MUSCLE,JOINTS AND TENDONS

Bone is the main tissue of the skeleton, known for its strength and hardness.
Composed of bone cells embedded in a matrix containing collagen and calcium salts.
Particularly strong under compression forces, allowing for weight-bearing capabilities.
Compact bone is dense and heavy, located in long bones.
Spongy bone has a lighter, open structure and is found in areas like the pelvis and femur.

Cartilage is a flexible yet hard tissue comprising chondrocytes within an organic matrix with collagen fibrils.
Elasticity allows cartilage to stretch and return to its original shape, making it a good shock absorber.
Two main types:
- Hyaline Cartilage: Found at the ends of bones, in the nose, airways, and parts of the ear.
- White Fibrous Cartilage: Dense bundles of collagen provide tensile strength, found in intervertebral discs and joint spaces.

Tendons consist largely of white fibrous tissue, forming strong, inelastic connections between muscles and bones.
Tendons serve crucial roles:
- Securely attach muscles to bones.
- Provide limited shock absorption during sudden joint stretches.
Ligaments are elastic tissues that hold bones together and maintain joint alignment through capsules.
Variations in ligament properties arise from different amounts of collagen and white fibrous tissue.

Joints lined with rubbery cartilage prevent bone wear by ensuring smooth movement.
Synovial fluid lubricates mobile joints for friction-free articulation.
Joint end shapes determine movement capabilities; for example:
- Ball-and-socket joints (hip and shoulder) allow free movement.
- Hinge joints (knees) restrict movement to bending and straightening.

Extensors are muscles that extend joints; Flexors are muscles that bend joints, working in opposition as antagonistic pairs.

Skeletal muscle consists of long bundles called muscle fibers.
Each muscle fiber's cell membrane is known as the sarcolemma, which has inward folds (T tubules) spreading electrical impulses throughout the fiber.
The sarcoplasmic reticulum, a network of membranes within the sarcoplasm, stores and releases calcium ions essential for muscle contraction.