bicepsThe arm muscle whose name means two heads. It lies at the front of the arm, above the elbow. It bends the elbow and turns the palm upward.
cardiac muscleThe muscle that heart walls are built from. It is striped like skeletal muscle but works on its own. Its beat is strong and rhythmical.
contractTo bunch up and pull, as a working muscle does. A muscle can only pull. When its fibers shorten, the bones they are joined to are drawn closer together.
heartThe fist-sized pump that keeps blood moving. Every minute an adult heart moves about 5 liters of blood. Its wall is thickest around the chambers that have to pump hardest.
involuntary muscleA muscle that works without your thinking about it. Smooth muscle and cardiac muscle are involuntary. They go on working while you sit perfectly still.
muscular systemAll of the body's muscles, counted as one system. The body has more than 600 muscles. They account for roughly 40 percent of body weight.
Show all 36 terms (30 more)
Kinds of muscle, continued
relaxTo loosen and go back to full length after a pull. A relaxed muscle cannot push a bone back. A second muscle has to pull it the other way.
skeletal muscleThe striped muscle that tugs on bones to move you. Each of its long cells is called a muscle fiber and has many nuclei. One muscle may hold hundreds or thousands of fibers, bundled together.
smooth muscleThe unstriped muscle found in gut and vessel walls. Each of its cells is spindle-shaped, with a single nucleus. It contracts slowly and rhythmically.
tendonThe collagen cord at each end of a muscle. It fastens the muscle to a bone and has to withstand tension. An adult has about 4,000 tendons.
tricepsThe biceps' opposite number, behind the upper arm. It straightens the elbow. Its name is Latin for three-headed.
voluntary muscleA muscle you move on purpose, by deciding to. Skeletal muscles are voluntary. The brain sends them electrical messages to raise a hand, chew or kick a ball.
How muscles move bones 12
antagonistic pairTwo muscles that pull one joint in opposite ways. The biceps and the triceps are one. While the first contracts, the second relaxes.
effortThe force put into a lever to make it move. It is also called the input. In tweezers and in the jaw the effort is applied between the fulcrum and the load.
extensorA muscle that brings a bent joint back to straight. Muscle names often tell the action: an extensor extends, and a levator lifts.
flexorA muscle that bends a joint when it contracts. The word is built on flex. The iliopsoas, a muscle at the front of the body, flexes the thigh.
forearmThe stretch of arm that the biceps lifts. It runs from the elbow to the wrist. The 20 or more muscles that move the wrist, hand and fingers lie along it.
fulcrumThe support that a lever rocks on. On a seesaw it sits in the middle. Moving the fulcrum nearer the load means less effort is needed.
hamstringA muscle behind the thigh that bends the knee. There are three: the semimembranosus, the semitendinosus and the biceps femoris. They work against the quadriceps.
jointA spot such as the knee, where the skeleton can bend. Bones cannot move on their own. A muscle usually spans a joint, with a tendon fastened to a bone at each end.
leverThe simple machine that a bone and a muscle make. A lever is a rigid bar that turns about a fixed point. Tweezers, a fishing rod and the lower jaw are all levers of one class.
limbA jointed body part used for walking or grasping. An arm is a limb, and so is a leg or a wing. The word comes from Old English lim.
loadThe weight that a lever has to move. It is also called the output. In a wheelbarrow the load sits between the wheel and the handles.
quadricepsThe knee-straightening muscles, known as quads. Four muscles of the front thigh make up the group.
Nerves, fuel and fitness 12
ATPThe molecule that powers every contraction. ATP stands for adenosine triphosphate. Living cells use it as their supply of energy.
enduranceThe capacity to stay active without tiring out. How long is long depends on the effort: minutes of all-out work, hours of gentle work.
exercisePhysical activity done to keep the body fit. Walking, jogging, dancing, swimming and biking all count. The heart is a muscle, so any activity that makes it pump faster exercises it.
fatigueA muscle's loss of force after long or hard use. It has two main causes: the nerve's signal weakens, or the fiber itself is less able to contract.
flexibilityEase of bending, the opposite of stiffness. It is the range through which a joint and the muscles that cross it can move. It varies from person to person.
glycogenGlucose stored for later in muscle and in the liver. It is a branched chain of glucose units. Glycogen is the short-term energy reserve; body fat is the long-term one.
lactic acidWhat muscle makes from glucose when oxygen is short. In hard exercise the heart and lungs cannot always bring enough oxygen. The muscles go on contracting, but less efficiently.
mitochondrionThe organelle nicknamed the cell's powerhouse. The plural is mitochondria. It uses oxygen to make ATP.
motor neuronA nerve cell that tells a muscle when to contract. Its cell body lies in the brain or the spinal cord. One motor neuron and all the muscle fibers it connects to are a motor unit.
neuromuscular junctionThe gap where a nerve cell signals a muscle fiber. The nerve ending releases a chemical, acetylcholine, which crosses the gap and sets off the contraction.
reflexA split-second response made without any thought. The knee jerk is one. Reflex signals do not always go to the brain, which is why no thought is needed.
strengthThe most force that a muscle can produce. Building it is the goal of strength training. A muscle can be strong without being big.
How this list was compiled: Term list chosen for this site on 2026-10-12. Each meaning is written in our own words and was checked that day against the article on the term in the English Wikipedia (https://en.wikipedia.org/), whose text is under the Creative Commons Attribution-ShareAlike license: Muscular system, Cardiac muscle, Tendon, Biceps, Triceps, Quadriceps, Hamstring, Limb (anatomy), Forearm, Lever, Motor neuron, Neuromuscular junction, Reflex, Adenosine triphosphate, Glycogen, Lactic acid fermentation, Mitochondrion, Physical strength, Endurance, Flexibility (anatomy) and Muscle fatigue. Flexor, extensor, antagonist, limb, fulcrum, effort, load and bicep rest on their entries in Wiktionary, the free dictionary (https://en.wiktionary.org/). The three kinds of muscle, voluntary and involuntary control, muscle fibers, tendons at both ends of a muscle, the count of muscles and their share of body weight, heat from muscle, the muscles of the arm and the thigh and the names built on flexor, extensor and levator were checked against the Muscular System pages of the SEER Training Modules of the National Cancer Institute (https://training.seer.cancer.gov/anatomy/muscular/): Introduction, Structure of Skeletal Muscle, Muscle Types, Muscle Groups, Muscles of the Upper Extremity and Muscles of the Lower Extremity. The heart rests on its Heart and Structure of the Heart pages (https://training.seer.cancer.gov/anatomy/cardiovascular/heart/), and bones as levers on its Introduction to the Skeletal System. Voluntary and involuntary muscle, the heart as a muscle and exercise were checked against Healthy Muscles Matter of the National Institute of Arthritis and Musculoskeletal and Skin Diseases (https://www.niams.nih.gov/health-topics/kids/healthy-muscles). Contract and relax, muscles that only pull, antagonistic pairs, joints, the parts of a lever and what muscles make when oxygen runs short were checked against four BBC Bitesize pages (https://www.bbc.co.uk/bitesize/): Skeletal muscles, How do your muscles work?, Energy systems in muscle cells and What are levers?. The fact after each meaning is from the same pages. Licence: own work
How it works
This muscular system vocabulary worksheet prints skeletal, cardiac and smooth muscle, tendon, contract, relax, biceps and triceps, among twelve terms, to match to their meanings. The answer key is the last page.
Read the full guide
How muscles move bones
Set opens on Kinds of muscle. The second set has antagonistic pair, flexor, extensor, quadriceps, hamstring, joint, limb, forearm, lever, fulcrum, effort and load.
Nerves, fuel and fitness
The third set has motor neuron, neuromuscular junction, reflex, ATP, glycogen, lactic acid, mitochondrion, strength, endurance, flexibility, exercise and fatigue.
Deltoid, trapezius, pectoralis and gluteus maximus are words on the muscular system word search, not terms here.
Questions and answers
What are the functions of the muscular system?
Movement, posture, steady joints and heat. Muscles hold the body upright, their tendons steady joints such as the knee and the shoulder, and nearly 85 percent of the body's heat comes from muscle contraction.
Is the heart a muscle?
Yes. The heart is a muscular pump whose walls are cardiac muscle. A special area of that muscle sends out electrical messages in a steady rhythm, so the heart beats without being told.
What is the difference between a tendon and a ligament?
A tendon joins a muscle to a bone, and a ligament joins a bone to a bone. Both are strong cords made of collagen.
Is it bicep or biceps?
Biceps, even for one muscle: the word is Latin and already ends in s. Bicep is common in everyday speech, though some call it a mistake. The sheet prints biceps.