Thanks to the contraction of your 600 or so skeletal muscles, your body can move in several directions. A skeletal muscle comprises fibers held together by fascia and typically attaches to two bones via the tendons. For each movement, one bone, called the origin, remains stable while the other, the insertion, is the one that moves. The muscle contracts when stimulated and relaxes after contraction.
Head and Neck
Your head contains your smallest muscle: the stapedius is in your inner ear. Facial muscles situated under your skin, control your expressions. Your tongue contains 16 muscles that allow you to talk and chew. Your sternocleidomastoid muscle, along the sides of your neck, turns your head from side to side and up and down.
Shoulders and Arms
Your shoulder muscles move and stabilize your shoulder blades, or scapular; collarbone, or clavicle; and upper arm bone, or humerus. Your serratus anterior and trapezius muscles help stabilize your scapula, while the levator scapulae and rhomboids help it move. Your deltoids and your rotator-cuff muscles -- subscapularis, infraspinatus, teres minor and supraspinatus -- move your humerus, while your triceps and biceps move your forearm. Pectoralis major, in the front of your chest, and latissimus dorsi, on your lower back and teres major, under your arms, also help you move your arms.
Trunk
Your back muscles help you stand straight. They include quadratus lumborum, for bending sideways; erector spinae, for correct spine curvature; and multifidus, which maintains your spinal posture. Abdominal muscles are your rectus abdominis, the front muscles that make a six-pack; the transversus abdominis, which helps build your core; and your internal and external obliques along your sides.
Hips
Your hips contain six deep muscles: piriformis, obturator internus, obturator externus, gemellus superior, gemellus inferior and quadratus femoris. Psoas major and iliacus control your hip movements. Your largest muscle is your gluteus maximus. The much smaller gluteus medius and gluteus minimus help you move your legs.
Legs and Feet
Quadriceps are the four front thigh muscles -- rectus femoris, vastus lateralis, vastus medialis and vastus intermedius -- that help you straighten your knee. Your hamstrings -- semimembranosus, semitendinosus and biceps femoris -- help you bend your knee. Your calf muscle is the gastrocnemius, which begins at the back of your knee and attaches to your heel with your Achilles tendon. Your feet each contain 20 muscles.
References
- National Institutes of Health: X-Plain Muscles - Reference Summary; 2008
- "Anatomy of Movement"; Blandine Calais-Germain; 1993
- Sports Injury Clinic: Muscles of the Human Body
