Types, structure and functions of muscles

Skeletal Muscles

Other names for the skeletal muscle are voluntary muscle and striated muscle. This kind of muscle joins with the skeleton of the body. The largest type of muscle fibers, skeletal muscle fibers are multi-nucleated, cigar-shaped cells. It is a voluntary muscle since it is the only type of muscle that can be manipulated intentionally. Striations (protein bands) can be visible when skeletal muscle tissue is viewed under a microscope. As a result, the striated muscle is another name for the skeletal muscle. Skeletal muscle is shielded by connective tissue in three levels. The epimysium, which surrounds the muscle, is its topmost layer. The perimysium encircles collections of muscle fibers. Each muscle fiber is separated from the others by endomysium.

Characteristics of Skeletal Muscles

• Controllable consciously.
• Multiple nuclei.
• In cigar form.
• Connects to the skeleton of the body.
• Soft and delicate
• Its tissue is capable of quick and powerful contraction.
• Tires quickly.
• Contraction occurs suddenly and quickly.

Microscopic Structure of Skeletal Muscle

Numerous elongated muscle cells, often known as muscle fibers, make up the skeletal muscular bundles. A cylindrical cell called a muscle fiber houses multiple nuclei that are situated right below the cell membrane (sarcolemma). Myofibrils are found inside the cytoplasm, or sarcoplasm, of every muscle fiber. A thread-like structure known as a myofibril runs from one end of a muscle fiber to the other. Actins, also known as thin myofilaments, and myosin, also known as thick myofilaments, are the two main types of protein fibers found in myofibrils. Actin and myosin are two types of contractile proteins that produce force when muscles contract. They transform the ATP chemical energy into mechanical energy for motion or force production.

Myofibrils are created when actin and myosin myofilaments are united end to end to create sarcomers, which are highly organized entities. A structural and useful component of muscle tissue is the sarcomere. A sarcomere's ends are made up of a network of protein fibers that, when viewed from the side, form the Z-lines. For actin myofilaments, the Z-lines serve as an attachment site. Because the myofibril appears darker where the actin and myosin myofilaments overlap, the arrangement of the actin and myosin myofilaments in a sarcomere gives the myofibril a banded appearance. The sarcomers' alternating light (I-band) and dark (A-band) regions are what cause striation. A muscle fiber's sarcolemma produces blind-ended sacs, also known as T-tubules, that enter the cell and occupy the spaces between the myofibrils. The T-tubules do not open into the core of the muscle fiber but instead hold interstitial fluid. The sarcoplasmic reticulum is a vast network of branching and anastomosing channels found within the sarcoplasm of muscle fibers (this structure is a modifie endoplasmic reticulum). Sarcoplasmic reticulum channels, which house calcium storage, are in close proximity to the ends of T-tubules.

Types of Muscle Contraction

Isometric or isotonic muscular contractions are the two categories. When a muscle contracts isotonically, the amount of tension it produces remains constant, but the muscle's length changes, as when the fingers move to form a fist. When a muscle contracts isometrically, its length stays the same, but the amount of tension increases as the muscle contracts. One illustration is clenching the fist more and more firmly. The majority of movements consist of alternating isometric and isotonic contractions. When shaking hands, for instance, the muscles shrink a certain distance (isotonic contractions), and the level of tension is maintained by the body's muscles for extended periods of time. An increase in muscle tone causes (isometric contractions). Additionally, isometric contractions are in charge of maintaining muscle tone, posture, such as keeping the back and legs straight, the head held up, and the abdomen from sagging. Motor neurons in the muscles are excited by neurons in the brain and spinal cord, which maintains the muscle tone.

Muscle Attachments

Most muscles cross at least one moveable joint as they extend from one bone to another. The majority of movements of the body are produced by contraction, which pulls one bone toward the other across the movable joint. Some muscles have only one end that is joined to the bone. For instance, when certain facial muscles contract, the skin where those muscles are attached moves. The origin and insertion of every muscle serve as its points of attachment.

A tendon attaches the muscle to the bone at these places of attachment. The end of the muscle that is fixed is called the origin, and the end that is joined to the bone that is moving the most is called the insertion. Although certain muscles have several origins, the concept remains the same. In order for the insertion to move, the muscle must be held or anchored at the origin. For instance, the biceps brachii moves the radius, which causes the forearm to flex. Three origins make up the triceps brachii muscle: two on the humerus and one on the scapula. When contracted, the triceps brachii, whose insertion is on the ulna, extends the forearm.

The muscle that is primarily responsible for creating a certain movement is referred to as the prime mover for that movement among all the muscles that are concurrently contracting. Synergists are the additional muscles that assist in producing the movement. At a joint, antagonist muscles relax as prime movers and synergist muscles contract. When those antagonist muscles contract, they result in a movement that is the polar opposite of what those prime movers and their synergist muscles create.

Naming Skeletal Muscles

The majority of skeletal muscles have names based on one or more of the following criteria:

• Muscle fiber orientation in relation to the body's midline or the longitudinal axis of a structure
• Rectus refers to fibers that run perpendicular to the body's midline or the longitudinal axis of a structure. the rectus abdominis, for instance. Transverse abdominis is an example.
• Transverse fibers are those that cross a structure's midline longitudinal axis. For instance, external oblique.
• Oblique refers to the direction of the fibers with respect to the structure's midline longitudinal axis.
• The location-structure that a muscle is situated in close proximity to For instance, tibialis anterior, a muscle close to the front of the tibia, and frontal, a muscle next to the frontal bone
• Muscle size in relation to other organs
• Maximus is Latin for biggest. as in the gluteus maximus
• Minimus is Latin for little. as in the gluteus minimus
• The longest is longus. as in the adductor longus
• Brief is brevis. Peroneous brevis femoris is one example.
• Number of origins: Biceps refers to muscles with two sources, for example, the biceps brachii. Triceps and quadriceps are muscles with three and four origins, respectively.
• Shape: The muscle's relative shape
• Deltoid denotes a triangle. as in: deltoid The word "trapezius" is Latin for "trapezoid." as in: trapezius
• Serratus translates to sawtooth. like as: serratus anterior
• Rhomboideus: The word "rhomboideus" denotes a rhomboid or diamond shape. such as Rhomboideus
• Origin and inserts: Major places where muscles originate and insert: their origin and insertion. For instance, the sternocleidomastoid muscle inserts on the temporal bone's mastoid process after originating on the sternum and clavicle.
• Action: The muscle's main mechanism of action
• Flexor: Reduce the angle of a joint with a flexor. such as the flexor carpiradialis
• Extensor: They make a joint's angle bigger. such as the extensor carpiulnaris
• Abductor: A bone is brought closer to the midline by the adductor. example: adductor longus
• Adductor: Moves a bone closer to the midline. eg: adductor longus
• Levator: Reates an upward motion. such as the superior levator labii
• Depressor: Produces a downward movement. eg: depressor labii inferioris Supinator: turns the palm upward or anteriorly. eg: supinator
• Supinator: The palm is rotated anteriorly or upward. a.k.a. supinator
• Pronator: The palm is turned posteriorly or downward. like as: pronator teres Control the size of an aperture with a sphincter. such as the external anal sphincter
• Tensor: Increases the rigidity of a body part. such as: tensor fasciae latae
• Rotator: A bone is rotated about its longitudinal axis by a rotator. such as: obturator externus