The muscular system controls the movement of the body. The bones of the skeletal system are about 700 muscles that encompass roughly half of a person’s body weight. Each of these muscles is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendon, and nerves. Muscle tissue is also located inside of the heart, blood vessels, digestive organs. In these organs, muscle serves to move substances throughout the body.
Muscular System Anatomy
There are three types of Muscle tissue: Cardiac, Visceral and skeletal
1. Visceral Muscle, Visceral muscle is found within the organs such as the stomach, intestines, and blood vessels. The weakness of ll muscle tissues, visceral muscles allow the organs to contract to move substances through the organ. Becuase visceral muscle is controlled by unconscious part of the brain; it is known as involuntary muscle can not be directly managed by the conscious mind. The term: smooth muscle: is often used to represent visceral muscles due to its smoothness, uniform appearance when viewed under a microscope. This smooth appearance starkly contracts with the banded appearance of cardiac and skeletal muscles.
2.Cardiac Muscle These are located only within the heart. The cardiac muscles pump blood through the body. Cardiac muscle tissue is an involuntary muscle, and this muscle can not consciously control it. Signals and muscles from brain regulate the rate of contraction; cardiac muscle activates itself to contract. The pacemaker of the heart is made of cardiac muscle tissue that stimulates other cardiac muscle cells, causing them to contract. Because of its self-stimulation, cardiac muscle is acknowledged to be autorhythmic or intrinsically controlled.
The cells or cardiac muscle tissue are striated-that is, they appear to have light and dark stripes when viewed under a microscope. The arrange of protein fibers inside of the cells causes the light and dark bands; Striation indicates that a muscle cell is adamant, unlike visceral muscles.
The cells of cardiac muscle are branched X or Y-shaped cells tightly connect by different junctions called intercalated disk. Intercalated disks ar made up of finger projections from two neighboring cells that interlock and provide a strong bond between the cells. The branch structure and intercalated disk allow the muscle cells to resist high blood pressure and the stress of pumping blood through a lifetime. This features also help to spread electrochemical signals quickly from cell to cell so that the various heart muscles beat as one.
3. Skeletal Muscle Skeletal Muscle is the only intentional muscle tissue in the human body- it is controlled consciously. Every physical movement that a person consciously performs ( speaking writing, walking) needs skeletal muscle. The purpose of skeletal muscle is to contract to move parts of the body closer to the bone that the muscle is connected to. Most skeletal muscles are attached to two bone across a joint, so the muscle helps to move parts of those bones nearer to each other.
Skeletal muscle cells, form when multiple smaller progenitor cells lump themselves together to form long, straight, multinucleated fibers. Started just like cardiac muscles, these skeletal muscle fibers are very strong. Skeletal muscle derives its name from the fact that these muscles always connect to the skeleton in at least one place.
Gross Anatomy of a skeletal Muscle
Most Gross anatomy of a skeletal are attached to two bones through tendons. Tendons are tough cords of dense regular connective tissue whose strong collagen fibers tightly muscle tissues to bones. Tendons go under intense stress when muscles pull on them, so they are very durable and are woven into the covering of both muscles and bones.
Muscles move by reducing their length, pulling on tendons, and moving bones closer to each other. One bone is pulled towards the other bone, which remains stationary. The position of the stationary bone that is connected by tendons to the muscles is called the origin. The area on the moving bone that is attached to muscles via tendons is named the insertion. The belly of the muscle is the plump part of the muscle in between the tendons that does that actual contraction.
Names of Skeletal Muscles
Skeletal muscles are defined based on many various functions, locations, orgin, and insertion, umber of orgins, size, shape, function, direction.
Location- Many of the body’s muscles derive their name from their antomical region. The rectus abdominis and transverse abdominis are located in the abdominal region. Several muscles, like the tibialis anterior, are named after the part of the bone ( the anterior portion of he tibia) that they are attached. Other muslce use a hybrid of these two, like the brachioradialis, whih s named after a region (brachial) and bone (radius)
Origin and insertion – Other muscles are and based upon their connection to a stationary bone (origins). These muscles are very easy to identify once you remember the names of the bones that they are attached with. Examples of this type of muscle are the sternocleidomastoid (which connects to the sternum as well as the clavicle to the mastoid process of the skull ) and the occipitofrontalis (connecting the occipital bone to the frontal bone).
Number of Origins. Some muscles muscle attach to more than one bone or two more than one place on a bone, and hence have more than one orgin. Muscle with two orgins is called a biceps, A muscle with three origins is a triceps muscle. Finally, a muscle with our origins is a quadriceps muscle.
Size, Shape, and Direction. We also identify muscles by their shapes. An example of this are deltoids, which have a delta or triangular shapes. The rhomboid major is a rhombus or diamond shape muscle. Also, serratus muscles have a serrated or saw-like shape. The size of the muscle can be used to differentiate between two muscles found in the same region. The gluteal region contains three muscle separated by size the Gluteus Maximus (large) gluteus medius *(medium) and gluteus minums ( smallest) Finally the direction in which the muscles fibers run can be used to identify a muscle. In the abdominal region, there are various sets of wide flat muscles. The muscle whose fibers run straight up and down are the rectus abdominis, the ones flowing transversely (left to right) are the transverse abdominis, finally the ones flowing at an angle are the obliques.
Function. Muscles are sometimes are sometimes classified by the type of function that they perform. Most of the muscles of the forearms are named based on their function because they are located in the same region and have simlar shapes and sizes. For example the flexor group of the forearm flexes at the wrist and the fingers. The supinator is a muscle that supinates the wrist by rotating it over the palm face up. In the leg, there are mucles called adductors whose role is to adduct (pull together) the legs.
Skeletal Muscle Group Action
Skeletal muscles rarely work by themselves to achieve movements in the body. These muscle groups produce precise movements. The muscle that produces particular movement of the body is known as an agnoist or prime mover. The agnostic always pairs with an antagonist muscle that produces the opposite effect on the same bones. For example, the biecps brachii muscle flexes the arm at the elbow. AAs the antagonist for this motion, the trip brachii muscle extends the arms as the elbow. When the triceps are extending the arm, the biceps would be considered the antagonist.
In addition to the agonist/antagonist pairing, other muscles work to support the movements of the agonists. Synergists are muscle groups that help to stabilize a transition and reduce stressful movements. They are typically found in regions near the agonist and often connect to the same ones. Because skeletas muscles induce the insertion closer to the immobile origin, fixator muscles aid in movement by holding the origin stable. If you lift anything heavy with your arms, fixators in the trunk region hold your body upright and immoble so that you maintain your balance while lifting.
Skeletal Muscle Histology
Skeletal muscle fibers differ significantly from other tissues of the body due to their highly specialized funtions. Many orgnells that encompass the muscle fiber are unique to these type of cell.
The sarcolemma is a cell membrane of muscle fibers. The sarcolemma acts as a conduit for electrochemical signals that stimulate muscle cells. The sarcolemma is connected to transverse tubules (T-tubules) to help carry these electrochemical signals into the middle of the muscle fiber. The sarcoplasmic reticulum function as a storage place for calcium ion (Ca2+) that are critical for muscle contraction. Mitochondria , are where the power and energy originate from in the muscle. Mitochondria is abundant in muscle cells to break down sugar and provides energy in the form of ATP to active muscles. Most of the muscle fiber’s structure are made up of myofibrils; which are contractile structures of the cell. Myofibrils are mad up of many proteins fiber arrange into repeating subunits called sarcomeres. The sarcomere is the functional unit of muscle fibers.
Sarcomeres are composed of two types of protein fibers: thick filmenst and thin filaments.
Thick filaments: Thick filaments are made fo many bonded units of the protein myosin. Myosin si the protein that causes muscles to contract.
Thin filaments Thin filaments are made of three proteins:
1. Actin forms a helical structure that makes the majority of thin filament mass. Actin contains a myosin-binding site that allows myosin to connect to and move actin during muscle contraction.
2. Tropomyosin. Tropomyosin is a long protein fiber that covers around actin and coat the myosin binding site on actin
3. Troponin Bound very tightly to tropomyosin-troponin moves tropomyosin away from myosin binding sites during muscle contraction.