Muscle (from Latin musculus, iminutive of mus "mouse") is contractile tissue of the body and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to produce force and cause motion. Muscles can cause either locomotion of the organism itself or movement of internal organs. Cardiac and smooth muscle contraction occurs without conscious thought and is necessary for survival. Examples are the contraction of the heart and peristalsis which pushes food through the digestive system. Voluntary contraction of the skeletal muscles is used to move the body and can be finely controlled. Examples are movements of the eye, or gross movements like the quadriceps muscle of the thigh. There are two broad types of voluntary muscle fibers: slow twitch and fast twitch. Slow twitch fibers contract for long periods of time but with little force while fast twitch fibers contract quickly and powerfully but fatigue very rapidly.

Trivia about muscles

  • The body has over 600 of these, including extensors & flexors
  • Botulinum toxin gets rid of wrinkles between your eyebrows by paralyzing some of these
  • Myology is the study of these, like biceps
  • Nearly half your body weight comes from these, which include the omohyoid, the brachialis & the deltoid
  • About 40% of your body weight consists of 100s of these contracting tissues
  • Types of these include flexors & adductors
  • Your body has about 650 of these including the biceps and hamstrings
  • Among these in the body are the abs, pecs & biceps
  • Body tissues named for their "mouselike" movements
  • There are about 700 of these in the human body, including biceps & triceps
  • The human body has 3 types of these: skeletal, smooth & cardiac, a combination of skeletal & smooth
  • Mycology is the study of fungi; myology is the study of these body parts
  • Depending on what they're doing, these body parts are called agonists or antagonists