Anatomy: Directions and Positions

Anatomical Position

• Superior: Above or closer to the head
• Inferior: Below or closer to the feet
• Proximal: Closer to the point of attachment or center of the body (for limbs)
• Distal: Farther from the point of attachment or center of the body (for limbs)
• Medial: Closer to the midline or center of the body
• Lateral: Farther away from the midline or center of the body
• Posterior: Towards the back or behind
• Anterior: Towards the front or in front
• Superficial: Closer to the surface or outer layer of the body
• Deep: Farther away from the surface, towards the inner layers of the body

Body Segments

• Bones are connected to each other at joints (articulations)
• Tendons connect muscles to bones
• Joints: Shoulder (Humerus and Scapula), Elbow (Humerus, Radius, and Ulna), Wrist (Radius, Ulna, and Carpal bones)
• Bones: Humerus (upper arm), Scapula (shoulder blade), Radius and Ulna (forearm), Carpal (wrist), Femur (thigh), Tibia (shin), Fibula (lower leg), Tarsal (ankle)

Skeletal System

• Composed of bones and cartilage
• Bones: rigid, contain blood vessels, and can be repaired
• Classification of bones: Compact and Spongy
• Cartilage: semi-rigid, found in joints, and avascular
• Classification of cartilage: Hyaline (articular), Fibrocartilage (vertebral)
• Appendicular Skeleton: bones associated with the shoulder, upper limbs, pelvis, and lower limbs
• Axial Skeleton: bones of the skull, vertebral column, and thorax (cage, sternum, and ribs)

Bony Features and Landmarks

• Caused by things attached to bones (e.g., muscles)
• Bony features: Elevations (bumps), Indentations (holes), and Features associated with joints
• Elevations: Tuberosity (large rough bump), Tubercle (small rounded bump), Trochanter (large rounded bump), Crest (long ridge of bone), Line (a ridge of bone not as big as a crest)
• Indentations: Foramen (hole), Fossa (depression/sunken part), Groove/sulcus (bone channel)
• Features associated with joints: Condyle (smooth part of bone), Head (rounded, ends of long bones), Acetabulum (large, circular depression in hip bone), Cavity (smaller, circular depression on scapula)

Muscles

• Made of cells called myocytes (muscle fibers)
• All muscle fibers run from one end of the muscle to the other
• All muscle fibers lie parallel to each other (Fibre direction)
• Always pull
• Cross joints
• Muscle forces tend to pull the insertion towards the origin
• Can cause movement at all joints they cross
• Often perform multiple movements

Types of Muscle Contraction

• Concentric Muscle Contraction: Shortening in length
• Eccentric Muscle Contraction: While getting longer (e.g., moving with gravity)
• Isometric Muscle Contraction: No movement

Functions of Muscles

• Agonist/Prime Mover: Main muscle responsible for producing movement (contracts concentrically)
• Antagonist: Muscle that opposes the prime mover
• Synergist: Assists the prime mover (contracts concentrically)
• Fixator: Muscle that keeps the proximal segment/joint steady during movement

Muscle Properties

• A muscle cannot create the same amount of force throughout a full range of movement
• When shortened, generates almost no force
• When lengthened, generates almost no force
• In between, generates the most amount of force
• Origin (IMMOBILE) and Insertion (MOBILE)