C

Skeletal System: Structure and Function Notes

Bone Structure and Functions

  • Haversian System (Osteon): An example of a conversion system in bone.

    • Lamella: Concentric rings of bone matrix.

    • Lacunae: Spaces between lamellae.

    • Osteocytes: Mature bone cells located within the lacunae.

    • Canaliculi: Tiny canals connecting lacunae, allowing nutrient and waste exchange.

    • Central Canal (Haversian Canal): Contains arteries, veins, and nerves, running longitudinally through the osteon.

  • Identification: It is crucial to be able to identify these structures via models, pictures, or under a microscope.

  • Functions of Bones:

    • Frame: Provides the body's structural framework.

    • Protection: Safeguards major internal organs.

    • Mineral Storage: Stores essential minerals (e.g., calcium, phosphate).

    • Fat Storage: Stores fat in yellow bone marrow.

    • Hematopoiesis: Produces red blood cells in red bone marrow.

    • Leverage for Movement: Acts as levers for muscle attachment, enabling movement.

Classifications of Bones

  • Types of Bones:

    • Long Bones: (e.g., Humerus, Femur)

    • Short Bones: (e.g., Carpals, Tarsals)

    • Irregular Bones: (e.g., Vertebrae)

    • Sesamoid Bones: (e.g., Patella)

    • Flat Bones: (e.g., Scapula, Cranial bones)

    • Wormian Bones (Suture Bones): Small, irregular bones found within cranial sutures.

Divisions of the Skeleton

  • Axial Skeleton:

    • Comprises 80 bones.

    • Forms the central axis of the body (skull, vertebral column, thoracic cage).

    • Vertebral Column:

      • Cervical Vertebrae (C1-C7).

      • Thoracic Vertebrae (T1-T12).

      • Lumbar Vertebrae (L1-L5).

      • Sacrum: One as an adult, formed from 5 fused sacral segments.

      • Coccyx: One as an adult, formed from 4 to 7 coccygeal segments.

    • Intervertebral Discs: Located between vertebrae from below C2 all the way to below L5. There are no intervertebral discs above C1 or below C1.

    • Special Cervical Vertebrae:

      • C1 is known as the Atlas.

      • C2 is known as the Axis.

      • The Odontoid Process (Dens) is a prominent projection from the body of the Axis (C2) that articulates with the Atlas (C1).

    • Hyoid Bone: A U-shaped bone located in the neck, superior to C1 and C2.

  • Appendicular Skeleton:

    • Comprises 126 bones.

    • Includes the upper and lower limbs and the girdles that attach them to the axial skeleton.

Appendicular Skeleton: Upper Limb and Girdle

  • Pectoral Girdle:

    • Clavicle (Collarbone): Articulates with the sternum and scapula.

    • Scapula (Shoulder Blade):

      • AC Joint (Acromioclavicular Joint): Where the clavicle and scapula articulate.

      • Acromion: A large projection forming the highest point of the shoulder, branching off the scapular spine.

      • Glenoid Cavity (Glenoid Fossa): A shallow depression that articulates with the head of the humerus.

      • Supraspinatus Fossa: Located posteriorly on the scapula.

      • Subscapular Fossa: Located anteriorly on the scapula, smooth.

      • Left Scapula Identification: The glenoid cavity is always lateral, and the smooth subscapular fossa is always anterior.

  • Humerus (Upper Arm Bone):

    • Humeral Head: Articulates with the glenoid cavity of the scapula.

    • Greater and Lesser Tubercles: Prominences on the proximal humerus for muscle attachment.

    • Olecranon Fossa: A depression on the posterior distal humerus that articulates with the olecranon process of the ulna during elbow extension.

  • Forearm Bones:

    • Ulna: The medial bone of the forearm.

    • Radius: The lateral bone of the forearm.

    • Radial Head: Proximal end of the radius, moves on the radial notch of the ulna to allow supination and pronation of the forearm.

    • Radial Styloid Process: Distal, pointed projection of the radius.

    • Ulnar Styloid Process: Distal, pointed projection of the ulna.

    • Ulnar Head: Distal end of the ulna.

  • Wrist and Hand Bones:

    • Carpal Bones: 8 bones of the wrist, arranged in two rows of four.

    • Metacarpal Bones: 5 bones of the palm.

    • Phalanges: 14 bones forming the fingers (5 rows). Each finger has 3 phalanges (proximal, middle, distal), except the thumb which has 2 (proximal, distal).

Appendicular Skeleton: Lower Limb and Girdle

  • Pelvic Girdle (Os Coxa / Coxal Bones): Formed by the fusion of three bones in an adult.

    • Ilium: The superior, largest part.

      • Iliac Crest: The superior border of the ilium.

      • Anterior Superior Iliac Spine: Prominent anterior projection on the iliac crest.

      • Posterior Superior Iliac Spine: Prominent posterior projection on the iliac crest.

      • Iliac Fossa: Large, smooth, concave surface on the inner side of the ilium.

    • Ischium: The inferior and posterior part.

      • Ischial Tuberosity: The rough edge on the bottom of the ischium, bears weight when sitting.

      • Ischial Spine: A pointed projection superior to the ischial tuberosity.

    • Pubis: The anterior and inferior part.

      • Pubic Symphysis: Where the two pubic bones connect anteriorly.

    • Acetabulum: The hip socket formed by the fusion of the ilium, ischium, and pubis, articultates with the femoral head.

  • Femur (Thigh Bone):

    • Femoral Head: Articulates with the acetabulum.

    • Anatomical Neck: The narrow region distal to the femoral head.

    • Surgical Neck: A common site for fractures, distal to the anatomical neck.

    • Greater Trochanter: A large, irregular projection on the lateral side of the femur.

    • Lesser Trochanter: A small, conical projection on the medial side of the femur.

    • Patellar Surface: Smooth surface on the anterior distal femur for articulation with the patella.

    • Medial Condyle and Lateral Condyle: Large, rounded projections on the distal femur that articulate with the tibia.

  • Lower Leg Bones:

    • Tibia (Shin Bone): The medial and larger bone of the lower leg.

      • Medial Malleolus: A prominent projection on the medial side of the distal tibia.

      • If the medial malleolus is present, it indicates the tibia is medial, aiding in left/right identification.

    • Fibula: The lateral and smaller bone of the lower leg.

      • Lateral Malleolus: A prominent projection on the lateral side of the distal fibula.

  • Ankle and Foot Bones:

    • Tarsal Bones: 7 bones of the ankle.

      • Calcaneus: The heel bone.

      • Talus: Articulates with the tibia and fibula to form the ankle joint.

    • Metatarsal Bones: 5 bones of the foot.

    • Phalanges: 14 bones forming the toes.

Internal and External Bone Structures

  • Periosteum: The tough, fibrous membrane covering the outer surface of bone.

  • Medullary Canal (Marrow Cavity): The hollow space within the diaphysis of long bones.

    • Endosteum: The thin membrane lining the inside of the medullary canal.

    • Contains Red Bone Marrow (produces blood cells) and Yellow Bone Marrow (stores fat).

  • Cancellous Bone (Spongy Bone): Porous bone tissue, found inside the medullary canal and at the ends of long bones, containing trabeculae.