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The human body has over 600 muscles that help us move, breathe, and stay alive. Muscles are pieces of soft tissue that work together to control the movements of the human body. They can be categorised by shape, such as triangular or circular, or by function, such as prime movers, synergists, or stabilisers. Skeletal muscles are the only voluntary muscles in the body, allowing us to perform conscious actions such as speaking, walking, or writing. Smooth muscles and cardiac muscles are involuntary, with smooth muscles helping our lungs expand when we breathe and aiding our digestive system, and cardiac muscles making up the heart and pumping blood through our bodies.
| Characteristics | Values |
|---|---|
| Number of muscles in the human body | More than 600 |
| Muscle function | Help the body move, breathe, swallow, pump blood, and stay alive |
| Types of muscles | Skeletal, smooth, and cardiac |
| Skeletal muscle | Controlled consciously; contracts to move parts of the body |
| Smooth muscle | Involuntary; found in walls of blood vessels, urinary bladder, intestines, stomach, and reproductive system |
| Cardiac muscle | Involuntary; makes up the heart and pumps blood through the cardiovascular system |
| Muscle actions | Dorsiflexion, plantar flexion, abduction, adduction, supination, pronation, elevation, depression, flexion, extension, side bending, and rotation |
| Muscle attachments | Origin (stationary bone), insertion (moving bone) |
| Muscle shapes | Triangular, circular, delta or triangular, serrated or saw-like, diamond or rhombus |
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What You'll Learn
- Skeletal muscles allow for a wide range of movements and functions
- Cardiac muscles pump blood around the body
- Involuntary muscles, such as visceral muscles, are controlled by the unconscious part of the brain
- Agonist muscles provide the primary force driving an action
- Antagonist muscles provide resistance and/or reverse a given movement
Skeletal muscles allow for a wide range of movements and functions
The human body has over 600 muscles, which enable a wide range of movements and functions. Muscles are pieces of soft tissue that help us move, breathe, swallow, and stay alive. They work by contracting or relaxing to cause movement.
Skeletal muscles, in particular, are responsible for all physical actions that a person consciously performs, such as speaking, walking, or writing. They are the only voluntary muscle tissue in the human body. They derive their name from the fact that they always connect to the skeleton in at least one place. Most skeletal muscles are attached to two bones across a joint through tendons, allowing them to move parts of the bones closer to each other. For example, the triceps brachii play a significant role in extending the elbow joint from a bent to a straight position.
The shape and size of skeletal muscles vary. For instance, the deltoid muscles of the shoulder are triangular, while the muscles surrounding the mouth, pupils, and anus are circular. The size of a muscle can also be used to distinguish between muscles in the same region, such as the gluteal region's maximus, medius, and minimus muscles.
Skeletal muscles are also named based on their location, origin, insertion, number of origins, direction, and function. The direction of muscle action can be ipsilateral, which refers to movement in the direction of the contracting muscle, or contralateral, which is movement away from the contracting muscle. For example, the sternocleidomastoid muscle in the neck region is responsible for ipsilateral neck flexion and contralateral neck rotation.
Additionally, muscles can be classified as prime movers, antagonists, or synergists. Prime movers, or agonists, provide the primary force for an action, while antagonists oppose the prime mover by providing resistance or reversing the movement. Synergists assist the prime mover in its role.
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Cardiac muscles pump blood around the body
The human body is an intricate machine, with over 600 muscles that help us perform a variety of actions, from breathing to complex physical activities. One of the most vital functions of our body is performed by cardiac muscles, which pump blood throughout our system.
The heart, a powerful muscle, acts as a hub, ensuring the continuous flow of blood to all parts of the body. This blood carries oxygen and essential nutrients to our organs, muscles, and tissues, keeping us alive and healthy. The heart beats thousands of times a day, tirelessly pumping oxygen-rich blood through a complex network of arteries and veins.
Cardiac muscle, also known as myocardium, is unique to the heart and forms its middle layer. This muscle contracts and relaxes rhythmically, generating enough force to pump blood into circulation. The contractile functions of the cardiac muscle are involuntary and rely on electrical impulses and ATP, which can be derived from various sources, including fatty acids and carbohydrates.
The heart's electrical rhythms, or electrocardiogram (ECG), cause depolarization, leading to the contraction of the myocardium. This contraction is essential for the pumping action, ensuring that blood reaches every part of the body, from the major organs to the smallest tissues. The cardiac muscle must contract with sufficient force to meet the metabolic demands of the entire body.
Cardiac muscle plays a crucial role in maintaining the health and functionality of our bodies. Its continuous pumping action ensures that our organs and tissues receive the oxygen and nutrients they need, while also facilitating the removal of waste products, such as carbon dioxide. This intricate process occurs every second of every day, showcasing the tireless work of our cardiac muscles in pumping blood around our bodies.
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Involuntary muscles, such as visceral muscles, are controlled by the unconscious part of the brain
The human body has more than 600 muscles that help us perform a variety of actions, from moving our body to breathing and even keeping us alive. These muscles can be categorised into skeletal, cardiac, and visceral or smooth muscles. While skeletal muscles are the only voluntary muscles in the human body, cardiac and visceral muscles are involuntary, meaning they function without our conscious control.
The medulla oblongata, a part of the hindbrain, is primarily responsible for controlling involuntary actions in the body. It is located below the midbrain and continues to form the spinal cord, which also plays a role in executing reflex actions. The midbrain, which connects the forebrain and hindbrain, also has some influence over involuntary actions.
In contrast, the forebrain is involved in voluntary actions and houses specialised regions for sense organs. The autonomic nervous system, which includes the sympathetic and parasympathetic nervous systems, is also integral to controlling involuntary processes. This system connects the brain to most internal organs and manages vital processes such as heartbeat, blood pressure, digestion, and sexual functions.
While the conscious mind cannot directly control visceral muscles, hormones and signals from the brain can influence the rate of contraction. For example, the autonomic nervous system can cause the release of tears, a runny nose, or salivation, all of which are involuntary responses. Thus, involuntary muscles, including visceral muscles, are regulated by the unconscious part of the brain through various neural pathways and systems.
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Agonist muscles provide the primary force driving an action
The human body has over 600 muscles, which help us do everything from moving our body to breathing and staying alive. While many muscles may be involved in any given action, the principal muscle involved is called the prime mover or agonist. The agonist provides the primary force driving the action. For example, the biceps brachii is the prime mover during forearm flexion, such as when lifting a cup.
The term "antagonist muscle" refers to a muscle that opposes the prime mover by providing resistance or reversing a 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 instance, when extending the leg at the knee, the quadriceps femoris are the agonists, while the hamstrings are the antagonists. However, when flexing the leg at the knee, the hamstrings become the agonists, and the quadriceps femoris become the antagonists.
Synergists are muscles that assist the prime mover in its role. For example, during forearm flexion, the biceps brachii is assisted by the brachialis, which is a synergist in this action. A synergist can also act as a fixator, stabilising the muscle's origin. Stabilizers are another type of muscle that help keep bones immobile when needed. For example, your back muscles act as stabilizers when maintaining a sturdy posture.
The human body has various types of muscles, including skeletal, cardiac, and smooth muscles. Skeletal muscles are the only voluntary muscles in the human body, allowing us to perform conscious actions such as speaking, walking, or writing. They attach to bones, usually at two points, and move body parts closer to the bone they are attached to. Cardiac muscles, on the other hand, make up the middle layers of the heart and are responsible for pumping blood through the cardiovascular system. Smooth muscles line the inside of some organs and play essential roles in systems like the digestive and respiratory systems.
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Antagonist muscles provide resistance and/or reverse a given movement
The human body has over 600 muscles, which help us do everything from breathing to complex physical actions like jumping jacks. The primary muscle that carries out the movement is known as the agonist muscle or the prime mover. Antagonist muscles, on the other hand, oppose the action of the agonist or prime mover muscle. They do this by providing resistance and/or reversing a given movement.
Antagonist muscles work in complementary or opposite directions to agonist muscles. When an agonist muscle contracts, it pulls on tendons and moves bones closer to each other. Antagonist muscles then relax and lengthen to return the bones to their original position. For example, when you extend your elbow joint from a bent to a straight position, the triceps brachii acts as the prime mover. To return the elbow to its bent position, the biceps would be the antagonist muscle, opposing the contraction of the triceps.
The co-activation of agonist and antagonist muscles is critical for any body movement. This is because a certain level of stiffness or resistance at the joint is essential for maintaining joint stability. For example, when you lift your arm to drink from a cup, the biceps brachii acts as the prime mover, while the brachialis acts as a synergist or assistant. To lower your arm back down, the roles reverse, with the biceps becoming the antagonist and the brachialis assisting as a synergist.
The hamstrings and quadriceps femoris in the leg also demonstrate the role of antagonist muscles. When you extend your leg at the knee, the quadriceps femoris are the agonists, while the hamstrings are the antagonists, slowing or stopping the movement. When you flex your leg at the knee, the hamstrings become the agonists, and the role of the quadriceps femoris reverses to that of an antagonist.
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Frequently asked questions
Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of your total body mass. They are attached to the bones and allow you to perform a wide range of movements and functions. They also help to maintain body temperature, store nutrients, and stabilize joints.
Cardiac muscles are responsible for pumping blood throughout the body. They are found only in the heart and cannot be controlled consciously, so they are considered involuntary muscles.
Involuntary movements are actions that happen automatically without conscious thought. Muscles in your urinary system, for example, help rid your body of waste and toxins without you having to think about it. Another example is the process of shivering when you are cold.
Skeletal muscles are responsible for a wide range of movements. Some examples include flexion (bending) and extension (straightening) of the limbs, protraction and retraction of the mandible (moving the jaw forward and backward), and inversion and eversion of the foot (turning the sole of the foot inward and outward).
