Logan Steele
The human body has over 600 muscles that support a range of functions, from pumping blood and supporting movement to lifting heavy weights and giving birth. They are pieces of soft tissue that help us move, breathe, swallow, and stay alive. The three main types of muscles are skeletal, smooth, and cardiac. Skeletal muscles are the most common type and are attached to bones to support movement. Smooth muscles are involuntary and help with digestion, while cardiac muscles make up the heart and pump blood through the body. Together, the bones, muscles, and joints form our musculoskeletal system, enabling us to perform everyday physical activities.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | 600 |
| Types of muscles | Skeletal, Cardiac, Smooth |
| Skeletal muscle composition | 30% to 40% of total body mass |
| Skeletal muscle control | Voluntary |
| Cardiac muscle location | Middle layers of the heart |
| Smooth muscle control | Involuntary |
| Smooth muscle location | Internal structures like the digestive tract, uterus, blood vessels, stomach, intestines, and walls of the heart chambers |
| Muscle movement | Contraction, Relaxation |
| Muscle functions | Movement, Chewing, Breathing, Swallowing, Supporting weight, Pumping blood, Maintaining body temperature |
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What You'll Learn
Movement and stability
The human body has over 600 muscles, which are pieces of soft tissue that help us move, breathe, swallow, and stay alive. Muscles move by contracting and relaxing, pulling on tendons and moving bones closer to each other. Tendons are cord-like connective tissues that attach skeletal muscles to bones.
Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of our total body mass. They are attached to bones and allow us to perform a wide range of movements and functions. These muscles are voluntary, meaning we control how and when they work. They are responsible for our everyday movements, such as reaching for a book on a shelf, which involves the skeletal muscles in our neck, arm, and shoulder. Skeletal muscles also help to stabilize our joints and contribute to joint flexibility. For example, the knee and shoulder joints rely on muscle tendons for stability.
Smooth muscles, on the other hand, are involuntary muscles that line the inside of some organs and perform essential functions without our conscious control. They are found in the digestive tract, uterus, and blood vessels. In the digestive system, smooth muscles help break down food and move it through the intestines. In the blood vessels, they contract to regulate blood pressure. Cardiac muscle, found in the heart, is also an involuntary muscle that contracts and relaxes to pump blood through our cardiovascular system.
To maintain muscle health, it is important to seek medical advice for persistent muscle pain and to engage in physical activities that promote strength and overall health.
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Breathing and swallowing
Breathing is defined as pulmonary ventilation, which involves two events: inspiration, when air moves into the lungs, and expiration, when air leaves the lungs. The diaphragm is located below the lungs and plays an integral role in the respiratory system. During inspiration, the diaphragm contracts, increasing the space in the thoracic cavity, which is enclosed by the ribs, vertebral column, and sternum. This enables the lungs to expand. During expiration, the diaphragm relaxes, and the lungs recoil back to their original volume, decreasing the size of the thoracic cavity and allowing air to flow out.
The intercostal muscles, located between the ribs, also assist in breathing. They contract during inspiration, assisting in the elevation of the ribs and sternum, which expands the thoracic cavity. The sternocleidomastoid and scalene muscles on the neck act as accessory muscles during inspiration, helping to elevate the sternum and clavicle, and subsequently lifting the ribs. The accessory expiratory muscles are the abdominal muscles: rectus abdominis, external oblique, internal oblique, and transversus abdominis.
Swallowing is a complex action that requires precise coordination with breathing, as both processes share the same entrance to the pharynx. It involves over 20 muscles of the mouth, throat, and oesophagus, which are controlled by cortical areas and swallowing centres in the brain stem. During swallowing, the larynx and vocal folds contract, covering the entrance to the trachea to protect the airways, and the upper oesophageal sphincter opens to allow food or liquid to pass through.
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Heart function
The heart is a vital organ that pumps blood throughout the body. It is the main organ of the cardiovascular system, which is made up of the heart and blood vessels. The heart works with the nervous system and endocrine system to control heart rate and other body functions. The nervous system helps control heart rate by sending signals that tell the heart to beat slower during rest and faster during stress. The endocrine system releases hormones that tell blood vessels to constrict or relax, which affects blood pressure.
The heart is made of muscle. The muscular walls contract and relax to pump blood to the arteries. The heart is composed of cardiac muscle, also known as myocardium, which is one of three major categories of muscles in the human body, along with smooth and skeletal muscle. Cardiac muscle makes up the middle layers of the heart and does not exist anywhere else in the body. The walls of the heart's chambers are composed almost entirely of muscle fibres.
Cardiac muscle is an involuntary muscle, meaning it works without conscious input. It contracts and relaxes to pump blood through the cardiovascular system. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. The heart's electrical system is the power source that makes the heart beat possible. Electrical impulses travel through a special pathway in the heart, starting in the SA node (sinoatrial node), known as the heart's natural pacemaker. These electrical impulses cause the atria and ventricles to contract and relax, making the heart beat and pump blood.
The heart's valves work like one-way valves in plumbing, preventing blood from flowing in the wrong direction. Each valve has flaps, called leaflets or cusps, which are supported by a ring of tough, fibrous tissue called the annulus. The leaflets of the mitral and tricuspid valves are also supported by tough, fibrous strings called chordae tendineae, which extend from the valve leaflets to small muscles called papillary muscles.
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Body temperature regulation
Muscles are pieces of soft tissue that help the body move, breathe, swallow, and stay alive. There are three types of muscles in the body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning an individual has control over how and when they move and work. They contribute to maintaining temperature homeostasis in the body by generating heat. Muscle contraction requires energy and produces heat as a byproduct of metabolism. All types of muscles produce heat, but because skeletal muscles constitute 30% to 40% of total body mass, they contribute the most to heat production. This is evident during exercise, when sustained muscle movement causes body temperature to rise.
In cases of extreme cold, shivering produces random skeletal muscle contractions to generate heat as part of the negative feedback mechanism of maintaining body temperature. The body can use skeletal muscle contractions to maintain body temperature when it is cold, but excessive contractions can lead to overheating. This can result in malignant hyperthermia, a condition that develops in genetically susceptible individuals.
Cardiac muscle, or myocardium, makes up the middle layers of the heart. It is an involuntary muscle that squeezes and relaxes to pump blood through the cardiovascular system. Smooth muscles are also involuntary and 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 are also found in the walls of blood vessels, where they help maintain blood pressure by squeezing the stream of blood flowing through the vessels.
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Digestion
The muscular system plays a crucial role in the digestive process, from the beginning to the end of the gastrointestinal (GI) tract. The GI tract is a series of hollow organs, including the oesophagus, stomach, small intestine, and large intestine, that are surrounded by layers of muscle. These muscles contract and relax in a wave-like motion called peristalsis, which pushes food and liquid through the GI tract.
At the start of the digestive process, the muscles of the jaw and tongue break down food into smaller pieces, and the throat muscles help move the food down the oesophagus. Once in the stomach, the muscles there mix the food with digestive juices, breaking it down further. The stomach muscles, or smooth muscles, contract irregularly, churning food through a grinding motion.
As food moves into the small intestine, the muscles there mix the food with digestive juices from the pancreas, liver, and intestine. The small intestine muscles, also smooth muscles, contract regularly and rhythmically to move food through the digestive tract. These contractions also help push waste products of digestion into the large intestine, where water is absorbed, and waste is changed from liquid into stool.
The abdominal organs are surrounded by muscles, including the transverse abdominis, internal obliques, and external obliques. These muscles help compress abdominal contents and aid in regurgitation and defecation. Stress can create chronic abdominal tension and imbalance in these stomach muscles, affecting digestion.
Overall, the muscular system is essential for the mechanical breakdown of food, the movement of food through the GI tract, and the mixing of food with digestive juices.
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Frequently asked questions
Muscles are pieces of soft tissue throughout the body that help us move, breathe, swallow, and stay alive. There are about 600 muscles in the human body, and they work by either contracting or relaxing to cause movement. The three main types of muscle are skeletal, smooth, and cardiac.
Skeletal muscles are the most common type of muscle in the body and are under our conscious control, meaning they are voluntary muscles. They work with bones and joints to give the body power and strength and help with everyday movements such as lifting heavy things and pushing food through the digestive system. They also help with posture and balance.
Smooth and cardiac muscles are involuntary muscles that work without conscious awareness. Smooth muscles are located in various internal structures, including the digestive tract, uterus, and blood vessels. They help with focusing the eyes, moving food through the body, and going to the bathroom. Cardiac muscles make up the heart and contract and relax to pump blood through the body.
