Joints: Functional and Structural Classification

• Joints, also known as articulations, connect bones
• Joints are classified by functional and structural approaches

Functional Classification (Based on Movement)

• Synarthrotic joints have no movement
• Amphiarthrotic joints allow limited movement
• Diarthrotic joints are freely moveable

Structural Classification (Based on Connection)

• Fibrous joints connect bones with fibrous connective tissue
• Cartilaginous joints connect bones with cartilage
• Synovial joints connect bones with a joint cavity enclosed in a fibrous capsule
• All synovial joints are diarthrotic and freely movable

Fibrous Joints

• Connect bones with no joint space and fibrous tissue
• Suture joints are found in the skull, tightly connected, and don't move (synarthrotic)
• Gomphosis Joints are peg-in-socket connections, like teeth in the jaw, that do not move (synarthrotic)
• Syndesmosis Joints connect by fibrous tissue and allow slight movement (amphiarthrotic); an example is the connection between the tibia and fibula

Types of Suture Joints

• Serrated Suture is like interlocked fingers; an example is the sagittal suture (top of skull)
• Lap Suture overlaps bones at an angle; an example is the squamous suture (temporal & parietal bones)
• Plane Suture's bones touch side by side; an example is the intermaxillary joint (upper jaw)

Cartilaginous Joints

• Connect bones with no joint space and cartilage
• Synchondrosis Joints connect by hyaline cartilage and have no movement (synarthrotic); an example is sternocostal joints
• Symphysis Joints connect by fibrocartilage and allow slight movement (amphiarthrotic); examples are pubic symphysis & intervertebral joints

Synovial Joints

• Synovial joints are the most movable and always diarthrotic
• They contain a joint cavity filled with synovial fluid for smooth movement
• A fibrous capsule surrounds them, and a synovial membrane inside produces synovial fluid to reduce friction

Types of Synovial Joints & Movements

• Hinge Joint (Monoaxial): Moves in one plane, like a door hinge.
• Example: Elbow and knee
• Movement Plane: Sagittal (flexion & extension)
• Pivot Joint (Monoaxial): Rotates around a fixed point
• Example: Atlanto-axial joint (neck, shaking head “no”)
• Movement Plane: Transverse (rotation)
• Gliding Joint (Non-axial): Bones slide past each other with limited movement
• Example: Intercarpal (wrist) & intertarsal (ankle) joints
• Movement Plane: No specific axis (slight gliding motion
• Condyloid Joint (Biaxial): Moves in two planes
• Example: Metacarpophalangeal joints (knuckles)
• Movement Planes: Sagittal (flexion & extension); Frontal (abduction & adduction)
• Saddle Joint (Biaxial): Similar to condyloid but allows for opposition (thumb movement)
• Example: First carpometacarpal joint (thumb)
• Movement Planes: Sagittal (flexion & extension); Frontal (abduction & adduction); Opposition (unique to thumb)
• Ball and Socket Joint (Triaxial): Moves in all three planes
• Example: Shoulder & hip joints
• Movement Planes: Sagittal (flexion & extension); Frontal (abduction & adduction); Transverse (rotation & circumduction)

Intervertebral Joint

• Annulus Fibrosus (AF): The outer layer is made of fibrocartilage for support and shock absorption
• Nucleus Pulposus (NP): The gel-like center acts as a cushion and is a remnant of the notochord

Ligaments Supporting the Vertebral Column

• Anterior Longitudinal Ligament supports the front of the vertebral body
• Posterior Longitudinal Ligament supports the back of the vertebral body
• Ligamentum Flavum is inside the vertebral arch
• Interspinous Ligaments are between spinous processes
• Intertransverse Ligaments are between transverse processes
• Supraspinous Ligament is along the back edge of spinous processes

Herniated Disc

• Caused by poor posture, a weak core, or injury
• Increased pressure on the front of the disc forces the nucleus pulposus backward, possibly pressing on spinal nerves causing possible harm

Knee Joint Bones

• Femur
• Patella
• Tibia
• Fibula

Ligament Structures Supporting the Knee

• Anterior Support: includes the Quadriceps tendon, Patellar tendon, Patellar retinaculum, Joint capsule
• Lateral Support: Fibular/Lateral Collateral Ligament (Fibulofemoral ligament)
• Medial Support: Tibial/Medial Collateral Ligament (Tibiofemoral ligament)
• Posterior Support: Joint capsule, Popliteal ligaments, Hamstring tendons (Semitendinosus, Semimembranosus, Biceps Femoris)
• Internal Support: Anterior Cruciate Ligament (ACL), Posterior Cruciate Ligament (PCL)

Menisci & Their Function

• The medial & lateral meniscus is made of fibrocartilage, and their function is shock absorption and stability

Unhappy Triad of the Knee

• It is a sports injury caused by a lateral force to the knee while the foot is planted
• Damages: Anterior Cruciate Ligament (ACL), Medial Collateral Ligament (MCL/Tibiofemoral Ligament), Medial & Lateral Meniscus
• It leads to severe knee instability and requires long recovery

Muscle Tissue Types

• Cardiac muscle: Found in the heart, made of branched cylindrical cells with a central nucleus, has gap junctions in intercalated discs, and is controlled involuntarily by the autonomic nervous system
• Smooth muscle: Found in organs, made of spindle-shaped cells with a central nucleus, lacks striations, and is controlled involuntarily by the autonomic nervous system Skeletal muscle: Attached to bones, made of long cylindrical multinucleated fibers with visible striations, and is controlled voluntarily by the somatic nervous system

Microscopic Anatomy of Skeletal Muscle Fibers

A muscle fiber is a muscle cell

• The sarcolemma is the muscle cell membrane, continues with t-tubules, which help carry electrical signals inside the cell
• The sarcoplasmic reticulum (SR) is a specialized organelle that stores calcium, which is essential for muscle contraction

Myofibrils and the Sarcomere

• Myofibrils are protein structures inside muscle fibers that allow contraction
• The sarcomere is the basic unit of muscle contraction, formed by repeating units of thick and thin filament

Sarcomere Structure and Sliding Filament Theory

• Thick filament is made of myosin, which has a head and tail
• Thin filament contains actin, troponin, and tropomyosin
• The sarcomere extends from Z-line to Z-line
• A band contains the thick filament
• I band contains only thin filaments
• H zone contains only thick filaments
• During contraction, thin filaments slide toward the sarcomere center, decreasing the I band and H zone while the A band remains unchanged

How We Move

• Movement occurs when skeletal muscles exert force on bones, forming lever systems
• Parts of the Lever: Fulcrum (F) or the pivot point where movement occurs,Effort (E) or the force applied by muscles, and Resistance (R) or the load or weight being moved

Types of Levers

• First-Class Lever (RFE): The fulcrum is between the resistance and effort, like a see-saw; Atlanto-occipital joint (head nodding "yes") is an example with the Atlanto-occipital joint being the Fulcrum, the posterior neck muscles are the Effort, Weight of the head is the Resistance
• Second-Class Lever (FRE): The resistance is between the fulcrum and effort, like a wheelbarrow; the example is the ball of the foot; standing on tiptoes; Metatarsophalangeal joint is the Fulcrum, the calf muscles (gastrocnemius/soleus) are the effort and the body weight at the talus is the resistance
• Third-Class Lever (FER): Fulcrum, effort, resistance; the example is the elbow joint; The Effort has the fulcrum and resistance, like a broom; Elbow joint is the Fulcrum, bending the arm is an example, and biceps brachii muscle is the effort and the weight in the hand is the resistance

Explore the classification of joints based on their function (synarthrotic, amphiarthrotic, diarthrotic) and structure (fibrous, cartilaginous, synovial). Learn about the characteristics of each type of joint, including examples like sutures, gomphosis, and syndesmosis.