Anatomy Module 1: Introduction to Human Anatomy

Muscular system

All muscles; how they move joints

Cardiovascular (arterial/venous) system

Heart + vasculature; pumps blood throughout body

Respiratory (pulmonary) system

Nasal/oral cavity → trachea → lungs (lobes, covered by pleura); site of gas exchange

Digestive (GI) system

Mouth → esophagus → stomach → small intestine (nutrient absorption) → large intestine (waste/water/electrolyte disposal) → rectum/anus

Lymphatic system

Lymph = interstitial fluid (byproduct of blood); mobilizes lipids/proteins from interstitial spaces between cells back into bloodstream

Endocrine system

Hormone production and regulation

Integumentary system

Largest organ system; skin, hair, nails

Nervous system

Master regulatory system — controls heart rate, breathing depth, sweating, hormone release, etc.; coordinates all other systems toward the goal of keeping the body alive and thriving

arteries

carry oxygenated blood away from the heart (~99% of the time — exception discussed later, e.g., pulmonary artery)

veins

carry blood toward the heart

Levels of biological organization

1. Cell (e.g., osteoblasts, osteoclasts)

2. Tissue (e.g., bone tissue)

3. Organ (e.g., a single bone)

4. Organ system (e.g., skeletal system)

5. Organism (multiple organ systems → whole human body)

Systemic approach

Studies the body by organ system, looking at each system in isolation across the whole body

Regional approach

Studies all systems together within a specific body region (bones, muscles, tendons, ligaments, vessels, nerves, lymphatics, skin — all studied together for that region).

Clinical approach

Frames anatomy in terms of clinical relevance and consequences of injury/dysfunction rather than pure structure

Imaging approach

Uses medical imaging to understand structural relationships:

• X-ray — bone position/connections

• MRI — soft tissue relationships

• CT scan — differentiates fluid-filled vs. non-fluid-filled structures

• Ultrasound — real-time visualization; used in this professor's PA program (students scan each other to locate heart, lungs, etc.)

• Advanced/novel method: CT scans of cadavers converted into 3D holograms, viewed via VR goggles, used by orthopedic residents to preview tissue layers before dissection/surgery.

Anatomical position

The standardized baseline reference posture used for all anatomical descriptions, measurements, and documentation.- eliminates ambiguity, serves as reference point, and gives relativity for directional terms

• Standing upright

• Palms facing forward

• Shoulders level

• Head facing forward

• Feet shoulder-width apart, facing forward

superficial

closer to the outside/external surface

deep

 farther inside, beneath another structure

intermediate

between superficial and deep

superficial/intermediate/deep

Describes depth/layering relative to another structure.

1. Skin (most superficial)

2. Biceps (intermediate — relative to skin & brachialis)

3. Brachialis (deep to biceps)

4. Ligaments (deep to brachialis)

5. Bone (deepest)

medial/lateral

Describes position relative to the midline of the body (an imaginary line dividing the body into right and left halves).

• Clavicle (collarbone): has a medial end (near sternum/midline) and a lateral end (toward shoulder)

• Femur (knee): medial condyle (inner bony prominence) vs. lateral condyle (outer bony prominence)

medial

closer to the midline

lateral

 farther from the midline

anterior

toward the front

posterior

toward the back

ventral/dorsal

Functionally equivalent to anterior/posterior, but used in specific contexts — especially the spine, hand, and foot

Important: This relationship is defined relative to anatomical position. If you rotate the palm, the ventral surface doesn't "become" dorsal — the terminology stays fixed to the anatomical position reference, not to the momentary orientation of the limb

ventral

anterior (front)

dorsal

posterior (back)

proximal/distal

Describes position relative to the trunk/midpoint of the body (point of attachment/origin), rather than the midline.

Important nuance: Proximal/distal can overlap in meaning with either superior/inferior or medial/lateral, depending on the structure:

Comparable to...	Example
Superior/Inferior	Shoulder (proximal/superior) vs. elbow (distal/inferior)
Medial/Lateral	Medial end of clavicle = proximal end; lateral end = distal end

Think of proximal/distal in terms of a central reference circle at the body's core/trunk — proximal = closer to that center, distal = farther away — rather than strictly "above/below" or "toward/away from midline."

proximal

closer to the trunk/center of the body

distal

farther from the trunk/center of the body

cephalad/caudal

Used specifically for the axial skeleton (spine/vertebral column) — less commonly used for peripheral structures.

Examples:

• The head end of the spinal cord (toward the brainstem) = cephalad

• The cauda equina (bottom of spinal cord) = caudal end

Functionally interchangeable with superior/inferior, but conventionally reserved for spinal/axial skeleton descriptions. In general conversation, people are more likely to say "superior/inferior" than "cephalad/caudal."

cephalad

toward the head (Latin: "ceph/cephal" = head — same root as biceps/triceps, referring to number of muscle "heads")

caudal

toward the tail/sacrum (Latin: "caudal" = tail)

plane

an imaginary flat surface (think: a sheet of paper) placed through/over a joint that shows the direction in which motion is occurring

Also used in radiology/imaging to describe the view or section of a patient being examined.

frontal/coronal plane

orientation: viewed from the front

typical motions: abduction/adduction

axis it rotates around: Anterior–Posterior axis (also called frontal/coronal axis)

sagittal plane

orientation: viewed from the side

typical motions: flexion/extension

axis it rotates around: Medial–Lateral axis

horizontal/transverse plane

orientation: viewed from above, across the body

typical motions: internal/external rotation

axis it rotates around: longitudinal (vertical) axis

Uniplanar/uniaxial joints

• move in only 1 plane

  • Example: Elbow, knee → sagittal plane only (flexion/extension); no meaningful ab/adduction or rotation

biplanar joints

• move in 2 planes

  • Example: Knuckles (MCP joints of fingers) → frontal plane (abduction/adduction = spreading fingers) and sagittal plane (flexion/extension)

multiplanar/multiaxial joints

• move in all 3 planes

  • Example: Shoulder and hip (ball-and-socket joints) — the most mobile joint type, with the greatest number of planes of motion

head and neck motion

Because the head/neck is a central/midline structure (not paired left/right like a limb), its motions get unique names instead of "abduction/adduction":

• Moving head to either side (frontal plane) = side flexion

• Rotating head to look side to side (horizontal plane) = rotation (simply "right rotation" / "left rotation" — not internal/external, since it moves toward both sides)

side flexion (head)

Moving head to either side (frontal plane)

rotation (head)

• Rotating head to look side to side (horizontal plane)

abduction

moving a body part away from the midline

frontal plane

Occurs around the anterior-posterior axis

adduction

moving a body part back toward the midline

frontal plane

Occurs around the anterior-posterior axis

flexion

brings a segment anteriorly

sagittal plane

Applies to: shoulder, elbow, wrist, hip, knee, head/neck

extension

brings a segment posteriorly

sagittal plane

Applies to: shoulder, elbow, wrist, hip, knee, head/neck

flexion/extension exceptions and nuances

• Hip: flexion moves the thigh anteriorly (as expected), but the "logic" of anterior/posterior can feel reversed depending on viewing angle — regardless of direction, it is still sagittal plane motion.

• Knee: flexion brings the lower leg posteriorly (bending backward), still classified as sagittal plane motion.

• Foot/ankle: flexion/extension are renamed:

  • Dorsiflexion = bringing the top (dorsum) of the foot upward

  • Plantarflexion = pointing the foot downward (standing on tiptoes), named for the plantar (sole) surface

dorsiflexion

bringing the top (dorsum) of the foot upward

plantarflexion

pointing the foot downward (standing on tiptoes), named for the plantar (sole) surface

flexion/extension

sagittal plane

Applies to: shoulder, elbow, wrist, hip, knee, head/neck

abduction/adduction

frontal plane

Occurs around the anterior-posterior axis

Examples: shoulder abduction/adduction, hip abduction/adduction, finger abduction/adduction

internal (medial)/external (lateral) rotation

horizontal plane

Occurs mainly in multiaxial joints (shoulder, hip)

• Important tip: Always assess rotation by watching the movement of the proximal long bone (humerus or femur), NOT the distal segment (forearm/lower leg) — the distal part can be misleading since it "goes along for the ride."

  • Example: turning the foot outward while the knee is bent actually reflects internal rotation of the femur.

internal/medial rotation

rotating the limb inward

external/lateral rotation

rotating the limb outward

pronation/supination

describe how your feet roll when you walk or run, or how your hands and forearms rotate

• Key point: This motion technically occurs in the forearm (rotation between the radius and ulna), not the wrist — the hand/wrist simply moves along with the forearm.

• Foot pronation/supination is more complex — it results from multiple joints acting together (not a single joint like the forearm). This will be covered later when discussing foot arches/biomechanics.

supination

palm-up position (think: "holding a bowl of soup")

pronation

 palm-down position (think: "dropping the bowl")

protraction

moving a structure forward

retraction

moving a structure backward

protraction/retraction

• Occurs at:

  • Scapula/shoulder blades — protraction (shoulders forward) vs. retraction (shoulders back, like rowing)

  • Head/neck — forward head motion ("pigeon" motion) vs. pulling head back

  • Jaw — protracting/retracting the lower jaw

elevation

moving a structure upward (e.g., shrugging shoulders up)

depression

moving a structure downward (e.g., shoulders back down)

functional plane of the shoulder

• In addition to the 3 anatomical planes, the shoulder has a functional plane — the natural resting angle of the scapula on the rib cage, angled roughly 30° anterior to the frontal plane.

• This is not one of the 3 anatomical planes (not frontal, sagittal, or horizontal) — it's a real-world/biomechanical positioning concept.

• Clinical relevance: When asked for the anatomical planes of motion of the shoulder, the standard answers still apply (abduction = frontal, flexion/extension = sagittal, rotation = horizontal).

  • However, in rehab/orthopedic practice, exercises (e.g., strengthening the rotator cuff/abductors) are performed in the functional plane — because that's the plane in which the shoulder actually moves during real-life/functional activities — rather than strictly on the anatomical frontal plane.