RJ Perz-Edwards Lab 6: Muscle Histology Notes 9/10/13 Skeletal Muscle Vocabulary Myo = muscle, Greek (Myofiber, myofibril, myofilaments) Sarco = flesh (muscle), Greek (Sarcomere, Sarcolemma, Sarcoplasmic reticulum) Epimysium → Perimysium → Endomysium = CT sheathes around muscle, fascicles & fibers, respectively Muscle → Fascicle → Fiber → Fibril → Filaments (Need EM!) Mind the accents: FIB-er –vs– fib-RIL Two new organelles and one new membrane trick Sarcoplasmic reticulum = specialized smooth ER that sequesters Ca 2+ ions. Myofibril = the contractile machinery of striated muscle. T-tubules = invaginations of sarcolemma to carry depolarization into interior of cell Key Identifying Features LS o Fibrous = very long cells (up to cms), 20-100 µm diameter o Striations = stripes = A-I banding, 2-4 µm long o Peripheral, cigar-shaped nuclei, multiple nuclei per cell CS o Large, polygonal cells, 20-100 µm diameter o Stippled appearance = 1-µm dots = myofibrils in CS. o Peripheral nuclei Other cell types or structures
Two new organelles and one new membrane trick Sarcoplasmic reticulum = specialized smooth ER that sequesters Ca2+ ions. Myofibril = the contractile machinery of striated muscle. T-tubules = invaginations of sarcolemma to carry depolarization into interior of cell
Key Identifying Features LS
o Fibrous = very long cells (up to cms), 20-100 µm diametero Striations = stripes = A-I banding, 2-4 µm longo Peripheral, cigar-shaped nuclei, multiple nuclei per cell
Other cell types or structuresFibroblasts or endothelial cells = small dark nuclei clearly outside myofibersSatellite cells, spindle cells, you won’t see these in the slides
Look-alikes: Cardiac muscle (but not on first practical exam!)
Smooth Muscle = The Good, The Bad, and the UglyKey Identifying Features
Smooth = no striations Fibrous = cells longer than wide. Usually 5-10 µm diameter x 20-500 µm long Spindle-shaped cells (if well preserved enough) http://tinyurl.com/spindleshaped Centrally located, pale, cigar-shaped nuclei (one/cell). May have corkscrew-shaped nuclei. http://tinyurl.com/corkscrewnuclei May see uneven red/white staining = contracture bands. http://tinyurl.com/contracturebands Oriented = arranged in layers or fascicles. http://tinyurl.com/smfascicles Always identify orientation! LS, CS, or oblique Check large blood vessel to see how SmM stains in slide (can look a little different)
http://tinyurl.com/smbloodvessels
Look-alikesDense irregular connective tissue (fibers go many different directions, nuclei outside fibers)Nerves (Perinurium, C-shaped Schwann cells, myelin ghosts)Multilocular fat (but this won’t be on exam)
