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Dance 101

Glossary of Human Anatomy Terms

Image of a human anatomy drawing [Patrick Hermans]

Human anatomy is the branch of science concerned with the structure and function of the body.

The human body is the dancer's instrument of expression. Understanding how the body works can help a dancer stay in shape, improve performance, increase confidence and add longevity to his or her performing career. It can also help a dancer avoid injury. If an injury does occur, knowledge of human anatomy can contribute to a safe process of healing and recovery.

I. General Anatomical Terms

Anatomical position: Descriptions in human anatomy are expressed in relation to anatomical position. These positions describe where different body parts are found or what the direction of a movement is relative to the midline of the body or to another body part. Anatomical positions are referred to according to their orientation:

Superior - toward the head
Inferior - toward the feet
Anterior - toward the front of the body
Posterior - toward the back of the body
Medial - toward the midline of the body
Lateral - away from the midline of the body

Body cavity: Houses the internal organs. There are three main body cavities:

The thoracic cavity is the space above the diaphragm. It encloses the heart and lungs within the ribcage, sternum (breastbone) and twelve thoracic vertebrae.
The abdominal cavity, which houses the abdominal viscera, begins below the diaphragm and ends at the top of the pelvis, at about waist level.
The pelvic cavity extends from the end of the abdominal cavity to the pelvic floor.

Organ: A group of tissues that perform a particular function. For example, the heart, lungs, liver and kidney are all organs.

Pelvic floor: A group of muscles that reach from the pubic bone back to the sacrum. One function of the pelvic floor is to support the internal organs.

Tissue: A group or collection of similar cells and their intercellular substance that act together to perform a particular function. The primary tissues are epithelial, connective, skeletal, muscular, glandular and nervous.

Viscera: Any internal organ.

II. The Systems of the Body

System: Organs that work together to perform major body functions like breathing, digesting, moving and reacting to external stimuli. Some examples of systems include:

Cardiovascular: composed of the heart, blood and blood vessels (arteries, veins and capillaries)
Digestive: composed of the oral cavity, pharynx, stomach and intestines
Endocrine: involving glands that secrete hormones
Integumentary: composed of skin, hair and nails
Muscular: composed of skeletal, smooth and cardiac muscles
Nervous: composed of the brain, spinal cord, peripheral nerves and sensory organs
Respiratory: composed of airways and lungs
Skeletal: composed of bones and cartilage

All systems are important for normal body functioning but, for a dancer, sound knowledge of the following systems is particularly helpful:

The muscular and skeletal systems are often grouped together and called the musculoskeletal system. This system's primary function is movement.
The nervous system is comprised of three main parts:

The central nervous system involves the brain and the spinal cord. It is the control centre of the nervous system.
The peripheral nervous system consists of any nervous tissue that is not encased in the skull or vertebral column. It includes the peripheral nerves and the sensory organs they stimulate in different parts of the body. The peripheral nervous system is important in balance.
The autonomic nervous system is chiefly concerned with the regulation of visceral activity. It is involuntary.

III. Bones

Bone (osseus tissue): A specialized form of dense connective tissue consisting of bone cells (osteocytes) embedded in a matrix of calcified intercellular substance. The main functions of bone are to:

Protect vital structures
Support the body
Provide a basis for movement through muscle and tendon attachments
Provide attachment points for ligaments
Store important mineral salts such as calcium
Produce red blood cells which transport oxygen and carbon dioxide to and from tissues

Bones give shape and structure to the body. They provide points of attachment for muscles and become the levers making movement possible. Bones are classified as follows:

Flat, e.g. scapula (shoulder blade) and sternum (breast bone)
Irregular, e.g. talus (ankle bone) and vertebrae (spinal bones)
Long, e.g. femur (thighbone) and ulna (one of the forearm bones)
Short, e.g. navicular (a small bone in the arch of the foot)
Sesamoid, e.g. patella (knee cap, where the bone is free but a tendon runs through it)

Trochanter: A bony protuberance by which muscles are attached between the pelvis and the upper part of the thighbone (femur).

IV. Muscles and Related Terms

Core: The dancer's centre, or core, involves a balance of stability and strength between the abdominal muscles (transversus abdominis, rectus abdominis, and internal and external obliques), the back muscles and the pelvic floor muscles. The diaphragm is also an important part of the dancer's core. A strong core is very important in maintaining good posture and control of limb movement.

Diaphragm: The diaphragm is the most important breathing muscle. It spans from front to back and side to side at the level of the lower ribs. After exhaling, the diaphragm is shaped like a dome. The lungs sit on top of the dome and when they fill with air the dome flattens. This flattening pushes the ribs up and out, and also pushes down on the abdominal contents, which is why the belly gets pushed out when a deep, diaphragmatic breath is taken.

Hip joint muscles:

The adductors (e.g. adductor longus, adductor brevis and adductor magnus) are the muscles running along the inside of the leg from the groin area. Flexibility in the adductors makes it possible to do side splits.
The lateral rotators (e.g. piriformis and posterior fibres of gluteus medius) are found deep in the buttock region. They are often very well developed in the ballet dancer who performs many movements in the "turned-out" position.
The medial rotators (e.g. gluteus minimus and anterior fibres of gluteus medius) have the dual function of internal rotation (opposite to the turned-out position) and abduction (moving the leg away from midline). They are the antagonistic, or opposite, muscle group to the lateral rotators.
The extensors (e.g. gluteus maximus and the hamstrings) are used in moving the leg backwards, in jumping and in straightening from a crouched position.
The flexors (e.g. iliopsoas and rectus femoris) bring the leg forward or the knee toward the chest.

Iliotibial band: A fibrous muscle structure running from the outside of the hip joint to the lower leg just below the knee joint. It is a continuation of the gluteus maximus muscle, which is the largest muscle in the buttock.

Hamstring: A group of muscles found along the back of the leg running from the pelvis to just below the knee that effect hip and knee movements. The semitendinosus and the semimembranosus are found on the medial side and the biceps femoris is found on the lateral side.

Muscle: Composed of contractile tissue with elastic properties. The special characteristics of muscle include shortening and contracting, and also stretching. In general, an overstretched or lengthened muscle is weak. There are three kinds of muscle:

Smooth muscle acts involuntarily and is found principally in the internal organs.
Cardiac muscle also acts involuntarily and is found around the heart.
Skeletal muscle is striated because of different groups of fibres bundled together. It is usually found in the limbs. Skeletal muscles, which produce voluntary movement, are the ones a dancer uses to gain and maintain a certain posture, to start and stop limb movement, and to stretch or strengthen.

Posture: Involves maintaining a certain alignment of the body. A dancer's ability to achieve certain postures requires muscle strength and flexibility of the musculoskeletal system, as well as balance and body awareness involving the nervous system.

Respiration (breathing): A means of revitalizing tissues. When a dancer takes in air, he or she is taking in oxygen, or fuel, bringing energy to the muscles and vital organs. Without oxygen it would be impossible to move and control the body. Breathing also helps the dancer gain awareness of physical states like muscle tension and relaxation.

Rotator cuff: A group of four muscles extending from the scapula (shoulder blade) to the head of the humerus (shoulder). These muscles are very important for stability and mobility of the shoulder throughout all movements. The four individual muscles of the rotator cuff are the supraspinatus, infraspinatus, teres minor and subscapularis.

Tendon: The longer fibrous end of a muscle that serves to attach it to the periosteum (outer layer of bone). Tendons are strong, but inelastic. They are slow to heal if injured. A well-known tendon is the Achilles tendon, which attaches the calf group of muscles (the medial and lateral gastrocnemius and soleus muscles) to the heel bone (the calcaneum).

V. Joints and Related Structures

Bursa: A padlike sac usually found near a joint. It is lined with a synovial membrane and contains synovial fluid that reduces friction between tendon and bone, tendon and ligament, or other structures where friction is likely to occur. [See: Bursitis ]

Cartilage: Dense, bluish-white or grey connective tissue, like what is seen at the end of a chicken bone. There are different types of cartilage, including:

Articular, a thin layer of smooth, elastic cartilage located on the joint surfaces of bone. It protects the end of the joint.
Semilunar, found in-between the joint like the middle of a sandwich. Two good examples are the intervertebral discs, and the medial and lateral menisci in the knee joint.
Cricoid, the lowermost cartilage of the larynx (throat).
Costal, connects the ends of the first ten ribs (true ribs) with the sternum (breast bone).

Joint (articulation): The area where two or more bones are joined together along with their associated structures, such as ligaments. Joints are classified into three types according to the material uniting the articulating bones:

Fibrous joints: united by fibrous tissue (e.g. sutures of the skull bones).
Cartilaginous joints: united by cartilage (e.g. vertebrae and their intervertebral discs) or a combination of cartilage and fibrous tissue (e.g. sacroiliac joint).
Synovial joints: united by cartilage with a synovial membrane enclosed in the joint cavity. These are the most common joints and are the ones that provide free movement between the bones they join. They are typical of nearly all the joints of the limbs. Synovial joints are named after the synovial fluid they contain. This lubricating substance allows the dancer's joints to move freely and smoothly.

Joint axes: Joints may move in one (uniaxial) or several directions. A hinge-type joint such as the elbow or the knee is a bi-axial joint and permits movement in two directions: flexion or extension only. A ball-and-socket-type joint such as the hip or shoulder is a multi-axial joint as it allows movement in several directions.

Joint capsule: A sleeve that is over the joint. Made of fibrous tissue, it helps keep everything in the joint together, such as the cartilage, synovial fluid and some ligaments.

Ligament: A band of strong, fibrous connective tissue that connects one bone to another. Ligaments either allow or prevent a specific movement between two bones. They are passive structures so we do not have voluntary control over them. Examples of ligaments are the ACL (anterior cruciate ligament) and PCL (posterior cruciate ligament). These two ligaments are found in the knee and are called "cruciate ligaments" because they cross.

VI. Common Dance-Related Injuries

Bursitis: An acute, painful inflammation of the bursa usually caused by repetitive friction from a tight muscle or a poorly executed movement. Hip bursitis occurs when the tendon of the iliotibial band rubs the greater trochanter of the femur (thighbone).

Joint sprain: A tear of the ligament classified from a Grade 1 (minor) to a Grade 3 (total tear). Joint sprain occurs when a ligament is overstretched or when a joint is bent in the wrong direction. A classic example is rolling over on the ankle. It is not uncommon for more than one ligament to be injured at a time.

Muscle strain: A muscle tear that can range from a Grade 1 (minor) to a Grade 3 (total tear). Muscle strain often occurs from quick movements requiring a sudden, hard muscle contraction, especially when a dancer is not completely warmed up.

Shin splints: Pain in the front of the lower leg. Their cause is unclear, but they tend to develop after prolonged and/or repetitive use of the legs in weight-bearing activities like running and jumping.

Stress fractures: An incomplete break in the bone. In dance they are often caused by repetitive landings from jumps. On an X-ray they appear as a thin line through the bone. In order to heal a stress fracture it is necessary to rest and reduce impact on the fractured bone, which usually means taking a break from dancing for a period of time. Shin splints are one result of stress fractures.

VII. Anatomical Tidbits

The arch of the foot is formed by: the structure of the bones, the navicular being the high point of the arch; the plantar fascia, a fibrous band extending from the heel to the ball of the foot; ligaments, the main one being the spring ligament acting as a supporting sling to the navicular bone; and muscles both starting and ending in the foot, as well as muscles originating from the lower leg area. The primary role of the long arch of the foot is to absorb shock.

The arm is divided into two parts: the upper arm and the forearm. The long bone of the upper arm is called the humerus and extends from the ball-and-socket multi-axial-type shoulder joint to the hinge-type elbow joint. The forearm consists of two bones, the ulna and the radius, which extend from the elbow to the wrist. The main muscles in the upper arm are the deltoids, triceps and biceps. The muscles of the forearm mostly start at the elbow and continue into the hand controlling movement of the wrist and hand.

Arteries are blood vessels containing oxygenated blood that is pumped from the heart to other organs of the body. After the organs have taken the oxygen out of the blood for fuel, another set of blood vessels called veins carry the de-oxygenated blood back to the heart, thereby completing the circuit.

Normal body temperature for a healthy adult at rest is 37 degrees Celsius.

The scapula or shoulder blade acts like a pulley and has muscle attachments to the head, neck, spinal column, sacrum and upper arm.

The spine is made up of seven cervical, twelve thoracic and five lumbar vertebrae; the sacrum (five fused vertebrae); and the coccyx (four fused vertebrae), which is the remnant of the human tail. The spinal cord running down the centre of the vertebrae is a continuation of the brain and ends at L1-L2 (the 1st and 2nd lumbar vertebrae). The rest of the spinal column after L2 is filled with a bunch of nerves that look like a horse's tail and is called the cauda equina.

The human body has different structural levels of organization. These levels start with atoms, molecules and compounds, increasing in size and complexity to cells, tissues, organs and, finally, systems.