
Acetylcholinesterase
Rank the sequence of events at the NMJ that initiate an action potential in the muscle fiber, from first to last.
Step 1: Action potential arrives at the axon terminal.
Step 2: Calcium Ions enter the Axon Terminal.
Step 3: Synaptic Vesicles fuse to membrane of Axon Terminal.
Step 4: Acetylcholine is released into the Synaptic Cleft.
Step 5: Acetylcholine binds to its receptors on the Junctional Folds.
Step 6: Junctional Folds become Depolarized.
Step 7: Action Potential is initiated on the Sarcolemma.
If the cytosol loses K+ ions through leak channels, it will become:
More negative.
Which of the following membrane proteins is involved in active transport?
Na+ voltage-gated channel
K+ leak channel
Na+/K+ pump
Na+ leak channel
Na+/K+ pump
For every ATP split into an ADP and a phosphate, the Na+/K+ pump moves _____ out of the cell and ______ into the cell.
3 Na+; 2 K+
A crossbridge forms when:
a myosin head binds to actin.
Which of the following steps of the cross-bridge cycle occurs immediately before the power stroke?
Myosin heads detach from actin.
A crossbridge forms.
Calcium ions bind to myosin.
ATP hydrolysis “cocks” the myosin head.
A cross-bridge forms
As myosin heads complete the power stroke, actin filaments
slide toward the M line of the sarcomere.
Which of the following causes myosin to detach from actin?
An ATP molecule binds to myosin.
In the absence of ATP in the muscle, which of the following is most likely to occur?
Some myosin heads will remain attached to actin molecules but are unable to perform a power stroke.
What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell?
the arrival of an action potential
The binding of calcium to which molecule causes the myosin binding sites to be exposed?
troponin
A myosin head binds to which molecule to form a cross bridge?
actin
What causes the myosin head to disconnect from actin?
binding of ATP
What causes the power stroke?
release of ADP and Pi
In preparation for contraction, calcium ions bind to:
Troponin.
The protein that binds to actin when tropomyosin moves off of the active sites of actin, is:
Myosin.
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine (ACh)
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
exocytosis
The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?
Binding of the neurotransmitter causes chemically gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell.
How is acetylcholine (ACh) removed from the synaptic cleft?
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
The action potential on the muscle cell leads to contraction due to the release of calcium ions. Where are calcium ions stored in the muscle cell?
terminal cisterns (cisternae) of the sarcoplasmic reticulum
Action potential propagation in a skeletal muscle fiber ceases when acetylcholine is removed from the synaptic cleft. Which of the following mechanisms ensures a rapid and efficient removal of acetylcholine?
Acetylcholine is degraded by acetylcholinesterase.
The neuromuscular junction is a well-studied example of a chemical synapse. Which of the following statements describes a critical event that occurs at the neuromuscular junction?
Acetylcholine is released by axon terminals of the motor neuron.
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
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.
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels
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.
EGTA is a substance that binds calcium ions. Imagine an experimental setup with a motor neuron and a muscle fiber. Stimulation of the motor neuron causes contraction of the muscle fiber through activity at the neuromuscular junction and excitation-contraction coupling. Now, inject the muscle fiber with EGTA. Which of the following effects would EGTA have on excitation-contraction coupling after the neuron releases acetylcholine at the neuromuscular junction?
It would prevent myosin from forming cross bridges with actin.
What causes the release of calcium ions into the sarcoplasm from the terminal cisterns?
An action potential traveling along the t tubule
Conduction of an action potential along the sarcolemma depends upon ___________.
diffusion of sodium ions through voltage-gated channels
receive(s) stimulus from the motor neuron
Junctional Folds
block(s) binding sites on actin.
Tropomyosin
conduct(s) action potentials throughout the interior of the muscle fiber.
T Tubule
release(s) calcium ions into the sarcoplasm
Terminal Cistern
change(s) shape upon binding with calcium ions
Troponin
What are the components of a triad?
Two terminal cisternae of the sarcoplasma reticulum (SR) and one T-tubule
Excitation-contraction coupling results in an increase of calcium ion concentration:
in the cytosol of the muscle fiber
Predict the effect of Tetrodotoxin, a powerful blocker of voltage-gated sodium ion channels:
There will be no action potential generated in the muscle fiber.
What is the type of chemical reaction used to rebuild ADP into ATP?
dehydration synthesis
Which of the following processes produces molecules of ATP and has two pyruvic acid molecules as end products?
glycolysis
Which of the following processes produces the most ATP?
Krebs cycle and oxidative phosphorylation
The “rest and recovery” period, where the muscle restores depleted reserves, includes all of the following processes EXCEPT __________.
ATP is used to rephosphorylate creatine into creatine phosphate.
Oxygen rebinds to myoglobin.
Glycogen is synthesized from glucose molecules.
Pyruvic acid is converted back to lactic acid.
Pyruvic acid is converted back to lactic acid.
Which type of muscle fiber has a large quantity of glycogen and mainly uses glycolysis to synthesize ATP?
white fast twitch fibers
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)
Which of the following can cause relaxation?
Release of ACh from the synaptic terminal
Inhibition of acetylcholinesterase (AChE)
End of neural stimulation
Increase in the calcium ion concentration inside the muscle fiber
End of neural stimulation
When the sarcolemma repolarizes and returns to rest:
the inside of the sarcolemma is more negatively charged than the outside
The progressive stiffening of muscles after death, known as rigor mortis, is due to:
ATP depletion, which leads to high cytosolic calcium and inability of crossbridges to detach
Which of the following is responsible for preventing a muscle from contracting?
Calcium ions are released from the terminal cisterns during depolarization of the T tubule.
ATP binds to the myosin head to cause cross bridge detachment.
Sodium ions enter into the sarcoplasm through voltage-gated channels.
Calcium ions are removed from the sarcoplasm by active transport.
Calcium ions are removed from the sarcoplasm by active transport.
Which of the following is NOT a role of ATP in muscle contraction?
Exposing myosin binding sites on actin
Detaching the cross bridge from actin
Transporting calcium ions into the sarcoplasmic reticulum
Exposing myosin binding sites on actin
