Victor Forge
The human body is an intricate machine, and muscles are the driving force behind most of its movements. Muscles are tissues that contract and relax to enable various functions, from the obvious actions like walking and running to more subtle tasks like eye movements and facial expressions. The muscular system, comprising skeletal, cardiac, and smooth muscles, is responsible for our body's posture, stability, and even heat production. While the skeletal muscles are under our conscious control, the cardiac and smooth muscles work involuntarily to keep our organs functioning without us thinking about it. This includes everything from breathing and speaking to pumping blood through our hearts. So, are muscles an organ system? Let's delve into the fascinating world of our bodies to find out.
| Characteristics | Values |
|---|---|
| Definition | The muscular system is composed of specialized cells called muscle fibers. |
| Function | The main function of the muscular system is movement. Muscles are the only tissue in the body that has the ability to contract and therefore move the other parts of the body. |
| Types of Muscle | There are three types of muscles in the body: skeletal, cardiac, and smooth muscle. |
| Types of Movement | Muscles perform two types of movements: voluntary and involuntary. |
| Muscle Composition | Muscles are made of thousands of small fibers woven together. |
| Muscle Tissue | Smooth muscle tissue lines some of the organs, but most organs are also made of other types of tissue. |
| Muscle Groups | Healthcare providers often group muscles by their location (e.g. chest, leg, or back muscles) or by the type of movement they perform (e.g. abductors, flexors, or extensors). |
| Muscle Control | Skeletal muscles are voluntary muscles, meaning an individual can control how and when they move and work. Cardiac and smooth muscles are involuntary. |
| Muscle Mass | Skeletal muscles comprise 30% to 40% of total body mass. |
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What You'll Learn
- Skeletal muscles are voluntary that help with movement and function
- Cardiac muscle is an involuntary muscle that pumps blood through the body
- Smooth muscle is an involuntary muscle that lines the inside of some organs
- Muscle contraction is caused by nerve impulses and regulated by the nervous system
- Muscles are composed of muscle fibres and are surrounded by connective tissue
Skeletal muscles are voluntary that help with movement and function
The human body has three types of muscles: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles, meaning an individual can control how and when they move and work. They are attached to bones by tendons and help with movement and function. Skeletal muscles comprise 30% to 40% of an individual's total body mass and are the most common type of muscle in the body.
Skeletal muscles are composed of muscle cells, called muscle fibres, which are in turn made up of myofibrils. Myofibrils are composed of sarcomeres, the basic building blocks of striated muscle tissue. Upon stimulation by an action potential, skeletal muscles contract in a coordinated manner by shortening each sarcomere. The actin and myosin fibres within the sarcomere overlap in a contractile motion towards each other. The myosin filaments have club-shaped heads that project towards the actin filaments, providing attachment points on binding sites. The myosin heads then swivel towards the centre of the sarcomere, detach, and reattach to the nearest active site of the actin filament. This is known as a ratchet-type drive system.
The contraction of skeletal muscles is controlled by the somatic nervous system, which sends signals to make them function. Skeletal muscles are responsible for producing movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilising joints. They also play a role in basal energy metabolism, serving as a storage site for essential substrates such as carbohydrates and amino acids.
Additionally, skeletal muscles contribute to the production of body heat, which is a by-product of muscular activity. In response to extreme cold, muscles are signalled to contract and produce shivering to generate heat. Skeletal muscles also have a short-term energy store in the form of creatine phosphate, which can regenerate ATP when needed. They also store glucose in the form of glycogen, which can be rapidly converted to glucose during periods of high-energy demand.
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Cardiac muscle is an involuntary muscle that pumps blood through the body
The human body contains three kinds of muscle tissue: skeletal, smooth, and cardiac. Cardiac muscle, also called the myocardium, is one of three major categories of muscles found within the human body. It is a specialized, organized type of tissue that exists only in the heart.
Cardiac muscle is an involuntary muscle. This means that its movements are automatic and cannot be controlled by a person. The heart also contains specialized types of cardiac tissue containing "pacemaker" cells. These contract and expand in response to electrical impulses from the nervous system. The pacemaker cells control heart rate and determine how fast the heart pumps blood.
Cardiac muscle tissue gets its strength and flexibility from its interconnected cardiac muscle cells, or fibers. These interconnections allow the cardiomyocytes to contract together synchronously to enable the heart to work as a pump. Each cardiomyocyte needs to contract in coordination with its neighboring cells, working to efficiently pump blood from the heart. If this coordination breaks down, the heart may not pump at all, as may occur during abnormal heart rhythms such as ventricular fibrillation.
The heart is made up of three layers: the pericardium, myocardium, and endocardium. The cardiac muscle forms a thick middle layer between the outer layer of the heart wall (the pericardium) and the inner layer (the endocardium). The endocardium is not cardiac muscle and is comprised of simple squamous epithelial cells and forms the inner lining of the heart chambers and valves. The pericardium is a fibrous sac surrounding the heart, consisting of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium. The cardiac muscle is responsible for the contractility of the heart and, therefore, the pumping action. The cardiac muscle must contract with enough force and blood to supply the metabolic demands of the entire body.
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Smooth muscle is an involuntary muscle that lines the inside of some organs
Smooth muscle plays an important role in many organ systems, including the female and male reproductive systems, the urinary system, the respiratory system, and the digestive system. In the cardiovascular system, for example, smooth muscle helps to maintain blood pressure and flow by contracting to regulate the lumenal diameter of small arteries and arterioles. It also contributes to the regulation of blood flow and vessel stability. In the digestive system, smooth muscle contracts in a rhythmic peristaltic fashion, forcing foodstuffs through the digestive tract.
Smooth muscle is also involved in the movement of waste through the intestines and helping the lungs expand during breathing. In the skin, smooth muscle cells cause hair to stand erect in response to cold temperatures or fear. Smooth muscle is even involved in the disease process throughout the body, such as in the case of asthma, which results from smooth muscle contraction. Additionally, medications can act on smooth muscle, such as bronchodilators, which relax airway smooth muscle, and metoclopramide, which stimulates gastric emptying by increasing smooth muscle signalling.
Smooth muscle is controlled and influenced by a combination of different neural elements, including the autonomic nervous system, hormones, and local chemical signals. This allows for gradual and sustained contractions, which are important for maintaining organ dimensions and contractile tone in organs like the urinary bladder. Smooth muscle is distinct from skeletal muscle, which is voluntary and composed of muscle fibres that are laterally connected, and cardiac muscle, which is found only in the heart.
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Muscle contraction is caused by nerve impulses and regulated by the nervous system
The human body is capable of two types of movements: voluntary and involuntary. Voluntary movements are actions that we consciously control, such as sprinting or scrolling through articles on a phone. These movements are controlled by the nervous system. Involuntary movements, on the other hand, happen automatically without conscious thought, such as the beating of the heart or the movement of waste through the intestines. These movements are controlled by the unconscious part of the brain.
The muscular system is responsible for movement and the maintenance of posture and body position. There are over 600 muscles located throughout the human body, and they are the only tissue capable of contraction, allowing for movement of the other body parts. The heart is the only organ that is also a muscle, composed of cardiac muscle tissue. This tissue is under involuntary control, as are smooth muscles, which line some organs and control essential functions such as breathing and digestion.
Muscle contraction is initiated by nerve impulses from the nervous system. These impulses, called action potentials, travel through motor neurons to the neuromuscular junction, where the neuron reaches a muscle cell. When the impulse reaches the neuromuscular junction, a chemical message, or neurotransmitter, called acetylcholine is released. Acetylcholine binds to receptors on the outside of the muscle fiber, starting a chemical reaction within the muscle. This reaction causes a reorganization of the proteins inside the muscle fibers, leading to contraction and relaxation.
The contractile motion of muscle fibers is described by the sliding filament model of muscle contraction. Actin and myosin fibers, which make up striated muscle, overlap and move towards each other in a coordinated, ratchet-type drive system. Calcium ions are required for this process, as they facilitate the interaction between actin and myosin. The release of calcium ions from the sarcoplasmic reticulum into the sarcomere, a part of the muscle fiber, causes the actin-binding sites to be uncovered. When the muscle no longer needs to contract, the calcium ions are pumped back into storage in the sarcoplasmic reticulum.
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Muscles are composed of muscle fibres and are surrounded by connective tissue
The human body is composed of several organ systems, one of which is the muscular system. The muscular system is responsible for all body movements, as well as the maintenance of posture and body position. The heart is the only organ that is also a muscle.
Skeletal muscle fibres are organised into bundles called fascicles, which are surrounded by a middle layer of connective tissue called the perimysium. Each individual muscle fibre is encased in a thin layer of connective tissue called the endomysium, composed of collagen and reticular fibres. The endomysium surrounds the extracellular matrix of the cells and plays a role in transferring force produced by the muscle fibres to the tendons. The outermost layer of connective tissue covering each muscle is called the epimysium.
The connective tissue covering provides support and protection for the delicate muscle cells and allows them to withstand the forces of contraction. The collagen in the three connective tissue layers intertwines with the collagen of a tendon, which attaches the muscle to a bone, making movement possible.
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Frequently asked questions
Yes, the muscular system is an organ system. Each muscle is an organ of the muscular system and consists of skeletal muscle tissue, connective tissue, nerve tissue, and blood or vascular tissue.
The main function of the muscular system is movement. Muscles are the only tissue in the body that can contract and therefore move the other parts of the body.
There are three types of muscles in the body: skeletal, cardiac, and smooth muscle. Skeletal muscles are voluntary muscles that you can control, while cardiac and smooth muscles are involuntary.
Involuntary movements are actions that happen automatically without conscious thought. Examples include breathing, digesting food, and getting rid of waste.
Voluntary movements are actions that you consciously control. Examples include sprinting, lifting something heavy, or even just flicking your thumb to scroll through articles on your phone.
