voluntary muscles
Voluntary muscles are muscles that can be moved by a person's free will and are almost always associated with the skeletal system.
- These muscles are attached to bones by tendons, and they are responsible for various movements in vertebrates.
- Voluntary muscles make up about 40% of the body's total weight and are usually long and found near bones.
- Voluntary muscles are striated muscles because the muscles are composed of long, thin, multinucleated muscle fibers that cross in a regular pattern of red and white lines, creating a striated appearance.
- Every muscle cell has a nucleus, which is retained at the periphery of the cell.
- Muscle fibers are further covered by specialized cell membranes called sarcolemma or sarcolemma.
- The sarcolemma in voluntary muscles is thick and connects muscle fibers to connective tissue.
- Additionally, muscle fibers have contractile units called sarcomeres, which shorten, causing the muscle to contract and relax. Sarcomeres contain actin and myosin, which together cause muscle contraction by sliding against each other.
- Each muscle fiber is connected to each other through connective tissue and interacts through nerves and blood vessels.
- Autonomic control of these muscles is regulated by a part of the peripheral nervous system called the somatic nervous system.
- The somatic nervous system consists of afferent nerves, which carry information to the central nervous system, and efferent nerves, which carry information from the CNS to voluntary muscles for contraction.
- These muscles are not myogenic and require external nerve stimulation to contract.
- The contraction and relaxation of voluntary muscles require large amounts of energy. Therefore, they possess multiple mitochondria to meet their energy needs.
- In contrast to involuntary muscles, voluntary muscles exhibit rapid contraction and relaxation. However, they also tire quickly and require regular breaks.
- These muscles are essential as they are involved in the movement of body parts and the movement of the body.
- Some examples of voluntary muscles include biceps, triceps, quadriceps, diaphragm, pecs, abdominals, hamstrings, etc.
involuntary muscle definition
Involuntary muscles are muscles that cannot be controlled by will or consciousness and are usually associated with organs that exhibit slow and regular contractions and relaxations.
- Involuntary muscles are also called smooth muscles or non-striated muscles because they have no striations when viewed under a microscope.
- These muscles are found mainly in the walls of internal organs such as the stomach, intestines, bladder, and capillaries.
- The individual muscle cells in smooth muscle are long, thin, spindle-shaped, with the nucleus in the center.
- The sarcolemma or sarcolemma exists as the cell membrane of muscle fibers and its function is to connect the muscle fibers to each other. The sarcolemma present is relatively thin and less concentrated.
- One example of an involuntary muscle is the cardiac muscle, which is structurally and functionally different from other involuntary muscles.
- The heart muscle is composed of individual heart muscle cells called cardiomyocytes, which are connected together by intercalary disks. These muscle cells are surrounded by collagen fibers and other substances that form the extracellular matrix.
- The contraction of cardiac muscle is different from the contraction of skeletal and smooth muscle. Action potentials are generated within muscles in the form of electrical stimulation.
- This potential results in the release of calcium ions from the cell into the sarcoplasmic reticulum. The rise in calcium ions causes the myofilaments to slide past each other, causing excitation-contraction.
- Myocardium is myogenic, in which nerve stimulation occurs within the muscle.
- Most muscle cells within the muscle fibers of involuntary muscles function as a single unit, in which contraction and relaxation occur simultaneously.
- Involuntary muscles are controlled by the autonomic nervous system of the peripheral nervous system.
- The motor nerves of the autonomic nervous system consist of neurotransmitter-filled bumps called varicose veins.
- Because gap junctions connect cells in involuntary muscles, neuronal signals can be transmitted from one cell to another via neurotransmitters.
- Involuntary muscle contractions and relaxations are slow and occur at regular intervals.
- As a result, these muscles do not tire quickly and can work continuously.
- They also have less energy requirements and therefore fewer mitochondria than voluntary muscles.
- Involuntary muscles are involved in the movement of internal organs and also aid in the passage of fluid and food in the digestive system .
- Some examples of involuntary muscles include cardiac and smooth muscles of the intestines, blood vessels, genitourinary tract, respiratory tract, etc.
