Musculoskeletal System Overview

Musculoskeletal System Overview

• The musculoskeletal system is a system that includes bones, joints, and cartilage.
• The skeleton provides the framework for muscles, giving the body its shape.
• Muscles contract to pull on bones, creating movement or maintaining stable positions.
• The human skeleton has 206 bones in adults and it has 300 bones in newborns.
• In development, some bones fuse together.
• The femur is the largest bone in the human body.
• The smallest bones in the human body are the ossicles of the middle ear.

Types of Tissue

• Compact bone (cortical bone): A hard, dense, and strong outer layer, comprising about 80% of adult bone mass.

• Spongy or cancellous bone: A network of trabeculae (rod-like structures) with lower density and higher flexibility than compact bone.

• Bones consist of: Osteoblasts (bone-forming cells), osteoclasts (bone-resorbing cells), osteocytes (mature bone cells), inorganic mineral salts, nerves, and blood vessels. Bone marrow is also found in bone.

• Cartilage: A type of connective tissue with a rubbery matrix, found at the ends of bones and where joints meet.

Bone Remodeling

• Bone is constantly being remodeled, a two-part process.
• Resorption: Occurs when osteoclasts break down and remove bone tissue.
• Formation: Occurs when new bone tissue is laid down by osteoblasts.
• Remodeling helps fix damaged bone, reshape the skeleton during growth, and regulate calcium levels. Approximately 10% of an adult's skeleton is replaced annually.

Main Functions of the Skeletal System

• Movement: Bones act as levers, allowing for whole-body and individual part movements. Joints and muscles work together.
• Support and Protection: Bones support the body and protect vital organs (e.g., brain, heart, lungs, spinal cord).
• Storage of Minerals: Bones store calcium and phosphorous, which can be released when the body needs them.
• Production of Blood Cells: Bone marrow in certain bones produces red blood cells, white blood cells, and platelets.
• Attachment of Muscles: Bones provide surfaces for muscles to attach, enabling movement.

Types of Bone

• Long Bones: Cylindrical, found in limbs; act as levers. (e.g., femur)
• Short Bones: Small, compact, equal in length and width; designed for strength and weight-bearing. (e.g., carpals)
• Flat Bones: Flat surfaces, protect internal organs. (e.g., ribs)
• Irregular Bones: Complex shapes, variety of functions including protection and muscle attachment. (e.g., vertebrae)

Joints of the Skeletal System

• Joint: Where two or more bones meet; also called an articulation.
• Connective Tissues: Ligaments, cartilage, and tendons hold joints together and provide stability.
• Cartilage: Cushions joints, reducing friction.
• Tendons: Attach muscles to bones.
• Ligaments: Connect bones to bones, providing stability.

Connective Tissue Functions

• Connective tissue binds body tissues together, supports the body, and protects structures.
• Variations in blood supply exist: some tissues are very vascular (well supplied), while others (e.g., external ear) have poor vascularization.

Connective Tissue

• Connective tissue consists of ground substance (mostly water with adhesion proteins and polysaccharides) and fibers.
• Fibers are produced by cells and include collagen and elastic fibers.

Connective Tissue Types - Bone

• Bone (osseous tissue) is a type of connective tissue.
• Bone is composed of bone cells in lacunae, hard calcium salt matrix, and numerous collagen fibers.
• It plays a crucial role in protecting and supporting the body.

Cartilage Types

• Hyaline Cartilage: Most common type, abundant collagen fibers, rubbery matrix; makes up the entire fetal skeleton.
• Elastic Cartilage: Provides elasticity; found in external ear.
• Fibrocartilage: Highly compressible; found in cushion-like discs between vertebrae.

Cartilage Locations

• Hyaline cartilage is found in many locations throughout the body including the external ear, joints, and ribs.
• Elastic cartilage is located in the external ear, parts of the larynx.
• Fibrocartilage helps to cushion and support joints in areas like the intervertebral disks of the spine, and menisci of the knee.

Synovial Joints

• Allow free movement for skills during physical activity.
• Contain synovial fluid in the joint cavity, lubricating movement.
• Ends of bones are covered in articular cartilage, cushioning and reducing friction.
• The articular capsule prevents wear and tear.

Main Features of a Synovial Joint

• Bone.
• Articular cartilage.
• Articular capsule.
• Synovial membrane.
• Synovial fluid

Dense Connective Tissue

• The main matrix element is collagen fibers, produced by fibroblasts.
• Tendons attach muscle to bone and ligaments attach bone to bone.

Function of Ligaments

• Connect bones in a joint; help keep it together.
• Stabilize the joint, preventing dislocation during movement.
• Absorb shock due to elasticity.
• They help maintain correct posture and movement.

Types of Joints

Four main types of joints:

• Ball and socket: Found in shoulders and hips; allow for wide range of motion.
• Hinge: Found in elbows, knees, and ankles; permit flexion/extension.
• Pivot: Found in the neck and allow rotation.
• Condyloid: Found in wrists; allow flexion/extension, abduction, adduction, and circumduction.

Types of Synovial Joints

• Hinge: Found in elbows, knees, and ankles; allow flexion and extension.
• Pivot: Found in the neck; allows rotation.
• Ball and socket: Found in shoulders and hips; allows movement in multiple directions.
• Condyloid: Found in wrists; permits flexion/extension, abduction/adduction, and circumduction.

Summary

• 206 bones in adults, femur (largest), middle ear (smallest)
• Types of bones by tissue
• Bone remodeling (resorption/formation)
• Synovial joints (types)
• Connective tissues (bone, cartilage, types, tendon, ligament, ground substance, fibers)

Explore the complex structure of the musculoskeletal system, including bones, joints, and cartilage. Learn about the functions of muscles and how they interact with various types of tissues. This overview highlights key aspects such as bone composition and the differences between compact and spongy bone.