Bones & Skeletal Tissue

Osseous Tissue Types

The human skeleton is composed of two main types of osseous (bone) tissue: compact bone and spongy bone. Each type has distinct structural and functional characteristics.

• Compact Bone: Located deep to the periosteum, composed of osteons (Haversian systems), provides strength and support.

• Spongy Bone: Lacks Haversian canals, composed of trabeculae, found deep to compact bone, contains red bone marrow, resists compression.

Bone tissue functions: Mineral storage, movement, protection, red blood cell formation, triglyceride storage, and support.

Bone Cells and Structure

• Osteocytes: Mature bone cells found in lacunae.

• Osteons: Functional subunits of compact bone, consisting of concentric lamellae surrounding a central canal.

• Canaliculi: Tiny channels connecting lacunae, allowing communication and nutrient exchange.

Bone Shapes

• Short bones: Carpals

• Long bones: Humerus

• Irregular bones: Vertebrae

• Sesamoid bones: Patella

• Flat bones: Scapula

Bone Anatomy

• Periosteum: Outer layer of compact bone, anchored by Sharpey's fibers.

• Lamellae Types:

  • Circumferential: Run parallel to bone surface.

  • Concentric: Circular layers around central canal.

  • Interstitial: Fill gaps between osteons.

• Central (Haversian) Canal: Contains blood vessels and nerves, runs longitudinally.

• Perforating (Volkmann's) Canal: Runs perpendicular, connects central canals.

The Skeletal System

Axial Skeleton

The axial skeleton forms the central supporting axis of the body and includes the skull, vertebrae, sacrum, sternum, ribs, and hyoid bone.

• Accessory structures: Hyaline cartilage, fibrocartilage, elastic cartilage.

Rib Cage Anatomy

• True ribs (1-7): Directly attached to sternum via costal cartilage.

• False ribs (8-10): Indirectly attached to sternum.

• Floating ribs (11-12): Not attached to sternum.

• Sternum: Bone to which costal cartilage attaches.

Appendicular Skeleton

The appendicular skeleton consists of the limbs and girdles, excluding the vertebral column, trunk, and skull.

• Scapula: Right or left determined by anatomical landmarks.

• Clavicle: Medial (sternal) and lateral (acromial) ends.

• Humerus: Right or left determined by deltoid tuberosity and anatomical neck.

Wrist and Hand Anatomy

• Carpals: Scaphoid, lunate, triquetrum, pisiform, hamate, capitate, trapezoid, trapezium.

• Metacarpals: Head, body, base.

• Phalanges: Distal, middle, proximal.

• Pollex: Thumb region.

Joints

Classification of Joints

Joints are classified by structure and function.

• Structural types:

  • Fibrous: Skull sutures, gomphosis, syndesmosis.

  • Cartilaginous: Synchondrosis (costochondral), symphysis (intervertebral discs).

  • Synovial: Shoulder, knee.

• Functional types:

  • Synarthrosis: Immovable

  • Amphiarthrosis: Slightly movable

  • Diarthrosis: Freely movable

Synovial Joint Movements

• Non-axial: Plane joints (intercarpals)

• Uni-axial: Pivot (atlantoaxial), hinge (elbow)

• Bi-axial: Condylar (metacarpophalangeal), saddle (thumb)

• Multi-axial: Ball and socket (shoulder, hip)

Muscle Tissue

Muscle Tissue Types and Structure

Muscle tissue is classified as skeletal, cardiac, or smooth, each with unique features.

• Skeletal muscle: Multinucleated, striated, voluntary, contains fascicles.

• Cardiac muscle: Branched, involuntary, contains intercalated discs.

• Smooth muscle: Involuntary, lacks striations and intercalated discs.

Muscle Cell Anatomy

• Sarcolemma: Plasma membrane of muscle cells.

• Sarcoplasm: Cytoplasm of muscle cells.

• Myofibrils: Rod-like structures containing contractile elements.

• Sarcoplasmic reticulum: Stores and releases calcium ions.

• T-tubules: Carry action potentials deep into muscle fibers.

• Striations: Alternating dark (A bands, myosin) and light (I bands, actin) bands.

• Sarcomere: Smallest functional unit of muscle contraction.

Muscle Contraction Process

1. Excitation: Acetylcholine (ACh) triggers action potential in motor end plate.

2. Excitation-Contraction Coupling: Action potential travels down T-tubules, triggers calcium release from sarcoplasmic reticulum.

3. Preparation for Contraction: Calcium binds to troponin, tropomyosin moves away from actin's active site.

4. Contraction: Actin and myosin bind, myosin powerstroke, ATP detaches actin and myosin, cycle repeats.

5. Relaxation: ACh degraded, calcium returns to normal, actin and myosin sites blocked, muscle relaxes.

Muscle Attachments and Naming

• Origin: Stationary bony attachment.

• Insertion: Mobile bony attachment.

• Belly: Region between origin and insertion.

• Innervation: Nerve stimulating muscle contraction.

• Muscle actions: Flexor, extensor, abductor, adductor.

• Shapes: Deltoid (triangle), trapezius (trapezoid).

• Sizes: Maximus, longus, brevis.

• Fiber directions: Rectus (parallel), transversus, oblique.

• Origins: Biceps, triceps, quadriceps.

Fascicle Arrangements

• Circular: Sphincters

• Convergent: Single tendon

• Parallel: Strap-like or fusiform

• Pennate: Unipennate, bipennate, multipennate (diagonal fibers)

Muscles of the Body

Neck Muscles

• Sternocleidomastoid: Flexes and rotates the head.

• Splenius capitis: Extends and rotates the head.

Thoracic Muscles

• Diaphragm: Separates thoracic and abdominopelvic cavities, contracts for inhalation.

• External intercostals: Aid inhalation.

• Internal intercostals: Aid exhalation.

Shoulder and Arm Muscles

• Deltoid: Abducts arm.

• Pectoralis major: Flexes, adducts, and rotates arm.

• Rotator cuff: Supraspinatus, infraspinatus, teres minor, stabilize shoulder.

• Latissimus dorsi: Extends, adducts, and rotates arm.

Thigh Muscles

• Quadriceps femoris: Vastus lateralis, vastus intermedius, vastus medialis, rectus femoris; extend knee.

Lower Leg Muscles

• Anterior: Tibialis anterior, extensor digitorum longus.

• Lateral: Fibularis longus, fibularis brevis.

• Posterior: Gastrocnemius, soleus, flexor digitorum longus, tibialis posterior.

Summary Table: Bone and Muscle Features

Key Equations

Muscle contraction:

Bone strength:

Additional info:

• Some muscle and bone names are inferred based on standard anatomical knowledge.

• Tables and images are recreated and expanded for clarity and completeness.