Skeletal System

Bone Histology

The study of bone histology involves understanding the microscopic structure of bone tissue, including the identification of bone cells and the organization of bone matrix.

• Osteon: The fundamental structural unit of compact bone, consisting of concentric lamellae arranged around a central canal.

• Spongy Bone vs. Compact Bone: Spongy bone (cancellous bone) contains trabeculae and spaces filled with bone marrow, while compact bone is dense and forms the outer layer of bones.

• Bone Surfaces: Periosteum covers the outer surface of bones; endosteum lines the inner surfaces.

• Bone Cells: Osteocytes (mature bone cells), osteoblasts (bone-forming cells), and osteoclasts (bone-resorbing cells).

Example: Under a microscope, compact bone shows osteons with central (Haversian) canals, while spongy bone shows a network of trabeculae.

Skeletal Gross Anatomy

Gross anatomy of the skeleton includes the identification and classification of bones, their shapes, and their specific functions, as well as the sutures of the skull.

• Types of Bones: Long (e.g., femur), short (e.g., carpals), flat (e.g., sternum), irregular (e.g., vertebrae), sesamoid (e.g., patella).

• Skull Bones: Parietal, temporal, sphenoid, external acoustic meatus, frontal, zygomatic, nasal, maxilla, occipital, mandible, mental foramen, ethmoid, sagittal suture, coronal suture, lacrimal, condylar process, coronoid process, squamosal suture, lambdoid suture, supraorbital margin, styloid process, mastoid process.

Example: The sagittal suture separates the left and right parietal bones of the skull.

Axial Skeleton

The axial skeleton forms the central axis of the body and includes the skull, vertebral column, and thoracic cage.

• Components: Skull, hyoid bone, sternum (manubrium, body, xiphoid process), ribs, vertebrae (7 cervical, 12 thoracic, 5 lumbar, 1 sacrum, 1 coccyx).

• Vertebrae: Each type of vertebra has distinguishing features; cervical vertebrae have transverse foramina, thoracic vertebrae articulate with ribs, lumbar vertebrae are large and robust.

Example: The atlas (C1) and axis (C2) are specialized cervical vertebrae that support and rotate the head.

Appendicular Skeleton

The appendicular skeleton includes the bones of the limbs and girdles that attach them to the axial skeleton.

• Upper Limb: Clavicle, scapula, humerus, radius, ulna.

• Lower Limb: Femur, patella, tibia, fibula, tarsals, metatarsals, phalanges.

• Pectoral Girdle: Clavicle and scapula.

• Pelvic Girdle: Ilium, pubis, ischium, sacrum, coccyx.

Example: The humerus articulates proximally with the scapula at the shoulder and distally with the radius and ulna at the elbow.

Distinguishing Male and Female Skeletons

Male and female skeletons can be distinguished by features such as pelvic shape (wider in females for childbirth) and skull characteristics.

Spinal Curvatures and Disorders

The vertebral column has natural curves that help absorb shock and maintain balance. Abnormal curvatures can lead to clinical conditions.

• Kyphosis: Exaggerated thoracic curvature (hunchback).

• Lordosis: Exaggerated lumbar curvature (swayback).

• Scoliosis: Lateral curvature of the spine.

Articulations and Movements

Articulations (joints) are classified by structure and function. Synovial joints are the most movable type and have a complex structure.

• Types of Synovial Joints: Ball-and-socket, hinge, pivot, saddle, condyloid, plane.

• Joint Motions: Flexion/extension, abduction/adduction, circumduction, pronation/supination, dorsiflexion/plantar flexion, elevation/depression, protraction/retraction, lateral/medial rotation.

Example: The knee is a hinge joint allowing flexion and extension.

Muscular System

Muscle Histology

Muscle histology focuses on the microscopic structure of muscle tissue, including the identification of muscle types and their organization.

• Types of Muscle: Skeletal (striated, voluntary), cardiac (striated, involuntary, intercalated discs), smooth (non-striated, involuntary).

• Locations: Skeletal (attached to bones), cardiac (heart), smooth (walls of hollow organs).

• Functions: Movement, posture, heat production, circulation, digestion.

• Sarcomere: The functional unit of striated muscle, defined by Z-discs; contains actin (thin) and myosin (thick) filaments.

• Connective Tissue Organization: Muscle fiber (cell), endomysium (surrounds fiber), fasciculus (bundle), perimysium (surrounds fasciculus), epimysium (surrounds muscle), fascia (surrounds groups of muscles).

Example: Under a microscope, skeletal muscle shows striations and multiple peripheral nuclei, while smooth muscle lacks striations and has a single central nucleus.

Muscle Physiology

Muscle physiology examines how muscles contract and the factors that influence muscle force and movement.

• Sliding Filament Theory: Muscle contraction occurs as actin and myosin filaments slide past each other, shortening the sarcomere.

• Effect of Stimulus: The force generated by a muscle depends on the voltage, frequency, and length of the muscle at the time of stimulation.

• Physiological Experiments: Experiments can demonstrate the relationship between stimulus and muscle response (e.g., twitch, summation, tetanus).

Equation:

Example: Increasing the frequency of stimulation can lead to tetanic contraction, where the muscle remains contracted.

Gross Muscle Anatomy

Gross muscle anatomy involves the identification of major muscles and their locations, origins, insertions, and actions.

• Muscle Groups: Muscles are grouped by region (e.g., upper limb, lower limb, trunk) and function (e.g., flexors, extensors).

• Attachment Points: Muscles attach to bones via tendons; the origin is the fixed attachment, and the insertion is the movable attachment.

Example: The biceps brachii originates on the scapula and inserts on the radius, allowing flexion of the forearm.

Additional info: Some links and references to online resources were present in the original notes for further practice and labeling exercises. These are not included here but are recommended for interactive study.