Muscle I

In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter? norepinephrine dopamine serotonin acetylcholine (ACh)

When an action potential arrives at the axon terminal of a motor neuron, which ion channels open? voltage-gated potassium channels voltage-gated sodium channels voltage-gated calcium channels chemically gated calcium channels

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft? exocytosis a channel a protein carrier

The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur? Binding causes voltage-gated sodium channels to open in the motor end plate (junctional folds of the sarcolemma) and sodium enters the cell. Binding causes potassium voltage-gated channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell. 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. Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell.

How is acetylcholine (ACh) removed from the synaptic cleft? simple diffusion away from the synaptic cleft and endocytosis into the muscle fiber acetylcholinesterase (AChE; an enzyme) and endocytosis into the muscle fiber simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme) acetylcholinesterase (AChE; an enzyme) only

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? sarcolemma T tubule cytosol terminal cisterns (cisternae) of the sarcoplasmic reticulum

What causes the release of calcium from the terminal cisternae of the sarcoplasmic reticulum within a muscle cell? arrival of an action potential ATP troponin calcium ion pump

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

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

What causes the myosin head to disconnect from actin? binding of ATP hydrolysis of ATP binding of calcium binding of troponin

What causes the power stroke? calcium release of ADP and Pi hydrolysis of ATP binding of ATP

Which of the following best summarizes the events of excitation-contraction coupling? Choose the best answer. The actin filament slides towards the sarcomere and the muscle contracts. An acetylcholine signal from the motor neuron is converted into an electrical signal in the muscle fiber. Muscle action potentials initiate calcium signals that activate a contraction-relaxation cycle. Cross-bridges release and the muscle relaxes. Submit

Which of the following statements best describes the neuromuscular junction? Choose the best answer. the point of synapse between a motor neuron and the muscle fiber that it innervates the release of calcium from the sarcoplasmic reticulum as a result of the action potential traveling down the t-tubule the release of acetylcholine from the axon terminal of the motor neurons the act of myosin and actin sliding past each other in order to produce a contraction

Which of the following structures is/are necessary to initiate the muscle action potential? ryanodine receptor tropomyosin calcium ACh receptor-channels muscle fiber troponin myosin t-tubule motor end plate Ca2+-ATPase actin acetylcholine motor neuron

An area that contains many synaptic vesicles filled with acetylcholine

A change in membrane voltage that travels down the T-tubule to cause opening of Ca2+ channels

An area of muscle fiber membrane that is in close association with the axon terminal of the motor neuron, contain receptors for acetylcholine

A structure that when bound to a ligand opens a divalent channel for the movement of both Na+ and K+

Putting the Events at the Neuromuscular Junction in Order: rank from earliest to latest.

Which of the following best describes the contraction phase of the excitation-contraction coupling reaction? Choose the best answer. An action potential travels down the t-tubule in order to release Ca2+ from the sarcoplasmic reticulum. Actin pushes on myosin to shorten its length, thereby shortening the muscle. Actin and myosin filaments slide past each other to shorten the sarcomere, bringing Z disks closer together. An action potential travels down the axon of a motor neuron in order to release acetylcholine onto the motor end plate.

Which of the following best describes the role of calcium (Ca2+ ) in the excitation-contraction coupling reaction? Choose the best answer. Ca2+ will bind directly to tropomyosin, resulting in a conformational shift which reveals the binding sites for myosin on actin. Ca2+ will bind to troponin, which leads to a conformational shift in tropomyosin, allowing for actin and myosin to attach. Ca2+ binds to specific receptors which control the release of ATP into the cytoplasm of the muscle fiber. Ca2+ gives the myosin heads the energy necessary for the power stroke.

Putting the Events of Contraction in Order: Rank from earliest to latest.

Which of the following is the most direct cause of muscle relaxation? Choose the best answer. Ca2+ unbinds from troponin, which results in tropomyosin re-covering myosin binding sites. The cytoplasm of the muscle fiber exhausts all of its available ATP. The voltage created along the t-tubule fades and the muscle fiber membrane returns to a resting potential value. The delivery of action potentials from the motor neuron stops.

Putting It All Together: Put excitation-contraction coupling and muscle relaxation so that they occur in the correct sequential order. Rank from earliest to latest.

Which loss of function would occur if you introduced a chemical that functioned as an inhibitor of the ryanodine receptor channel? Choose the best answer. Ca2+ ions would not be actively pumped back into the sarcoplasmic reticulum Na+ ions would not be able to flow into the muscle cell in order to depolarize it Myosin would not be able to bind to actin in order to cause shortening of the sarcomere The axon terminal of the motor neuron would not release acetylcholine

A patient has damage to one somatic motor neuron. What will this affect? One muscle fiber Many muscles Many muscle fiber types One motor unit

Which is a difference between summation and tetanus? Summation can cause tetanus, but tetanus cannot cause summation . Muscles relax between action potentials in summation but not in tetanus. Sarcomeres shorten in tetanus but not in summation. Muscles reach maximal tension in summation but not in tetanus.

What happens when skeletal muscle sarcomere length increases beyond about 2.3 micrometers (μm)? More myosin heads can bind to the thin filament. Less calcium is released from the SR. Tension decreases. The fiber can produce more force.

Compared to fast-twitch glycolytic fibers (type IIX), slow-oxidative muscle fibers (type I) are characterized by a smaller diameter and __________. the presence of myoglobin faster pumping of Ca2+ into the SR the development of tension 2-3 times more quickly fewer mitochondria

Which enzyme catalyzes the phosphorylation of ADP? Ca2+-ATPase Phosphocreatine Creatine kinase Na+-K+-ATPase

Which of the following would stop muscle contraction? Pulling away of tropomyosin from the myosin-binding site on actin A lack of ATP Pumping of calcium ions into the SR Binding of acetylcholine to ACh receptors

How is the energy released by ATP hydrolysis used during the contractile cycle in skeletal muscle? ATP hydrolysis stabilizes actin to prevent actin filament's shortening during contraction. It causes rotation of the myosin head, thus "cocking" it. It allows the release of calcium from the SR. It provides energy for the myosin head to pull on the actin filament. This "uncocks" the myosin head.

What happens when calcium binds troponin? Tropomyosin is pulled away from the myosin-binding site on actin. Troponin releases myosin and activates actin. Troponin binds to actin and causes sarcomere shortening. Troponin changes shape and covers the SR calcium channel, which is a form of negative feedback.

__________ occurs when myosin crossbridges attach to actin filaments and pull them toward the middle of the sarcomere. Myosin head rotation An action potential A power stroke Hydrolysis

Which of the following would NOT change size during a muscle contraction? I band Sarcomere A band H zone

Which of the following is the smallest structure? Myofibril Muscle fascicle Myosin Muscle fiber

Which type of skeletal muscle causes two bones to move away from one another? Tendon Antagonist Flexor Extensor

Which is a similarity between summation and tetanus? Both occur when there are less frequent action potentials. Both reach maximum tension. In both, muscle contraction is shorter than muscle action potentials. In both, muscle action potentials are shorter than muscle contraction.

What immediately follows hydrolysis of ATP during muscle contraction? The power stroke Rotation of the myosin head to the cocked position Myosin binding to actin Myosin releases actin

Thick filaments are made up of __________. titin myosin actin nebulin

Because of their shape, muscle cells are also known as __________. muscle fibers fascicles tubules myofibrils

Skeletal muscle moves a bone at a joint, such as flexing the forearm at the elbow. How is the opposite action produced (for example, extension at the elbow)? An antagonistic muscle produces the opposite movement. The muscle that produces flexion extends to produce extension. An antagonistic neuron secretes a different neurotransmitter onto the same muscle to produce the opposite skeletal movement. The muscle that produces flexion relaxes to produce extension.

The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge? Troponin bound to tropomyosin ATP bound to a myosin head A myosin head bound to actin Calcium bound to troponin

What structure is the functional unit of contraction in a skeletal muscle fiber? The cross bridge The junctional folds of the sarcolemma The sarcomere The triad

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 mitochondria. Calcium ions are stored in the transverse tubules. Calcium ions are stored in the nuclei. 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? Acetylcholine binds to receptors in the junctional folds of the sarcolemma. Calcium ions bind to troponin. ATP binds to the myosin head. ADP and inorganic phosphate are bound to the myosin head.

How does the myosin head obtain the energy required for activation? The energy comes from the hydrolysis of ATP. The energy comes from the hydrolysis of GTP. The energy comes from the direct phosphorylation of ADP by creatine phosphate. The energy comes from oxidative phophorylation.

What specific event triggers the uncovering of the myosin binding site on actin? Calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm. Calcium ions bind to tropomyosin and change its shape. Calcium ions bind to troponin and change its shape. Sodium ions bind to troponin and change its shape.

When does cross bridge cycling end? Cross bridge cycling ends when ATP binds to the myosin head. Cross bridge cycling ends when calcium release channels in the sarcoplasmic reticulum open. Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin. Cross bridge cycling ends when calcium ions are passively transported back into the sarcoplasmic reticulum.

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 refers to the release of calcium ions from the sarcoplasmic reticulum. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma. Excitation, in this case, refers to the propagation of action potentials along the sarcolemma. Excitation refers to the propagation of action potentials along the axon of a motor neuron.

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. Voltage-sensitive proteins change shape. Action potentials propagate into the interior of the skeletal muscle fiber. Sodium 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. Myosin cross-bridge binding sites. Potassium leak channels. Voltage-gated sodium channels.

What is name given to the regularly spaced infoldings of the sarcolemma? motor endplates transverse or T tubules sarcoplasmic reticulum terminal cisternae

Which of the following is most directly responsible for the coupling of excitation to contraction of skeletal muscle fibers? Acetylcholine. Sodium ions. Action potentials. Calcium ions.

What is the relationship between the number of motor neurons recruited and the number of skeletal muscle fibers innervated? A skeletal muscle fiber is innervated by multiple motor neurons. A motor neuron typically innervates only one skeletal muscle fiber. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron. Motor neurons always innervate thousands of skeletal muscle fibers.

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. Acetylcholine is transported back into the axon terminal by a reuptake mechanism. Acetylcholine diffuses away from the cleft. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis.

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. Acetylcholine binds to its receptor in the junctional folds of the sarcolemma. Its receptor is linked to a G protein. Acetylcholine is released and moves across the synaptic cleft bound to a transport protein. When the action potential reaches the end of the axon terminal, voltage-gated sodium channels open and sodium ions diffuse into the terminal.

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 extend from the brain to the sarcolemma of a skeletal muscle fiber arise in the epimysium of a skeletal muscle and extend to individual skeletal muscle fibers extend from the spinal cord to the sarcolemma of a skeletal muscle fiber

Calcium entry into the axon terminal triggers which of the following events? Acetylcholine binds to its receptor. Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal. Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal. 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 calcium-release channels the opening of ligand-gated anion channels the opening of ligand-gated cation channels the opening of voltage-gated calcium channels

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why? The outside surface of the sarcolemma is negatively charged compared to the inside surface. Potassium ions diffuse outward along favorable chemical and electrical gradients. The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients. The outside surface of the sarcolemma is negatively charged compared to the inside surface. Sodium ions diffuse outward along favorable chemical and electrical gradients. The inside surface of the sarcolemma is negatively charged compared to the outside surface. Potassium ions diffuse inward along favorable chemical and electrical gradients.

Which of the following is a similarity between isometric and isotonic contractions? Sarcomeres lengthen. Muscles shorten. A load is moved. Tension develops.

A muscle moving a load goes through two phases of contraction. Which phase occurs first, and what happens inside the muscle during this phase? Isotonic; elastic elements stretch Isotonic; sarcomeres shorten greatly Isometric; sarcomeres shorten greatly Isometric; elastic elements stretch

Which of the following structure(s) must always be present in order for you to have a skeletal muscle reflex arc? afferent neuron integrating center receptor target cell stimulus efferent neuron interneuron

Skeletal muscle reflexes can be either monosynaptic or polysynaptic. Which of the following statements is true regarding monosynaptic versus polysynaptic skeletal muscle reflexes? Choose the best answer. Polysynaptic reflexes are composed of only two neurons between the stimulus and target cell, while monosynaptic reflexes contain three or more neurons. Monosynaptic reflexes are composed of only two neurons between the stimulus and target cell, while polysynaptic reflexes contain three or more neurons. Both monosynaptic and polysynaptic reflexes are composed of only two neurons between the stimulus and target cell. Both monosynaptic and polysynaptic reflexes are composed of three or more neurons between the stimulus and target cell.

Below is a picture of the patellar tendon reflex arc. Use this figure to answer the following question in the coaching activity. Application of Knowledge to the Patellar Tendon Reflex.

Use the same figure as in Part D to answer the following question. Is the patellar tendon reflex a monosynaptic or polysynaptic reflex? Choose the best answer. polysynaptic monosynaptic both neither

Ordering the Events of the Crossed Extensor Reflex: Rank from earliest to latest.

Is the cross extensor reflex a monosynaptic or polysynaptic reflex? Choose the best answer. monosynaptic polysynaptic both neither

What would happen if a person were to sustain an injury that severed the alpha motor neurons leading to the leg muscles in the crossed extensor portion of the reflex? Choose the best answer. A person would not be able to feel a painful stimulus. A person would not be able to withdraw their leg in the presence of a painful stimulus. The sensory signal delivered by the afferent neuron would not be properly transduced at the spinal cord. Upon a painful stimulus, a person would withdraw their leg and then lose their balance and possibly fall over.

The three types of proprioceptors include muscle spindles, Golgi tendon organs, and __________. spatial receptors intrafusal fibers joint capsules joint receptors

Which stimulus initiates a flexion reflex? Pain Loss of balance Touch Sound

What is the response of a muscle stretch reflex? Contraction of the agonist muscle Inhibition of alpha motor neuron activity Relaxation of the agonist muscle Contraction of the antagonist muscle

A muscle spindle is a tonic proprioceptor. What happens to the signal on the sensory afferent neurons that come from the spindle when the muscle spindle is stretched? The signal is inhibited. The signal increases in frequency. The signal begins as the stretch begins. The signal increases in magnitude.

Choose the FALSE statement about reflexes. Reflexes are useful primarily for medical diagnosis; they serve little practical purpose otherwise. The crossed extensor reflex is a postural reflex to maintain balance when one foot is lifted from the ground. The limb withdrawal that occurs during a withdrawal reflex primarily involves flexor muscles. Some reflexes involve activity in inhibitory neurons, which can cause a muscle to relax.

Which structure responds to muscle stretch? Golgi tendon organ Alpha motor neuron Muscle spindle Extrafusal muscle 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 blocks the release of acetylcholine (botulinum toxin) a drug that binds to the acetylcholine receptor and prevents it from opening (curare) a drug that binds to and inactivates acetylcholinesterase (neostigmine) a drug that prevents acetylcholine from being loaded into synaptic vesicles (vesamicol)

Inadequate calcium in the neuromuscular junction would directly affect which of the following processes? Breakdown of acetylcholine by acetylcholinesterase Depolarization of the junctional folds Conduction of action potentials by the motor neuron Release of acetylcholine from the synaptic vesicles

What structure most directly stimulates a skeletal muscle fiber to contract? Motor neuron Voltage-gated calcium channels Synaptic cleft Acetylcholinesterase

neuromuscular junction at rest

neuromuscular junction active

Match the term in the left column to the blanks near their definition on the right.

Arrange the sequence of events at the NMJ from first to last. -Rank the sequence of events at the NMJ that initiate an action potential in the muscle fiber, from first to last.

Drag the labels onto the diagram to label the steps of smooth muscle activation and deactivation.

How are cardiac muscle cells similar to smooth muscle cells? They lack striations. They are branched. They do not contain sarcomeres. They are electrically linked to one another.

Compared with skeletal and cardiac muscle, which of the following is not in smooth muscle? ____ in skeletal and cardiac muscle but not in smooth muscle. Sarcomeres are Actin is Calcium ion are used in regulation of contraction of Myosin is

Which type(s) of muscle fiber is/are uninucleate? Smooth only Smooth and skeletal Skeletal and cardiac Smooth and cardiac

Which of the following is a similarity between slow wave potentials and pacemaker potentials? Both involve depolarizations followed by repolarizations. Both create regular rhythms of contraction. Both always fire action potentials. Both have subthreshold depolarizations.

How does the process of smooth muscle contraction differ from contraction in skeletal muscle? There is no active myosin ATPase producing energy for the myosin heads. Ca2+ comes from the extracellular fluid and the SR. Relaxation occurs when calmodulin is released from its receptors. Myosin pulls on troponin instead of actin.

A patient is born with a mutation in her calmodulin gene. This could affect the contraction of ________ muscles. smooth cardiac and skeletal smooth and cardiac all three types of