University:
American Career College
Course:
MICR112 | General Microbiology
Academic year:

2019
Views:

223

Pages:

29
Author:

astralniew2

Contraction  1- Myofilaments ◦ Thin filament ◦ Thick filament ◦ Accessory filament ◦ 2 - Impalse ◦ 3 - Ca ions Neuromuscular Junction Skeletal Muscle T-tubules are long tubular invaginations of cell membrane that intertwine among myofibrils They lie at the junction of A-band and I-band in close association to dilated portion of sarcoplasmic reticulum known as terminal cisternae forming Triad Intermediate filaments (desmin and vimentin) secure the periphery of the Z-disk of neighboring myofibrils to each other Triad Action Potentials and Muscle Contraction Sliding Filament Model I:  Actin myofilaments sliding over myosin to shorten sarcomeres ◦ Actin and myosin do not change length ◦ Shortening sarcomeres responsible for skeletal muscle contraction  During relaxation, sarcomeres lengthen Three types of skeletal muscle fibers(red, white, and intermediate)  Skeletal muscle fibers differ in diameter and in their natural color in vivo.  The color differences are not apparent in H&E stained sections. Skeletal Muscle 3 Types of Skeletal Muscle Fibers Red fibers: high myoglobin, many mitochondria, slow contraction, oxidative metabolism, mammal limbs, migrating bird flight muscle, low glycogen White fibers: low myoglobin, fewer mitochondria, breast muscle of chicken and turkey, rapid contraction, low endurance, anaerobic, high glycogen Intermediate fibers: properties are between extremes of red and white Muscle spindle Muscle spindle is composed of a fusiform capsule of collagenous connective tissue continuous with perimysium Two type of intrafusal fibers: nuclear chain fibers and nuclear bag fibers Special afferent(sensory) and special efferent(motor) nerve fibers innervate intrafusal fibers Muscle spindle sensing stretch and tension Cardiac Muscle Tissue Cardiac Muscle      Cells joined end-to-end by intercalated disks Cells branched and arranged in layers(Lamina) separated by slender CT sheets that convey vessels and nerves and conducting system 15 mm diameter, 80 -100 mm long 1-2 central euchromatic oval nuclei Diad forms by SER and T-tubules in vicinity to Z line Cardiac Muscle Ca ions through T-tubule and calcium-sodium channels Has more mitochondria (50% of volume), lipid droplets, abundant myoglobin Atrial cell secrete atrial natriuretic peptide, cause Na and H2O loss via kidney Intercalated disks are specialized cell junctions Cell membrane in these disks approximate each other Have a transverse portion where there are desmosomes and fascia adherents and a lateral portion which has many gap junctions Smooth Muscle Involuntary, in the wall of hollow viscera usually form sheets Fusiform, 30-200 mm long 1 central nucleus No striations, no T-tubule system Surrounded by an external lamina Smooth muscle Dense bodies adhering to cytoplasmic aspects of cell membrane formed of α-actinin and other Z disk associated proteins Thin filaments are composed of actin with tropomyosin but no troponin Thick filaments are composed of myosin Comparison of Role of Calcium In Bringing About Contraction in Smooth Muscle and Skeletal Muscle Muscle Regeneration Skeletal muscle don’t have mitotic activity but regenerates by mitosis of satellite cells (inactive myoblasts) Cardiac muscle shows very little or no regeneration; infarcts replaced by scar Smooth muscle retain their mitotic activity and so can regenerate by mitosis