Victor Forge
The muscular system is an organ system that enables the body to move, maintain posture, and circulate blood. While the muscular system is generally controlled by the nervous system, some muscles, such as the cardiac muscle, can be completely autonomous. These involuntary muscles are controlled by the autonomic nervous system, which manages unconscious tasks such as breathing, heartbeat, and digestion. In contrast, skeletal muscles are voluntary muscles, meaning that individuals control how and when they move and work.
| Characteristics | Values |
|---|---|
| Muscular system controlled by | Nervous system |
| Types of muscles | Skeletal, cardiac, smooth |
| Skeletal muscles | Voluntary |
| Cardiac muscles | Involuntary, autonomous |
| Smooth muscles | Involuntary |
| Muscle contraction | Caused by actin sliding against myosin |
| Muscle relaxation | Caused by actin sliding against myosin |
| Skeletal muscle contraction | Stimulated by nervous impulses |
| Skeletal muscle contraction | Stimulated by acetylcholine |
| Smooth muscle contraction | Stimulated by acetylcholine |
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What You'll Learn
Cardiac muscle is autonomous
The muscular system is an organ system consisting of skeletal, smooth, and cardiac muscle. While the muscular system in vertebrates is generally controlled by the nervous system, cardiac muscle, or heart muscle, is unique in that it can be completely autonomous. This means that it does not contract as a result of conscious effort. Instead, the heart's contractions are involuntary and occur without conscious thought.
Cardiac muscle, also called the myocardium, is one of the three major categories of muscles in the human body, along with smooth muscle and skeletal muscle. The heart is made up of three layers: the pericardium, myocardium, and endocardium. The endocardium is not cardiac muscle but rather a simple squamous epithelial cell layer that forms the inner lining of the heart chambers and valves. The pericardium, on the other hand, is a fibrous sac surrounding the heart and consists of the epicardium, pericardial space, parietal pericardium, and fibrous pericardium.
The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. This force is termed cardiac output and is defined as heart rate multiplied by stroke volume, which is determined by the contractile forces of the cardiac muscle and the frequency of their activation. The contractile functions of the heart require ATP, which can be obtained from various substrates, including fatty acids, carbohydrates, proteins, and ketones.
Cardiac muscle cells, or cardiomyocytes, are striated, branched, and contain many mitochondria. They are responsible for the contractility of the heart, which is facilitated by the presence of sarcomeres. The coordinated contractions of cardiac muscle cells are made possible by gap junctions, which allow for the propagation of electrical impulses from one cell to the next. These impulses are essential for maintaining the structural integrity of the heart and ensuring the proper functioning of the cardiac muscle.
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Skeletal muscles are voluntary
Skeletal muscles are under voluntary control, meaning that they can be consciously controlled. These muscles are attached to bones, such as the muscles in the arms, legs, neck, back, and trunk. They are responsible for producing movement, sustaining body posture and position, maintaining body temperature, storing nutrients, and stabilizing joints. Skeletal muscle comprises approximately 40% of the human body weight and contains 50-75% of all body proteins.
The contraction of skeletal muscle is stimulated by nervous impulses that release acetylcholine at the neuromuscular junction, creating action potentials along the cell membrane. Acetylcholine is a neurotransmitter that binds to receptors on the surface of the muscle cell, leading to the release of calcium from its storage area in the cell's sarcoplasmic reticulum. This results in a single, short muscle contraction called a muscle twitch. Skeletal muscle is composed of muscle cells, called muscle fibers, which are in turn made up of myofibrils. These myofibrils are composed of sarcomeres, the basic building blocks of striated muscle tissue.
The brain plays a crucial role in voluntary muscle control by sending signals, in the form of action potentials, through the nervous system to the motor neurons that innervate the muscle fibers. These signals can also originate from the spinal cord in the case of reflexes, which are fast, unconscious muscular reactions to unexpected physical stimuli. Nerves communicate with skeletal muscles through the release of neurotransmitters at the neuromuscular junction, allowing for conscious control of muscle movement.
Disorders of the voluntary skeletal muscles, such as muscular dystrophies, congenital myopathies, and inflammatory disorders, can result in significant muscle weakness, atrophy, or pain. These disorders may be caused by genetic factors or problems with the immune system. Additionally, issues with voluntary control can indicate underlying health conditions, such as neuromuscular disorders or electrolyte imbalances.
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Smooth muscles are involuntary
Smooth muscles, also known as involuntary muscles, are one of the three types of muscles in the body, the other two being skeletal and cardiac muscles. Smooth muscles are found in the walls of hollow organs like the stomach, intestines, bladder, and uterus, as well as in the tracts of the respiratory, urinary, and reproductive systems. They are also present in the eyes, skin, and blood and lymph vessels (excluding capillaries).
Smooth muscle cells are spindle-shaped with a single, centrally located nucleus, and unlike skeletal muscles, they do not show cross stripes under microscopic magnification. They contract slowly and automatically, and this contraction is necessary for the functioning of internal organs and the digestive system. For example, in the gastrointestinal tract, smooth muscles work together with interstitial cells of Cajal (ICCs) and platelet-derived growth factor receptor alpha (PDGFRα) to push food through the digestive system. Smooth muscles also help regulate pupil size, cause hair to stand erect in response to cold or fear, and play a role in the menstrual cycle.
The unique structure of smooth muscles gives them greater elasticity and the ability to stretch while maintaining contractility, which is crucial for organs like the intestines and urinary bladder. Smooth muscles differ from skeletal and cardiac muscles in terms of structure, function, regulation of contraction, and excitation-contraction coupling. While smooth muscle contractions are often stimulated by the neurotransmitter acetylcholine, they are controlled and influenced by a combination of neural elements, with some degree of cell-to-cell communication and local production of activators and inhibitors.
Smooth muscles are considered involuntary because their contractions are not typically the result of conscious effort or signals originating from the brain. Instead, they are autonomic and function without conscious thought, much like the contractions of the heart. This autonomous nature of smooth muscles is essential for the body's survival and maintenance of vital functions.
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Autonomic nervous system controls unconscious tasks
The autonomic nervous system is a network of nerves that controls unconscious processes in the body. These are vital functions that occur without conscious thought, such as breathing, heart rate, blood pressure, and digestion. The autonomic nervous system is always active, even when an individual is asleep, and is essential for survival. It is a part of the overall nervous system that connects the brain to most internal organs.
The autonomic nervous system can be further divided into two subsystems: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system activates bodily processes that aid in times of stress or danger, triggering the body's "fight-or-flight" response. On the other hand, the parasympathetic nervous system promotes ""rest-and-digest" processes, essentially doing the opposite of the sympathetic nervous system.
The autonomic nervous system has a wide range of effects on the body's systems. For example, it manages the width of the airways and the network of passages that carry air into and out of the lungs. It also controls the muscles that cause hair to stand up, commonly known as "goosebumps." Additionally, it regulates the width of blood vessels, tear production in the eyes, and the running of the nose.
While the autonomic nervous system primarily operates unconsciously, some aspects can be brought under conscious control. For instance, individuals can choose to hold their breath or swallow rapidly. However, certain functions, such as altering heart rate or blood pressure, are not under conscious control.
The muscular system, which includes skeletal, smooth, and cardiac muscle, is typically controlled by the nervous system. However, some muscles, particularly the cardiac muscle, can act completely autonomously. This autonomy allows for necessary functions like the contraction of the heart and peristalsis, which pushes food through the digestive system.
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Muscles are contractile tissue
Skeletal muscles are attached to the skeleton and are under voluntary control. They are responsible for supporting your weight and moving your body. When you want to move a part of your body, the brain sends signals through the nervous system to the motor neuron that innervates the skeletal muscle fibre, causing it to contract.
Smooth muscle fibres are located in the walls of hollow visceral organs, such as the liver, pancreas, and intestines. They are under involuntary control and help to move your organs and keep your body working properly.
Cardiac muscle, also known as myocardium, makes up the middle layers of the heart. The heart is the only organ in the body that is also a muscle. It is under involuntary control and beats thousands of times a day to keep you alive.
There are also different types of muscle fibres within these categories, such as Type I and Type II muscle fibres, which differ in their contractile speed and ability to sustain aerobic activity.
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Frequently asked questions
Yes, some muscles, like cardiac muscle, can be completely autonomous.
The muscular system permits movement of the body, maintains posture, and circulates blood throughout the body.
There are three basic types of muscles in the body: smooth, cardiac, and skeletal.
Skeletal muscles are voluntary muscles, meaning you control how and when they move and work. They comprise 30 to 40% of your total body mass.
The autonomic nervous system is a network of nerves that handle unconscious tasks like heartbeat, breathing, blood pressure, and digestion. It is a key part of your survival processes and is always active, even when you're asleep.
