Victor Forge
The human body is home to over 600 muscles, which make up around 30-40% of our total body mass. These muscles are responsible for a wide range of movements and functions, from helping us breathe, swallow, and digest food, to pumping blood through our cardiovascular system. But what about the muscles that move our internal organs? These muscles are known as visceral or smooth muscles, and they line the inside of our organs and blood vessels. Smooth muscles are found in the stomach, intestines, and blood vessels, where they aid in digestion, nutrient collection, and circulation. They are controlled involuntarily, meaning we don't have to think about making them work. In this way, smooth muscles work tirelessly to keep our bodies functioning properly.
| Characteristics | Values |
|---|---|
| Types of muscle tissue | Visceral, cardiac, and skeletal |
| Location of visceral muscle tissue | Stomach, intestines, blood vessels, liver, pancreas, and other visceral organs |
| Control of visceral muscle tissue | Involuntary |
| Location of cardiac muscle tissue | Middle layers of the heart |
| Control of cardiac muscle tissue | Involuntary |
| Location of skeletal muscle tissue | Attached to bones throughout the body, including the eye, neck, arm, shoulder, back, chest, leg, abdomen, and hamstring |
| Control of skeletal muscle tissue | Voluntary |
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Skeletal muscles
Skeletal muscle is the only voluntary muscle tissue in the human body and is controlled consciously. Every physical action that a person consciously performs requires skeletal muscle. For example, if you reach for a book on a shelf, you are using skeletal muscles in your neck, arm, and shoulder. Running, chewing, and writing are also examples of activities that require skeletal muscles.
Six skeletal muscles around the eye control its movements. These muscles work quickly and precisely and allow the eye to move. Muscles in the torso also protect the internal organs at the front, sides, and back of the body.
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Cardiac muscles
The human body has three types of muscles: skeletal, cardiac, and smooth muscle. The cardiac muscle, also called the myocardium, is a thick middle layer of the heart, sandwiched between the inner endocardium and the outer epicardium (or visceral pericardium). The heart is the only organ that is also a muscle, and it is the only place in the body that has cardiac tissue.
Cardiac muscle is an involuntary, striated muscle, meaning it works without conscious thought. It is composed of individual cardiac muscle cells called cardiomyocytes, which are joined by intercalated discs. Cardiomyocytes are tubular structures made up of chains of myofibrils, which are rod-like units within the cell. The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells. Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments. Thin myofilaments contain the protein actin, and thick myofilaments contain the protein myosin.
The primary function of the cardiac muscle is to pump blood into circulation by generating sufficient force. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. The cardiac muscle must contract with enough force to pump blood through the cardiovascular system and meet the metabolic demands of the entire body.
The coordinated contraction of cardiomyocytes is essential for the pumping action of the heart. Gap junctions between adjacent cardiomyocytes allow for the propagation of electrical impulses, which trigger the release of calcium from the sarcoplasmic reticulum. This release of calcium causes the myofilaments to slide past each other in a process called excitation-contraction coupling, resulting in the contraction of the heart and the generation of force.
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Smooth muscles
Smooth muscle is one of the three main types of muscle in the body, the other two being skeletal and cardiac. It is a type of muscle tissue that works automatically and is found throughout the body. Smooth muscle is controlled by the autonomic nervous system and is, therefore, an involuntary muscle that moves without conscious thought.
Smooth muscle is involved in some of the body's most important functions, including blood pressure and circulation, digestion, and vision. It is also involved in the body's automated self-management processes, such as waste removal and toxin elimination through the urinary system. Smooth muscle is found in the stomach, intestines, and blood vessels, where it helps with digestion and nutrient collection. It also plays a vital role in the regulation of blood pressure and tissue oxygenation.
Smooth muscle cells have a unique structure, with narrow ends, a wider middle, and a shorter length compared to skeletal muscle cells. They have thick and thin filaments that do not arrange into sarcomeres, resulting in a non-striated pattern. On microscopic examination, smooth muscle appears homogeneous. The cytoplasm of smooth muscle contains large amounts of actin and myosin, which are the main proteins involved in muscle contraction.
Smooth muscle is also involved in passage width control within the body. It can flex together to push substances through tubelike passages, such as in the digestive tract. Smooth muscle in sphincters, such as the bladder or anus, stays flexed and only relaxes when needed. Additionally, smooth muscle plays a role in skin functions, such as causing goosebumps, and in eye functions, such as controlling the dilation and constriction of pupils.
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Visceral muscles
The human body is made up of about 700 named muscles, which constitute roughly half of a person's body weight. These muscles are classified into three types: skeletal, cardiac, and visceral.
Smooth muscle is further divided into two types: single-unit and multi-unit. Most smooth muscle is of the single-unit type, found in the walls of most internal organs, lining blood vessels, the urinary tract, and the digestive tract. It is controlled by the autonomic nervous system and works without conscious thought, ensuring the body's survival.
In contrast, skeletal muscles are voluntary muscles that move in response to conscious thought. They make up 30-40% of total body mass and are connected to bones through tendons, enabling a wide range of movements. Cardiac muscle, on the other hand, is found only in the heart and is responsible for pumping blood through the cardiovascular system.
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Involuntary muscles
There are three types of muscles in the human body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning you control how and when they move and work. Cardiac and smooth muscle are involuntary muscles. Cardiac muscle is found only in the heart and aorta. Smooth muscles are found in most hollow internal organs and blood vessels. Smooth muscles are the nonstriated involuntary muscles that line the viscera or the internal hollow organs like the urinary tract, blood vessels, and intestinal tract. The ciliary muscle present in the eye is an example of a smooth muscle. Cardiac muscles never regenerate when injured, while smooth muscles can.
The heart is the only organ that is also a muscle. It is made of a special type of muscle tissue called cardiac muscle. The heart is the only place in the body that has cardiac tissue. The heart is an involuntary muscle—it beats on its own without your input. Cardiac muscle squeezes and relaxes to pump blood through your cardiovascular system. Cardiac muscle is innervated by the autonomic nervous system through the cardiac pacemaker. Cardiac muscle is controlled by both the autonomic nervous system and its own pacemaker cells, causing it to contract automatically and rhythmically.
Smooth muscles are found lining the internal organs (such as the oesophagus, stomach, intestines, etc.) and blood vessels. Smooth muscles are made up of thick and thin filaments that are not arranged into sarcomeres, resulting in a nonstriated pattern. Smooth muscles also have a calcium-containing sarcoplasmic reticulum. This is responsible for prolonged contraction. Smooth muscles play an important role in many body systems, including the female and male reproductive systems, and the urinary system.
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Frequently asked questions
There are three types of muscles in the human body: skeletal, smooth, and cardiac. Skeletal muscles are the only muscles that can be consciously controlled. Smooth muscles, also known as visceral muscles, are found in the walls of hollow visceral organs such as the liver, pancreas, stomach, and intestines. Cardiac muscles are located in the walls of the heart and are under involuntary control.
Skeletal muscles are attached to bones and allow you to perform a wide range of movements and functions. They are the only voluntary muscle tissue in the human body and are controlled consciously.
Smooth muscles are found throughout the body and serve a variety of functions. They line the inside of blood vessels and visceral organs, helping with digestion and nutrient collection, maintaining blood circulation, and ridding the body of toxins. Smooth muscles act involuntarily and cannot be consciously controlled.
Cardiac muscles are located in the walls of the heart and are under involuntary control. They squeeze and relax to pump blood through the cardiovascular system.
