1. Skeletal System
Functions: Supports the body, protects organs, site of blood cell formation Components: Bones, joints, ligaments

2. Skeletal System: Bone Structure
Bones are a solid network of living cells and protein fibers that are surrounded by deposits of calcium salts.

3. Skeletal System: Bone Structure
Periosteum: tough outer layer
Haversian canals: where nerves and blood vessels run
Spongy bone: less dense tissue under the outer layer
Bone marrow: soft tissue that stores fat and produces blood cells

4. Skeletal System: Bone Development
- Cartilage is connective tissue without blood vessels. Human embryos have skeletons made of cartilage.
- Cartilage is replaced by bone during ossification (bone formation). This begins 7 months before birth as cells secrete minerals that replace cartilage.

5. Skeletal System: Bone Repair
Osteoblasts: cells that build bone tissue. Osteoclasts: cells that break down bone minerals. Osteoporosis: disorder in which osteoclasts break down bone faster than osteoblasts build it.

6. Skeletal System: Joints
location where two bones “connect”

7. Skeletal System: Ligaments
tissue that holds bones together in a joint

8. Skeletal System: Injury
Torn ACL (Anterior Cruciate Ligament) - in center of knee - prevents tibia (shin) from moving too far forward - if torn, knee is unstable and easily injured

9. Muscular System Function: Movement (voluntary and involuntary)
Components: skeletal muscle, smooth muscle, cardiac muscle

10. Muscular System: Skeletal Muscle
- Attached to bones
Allow for voluntary movements
Controlled by nervous system (motor neurons)

11. Muscular System: Smooth Muscle
- Involuntary movements
- Controls: pupil size, food movement, blood flow
- Functions without stimulus from nervous system (electrical impulses travel between cells)

12. Muscular System: Cardiac Muscle
- Found in the heart
- Functions without stimulus from the nervous system (electrical impulses travel between the cells)

13. Muscular System: Muscle Contractions
Motor neuron releases neurotransmitter (acetylcholine, ACh)
ACh received by muscle cell
Muscle cell contracts (see picture) until ACh is no longer received.

14. Bone and Muscle Interactions
Tendons
Skeletal muscles are joined to bones by tendons.
Tendons pull on the bones to make them move.

15. Flexibility
Flexibility: range of movement in a joint or joints, and length in muscles that cross the joints.