Anatomy: Introduction

Anatomical Directions

• Medial (internal) refers to a structure located near the midline of the body
• Lateral (external) refers to a structure located farther away from the midline of the body
• Superior (cranial; cephalic) refers to a higher level relative to the upper end of the body
• Inferior (caudal) refers to a lower level relative to the lower end of the body
• Ipsilateral refers to a position on the same side as a reference point
• Contralateral refers to a position on the opposite side from a reference point

Movements

• Flexion: movement that decreases the angle between two bones
• Extension: movement that increases the angle between two bones
• Adduction: movement that brings a body part towards the midline
• Abduction: movement that moves a body part away from the midline
• Rotation: movement of a body part around its long axis
• Medial rotation: movement that results in the anterior surface of the part facing medially
• Lateral rotation: movement that results in the anterior surface of the part facing laterally
• Circumduction: complex sequence of movements combining flexion, extension, abduction, adduction, and rotation
• Pronation: turning the forearm medially so that the palm of the hand faces posteriorly
• Supination: turning the forearm laterally so that the palm of the hand faces anteriorly
• Protraction: moving a body part forward
• Retraction: moving a body part backward

Body Positions

• Prone position: lying face downward
• Supine position: lying on the back

Skin

• Divided into two parts: epidermis and dermis
• Epidermis: stratified epithelium with cells that flatten as they mature and rise to the surface
• Dermis: composed of dense connective tissue containing blood vessels, lymphatic vessels, and nerves
• Skin folds: areas where the skin is thinner and firmly tethered to underlying structures by strong bands of fibrous tissue
• Appendages of the skin: nails, hair follicles, sebaceous glands, and sweat glands

Joints

• Joint: a site where two or more bones articulate, or come together
• Types of joints: no movement (e.g., sutures of the skull), slight movement (e.g., superior tibiofibular joint), and freely movable (e.g., shoulder joint)

Bursae and Synovial Sheath Trauma and Infection

• Bursae and synovial sheaths are prone to traumatic or infectious disease
• Bursitis is inflammation of a bursa (e.g., prepatellar bursa, or "housemaid's knee")
• Tenosynovitis is inflammation of a tendon and its synovial sheath (e.g., extensor tendon sheaths of the hand)
• Notable tenosynovitis can lead to contracture of the synovial sheath and obstruct efficient sliding of the tendon

Muscle

• Three types of muscle: skeletal, smooth, and cardiac
• Skeletal muscles:
  • Act to produce movements of the skeleton
  • Made up of striated muscle fibers
  • Have two or more attachments: origin (more proximal, less mobile) and insertion (more distal, more mobile)
  • Fleshy part of the muscle is referred to as its belly
  • When a muscle contracts, the insertion is drawn proximally toward the origin

Cartilage

• Form of connective tissue in which cells and fibers are embedded in a gel-like matrix
• Fibers lend firmness and resilience
• Perichondrium covers the cartilage except on exposed surfaces in joints
• Three types of cartilage: hyaline, fibrocartilage, and others
• Hyaline cartilage has a high proportion of amorphous matrix and plays an important part in the growth of long bones

Joints

• Types of joints:
  • Ball-and-socket joint (e.g., glenohumeral joint, hip joint)
  • Ellipsoid joint (e.g., radiocarpal joint)
  • Saddle joint (e.g., carpometacarpal joint of the thumb)
  • Condyloid joint (e.g., metacarpophalangeal joint)
  • Hinge joint (e.g., humeroulnar part of the elbow joint)
  • Pivot joint (e.g., medial atlantoaxial joint)
  • Plane joint (e.g., sternoelavicular and acromioelavicular joints)
• Stability of a joint depends on three main factors: morphology of the bony articular surfaces, ligaments, and tone of the muscles around the joint
• Articular surfaces: shapes of the bones and their articulating surfaces cause the bones to form a relatively stable joint

Muscle Action

• Skeletal muscle action is the result of the coordinated action of many muscles
• A muscle can work in four ways:
  • Agonist (prime mover): chief muscle or member of a group responsible for a particular movement
  • Antagonist: opposes the action of an agonist
  • Fixator: stabilizes a joint or bone to allow efficient movement
  • Synergist: assists the action of an agonist
• Examples of muscle action: quadriceps femoris extending the knee, biceps femoris flexing the knee, muscles around the shoulder girdle fixing the scapula for abduction

Long Bones Development

• Develop by endochondral ossification, a slow process that is not completed until age 18 to 20 years or even later.
• The center of bone formation found in the shaft of the bone is the diaphysis.
• The centers at the ends of the bone are epiphyses.
• The plate of cartilage at each end, lying between the epiphysis and diaphysis in a growing bone, is the epiphyseal plate.
• The metaphysis is the part of the diaphysis that abuts onto the epiphyseal plate.

Fracture of a Bone

• Accompanied by a considerable hemorrhage of blood between the bone ends and into the surrounding soft tissue.
• The blood vessels and the fibroblasts and osteoblasts from the peristeum and endosteum take part in the repair process.

Rickets

• A defective mineralization of the cartilage matrix in growing bones.
• Produces a condition in which the bones are soft and pliable.

Joints

• Types of joints: synovial joints, synchondroses, and symphyses.
• Synovial joints: plane, hinge, pivot, condyloid, ellipsoid, saddle, and ball-and-socket.
• Examples of synovial joints: sternoelavicular and acromioclavicular joints (plane), humeroulnar part of the elbow joint (hinge), medial atlantoaxial joint (pivot), metacarpophalangeal joint (condyloid), radiocarpal part of the wrist joint (ellipsoid), carpometacarpal joint of the thumb (saddle), and hip joint (ball-and-socket).

Joint Stability

• Three main factors: shape of articular surfaces, ligaments, and muscle tone.
• Ligaments: cord or band of fibrous connective tissue uniting two or more structures.
• Types of ligaments: fibrous and elastic.
• Fibrous ligaments: composed of dense bundles of collagen fibers and are not stretchable under normal conditions.
• Elastic ligaments: composed largely of elastic tissues and can regain their original length after stretching.

Bursae and Synovial Sheaths

• Bursae: closed fibrous sac lined internally with synovial membrane.
• Synovial membrane secretes a film of viscous fluid that fills the sac.
• Bursae are typically found in areas subject to friction and serve to reduce friction.

Joint Examination

• Assess the normal range of movement of all joints.
• Dislocation of a joint occurs when the bones of a joint are no longer in their normal anatomic relationship with one another.

Tendon Reflexes

• Important tendon reflexes used in medical practice include the biceps brachii tendon reflex (C5, 6, and 7), brachioradialis tendon reflex, and Achilles tendon reflex (S1 and S2)
• The Achilles tendon reflex, also known as the ankle jerk, is elicited by tapping the Achilles tendon, which causes flexion of the ankle joint

Clinical Modification of Autonomic Nervous System Activities

• The Autonomic Nervous System (ANS) activity can be modified by various means, including drugs and surgical procedures
• One example is administering drugs to lower blood pressure by blocking sympathetic nerve endings and causing vasodilation of peripheral blood vessels
• In cases of severe arterial disease, sectioning the sympathetic innervation to the blood vessels can produce vasodilation and allow adequate blood flow through collateral circulation, thereby saving the limb

Blood Vessels

• The three types of blood vessels are arteries, veins, and capillaries (Fig. 1.27)
• Anatomic end arteries are vessels whose terminal branches do not anastomose with branches of arteries supplying adjacent areas
• These vessels provide the sole source of blood to a specific target area