Muscle relationships and types of contractions Muscle Physiology Muscle relationships and types of contractions

Muscle Tissue Skeletal Muscle Cardiac Muscle Smooth Muscle There are three types of muscle tissue in the body. Skeletal muscle is the type that attaches to our bones and is used for movement and maintaining posture. Cardiac muscle is only found in the heart. It pumps blood. Smooth muscle is found in organs of the body such as the GI tract. Smooth muscle in the GI tract moves food and its digested products.

Cardiac Muscle Branching cells One/two nuclei per cell Striated Involuntary Medium speed contractions Cardiac muscle tissue is only found in the heart. *Cardiac cells are arranged in a branching pattern. * Only one or two nuclei are present each cardiac cell. *Like skeletal muscle, cardiac muscle is striated. *Cardiac muscle is involuntary. *Its speed of contraction is not as fast as skeletal, but faster than that of smooth muscle.

Smooth Muscle Fusiform cells One nucleus per cell Nonstriated Involuntary Slow, wave-like contractions Smooth muscle is found in the walls of hollow organs. *Their muscle cells are fusiform in shape. *Smooth muscle cells have just on nucleus per cell. *Smooth muscle is nonstriated. *Smooth muscle is involuntary. *The contractions of smooth muscle are slow and wave-like.

Skeletal Muscle Long cylindrical cells Many nuclei per cell Striated Voluntary Rapid contractions Skeletal muscle attaches to our skeleton. *The muscle cells a long and cylindrical. *Each muscle cell has many nuclei. *Skeletal muscle tissue is striated. It has tiny bands that run across the muscle cells. *Skeletal muscle is voluntary. We can move them when we want to. *Skeletal muscle is capable of rapid contractions. It is the most rapid of the muscle types.

Skeletal Muscle Produce movement Maintain posture & body position Support Soft Tissues Guard entrance / exits Maintain body temperature Store nutrient reserves

Skeletal Muscle Structure Organization of Connective Tissues Muscle attachments Endomysium, perimysium, and epimysium come together at ends of muscles to form connective tissue attachment to bone matrix i.e., tendon (bundle) or aponeurosis (sheet) Nerves Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord) Blood Vessels Muscles have extensive vascular systems that 1) Supply large amounts of oxygen 2) Supply nutrients 3) Carry away wastes Skeletal Muscle fibers are: Are very long Develop through fusion of mesodermal cells (myoblasts) Become very large Contain hundreds of nuclei

Skeletal Muscle Fiber Internal Organization of Muscle Fibers The sarcolemma The cell membrane of a muscle fiber (cell) Surrounds the sarcoplasm (cytoplasm of muscle fiber) A change in transmembrane potential begins contractions Transverse tubules (T tubules) Transmit action potential through cell Allow entire muscle fiber to contract simultaneously Have same properties as sarcolemma Myofibrils Lengthwise subdivisions within muscle fiber Made up of bundles of protein filaments (myofilaments) Myofilaments are responsible for muscle contraction Types of myofilaments: thin filaments: made of the protein actin thick filaments: made of the protein myosin Sarcoplasmic reticulum (SR) A membranous structure surrounding each myofibril Helps transmit action potential to myofibril Similar in structure to smooth endoplasmic reticulum Forms chambers (terminal cisternae) attached to T tubules Triad Is formed by one T tubule and two terminal cisternae Cisternae: concentrate Ca2+ (via ion pumps) release Ca2+ into sarcomeres to begin muscle contraction

Sarcomere Internal Organization of Muscle Fibers M Lines and Z Lines: Sarcomeres The contractile units of muscle Structural units of myofibrils Form visible patterns within myofibrils Muscle striations A striped or striated pattern within myofibrils: alternating dark, thick filaments (A bands) and light, thin filaments (I bands) M Lines and Z Lines: M line: the center of the A band at midline of sarcomere Z lines: the centers of the I bands at two ends of sarcomere Zone of overlap: the densest, darkest area on a light micrograph where thick and thin filaments overlap The H Band: the area around the M line has thick filaments but no thin filaments Titin: Strands of protein reach from tips of thick filaments to the Z line stabilize the filaments

The Ca ions bind to the troponin This binding weakens troponin-tropomoysin complex and actin Troponin moiecule changes position, rolling the tropomyosin away from the active sites on actin Thus allowing them to interact with energized myosin heads

With the active sites on the actin exposed, the myosin heads bind to the, forming cross-bridges

After cross-bridge formation, the ATP present in the myosin is used to “cock” (the opposite direction from its resting state). As the ATP is used and the ADP + P is released, the “power stroke” occurs as the myosin pivots toward the M line.

When another ATP molecule attaches to the myosin head, the cross-bridge between the active site of the actin molecule and myosin head is broken. Thus freeing up the head to make another bridge and complete the contraction.

Myosin splits the ATP into ADP + P and uses the released energy to re-cock the myosin head (reaching forward). Cycle can be repeated endlessly as along as calcium ion concentration remain high and sufficient ATP is present. ATP produced in cells – aerobic vs. anaerobic Ca controlled by what?

Muscle Relationships Anonist – The muscle which the load/tension is going through. Antagonist – The muscle which is relaxing through the movement. Stabilisers – groups of muscles which hold the movement in place.

Muscle Contraction Types Isotonic contraction – Concentric - Eccentric Isometric contraction

Muscle Contraction Types Isotonic contraction Isometric contraction Two Types of Skeletal Muscle Tension Isotonic Contraction Skeletal muscle changes length: resulting in motion If muscle tension > load (resistance): muscle shortens (concentric contraction) If muscle tension < load (resistance): muscle lengthens (eccentric contraction)

Muscle Contraction Types Isotonic contraction Isometric contraction Two Types of Skeletal Muscle Tension Isometric contraction Skeletal muscle develops tension, but is prevented from changing length Note: iso- = same, metric = measure Produces no movement Used in Standing Sitting Posture