Understanding Muscle Cells - AP Biology

Type IIb skeletal muscle tissue is a subtype of skeletal muscle tissue that is anaerobic and has fewer mitochondria than type IIa.

Type IIx skeletal muscle tissue is the fastest muscle type in humans. This subtype of skeletal muscle tissue is characterized by short bursts of anaerobic contraction. It is also able to contract more quickly than aerobic muscles.

Sarcomeres are considered to be the functional units of muscles and are defined as the areas between two Z lines. Sarcomeres are the units that are responsible for the striated appearance of certain muscle types (skeletal and cardiac).

Muscle tissue can be divided into red—fast twitch—and white—slow twitch—muscle types. Red muscles have many capillaries, mitochondria, and myoglobin. Red muscles also perform aerobic activity.

The sarcoplasmic reticulum (SR) is a specialized type of smooth endoplasmic reticulum in striated muscle tissue. The SR has a different function than the smooth ER. The SR is involved in calcium ion storage that is critical in contraction while the smooth ER synthesizes new molecules.

During embryogenesis, the process of myogenesis forms myocytes and muscle tissue.

The sarcoplasm in muscle cells is comparable to the cytoplasm in other types of cells. The sarcoplasm is specialized in the high amount of myoglobin present. Its specialized regulation of calcium ion concentrations controls muscle contractions.

Intercalated disks are structures that connect cardiac muscle cells, allowing them to work together and communicate within the heart. Intercalated disks are made up of different types of cell junctions and are observable under the microscope. This makes cardiac muscle tissue distinguishable.

The calcium ions bind to troponin, which causes the release of the tropomyosin from actin as a result of the troponin-tropomyosin complex detaching. This makes the binding site on actin available for myosin to attach to. The sarcoplasmic reticulum stores calcium for its quick release to facilitate muscle contraction.

Human muscle contraction relies on the action of the motor proteins actin and myosin. Muscles contract through the sliding of myosin and actin filaments along one another.

Muscle cells are often referred to as “myocytes.” Myocytes are tubular cells that develop during a process called myogenesis and specialize based on their association with specific muscle types.

Smooth muscle is used for numerous involuntary actions of the body. It is not striated and has a single, central corkscrew nucleus.

Skeletal muscles are used for voluntary movement of the body. They are striated and have multiple nuclei at the periphery of each cell.

Cardiac muscle is used for involuntary contractions of the heart, allowing for the movement of blood. Cardiac muscles are striated and have a single, central nucleus in each cell.

Sarcomeres represent the basic contractile unit of the muscle and can be used to show the process of contraction. Numerous sarcomeres make up myofibril, which combine to form a muscle fiber (myocyte), which combine to form a fasciculus, which combine to form muscle.

During muscle contraction thick filaments (myosin) remain stationary, while thin filaments (actin) move towards one another. In the process, the H zone and I band shorten, as the Z lines get closer together. The A band, however, never changes in length.

Skeletal muscle is attached to bones by tendons, allowing you to move around. These are the muscles that you can consciously control.

Smooth muscle and cardiac muscle are not controlled consciously. You cannot consciously control your heart beat or your blood vessels constriction.

Swallowing involves both skeletal muscle and smooth muscle. While skeletal muscle is voluntary (somatic), smooth muscle is involuntary (autonomic). Swallowing involves both of these systems. One can voluntarily induce swallowing, but will also swallow involuntarily, such as while sleeping.

Most of the muscles in the esophagus are smooth muscle; these will be the muscles largely responsible for counter-acting gravity in the example. The upper region of the esophagus (the pharynx) and the tongue are composed of skeletal muscle, allowing us to induce the swallowing motion voluntarily.

The three types of muscle in the body are smooth, skeletal, and cardiac muscle. The type of muscle lining artery walls is smooth muscle, which is also present in many organs such as the intestines and the urinary bladder. Unlike skeletal muscle, smooth muscle control is involuntary and, unlike both skeletal and cardiac muscle, it is non-striated. Smooth muscle around the arteries and arterioles is important for regulating blood pressure and directing blood flow in the body.