Somatic Motor Pathways and Skeletal Muscle Flashcards

The narrow space between the axon terminal and the motor end plate is called the:

1. Synaptic cleft
2. vesicle
3. axon
4. sarcolemma

Stimulation of acetylcholine (ACh) receptors by ACh will primarily result in:

1. potassium ions entering the muscle fiber
2. chloride ions entering the muscle fiber
3. sodium ions entering the muscle fiber
4. ACh entering the muscle fiber

The end-plate potential is:

1. a depolarization caused by sodium ion movement into the extra cellular fluid
2. a depolarization caused by sodium ion movement into the cytosol
3. a depolarization caused by sodium movement into the cytosol
4. a depolarization caused by sodium ion movement into the extra cellular fluid

The neurons of patients with multiple sclerosis are unable to transmit action potentials down the axon. How will that affect skeletal muscle stimulation?

1. the muscle will be stimulated and will contract
2. the muscle will not be stimulated, but will still contract
3. the muscle will be stimulated, but will not be able to contract
4. 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:

1. increased excitability of the muscle fibers at the site of injection
2. increased levels of ACh in the synaptic cleft
3. muscle paralysis at the site of injection
4. decreased production of ACh

When muscle fibers are stimulated so frequently they do not have an opportunity to relax, they are experiencing:

1. wave stimmulation
2. twitch
3. unfused or incomplete tetanus
4. fused or complete tetanus

The corticospinal pathways

1. Are descending motor pathways
2. Begin in the cortex of the cerebellum
3. Consist of 3 or more neurons linked synaptically
4. All of the choices are correct

The cross bridge cycle starts when ________.

1. Ca²⁺ from the sarcoplasmic reticulum binds to troponin
2. Ca²⁺ is actively transported into the sarcoplasmic reticulum
3. Ca²⁺ from the sarcoplasmic reticulum binds to tropomyosin
4. acetylcholine diffuses away from the synaptic cleft
5. ATP binds to troponin and is hydrolyzed to ADP and P_i

The sarcomere shortens when the myosin heads of thick filaments, in a cocked position, form cross bridges with the actin molecules in thin filaments. Steps that occur during a single cross bridge cycle in the correct order:

Clostridium botulinum is a bacterium that produces botulinum toxin that inhibits the release of acetylcholine. Which description best fits how muscle cells will respond to a lack of acetylcholine?

1. Muscle cells will produce a greater tension when there is a lack of acetylcholine
2. Muscle cells will produce sustained contractions without relaxation when there is a lack of acetylcholine
3. Muscle cells will become paralyzed when there is a lack of acetylcholine
4. Muscle cells will experience fused or complete tetanus when there is a lack of acetylcholine

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?

1. Excitation, in this case, refers to the propagation of action potentials along the sarcolemma.
2. Excitation refers to the shape change that occurs in voltage-sensitive proteins in the sarcolemma.
3. Excitation refers to the release of calcium ions from the sarcoplasmic reticulum.
4. 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?

1. Voltage-sensitive proteins change shape.
2. Calcium release from the sarcoplasmic reticulum initiates the contraction.
3. Sodium release from the sarcoplasmic reticulum initiates the contraction.
4. Action potentials propagate into the interior of the skeletal muscle fiber.

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

1. Myosin cross bridge binding sites
2. potassium leak channels
3. voltage-gated sodium channels
4. a series of proteins that control calcium release

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

1. Motor endplates
2. terminal cisternae
3. sarcoplasmic reticulum
4. transverse or T tubules

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

1. Acetylcholine
2. Sodium ions
3. Calcium ions
4. Action Potentials

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

1. Motor neurons always innervate thousands of skeletal muscle fibers.
2. A motor neuron typically innervates only one skeletal muscle fiber.
3. Typically, hundreds of skeletal muscle fibers are innervated by a single motor neuron.
4. A skeletal muscle fiber is innervated by multiple motor neurons.

Increase in tension by increasing the number of motor units that are stimulated is called _______.

1. muscle tone
2. autorhythmicity
3. recruitment
4. hypertonia

Latroxin, produced by the poisonous black widow spider, increases the release of acetylcholine. How do muscle cells respond?

1. Muscle cells will become paralyzed when excess acetylcholine exists
2. Muscle cells twitch irregularly when excess acetylcholine exists
3. Muscle cells will experience a longer latent period when excess acetylcholine exists
4. Muscle cells will experience fused or complete tetanus when excess acetylcholine exists

What parts of the brain ultimately plan and coordinate complex motor activities?

1. cerebrum, cerebellum, and basal nuclei
2. cerebrum and basal nuclei
3. cerebrum and cerebellum
4. cerebellum and basal nuclei

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

1. arrival of an action potential
2. ATP
3. calcium ion pump
4. troponin

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

1. actin
2. tropomyosin
3. myosin
4. troponin

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

1. actin
2. tropomyosin
3. troponin

What causes the myosin head to disconnect from actin?

1. hydrolysis of ATP
2. binding of troponin
3. binding of ATP
4. binding of calcium

What causes the power stroke?

1. binding of ATP
2. release of ADP and P_i
3. calcium
4. hydrolysis of ATP

The primary motor area

1. contains sensory neurons for the face in its inferior portion
2. contains a smaller area for control of the hands than for control of the legs
3. contains neurons that control smooth muscle
4. contains a larger area for control of the hand and fingers than for control fo the arm and elbow

What is the function of the muscle cell feature indicated by the arrow? (Pointing to the sarcoplasmic reticulum)

1. part of coupling the action potential to contraction
2. houses the genetic material of the cell
3. making of ATP- the "power house" of the cell
4. storage of calcium

When a muscle cell generates tension but does not change length, a(n) _______ contraction occurs.

1. isometric
2. isotonic
3. concentric
4. eccentric

A drug that interferes with the active transport of calcium ions from the sarcoplasmic back into the sarcoplasmic reticulum would result in

1. relaxation of the muscle fiber
2. contraction with no relaxation
3. muscle hypertrophy
4. an imbalance of blood calcium

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?

1. Acetylcholine is transported into the postsynaptic neuron by receptor-mediated endocytosis.
2. Acetylcholine diffuses away from the cleft.
3. Acetylcholine is transported back into the axon terminal by a reuptake mechanism.
4. 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?

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

Action potentials travel the length of the axons of motor neurons to the axon terminals. These motor neurons __________.

1. extend from the brain to the sarcolemma of a skeletal muscle fiber
2. extend from the spinal cord to the sarcolemma of a skeletal muscle fiber
3. extend from the brain or spinal cord to the sarcolemma of a skeletal muscle fiber
4. arise in the epimysium of a skeletal muscle and extend to individual skeletal muscle fibers

Calcium entry into the axon terminal triggers which of the following events?

1. Synaptic vesicles fuse to the plasma membrane of the axon terminal and release acetylcholine.
2. Acetylcholine is released into the cleft by active transporters in the plasma membrane of the axon terminal.
3. Acetylcholine binds to its receptor.
4. Cation channels open and sodium ions enter the axon terminal while potassium ions exit the axon terminal.

Acetylcholine binds to its receptor in the sarcolemma and triggers __________.

1. the opening of voltage-gated calcium channels
2. the opening of ligand-gated anion channels
3. the opening of calcium-release channels
4. the opening of ligand-gated cation channels

Sodium and potassium ions do not diffuse in equal numbers through ligand-gated cation channels. Why?

1. The inside surface of the sarcolemma is negatively charged compared to the outside surface. Potassium ions diffuse inward along favorable chemical andelectrical gradients.
2. The outside surface of the sarcolemma is negatively charged compared to the inside surface. Potassium ions diffuse outward along favorable chemical and electrical gradients.
3. The inside surface of the sarcolemma is negatively charged compared to the outside surface. Sodium ions diffuse inward along favorable chemical and electrical gradients.
4. 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 transverse tubules in a skeletal-muscle fiber

1. Store calcium ions
2. Provide a means of transmitting an action potential in the muscle plasma membrane to central portions of the fiber
3. Store ATP
4. Stores glycogen

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

1. dopamine
2. serotonin
3. acetylcholine (ACh)
4. norepinephrine

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

1. chemically gated calcium channels
2. voltage-gated potassium channels
3. voltage-gated calcium channels
4. voltage-gated sodium channels

What means of membrane transport is used to release the neurotransmitter into the synaptic cleft?

1. a channel
2. exocytosis
3. a protein carrier

The binding of the neurotransmitter to receptors on the motor end plate causes which of the following to occur?

1. Binding causes chemically gated potassium channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell.
2. Binding causes potassium voltage-gated channels to open in the motor end plate (junctional folds of the sarcolemma) and potassium enters the cell.
3. 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.
4. Binding causes voltage-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?

1. acetylcholinesterase (AChE; an enzyme) only
2. simple diffusion away from the synaptic cleft and acetylcholinesterase (AChE; an enzyme)
3. acetylcholinesterase (AChE; an enzyme) and endocytosis into the muscle fiber
4. simple diffusion away from the synaptic cleft and endocytosis into the muscle fiber

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?

1. T tubule
2. cytosol
3. terminal cisterns (cisternae) of the sarcoplasmic reticulum
4. sarcolemma

Place the following events of excitation in the correct order.
1) ion channels on the sarcolemma open and sodium ions enter the muscle fiber
2) the entry of sodium ions into the muscle fiber depolarizes the sarcolemma locally
3) acetylcholine is released from vesicles in the motor neuron into the synaptic cleft
4) an action potential arrives at the axon terminal of a motor neuron
5) acetylcholine binds to ligand-gated sodium ion channels in the motor end plate

1. 4, 3, 5, 1, 2
2. 2, 4, 3, 5, 1
3. 3, 4, 5, 1, 2
4. 4, 5, 3, 2, 1

List the following structures in order from smallest to largest.
(1) muscle fiber
(2) myofilament
(3) myofibril
(4) muscle fasciculus

1. 4, 2, 3, 1
2. 2, 1, 4, 3
3. 3, 1, 4, 2
4. 2, 3, 1, 4

A crossbridge forms when:

1. a myosin head binds to ATP.
2. an actin head binds to myosin.
3. a myosin head binds to actin.
4. an actin head binds to ATP.

Which of the following steps of the crossbridge cycle occurs immediately before the power stroke?

1. A crossbridge forms.
2. ATP hydrolysis "cocks" the myosin head.
3. Myosin heads detach from actin.
4. Calcium ions bind to myosin.

As myosin heads complete the power stroke, actin filaments:

1. slide toward the M line of the sarcomere.
2. move closer to myosin.
3. move farther away from myosin.
4. slide away from the M line of the sarcomere.

Which of the following causes myosin to detach from actin?

1. A calcium ion binds to myosin.
2. An ATP molecule binds to myosin.
3. An ADP molecule is hydrolyzed to ATP.
4. Troponin binds to myosin.

In the absence of ATP in the muscle, which of the following is most likely to occur?

1. All myosin heads will continuously be in the "cocked" position.
2. Some myosin heads will remain attached to actin molecules, but are unable to perform a power stroke.
3. The crossbridge cycle will be much slower.
4. The crossbridge cycle will continue as normal, because ATP is not necessary for muscle contraction.

If the Na⁺ voltage-gated channels in a muscle cell open, what will be the result?

1. The same result happens as if K+ voltage-gated channels have opened
2. repolarization
3. depolarization
4. The cell will remain at resting membrane potential

In preparation for contraction, calcium ions bind to:

1. tropomyosin
2. troponin
3. myosin
4. sodium ions

The protein that binds to actin when tropomyosin moves off of the active sites of actin, is:

1. titin
2. troponin
3. calcium ions
4. myosin

What type of contraction is this? (Muscle stays the same length)

1. concentric contraction
2. eccentric contraction
3. isometric contraction
4. isotonic contraction

Heat released from contracting muscles functions to ________.

Voluntary control over swallowing, defecation, and urination is provided by muscles that ________.

The permission surrounds a bundle of muscle fibers called a __________.

Which connective tissue layer wraps the entire muscle?

Which structure in a muscle fiber or muscle cell is continuous with the sarcolemma and carries the signal to contract deep into the muscle cells?

The repeating functional units seen on the myofibrils are ________.

Which of the following is NOT found in a thin filament?

Which of the following is the dark band seen on myofibrils?

The neurotransmitter required to trigger skeletal muscle contraction is __________.

What must bind to troponin in order to expose the active sites on actin?

In a twitch, what is the phase in which tension rises to a peak?

All the muscle fibers and the single motor neuron that innervates them are called a __________.

What is the type of contraction in which the muscle does NOT change length and the contraction does NOT produce tension that exceeds the load?

Which of the following produces ATP from glucose anaerobically?

When glycolysis produces pyruvic acid faster than it can be used by the mitochondria, pyruvic acid is converted to _________, which lowers the pH of body fluids.

What muscle fiber type contains abundant myoglobin and is specialized to contract for extended periods of time?

What is the name of the structure that contains gap junctions and desmosomes and joins the plasma membranes of two cardiac muscle cells together?

What is the term for the ability of cardiac muscles cells to contract without neural stimulation?

Which of the following is NOT a characteristic of smooth muscle tissue?

What is the term for the ability to function over a wide range of lengths?