Muscles

The Muscular System Muscles are responsible for all types of body movement Function of a muscle is contraction (shortening) Three basic muscle types are found in the body ▫ Skeletal muscle ▫ Cardiac muscle ▫ Smooth muscle

Function of Muscles Produce Movement ▫ Allow us to escape danger, move, manipulate things, express emotion Maintain Posture ▫ Muscles function constantly making tiny adjustments to maintain erect or seated posture despite gravity Stabilize Joints ▫ Muscle tendons reinforce joints at their articulating surface Generate Heat ▫ ATP is used to power muscle contractions 75% of this energy escapes as heat ▫ It maintains our body temperature

Skeletal Muscle Muscle fibers are bundled together by connective tissue called endomysium Groups of muscle fiber are then wrapped again by a coarser fiber called perimysium which forms bundles of fibers called a fascicle Many fascicles are wrapped together by a connective tissue called the epimysium which covers the entire muscle. The epimysia blend in to make the tendons which connect muscle to bone

Microscopic Anatomy of Muscle Multinucleate Sarcolemma—Plasma membrane of the muscle cell In the muscle cell are long ribbon like fiber called myofibrils. Very little cytoplasm in a muscle cell—filled with myofibrils

Microscopic Anatomy Myofibrils are chains of contractile units called sarcomeres aligned end to end In a sarcomere there are myofilaments There are 2 types of myofilaments Thick filaments which contain a protein called myosin ▫ Myosin splits ATP which gives power for muscle contraction ▫ End has projections which connect the thick and thin fibers during contraction Thin filaments called actin

Nerve Stimulus Skeletal muscles are stimulated to move by nerve cells The nerve and the muscles it stimulates are called a motor unit The axons of a nerve reaches the muscles at the sarcolemma it is called a neuromuscular junction There is a gap called a synaptic cleft filled with interstitial fluid

Nerve Stimulus--Physiology When the nerve impulse reaches the terminal a neurotransmitter is released Neurotransmitter is a chemical called acetylcholine (Ach) ( Later reabsorbed by : Acetylchoinestersae) It triigers the membrane to accept Na ions (called depolarization of the membrane): Lots of sodium ions enter and some potassium ions leave This causes an upset in the electrical conditions –this upset is called an action potential

At the NMJ Mitochondria produce energy: ATP Energy used for muscle contraction ATP: made with ADP + P P=Creatine Phosphate Mitochondria Role in Muscle Contraction

Nerve Stimulus--Physiology This action potential sends electrical current from one end of the cell to another This causes muscle contraction Myosin heads attach their tiny “oars” and slide the actin together= muscle contraction To relax myosin detach from Actin filament and actin slides apart Then Ca +2 reabsorbed, Na + /K + pump starts to reset muscle so it can contract again