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The human body is made up of more than 600 muscles, which help us move, breathe, swallow, pump blood, and stay alive. There are three types of muscles: skeletal, cardiac, and smooth muscles. Skeletal muscles are voluntary muscles, which means we control how and when they move. They make up 30-40% of our body weight and are attached to our bones by tendons. Cardiac and smooth muscles are involuntary muscles, controlled by the autonomic nervous system. They work without our conscious thought, such as when our heart beats. The brain, nerves, and skeletal muscles work together to cause movement, and this is known as the neuromuscular system.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Types of muscles | Skeletal, cardiac, and smooth muscle |
| Muscle movement | Voluntary and involuntary |
| Muscle composition | Thousands of small fibres woven together |
| Muscle fibres | Actin (thin filaments), myosin (thick filaments), and support proteins |
| Muscle functions | Movement, breathing, swallowing, pumping blood, supporting joints, maintaining posture, balance, and temperature |
| Muscle disorders | Myopathy, muscular dystrophy, congenital myopathies, inflammatory disorders, etc. |
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What You'll Learn
- Skeletal muscles are controlled by the brain, nerves and motor neurons
- Cardiac muscles are controlled by the autonomic nervous system
- Smooth muscles are controlled by the autonomic nervous system, hormones and local chemical signals
- Muscles that perform fine movements, like those of the eyes, are controlled by the brain
- Muscles are controlled by the release of neurotransmitters
Skeletal muscles are controlled by the brain, nerves and motor neurons
Skeletal muscles are a type of voluntary muscle, meaning that humans can control how and when they move and work. They are the most common type of muscle in the body, comprising 30% to 40% of total body mass. These muscles are attached to bones and allow us to perform a wide range of movements and functions. For example, when you reach for a book on a shelf, you are using the skeletal muscles in your neck, arm, and shoulder.
The brain plays a crucial role in controlling skeletal muscles. Motor centers in the brain, along with the spinal cord, regulate skeletal muscle tonus, a constant state of slight tension that keeps the muscle ready for activation. When a person intends to perform a physical action, the brain sends signals to the muscles via motor neurons, leading to muscle contraction and the desired movement.
Motor neurons are essential in the control of skeletal muscles. Each skeletal muscle fiber is innervated by only one motor neuron, forming a motor unit. When a motor neuron is activated, it sends impulses to the muscle fibers it innervates, leading to the generation of electrical signals and subsequent contraction of the muscle fibers. This process allows for coordinated and controlled movements.
Additionally, nerves are integral to the control of skeletal muscles. The somatic nervous system sends signals to make skeletal muscles function. Specifically, somatic motor nerves carry signals in the form of nerve impulses to stimulate the contraction of skeletal muscles. This neural control is crucial for the voluntary movement of skeletal muscles.
In summary, skeletal muscles are controlled by a complex interplay between the brain, motor neurons, and nerves. This coordination allows for the voluntary activation and precise control of skeletal muscles, enabling humans to perform a diverse range of movements and activities.
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Cardiac muscles are controlled by the autonomic nervous system
The human body has more than 600 muscles that help us perform a wide range of functions, from pumping blood and supporting movement to lifting heavy weights. There are three types of muscles in the body: skeletal, cardiac, and smooth muscles. While skeletal muscles are voluntary muscles, cardiac and smooth muscles are involuntary.
Cardiac muscles, also known as myocardium, make up the middle layers of the heart. They contract and relax without our conscious awareness. The cardiac muscles are controlled by the autonomic nervous system (ANS), which is the component of the peripheral nervous system that controls cardiac muscle contraction, visceral activities, and glandular functions of the body. The ANS can regulate heart rate, blood pressure, rate of respiration, body temperature, sweating, gastrointestinal motility, and secretion, as well as other visceral activities that maintain homeostasis.
The ANS functions continuously without conscious effort. It has two interacting systems: the sympathetic and parasympathetic systems. The sympathetic system prepares the body for energy expenditure, emergency, or stressful situations, i.e., the \"fight or flight\" response. On the other hand, the parasympathetic system has inhibitory effects on heart functions. The ANS influences most heart functions by affecting the SA node, AV node, myocardium, and small and large vessel walls.
The cardiac plexus, a complex network of nerves, is part of the autonomic nervous system that controls the heart. It consists of sympathetic, parasympathetic, and cardiac nerves, as well as some tiny parasympathetic ganglia, which all work together to control cardiac activity. The cardiac plexus is divided into two parts: the superficial part, located in the aortic arch concavity, and the deep part, located between the trachea and the aortic arch. Both parts are connected to provide cardiac autonomic innervation.
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Smooth muscles are controlled by the autonomic nervous system, hormones and local chemical signals
Smooth muscles, unlike skeletal muscles, are involuntary muscles that are controlled by the autonomic nervous system. They are sheets or layers of smooth muscle cells that line the walls of various organs and tubes in the body, including the blood vessels, stomach, intestines, bladder, airways, uterus, and the penile and clitoral cavernosal sinuses. Smooth muscles also attach to the hairs of the skin and to the iris and lens of the eye.
The autonomic nervous system controls the contractile state of smooth muscles, which is also influenced by hormones and local chemical signals. The nervous system uses hormones, neurotransmitters, and other receptors to control smooth muscle spontaneously. For example, the use of bronchodilators to relax airway smooth muscle is a life-saving treatment for asthmatics. Similarly, medications like metoclopramide can stimulate and promote gastric emptying by increasing smooth muscle signalling.
Smooth muscle contraction is initiated by a Ca2+-calmodulin interaction, which stimulates the phosphorylation of the light chain of myosin. This interaction is signalled by the RhoA/Rho kinase pathway, which maintains force generation by inhibiting the dephosphorylation of the light chain by myosin phosphatase. The removal of Ca2+ from the cytosol and the stimulation of myosin phosphatase initiate the process of smooth muscle relaxation.
Smooth muscles play a vital role in the body's subsystems, such as the regulation of blood pressure and tissue oxygenation, digestion, and nutrient collection. They also help the body get rid of toxins and maintain electrolyte balance. Smooth muscles are essential for basic bodily functions, and their widespread presence throughout the body makes them an important area of study for medical professionals.
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Muscles that perform fine movements, like those of the eyes, are controlled by the brain
The human body has over 600 muscles that help us move, breathe, swallow, and stay alive. There are three types of muscles in the body: skeletal, cardiac, and smooth muscle. Skeletal muscles, which are voluntary muscles, make up 30% to 40% of our total body mass. They are attached to bones and allow us to perform a wide range of movements. We can control how and when these muscles work. For example, when we reach for a book on a shelf, we are using the skeletal muscles in our neck, arm, and shoulder.
On the other hand, cardiac and smooth muscles are involuntary muscles controlled by the autonomic nervous system. They work without our conscious thought, such as the muscles in our urinary system that help eliminate waste and toxins from our bodies.
The brain plays a crucial role in controlling muscles and initiating body movements. It sends and receives chemical and electrical signals throughout the body, and different signals control different processes. The brain is responsible for interpreting these signals, which can evoke various responses, from feeling tired to experiencing pain.
The brain also plays a specific role in controlling the fine movements of the eyes. The cortex, particularly the frontal cortex, is involved in controlling voluntary eye movements. Within the frontal cortex, regions like the frontal eye field (FEF) and the supplementary eye field (SEF) are part of the oculomotor circuit and play a critical role in eye movement control. Additionally, the parietal lobe, specifically the posterior part known as the PPC, is also implicated in the control of saccades and attention, contributing to the coordination of eye movements and visual focus.
In summary, muscles, particularly skeletal muscles, enable us to perform various movements, both voluntary and involuntary. The brain is integral to this process, sending and interpreting signals that govern muscle contractions and facilitate precise actions, such as the delicate movements of the eyes.
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Muscles are controlled by the release of neurotransmitters
The human body is composed of more than 600 muscles, which are pieces of soft tissue that help us move, breathe, swallow, pump blood, and stay alive. There are three types of muscles in the body: skeletal, cardiac, and smooth muscle.
Skeletal muscles are voluntary muscles, meaning that we can control how and when they move and work. These muscles are attached to our bones and allow us to perform a wide range of movements and functions. Skeletal muscles comprise approximately 30% to 40% of our total body mass. They are controlled by our somatic nervous system, which sends signals to make them function.
Cardiac and smooth muscles, on the other hand, are involuntary muscles that are controlled by our autonomic nervous system. These muscles work without our conscious thought, such as the muscles in our urinary system that help rid our bodies of waste and toxins.
The contraction of skeletal muscles is stimulated by the release of neurotransmitters from motor neurons. These motor neurons attach to skeletal muscles at a point called the neuromuscular junction (NMJ) and release neurotransmitter chemicals that bond to the motor end plate. The muscles continue to contract as long as they are stimulated by these neurotransmitters. When the release of neurotransmitters stops, the process of contraction reverses, and the muscle returns to its resting state.
The strength of a muscle's contraction can be controlled by two factors: the number of motor units involved in the contraction and the amount of stimulus from the nervous system. Muscles that require fine motor control, such as those in the eyes or fingers, have fewer muscle fibers in each motor unit, allowing for more precise control. In contrast, muscles that require more strength, such as leg or arm muscles, have many muscle cells in each motor unit.
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Frequently asked questions
Muscles are controlled by the nervous system. There are two types of muscle movement: voluntary and involuntary. Voluntary movements are actions that you control, such as sprinting or scrolling through your phone. Involuntary movements happen automatically, such as your heart beating or breathing.
Voluntary muscles are also known as skeletal muscles. Skeletal muscles are attached to bones and allow you to perform a wide range of movements. Examples include your shoulder muscles, hamstring muscles, and abdominal muscles.
Involuntary muscles include cardiac and smooth muscles. Smooth muscles are located in the digestive tract, uterus, and blood vessels. Cardiac muscles are specific to the heart and are controlled by the sinus node influenced by the autonomic nervous system.
