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Terminology and Basic Concepts in Anatomy

Original Editor - Daphne Xuan

Top Contributors - Ewa Jaraczewska and Jess Bell  

Introduction

When we study or discuss anatomy, we use specialised terminology to describe the structures of the human body, their location and their relationship to one another. General rules of anatomical terminology include: (1) avoid synonyms, (2) ensure linguistic and grammatical correctness, (3) avoid eponyms, (4) be consistent (5) be precise and (6) keep things simple.[1]

"The use of obsolete or invalid anatomical names in clinical practice or teaching enhances the risk of miscommunication, which may increase the risk of poor or even fatal outcomes."[1]

Anatomical Locations

While the human body can vary in terms of volume, shape, structure, position, etc.,[2] we must be able to precisely describe the locations of specific body structures.

Anatomical Position

The standard anatomical position in human anatomy is standing upright, with the arms at the sides, palms facing forward, and feet with the second toe pointing straight ahead.

Several terms are used to describe the relative positions of body parts.

Superior (or cranial) describes a location above another part of the body or towards the head. Inferior (or caudal) describes a position below another structure or closer to the feet.

  • Example: a patient complains of neck pain after falling from a height. Upon examination, you note their neck is tender. Your documentation indicates that the tenderness is superior (towards the head) to the right clavicle. Additionally, the patient complains of right shoulder pain, which is inferior (towards the feet) to the site of the neck injury.

Anterior (or ventral) refers to structures towards the front of the body. Posterior (or dorsal) refers to structures that are further back in the body. In the feet, the dorsal aspect is the top surface facing upwards, while the plantar aspect is the bottom surface touching the ground.

  • Example: a patient presents with anterior chest pain (i.e. at the front of their chest) which could indicate a heart issue. Another patient presents with back pain. This pain is posterior and could be related to muscle strain.
  • Example: A patient complains of pain on the dorsal aspect of their foot (i.e. the top surface). If they had pain on the bottom of their foot, it would be described as plantar pain and could be caused by conditions such as plantar fasciitis or plantar heel pain.

Medial describes a position towards the body's midline. Lateral means moving away from the midline.

  • Example: a patient has shoulder pain. You identify that the pain is located near their sternoclavicular joint, which is medial (closer to the midline) to the laterally-positioned acromioclavicular joint.
  • Example: a patient sprains the outside of their ankle (the side that aligns with their fifth toe). This is called a lateral ankle sprain.

Proximal describes a location closer to the body's trunk or point of origin (e.g. the shoulder is proximal to the hand). Distal refers to a position further from the trunk or point of origin (e.g. the foot is distal to the hip).

  • Example: a patient fractured their humerus. The fracture (break) is closer to the shoulder, so it is described as a proximal (nearer to the trunk) humerus fracture. In contrast, if the fracture were closer to the elbow, it would be described as a distal humerus fracture.

Superficial indicates a position closer to the body's surface. Deep means further away from the body's surface.

  • Example: a patient has a laceration on their thigh. It is a superficial cut as it is close to the surface, only affecting the skin and superficial tissues. A deeper laceration would impact structures like the muscles or bones beneath and could require more intensive treatment.

These directional terms provide a clear and consistent way to describe the location of structures within the human body, allowing for precise communication.

Planes and Axes of Movement

Body parts move in a plane around an axis.

Planes

"A plane is an imaginary flat surface passing through the body."[3]

Sagittal plane: divides the body or body part vertically into left and right portions. Flexion and extension of the arm, or arm swings, during walking occur in the sagittal plane.

Frontal or coronal plane: divides the body or body part vertically into anterior and posterior portions. Abduction (lifting your arm or leg to the side, away from the body) and adduction (bringing your arm or leg towards the midline) occur in the frontal plane.

Transverse plane: divides the body or body part horizontally into upper and lower portions. Rotational or turning movements (e.g. single-leg hip rotation exercise) occur in the transverse plane.

Axes

"An axis is a straight line around which an object rotates."[3]

Sagittal, frontal and transverse movements occur around a pivotal point called an axis, which is always perpendicular to its plane. Sagittal plane movements pivot around the frontal axis. During arm swing, an imaginary axis passes through the shoulder from right to left.

Movement in the sagittal plane around the frontal axis

Frontal plane movements pivot around the sagittal axis. During arm abduction and adduction, an imaginary axis passes through the shoulder from front to back (or anterior to posterior).

Movement in the frontal plane around the sagittal axis

Transverse plane movements pivot around the longitudinal axis. During single-leg hip rotation, an imaginary axis runs superiorly to inferiorly through the hip.

Movement in the transverse (horizontal) plane around the vertical (longitudinal) axis

Joint Movements

When muscles contract, they produce movement in a specific direction, such as: (1) flexion, (2) extension, (3) abduction, (4) adduction, (5) right rotation, (6) left rotation, (7) internal (medial) rotation, (8) external (lateral) rotation, (9) inversion, and (10) eversion.

Flexion and extension: occur in the sagittal plane around a frontal axis. Flexion is usually an anterior-directed movement, and extension is typically a posterior-directed movement, with some exceptions (e.g. knee flexion is a posterior-directed movement and knee extension is an anterior-directed movement).

Abduction and adduction: frontal plane movements around the sagittal axis. Abduction generally describes movement of the body part away from the centre or midline of the body, while adduction is usually a movement of the body part towards the centre or midline of the body.

Rotation: usually occurs in the transverse plane around the longitudinal (vertical) axis. A rotational movement in the trunk, head and neck is referred to as right or left rotation. In contrast, rotational movements of the extremities (arms and legs) are called internal (towards the body's midline) and external (away from the body's midline) rotation.

Inversion and eversion: usually occur in the frontal plane. Inversion is the movement of turning the sole of the foot inward, towards the midline of the body. The inner edge of the foot lifts while the outer edge bears more weight. Eversion is the opposite movement, where the sole of the foot turns outward, away from the midline of the body. The outer edge of the foot lifts while the inner edge bears more weight.

Anatomic Laterality

Unilateral refers to something that is only on one side of the body. Example: a patient experiences facial paralysis on one side of the face due to dysfunction of the facial nerve (cranial nerve VII). The symptoms, which include the inability to close the eye or move facial muscles, are unilateral as they are confined to one side.

Bilateral refers to something that is on both sides of the body. Example: a patient has osteoarthritis in both knees, so they are diagnosed with bilateral knee osteoarthritis.

Ipsilateral refers to something that occurs on the same side of the body as another condition or symptom. Example: in Brown-Séquard syndrome (spinal cord hemisection), damage to one side of the spinal cord results in motor weakness or paralysis and loss of proprioception on the ipsilateral (same) side as the injury.

Contralateral refers to something that occurs on the opposite side of the body relative to another condition or symptom. Example: a patient has a left cerebral hemisphere stroke. They present with weakness or paralysis on the contralateral (opposite) side of the body.

Types of Joints

Arthrology refers to the study of joint anatomy, function and dysfunction. An articulation or joint is the place where two bones are anatomically connected, sometimes allowing movements between the bones.

Three movements can occur in mobile joints depending on the shape of the connecting surfaces: (1) rolling, when one joint surface rolls on another joint surface, (2) gliding, when one point on the joint surface contacts a new point on the adjacent joint surface, and (3) spinning, when one joint surface rotates relative to another joint surface.[4]

Joints can be classified by structure or function. The functional classification divides joints into three types: (1) immovable synarthrosis joints, (2) slightly movable amphiarthrosis joints, and (3) freely movable diarthrosis joints.[4] The structural classification divides joints into: (1) fibrous joints, where bones are connected by fibrous connective tissue, (2) cartilaginous joints, where bones are connected by cartilage, and (3) synovial joints, where bones come in contact with each other in a cavity filled with fluid.[4][5]

All synovial joints are diarthrosis joints. Based on shape, synovial joints can be divided into six types.[4][3]

Pivot joint: one bone is enclosed within a ring, allowing rotation around an axis. The other bone remains stationary (e.g. atlantoaxial joint).

Hinge joint: the concave end of one bone articulates with the convex end of another bone. This type of joint allows a hinge-like movement in one plane (e.g. elbow joint).

Condyloid or ellipsoid joint: the convex surface of one bone fits into the concave surface of another bone, allowing movement in two planes (e.g. metacarpophalangeal or knuckle joint in the hand).

Saddle joint: sometimes considered a modified condyloid joint. In saddle joints, there is an articulation between two saddle-shaped surfaces - i.e. they are concave in one direction and convex in the other (e.g. first carpometacarpal joint at the base of the thumb).

Plane joint: two relatively flat surfaces slide against each other, allowing gliding movements (e.g. acromioclavicular joint).

Ball-and-socket joint

Ball-and-socket joint: the rounded end of one bone articulates with the concave surface of another, allowing for movements in multiple directions, including flexion, extension, abduction, adduction, and internal and external rotation[6] (e.g. hip joint).

Based on the type of movement they permit, synovial joints can be classified as:[7]

  • non-axial: allow gliding movement only with no rotation around an axis (e.g. intercarpal and intertarsal joints of the wrist and foot)
  • uniaxial: movement occurs in one plane around one axis (e.g. elbow joint, which allows flexion and extension)
  • biaxial: movement occurs in two planes around two axes (e.g. metacarpophalangeal joint of the hand)
  • triaxial (multi-axial): movement can occur in three planes around three axes, including flexion-extension, abduction-adduction, and rotation (e.g. hip and shoulder joints)

Open and Close-Packed Positions

Open and close-packed positions describe the degree of congruency between articular surfaces and its effect on joint stability.

In a close-packed position, there is maximum contact between joint surfaces. In this position, the articulating surfaces are tightly compressed, making it difficult to separate or distract them. Stabilising structures, such as the joint capsule or ligaments, are taut or tight. This position is important for activities that require joint stability (e.g. standing). Example: the close-packed position of the knee is full extension.

In an open-packed position, the area of contact between the joint surfaces is reduced. The joint surfaces are not maximally congruent and surrounding ligaments and the joint capsule are less taut. As a result, there is less joint stability in an open-packed position compared to a closed-packed position. This position allows for greater mobility. In clinical practice, joint mobilisations are performed in open-packed positions. Example: the open-packed position of the knee is around 25-30 degrees of knee flexion.

Muscle Action

Skeletal muscles are striated muscles. Each muscle is made up of bundles of muscle fibres, also known as myofibers (muscle cells).[8] A myofiber contains a number of myofibrils, which are the contractile elements of the muscle. Each myofibril is composed of repeating, functional units called sarcomeres. Sarcomeres contain actin (thin) and myosin (thick) proteins (or filaments). Actin and myosin proteins interact to shorten the sarcomeres, and, consequently, the muscle itself.[9]

Skeletal muscles contract and generate tension in three ways:[10]

  • concentric: the origin and insertion of the muscle move closer together, shortening the muscle
  • eccentric: the muscle lengthens (i.e. moves back to its original position)
  • isometric: a static contraction; tension is generated in the muscle, but the distance between the muscle attachments remains the same

Origin and Insertion of Muscles

Skeletal muscles attach to bones through dense connective tissue called tendons.[3]

Each skeletal muscle has an origin and insertion:

  • origin: the end of the muscle attached to the fixed bone
  • insertion: the end of the muscle attached to the bone being pulled

Example: the brachialis muscle originates at the distal anterior humerus and inserts onto the ulnar tuberosity and coronoid process. When the brachialis contracts concentrically, it pulls the ulna towards the humerus, resulting in elbow flexion.

Some muscles have multiple origin points. For example, the biceps brachii originates at the apex of the coracoid process of the scapula (the short head) and the supraglenoid tubercle of the scapula (the long head). Both heads insert onto the radial tuberosity.

Fascicle Organisation in a Muscle

Fascicles are bundles of muscle fibres (myofibers) grouped together. Bundles of fascicles form muscle tissue.[8] Fascicle organisation informs muscle action.[3]

Fusiform muscles have long muscle fibres that run in parallel to the longitudinal axis of the muscle.[11] A fusiform muscle can usually achieve more range and increased joint velocity (e.g. biceps brachii).[12]

Circular muscles are concentrically arranged. They reduce the size of an opening when they contract (e.g. orbicularis oris).[3]

Convergent (triangular) muscles start with an expansion over a larger area but then converge to a single point (e.g. pectoralis major).[3]

Pennate muscles have short, diagonal fibres. Pennate muscles attach to a central tendon that runs along the length of the muscle like a feather, which causes them to contract at an angle.[13] This arrangement occurs in muscles that need to produce enough force to support or move the body (e.g. rectus femoris, gastrocnemius).[14] Pennate muscles can be divided as follows:[3]

  • unipennate muscles have fascicles on one side of the tendon only (e.g. digitorum longus)
  • bipennate muscles have fascicles on both sides of the tendon (e.g. rectus femoris)
  • multipennate muscles have fascicles wrapping around the tendon with the fibres oriented in different directions (e.g. deltoid, subscapularis)

Active Insufficiency

"Active insufficiency occurs when a multi-joint muscle contracts over all the joints it crosses and shortens so much it cannot develop tension effectively."[3]

Active insufficiency is reached when a prime mover (agonist) becomes shortened to the point that it cannot generate or maintain active tension. Example: shortening the rectus femoris limits full hip flexion when the knee is fully extended.

Passive Insufficiency

"Passive insufficiency results when a multi-joint muscle is stretched maximally over the joints it crosses, but the inherent length limitation of multi-joint muscles prevents simultaneous full range of motion at each joint crossed."[3]

When the opposing muscle (antagonist) is stretched to a point where it can no longer lengthen and allow further movement, passive insufficiency is reached. This limitation is a normal property of multi-joint muscles and helps optimise the relation between muscle length and tension. Examples: full finger flexion cannot be achieved during wrist flexion.

You can read more about active and passive insufficiency here.

Kinetic Chain

"The kinetic chain or kinetic link principle describes how the human body can be considered in terms of a series of interrelated links or segments."[15]

Kinetic chain

A kinetic chain is a “combination of several successively arranged joints constituting a complex motor unit.”[16] Each bone of the lower and upper limb acts as a solid link in the chain. The joints act as connections between these links, and there is a sequential transfer of energy between segments.

For example, in the lower limb, the foot, tibia, fibula, femur and pelvis are the solid links and the subtalar, ankle, knee, and hip joints act as the connections.[17] When external forces are applied to any segment of the link, they can influence movement patterns at the other joints in the chain.

Similarly, the upper limb, starting at the trunk and continuing through the scapulothoracic articulation, glenohumeral joint, and to the distal arm regions (humerus, radius, ulna and hand), is another example of a kinetic chain. While each segment can work independently, they also work as a unit to achieve functional tasks.[15]

Open Kinetic Chain

Steindler defined an open kinetic chain as “a combination of successively arranged joints in which the terminal segments can move freely”.[16] This means that the distal segment of the extremity is free to move in space. Examples include waving your hand and moving your ankle without moving other joints in your leg.

Closed Kinetic Chain

In closed kinetic chains, the distal part is fixed and moving one joint in the chain will move the others. For example, in standing, your feet are fixed to the ground. In order to bend your ankles, you also need to bend your knees and hips.

If you would like to learn more, please see: Kinetic Chain.

Nerves

The peripheral motor nervous system includes 31 pairs of spinal nerves.[4] There are eight cervical nerve pairs (C1-C8), twelve thoracic (T1-T12), five lumbar (L1-L5), five sacral (S1-S5), and a single coccygeal nerve pair:[18][3]

  • spinal nerves carry motor and sensory information between the central and peripheral nervous systems
  • spinal nerves project bilaterally from the vertebral column through openings between the vertebrae
  • all cervical nerves except C1 exit below their corresponding vertebrae (e.g. C8 exits below C7)
  • after exiting the vertebral column, spinal nerves split into ventral and dorsal rami: both rami can contain motor fibres, but the ventral rami are larger and contribute to all the major neural plexuses, which are networks of peripheral nerves that innervate the muscles
  • there are five major plexuses: cervical, brachial, lumbar, sacral, and pudendal[4]
  • muscles are innervated by the rami directly or by branches of the rami and plexuses

If you would like to learn more about the spinal nerves and general spinal cord anatomy, please see: Spinal Cord Anatomy.

Blood Supply

The cardiovascular system is made up of the heart and blood vessels. Its primary role is to deliver oxygen, nutrients and hormones to muscles, tissues and organs and to remove waste products.[3]

The heart pumps oxygenated blood through arteries to the body. All arteries in the systemic circuit originate from the aorta, which ascends from the left ventricle of the heart. The ascending aorta becomes the aortic arch, which branches into the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery. The left common carotid artery and the left subclavian artery branch off and supply the head and the upper extremities. The aortic arch then descends into the descending thoracic and abdominal aorta, which supply the thorax, abdomen, pelvis, and lower extremities.[19]

After nutrients and hormones are delivered to the body and waste products are collected, deoxygenated blood and carbon dioxide return to the heart via the veins. The heart sends the blood to the lungs for reoxygenation, completing the cycle.

Resources

References

  1. ↑ 1.0 1.1 Chmielewski PP, Strzelec B. Should Terminologia Anatomica be revised and extended? A critical literature review. Folia Morphol (Warsz). 2020;79(1):1-14.
  2. ↑ Kachlík D, Varga I, Báča V, Musil V. Variant Anatomy and Its Terminology. Medicina (Kaunas). 2020 Dec 18;56(12):713.
  3. ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 Xuan D. Terminology and Basic Concepts in Anatomy Course. Plus, 2024.
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Behnke RS, Plant J. Kinetic anatomy. Human Kinetics; 2021 Jul 6.
  5. ↑ Karpiński R, Prus A, Baj J, Radej S, Prządka M, Krakowski P, Jonak K. Articular cartilage: structure, biomechanics, and the potential of conventional and advanced diagnostics. Applied Sciences. 2025; 15(12):6896.
  6. ↑ Juneja P, Munjal A, Hubbard JB. Anatomy, Joints. [Updated 2024 Apr 21]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507893/
  7. ↑ Cruz-Flores F, Sánchez-Brito AL, Campos Amezcua R, Barrera Sánchez A, Azcaray Rivera HR, Martínez Mata AJ, Blanco Ortega A. A review of assistive devices in synovial joints: records, trends, and classifications. Technologies. 2025; 13(7):292.
  8. ↑ 8.0 8.1 Mukund K, Subramaniam S. Skeletal muscle: A review of molecular structure and function, in health and disease. Wiley Interdiscip Rev Syst Biol Med. 2020 Jan;12(1):e1462.
  9. ↑ Krans JL. The sliding filament theory of muscle contraction. Nature Education, 2010;3(9):66.
  10. ↑ Physiopedia. Assessing Muscle Strength.
  11. ↑ Miyazawa T, Sasaki F, Hanawa H, Kubota K, Hirata K, Fujino T . Development of an automated method for analyzing muscle dynamics across different morphologies based on B-mode ultrasound images. Journal of Biomechanics. 2026;196:113162.
  12. ↑ Chen CN (Joyce), Thompson LDV, Snow LA. Muscle structure and function. In: Placzek JD, Boyce DA editors. Orthopaedic physical therapy secrets (Third Edition). Elsevier, 2017. p1-9.
  13. ↑ Walter F, Leichsenring K, Siebert T, Böl M. Aponeurosis shape change as an indirect indicator for the force transmission mechanics in pennate muscles-A pilot study. J Mech Behav Biomed Mater. 2026 Sep;181:107514.
  14. ↑ Mansfield PJ, Neumann DA. Structure and function of skeletal muscle. In: Mansfield PJ, Neumann DA editors. Essentials of kinesiology for the physical therapist assistant (Third Edition). Mosby, 2019. p34-49.
  15. ↑ 15.0 15.1 Ellenbecker TS, Aoki R. Step by Step Guide to Understanding the Kinetic Chain Concept in the Overhead Athlete. Curr Rev Musculoskelet Med. 2020 Apr;13(2):155-163.
  16. ↑ 16.0 16.1 Steindler A.  Kinesiology of the human body under normal and pathological conditions. Springfield: Charles C Thomas Publisher; 1977.
  17. ↑ Lefever SL. Closed kinetic chain training. Therapeutic Exercise: Moving Toward Function. Philadelphia: Lippincott Williams & Wilkins/Walters Kluwer. 2005:283-307.
  18. ↑ Ganapathy MK, Reddy V, Tadi P. Neuroanatomy, Spinal Cord Morphology. [Updated 2022 Oct 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from https://www.ncbi.nlm.nih.gov/books/NBK545206/ [last access 11.9.2024]
  19. ↑ Atkins AD, Reardon MJ, Atkins MD. Endovascular Management of the Ascending Aorta: State of the Art. Methodist Debakey Cardiovasc J. 2023 Mar 7;19(2):29-37.
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