III. Independent Work: Muscle Tissues

Exercise 1. Read the text.

Muscle Tissues

Muscle is composed of elongated cells which have the power of contracting or reducing their length. This property of contraction is ultimately a molecular phenomenon and is due to the presence of protein molecules which can stretch out or shorten. The following three types of muscle occur in the body.

Smooth muscle is found in sheet or tubes forming the wall of many hollow or tubular organs, for example the bladder, the intestines or blood vessels. The cells forming this tissue are long spindles with a central oval nucleus. They are usually packed together with a little connective tissue between them.

Striated muscle is found in masses of various shapes usually directly or indirectly attached to bone and forms the fleshy party of the body. It is composed of cylindrical fibers often of great length in which separate cells cannot be distinguished. Many small nuclei are found in the fibers and lie just under the surface. Fibrils are present running lengthwise along the muscle fibers and show alternate light and dark bands which give an appearance of striations across it. Bundles of fibers form the muscle which is embedded in connective tissue.

Cardiac muscle which is found only in the heart forms the bulk of its substance and resembles striated muscle except that the nuclei are placed centrally. The fibers form a continuous network but each cell functions as separate unit.

These three types of muscle have different types of action as follows:

1. Smooth muscle cells act in conjunction with one another though influenced by nerves, can function when they have no connection with the central nervous system. They contract slowly but can maintain this contraction for long periods.

2. Striated muscle, on the other hand, contracts quickly, rapidly becomes fatigued and has no function unless it is connected through nerves with the central nervous system.

3. Cardiac muscle has the power of rhythmical spontaneous contraction which is affected by nervous influences but carries on independently of its nervous connection.

Exercise 2. Make up a plan of the text.

Exercise 3. Choose sentences about the differences in muscles structure. Exercise 4. Put sentences in the correct order.

1. Bundles of fibers form the muscle which is embedded in connective tissue. 2. Cardiac muscle has the power of rhythmical spontageous contraction. 3. The following three types of muscle occur in the body. 4. Striated muscle is found in masses of various shapes. 5. Smooth muscle is found in sheet or tubes forming the wall of many hollow or tubular organs. 6. Muscle is composed of elongated cells.

UNIT NINE

1	Speaking	Skin (Integumentary System)
II	Grammar	1. Prepositional Infinitive Complex (§99). 2. Особливості перекладу інфінітивних комплексів(§100)
III	Independent Work	Taking Care of Skin and Its Appendages