Functions of Muscles 1. Produce movement – all movements of the human body are produced by muscles 2. Maintain posture – some muscles are in a partial state of contraction at all times 3. Stabilize joints – muscle tendons reinforce and stabilize joints 4. Generate heat – ¾ of the energy used to contract muscles is lost as heat. Needed to maintain body temperature

Skeletal Muscle Characteristics Most are attached by tendons to bones Cells are multinucleate Striated – have visible banding Voluntary – subject to conscious control Cells are surrounded and bundled by connective tissue called Fascia

Smooth Muscle Characteristics Has no striations Spindle-shaped cells Single nucleus Involuntary – no conscious control Found mainly in the walls of hollow organs

Cardiac Muscle Characteristics Has striations Usually has a single nucleus Joined to another muscle cell at an intercalated disc Involuntary Found only in the heart

General Structure of Muscles A muscle is composed of bundles of muscle fibers called fascicles separated by connective tissue (perimysium) Fascicles are surrounded by a tough connective tissue layer called the Epimysium, which covers the entire muscle The epimysia extend beyond the end of the muscle and form the Tendon which connects it to bone The epimysia can also form a broad sheet-like connection to an adjacent muscle called an Aponeurosis

Each fasciculi is composed of bundles of smaller fibers that are the individual muscle cells. Each cell is composed of smaller fibers called myofibrils surrounded by a cell membrane (sarcolemma) The myofibrils are made of filaments of actin and myosin protein arranged in units called sarcomeres

Neuromuscular Junction Sarcolemma is folded to form the motor end plate. Many Mitochondria in the region Nerve fiber forms Synaptic Clefts into the recesses of the sarcolemma. The nerve contains synaptic vesicles that contain neurotransmitter When a nerve impulse reaches the junction it causes the release of the neurotransmitters The specific neurotransmitter that stimulates skeletal muscle cells is acetylcholine

Skeletal Muscle Contraction 1. Nerve impulse causes the release of acetylcholine by the synaptic vessels into the synaptic cleft 2. The acetylcholine stimulates a muscle impulse along the length of the sarcolemma 3. The impulse cause the sarcoplasmic reticulum to release Calcium ions into the sarcoplasm of the muscle cell 4. Ca ++ ions cause an attractive force between actin and myosin and the sarcomere becomes shorter 5. Ca ++ ions are removed by active transport and acetylcholine is decomposed by an enzyme

Energy for Contractions Energy for the contraction comes from ATP. ATP→ADP + Energy 4 – 6 seconds worth of ATP is stored in muscles Another 20 seconds worth can be generated from Creatine Phosphate The rest must be generated via aerobic and anaerobic respiration. Aerobic respiration is slow but efficient (36 ATP per molecule of glucose Anaerobic respiration is fast but inefficient (2 ATP per glucose molecule)

Muscle Fatigue - Muscle loses the ability to contract. Due mainly to the buildup of lactic acid from anaerobic respiration Myoglobin – Reddish brown pigment found in muscles that combines with oxygen to store it in muscles Cramps – Muscle contracts but does not relax. Caused by lack of ATP. Can’t move Ca ++ ions out. Muscle Tone – Sustained contraction that occurs in some fibers of most muscles. Maintains Posture. Involuntary

Twitch Contraction – Quick contraction (fraction of a second) in response to a single stimulus. Example - Eye blink Tetanic Contraction – Sustained contraction in response to continuous stimuli. Most muscle contractions are tetanic. Origin – Point of attachment to the immovable or less movable bone. Insertion – Point of attachment to the movable bone

Muscle Atrophy – Decrease in the size of the muscle due to disuse Muscle Hypertrophy – Increase in the size of muscles from exercise Muscles Act In Groups Prime mover – is responsible for most of a certain movement Synergist – assist the prime mover Antagonist – capable of resisting the prime mover’s action. Responsible for movement in the opposite direction.