The Skeletal System – Part 3
1. Vertebral Column (Spine)
The vertebral column is composed of individual vertebrae:
7 Cervical vertebrae
12 Thoracic vertebrae
5 Lumbar vertebrae
5 Sacral vertebrae (fused to form the sacrum)
4–5 Coccygeal vertebrae (fused to form the coccyx)
Key features:
Atlas and Axis: These are the first two cervical vertebrae, crucial for head movement.
Sacroiliac joints: Connect the sacrum to the hip bones.
Coccyx (tailbone): Serves as an attachment point for muscles.
2. Spinal Curvature Abnormalities
These are deviations from the spine's natural curves:
Scoliosis: A lateral (side-to-side) curvature of the spine.
Kyphosis: An exaggerated forward curve in the thoracic spine, often called "hunchback."
Lordosis: An exaggerated inward curve in the lumbar spine, often called "swayback."
3. Rib Cage
The rib cage consists of 12 pairs of ribs and the sternum (breastbone).
The sternum has three parts:
Manubrium
Body
Xiphoid process
Rib types:
True ribs (1–7): Connect directly to the sternum.
False ribs (8–10): Connect indirectly to the sternum (via cartilage of rib 7).
Floating ribs (11–12): Do not connect to the sternum at all.
Functions: The rib cage protects vital organs like the heart, lungs, liver, and spleen, and it plays
a key role in breathing.
4. Shoulder and Arm
Shoulder Girdle
The shoulder girdle is formed by the scapula (shoulder blade) and clavicle (collarbone).
Scapula features: Includes the spine, coracoid process, and glenoid fossa.
Clavicle: Connects the scapula to the manubrium of the sternum.
Upper Arm
The humerus (upper arm bone) forms joints with the scapula (shoulder joint) and the ulna
(elbow joint).
Forearm
The forearm consists of the radius (on the thumb side) and the ulna (on the little finger side),
which allow for hand rotation.
Wrist & Hand
Carpals: Eight wrist bones that form gliding joints.
Metacarpals: Five bones forming the palm of the hand.
Phalanges: The bones of the fingers.
Carpometacarpal joint: The saddle joint of the thumb, essential for grip.
5. Pelvic Girdle and Leg
Pelvic Girdle
The pelvic girdle is made up of two hip bones, each composed of the ilium, ischium, and
pubis. These bones connect at the pubic symphysis.
Acetabulum: The hip socket where the femur connects.
Thigh
The femur (thigh bone) is the longest bone in the body, forming a ball-and-socket joint at the hip
and a hinge joint at the knee.
Patella (kneecap): A sesamoid bone embedded within the quadriceps tendon.
Lower Leg
Tibia: The main weight-bearing bone (medial malleolus forms the inner ankle).
Fibula: A thinner bone that stabilizes the ankle (lateral malleolus forms the outer ankle).
Ankle & Foot
Tarsals: Seven ankle bones, including the calcaneus (heel bone).
Metatarsals: Five bones forming the main part of the foot.
Phalanges: The bones of the toes.
Articular System – Part 4
What is an Articulation (Joint)?
A joint is the point where two or more bones meet, regardless of how much movement is
allowed.
1. Tendon
Definition: A band of tissue that connects muscle to bone.
Nature: Inelastic and tough.
Types: Connective tissue.
Function: Connects the end of muscles to any place on the bone.
2. Ligament
Definition: An elastic band of tissue that connects bone to bone and provides stability to the
joint.
Nature: Elastic and strong.
Types: Connective tissue.
Function: Connects bones to bones at joints.
3. Cartilage
Definition: A soft, gel-like padding between bones that protects joints and facilitates movement.
Nature: Stiffer than ligaments.
Types: Skeletal tissues.
Function: Protects bones and stops them from knocking together by acting as a cushion in
between bones.
Classification of Joints
* Bones: The articulating surfaces.
* Articular Cartilage: A smooth, protective layer covering the bone ends, reducing friction.
* Synovial Membrane: A lining inside the joint capsule that secretes synovial fluid.
* Articular Capsule: A fibrous structure enclosing the entire joint.
* Joint Cavity with Synovial Fluid: The space within the capsule filled with a lubricating fluid that
reduces friction, absorbs shock, and nourishes the cartilage.
Joints are categorized by structure and degree of movement.
1. Synarthroses – Immovable Joints
Examples:
• - Suture: Bones joined by fibrous tissue (e.g., skull sutures).
• - Syndesmosis: Bones connected by ligaments (e.g., tibia–fibula, radius–ulna).
• - Gomphosis: Peg-in-socket joint (e.g., tooth in jaw).
2. Amphiarthroses – Slightly Movable Joints
Examples:
• - Symphysis: Bones joined by fibrocartilage (e.g., pubic symphysis).
• - Synchondrosis: Bones joined by hyaline cartilage (e.g., epiphyseal growth plate).
3. Diarthroses (Synovial Joints) – Freely Movable, has a joint capsule containing synovial fluid.
Includes ligaments, cartilage, tendons, and muscle.
Functions: Bear weight, enable motion, maintain stability, lubricate and nourish cartilage.
Joint Movements
Basic Movements:
• - Flexion: Decreases angle between bones.
• - Extension: Increases angle.
• - Hyperextension: Extends beyond normal limit.
• - Dorsiflexion: Lifting foot upward.
• - Plantar Flexion: Pointing foot downward.
• - Abduction: Away from midline.
• - Adduction: Toward midline.
• - Rotation: Around an axis.
• - Circumduction: Circular motion.
• - Supination: Palm faces up.
• - Pronation: Palm faces down.
• - Eversion: Sole of foot outward.
• - Inversion: Sole of foot inward.
• - Protraction: Forward movement.
• - Retraction: Backward movement.
• - Elevation: Raising body part.
• - Depression: Lowering body part.
• - Opposition: Thumb to fingertip.
• - Reposition: Returning thumb to original position.
6 Types of Synovial Joints (Diarthroses)
1. Ball-and-Socket (Multiaxial): Shoulder, hip.
2. Hinge (Uniaxial): Elbow, knee, phalanges.
3. Pivot (Uniaxial): Atlas–axis (neck).
4. Condyloid (Ellipsoidal, Biaxial): Wrist.
5. Saddle (Biaxial): Thumb.
6. Gliding (Multiaxial): Vertebrae.
Bursae
Fluid-filled sacs that reduce friction in joints.
Types:
• - Subcutaneous: Between skin and bone.
• - Subfascial: Between muscles.
• - Subtendinous: Between tendon and bone.
Common Joint Disorders and Conditions
• - Bursitis: Inflammation of bursa due to stress.
• - Arthritis: Inflammation of entire joint.
• - Rheumatic Fever: Childhood infection that may cause arthritis.
• - Rheumatoid Arthritis: Autoimmune disorder causing joint destruction.
• - Primary Fibrositis: Inflammation of joint connective tissue.
• - Osteoarthritis: Degenerative joint disease (age, weight).
• - Gout: Uric acid crystals in joints.
• - Sprain: Torn ligament (e.g., ankle, wrist).
• - Slipped Disk: Herniated intervertebral disc.
• - Dislocation: Bone out of joint socket.
• - Gingivitis: Gum inflammation from poor hygiene.
• - Hyperextension: Excessive joint extension.
• - Dislocated Hip: Femur head out of hip socket.
