Muscles What are the muscles in the body?Muscles are specialized soft tissues/ fibers designed to produce movements and stabilize the body's structures. Muscles produce movements in the joints, heart, blood vessels, and other internal organs. Almost all body movements are the result of muscle contraction except the action of cilia and cellular movements. In this article, we will explore everything you need to know about muscles.How many muscles are in the human body?There are more than 600 muscles in the human body. This count will vary from person to person. In 2023, Rachel E. Noto reported that muscles account for about 40% of the weight of the human body. What are the types of muscles?There are 3 types of classification in the muscles based on the location, control of action, and striations. Based on the location - muscles are divided into 3 types: skeletal muscles, cardiac muscles, and smooth muscles. Commonly, this is considered a type of muscle. Based on the control - muscles are divided into 2 types: voluntary muscles and involuntary muscles. Voluntary muscle is the muscle that is controlled by the will. Skeletal muscles are voluntary muscles. These muscles are innervated by somatic nerves. Muscles that cannot be controlled by the will are called involuntary muscles. Cardiac muscle and smooth muscle are involuntary muscles. These muscles are innervated by autonomic nerves. Based on the striations - muscles are divided into 2 types: striated muscles & non-striated muscles. Striated muscle is the muscle that has a large number of cross-striations (transverse lines). Skeletal muscle and cardiac muscle belong to this category. A muscle that does not have cross-striations is called a non-striated muscle. It is also called plain muscle or smooth muscle. It is found in the walls of the visceral organs.1. Skeletal musclesSkeletal muscle is situated in the bones and forms the skeletal system. The skeletal muscles form 40% to 50% of body mass and are voluntary and striated. These muscles are supplied by somatic nerves.2. Cardiac musclesCardiac muscle forms the musculature of the heart. That is, these muscles are present in the heart. These muscles are striated and involuntary. Cardiac muscles are supplied by autonomic nerve fibers.3. Smooth musclesSmooth muscle is situated in the blood vessels and viscera. It is also called a visceral muscle. It is different from skeletal and cardiac muscles because of the absence of cross striations, hence the name smooth muscle. Smooth muscle is supplied by autonomic nerve fibers. What are the anatomy of muscles? Muscle tissue is made up of a large number of individual muscle cells, or myocytes. The muscle cells are commonly called muscle fibers because these cells are long and slender in appearance. Muscle is separated from the neighboring tissues by a thick fibrous tissue layer known as fascia. Beneath the fascia, the muscle is covered by a connective tissue sheath called the epimysium. In the muscle, the muscle fibers are arranged in various groups called bundles or fasciculi. The connective tissue sheath that covers each fasciculus is called the perimysium. Each muscle Fiber is covered by a connective tissue layer called the endomysium. Every muscle fiber contains myofibrils. Inside the myofibrils, sarcomere will be there, that is contractile unit of a muscle. What are the Types of muscle fiber?Muscle fibers differ widely in metabolic profile and contracting speed. Fibers are generally classified as slow twitch and fast twitch, with type I (slow oxidative) being the slowest, type IIa (fast oxidative glycolytic) being faster than type 1, and type IIx (fast glycolytic) being the fastest. Type of Muscle Fiber Type I Type IIa Type IIx Other Names Red fibers, Slow oxidative, Slow twitch Fast oxidative White fibers, Fast glycolytic, Fast twitch Metabolism Oxidative (aerobic) Primarily aerobic Anaerobic glycolysis Fatigability Low Moderate High Oxidative Capacity High High Low Substrate for ATP Production Fatty acids Glucose Glucose Fiber Size Small Moderate Large Myoglobin High, more capillaries Moderate Low Mitochondria More Moderate Less How do muscles contract?The sarcomere is defined as the structural and functional unit of a skeletal muscle. It is also called the basic contractile unit of the muscle. Electron microscopic studies reveal that the sarcomere consists of many thread-like structures called myofilaments and sarcotubular systems (calcium storage centers). Myofilaments are of two types: Actin filaments Myosin filaments. These 2 are the contractile proteins. But sarcomere has other non-contractile proteins also such as titin, desmin, actinin, etc. Whenever our brain decides to move our body, the central nervous system (CNS) will send signals to the peripheral nervous system (PNS). The muscles responsible for the desired movement will get stimulated by this peripheral nervous system through neuromuscular junction. Once the calcium binds to the troponin part of actin filaments, movements of actin and myosin will occur, which will lead to muscle contraction. Types of muscle contraction:There are 3 types of muscle contraction based on the length, tension, and speed of a muscle. These are isometric contraction, isotonic contraction, and isokinetic contraction. What are the functions and movement of muscles?As we discussed above, muscles have 2 movements/ functions that are voluntary movements (skeletal muscles) and involuntary movements (cardiac and smooth muscles). The brain sends signals to skeletal muscles by transmitting electrical impulses through nerve cells called neurons, which travel down the spinal cord and reach the muscles via motor neurons, causing them to contract voluntarily and produce movement; this process is facilitated by the release of chemical neurotransmitters at the neuromuscular junction where the nerve meets the muscle fiber. The smooth & cardiac muscles are controlled by the autonomic nervous system. It is divided into sympathetic and parasympathetic systems. The sympathetic nervous system prepares the body for an activity (fight & flight response). The parasympathetic nervous system relaxes the body and inhibits/slows many functions (rest & digest)How do muscles grow? Muscle growth, or hypertrophy, happens when you lift weights or do intense physical activity/ exercise because it creates tiny tears in the muscle fibers. After exercise, your body works to repair those muscle fibers, fusing them and increasing their size. This process is called muscle protein synthesis (MPS). Some hormones like testosterone, growth hormone, cortisol, and insulin-like growth factors are responsible for muscle growth. Along with this, nutrition and rest also play a major role in muscle growth. Nutrition: Eating enough protein (especially after exercise) provides the building blocks for muscle repair. Carbs and fats also support energy for recovery. Rest: Muscles grow when you rest, not during the workout. Proper recovery allows your muscles to rebuild stronger.What are the common muscle injuries and their prevention?Common muscle injuries are strains, ruptures, tendon injuries, and cramping.Strains: slight tearing of muscle fibers, often from overstretching or sudden lengthening movements.Muscle Tears (Ruptures): Severe strain causes a partial or complete tear in muscle fibers.Tendonitis/ tendinopathy: Inflammation of a tendon, often from repetitive motion or overuse.Cramping: Sudden, involuntary muscle contractions, typically due to dehydration, fatigue, or electrolyte imbalances. Prevention of these muscular injuries involves,Proper Warm-Up: Prepares muscles and joints before the activity/ exerciseProgressive Load Management (Strengthening): Gradually increase intensity and load over time. Work on eccentric exercises (where muscles lengthen under tension) to strengthen tendons and prevent strains.Rest & Recovery: Allow muscles to recover with adequate rest & Avoid overtraining or working the same muscle group too frequently.Nutrition: Ensure sufficient intake of protein, hydration, electrolytes, and carbs, which are essential for muscle growth and health.Listen to Your Body: Pay attention to your body.