What kind of muscles are skeletal muscles

The basic unit is the muscle fiber with many nuclei. These muscle fibers are striated having transverse streaks and each acts independently of neighboring muscle fibers. Smooth muscle , found in the walls of the hollow internal organs such as blood vessels, the gastrointestinal tract , bladder , and uterus , is under control of the autonomic nervous system. Smooth muscle cannot be controlled consciously and thus acts involuntarily.

A typical muscle is serviced by anywhere between 50 and or more branches of specialised nerve cells called motor neurones. These plug directly into the skeletal muscle. The tip of each branch is called a presynaptic terminal. The point of contact between the presynaptic terminal and the muscle is called the neuromuscular junction. To move a particular body part: The brain sends a message to the motor neurones.

This triggers the release of the chemical acetylcholine from the presynaptic terminals. The muscle responds to acetylcholine by contracting. Shapes of skeletal muscle Generally speaking, skeletal muscles come in four main shapes, including: Spindle — wide through the middle and tapering at both ends, such as the biceps on the front of the upper arm.

Flat — like a sheet, such as the diaphragm that separates the chest from the abdominal cavity. Triangular — wider at the bottom, tapered at the top, such as the deltoid muscles of the shoulder.

Circular — a ring-shape like a doughnut, such as the muscles that surround the mouth, the pupils and the anus. These are also known as sphincters. Muscle disorders Muscle disorders may cause weakness, pain, loss of movement and even paralysis. The range of problems that affect muscles are collectively known as myopathy. The three main types of muscle include skeletal, smooth and cardiac. The brain, nerves and skeletal muscles work together to cause movement — this is collectively known as the neuromuscular system.

More information here. A person in good health can consciously control their skeletal muscles. Most visible body movements — such as running, walking, talking, and moving the eyes, head, limbs, or digits — occur when the skeletal muscles contract. Skeletal muscles also control all facial expressions, including smiles, frowns, and mouth and tongue movements.

Together with the tendons, they keep the bones in the right position so that the joints do not dislocate. Skeletal muscles also generate heat when they contract and release, and this helps maintain body temperature.

The two main types of skeletal muscle are slow-twitch and fast-twitch. These are dense and rich in myoglobin and mitochondria. They have capillaries, which give them their red color. This type of muscle can contract for a long time without much effort. Type I muscles can sustain aerobic activity using carbohydrates and fats as fuel. These muscles can contract rapidly and with a lot of force.

The contraction is strong but short-lived. Compared with slow-twitch muscle, it is less dense in myoglobin and mitochondria. Skeletal muscles are striated , which means that they consist of thousands of equally sized sarcomeres, or muscle units, which have transverse bands. A striated muscle appears striped under a microscope because of these bands. Different bands within each muscle interact, allowing the muscle to move powerfully and smoothly.

Smooth muscles are responsible for movements in the stomach, intestines, blood vessels, and hollow organs. The smooth muscles in the bowel are also called visceral muscles. These muscles work automatically, with a person being unaware that they are using them. Unlike skeletal muscles, they do not depend on conscious thought. Many different bodily movements depend on smooth muscle contractions. These include the intestinal walls pushing food forward, the uterus contracting during childbirth, and the pupils shrinking and expanding to accommodate the amount of light available.

Smooth muscles are also present within the walls of the bladder and the bronchi. The arrector pili muscles in the skin, which make the hair stand up, also comprise smooth muscle fibers. Cardiac muscles are responsible for the heartbeat and only exist in the heart. Smooth muscle is found in the walls of hollow organs throughout the body. Smooth muscle contractions are involuntary movements triggered by impulses that travel through the autonomic nervous system to the smooth muscle tissue.

The arrangement of cells within smooth muscle tissue allows for contraction and relaxation with great elasticity. The smooth muscle in the walls of organs like the urinary bladder and the uterus allow those organs to expand and relax as needed. The smooth muscle of the alimentary canal the digestive tract facilitates the peristaltic waves that move swallowed food and nutrients. In the eye smooth muscle changes the shape of the lens to bring objects into focus.

Artery walls include smooth muscle that relaxes and contracts to move blood through the body. The heart wall is composed of three layers. Cardiac muscle, found only in the myocardium, contracts in response to signals from the cardiac conduction system to make the heart beat.