Unit 10 Slides

In Unit 2 you studied a variety of animal tissues. The following material is designed as a review and amplification of the material presented previously. Here you will be concentrating on connective tissue (specifically bone and cartilage) and muscle tissue.

Connective Tissue

Slide 1 is of hyaline cartilage, the most common type of cartilage. Note the clusters of large cartilage cells located in spaces in the extracellular gel matrix. In cartilage the cells are embedded in an amorphous matrix of ground substance reinforced by an interlacing network of fine collagen fibers which cannot be distinguished by light microscopy. These fibers give the matrix a rubbery consistency. Cartilage can support great weight, yet it is often flexible and somewhat elastic. Note that there is no well-developed blood supply in cartilage, which is why damage to cartilage takes so long to heal.

Slide 2 is a cross-section of compact bone. Bone is living tissue and has a hard, relatively rigid matrix. The matrix contains numerous collagen fibers and is impregnated with inorganic salts, primarily calcium phosphate. Compact bone is composed of numerous structural units called Haversian systems. Each Haversian system is seen as a nearly round area. The circular core of each system is the Haversian canal that runs lengthwise through the bone. Blood vessels and nerves run through the Haversian canals. Around the Haversian canal is a series of concentrically arranged hard lamellae, perforated by elongate dark areas, called lacunae, in which the bone cells (osteocytes) are located. The numerous very thin dark lines running radially from the central canal across the lamellae to the lacunae are the canaliculi. These channels connect the bone cells to one another and to the Haversian canal. They provide the "highways" through which tissue fluid, oxygen, and nutrients can reach the widely separated bone cells, imprisoned as they are in a desert of solid matrix.

Transverse sections of compact bone. At left, polarized light micrograph of human bone showing Haversian Canals (small dark areas). Human compact bone is composed of parallel columns made up of concentric bony layers (lamellae) organized around channels containing blood vessels, lymph vessels and nerves - the Haversian Canals. The bony columns are arranged in parallel to the axes of long bones. The central canals and their surrounding lamellae are known collectively as Haversian systems. Deposition of bone occurs concentrically from the periphery of the originally broad Haversian channel, with the bone lamellae being layed down by osteoblast cells.

	Slide 3 is a longitudinal section of compact bone. Note the Haversian canals (HC) running lengthwise throughout the bone. The lacunae are the elongated brown specks arranged in concentric layers around the Haversian canals.
	Slide 4 is a scanning EM of a Haversian canal running lengthwise through the bone. Blood vessels, lymph vessels, and nerves run through the canal. Note the openings of the canaliculi.
	Slide 5 is of spongy bone from the end of the femur. Spongy bone is made up of slender bars of bony tissue that interlace with one another. The spaces between are filled with dark red tissue, the red bone marrow. The long bones of the limbs are composed of a tube of hard compact bone (Slide 2) while the ends are composed of spongy bone covered by a shell of compact bone. Spongy bone does not contain Haversian systems.

Muscle or Contractile Tissue

	Slide 6 is a longitudinal section of striated muscle. Notice that each cell (or fiber, as it is usually called) is roughly cylindrical, contains many nuclei (dark spots, usually found at the edge of the fiber) and is crossed by alternating dark and light bands called striations. The fibers are usually bound together by connective tissue into bundles.
	Slide 7 is a cross-section of a skeletal muscle. Note the peripheral location of the nuclei. In the unfixed tissue the fibers are round but during fixation they become artificially polyhedral. (C = blood capillaries; P = strand of connective tissue.)
	Slide 8 is a high-power view of a single striated muscle fiber in longitudinal view. Note the peripheral locations of the nuclei and the definite striations.
	Slide 9 shows several neuromuscular junctions. The dark lines entering from the center right and going to the individual muscle fibers are motor neurons. A specialized structure, the neuromuscular junction is formed from the end of the axon and the adjacent portion of the muscle surface. Transmission across this gap is by transmitter chemicals. Cells of skeletal muscle are innervated by a single nerve fiber from the somatic nervous system.
	Slide 10 is a longitudinal section of smooth muscle. Smooth muscle fibers interlace to form sheets of muscle rather than bundles. Each fiber is elongate, pointed at each end, and contains a single, centrally located nucleus. There are no striations. Smooth muscle fibers are innervated by the autonomic nervous system; each fiber has both SANS and PANS innervation.
	Slide 11 is a longitudinal section of cardiac muscle. Cardiac cells often branch and interdigitate, thus forming the complex three-dimensional network seen here. The tiny brown cells seen in spaces between the fibers are red blood cells; cardiac muscle is well supplied with blood. Notice that cardiac muscle has some of the attributes of smooth muscle, and some of striated muscle. There are striations but these are not as apparent as in striated muscle. Like smooth muscle, each fiber has a single nucleus. Cardiac muscle is innervated by both divisions of the autonomic nervous system.
	Slide 12 is a longitudinal section of cardiac muscle at a higher magnification. The muscle fibers branch and interdigitate, but each is a complete unit surrounded by a cell membrane. The thick dark line in the center, marking the junction between two cells, is an intercalated disk. These are places where one cell ends and the next begins; here the membranes of both fibers parallel each other through an extensive series of folds. They provide a strong union between fibers, so a pull of one contractile unit can be transmitted along its axis to the next. These are also places where electrical stimuli can pass directly from one cell to the next.
	Slide 13 shows bacterial flagella. Many bacteria actively move about by means of flagella arising from one or both ends of a cell, or from the entire surface. These flagella are quite different from the flagella and cilia of eukaryotes. Eukaryotic flagella propel cells with a wavelike motion, utilizing the energy of ATP. By contrast, bacterial flagella are thin helical filaments that propel the cells with a propeller-like, rotating motion. The energy for this process does not come from ATP directly; a proton pump is involved. When a cell has more than one flagellum, the flagella cluster together and rotate as a single bundle. The flagella propel the cell by rotating in a fashion similar to the propeller of a ship.
	Slide 14 shows longitudinal and cross-sections of eukaryotic flagella. Note the 9 + 2 arrangement of the microtubules.