Logan Steele
Bones, muscles, and joints form the musculoskeletal system, which enables us to perform everyday physical activities. Bones cannot move without muscles. Tendons, which are tough bands of connective tissue, attach skeletal muscles to bones throughout the body. Skeletal muscles are voluntary muscles, meaning that we can control how and when they move and work. When the fibres of these muscles contract, they get shorter, which pulls the bones they are connected to closer together.
| Characteristics | Values |
|---|---|
| Can bones move without muscles? | No, muscles control all movement in the body. Bones and muscles work together to allow movement. |
| How do muscles and bones work together? | Muscles are connected to bones by tendons, a type of tissue. When muscles contract, they pull on the bones they are connected to, causing movement. |
| What types of muscles are there? | There are skeletal, smooth, and cardiac muscles. Skeletal muscles are voluntary, while smooth and cardiac muscles are involuntary. |
| What do skeletal muscles do? | Skeletal muscles are the most common type of muscle in the body and are controlled by the somatic nervous system. They allow for a wide range of movements, such as reaching for a book. |
| What do smooth muscles do? | Smooth muscles are controlled by the nervous system and are found in the stomach, intestines, and blood vessels. They help with digestion and maintaining blood pressure. |
| What do cardiac muscles do? | Cardiac muscles make up the heart and help pump blood throughout the body. They are involuntary and controlled by the autonomic nervous system. |
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What You'll Learn
Tendons: Connective tissue between muscles and bones
Bones cannot move without muscles. Bones, muscles, and joints form the musculoskeletal system, which enables us to perform everyday physical activities. Muscles control all movement in the body and work together with bones to help us move. There are more than 650 muscles in the human body, and they are all connected to bones by tendons.
Tendons are cord-like connective tissues that attach muscles to bones. They are found throughout the body, including in the legs, arms, and face. Tendons are made up of thousands of small elastic fibres, similar to rubber bands, that contract and relax to cause movement. When the fibres contract, they get shorter, pulling the bones they are connected to closer together.
Skeletal muscles are voluntary muscles, meaning that we can control how and when they move and work. They are attached to bones by tendons and are made up of flexible muscle fibres that can range from less than half an inch to just over three inches in diameter. These fibres contract, or tighten, allowing the muscles to move bones and enabling us to perform various movements.
Tendons can be injured through repetitive or intense motions, causing a condition known as tendonitis, which results in pain and swelling. It is important to keep muscles healthy through physical activity, proper nutrition, and maintaining a healthy body weight.
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Ball-and-socket joints: Allow freedom of movement
Bones, muscles, and joints form the musculoskeletal system, which enables us to perform everyday physical activities. Joints are places where two bones make contact. They can be classified histologically or functionally. Histological classification is based on the predominant connective tissue type composing the joint, while functional classification is based on the amount of movement the joint permits.
The three functional joint types include the immovable synarthrosis, the slightly moveable amphiarthrosis, and the freely moveable diarthrosis. Ball-and-socket joints are an example of the latter type and are the most mobile of all joints in the human body. They are termed polyaxial (multiaxial/triaxial) joints because they allow movement in all three planes and about all three axes.
Ball-and-socket joints get their name from the spherical shape (ball) of one bone articulating with the cup-shaped (socket) surface of another bone. The body's only ball-and-socket joints are the hip and shoulder (glenohumeral) joints. The hip joint involves the head of the femur (ball) and the acetabulum of the pelvis (socket). The shoulder joint involves the head of the humerus (ball) and the glenoid fossa of the scapula (socket).
The glenoid cavity's shallow socket permits an extensive range of motion in the shoulder. In contrast, the deep acetabular socket and the surrounding ligaments constrain femoral movement in the hip joint. Movements permitted by ball-and-socket joints include flexion and extension, abduction and adduction, and medial and lateral rotation.
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Smooth muscles: Controlled by the nervous system
Smooth muscles are involuntary muscles that are controlled by the nervous system. Unlike skeletal muscles, smooth muscles are not under our conscious control. Instead, they are regulated by the autonomic nervous system, which is responsible for smooth muscle contraction. This system uses hormones, neurotransmitters, and other receptors to control smooth muscle activity spontaneously.
Smooth muscles are found throughout the body and serve a variety of essential functions. They are present in the stomach and intestines, where they aid in digestion and nutrient absorption. Additionally, they play a crucial role in the urinary system, helping the body eliminate toxins and maintain electrolyte balance. Smooth muscles are also found in the walls of blood vessels, where they regulate blood pressure and tissue oxygenation.
The sympathetic, parasympathetic, and enteric nervous systems all work together to contract smooth muscles. Sympathetic stimulation of smooth muscles originates from spinal levels T1 to L2 and is transmitted through the sympathetic trunk, which supplies autonomic nerves to various organs and tissues. The parasympathetic nervous system, on the other hand, functions through the cranial nerves, vagus nerve, and pelvic splanchnic nerves, with each nerve regulating specific body regions.
The vagus nerve, for example, innervates the gastrointestinal tract, sending branches to the heart, larynx, trachea, bronchi, liver, and pancreas. Smooth muscles play a significant role in maintaining vital bodily functions, and their regulatory effects are important considerations during surgical procedures. For instance, the treatment of certain neuroendocrine tumors or disorders like peptic ulcer disease may involve modifying the function of smooth muscles.
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Skeletal muscles: Striated and under our control
Skeletal muscles are the most common muscles in the human body. They are attached to the bones by tendons, allowing us to move our bones and perform a wide range of movements and functions. They help us perform everyday activities like chewing food, communicating through facial expressions, and exercising to stay physically fit. Skeletal muscles also play a role in holding the skeleton together and giving the body its shape.
These muscles are called striated muscles because, when viewed under a microscope, they are made up of fibres that exhibit horizontal stripes. This unique structure is due to the arrangement of actin and myosin, which are thin and thick filaments, respectively, along with support proteins. The stripes create functional units called sarcomeres, which are arranged longitudinally and include components like the M line, Z disk, H band, A band, and I band.
Skeletal muscles are under voluntary control, meaning we can consciously control how and when they work. They receive neural inputs that facilitate this conscious control. Skeletal muscles comprise approximately 30% to 40% of an individual's total body mass and contain 50% to 75% of all body proteins. They are composed of bundles of muscle fibres called myofibers, which are multinucleated cells ranging from 10 to 100 micrometers in diameter and can be several centimetres long.
Skeletal muscles can be injured or affected by various conditions, including strains, tendonitis, and more severe disorders like muscular dystrophies and inflammatory issues. Maintaining strong and healthy muscles is crucial, as muscle injuries and diseases can significantly impact one's life. Additionally, muscle mass tends to decrease with age, starting around age 40, and this loss of muscle mass can lead to balance issues and reduced mobility.
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Cardiac muscles: Striated and involuntary
Bones cannot move without muscles. Muscles pull on the joints, allowing us to move. They also help the body perform functions such as chewing food and moving it through the digestive system.
Cardiac muscle, also called the myocardium, is one of the three major categories of muscles in the human body, the other two being smooth muscle and skeletal muscle. Cardiac muscle is striated, meaning it appears striped when viewed under a microscope. This is because it contains sarcomeres, which are packed into highly regular, repeating arrangements of bundles. Cardiac muscle is found in the heart, with the walls of the heart's chambers being composed almost entirely of muscle fibres.
Cardiac muscle is involuntary, meaning it is not under conscious control. Instead, it is controlled by the nervous system. The primary function of cardiac muscle is to pump blood into circulation by generating sufficient force. The contractile functions of the heart require ATP, which can be obtained through various substrates, including fatty acids, carbohydrates, proteins, and ketones. The cardiac action potential lasts approximately 200 ms and is divided into five phases: resting, upstroke, early repolarization, plateau, and final repolarization.
The generation of a cardiac action potential is involuntary and proceeds via a process known as excitation-contraction coupling (ECC). Action potentials travel along the sarcolemma and into the t-tubules to depolarize the membrane. Voltage-sensitive dihydropyridine (DHP) receptors on the t-tubules allow calcium to enter the cell during the plateau phase. This increased intracellular calcium concentration triggers the release of more calcium through the ryanodine receptor, known as calcium-induced calcium release. The released calcium attaches to troponin C, causing tropomyosin to detach from the myosin-binding sites on actin. Actin and myosin then form a cross-bridge, and contraction occurs.
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Frequently asked questions
No, muscles control all movement in the body. Bones and muscles work together to enable everyday physical activities.
Muscles are made up of thousands of small elastic fibres that contract and relax to cause movement. When the fibres contract, they get shorter, which pulls the bones they are connected to closer together. Tendons, a type of tissue, connect muscles to bones.
Tendons are tough bands of connective tissue that attach skeletal muscle tissue to bones. Tendons can be injured through repetitive or intense motions, causing tendonitis, which is painful and causes swelling.
