The muscular system makes up all the muscles of our body and thus they are responsible for the movement of the human body on day to day basis. These muscles are attached to the bones of the skeletal system. There are about 600 named muscles in a body and them that makeup roughly half of the body weight of the person’s body weight. Muscles are found everywhere in our body and are responsible for most of the body mass.
Each of these muscles is a combination of the skeletal muscle tissue, nerves, blood vessels, and tendons. Heart, digestive organs, and blood vessels all are made up of the muscles. Muscles help in the movement of the body parts and also in the movement of the substances.
There are many functions that can be fulfilled by the muscular system. These functions can be something like body posture, joint stability or production of heat. The posture of the body is maintained due to the contraction of the muscles. The skeletal muscles are responsible for making the fine adjustments that help in maintaining the body in the stationary positions. In the knee and shoulder joints, the tendons of the muscles extend over the joints and thus maintain the stability. The muscular system also helps in the heat production which helps in maintaining the body temperature. More than half of the body heat is produced as a result of the muscle contraction and it is an important by-product of muscle metabolism.
TYPES OF MUSCLE TISSUES
There are three types of muscle tissue:
Visceral Muscle (Smooth muscle)
In organs like intestines and blood vessels, visceral tissue can be found. This muscle is the weakest of all the other muscle tissues in our body. Visceral muscles help in the contraction of the organ so that it can move the substances.
These muscles are not under our control and hence, are controlled by the unconscious part of the brain. They are termed as the involuntary muscle and are also known as the smooth muscles.
They are termed as smooth muscle as they have a smooth, uniform appearance under the microscopic appearance. These muscles can be differentiated from the other two kinds as they both have banded appearance and are not smooth.
This muscle is only found in one organ in our body and that is our heart. The muscle’s main function is the pumping of the blood throughout our body. Cardiac muscle tissue cannot be controlled consciously by the person as the heart beats all the time, hence; they are also the involuntary muscle.
Cardiac muscles stimulate itself for contraction and the hormones and signals from the brain help in determining the rate of contractions. The beatings of the heart are dependent on the pacemakers which are also made of the cardiac muscles. They help in transmission of the conduction from one part of the heart to another.
Cardiac muscle is termed as autorhythmic and is intrinsically controlled.
When viewed under the microscope the cells of the cardiac muscle tissue are seen as striated. They are made up of the light and dark stripes if they are viewed under the light microscope.
The muscles are arranged in the form of protein fibers which are present inside of the cells. This is the reason the muscles have the light and dark bands. The striation is the reason the muscle is termed as strong. The smooth muscle doesn’t have these striations and hence they are termed as weak muscles.
The cardiac muscle has branched X or Y shaped cells. These cells are tightly connected together with the help of the special junctions known as the intercalated disks. Intercalated disks have small fingerlike projections which arise from the two neighboring cells. These cells interlock together and provide a bond in the cells which are quite strong. This branched structure and intercalated disks are very helpful to the human body as they allow the muscle cells in resisting the high blood pressure and also the strain that might be caused by the regular pumping of the blood throughout a lifetime. Due to this way the electrochemical signals are transferred quickly from one cell to another so that the heart can beat as a unit.
Skeletal muscles are the voluntary muscle tissue in our body. The work voluntary in layman term means that they can be controlled by the person. All the physical action that a person can perform e.g. speaking, running, walking, talking or writing is a result of the skeletal muscles movement.
Skeletal muscle functions to contract the particular part of the body and to move the part of the body close to the bone to which the muscle adheres. Skeletal muscles are simultaneously attached to two bones to make a joint. These muscles serve to move these parts of the bones close to one another.
Skeletal muscle is composed of small progenitor cells that lump together. They form a chain of long, straight and multinucleated fibers.
Skeletal muscles are also striated like the cardiac muscles. Hence these muscles fibers are very strong, unlike the smooth muscles.
Skeletal muscle is named as they always connect to the skeleton at least at one place and performs their function.
Skeletal muscles are attached with the help of tendons to the other two bones. Tendons are a dense regular form of connective tissue; the collagen fibers firmly help in attaching the muscles to the bones. Tendons are stressed when the muscles pull on them. These tendons are quite strong and are woven in the coverings of the muscles and the bones.
Muscles are named according to the different factors like their location, origin, insertion, shape, and size, number of origins, direction, and function. All these are discussed below.
Many of the muscles are named according to their anatomical region. For example, the muscle rectus abdominis and the transverse abdominis are the muscles of the abdominal region. The tibialis anterior muscle is named after the part of the bone to which it is attached. Therefore, from the name, we can easily determine that the muscle is attached to the anterior part. Some muscles have a little different mechanism and they are named after the hybrid of the two muscles, like the brachioradialis, which is named after the brachial and the radius muscle.
ORIGIN AND INSERTION-
Some of the muscles get their name form the connection to the stationary bone which is known as the origin and also to the moving bone known as the insertion. These muscles can be easily identified if we know the names of the bone it is attached to. For example, the sternocleidomastoid and the occipitofrontalis muscle can be easily determined b their names.
NUMBER OF ORIGINS-
A muscle can have multiple origins and the one with two origins is known as a biceps. Whereas a muscle with three origins is known as the triceps muscle. And similarly, a muscle with four origins is termed as quadriceps muscle.
Muscles can also be classified according to their shapes. The deltoids muscle has a delta or triangular shape. The serratus muscles are like saw shaped. The rhomboid major has a diamond shape. Therefore, some muscles are named according to their shape.
The size of the muscle is also quite helpful in distinguishing the muscle, for example, the gluteal region contains three muscles differentiated by size, the gluteus maximus, gluteus medius, and gluteus minimus.
The direction in which the muscle fibers run are also helpful in identifying a muscle, as in the abdominal region we have several sets of wide and flat muscles that help in performing the functions.
Muscles are also classified according to the function, for example, the flexor group of the forearm helps in the flexion of the wrist and the fingers. The other muscle known as the supinator is a muscle that performs the function of supination of the wrist.
SOME FUN FACTS ABOUT THE MUSCULAR SYSTEM
- The human body is made up f about 600 muscles and they account for half of our body weight. The muscles of the human skeleton vary in shapes and sizes. They extend to each part of our body and help in its movement. The muscles make up of about 40% mass of our bodies. Muscles are innervated by the blood vessels and the nerves so that they get the nutrition to work properly. Each and every muscle has a different function and any damage can paralyze that part of our body.
- Muscles are in direct contact with the bones and they contract and relax to move the body part. When the signals are received from the nerves the muscles contract and perform the function unless and until the signal is no more received. The muscles then relax and bring the body part to normal.
- Many organs are made up of muscles. They are made up of the smooth muscle and not the skeletal muscle. These body organs help in facilitating many body functions. Esophagus, intestines, stomach, urinary bladder, heart and blood vessels are made up of muscles. These organs contract and relax to help in movement of the nutrients or the bodily fluids through them.
- Muscular system and the nervous system have a coordination of their own. They both work together to move a single part of our body. Cerebral cortex helps in sending somatic signals that help in the movement. Spinal nerves help in the innervations of the skeletal muscles.
The function of human body is not possible without muscles. Along with skeletal system, muscles allow different movements in the body. There are more than 600 muscles in the body that give shape and enable body movement. Based on the functions, muscles are divided into three main types: Voluntary muscle, involuntary muscle and cardiac muscle.
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Skeletal muscle or voluntary muscles:
These muscles of the body are striated and voluntary and can be consciously controlled. They are multinucleated and non-branched. Skeletal muscles are involved in all the physical actions of the body like jumping, running, walking, writing etc. Skeletal muscles are named based on their location, shape, size and function. Some of the major skeletal muscles along with their functions are described below:
- Deltoid: Allows sideways raising of arms.
- Biceps: Helps in bending of arm at the elbow point.
- Abdominals: Allows truck flexion allowing forward bending.
- Quadriceps: Helps in strengthening of leg.
- Pectorals: Helps in raising arms at the shoulder allowing it to draw across the chest.
- Latissimus dorsi: Helps to pull back the arm and allows it to draw behind the back.
- Trapezius: Helps in movement of head backward and sideward. Also allows rotation of the shoulder.
- Triceps: Helps in strengthening of arm at the elbows.
- Gluteals: Helps in sideways bending of leg.
- Hamstrings: Allows bending of leg at the knee.
- Gastrocnemius: Allows standing on tip toes.
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Skeletal muscles fibers also called myofibers are long and constricted. Most of these muscle fibers have cylindrical bundle of contractile protein called myofibrils. The alternating light and dark band in the muscle fiber are due to the length and thickness of protein filament in the myofibrils. The cytoplasm of skeletal muscle fiber is named sarcoplasm that is enclosed by a bilayer membrane of lipid called sarcolemma. At the surface, skeletal muscle fibers are striated. Moreover due to the high protein contain skeletal muscle fibers are also multinuclear.
Contrary to voluntary muscles, these muscles work involuntarily and are not under conscious control of our brain. They are non- striated and tapered with single nucleus. Due to the smooth appearance of these muscles, they are also called smooth muscles. The tissue of involuntary muscles look like a telephone cable. Each tissue is made of muscle fiber and each fiber is constructed from even smaller bands named myofibrils that have interlocked strand of muscle protein. The muscles of stomach, intestine, blood vessels etc. are involuntary in nature.
These are the muscles of heart that are also involuntary in nature. These muscles are striated and branched with single nucleus. Along with nerves, chemicals, blood vessels etc., these muscles allows rhythmic expansion and contraction of heart.
Cardiac muscle tissue is formed by the combination of cells and fibers. Each cardiac muscle has single nucleus and is striated having light and dark bands. Between the dark bands are present thin filaments that are made of actin protein allowing light to pass through it. Cardiac muscles cells are branched establishing the contact with three or more cardiac muscle cells. The finger like extension at the end of each cardiac cells is called intercalated disk that forms tight junctions between the cells in order to allow quick flow of electrochemical signal and resist the pressure of pumping action. Image reference: http://anatdelosanimalesdomesticos.blogspot.in/2015/02/miologia_12.html
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