The Muscular System Part II: Revenge of the Sarcomere Yet again you DON’T have to write the stuff in red, but if you plan on taking future anatomy courses you might want to.

Prac discussion (starts pg. 21) You should have answered these questions: What did your hand look like when you took it out of the water? Why did it look like that? What happened to your writing? Why?

Why does the cold effect muscle performance? The energy producing chemical reactions in the body rely on enzymes. The optimum temperature for most enzymes is around 37 degrees C (body temp). Therefore energy producing reactions are slower in the cold. Cold stress initially induces vasoconstriction (oh the pain, the agony!) but later alternates between vasoconstriction and vasodilation. Vasodilation occurs when the stress is removed (red hands). Vasoconstriction = narrowing of the blood vessels, less blood flow. Vasodilation = widening of the blood vessels, more blood flow.

Muscle Structural Organisation pg. 31 Muscles have a connective tissue covering called epimysium. Connected to bones via tendons. Muscle is made up of muscle bundles (fascicles), each of which are also covered in connective tissue called perimysium. Muscle bundles are made up of muscle fibres (cells) each cell is covered in connective tissue called endomysium

Muscle fibres have cell membranes called sarcolemma Muscle fibres have cell membranes called sarcolemma. Fibres are made up of myofibrils. Myofibrils are made up of the fundamental contractile units called sarcomeres. The number of myofibrils increase when we build up our muscles. When their number decreases we called the process muscular atrophy. Sarcomeres are made from the proteins actin and myosin.

Pg. 32 Actin – is the protein that makes up the thin filaments of the sarcomeres. Actin is what myosin pulls on to make the sarcomeres contract. Myosin – is the protein that actively causes muscle contractions. Myosin gets energy by breaking down ATP into ADP and Phosphate (Pi). It is the myosin heads that actually move. Ca2+ is needed for the myosin heads to attach to actin. ATP provides both energy for movement and it lets myosin detach from actin.

Random Fact: Muscle is a fractal A fractal is a shape that looks similar at different magnifications

3 Methods of energy production Creatine phosphate – restores ADP to ATP by donating a phosphate group directly. For ~15 second bursts of energy. Uses no oxygen. Creatine phosphate + ADP + Pi  Creatine + ATP Anaerobic –produces ATP and lactic acid. For 30-60 second bursts of energy. Uses no oxygen. 2 Pyruvic acid + 2ADP + 2Pi  Lactic acid + 2 ATP Aerobic – fully burns glucose water, CO2 and ATP. For endurance rather than strength activities. It is a slower process than anaerobic respiration but it produces 18 times more ATP (36 per glucose compared to 2). Glucose + O2  36 ATP + CO2 + Water

Oxygen debt After we use anaerobic respiration we have to restore our glycogen (chains of glucose) levels, turn convert lactic acid back to pyruvic acid, re-synthesise creatine phosphate and build up our stored supply of ATP. The amount of oxygen require to do this is called oxygen debt. Example: If you do something that requires 6L of oxygen but you only take in 2L then your oxygen debt is 4L.

Muscle functional classes Flexor = a muscle which bends a joint e.g. Biceps. Extensor = a muscle which straightens a joint e.g. Triceps. Prime mover (or agonist) = the main muscle for a specific movement. E.g. Biceps is the main elbow flexor. Antagonist = the main muscle opposing the prime mover. For the above Triceps. Synergist = A muscle that works with a prime mover to produce the same movement. Fixators = help immobilise bones e.g. scapula.

Muscle Tone Muscle tone is a constant low level of contraction in relaxed muscles that helps maintain posture and muscle health.