Since we ll be studying muscular and nervous tissue extensively later on in the year, this is just a brief overview of these two tissue types.

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2 Since we ll be studying muscular and nervous tissue extensively later on in the year, this is just a brief overview of these two tissue types. Muscular tissue is unique because it is the only tissue whose cells can contract (shorten). This allows movement. Note that there are two types of movement: Somatic (voluntary) movement refers to moving the bones or skin of the face. Visceral (involuntary) movement refers to internal movement, usually of moving substances (blood, food, lymph, urine, etc.) through the body. 2

3 There are three types of muscle tissue you should be familiar with. For each, be sure you know where the tissue is found in the body, what it does, and what it looks like under the microscope. 3

4 Skeletal muscle is involved mostly with voluntary movement. At least one end of a skeletal muscle is attached to bone. The other end may insert on either another bone across a joint or on the skin of the face. Skeletal muscles allow body movement and facial expression. Although we can say that skeletal muscle is generally involved in voluntary movement, skeletal muscles are also used for reflexes and breathing. Histologically, skeletal muscles look very unique. They are very long, sometimes even a few feet long (think of the back and thigh muscles, for example) and are cylindrical. The cells have a characteristic striated (striped) appearance that makes them look kind of like candy canes when stained under a microscope. Because the cells can get so long, they have many nuclei to control protein synthesis at all parts of the muscle. 4

5 The striated appearance of skeletal muscles is caused by the arrangement of contractile protein fibers inside the muscle cells. Places where many fibers overlap stain darker than areas where few protein fibers overlap. We ll learn more about this arrangement when we study the muscular system later. 5

6 Cardiac muscle makes up the wall of the heart and is responsible for the contractions that pump blood and generate blood pressure. Histologically, cardiac muscle cells are striated like skeletal muscle cells, but they are much smaller. Adjacent cardiac muscle cells are joined together at dark-staining lines called intercalated discs, which allow the cells to contract as a unit. Since the cells are small, they only need one nucleus apiece. 6

7 Smooth muscle (also called visceral muscle) is responsible for most of the internal, involuntary movements, other than the beating of the heart. Generally speaking, smooth muscle is found surrounding most of the hollow organs of the body (stomach, intestines, urinary bladder, blood vessels, etc.). When the smooth muscle contracts, substances inside the organs are propelled forward. There is also smooth muscle in the skin that causes your hair to stand on end when cold and in the iris of the eye to control pupil size. Smooth muscle cells are short and spindle-shaped (tapered at both ends) and are uninucleate. It is called smooth muscle because there are no real striations to be seen under the microscope. 7

8 Nervous tissue is the only tissue type that can communicate electrochemically. Impulses are exchanged between the sensory receptors, central nervous system, muscles, and glands. 8

9 The main functional type of cell that makes up nervous tissue is the neuron. There are several different types of neurons, but they all have communication in common. Generally speaking, neurons receive impulses from several inputs and send just one impulse out. 9

10 While there are many, many different types of neurons, each one has a receiving end (the dendrites) and a sending end (the axon). We ll learn more about neurons and how they work when we study the nervous system later. 10

11 Note how richly-branched the dendrites of this neuron is. It can receive inputs from thousands and thousands of other neurons. Since it only has one axon, it only sends out a single impulse, though. This is an example of how the nervous tissue integrates information. 11

12 The other type of cell that makes up nervous tissue is neuroglia (or glia for short). Neuroglial cells do not communicate with other cells. Instead, they support the nervous system and allow the neurons to do their jobs. Some glia, for example, hold the neurons processes in place. Some devour invading bacteria. Some repair damaged neurons in the periphery. Etc. 12