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The human body has more than 600 muscles, which are pieces of soft tissue that help us move, breathe, swallow, and stay alive. There are three types of muscle tissue: visceral, cardiac, and skeletal. Visceral muscle is the weakest type of muscle tissue and is found inside organs like the stomach, intestines, and blood vessels. Cardiac and smooth muscles are involuntary muscles controlled by the autonomic nervous system. Skeletal muscles are the most common type of muscle in the body and are the only voluntary muscles, meaning we can control how and when they work. They are attached to the bones of the skeletal system and make up about half of a person's body weight. They help us perform a wide range of movements and functions, from holding our body still to running a marathon.
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What You'll Learn
Muscles in the arms, legs, chest, back, and neck
There are more than twenty muscles in the upper arm and forearm. These muscles help with both small and large movements, such as wiggling your fingers or doing push-ups. The upper arm has four main muscles: the biceps brachii, brachialis, coracobrachialis, and triceps brachii.
The neck has about 30 muscles that extend from the base of the skull and jaw down to the shoulder blades and collarbone. These muscles support and stabilise the head and neck and assist with movements such as chewing, swallowing, and breathing.
The back muscles support the torso and enable movement and breathing. They run from the neck, down the spine, to just above the hips. Back strains are the most common back muscle injury, caused by overuse or incorrect lifting.
The chest muscles are constantly at work, especially with modern daily activities such as using a phone or laptop. The pectoralis major is the largest and strongest muscle of the chest, responsible for bringing the arms closer to the body and moving the shoulders. The pectoralis minor, serratus anterior, and subclavius are also important chest muscles.
The leg muscles work in synergy to create movement. The hamstrings, located in the back of the leg, are responsible for bending the knees and moving the hips backward. The main skeletal muscles of the lower leg include the tibialis anterior, gastrocnemius, soleus, and posterior tibialis.
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Skeletal muscles, making up 30-40% of body mass
Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of an individual's total body mass. They are attached to the bones and allow for a wide range of movements and functions. Skeletal muscles are voluntary, meaning that an individual can control how and when they work. These muscles are composed of bundles of muscle fibres called myofibers, which contain several myofibrils. Each myofiber represents a muscle cell, with its basic cellular unit being the sarcomere.
The sarcomere is a functional unit created by the arrangement of actin and myosin, which gives skeletal muscle its microscopic striated appearance. Skeletal muscle fibres are multinucleated cells ranging from 10 to 100 micrometres in diameter and several centimetres in length. The nuclei are located in the cell's periphery, adjacent to the sarcolemma, which is a tubular sheath that encases and defines each muscle fibre. The sarcolemma also has a plasma membrane and a polysaccharide coating that fuses with tendon fibres.
Skeletal muscles serve many purposes, including producing movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilising joints. These muscles are essential for performing daily activities and play a crucial role in respiratory mechanics. They are also responsible for maintaining balance and can be found throughout the body. Examples of skeletal muscles include the shoulder muscles, hamstring muscles, abdominal muscles, deltoid muscles, and pectoral muscles.
It is important to keep skeletal muscles strong and healthy, as various medical conditions can arise from skeletal muscle dysfunction, such as myopathies, dysphagia, ataxia, weakness, tremors, and tendon ruptures.
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Involuntary muscles, like the heart
Involuntary muscles are those not under conscious control. Their contraction and relaxation are regulated by the autonomic nervous system, which controls the activity of organs and blood vessels needed for essential daily functions, such as digestion and breathing. The heart is an involuntary muscle and is composed of a specialized type of muscle cell called cardiac muscle or myocardium. This is only found in the heart and forms the thick middle layer of the heart wall. The myocardium is surrounded by a thin outer layer called the epicardium (or visceral pericardium) and an inner endocardium. Coronary arteries supply blood to the myocardium, and cardiac veins drain this blood.
Cardiac muscle cells, or cardiomyocytes, are the contractile myocytes of the cardiac muscle. They are rectangular, branching cells that typically contain only one centrally-located nucleus. Cardiomyocytes contain many mitochondria to produce large amounts of adenosine triphosphate (ATP) and myoglobin to store oxygen to meet the demands of muscle contraction. Humans are born with a set number of heart muscle cells, which increase in size as the heart grows during childhood development. Less than 50% of the cardiomyocytes present at birth are replaced during a normal lifespan, though they are slowly turned over during aging.
Cardiac muscle contracts similarly to skeletal muscle, although with some differences. Electrical stimulation triggers the release of calcium from the cell's internal calcium store, the sarcoplasmic reticulum, which causes the cell's myofilaments to slide past each other, resulting in muscle contraction. Cardiac fibres have their own pacemaker cells, such as the sinoatrial (SA) node, which set the rhythm of the heart contractions. These pacemaker cells can also receive input from the autonomic nervous system to increase or decrease the heart rate as needed.
Smooth muscles are another type of involuntary muscle that line the inside of some organs. They perform essential functions such as moving waste through the intestines and helping the lungs expand during breathing. Smooth muscles play a role in many body systems, including the female and male reproductive systems, the urinary system, the respiratory system, and the digestive system.
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Smooth muscles in the eyes, uterus, and organs
Smooth muscles are involuntary muscles that line the inside of some organs. They are essential for various bodily functions, including moving waste through the intestines and helping the lungs expand during breathing. Smooth muscles are found in the eyes, uterus, and organs, playing a crucial role in their respective systems.
The eye contains a smooth muscle called the ciliary muscle. It forms a ring in the eye's middle layer, known as the uvea or vascular layer. The ciliary muscle is responsible for adjusting the shape of the lens within the eye, enabling us to view objects at different distances. Additionally, it regulates the flow of aqueous humor into Schlemm's canal. The contraction and relaxation of the ciliary muscle affect the shape of the lens, allowing us to focus on objects at varying distances.
The uterus is composed of smooth muscle cells called the myometrium. During pregnancy, the myometrium stretches to accommodate the growing uterus and contracts during labour to facilitate childbirth. After delivery, it contracts again to expel the placenta, and the crisscrossing fibres in the middle layer compress blood vessels to minimise blood loss. The uterine smooth muscle exhibits a phasic pattern, alternating between contraction and maintenance of a resting tone with discrete, intermittent contractions.
Smooth muscles also line other organs in the body, such as the intestines and lungs. They are involved in moving waste through the digestive system and facilitating breathing by expanding the lungs. Smooth muscles are a vital part of various body systems, including the female and male reproductive systems, urinary system, respiratory system, and digestive system. They support and move organs, ensuring their proper functioning.
The human body contains over 600 muscles, and they are made of thousands of small fibres that work together to enable movement and support organs. These muscles are soft tissues that help us move, breathe, swallow, and perform essential functions to keep us alive.
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Strained, fatigued, and sore muscles
The human body is an intricate network of muscles, each with a specific function and location. When muscles become strained, fatigued, or sore, it can impact our daily lives and overall well-being. Muscle strain can occur when a muscle is stretched beyond its normal range of motion, resulting in tears to the muscle fibers and surrounding tissue. This can happen during physical activity, accidents, or even everyday movements if proper form is not used. Fatigued muscles, on the other hand, are often a result of prolonged or intense physical activity that exceeds the muscle's capacity for sustained contraction. Finally, sore muscles can be a result of both strain and fatigue, as well as lactic acid buildup, microscopic damage to muscle fibers, or even delayed-onset muscle soreness (DOMS), which typically sets in a day or two after strenuous activity.
To address strained muscles, it is important to rest and give the muscle time to heal. Icing the affected area can help reduce inflammation and pain, and compression can prevent further swelling. Elevation of the strained muscle, if possible, can also aid in reducing swelling. Anti-inflammatory medications can be useful in reducing pain and speeding up recovery. Fatigued muscles often benefit from a combination of rest and active recovery. Gentle activities that increase blood flow, such as walking or swimming, can help flush out lactic acid and promote the delivery of oxygen and nutrients to tired muscles.
For sore muscles, a multifaceted approach is often beneficial. Applying heat can help relax tight, sore muscles and improve flexibility, while foam rolling or self-myofascial release techniques can improve blood flow and reduce muscle tension. Light stretching can also aid in relieving soreness and improving recovery. It is important to listen to your body and not push through intense soreness, as this can lead to further injury. Hydration is another key factor in muscle recovery, as proper hydration helps flush out toxins and deliver nutrients to repair and replenish muscles.
Additionally, proper nutrition plays a vital role in muscle recovery. Ensuring adequate protein intake helps repair and rebuild muscle tissue, while carbohydrates replenish energy stores and aid in reducing muscle breakdown. Including anti-inflammatory foods such as omega-3 fatty acids, cherries, and turmeric can also help reduce muscle soreness and promote healing. Lastly, while muscle strain, fatigue, and soreness are common, it is important to seek medical advice if symptoms persist, are severe, or are accompanied by other concerning symptoms. Taking care of our muscles is essential for maintaining mobility, strength, and overall physical health.
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Frequently asked questions
There are more than 600 muscles located throughout the human body, making up roughly half of a person's body weight.
There are three types of muscle tissue: skeletal, visceral, and cardiac. Skeletal muscles are the most common type of muscle in the body and are the only voluntary muscles, meaning you can control how and when they work. Visceral muscles are involuntary muscles that line the inside of some organs, such as the stomach, intestines, and blood vessels. Cardiac muscles are also involuntary and include the heart muscle.
Skeletal muscles include shoulder muscles, hamstring muscles, and abdominal muscles. They are responsible for a wide range of movements and functions, including breathing, eating, and moving your bones. For example, the biceps brachii muscle flexes the arm at the elbow, while the hamstrings flex the knee joint.
