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Our bodies have over 600 muscles that help us perform a variety of functions, from involuntary actions like breathing and keeping our hearts pumping, to voluntary actions like jumping in the air or bending our limbs at the joints. Our muscles are pieces of soft tissue that move our bodies by contracting and then relaxing. They use energy from our food to produce movement and need signals from our brains to contract and move. When we want to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract.
| Characteristics | Values |
|---|---|
| How muscles move | Muscles move by contracting and relaxing, changing shape to move bones into different positions. |
| How muscles work together | The human body has three systems acting together to move: the muscular, skeletal, and nervous systems. |
| Muscle types | There are two types of muscle: striated (skeletal) and smooth. |
| Striated muscles | Striated muscles are controlled by the brain and are made of fibres that have horizontal stripes when viewed under a microscope. |
| Smooth muscles | Smooth muscles are not controlled by the brain and do not have stripes. They are controlled by the nervous system and are found in the walls of the stomach, intestines, and blood vessels. |
| Muscle control | Some movements are voluntary and can be controlled by the brain, while others are involuntary and cannot be consciously controlled. |
| Muscle movement and calcium | Calcium is a key messenger in the process of muscle contraction. A constant supply of calcium allows muscles to regulate blood flow. |
| Muscle repair | Muscles have an ability to repair themselves when damaged. Exercise can help build new muscles by taking advantage of this ability. |
| Muscle health | Muscle pain, weakness, and other symptoms can be signs of serious issues. It is important to visit a healthcare provider if you experience muscle pain or trouble moving. |
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What You'll Learn
Skeletal muscles and bones
The human body has three systems that work together to make it move: the muscular, skeletal, and nervous systems. The muscular system consists of over 600 skeletal muscles that allow us to move around. Skeletal muscles are attached to our bones through tendons, which are strong connective cords of tissue. They work with bones, tendons, and ligaments to support our weight and move us.
Skeletal muscles are the most common type of muscle in the body, comprising 30% to 40% of our total body mass. They are voluntary muscles, meaning we can control how and when they work. They are also known as striated muscles because they have regular stripes or striations when observed under a microscope. These stripes are due to the arrangement of muscle fibers, which form parallel lines.
Each skeletal muscle contains thousands of muscle fibers that contract and relax, allowing the muscles to move bones and perform different movements. These muscle fibers are surrounded by different types of sheaths or coverings: the epimysium (outermost layer), perimysium (middle layer), and endomysium (innermost layer). Skeletal muscle fibers are red and white, and they contract to move our bones, allowing us to perform a wide range of movements and functions.
The skeletal system, including bones, provides the body's main structural support and gives our body its shape. It holds our organs in place and protects them. For example, the skull protects our brain, the ribs shield our heart and lungs, and the vertebrae in our spine keep our spinal cord safe. Bones also store important minerals like calcium and vitamin D.
The musculoskeletal system, which includes bones, joints, muscles, tendons, ligaments, and cartilage, works together to enable movement. Joints connect bones and allow them to move, while cartilage acts as a shock absorber. Ligaments are bands of tissue that connect bones to other bones, and tendons connect muscles to bones. This system is essential for various movements, from walking and running to more complex activities like dancing.
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Smooth muscles
Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal and cardiac muscle. Smooth muscle is found throughout the body and is involved in many of the body's automated self-management processes. Smooth muscle is non-striated, meaning it has no sarcomeres and therefore no stripes or bands. It can be divided into two subgroups: single-unit and multi-unit smooth muscle. Single-unit smooth muscle, also known as visceral smooth muscle, is found in the walls of most internal organs, blood vessels excluding large elastic arteries and capillaries, the urinary tract, and the digestive tract. Multi-unit smooth muscle is found in the trachea, in the iris of the eye, and lining the large elastic arteries.
Smooth muscle differs from skeletal and cardiac muscle in terms of structure, function, and regulation of contraction. Smooth muscle cells are spindle-shaped with a wide middle and tapering ends, and a single nucleus. They are much shorter than skeletal muscle cells, ranging from 30 to 200 micrometers in length when relaxed. Smooth muscle is controlled by the autonomic nervous system and influenced by a combination of different neural elements, with cell-to-cell communication and local activators/inhibitors contributing to a coordinated response.
Smooth muscle functions involuntarily, without conscious thought, and is responsible for various important tasks in the body. It helps regulate blood pressure and circulation, and plays a role in vision and digestion. For example, smooth muscles in the digestive tract work together to transport substances, pushing the contents through the tract. Smooth muscles in sphincters, such as the bladder or anus, stay flexed and only relax when needed. Smooth muscle is also involved in controlling the width of passages in the body, such as the dilation and constriction of the pupil in the eye.
Smooth muscle is susceptible to various conditions, including anti-smooth muscle autoantibodies, where the immune system attacks and damages the smooth muscle, and muscular dystrophies, which cause muscles to gradually lose function. Smooth muscle is also vulnerable to spasms, which can lead to vasospasm in blood vessels or asthma in airways. Visceral myopathies are a group of smooth muscle diseases that can interfere with their function and, in some cases, be life-threatening.
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Muscle contractions
There are three types of muscle tissue: skeletal, cardiac, and smooth. Skeletal muscles are attached to our bones through tendons and help us move. They are under our conscious control and are considered voluntary muscles. Cardiac muscles make up the walls of the heart and are under involuntary control. Smooth muscles are found in our blood vessels, gastrointestinal tract, bronchioles, uterus, and bladder, and they are also under involuntary control.
The process of muscle contraction is complex and is called excitation-contraction coupling. It involves the release of acetylcholine, a neurotransmitter, at the neuromuscular junction, which causes the muscle fibres to contract and the muscle to move. This process is regulated by calcium, which is the key molecular messenger.
There are different types of muscle contractions, including concentric, eccentric, and isometric contractions. Concentric contractions occur when the muscle tension is sufficient to overcome the load, and the muscle shortens as it contracts. Eccentric contractions happen when the muscle is actively lengthened, such as when walking or lowering something heavy. Isometric contractions occur when the muscle is held at a set length, and the tension changes without any change in muscle length.
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Muscle repair
The human body has three systems working together for movement: the muscular, skeletal, and nervous systems. Skeletal muscles are attached to bones through tendons, which are strong connective tissues. These muscles contract and relax, causing bones to move into different positions. The nervous system controls these movements, specifically the brain, through the release of acetylcholine, an excitatory neurotransmitter.
To repair and strengthen muscles, adequate rest, hydration, and nutrition are essential. Consuming protein after a workout helps repair muscle damage, with 1.4–2.0 g of protein per kg of body weight recommended for building and maintaining muscle mass. Additionally, gentle stretching promotes healing by restoring the normal length of the muscles.
In cases of severe muscle pain or tears, medical attention is necessary. Immobilization and surgical repair may be required, along with following the RICE protocol: rest, ice, compression, and elevation.
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Muscle tone
The two types of hypertonia, spasticity and rigidity, are a result of dysfunction in the supraspinal pathways and the interaction between the spinal cord and muscle spindle. Dystonia and paratonia, two other disorders of altered tone, are not directly related to physiological dysfunction of the tone pathways but are instead due to network dysfunction. Paratonia, in particular, is associated with dementia.
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Frequently asked questions
Muscles contract and relax to generate movement. They receive signals from our brains and energy from our food to contract and move.
There are two types of muscle movements: voluntary and involuntary. Voluntary movements are actions that we control, such as walking or jumping. Involuntary movements are those that we do not actively control, such as keeping our hearts pumping or moving food through our guts.
When we decide to move, the motor cortex sends an electrical signal through the spinal cord and peripheral nerves to the muscles, causing them to contract. The cerebellum coordinates the muscle movements ordered by the motor cortex.
There are three types of muscles: striated, smooth, and cardiac. Striated muscles have regular stripes when observed under a microscope and are responsible for moving our body parts. Smooth muscles line the inside of organs such as the bladder, stomach, and intestines and are involved in involuntary functions. Cardiac muscle makes up the walls of the heart and powers its contraction and relaxation to enable circulation.
