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37 Cards in this Set
- Front
- Back
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Sarcomere
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The repeating unit of a myofibril |
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Neuron |
The functional unit of the nervous system, a nerve cell |
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Synapse |
The interface between a neuron and another cell |
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Neurotransmitter |
A chemical released by a neuron, which diffuses across the synaptic cleft, enabling the neuron to communicate with another cell. |
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Motor unit |
One motor neuron and all the muscle fibers it innervates |
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All-or-none law of skeletal muscle contraction |
An individual muscle fiber contracts maximally in response to an action potential |
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Subthreshold stimulus |
A stimulus too small to create an action potential in a neuron |
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Threshold stimulus |
A stimulus strong enough to create one action potential in a neuron |
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Submaximal stimuli |
Stimuli of increasing strength that create more action potentials along more neurons |
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Maximal stimulus |
A stimulus that is strong enough to create action potentials on all motor neurons to a particular muscle. |
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Muscle tone |
The state of partial contraction in a muscle, even when the muscle is not being used. |
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What are the four major functional characteristics of muscle tissue? |
Contractility, excitability, extensibility, elasticity |
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What are the three types of muscle tissue? |
Skeletal, cardiac, and smooth |
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Label the following structures of a whole muscle: |
a. Epimysium b. Perimysium c. Endomysium d. Muscle cell (fiber) e. Fasicle
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In terms of their nuclei, skeletal muscle fibers are different from most cells in two ways. What are those ways? |
Skeletal muscle cells have many nuclei rather than just one. Also, the nuclei are at the edge of the cell rather than near the center. |
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Label the parts of the sarcomere below: |
a. Actin myofilament b. Myosin myofilament c. Z-disk d. H-zone e. A-band f. I-band |
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When a muscle fiber contracts, what happens to the distance between the Z-disks? |
The distance between the Z-disks shortens. |
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When a muscle fiber contracts, what happens to the the length of the A-band? |
The length of the A-band remains the same. |
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When a muscle contracts, what happens to the length of the I-bands? |
The lengths of the I-bands decrease. |
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When a muscle fiber contracts, what happens to the length of the H-zone? |
The length of the H-zone shrinks. |
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When a muscle fiber contracts, what happens to the length of the myosin myofilament? |
The length of the myosin myofilament stays the same. |
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When a muscle fiber contracts, what happens to the length of the actin myofilament? |
The length of the actin myofilament stays the same. |
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The following steps occur for muscle contraction. Put them in the proper order:
a. The muscle action potential travels down a T-tubule. b. ACh is released from the presynaptic terminal. c. ATP binds to the myosin heads, making them release the active sites on the actin. d. Ca2+ binds to troponin, causing tropomyosin to move and exposing the active sites on the actin, allowing the myosin heads to bind the actin. e. ACh travels across the synaptic cleft. f. The return stroke. g. Ca2+ are released from the sarcoplasmic reticulum. h. The power stroke. i. An action potential travels down the axon of a motor neuron. j. ACh interacts with the muscle fiber membrane to create a muscle action potential. |
i. The action potential travels down the axon of a motor neuron. b. ACh is released from the presynaptic terminal. e. ACh travels across the synaptic cleft. j. ACh interacts with the muscle cell membrane to create a muscle action potential. a. The muscle action potential travels down a T-tubule. g. Calcium ions are released from the sarcoplasmic reticulum. d. Ca2+ binds to troponin, causing tropomyosin to move and exposing the active sites on the actin, allowing the myosin heads to bind the actin. h. The power stroke. c. ATP binds to the myosin heads, making them release the active sites on the actin. f. The return stroke. |
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The concentration of Ca2+ in the sarcoplasmic reticulum is decreasing. Is the muscle fiber starting to contract or has it finished contracting? |
The muscle fiber is starting to contract. |
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The myosin heads of a sarcomere have just received a boost of energy. Is the power stroke or the return stroke about to happen? |
The return stroke is about to happen. |
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A myosin head has ADP attached to it but not an individual phosphate. Which is going to happen next: the return stroke or the power stroke? |
The power stroke will happen next. |
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Label the parts of the neuromuscular junction: |
a. presynaptic terminal b. mitochondria c. synaptic vesicles d. synaptic cleft e. postsynaptic membrane |
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If you could look at several muscle fibers while they are in action, how could you determine which fibers are part of the same motor unit? |
All of the fibers in the same motor unit will contract identically at the same time. If you could see several muscle fibers always contracting in unison, that would be a motor unit. |
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What is the function of acetylcholinesterase? If it were not for acetylcholinesterase, what would happen to a muscle fiber? |
Acetylcholinesterase inactivates ACh after ACh has stimulated the postsynaptic membrane. If it were not for this enzyme, the muscle fiber could not relax once it started contracting! |
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There are two major roles that ATP plays in muscle contraction and relaxation. The first involves the sarcoplasmic reticulum, while the second involves myosin heads. What are those two roles? |
ATP provides the sarcoplasmic reticulum with energy for the active transport of calcium ions into itself. This is critical for muscle relaxation. ATP attaches to the myosin heads, making them release the active sites and giving them energy for the return stroke. Without this step, the myosin heads would never let go of the active sites, and the muscle could neither relax nor contract. |
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A muscle is stiff. It can neither relax nor contract. What is wrong in the sarcomere? What causes this? |
The myosin heads must be gripping the active sites and not letting go. This must be due to a lack of ATP in the sarcomere. |
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When a muscle fiber relaxes, does it automatically stretch back to its resting size? |
No. When a muscle cell relaxes, the myosin heads release the active sites. This makes it very easy for the muscle to stretch out, but that does not automatically happen. Something else (gravity or another muscle's contraction) must cause the relaxed muscle to extend. |
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A motor unit has just been recruited. What has just happened? |
When a motor unit is recruited, it is responding to a stimulus by sending action potentials down its axon. This stimulates contraction of the muscle fibers in its control, that is, the motor unit. |
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All of the motor units in a muscle have been recruited. If more stimulus is applied, what is that called? |
A supermaximal stimulus is being applied. This will not increase the force of the whole muscle's contraction, since all of its motor units are already "on." |
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A muscle is expending energy faster than it can be replaced by aerobic respiration. There is also no creatine phosphate left. What can the muscle fiber do? |
The only option left is anaerobic respiration. This is not as efficient as aerobic respiration, but it gets energy to the muscle cell quickly. |
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What will build up in the cell using anaerobic respiration? |
Lactic acid will build up in this muscle fiber. It is a byproduct of anaerobic respiration. This waste product must be eliminated from the cell. |
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When we breathe hard after we are finished exercising, what two things is the increased oxygen supply doing for the muscle fibers? |
The increased oxygen supply is fueling aerobic respiration. This provides energy for the muscle fibers to (1) remake creatin phosphate and (2) remake ATP for an energy reserve. The oxygen supply is also used by the liver cells, which convert lactic acid back into glucose. |
