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Muscles are contractile tissues found in animals that have the function of producing motion. The mechanism through which an organism interacts with its environment is movement, which is the complicated coordination of muscle and nerve fibres. An organism must move to find nourishment or can deliver food to itself if it is sedentary. Muscle cells generate mechanical energy by converting chemical energy in the form of adenosine triphosphate (ATP), which is generated from food metabolism. Muscles can be classified as skeletal, smooth, cardiac, or voluntary or involuntary depending on their function.
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Keywords: Locomotion, Movement, Muscular System, Fibres, Tissue, ATP, Contraction, Muscle Action,
What are Muscles?
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Muscle is derived from the Latin word "musculus," which alludes to a little mouse owing to the structure of some muscles or the contraction of muscles that resemble the movement of a mouse. Muscle is a type of soft tissue that both animals and humans have. Muscle cells are made up of actin and myosin protein filaments that glide past one another, causing contraction and changing the length and shape of the cell.
Muscles
Functions of Muscles
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Muscles in humans provide force and motion, and they are principally responsible for:
- The movement of blood cells around the body
- Locomotion
- Changing and maintaining bodily posture
- Internal organ movement, such as the contraction of the heart and the peristalsis movement of food through the digestive system.
More than 600 muscles make up the human muscular system, which accounts for 40 to 50 percent of total body weight. These muscles are generally made up of skeletal muscles, tissue, tendons, and nerves and are related to bones, blood vessels, and other internal organs of our body. Elastic tissue makes up the muscles that make up the human muscular system. Muscle contraction causes every movement in our body and may be found in every organ, including the blood vessels, heart, and digestive organs. Muscles in these organs work by transporting chemicals throughout the body. Muscles are categorised into three categories depending on their motions and structures. The oxidation of lipids, particularly carbohydrates, and the stored energy molecules adenosine triphosphate (ATP) provide most of the energy necessary for muscular action.
Also Read: Tissues
Types of Muscles
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There are three types of muscles in the human body, namely skeletal, cardiac, and smooth.
- Skeletal Muscles
Skeletal muscle is a type of muscular tissue that is connected to the bones and has a role in the function of many body components. These muscles are also known as voluntary muscles since they are controlled by the central nervous system.
Skeletal muscle is made up of lengthy, multinucleated muscle cells that form a network of muscular fibres. They are cylindrically formed connective tissues with branching cells joined to the bones by an elastic tissue or collagen fibres called tendons. A tendon connects the muscle to the bone at the end of each skeletal muscle and connects directly to the collagenous, the muscle's outer layer. The fascicles are a collection of muscular fibres found underneath the epimysium. Another protective layer made of collagen surrounds these muscle fibres. The perimysium, a connective tissue sheath that surrounds the muscle fibres, allowing nerves and blood vessels to pass through.
These muscles control body temperature and maintain body posture. They are connected to the skeleton and govern its movements. They oversee completing muscle involuntary motions as well as bodily movements like breathing, typing, and writing. They are also in charge of the body's upright posture. The sartorius muscles in the thighs control bodily mobility. Internal organs and tissues are protected by skeletal muscles, which also offer support to these fragile organs and tissues. These also support the body's entrance and exit locations. Some examples of skeletal muscles include those around the mouth, anus, and urinary tract.
- Cardiac Muscles
Cardiac muscles are striated muscles that pump and circulate blood throughout the body as well as execute muscular involuntary actions to maintain our hearts working. They are constantly contracting and relaxing in a cyclic pattern. The heart muscle tissue's interwoven muscle cells or fibres give strength and flexibility.
Only the human heart has cardiac muscle. The fibrous architecture of cardiac muscle is comparable to that of smooth muscles. The cylindrical, branching fibres and a centrally positioned nucleus make up these muscles. T-tubules, also known as transverse tubules, are ion channel-rich structures seen in atrial muscle cells. These are striated muscles with cylindrical-shaped cells and intercalated discs that connect neighbouring fibres.
The cardiac muscles are involuntary muscles that are engaged in movement and motility. They function automatically, causing the heart to contract for the heart to compress the blood vessels and then release, allowing the heart to refill with blood. The heart contains "pacemaker" cells, which are a particular form of cardiac tissue. Electrical impulses from the neurological system cause them to constrict and expand.
- Smooth Muscles
Smooth muscles are involuntary, non-striated muscles governed by the Autonomic Nervous System (ANS). These muscles may be found practically everywhere in the body, including the stomach, bladder, arteries, bile ducts, the eye, sphincters, and the uterus.
Smooth muscles are spindle-shaped muscle fibres with a single nucleus in the human muscular system. Smooth muscles have a thickness of 3-10 m and a length of 20 to 200 m, which is shorter than skeletal muscle. These muscles make their own connective tissue because they lack filaments, specific proteins, actin, and myosin.
Smooth muscles help close orifices and create collagen and elastin, which are connective tissue proteins. They convey chyme (a pulpy acidic fluid) for digestive tube contractions. Smooth muscle is essential to the circulatory system because it maintains and controls blood pressure and oxygen flow throughout the body. Smooth muscles are also in charge of contracting our irises, lifting the tiny hairs on our arms, and contracting our sphincters.
Also Read: Connective Tissues
Muscle Action
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Depending on whether the muscle shortens, lengthens, or keeps the same, muscular actions are classified as concentric, eccentric, or isometric. Voluntary and involuntary muscles are the two types of muscle actions.
- Involuntary Muscles
In the instance of heart muscle, involuntary muscles are striated and branched. The autonomic nerve system in the body oversees controlling the activities of involuntary muscles. Smooth muscles and cardiac muscles are examples of involuntary muscles.
- Voluntary Muscles
Long, multinucleated cells with sarcomeres organised in bundles make up voluntary muscles. These muscles are made up of cylindrical fibres that adhere to bones and the skin. They are primarily controlled by the somatosensory nervous system and serve a crucial function in allowing the body to move by contracting and relaxing. Skeletal muscles are among the voluntary muscles.
Things to Remember
- Muscles and tendons that link them to the bones make up the human muscular system. All muscle types can receive and respond to nerve stimulation as well as contract.
- These muscles are related to tendons and bones and are found beneath the layers of skin. They oversee movement and are subject to voluntary control.
- Only the heart contains this muscle. It oversees constricting and relaxing the blood moving around your body. The cardiac muscle is an uncontrollable muscle.
- The walls of the body's organs, glands, and blood arteries are formed by this muscle. It controls the circulation of blood and other fluids through the arteries and organs by expanding and contracting them. Smooth muscle is a passive muscle.
Sample Questions
Ques: What are some similarities between cardiac and skeletal muscles? (4 marks)
Ans: The cardiac and skeletal muscles have certain similarities.
- They both contribute to the creation of muscular tissues in the animal body.
- Both are found beneath the striated muscles.
- The nervous system of the body regulates and controls them both.
- These muscles are involved in the body's internal and exterior motions.
- Stretching promotes muscular strength in both circumstances.
Ques: What cells are present in muscle tissues and what are the functions of muscle tissues? (4 marks)
Ans: Myocytes, often known as muscle cells, are the cells that make up muscle tissue. There are three kinds of muscle cells in the human body: cardiac, skeletal, and smooth. Cardiac and skeletal myocytes are usually referred to as muscle fibres because of their long and fibrous structure.
The functions of muscle tissues are mentioned below:
- The basic function of muscle tissue is movement. They can contract, which is what allows body parts to move.
- They also assist in maintaining body posture and stance.
- The muscular system is a complex network of muscles that are vital to the life of the human body.
- Every action you execute involves your muscles. They help you move about, regulate your heart rate and breathing, and promote digestion.
Ques: What kind of tissues form the skeletal muscles? (3 marks)
Ans: Skeletal muscles contain connective tissue, blood vessels, and nerves. The three layers of connective tissue are epimysium, endomysium, and perimysium. Fascicules are skeletal muscle fibre clusters that are structured. After accessing the connective tissue, blood vessels and nerves branch in the cell.
Ques: Based on length, cell type, and form, distinguish between cardiac and skeletal muscles. (3 marks)
Ans:
- Cardiac muscles are shorter than skeletal muscles in length.
- The cardiac muscles are uninucleate, meaning they have only one nucleus, but the skeletal cells are multinucleated, meaning they contain several nuclei.
- Cardiac muscles are shaped like a semi-spindle, whereas skeletal muscles are cylindrical in form.
Ques: Explain why Ca2+ ions are important for muscular contraction. (4 marks)
Ans: Calcium has an important part in muscular contraction. During muscle contraction, an action potential travels from the motor endplate to the sarcolemma, T-tubules, and sarcoplasmic reticulum, causing it to release Ca2+ ions into the sarcoplasm. Calcium ions attach to troponin, changing its shape and location, which changes the position and shape of tropomyosin, which binds the troponin. This shift reveals the active sites on the F-actin molecule, prompting the myosin cross-bridges to attach to them.
Ques: What distinguishes slow-twitch muscle fibres from fast-twitch muscle fibres? (4 marks)
Ans: Slow-twitch muscle fibres allow for long-endurance exercises like distance running, while fast-twitch muscle fibres tyre faster and are employed in powerful bursts of motion. Slow-twitch muscles preserve energy by gently and evenly releasing it over time. This enables them to contract (work) for a lengthy amount of time without becoming exhausted. Fast-twitch muscles burn a lot of energy fast, then become tired and need to rest.
Ques: Mention the cardiac and skeletal muscles' functions, types of contractions, muscular weariness, and energy requirements. (4 marks)
Ans:
- Function- The cardiac muscles circulate blood throughout the body and are involved in involuntary muscular movement, whereas the skeletal muscles are involved in voluntary muscular movements and bodily motions such as running and walking.
- Contraction Type- Cardiac muscles contract in a rhythmic pattern, whereas skeletal muscles contract in a non-rhythmic pattern.
- Muscle Fatigue- Cardiac muscles do not become exhausted, however skeletal muscles do.
- Energy Requirement- Cardiac muscles have an energy need that is somewhere in the middle. Skeletal muscles have a modest energy need.
Ques: What does cardiac muscle consist of? (3 marks)
Ans: Each cardiac muscle cell's plasma membrane and transverse tubules in line with the Z lines, the longitudinal sarcoplasmic reticulum and terminal cisternae, and the mitochondria are all critical components involved in excitation and metabolic recovery processes. Cardiac muscular tissue is the muscle that surrounds the heart. The muscle, unlike skeletal muscles, is responsible for the mechanical motion of pumping blood throughout the body. The mobility is necessary for survival.
Ques: Where does the energy for muscle contractions come from? (3 marks)
Ans: Every myosin molecule contains myosin ATPase, an enzyme that is made from ATP. This enzyme is destroyed by ATP in the presence of Ca2+, Mg2+ ions, inorganic phosphate, and ADP to liberate energy from the myosin head. Myosin crosses bridges to bind to actin because of this energy. These electrified cross-bridges move, allowing the thin myofilaments to slide between the thick myofilaments, creating muscular contraction.
Ques: What distinguishes locomotion from movement? (2 marks)
Ans: The movement of a body from one location to another is known as locomotion. Movement, on the other hand, is the shifting of a body or a part of a body from its initial location.
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