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. g; perimysium c; fascicle
a. b. c. endomysium epimysium fascicle fiber myofibril myofilament perimysium sarcolemma sarcomere sarcoplasm tendon
1. 2. 3. 4. 5. 6. 7.
connective tissue ensheathing a bundle of muscle cells bundle of muscle cells contractile unit of muscle
d; fiber a; endomysium h; sarcolemma e; myofibril
d. a muscle cell thin reticular connective tissue surrounding each muscle cell plasma membrane of the muscle fiber a long filamentous organelle with a banded appearance found within muscle cells actin- or myosin-containing structure e. f. g. h. 1.
cord of collagen fibers that attaches a muscle to a bone
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
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? a tendon is a band or cord of the same tissue.
An aponeurosis is a sheet of white fibrous connective tissue;
t_o_o_t_h_er_m_u_sc_l_es_. _ How is an aponeurosis functionally similar to a tendon? _B_o_t_h_s_e'_II_e_t_o_a_tt_a_ch_m_u_s_c_le_s_to_b_o_ne_s_o_,_'
S. 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.
A band actin filament I band
d. e. f.
myosin filament T tubule terminal cisterna
g. h. i.
triad sarcomere Z disc
6. On the following figure, label a blood vessel, endomysium, epimysium, a fascicle, a muscle cell, perimysium, and the tendon. Perimysium
Review Sheet 14
7. Complete the following statements: The junction between a motor neuron's axon and the muscle cell membrane is called a neurornuseular junction or a _1_ junction. A motor neuron and all of the skeletal muscle cells it stimulates is called a _2_. The actual gap between the axon terminal and the muscle cell is called a _3_. Within the axon terminal are many small vesicles containing a neurotransmitter substance called_4_. When the _5_ reaches the ends of the axon, the neurotransmitter is released and diffuses to the muscle cell membrane to combine with receptors there. The combining 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. 1. 2. 3. 4. 5. 6. myoneural motor unit synaptic cleft acetylcholine nerve impulse (action potential) depolarization
8. The events that occur at a neuromuscular junction are depicted below. Identify by labeling every structure provided with a leader line.
Key: a. b. a e c. d. e.
axon terminal mitochondrion muscle fiber myelinated axon sarcolemma synaptic cleft synaptic vesicle T tubule
f. c g. h.
Junctional---R:: folds of the sarcolemma h -+-----.:r-!-I Part of a myofibril
Review Sheet 14