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14

1. Use the items in the key to correctly identify the structures described below.

1. connective tissue ensheathing a bundle of muscle cells

2. bundle of muscle cells

3. contractile unit of muscle

4. a muscle cell

5. thin reticular connective tissue surrounding each muscle cell

6. plasma membrane of the muscle fiber

7. a long filamentous organelle with a banded appearance found within muscle cells

8. actin- or myosin-containing structure

9. cord of collagen fibers that attaches a muscle to a bone

Key:

a. endomysium

b. epimysium

c. fascicle

d. fiber

e. myofibril

f. myofilament

g. perimysium

h. sarcolemma

i. sarcomere

j. sarcoplasm

k. tendon

2. List three reasons why the connective tissue wrappings of skeletal muscle are important.

3. Why are there more indirect�that is, tendinous�muscle attachments to bone than there are direct attachments?

4. How does an aponeurosis differ from a tendon structurally?

How is an aponeurosis functionally similar to a tendon?

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5. The diagram illustrates a small portion of several myofibrils. Using letters from the key, correctly identify each structureindicated by a leader line or a bracket.

Key: a. A band d. myosin filament g. triadb. actin filament e. T tubule h. sarcomerec. I band f. terminal cisterna i. Z disc

6. On the following figure, label a blood vessel, endomysium, epimysium, a fascicle, a muscle cell, perimysium, and the tendon.

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7. Complete the following statements:

The junction between a motor neuron�s axon and the muscle cell membrane iscalled a neuromuscular junction or a __1__ junction. A motor neuron and all of theskeletal muscle cells it stimulates is called a __2__. The actual gap between theaxon terminal and the muscle cell is called a __3__. Within the axon terminal aremany small vesicles containing a neurotransmitter substance called__4__. Whenthe __5__ reaches the ends of the axon, the neurotransmitter is released and dif-fuses to the muscle cell membrane to combine with receptors there. The combiningof the neurotransmitter with the muscle membrane receptors causes the membraneto become permeable to both sodium and potassium. The greater influx of sodiumions results in __6__ of the membrane. Then contraction of the muscle cell occurs.

1. ________________________

2. ________________________

3. ________________________

4. ________________________

5. ________________________

6. ________________________

Junctionalfolds of thesarcolemma

Part of amyofibril

Actionpotential

(a)

(b)

Nucleus

8. The events that occur at a neuromuscular junction are depicted below. Identify by labeling every structure provided with aleader line.

Key:

a. axon terminal

b. mitochondrion

c. muscle fiber

d. myelinated axon

e. sarcolemma

f. synaptic cleft

g. synaptic vesicle

h. T tubule