The Muscular System Chapter 6

Muscle Functions Producing movement – complex movement such as walking, or simple facial movement Maintain Posture – tiny adjustments happen constantly to keep balance Stabilizing Joints – muscles and tendons keep bones of various joints together. Generating Heat – Muscle activity produces heat

Smooth Muscle No Striation Involuntary. Walls of hollow organs Uninucleated Slow moving but tireless

Cardiac Muscle Only in Heart Striated Involuntary Branching cells

Skeletal Muscle Aka striated muscle Multinucleated cells Voluntary Soft and fragile, but can exert tremendous power.

Skeletal Muscle Muscle cells need to be wrapped and supported by connective tissue to make sure they do not rip apart. A pulled muscle can sometimes be a breaking of this connective tissue sheet. Muscles are bundled multiple times for added strength.

Tendons The connective tissue that surround muscle cells will gather at the ends of muscles to form tendons. Tendons are slender and strong, attaching the muscle to bones and other muscles. They are more durable then muscle cells and can wrap over bone without breaking, they are also thinner allowing for more to cross over joints.

Micro Lab

Skeletal Muscle Anatomy

Muscle Cell Anatomy The muscle cell is full of myofibrils. The striation or stripes of a skeletal muscle cell come from Sarcomeres – active section of the myofibrils that line up end to end like cars in a train.

Sarcomere Anatomy The sarcomere is made up of two main parts. Actin and Myosin. Myosin (red) Actin (blue) Notice the space between the actin – important for contractions

Mechanism of Muscle Contraction sliding filament

Sarcomere Anatomy When each individual sarcomere shortens the entire muscle shortens. This is a contraction. Contractions are started by nerve impulses, more on that next chapter.

Exercise Aerobic/Endurance – Increases blood flow to muscles, more mitochondria in cells. Muscle cells do not increase in size. Helps in digestion, strengthens skeleton, heart Resistance/Isometric – muscles are pitted against immovable objects. Actin and myosin filaments get thicker to be able to hold better. Makes the cells thicker. No new cells for the most part.

Isometric Contractions Muscles do not always contract when nerves signal them too. When pushing against an immovable object, myosin tries to grab and pull actin, however, their grip slips and actin doesn’t move. Think about a car spinning its wheels, gas is being used, but the car isn’t moving.

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Muscle Energy Millions of molecules or ATP are used just to contract one muscle once. Where does it come from? Aerobic Respiration – making ATP from breaking down food. 36 ATP : 1 Glucose Anerobic Respiration – lactic acid fermentation. Without oxygen, the muscle will make ATP and lactic acid through a type of fermentation. 2 ATP : 1 Glucose

Muscle Energy Direct phosphorylation by Creatine phosphate – Creatine phosphate found in the muscles can artificially add a phosphate to ADP to make ATP, giving it more energy again. Can only occur for about 20 seconds before the creatine is depleted.

Muscle Fatigue Usually due to oxygen debt. Muscles with good blood supply will fatigue less. Oxygen debt must be paid back, even after activity stops. We will breathe heavily and deeply after a run until our muscles receive the oxygen they lack.

Hand Dynamometer Activity

Muscle Attachment Origin – attachment to the immovable bone. Insertion – attachment to the movable bone

Five Golden Rules of Muscles Most muscles cross at least one joint Most of the muscle lies proximal to the joint crossed All muscles have at least two attachments. Muscles can only pull, never push During contraction, the insertion always moves toward the origin.

Finish Lab

Types of body movements Flexion – generally makes decreases the angle of the joint. Hinge joints Extension – opposite of flexion, increases the angle of the joint. Hyperextension – when the joint bends in a way that it normally wouldn’t

Types of body movements Rotation – movement of bones back and forth around an axis. Shaking your head no is a rotation.

Types of boy movements Abduction – moving a limb away from the midline of the body Adduction – moving a limb toward the midline of the body.

Types of body movements Circumduction – Combination of flexion, extension, abduction, and adduction. Seen in ball and socket joints.

Muscle interactions Muscles can only pull, never push. Because of this, muscles usually work in pairs, when one contracts, the other relaxes. Prime Mover vs. Antogonist. Synergists – muscles that help prime movers.

Face and Neck

Shoulder and Chest

Abdominal Muscles

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