Muscle Test
The following events happen in this sequence:
1. Action potential arrives at the axon terminal. 2. Calcium ions enter the axon terminal. 3. Synaptic vesicles fuse to the membrane of the axon terminal. 4. Acetylcholine is released into the synaptic cleft. 5. Acetylcholine binds to receptor sites on the motor end plate. 6. Motor end plate becomes depolarized. 7. Action potential is initiated on the sarcolemma. 8. Action potential propagates along the sarcolemma and down the T Tubules. 9. Calcium ions are released from the terminal cisternae. 10. The muscle cell contracts.
These things occur in the following order:
1.An action potential arrives at the axon terminal 2. Acetylcholine is released from the axon terminal into the synaptic cleft. 3.The motor end plate is depolarized. 4.The depolarization triggers an action potential which propagates along the sarcolemma and the T tubules. 5. The sarcomeres contract.
Which of the following is the dark band seen on the myofibrils
A band
The area where actin and myosin overlap
A-Band
The post-synaptic reaction on the sarcolemma is short in duration. Which of the following explanations describes why the reaction of the sarcolemma is short in duration?
ACh diffuses out of the synaptic cleft and AChE acts to breakdown the ACh in the synaptic cleft
Which of the following events most directly occurs due to an action potential generated by the motor neuron?
ACh is released at the synapse.
The characteristic muscle stiffness associated with rigor mortis is due to the inability of myosin filaments to detach from the active site on actin filaments. What molecule is essential for this detachment?
ATP
What is required to occur to allow myosin to detach from actin
ATP
Vesicles in the synaptic terminal contain
Acetylcholine
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.
Tamara's muscle weakness and fatigue becomes progressively worse over the course of the day. This is a hallmark sign of myasthenia gravis, an autoimmune disorder that affects the ability of a motor neuron to communicate with a muscle fiber. What synaptic events must happen first for excitation to occur?
Acetylcholine is released from the axon terminal and diffuses across the synapse to bind to a receptor in the surface of the motor end plate.
The injection that dramatically improved Tamara's symptoms was Tensilon, an acetylcholinesterase inhibitor. What is acetylcholinesterase, and why was this injection effective in relieving Tamara's symptoms?
Acetylcholinesterase is the enzyme that clears acetylcholine from the synapse. Inhibiting this enzyme will enable acetylcholine to be available for a longer period to bind to receptors.
More efficient use of glucose molecules for ATP production
Aerobic respiration
Used for long term, light-to-moderate exercise
Aerobic respiration
Used fro strenuous exercises
Anaerobic respiration
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.
What moves troponin and tropomyosin on the actin so that cross bridges can form?
Ca ions
What must be released from the SR in order for myosin to bind to actin?
Ca ions
Ca++ is stored in specialized pockets of the sarcoplasmic reticulum called
Cisternae
Which connective tissue layer wraps the entire muscle?
Epimysium
The perimysium surrounds a bundle of muscle fibers called a
Fascicle
Which of the following produces ATP from glucose anaerobically
Glycolysis
The part of the sarcomere that contains thick filament but no thin filaments is the
H band
The area where actin and myosin do not overlap and only actin is found is called the
I Band
Areas of a sarcomere with just actin
I band
The region of the sarcomere that always contains thin filaments is the
I band
The area where actin and myosin do not overlap and only actin is found is called the
I-Band
Myasthenia gravis is an autoimmune disorder that results in the production of antibodies that either block or cause the destruction of the ACh receptor. Why do you think that Tamara's symptoms become worse as the day progresses?
In the morning, the neuronal reserves of acetylcholine are larger, allowing for sufficient neurotransmitter release and resulting in effective muscle signaling. As the day progresses and the stores of acetylcholine become depleted, muscle function becomes progressively worse.
What is the type of contraction in which the muscle does NOT change length?
Isometric
Why is control over leg muscles LESS precise than control over the muscles of the eye
Many muscle fibers are controlled by a single motor neuron
What structure most directly stimulates a skeletal muscle fiber to contract?
Motor neuron
Myofibrils bundled together form
Muscle Fiber (cell)
How does the muscle fiber becomes positively charged during depolarization?
Na ions flood into the cell
Why do bodies go into rigor after death?
No ATP to release myosin from actin
Inadequate calcium in the neuromuscular junction would directly affect which of the following processes?
Release of acetylcholine from the synaptic vesicles
What is the functional unit of the muscle fiber (cell)?
Sacromere
The repeating functional units seen in the myofibrils are
Sarcomeres
Since each myofibril is attached at either end of the muscle fiber, when sarcomeres shorten, the muscle fiber
Shortens
When acetylcholine reaches receptors on the sarcolemma of muscle fibers, ____ channels open
Sodium (Na)
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.
Action potentials travel along the sarcolemma and reach the interior of the cell though
T tubules
Action potentials travel long the sarcolemma and reach the interior of the cell through
T tubules
infoldings of the sarcolemma called
T tubules
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.
Which of these statements about skeletal muscles is FALSE?
Their fibers branch.
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)
Sarcomere is best defined as __________.
a repeating unit of striated muscle
Acetylcholine receptor
a type of chemically-gated ion channel located on the junctional folds of the muscle fiber.
Calcium channel
a type of voltage-gated ion channel located on the axon terminal.
sodium channels
a type of voltage-gated ion channel located on the sarcolemma of the muscle fiber.
Neurotransmitter that is released from the axon terminal to cross the synaptic cleft
acetylcholine
Vesicles in the synaptic terminal contain
acetylcholine
In a neuromuscular junction, synaptic vesicles in the motor neuron contain which neurotransmitter?
acetylcholine (ACh)
The cytoplasm of the neuromuscular terminal contains vesicles filled with molecules of the neurotransmitter
acetylcholine.
Thin Filaments are also called
actin filaments
Thin filaments are also called
actin filaments
Which filaments =moves during muscle contraction?
actin or thin
The most important factor in decreasing the intracellular concentration of calcium ion after contraction is
active transport of calcium into the sarcoplasmic reticulum.
Creatine phosphate
acts as an energy reserve in muscle tissue
During the recovery period the body's need for oxygen is increased because
additional oxygen is required to restore energy reserves.
A resting muscle generates most of its ATP by
aerobic metabolism of fatty acids
Decreased blood flow to a muscle could result in all of the following except
an increase in intracellular glycogen.
After heavy exercise, if energy reserves in a muscle are depleted, ________ occurs.
an oxygen debt
Makes ATP faster
anaerobic respiration
Active sites on the actin become available for binding after
calcium binds to troponin.
In response to action potentials arriving along the transverse tubules, the sarcoplasmic reticulum releases
calcium ions
Branching, striated muscle tissue is called
cardiac
Ca ++ is stored in specialized pockets of the sarcoplasmic reticulum called
cisternae
Contraction where the muscle shortens
concentric
Contraction where the muscle shortens and does work
concentric
Fatigued muscles signify __________.
decreased pH
When the muscle cell becomes positively charged, it has been ____
depolarized
Contraction where the muscle lengths and does work
eccentric
Individual muscle fibers are covered by which connective tissue?
endomysium
Muscle fibers are directly surrounded by which thin layer of connective tissue?
endomysium
The capillaries that wrap around each muscle fiber are located within the __________.
endomysium
The outer connective tissue layer surrounding a group of fascicles is called
epimysium
Synaptic vesicles contain neurotransmitters that are released by ________ when the action potential arrives.
exocytosis
What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?
exocytosis
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
A group of muscle fibers are called
fascicles
Which of the following would not lead to increased oxygen consumption?
increased anaerobic respiration by muscle cells
A weight-lifter strains to lift a heavy weight and there is no movement of the person's arms holding on to the weight. This type of contraction is called a(n) ________ contraction.
isometric
Contraction of muscles that do not change length
isometric
Which of the following is a function of skeletal muscle?
maintain body temperature, produce movement, and maintain posture
Synaptic vesicle
membranous sac located in the axon terminal that contains neurotransmitter.
Organelle of ATP production
mitochondria
When acetylcholine binds to receptors at the motor end plate, the sarcolemma becomes
more permeable to sodium ions.
Acetylcholine crosses the synaptic cleft and binds to the receptors on the
motor end plate
Receptors for acetylcholine are located on the
motor end plate
A nerve that stimulates a muscle fiber
motor neuron
A motor neuron and all fibers it stimulates
motor unit
All the muscle fibers and the single motor neuron that innervates them are called a __________.
motor unit
One neuron and all the muscle cells it contains is called
motor unit
One nueron and all the muscle cells it controls is called
motor unit
Interactions between actin and myosin filaments of the sarcomere are responsible for
muscle contraction.
Myofribrils bundled together form
muscle fiber (cell)
In an isotonic contraction,
muscle tension exceeds the load and the muscle lifts the load.
The ability of a muscle to stay in a slightly contracted state is
muscle tone
In which of the following would the motor units have the fewest muscle fibers?
muscles that control the eyes
Muscle cells are made up of
myofibrils
Muscle cells are made up og
myofibrils
Thick filaments are also called
myosin filaments
Cross-bridges are portions of
myosin molecules
Each skeletal muscle fiber is controlled by a motor neuron at a single
neuromuscular junction.
Acetylcholine
neurotransmitter that stimulates skeletal muscle contraction.
What starts the 'relaxation' phase after a muscle contraction
no impulse sent down motor nueron
Why does muscle fatigue occur?
not enough ATP
Fascicles are covered by a layer of connective tissue called
perimysium
The advantage of having many nuclei in a skeletal muscle fiber is the ability to
produce large amounts of muscle proteins.
Which of the following is a function of skeletal muscle?
produce movement, maintain posture, and maintain body temperature
Muscle is responsible for all the following EXCEPT...
production of vitamin D
During anaerobic glycolysis,
pyruvic acid is produced oxygen is not consumed carbohydrate is metabolized ATP is produced.
A patient takes a medication that blocks ACh receptors of skeletal muscle fibers. What is this drug's effect on skeletal muscle contraction?
reduces the muscle's ability for contraction
The cell membrane in muscle cells is referred to as the
sarcolemma
The cell membrane of the muscle cell is called
sarcolemma
The plasma membrane of a skeletal muscle fiber is called the
sarcolemma.
Functional, repeating unit of all myofibrils
sarcomere
The basic functional unit of a skeletal muscle is the
sarcomere
The repeating unit of a skeletal muscle fiber is the
sarcomere.
Myofibrils are made up of repeating sub-units called
sarcomeres
The basic functional unit of skeletal muscle is the
sarcomeres
In response to an action potential along the transverse tubules, the __________ release(s) calcium ions into the sarcoplasm.
sarcoplasmic reticulum
Within the fiber, calcium ions are stored in the
sarcoplasmic reticulum
A high blood concentration of the enzyme creatine phosphate (CPK) usually indicates
serious muscle damage
How is acetylcholine (ACh) removed from the synaptic cleft?
simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
What are the three types of muscle tissue
skeletal, cardiac, smooth
Movement of the eyeball would be controlled by ____ motor units
small
Which type or muscle tissue do NOT contain sarcomeres?
smooth
Involuntary muscle(s)
smooth and cardiac
The space between the axon terminal and the muscle fiber
synaptic cleft
The narrow space between the synaptic terminal and the muscle fiber is the
synaptic cleft.
At each end of the muscle, the collagen fibers of the epimysium, perimysium, and endomysium, come together to form a
tendon
Muscles are held to bones by
tendons or aponeuroses
The contraction of a muscle exerts a pull on a bone because muscles attach to bones by
tendons.
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
An infection by the bacterium Clostridium tetani can cause the disease called
tetanus.
Acetylcholinesterase
the enzyme that breaks down acetylcholine in the synaptic cleft
Acetylcholine binds to its receptor in the sarcolemma and triggers __________.
the opening of ligand-gated cation channels
Synaptic cleft
the space between the axon terminal and junctional folds.
Which of the following best describes the term Z line?
thin filaments are anchored here
The action potential is conducted into a skeletal muscle fiber by
transverse tubules.
The release of Ca ions triggers the movement of
troponin/ tropomyosin complex
When an action potential arrives at the axon terminal of a motor neuron, which ion channels open?
voltage-gated calcium channels