Muscles (View Video)

Part I : Anatomy of Muscle

SEE HANDOUT

See handout FASCIA tendon

MUSCLE - INTERNAL STRUCTURE Below fascia: thick connective tissue called epimysium. surrounds the muscle but does not extend into the tendon may look like a white sheath. Below epimysium : Layer of connective tissue called the perimysium. Divides the muscle into bundles called "fascicles“ This makes the muscle look as if it is divided into small compartments. The perimysium is thinner than the epimysium.

Within each compartment / fascicle, there are groups of muscle fibers (muscle cells). Each muscle fiber is surrounded by another layer of connective tissue called endomysium. All of the connective tissue layers (fascia, epimysium, perimysium and endomysium) 1. allow the muscle fibers to move independently. 2. provide a passageway for nerves and blood vessels into and out of the muscle.

Muscle Cells = Muscle Fibers Facts Cell Shape: thin and cylinder shaped. The end of each fiber is attached to the C.T. associated with the muscle. Cell membrane : sarcolemma. Invaginations (called T-tubules or transverse tubules) are present. They remain open to the outer surface and also penetrate deeply into the interior of the muscle fiber. Function: plays a role in muscle contraction Cytoplasm : small amount, called sarcoplasm.

Other organelles: many small oval nuclei (multinucleated) many mitochondria thread-like structures called myofibrils. The myofibrils run parallel to each other. They are the portions of the muscle that actually contract. Surrounding each myofibril, there is a network of canals that form the sarcoplasmic reticulum. It is similar to the E.R. in other cells. Now, color muscles diagrams for study and work on review sheet!

Role of Sarcoplasmic Reticulum The sarcoplasmic reticulum forms a "sleeve" around each myofibril. It stores the Ca++ needed for muscle contraction. It releases the Ca++ when the muscle is stimulated. When the stimulation stops, the Ca++ return to these storage areas.

Sliding Filament Theory See movie link

Myofibrils are made of two protein filaments: Actin and myosin

Each myofibril contains two types of protein filaments Each myofibril contains two types of protein filaments. They are myosin filaments and actin filaments. The myosin filaments are thicker than the actin filaments

Myosin filaments Each myosin filament is composed of many rod-shaped proteins that are wound together into a spiral. The ends are "club-shaped" or "paddle-shaped“ called myosin heads. The myosin heads occur in clusters  

Actin Filaments The thin actin filaments are actually more complex than the myosin filaments. Each actin filament is composed of three types protein. They are: actin, tropomyosin and troponin. All three play a special role in muscle contraction!

actin = present in the largest amount. It forms two long strands of globular protein which are twisted together. 2. tropomyosin = This protein is long, double-stranded and twisted. It is not globular, therefore it is much thinner than actin and is twisted around the actin. 3. troponin = This is a globular protein. It is attached in clusters to the tropomyosin.

SKELETAL MUSCLE STRIATIONS coordinate with actin/myosin Section of myofibril The sarcomere is the actual contractile unit of the muscle fiber. There are many sarcomeres per myofibril. SKELETAL MUSCLE STRIATIONS coordinate with actin/myosin Muscle tissue has a definite pattern of "stripes" (striations) on the myofibrils. “Z” lines are a series of dark stripes at intervals. The region between two Z lines is called a sarcomere.

Moving inward from each Z line, light colored area called I band Moving inward from each Z line, light colored area called I band. This area only contains actin filaments. Continuing inward, there is a dark area. It is called the A band. In the center of the A band, there is a lighter, central stripe called the H zone. The H zone contains only myosin filaments. The rest of the A band is where the actin and myosin filaments overlap. When the muscle contracts, the H zone disappears and the I band becomes narrower until the muscle relaxes again.

Part II: Physiology of Muscle

Sliding Filament Theory See movie link

See movie link See handout on Union of Nerve and muscle Neuromuscular junction See Video ONE

See Two handouts: Picture Physiology of muscle contraction http://www.youtube.com/watch?v=gJ309LfHQ3M&feature=related http://www.youtube.com/watch?v=gJ309LfHQ3M&feature=related