Logan Steele
The human body is home to over 600 muscles, which make up over 40% of our body weight. These muscles are made of soft tissue and stretchy fibres, and they help us do everything from breathing and digesting to moving our bodies and staying alive. There are three types of muscles: skeletal, cardiac and smooth muscle. Skeletal muscles are voluntary muscles that we can control, while cardiac and smooth muscles are involuntary and controlled by our autonomic nervous system. Skeletal muscles are the most common type of muscle in our body, comprising 30% to 40% of our total body mass. They are attached to bones via tendons and help us perform a wide range of movements and functions, from lifting heavy objects to swinging a softball bat. Smooth muscles, on the other hand, are usually found in layers and help with essential functions like digestion and urination.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | More than 600 |
| Muscle composition | Soft tissue and stretchy fibres |
| Muscle functions | Movement, breathing, swallowing, pumping blood, digestion, keeping you alive |
| Types of muscles | Skeletal, cardiac, smooth |
| Skeletal muscle composition | Voluntary muscles that connect to bones via tendons |
| Skeletal muscle functions | Fine and fast movements, maintaining posture, lifting and pushing |
| Smooth muscle composition | Involuntary muscles in sheets or layers |
| Smooth muscle functions | Contraction and relaxation for digestion, urination, vomiting |
| Cardiac muscle composition | Involuntary muscles that contract and relax to pump blood |
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What You'll Learn
Muscles need to contract and relax to allow food to pass through the body
The human digestive system is a complex process involving many organs working together to move food and liquid through the body. The process starts when food is chewed and swallowed, moving from the mouth to the oesophagus, and then to the stomach. The oesophagus uses a process called peristalsis to send food to the stomach. Peristalsis is a type of involuntary muscle movement that occurs in the digestive system, involving the contraction and relaxation of muscles to push food through the body.
The oesophagus is a tube in the centre of the chest, behind the windpipe, and in front of the spine. At the end of the oesophagus, there is a ring-like muscle called the lower oesophageal sphincter, which controls the passage of food and liquid to the stomach. When food reaches the end of the oesophagus, the sphincter relaxes and lets food pass through. This sphincter usually stays closed to prevent food or liquid from flowing back into the oesophagus.
The stomach releases acid and enzymes that break down food, churning and mixing it with digestive juices. The stomach then slowly empties its contents, now a thick liquid called chyme, into the small intestine. The small intestine turns semi-solid food into a fluid to absorb nutrients, with the help of digestive juices from the pancreas and liver. The gallbladder also contributes bile to aid digestion.
The small intestine then sends leftover food waste to the large intestine. The large intestine absorbs water and any remaining nutrients, changing the waste from liquid into stool. The rectum stores the stool until it is pushed out of the body during a bowel movement. Peristalsis continues through the stomach and both intestines, where the process slows down to allow for segmentation, which is the mixing of contents.
The muscle movements of peristalsis are often described as wave-like, as they contract and relax in a continuous pattern to move food forward. The circular muscles squeeze and expand in a synchronised way to push food through the tube, while the longitudinal muscles propel everything forward. The wave-like pattern is more prominent earlier in the digestive process, with only a few contractions needed to push waste out at the end.
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Muscles need to pump blood around the body
The human body is an intricate system that relies on the continuous flow of blood to sustain life. At the heart of this process, literally and metaphorically, is the muscular organ that tirelessly pumps oxygenated blood to every corner of our being. But how does this happen, and what muscles are involved in this vital process?
The heart, nestled under the rib cage and between the lungs, is a muscular powerhouse. It beats, expands, and contracts approximately 100,000 times each day, pumping an astonishing 2,000 gallons of blood throughout the body. This fist-sized organ is composed of cardiac muscle, or myocardium, which forms the middle layers of the heart. The myocardium contracts and relaxes rhythmically, generating the force needed to propel blood through the cardiovascular system. This involuntary muscle works tirelessly, ensuring a constant supply of oxygen-rich blood to our organs and tissues.
While the heart is the primary pump, it doesn't work alone. Skeletal muscles, particularly those in the legs, play a crucial supporting role in blood circulation. When we walk, run, or even stand, the skeletal muscles of the legs contract and relax, compressing the deep-lying veins and increasing blood pressure. This compression, coupled with the presence of one-way valves in the veins, creates a pumping mechanism that prevents blood from pooling in the feet and calves due to gravity. As a result, blood is forced upwards, back towards the heart, ensuring a continuous flow against the force of gravity.
The interplay between the heart's pumping action and skeletal muscle contractions is a harmonious dance that keeps our blood flowing in the right direction. The harder the skeletal muscles work, the more vigorous the blood flow back to the heart. This is why activities like walking or exercising are recommended to promote healthy blood circulation, especially in the legs.
In summary, the heart's muscular walls and the skeletal muscles, particularly in the legs, work in tandem to pump blood around the body. The heart's involuntary contractions set the rhythm, while the skeletal muscles provide crucial support, ensuring that blood flows efficiently against the forces of gravity. Together, they keep us alive and moving forward.
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Muscles need to aid breathing
The diaphragm is a dome-shaped muscle located at the base of the lungs, and it is the most important muscle for breathing. During inhalation, the diaphragm contracts and moves down, increasing the length and diameter of the chest cavity, thereby expanding the lungs. This action also lowers the intrapulmonary pressure, allowing air to rush into the lungs. During exhalation, the diaphragm relaxes, and the lungs recoil to their original volume, causing the air to flow out.
In addition to the diaphragm, several other muscles assist in the breathing process. The intercostal muscles, located between the ribs, aid in breathing by elevating the rib cage during inhalation and relaxing during exhalation, allowing the rib cage to recoil back. The external intercostal muscles are the most superficial layer, while the internal and innermost intercostal muscles lie deeper.
The abdominal muscles are also involved in breathing. They help move the diaphragm and aid in exhalation. Additionally, the accessory inspiratory muscles, such as the sternocleidomastoid, scalenus anterior, pectoralis major, and minor, provide support during inhalation. The neck muscles and pectoral muscles further assist in moving the rib cage and facilitating breathing.
Breathing is a complex process that requires the coordination of various muscles and nerve impulses. The respiratory centre located inside the brain stem tightly controls the action of breathing. During inhalation, the dorsal respiratory group sends impulses to the diaphragm and external intercostal muscles, causing them to contract and expand the thoracic cavity. During exhalation, the dorsal respiratory group stops firing impulses, allowing the muscles to relax and the lungs to recoil.
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Muscles need to help us move
The human body has over 600 muscles, making up over 40% of body weight. These muscles help us move, breathe, swallow, and stay alive. There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle.
Skeletal muscles are the most common type of muscle in the body. They are attached to the bones via tendons and help us perform a wide range of movements and functions. They are voluntary muscles, meaning we can control how and when they work. Skeletal muscles come in many different sizes and shapes, allowing them to perform various tasks. Some of the most powerful skeletal muscles are the calf and thigh muscles, which give us the power to lift and push things. The deltoid muscles in our shoulders help us swing a softball bat or shrug our shoulders. The pectoralis muscles in our upper chest also aid in lifting heavy objects.
Cardiac muscle, also known as myocardium, is the muscle that makes up the heart. It contracts to pump blood out and then relaxes to let blood back in after circulation through the body. Cardiac muscle is an involuntary muscle, working without conscious control.
Smooth muscles are usually found in sheets or layers, with one layer behind the other. They are involuntary muscles, controlled by the autonomic nervous system. Smooth muscles are found in the stomach, digestive system, and bladder, contracting and relaxing to allow food to pass through the body. They also help in vomiting when we are sick and in holding urine until it can be released.
The size of motor units in muscles varies depending on their function. Muscles that perform fine movements, like those in the eyes or fingers, have fewer muscle fibers in each motor unit for improved precision. In contrast, muscles requiring strength, such as leg or arm muscles, have many muscle cells in each motor unit.
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Muscles need to help us swallow
The act of swallowing involves a complex mechanism of muscles, nerves, and reflexes. It is a process that we often take for granted, but it is a highly coordinated action that requires the precise interplay of various muscles. Swallowing is a vital function, as it not only directs food into the digestive tract but also serves as a protector of the airway.
The process of swallowing begins with the lips, which abduct to allow food or liquid to enter the oral cavity. The mandible then elevates, and the lips adduct to contain the food or liquid inside the mouth. This is followed by the stimulation of tactile receptors in the oropharynx, which initiates the swallow reflex. The tongue then plays a crucial role, pushing the food or liquid towards the back of the throat, into the pharynx. This is the first irreversible step in the swallowing mechanism, and it is under voluntary muscle control.
The pharyngeal phase involves a wave of coordinated stimuli lasting about a second. Efferent muscle fibers innervate the muscles of the larynx, pharynx, and esophagus to ensure a smooth transition of food from the mouth to the pharynx and then into the esophagus. The larynx and pharynx move down and then back up to their relaxed positions by elastic recoil. This movement requires the coordinated action of many muscles, including the hyoid.
To swallow effectively, the muscles involved in this process need to be strong and mobile. Tongue-strengthening exercises can help improve an individual's swallowing ability, especially when combined with other swallowing exercises. Larynx-lifting exercises are another type of swallowing exercise that can increase the strength and mobility of the laryngeal muscles, improving the ability to swallow. These exercises are often prescribed by healthcare providers and SLPs (speech-language pathologists) to treat dysphagia, a condition characterized by difficulty swallowing.
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Frequently asked questions
Muscles are pieces of soft tissue that help the body move, breathe, swallow, pump blood, and stay alive. There are over 600 muscles in the human body, and they work by contracting and relaxing.
When you decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract. The muscle then relaxes when the signal stops. This process is regulated by a protein called troponin.
When you bend your elbow, the bicep muscle contracts, and the tricep muscle relaxes. When you straighten your elbow, the tricep contracts, and the bicep relaxes. Cardiac muscles in the heart contract and relax to pump blood through the body.
