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The human body has over 600 muscles that help us move, breathe, swallow, and stay alive. These muscles are attached to bones and help us perform a wide range of movements and functions. Skeletal muscles, which are voluntary, make up 30-40% of our total body mass. They are controlled by our somatic nervous system. On the other hand, cardiac and smooth muscles are involuntary and are controlled by our autonomic nervous system. Muscle actions can be classified into concentric, eccentric, and isometric actions. Concentric actions occur when the proximal and distal muscle attachments move towards each other, while eccentric actions refer to the opposite movement. Isometric actions, meanwhile, involve no relative movement between the attachments, with the muscle length remaining constant.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | Over 600 |
| Muscle function | Help the body move, breathe, swallow, and stay alive |
| Types of muscles | Skeletal, cardiac, and smooth |
| Types of muscle action | Concentric, eccentric, and isometric |
| Types of muscle "contraction" | Isotonic, isometric, isokinetic, and isoinertial |
| Muscle attachments | Bones, muscles, or tissues |
| Muscle joints | Synovial joints are responsible for moving the body in space |
| Muscle function terminology | Prime mover, agonist, antagonist, synergist, and stabilizer |
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What You'll Learn
- Skeletal muscles are voluntary muscles that help with a wide range of movements and functions
- Cardiac muscles are involuntary muscles that make up the heart and stimulate their own contractions
- Smooth muscles are also involuntary and help with essential functions like digestion and maintaining blood circulation
- Prime movers are muscles that provide the primary force driving an action
- Antagonists are muscles that provide resistance or reverse a movement
Skeletal muscles are voluntary muscles that help with a wide range of movements and functions
Skeletal muscles are the most common type of muscle in the human body, accounting for 30% to 40% of total body mass. They are voluntary muscles, meaning that their movement is controlled by the brain. Skeletal muscles are attached to bones by tendons and allow for a wide range of movements and functions. They are responsible for producing movement, maintaining body posture, controlling body temperature, and stabilizing joints.
Skeletal muscles are composed of flexible muscle fibres that contract (tighten) to enable movement. These fibres are usually several centimetres long and range from less than half an inch to just over 3 inches in diameter. Each muscle can contain thousands of fibres, and these fibres are surrounded by different types of sheaths or coverings. The outermost layer is the epimysium, followed by the perimysium in the middle, and the endomysium as the innermost layer. Skeletal muscle fibres are also known as striated or multinucleated muscle cells, with nuclei located in the cell's periphery.
The movement of skeletal muscles is facilitated by the nervous system, which sends signals to the muscles. The somatic nervous system controls voluntary movements, while the autonomic nervous system controls involuntary movements. Skeletal muscles react to both voluntary and reflexive nerve stimuli, with the majority of muscle activity being volitional and directed by the brain.
Skeletal muscles play a crucial role in converting chemical energy into mechanical energy, generating force and power. They also contribute to basal energy metabolism, serving as a storage site for essential substrates such as carbohydrates and amino acids. Additionally, skeletal muscles are involved in producing body heat, which is a by-product of muscular activity.
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Cardiac muscles are involuntary muscles that make up the heart and stimulate their own contractions
The human body has over 600 muscles that help us move, breathe, swallow, and stay alive. There are three major categories of muscles: skeletal muscle, smooth muscle, and cardiac muscle.
Cardiac muscle, also called myocardium, is an involuntary, striated muscle that constitutes the main tissue of the heart wall. It is the only type of muscle found in the heart and makes up the middle layer of the three-layered structure. The cardiac muscle is responsible for the contractility of the heart, which is the force that pumps blood through the cardiovascular system.
The contractile myocytes of the cardiac muscle are called cardiomyocytes. These cardiac muscle cells are the contracting cells that allow the heart to pump blood. Each cardiomyocyte needs to contract in coordination with its neighbouring cells. This coordination is known as a functional syncytium. If this coordination breaks down, the heart may not pump at all, which can occur during abnormal heart rhythms such as ventricular fibrillation.
The functional unit of cardiomyocyte contraction is the sarcomere, which consists of thick (myosin) and thin (actin) filaments. The interaction between these filaments forms the basis of the sliding filament theory, where the actin and myosin muscle filaments slide past each other. This sliding action shortens the distance between the two attachments of the ends of a muscle group when a joint angle changes. The shortening of the muscle group is what we refer to as muscle contraction.
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Smooth muscles are also involuntary and help with essential functions like digestion and maintaining blood circulation
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, smooth, and cardiac. Smooth muscles are involuntary muscles that line the inside of some organs and help with essential functions like digestion and maintaining blood circulation.
Smooth muscles are found throughout the body and serve a variety of functions. They are present in the stomach and intestines, where they aid in digestion and nutrient collection. They also play a role in the urinary system, where they help to rid the body of toxins and maintain electrolyte balance. Smooth muscles are also found in arteries and veins, where they are responsible for regulating blood pressure and tissue oxygenation. This regulation is vital for maintaining the body's basic functions.
In the cardiovascular system, smooth muscles are used in vessels to maintain blood pressure and blood flow. They do so by contracting and relaxing, which helps pump blood through the body. Smooth muscles also open and close airways in the lungs, facilitating breathing. They play a crucial role in the gastrointestinal system, contributing to motility and nutrient absorption.
Smooth muscles differ from skeletal muscles in their ability to maintain tone for extended periods and contract involuntarily. They are composed of thick and thin filaments that create a non-striated pattern under microscopic observation. Smooth muscles contain high levels of actin and myosin, the primary proteins involved in muscle contraction. The nervous system regulates smooth muscle activity, allowing for tight unconscious control of critical functions such as digestion, respiratory rate, and heart rate.
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Prime movers are muscles that provide the primary force driving an action
The human body has over 600 muscles that help us move, breathe, swallow, and stay alive. These muscles are pieces of soft tissue that can contract or relax. When a muscle contracts, it may do so as a prime mover at a joint between two bones.
A prime mover is a muscle, typically the main muscle or a member of a group of muscles, that provides the primary force for a specific movement. It is also known as an agonist muscle. Prime movers are sometimes assisted by synergists, which are muscles that also cause a joint action but are not the prime mover.
An example of a prime mover muscle is the gluteus maximus, which is the prime mover of hip extension during exercises like the Ultimate Glute Bridge, lateral lunge, deadlift, or squat. Another example is the triceps brachii, which plays a big role in extending the elbow joint from a bent to a straight position.
Prime movers can be contrasted with antagonist muscles, which provide resistance or reverse a given movement. For example, the triceps brachii acts as an antagonist to the biceps brachii, which is the agonist or prime mover in this case.
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Antagonists are muscles that provide resistance or reverse a movement
The human body has over 600 muscles, which help us move, breathe, swallow, and stay alive. These muscles are attached to bones, tissues, or other muscles. The end of the muscle that is attached to the bone being pulled is called the muscle's insertion, and the end that is attached to a fixed bone is called the origin.
Muscles can only contract and pull; they do not push. Therefore, muscles are arranged in pairs, with an agonist that initiates a movement and an antagonist that opposes the action and returns the movement to its original position. For example, the bicep is the agonist that causes the arm to curl, and the tricep is the antagonist that straightens the arm back out. The functions of these antagonistic muscle groups are to pull against each other in opposite directions to allow the movements of flexion and extension.
The agonist is also called the prime mover, and it is the muscle that provides the primary force driving the action. The antagonist muscle is in opposition to the prime mover, providing resistance or reversing a given movement. Prime movers and antagonists are often paired up on opposite sides of a joint, with their roles reversing as the movement changes direction. For example, to extend the leg at the knee, the quadriceps femoris in the anterior thigh are activated as the agonists, and the hamstrings in the posterior thigh are activated as antagonists to slow or stop the movement. When the leg flexes at the knee, the roles reverse, with the hamstrings acting as agonists and the quadriceps femoris acting as antagonists.
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Frequently asked questions
Muscle actions are categorized as concentric, eccentric, or isometric depending on whether the muscle shortens, lengthens, or remains the same.
Concentric contraction occurs when the proximal and distal muscle attachments move towards one another. For example, the biceps brachii during the raising phase of a bicep curl. Eccentric contraction occurs when the proximal and distal muscle attachments move away from one another. For example, the biceps brachii during the lowering phase of a bicep curl.
Traditional types of muscle "contraction" are defined as: isotonic (constant muscle tension), isometric (constant muscle length), isokinetic (constant velocity of motion), and isoinertial (constant load).
