Microscopic Anatomy and Organization of Skeletal Muscle

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REVIEW SHEET NAME ______EXERCISE 14 LAB TIME/DATE ______Microscopic Anatomy and Organization of Skeletal Muscle

Skeletal Muscle Cells and Their Packaging into Muscles 1. Use the items in the key to correctly identify the structures described below. Key:

g; perimysium 1. connective tissue ensheathing a bundle of muscle cells a. endomysium

c; fascicle 2. bundle of muscle cells b. epimysium c. fascicle i; sarcomere 3. contractile unit of muscle d. fiber d; fiber 4. a muscle cell e. myofibril a; endomysium 5. thin reticular connective tissue surrounding each muscle cell f. myofilament h; sarcolemma 6. plasma membrane of the muscle fiber g. perimysium

e; myofibril 7. a long filamentous organelle with a banded appearance found h. sarcolemma within muscle cells i. sarcomere f; myofilament 8. actin- or myosin-containing structure j. sarcoplasm

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

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

The connective tissue wrappings (a) bundle the muscle fibers together, increasing coordination of their activity; (b) add strength to the

muscle; and (c) provide a route for entry and exit of blood vessels and nerves to the muscle fibers.

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

They conserve space (less bulky than fleshy muscle attachments) and are more durable than muscle tissue where bony prominences

must be spanned.

4. How does an aponeurosis differ from a tendon structurally? An aponeurosis is a sheet of white fibrous connective tissue;

a tendon is a band or cord of the same tissue.

How is an aponeurosis functionally similar to a tendon? Both serve to attach muscles to bones or to other muscles.

5. The diagram illustrates a small portion of several myofibrils. Using letters from the key, correctly identify each structure indicated by a leader line or a bracket. Key: a. A band d. myosin filament g. triad b. actin filament e. T tubule h. sarcomere c. I band f. terminal cisterna i. Z disc

h a c d b

f e

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

Perimysium

Blood vessel

Endomysium

Muscle cell (fiber)

Tendon Epimysium Fascicle

The Neuromuscular Junction 7. Complete the following statements:

The junction between a motor neuron’s axon terminal and the muscle cell 1. ______neuromuscular (myoneural) membrane is called a(n) __1__ junction. A motor neuron and all of the skeletal muscle cells it stimulates is called a(n) __2__. The actual gap between the axon 2. ______motor unit terminal and the muscle cell is called a(n) __3__. Within the axon terminal are many small vesicles containing a neurotransmitter substance called__4__. When 3. ______synaptic cleft the __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 combining 4. ______acetylcholine of the neurotransmitter with the muscle membrane receptors causes the membrane to become permeable to both sodium and potassium. The greater influx of sodium ions results in __6__ of the membrane. Then contraction of the muscle cell occurs. 5. ______action potential (nerve impulse)

6. ______depolarization

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

Key: d a. axon terminal

Action potential b. mitochondrion

c. muscle fiber a d. myelinated axon

e. sarcolemma Nucleus f. synaptic cleft c g. T tubule

h. vesicle containing ACh h b f

Junctional folds of the sarcolemma

Part of a myofibril