Glossary of the Muscular System

Angled view of the human muscular system

Musculoskeletal system

The muscles that move the human skeleton vary greatly in shape and size and extend to every part of our bodies. The muscular system contains over 600 skeletal muscles alone, which make up about 40% of our mass. See it in 3D!

System: Muscular, Skeletal

Region: All

Frontal view of the human muscular system

Muscle

At the simplest level, muscles allow us to move. They take direct instruction from the specific nerves that innervate each muscle. See it in 3D!

System: Muscular

Region: All

Pathologies: Muscular dystrophy, myositis, tendinitis

Tendon of the arm compared with the muscles of the arm

Tendon

Skeletal muscles are attached to the skeleton by tendons.

System: Muscular, Skeletal

Region: All

Pathologies: Muscular dystrophy, myositis, tendinitis

Computer generated model of the heart

Cardiac muscle

Cardiac muscle, found only in the myocardium of the heart, contracts in response to signals from the cardiac conduction system to make the heart beat.

System: Muscular

Region: Heart

The biceps and other muscles of the arm

Skeletal muscle

Skeletal muscles attach to the bones of the skeleton and contract voluntarily to produce movement. Skeletal muscle tissue is composed of long cells called muscle fibers that have a striated appearance.

System: Muscular

Region: All

The stomach with sections of smooth muscle highlighted

Smooth muscle

Smooth muscle lines the gastrointestinal tract, blood vessels of the circulatory system, urinary tract, and reproductive organs.

System: Muscular

Region: All

The origin and insertion point of various facial muscles

Origin and insertion

Skeletal muscles are attached to the skeleton by tendons. The areas where the tendons attach the muscles to two articulating bones are called the origin and insertion points.

System: Muscular

Region: All

Two sets of skeletal legs showing the muscles of the thigh: one flexing, the other at rest.

Agonist (prime mover) and antagonist

A muscle that contracts to generate the main force of an action is called the prime mover, or the agonist, for that action. Muscles that perform the paired and opposing action are called the antagonists.

System: Muscular

Region: All

Two skeletal arms both with the muscles and tendons of the hand and forearm: one open, the other in a fist.

Flexion and extension

Flexion: decreasing the angle between two bones (bending).
Extension: increasing the angle between two bones (straightening a bend).

System: Muscular

Region: All

Two skeletal legs: one lifted to the side, the other at rest

Abduction and adduction

Abduction: moving away from the body’s midline.
Adduction: moving toward the body’s midline.

System: Muscular

Region: All

Two skeletal arms reaching out: one with the palm turned up, the other turned down

Pronation and supination

Pronation: rotating the forearm so the palm is facing backward or down.
Supination: rotating the forearm so the palm is facing forward or up.

System: Muscular

Region: All

Two skulls with the muscles controlling the jaw: one with an open mouth, the other closed

Elevation and depression

Elevation: moving a body part up.
Depression: moving a body part down.

System: Muscular

Region: All

Two skulls with the muscles controlling the jaw: one with the jaw pushed forward, the other at rest

Protraction and retraction

Protraction: moving a bone forward without changing the angle.
Retraction: moving a bone backward without changing the angle.

System: Muscular

Region: All

Two legs with the muscles controlling the ankles: One foot tilted inwards, the other outwards

Inversion and eversion

Inversion: turning the sole of the foot inward.
Eversion: turning the sole of the foot outward.

System: Muscular

Region: All

Two legs with the muscles controlling the ankles: One foot tilted upwards, the other downwards

Dorsiflexion and plantarflexion

Dorsiflexion: bringing your foot upward toward your shin.
Plantarflexion: depressing your foot.

System: Muscular

Region: All

The bones of the torso and the muscles surrounding the spine

Synergists and stabilizers

Synergists are muscles that assist the prime mover in its role. Stabilizers act to keep bones immobile when needed.

System: Muscular

Region: All

Function: Your back muscles, for example, are stabilizers when they are keeping your posture sturdy.

Neuromuscular junction

Neuromuscular junction

Muscle contraction begins when the nervous system generates a signal. The signal, an impulse called an action potential, travels through a type of nerve cell called a motor neuron. The neuromuscular junction is the name of the place where the motor neuron reaches a muscle cell.

System: Muscular

Region: All

Acetylcholine

Acetylcholine

Acetylcholine is a widespread neurotransmitter found in the CNS and at neuromuscular junctions between peripheral nerves and muscles.

System: Muscular

Region: All

Sternocleidomastoid muscle

Sternocleidomastoid muscle

M. sternocleidomastoideus

The sternocleidomastoid muscle (r, l) is a muscle in the neck that is also often classified with the lateral cervical muscles.

System: Muscular

Region: Neck

Function: Draws head toward shoulder of same side, rotates head to opposite side, flexes cervical part of vertebral column, assists in elevating the thorax

Pathologies: Muscular dystrophy, myositis

Rotator cuff

Rotator cuff

The rotator cuff (r, l), a subdivision of the posterior shoulder girdle, comprises a group of muscles responsible for stabilizing the glenohumeral joint. These muscles also contribute to the proper motion of the upper limbs. See it in 3D!

System: Muscular

Region: Shoulder

Pathologies: Muscular Dystrophy, myositis, rotator cuff tendinosis

Deltoid muscle

Deltoid muscle

M. deltoideus (pars clavicularis, pars acromialis, pars spinalis)

The deltoid (r, l), one of the posterior shoulder joint muscles that form the muscular system’s shoulder girdle, is a large, thick, triangular muscle that covers the shoulder joint in front, behind, and laterally.

System: Muscular

Region: Shoulder

Function: It allows flexion and medial rotation of the humerus.

Pathologies: Muscle cramps, muscular dystrophy, myositis, polio/post-polio syndrome, sprains, strains, tendinitis

Pectoralis major

Pectoralis major

M. pectoralis major

The pectoralis major (r, l), one of the anterior shoulder muscles that form the muscular system’s shoulder girdle, is a thick, fan-shaped muscle situated at the upper and forepart of the chest.

System: Muscular

Region: Thorax

Function: Adducts and flexes the arm and rotates it medially (inward)

Pathologies: Muscular Dystrophy, myositis

Latissimus dorsi muscle

Latissimus dorsi muscle

M. latissimus dorsi

The latissimus dorsi (r, l) is one of the posterior shoulder joint muscles that form the muscular system’s shoulder girdle. The latissimus dorsi is a triangular, flat muscle that covers the lumbar region and the lower half of the thoracic region and is gradually contracted into a narrow fasciculus at its insertion into the humerus.

System: Muscular

Region: Thoracic/shoulder region

Function: The functions of the latissimus dorsi include joining the upper limb with the axial skeleton and facilitating the proper motion of the upper limb.

Pathologies: Muscular Dystrophy

Trapezius

Trapezius

M. trapezius

The trapezius (r, l), a muscle of the posterior thorax that acts on the pectoral girdle, is a flat, triangular muscle covering the upper and back part of the neck and shoulders.

System: Muscular

Region: Neck, Shoulder, Thorax

Function: Rotation, retraction, elevation, and depression of scapula, levitate clavicle; extends the neck; stabilizes the shoulder

Pathologies: Muscular dystrophy, myositis

Biceps

Biceps

M. biceps brachii (caput longum, caput breve)

Biceps brachii, long head (r, l) and biceps brachii, short head (r, l) are both anterior flexor muscles of the elbow joint. See it in 3D!

System: Muscular

Region: Upper Limb (Arm)

Function: Flexes and supinates the elbow

Pathologies: Muscular dystrophy, myositis, sprains and strains, tendinitis.

Triceps brachii muscle

Triceps brachii muscle

M. triceps brachii (caput mediale, caput longum, caput laterale)

The triceps brachii, a large upper limb muscle named for its three heads, comprises the triceps brachii tendon (r, l) and three heads: lateral (r, l), long (r, l), and medial (r, l).

System: Muscular

Region: Upper Limb (Arm)

Function: Extends the forearm at the elbow

Pathologies: Muscular dystrophy, myositis, tendinitis

Rectus abdominis muscle

Rectus abdominis muscle

M. rectus abdominis

The rectus abdominis (r, l) is a long, flat muscle of the abdomen. The rectus abdominis extends along the whole length of the front of the abdomen and is separated from its fellow of the opposite side by the linea alba. See it in 3D!

System: Muscular

Region: Abdomen

Function: Flexes vertebral column, tenses abdominal wall, compresses abdominal viscera

Pathologies: Muscle cramps, muscular dystrophy, myositis

Abdominal external oblique muscle

Abdominal external oblique muscle

M. obliquus externus abdominis

The external oblique (r, l), a muscle of the abdomen situated on the lateral and anterior parts of the abdomen, is the largest and the most superficial of the three flat muscles in the abdomen.

System: Muscular

Region: Abdomen

Function: Bilaterally: compresses abdomen and flexes (bends) the spine. Unilaterally: laterally flexes trunk to same side and rotates trunk to the opposite side.

Pathologies: Muscle cramps, muscular dystrophy, myositis.

Piriformis muscle

Piriformis muscle

M. piriformis

The piriformis muscle (r, l) is one of the lateral rotators of the hip that also facilitates hip abduction and extension.

System: Muscular

Region: Hip

Function: External rotation, abduction, and extension of the hip joint; aids in stabilization of the hip

Pathologies: Muscular Dystrophy

Buttocks

Buttocks

The muscles of the gluteal region are muscles located in the hip and gluteal region of the lower limbs and originate from the pelvis, insert into the femur, and act on the hip joint. The gluteal muscles include the gluteus minimus (r, l), the gluteus medius (r, l), and the gluteus maximus (r, l). See it in 3D!

System: Muscular

Region: Hip

Pathologies: Muscular dystrophy, myositis

Thigh

Thigh

The muscles of the proximal leg (r, l), a region within the muscular system’s lower limbs, are a group of muscles in the region between the hip joint and the knee joint—an area commonly called the thigh. The muscles of the thigh are further divided into anterior (r, l), medial (r, l), and posterior (r, l) compartments. See it in 3D!

System: Muscular

Region: Lower limbs

Pathologies: Muscular dystrophy, myositis

Quadriceps femoris

Quadriceps femoris

The quadriceps include the rectus femoris (r, l), and the vastus medialis (r, l), the vastus intermedius (r, l), and the vastus lateralis (r, l). See it in 3D!

System: Muscular

Region: Lower Limb

Function: All are extensors of the knee innervated by the femoral nerve (L02-L04).

Pathologies: Muscular dystrophy, myositis

Hamstring

Hamstring

The muscles of the posterior compartment are the biceps femoris, long head (r, l), the biceps femoris, short head (r, l), the semimembranosus (r, l), and the semitendinosus (r, l). See it in 3D!

System: Muscular

Region: Lower Limb

Pathologies: Muscular dystrophy, myositis

Calf

Calf

The muscles of the distal or lower leg are a group of muscles located between the knee joint and the ankle joint that act on the ankle joint, facilitating movement of the foot and toes. The muscles of the posterior compartment include the flexor digitorum longus (r, l), the flexor hallucis longus (r, l), the tibialis posterior (r, l), the popliteus (r, l), the plantaris (r, l), and the muscles of the triceps surae, the gastrocnemius (r, l) and the soleus (r, l). See it in 3D!

System: Muscular

Region: Lower Limb

Pathologies: Muscular dystrophy, myositis

Gastrocnemius

Gastrocnemius

M. gastrocnemius

The gastrocnemius (r, l) is a superficial two-headed muscle of the posterior compartment of the leg and one of the two muscles that make up the triceps surae.

System: Muscular

Region: Lower limbs

Function: Plantarflexion of foot, flexes leg at knee joint

Pathologies: Muscle cramps, muscular dystrophy, myositis, Polio and Post-Polio Syndrome

Soleus

Soleus

M. soleus

The soleus (r, l) is a superficial muscle of the posterior compartment of the leg and one of the two muscles that make up the triceps surae.

System: Muscular

Region: Lower Limb

Function: Plantarflexion of foot

Pathologies: Muscular dystrophy, myositis

Achilles tendon

Achilles tendon

Tendo calcaneus

The gastrocnemius (r, l) and soleus (r, l) of the posterior compartment (r, l) of the leg (r, l) unite their tendons to make the achilles tendon.

System: Muscular

Region: Lower Limb

Function: The tendon inserts on the calcaneus.

Pathologies: Muscular dystrophy, myositis, tendinitis