Understanding Muscle Cells - AP Biology

The contraction of muscle cells results from the controlled interaction between actin and myosin proteins.

Actin forms a thin filament coil structure comprised to two strands of actin and some additional regulatory proteins (troponin and tropomyosin). The actin coils are arranged above and below myosin bundles, which are also called thick filaments. One end of myosin forms a globular head shape that, in a relaxed state, is not able to bind to a site on actin. When the muscle is stimulated by a motor neuron, a signal cascade results in a conformational change that allows the myosin head to bind to actin and shift positions, allowing the muscle to shorten and contract.

While ATP is an essential component in the biochemistry of muscle contraction, it is not actually a protein. ATP is, instead, considered an amino acid derivative. Titin is the elastic protein that connects the ends of a sarcomere and allows the muscle to recoil when over-stretched.

Ca2+ plays a critical role in the regulation of muscle cell contraction and relaxation. Motor neuron stimulation and subsequent the action potential signals the release of Ca2+ from the sarcoplasmic reticulum. The ions bind to troponin—a protein found in a complex with tropomyosin and bound to actin filaments—and exposes the myosin-binding sites on the actin filament by shifting the troponin-tropomyosin complex. With the myosin-binding sites revealed, the myocyte will be able to contract.

In the absence of calcium in the cell, the binding sites on the actin filament cannot be made available and myosin will not bind. No contraction will occur.

There are three primary types of muscle: skeletal, smooth, and cardiac.

Skeletal muscle is multinucleated and striated. Smooth muscle is mononucleated and not striated. Cardiac muscle is mononucleated and striated. If we know that the muscle type is not multinucleated, then it must be mononucleated and could be either smooth muscle or cardiac muscle.

There are three types of muscle tissue: skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscle is under voluntary control and is mainly responsible for locomotion and skeletal movement. Smooth muscle is involuntary and surrounds the viscera to aid in vascular constriction and organ movement. Cardiac muscle is found only in the heart and is responsible for pumping the blood.

The smooth muscle of the digestive tract is responsible for the wavelike movement of peristalsis. In humans, peristalsis is primarily responsible for helping move food down the digestive tract. It is important to understand that peristalisis is an involuntary movement.

Muscle is a major type of tissue in the human body. They contract and enable movement. The three major types of muscle tissues include skeletal, cardiac, and smooth tissues.

Skeletal muscle tissue is one of three types of muscle tissue. Skeletal muscle, as the name implies, is anchored to bones by tendons and controls skeletal movement and posture.

Skeletal muscle tissue is a categorization of muscle tissue that controls skeletal movement and posture. Skeletal muscle tissue is striated and made up of myocytes, which are organized into myofibrils. Skeletal muscle tissue can be categorized further into type I, type IIa, type IIx, and type IIb. These types include red—oxygenated—and white—deoxygenated—tissues.

Skeletal muscle tissue is involved in voluntary skeletal movement. Skeletal muscle can be divided into type I, type IIa, type IIx, and type IIb categories. Type I tissues exhibit slow contractions and type II are involved in fast contractions.

Smooth muscle tissue is a categorization of muscle tissue that is involved in involuntary contractions. Smooth muscle tissue can be found within the walls of organs such as the bladder, intestines, and stomach.

Smooth muscle tissue is involved in involuntary contractions. This type of muscle tissue is not striated and is bundled by connective tissue.

In smooth muscle tissue, contraction is involuntary and is caused by the sliding of actin and myosin filaments over one another. The function and mechanics of these contractions are generally the same in every organ; however, the physiological impact of each contraction may differ.

Cardiac muscle tissue is only found in the heart.

Cardiac muscle tissue is a type of striated muscle tissue that is complex and interconnected. Cardiomyocytes are connected end-to-end by intercalated disks. This allows for quick transmission of electrical signals. Cardiomyocytes have one nucleus each.

Skeletal muscle fibers come in 3 types: red (type I), intermediate/pink (type IIA), and white (type IIB). Red muscle fibers produce slow movement and do not fatigue quickly; these muscles mainly utilize oxidative phosphorylation as an energy source. White muscle fibers work the fastest, but also fatigue much more rapidly; these muscles mainly utilize glycolysis as a source of energy. Intermediate muscle fibers consist of both red and white muscle fibers. All muscles contain some degree of intermediate muscle fibers, however the pectoralis major muscle is an example of a muscle group primarily composed of white muscle fibers. Cardiac muscle is found in the heart only, and smooth muscle is involuntary.

The correct answer to this question is lactic acid fermentation.

Lactic acid fermentation occurs in human muscle cells when oxygen is not available. Alcohol fermentation only occurs in yeast, fungi, and some bacteria. The other answers are unrelated to cramps and instead just are other concepts of respiration.

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.