Muscular System (bio test 4)

Tendons

connect muscle to bone

Antagonistic muscle

muscle pairs that work in opposition to one another; as one muscle contracts, the other relaxes or lengthens to allow precise, controlled movement. Because muscles can only pull and cannot push bones, these complementary pairs are essential for bending and straightening joints

Muscle fibers

parallel and consist of 1 long muscle cell

Muscle cell

cells in the muscle fibers

Myofibrils

• Each muscle cell contains parallel bundles of myofibrils

• dense bundles of contractile proteins called myofilaments (primarily actin and myosin)

• surrounded by E.R. (endoplasmic reticulum, fluid)

Sarcomeres

• Each myofibril contains sarcomeres

• a tiny, functional segment that allows muscles to contract, spanning from one boundary (Z-line) to the next. Thousands of sarcomeres lined up end-to-end create the banded, striated appearance of your muscles

Myosin filament heads

• bind and pull actin repeatedly → shortening the sarcomere

• sequence—detach, extend, attach, pull, detach—occurs again and again in a contracting muscle

Motor neuron

nerve cells that carry electrical signals from your brain and spinal cord to your muscles; responsible for controlling your body's movements

Steps of a muscle contraction

1. Before a muscle contraction begins, myosin heads start in a low-energy state, and Regulatory proteins troponin and tropomyosin block binding sites on actin molecules

2. An action potential in a motor neuron causes the axon to release neurotransmitter, acetylcholine, which depolarizes the muscle cell membrane

3. Sarcoplasmic reticulum releases Ca^2+ into the cytoplasm

4. Ca^2+ bind to the troponin/tropomyosin complex

5. The tropin/tropomyosin complex shifts ans unblocks the cross-bridge binding sites on actin

6. The thin filaments are ratcheted across the thick filaments by the heads of the myosin molecules using energy from ATP

7. Motor neurons stop sending Action potentials to muscle fibers and the ER pumps Ca^2+ out of the cytosol

8. Acting molecule binding sites become re-blocked, stopping sarcomere contractions and relaxing the muscle

Z Line proteins

a dark band separating sarcomeres and acting as an anchor for actin (thin filaments)

Thin filaments

contain mostly the protein actin and are attached to the ends of the sarcomere

Thick filaments

made up of the protein myosin and sit in the middle of a sarcomere

Laigament

connects bone to bone and stabilizes a joint by limiting excessive movement

Cartilage

• Cartilage is a strong, flexible connective tissue found in joints

• Cushions the ends of bones at joints.

• Reduces friction between bones during movement.

• Absorbs shock to protect bones and joints.

• Helps bones move smoothly without rubbing directly against each other