Cardiac muscle tissue cannot be controlled consciously, so it is an involuntary muscle. While hormones and signals from the brain adjust the rate of contraction, cardiac muscle stimulates itself to contract. The natural pacemaker of the heart is made of cardiac muscle tissue that stimulates other cardiac muscle cells to contract.
Because of its self-stimulation, cardiac muscle is considered to be autorhythmic or intrinsically controlled. The cells of cardiac muscle tissue are striated—that is, they appear to have light and dark stripes when viewed under a light microscope. The arrangement of protein fibers inside of the cells causes these light and dark bands. Striations indicate that a muscle cell is very strong, unlike visceral muscles. The cells of cardiac muscle are branched X or Y shaped cells tightly connected together by special junctions called intercalated disks.
Intercalated disks are made up of fingerlike projections from two neighboring cells that interlock and provide a strong bond between the cells. The branched structure and intercalated disks allow the muscle cells to resist high blood pressures and the strain of pumping blood throughout a lifetime.
These features also help to spread electrochemical signals quickly from cell to cell so that the heart can beat as a unit. Skeletal muscle is the only voluntary muscle tissue in the human body—it is controlled consciously. Every physical action that a person consciously performs e. The function of skeletal muscle is to contract to move parts of the body closer to the bone that the muscle is attached to. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other.
Skeletal muscle cells form when many smaller progenitor cells lump themselves together to form long, straight, multinucleated fibers. Striated just like cardiac muscle, these skeletal muscle fibers are very strong.
Skeletal muscle derives its name from the fact that these muscles always connect to the skeleton in at least one place. Most skeletal muscles are attached to two bones through tendons. Tendons are tough bands of dense regular connective tissue whose strong collagen fibers firmly attach muscles to bones.
Tendons are under extreme stress when muscles pull on them, so they are very strong and are woven into the coverings of both muscles and bones. Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other. One of the bones is pulled towards the other bone, which remains stationary.
The place on the stationary bone that is connected via tendons to the muscle is called the origin. The place on the moving bone that is connected to the muscle via tendons is called the insertion.
The belly of the muscle is the fleshy part of the muscle in between the tendons that does the actual contraction. Skeletal muscles are named based on many different factors, including their location, origin and insertion, number of origins, shape, size, direction, and function.
Skeletal muscles rarely work by themselves to achieve movements in the body. More often they work in groups to produce precise movements. The muscle that produces any particular movement of the body is known as an agonist or prime mover. The agonist always pairs with an antagonist muscle that produces the opposite effect on the same bones. For example, the biceps brachii muscle flexes the arm at the elbow. As the antagonist for this motion, the triceps brachii muscle extends the arm at the elbow.
When the triceps is extending the arm, the biceps would be considered the antagonist. That means that you can control their movement. Smooth muscle can be found in many different organ systems of your body, including but not limited to your:. Smooth muscle cells are often rounded at the center and tapered off at the sides.
Smooth muscle is involuntary. Each cell contains chains of filaments that can connect it to other neighboring cells, forming a mesh-like network that allows the cells to contract uniformly.
Cardiac muscle is found only in your heart. You may also see this type of muscle referred to as the myocardium. The myocardium is one of the three layers of tissue in your heart. Similar to skeletal muscle, cardiac muscle is organized into fibers and has a striated appearance.
Individual cardiac muscle cells are closely connected to each other, which helps enable your heart to beat in a coordinated fashion. Like smooth muscle, cardiac muscle is involuntary. It contracts in response to electrical impulses created by a special type of cell in your heart. Skeletal muscles can be found in all areas of your body. Here is a diagram of some of the most well-known and most used skeletal muscles, and what they do.
You may also see skeletal muscles divided according to which area of the body they serve, such as:. This includes the muscles that move your shoulders, arms, wrists, and hands. Examples of important muscles in this area include:. Reviewed by: KidsHealth Medical Experts. Larger text size Large text size Regular text size. Smooth Muscles Smooth muscles — sometimes also called involuntary muscles — are usually in sheets, or layers, with one layer of muscle behind the other.
Page 1 A Hearty Muscle The muscle that makes up the heart is called cardiac muscle. Skeletal Muscle. Face Muscles You may not think of it as a muscular body part, but your face has plenty of muscles.
Major Muscles Because there are so many skeletal muscles in your body, we can't list them all here. But here are a few of the major ones: In each of your shoulders is a deltoid say: DEL-toyd muscle. Your deltoid muscles help you move your shoulders every which way — from swinging a softball bat to shrugging your shoulders when you're not sure of an answer. The pectoralis say: pek-tuh-RAH-lus muscles are found on each side of your upper chest.
These are usually called pectorals say: PEK-tuh-rulz , or pecs, for short. When many boys hit puberty, their pectoral muscles become larger. Many athletes and bodybuilders have large pecs, too. They're often called abs for short. When you make a muscle in your arm, you tense your biceps say: BYE-seps muscle.
When you contract your biceps muscle, you can actually see it push up under your skin. Your quadriceps say: KWAD-ruh-seps , or quads, are the muscles on the front of your thighs. Many people who run, bike, or play sports develop large, strong quads. The muscles that move the human skeleton vary greatly in shape and size and extend to every part of our bodies. In the muscular system, skeletal muscles are connected to the skeleton, either to bone or to connective tissues such as ligaments.
Muscles are always attached at two or more places. When the muscle contracts, the attachment points are pulled closer together; when it relaxes, the attachment points move apart. Muscles contract and relax to move bones. The elbow joint bends flexes when muscles pull on the radius and ulna of the arm. Muscles contract when messages travel from nerves to muscles and trigger chemical reactions.
These reactions change the internal structures of muscle fiber cells, a process that shortens the muscle. The muscle fibers relax when the nervous system signal is no longer present, thus reversing the shortening. Not all muscle tissue is skeletal muscle.
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