Introduction Remember those four Basic Tissues? Here they are again: 1. Epithelial tissue 2. Connective tissues 3. Muscle tissue 4. Nervous tissue During this lab you will learn about the third Basic Tissues: Muscle. Muscle comes in three different flavors: smooth, cardiac and skeletal. You need to be able to recognize each type of muscle and also differentiate from other tissues that it may easily be confused with (such as connective tissue), which takes practice. Learning objectives and activities Using the Virtual Slidebox: A Identify the connective tissue component of skeletal muscle Examine the organization of connective tissue within a whole skeletal muscle. B Differentiate between muscle types Identify and distinguish between smooth, skeletal and cardiac muscle histologically in both longitudinal and transverse section. C Decipher an EM of a sarcomere Decipher the pattern of proteins that form a sarcomere by interpreting an electron micrograph of skeletal muscle. D Test your skills Complete the self-quiz to test your understanding and master your learning. IDENTIFY THE CONNECTIVE TISSUE COMPONENT OF SKELETAL MUSCLE i. Tendon Examine Slide 1(15) to review the structure of a tendon. i. Dense regular connective tissue and accompanying fibroblasts. Recall why this organization is the most optimal for a tendon. ii. ii. Deep fascia Examine Slide 2a (13) and Slide 3a to approximate the location of deep fascia. iii. Dense regular/irregular connective tissue that separates muscles into compartments. This layer is best seen in gross anatomy and is not iv. observed in these specimens. iii. Epimysium Examine Slide 2a (13) and Slide 3a to locate the epimysium. Dense irregular connective tissue that fascicle v. surrounds individual skeletal muscles, it is continuous with the connective tissue of the tendon. It is poorly preserved in this section. iv. Perimysium Examine Slide 2a (13) and Slide 3a to locate the perimysium. Loose irregular connective tissue surrounding fiber myofibril a collection of muscle fibers called a fascicle. v. Endomysium Examine Slide 2a (13) and Slide 3a to locate the endomysium. Loose irregular connective tissue surrounding an individual muscle fiber. DIFFERENTIATE BETWEEN MUSCLE TYPES 1. Skeletal muscle Observe these features of skeletal muscle cells in long Slide 2b (13) & cross Slide 2c (13) section Longitudinal section Cross section i. Cell size/shape Large: long and cylindrical Large: polyhedral ii. Nuclei Multinucleated: peripherally located Multinucleated: peripherally located iii. Striations Visible Not visible iv. Other features - Many capillaries in endomysium 2. Cardiac muscle Observe these features of cardiac muscle cells in long Slide 4a (31) & cross Slide 4b (31) section Longitudinal section Cross section i. Cell size/shape Short: branching cells Small: circular-polyhedral ii. Nuclei Mononucleated: centrally located Mononucleated: centrally located, few iii. Striations Visible Not visible iv. Other features Intercalated discs Plenty cytoplasm around nuclei 3. Smooth muscle Observe these features of smooth muscle cells in long Slide 5a (54) & cross Slide 5b (54) section Longitudinal section Cross section i. Cell size/shape Shortest: spindle-shaped cells Smallest: circular ii. Nuclei Mononucleated: centrally located Mononucleated: centrally located, many iii. Striations None None iv. Other features Cigar-shaped nuclei Sparse cytoplasm - nucleus occupies cell Compare and Contrast: It is essential that you can distinguish between the three muscle types. Compare and contrast the different features discussed above using Slide 6 (14) DECIPHER AN EM OF A SARCOMERE When observed in the microscope, longitudinally sectioned skeletal and cardiac muscle exhibit alternating dark and light banding known as cross-striations. The arrangement of actin and myosin in the myofibril creates this appearance. It is best seen in high resolution electron micrographs. A muscle fiber/cell Endomysium I-band A-band I-band H-zone Myofibril Z-line M-line Z-line Sarcomere Identify the different regions/bands in the diagram above, in the electron micrograph below or using Slide 7 and recall how these regions change in width/do not change in width during muscle contraction. I-band A-band I-band (actin/thin filaments) (mysoin/thick filaments) (actin/thin filaments) H-zone Z-line M-line Z-line (site of actin cross-linking (site of myosin cross-linking) (site of actin cross-linking Sarcomere TEST YOUR SKILLS You must be able to identify the following types of muscle and associated histological features in a variety of tissues: Skeletal muscle (in longitudinal and cross section) Epimysium Perimysium Endomysium Fascicle Muscle fiber Striations Skeletal muscle nuclei Cardiac muscle (in longitudinal and cross section) Striations Cardiac muscle nuclei Intercalated discs Smooth muscle (in longitudinal and cross section) Smooth muscle nuclei Musculo-tendinous junction Dense regular connective tissue (tendon) Fibroblasts Skeletal muscle Striated muscle (electron micrographs) A-band H-zone M-line I-band Z-line Actin Myosin Sarcomere.