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Human Anatomy

Standard Anatomical Position

  • Describes a formal posture to which anatomical terms refer.
  • Key features of the standard anatomical position include:
    • The body stands erect.
    • The body faces forward.
    • Head is level with eyes looking forward.
    • Arms are positioned at the sides with palms facing forward (thumbs outward).
    • Legs are straight and parallel.
    • Feet are flat on the floor with toes pointing forward.
  • Directional Terms should always be applied as if the body is in the anatomical position.

Orientation and Directional Terms (Table 1.1)

Superior (Cranial or Cephalic)
  • Definition: Toward the head end or the upper part of a structure or the body; above.
  • Example: The forehead is superior to the nose.
Inferior (Caudal)
  • Definition: Away from the head end or toward the lower part of a structure or the body; below.
  • Example: The navel is inferior to the breastbone.
Anterior (Ventral)
  • Definition: Toward or at the front of the body; in front of.
  • Example: The breastbone is anterior to the spine.
Posterior (Dorsal)
  • Definition: Toward or at the backside of the body; behind.
  • Example: The heart is posterior to the breastbone.
Proximal
  • Definition: Close to the origin of the body part or the point of attachment of a limb to the body trunk.
  • Example: The elbow is proximal to the wrist.
Distal
  • Definition: Farther from the origin of a body part or the point of attachment of a limb to the body trunk.
  • Example: The knee is distal to the thigh.
Superficial (External)
  • Definition: Toward or at the body surface.
  • Example: The skin is superficial to the skeleton.
Deep (Internal)
  • Definition: Away from the body surface; more internal.
  • Example: The lungs are deep to the rib cage.
Medial
  • Definition: Toward or at the midline of the body; on the inner side of.
  • Example: The heart is medial to the arm.
Lateral
  • Definition: Away from the midline of the body; on the outer side of.
  • Example: The arms are lateral to the chest.
Intermediate
  • Definition: Between a more medial and a more lateral structure.
  • Example: The collarbone is intermediate between the breastbone and the shoulder.
Note on Terminology
  • The term caudal, literally "toward the tail," is synonymous with inferior only for the inferior end of the spine.
  • The terms anterior and ventral are synonymous in humans, but not in four-legged animals (ventral refers to the animal's "belly"). Likewise, posterior and dorsal are the same in humans, but dorsal refers to an animal's back.

Regional Terms

HEAD & NECK
  • Cephalic (Head): Includes skull, face, eyes, nose, mouth, chin.
  • Cervical (Neck): Front, sides, and back of the neck.
TORSO (TRUNK)
  • Thoracic (Chest): Includes sternal, pectoral, and axillary.
  • Abdominal: Includes the navel and lower back.
  • Pelvic: Includes the groin, genital area, lower back, and buttocks.
UPPER LIMB
  • Shoulder & Arm: Includes shoulder, upper arm, elbow, and forearm.
  • Hand: Includes wrist, palm, and fingers.
LOWER LIMB
  • Thigh & Leg: Includes thigh, knee, shin, and calf.
  • Pedal (Foot): Includes ankle, heel, sole, and toes.

Body Divisions

  • Axial: Comprises the head, neck, and trunk.
  • Appendicular: Includes the limbs.
  • Regional terms designate specific areas within these body divisions.

Anatomical Variability

  • Human anatomy exhibits variations externally and internally.
  • Approximately 90% of all body structures match textbook descriptions.
  • There may be deviations such as misplaced nerves or blood vessels and missing muscles.
  • Extreme anatomical variations can be inconsistent with life.
  • Example: Lower ratios of the second digit to the fourth digit (2D:4D) and increased facial fluctuating asymmetry are correlated with higher levels of Dark Triad personality traits.
    • Reference: Borraz-Leon, J. I., Rantala, M. J., & Cerda-Molina, A. L. (2019). Digit ratio (2D:4D) and facial fluctuating asymmetry as predictors of the dark triad of personality. Personality and Individual Differences, 137, 50-55.
Specific Examples of Anatomical Variability
  • Supracondylar Process of the Humerus:
    • Also known as avian spurs, these are small bony projections on the anteromedial aspect of the humerus.
    • This process is an evolutionary remnant that is more prominent in certain animal species.
  • Cervical Ribs:
    • Extra ribs arising from the cervical (neck) vertebra.
    • Occurs in approximately 1 in 500 individuals.

Body Planes and Sections

  • Definition: Hypothetical planes used to divide the body to describe the location of structures or movement direction.
  • Three primary anatomical planes:
    • Sagittal Plane (Median): Divides the body into left and right sections.
    • Frontal Plane (Coronal): Divides the body into anterior and posterior sections.
    • Transverse Plane (Horizontal): Divides the body into superior and inferior sections.

Body Cavities

  • There are two sets of internal body cavities that are closed to the external environment:
    1. Dorsal: Protects the nervous system.
    2. Ventral: Houses internal organs (viscera).
Dorsal Body Cavity
  • Protects the nervous system.
  • Has two subdivisions:
    1. Cranial Cavity: Encases the brain.
    2. Vertebral Cavity: Encloses the spinal cord.
Ventral Body Cavity
  • Houses internal organs (viscera) and consists of two subdivisions separated by the diaphragm:
    1. Thoracic Cavity:
    • Contains two pleural cavities (each surrounding a lung).
    • Contains the pericardial cavity (enclosing the heart).
    • Contains the mediastinum (which contains the pericardial cavity and surrou