Anatomy of skeletal muscle ppt #1 Unit 4 Muscles Pgs. 322-323, Chapter 11.1

Muscular System Chapter 11

Muscle Intro Functions of muscles Movement: respiration, circulation, defecation Stability: resists gravity and provides tension to tendons Communication Heat Production: muscle provides 85% of body heat https://www.youtube.com/watch?v=Ktv-CaOt6UQ

Types of Muscle Skeletal – striated & voluntary Smooth – involuntary Cardiac - heart The word “striated” means striped. Skeletal muscle appears striped under a microscope.

Connective Tissues of Muscle Skeletal muscles are composed of muscular AND connective tissues. A skeletal muscle can be about 100um in diameter BUT up to 30cm in length!! Muscle Cell=Muscle Fiber Muscle fiber is surrounded by connective tissue, Endomysium (allows for nerves and blood capillaries to to reach each fiber) Muscle fibers are bundled into Fascicles (can be seen by naked eye, looks like strands)

Muscles and Muscle Fiber Structure Muscles are composed of many FIBERS that are arranged in bundles called FASCICLES

--Each Fascicle is separated (wrapped) from other fascicles by a connective tissue sheath, Perimysium --The entire muscle as a whole is surrounded by another connective tissue layer, Epimysium --The Epimysium gradually becomes connective tissue sheaths called Fascia Fascia thickens and becomes Deep Fascia (no fat) between adjacent muscles. --This becomes even thicker and becomes Superficial fascia between muscles and skin. Some places like buttocks and abdomen is very adipose.(fat)

EPIMYSIUM = outermost layer, surrounds entire muscle. PERIMYSIUM = separates and surrounds fascicles (bundles of muscle fibers) ENDOMYSIUM = surrounds each individual muscle fiber(cell) This model of the muscles uses straws to represent fibers. Green = endomysium Yellow = perimysium Blue = epimysium

Epimysium Perimysium Endomysium

Muscle Layers Muscle Fiber Endomysium Perimysium Epimysium

Individual muscles are separated by FASCIA, which also forms tendons

https://www.youtube.com/watch?v=XoP1diaXVCI

How are muscle cells created? In embryonic development, STEM CELLS called Myoblasts fuse to produce each muscle fiber. Muscle Cell Organization: Each muscle fiber, (1 muscle cell) has: many myofibrils (protein bundles) Each muscle fiber has: many flattened or sausage shaped nuclei pushed against the plasma membrane Each muscle fiber (cell) has: plasma membrane= Sarcolemma Each muscle fiber (cell) has: cytoploasm = Sarcoplasm Each muscle fiber (cell) has: many Mitochondria

Nucleus Sarcolemma Mitochondrion Sarcoplasm Myofibril

The Sarcoplasm also contains lots of Glycogen (stored carb) which provides energy and the red pigment Myoglobin which stores Oxygen. Other organelles are packed into the spaces between the myofibrils like: Sarcoplastic Reticulum: has channels to release FLOOD of Ca+ Forms a network around each myofibril . T Tubules= Transverse tubules which signal the SR to release Ca+ Mitochondria: Produces ATP from O2 and glucose (cellular respiration)

Structure of a Skeletal Muscle Fiber Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Muscle fiber Nucleus A band I band Z disc Mitochondria Openings into transverse tubules Sarcoplasmic reticulum T riad: T erminal cisternae T ransverse tubule Sarcolemma Myofibrils Sarcoplasm Figure 11.2 Myofilaments

Structure of Myofibrils Myofibrils are the long protein cords that fill most of the muscle cell Each Myofibril is a bundle of parallel protein microfilaments called:Myofilaments 3 kinds of Myofilaments: Thick Filaments: hundreds of strands of proteins called : MYOSIN looks like golf clubs

THICK FILAMENTS Single myosin Hundreds of myosin

Tropomyosin and Troponin are Regulatory proteins Thin Filaments: 2 intertwined strands of protein called: Fibrous ACTIN Fibrous Actin (F actin) with “globs” of Globular Actin (G actin) * each G-Actin (globular Actin)has an active site that binds to the head of myosin Thin Filaments also have 40-60 protein strands of Tropomyosin When muscle is relaxed, the tropomyosin blocks the G actins and prevents myosin from binding. Thin filaments also have Troponin: a Ca+ binding protein Tropomyosin and Troponin are Regulatory proteins Myosin and Actin are Contractile Proteins

Thin Myofilaments G act (c) Thin filament Figure 11.3c

Elastic Filaments: made of huge springy proteins called Elastic Filaments: made of huge springy proteins called Titan, this helps stabilize the thick filaments and helps prevent overstretching. flank each thick filament and anchor it to the Z disc helps stabilize the thick filament center it between the thin filaments prevents over stretching

Accessory Proteins include(more than 20 dif proteins) Dystrophin) 1. Links actin in outermost myofilaments and 2. transfers forces of muscle contraction to connective tissue around muscle cell Genetic defects in dystrophin produce the disease muscular dystrophy.

Myofibrils are made of 1. MYOSIN = thick filaments ACTIN = thin filaments Elastic filaments

Filament organization Actin and Myosin are in all cells and control motility . In muscle cells they areContractile proteins (act to shorten muscle fibers) Actin and Myosin are organized in a precise array which then is seen as striations in the muscle. Striated muscle has DARK A bands alternating with light I bands

Myofilaments ACTIN (thin) and MYOSIN (thick)   -- form dark and light bands A band = dArk • thick (myosin) I band = lIght • thIn (actin)

Overlap of Thick and Thin Filaments Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Thick filament Thin filament Bare zone Portion of a sarcomere showing the overlap of thick and thin filaments Figure 11.3d

Bands in muscle myofibrils: A bands= thick filaments lying side by side - very dark where thick and thin overlap H bands= lighter region with no overlap of thick and thin…just thick I Bands = is region with only thin filaments and is anchored to Z disc by elastic filaments Z disc = Protein disc to which thin and elastic filaments are anchored Sarcomere= segment of myofibril from one Z disc to the next Z disc

A muscle shortens because individual sarcomeres shorten and pull the z discs closer to each other. As discs are pulled closer they pull on the sarcolemma to achieve shortening of the cell.

Striations and Sarcomeres Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Nucleus Sarcomere 5 Z disc M line 4 H band Individual myofibrils 3 I band A band I band 2 1 (a) Visuals Unlimited Figure 11.5a sarcomere – functional contractile unit of the muscle fiber muscle shortens because individual sarcomeres shorten pulls z discs closer to each other

It is important to remember the hierarchy fasicles myofibrils myofilaments actin myosin