What Are Muscles Their Types Structure and Functions
In this article, students will learn about Muscles in our body, types, structure and functions of Muscles. Let's first know what muscle is.
A muscle is a soft tissue found in both humans and animals. The word muscle is derived from the Latin word “musculus” meaning little mouse as some Muscles resemble the shape of a small mouse or the contraction of Muscles look like a moving mouse.
Muscles are made up of protein filaments of myosin and actin that slide past each other and produce expanding and contracting movements of Muscles. This kind of movement changes both the shape and length of the muscle cells. Muscles function in humans by producing motion and force and help in circulation of blood, changing and maintaining body pressure, movement of internal organs like the movement of food down the digestive tract, and also helps in locomotion.
The human muscular system comprises more than 600 Muscles and makes up about 40-50% of our overall body weight. Muscles are essentially attached to blood vessels, bones and other internal organs. Muscles are composed of special kinds of elastic tissue, tendons, nerves and tissues.
The functioning of Muscles helps in making movements of every kind in the body and internal organs by transferring substances from these organs throughout the body. Muscles function by using up energy by oxidation of carbohydrates and fats, especially from the stored energy molecules adenosine triphosphate (ATP).
Types
There are three types of Muscles found in the body:
Cardiac Muscles
Smooth Muscles
Skeletal Muscles
Out of these three types, cardiac Muscles are involuntary Muscles which means that the movement of cardiac Muscles cannot be controlled by us according to our will.
Skeletal Muscles
Skeletal Muscles are voluntary Muscles and are attached to the bones and involved in different body parts functioning. They come under the central nervous system control of the body. Skeletal Muscles are long and multinucleated. They are cylindrically shaped with branched cells which are attached to the bones by collagen fibres and tendons, which are composed of connective tissues.
The function of Skeletal muscle can be summed up briefly as follows:
The primary function of Skeletal muscle is contraction. And thus, contraction helps produce heat in our body.
Skeletal muscle helps in maintaining the body posture and joint position by conveying information about the degree of muscle length and stretch to the central nervous system.
Skeletal Muscles produce ATP and store glucose in the form of glycogen. Glycogen can be converted into glucose when energy is needed.
Cardiac Muscles
Cardiac Muscles are found only in the heart and are involuntary like movement. They are made up of cylindrical-shaped cells. These are striated Muscles responsible for keeping the heart moving by circulating and pumping blood throughout the body. The interconnected Muscles provide flexibility and strength to the Cardiac muscle tissue and are involved in rhythmic relaxation and contraction of the heart Muscles . Cardiac Muscles are characterised by branched cylindrical fibres and a centrally located nucleus.
Cardiac Muscles are primarily found in humans and regulate rhythmic relaxation and contractions of the heart Muscles for pumping blood. The Cardiac Muscles have a specialised type of tissue called “pacemaker” cells that expand and contract by responding to electrical impulses of the central nervous system.
Smooth Muscles
Smooth Muscles are also involuntary Muscles that are non-striated and are present in major organs whose movements are not controlled by the will, such as the stomach, vessels, bladder, uterus, etc. They are spindle-shaped with a single nucleus. These Muscles are shorter than skeletal Muscles with a length ranging between 20 to 200 μm and thickness between 3-10 µm. These Muscles produce their connective tissue and lack actin, myosin and filaments.
Smooth Muscles perform various tasks in our body which can be given as follows:
Smooth Muscles maintain the diameter of arteries and thereby maintain blood pressure. Arteries have thick walls due to Smooth muscle present there, which helps them carry blood away from the heart.
In the digestive tract, Smooth muscle maintains the peristaltic movement and forces food through the digestive tract.
They are present in the eye responsible for shrinking the size of the pupil.
In the respiratory system, Smooth muscle helps air go from the trachea to the lungs.
In reproductive systems Smooth muscle helps sperm to move along the male reproductive system, during menstruation Smooth muscle helps to expel the uterine lining.
Smooth muscle in the uterus helps women to push out her baby during childbirth.
FAQs on Muscles in the Human Body Structure and Function
1. What are muscles in the human body?
Muscles are specialized tissues made of muscle fibers that contract to produce movement in the body. They are composed of elongated cells containing actin and myosin filaments that slide past each other to generate force. In the human body, muscles:
- Enable body movement and posture
- Help in circulation and breathing
- Support and stabilize joints
- Produce heat to maintain body temperature
2. What are the three types of muscles?
The three types of muscles are skeletal muscle, smooth muscle, and cardiac muscle. Each type has a specific structure and function:
- Skeletal muscle: Voluntary muscles attached to bones; responsible for body movement.
- Smooth muscle: Involuntary muscles found in walls of organs like the stomach and blood vessels.
- Cardiac muscle: Involuntary muscle found only in the heart; pumps blood continuously.
3. How do muscles contract?
Muscles contract through the sliding filament theory, where actin and myosin filaments slide past each other to shorten the muscle fiber. The process occurs in steps:
- A nerve impulse releases acetylcholine at the neuromuscular junction.
- Calcium ions are released inside the muscle cell.
- Myosin heads bind to actin forming cross-bridges.
- ATP provides energy for filament sliding.
4. What is the function of skeletal muscles?
The main function of skeletal muscles is to produce voluntary body movements by pulling on bones. These muscles are attached to bones by tendons and work in pairs. Their functions include:
- Movement such as walking and lifting
- Maintaining posture and balance
- Stabilizing joints
- Generating heat through contraction
5. What is the difference between voluntary and involuntary muscles?
Voluntary muscles are controlled consciously, while involuntary muscles function automatically without conscious effort. The key differences include:
- Voluntary muscles: Skeletal muscles; controlled by the somatic nervous system.
- Involuntary muscles: Smooth and cardiac muscles; regulated by the autonomic nervous system.
- Voluntary muscles move bones; involuntary muscles control internal organs.
6. What is a sarcomere in muscle tissue?
A sarcomere is the basic structural and functional unit of a myofibril responsible for muscle contraction. It lies between two Z-lines and contains organized actin and myosin filaments. Key features include:
- A band: Dark region containing myosin
- I band: Light region containing actin only
- H zone: Central region of myosin only
7. Where are smooth muscles found in the body?
Smooth muscles are found in the walls of internal organs and hollow structures of the body. They are non-striated and function involuntarily. Common locations include:
- Walls of the digestive tract
- Blood vessels
- Urinary bladder
- Uterus
8. Why are cardiac muscles unique?
Cardiac muscles are unique because they are striated like skeletal muscles but function involuntarily like smooth muscles. They are found only in the heart and have special features:
- Presence of intercalated discs for rapid electrical conduction
- Branched muscle fibers
- Rhythmic and continuous contractions
9. What is the role of ATP in muscle contraction?
ATP provides the energy required for muscle contraction by powering the interaction between actin and myosin. Its roles include:
- Detaching myosin heads from actin
- Energizing myosin heads for the next contraction cycle
- Fueling calcium ion pumps to relax the muscle
10. How do muscles work in pairs?
Muscles work in pairs called antagonistic pairs to produce opposite movements at a joint. When one muscle contracts, the other relaxes. For example:
- Biceps contracts to flex the elbow.
- Triceps relaxes during flexion.
- During extension, triceps contracts and biceps relaxes.
