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The human body is estimated to have around 600 to 700 muscles, which are responsible for movement, posture, and balance. These muscles are attached to the bones of the skeletal system and make up about half of a person's body weight. Learning about all these muscles can be daunting, but muscle diagrams are a great way to get an overview of the muscles within a specific body region. This approach can help you understand the location, shape, and surrounding structures of each muscle, and you can then test yourself by labelling the muscles on a diagram. Quizzes are also a good way to reinforce your learning and identify your weak spots.
| Characteristics | Values |
|---|---|
| Number of muscles in the body | 600-700 |
| Muscle diagrams | Helpful to get an overview of all the muscles within a body region |
| Muscle names | Determined by their anatomical location, shape, size, number of muscles in a group, direction of muscle fibers, and action |
| Muscle groups | Neck muscles, torso muscles, arm muscles, leg muscles, etc. |
| Muscle movements | Rotation, flexion, extension, and side bending |
| Muscle functions | Transforming the energy sent from the nervous system into movement |
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What You'll Learn
Muscle groups and their actions
Muscle diagrams are a great way to get an overview of the muscles within a specific body region. There are over 600 muscles in the human body, and they are typically grouped by their location, such as chest, leg, or back muscles. Alternatively, they can be grouped by the type of movement they enable, such as abductors, flexors, or extensors.
The human muscle system is often divided into three types: striated or skeletal muscle, smooth muscle, and cardiac muscle. Skeletal muscles are attached to the bones by tendons and are the only voluntary muscles in the human body. They are responsible for every physical action that a person consciously performs, such as speaking, walking, or writing. Most skeletal muscles are attached to two bones across a joint, allowing them to move parts of those bones closer together.
Smooth muscle, also known as visceral muscle, is found in the walls of blood vessels and organs like the urinary bladder, intestines, and stomach. It is the weakest of all muscle tissues and is responsible for involuntary movements, such as contracting organs to move substances through them.
Cardiac muscle is found only in the heart and is responsible for pumping blood throughout the body through rhythmic contractions. Like smooth muscle, cardiac muscle is also an involuntary muscle, contracting independently but with adjustments to the rate of contraction made by hormones and signals from the brain.
The muscles of the neck, for example, enable important movements such as rotation, flexion, extension, and side bending. Rotation is primarily accomplished by the sternocleidomastoid muscle, which bends the neck to the ipsilateral side and rotates the neck contralaterally. The anterior and middle scalene muscles, located at the sides of the neck, act ipsilaterally to rotate the neck and elevate the first rib. The splenius capitis and splenius cervicis muscles, located in the back of the neck, work to rotate the head and assist in neck side bending.
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Muscle names and etymology
Muscle names and their etymologies can be very instructive when it comes to understanding their function, location, and shape. The Greeks and Romans were the first to study the human body in Western culture, and as a result, the early pioneers of anatomy used Latin and Greek terminology to name the skeletal muscles.
The etymology of a word refers to how the root of that word entered a language and how its use evolved over time. For example, the term "flexor" comes from modern Latin, with "flexus" being the past participle of "flectere", meaning "bender". Thus, "flexor carpi radialis" can be broken down as "wrist bender at radial side of the forearm", with carpi meaning "wrist" and radialis referring to the radial side of the forearm. Similarly, "flexor carpi ulnaris" means "wrist bender at ulna", with ulnaris referring to the position at the ulna bone.
Muscle names often indicate the number of muscles in a group, such as "biceps" or "triceps", with "bi" meaning "two" and "tri" meaning "three". The location of a muscle's attachment can also be reflected in its name, such as "sternocleidomastoid", which refers to a dual origin in the sternum and clavicle. The shape of a muscle can also be reflected in its name, such as "orbicularis", which describes a circular shape. The size of muscles can also be indicated in their names, such as "gluteus maximus" (largest), "gluteus medius" (medium), and "gluteus minimus" (smallest).
The function or action of a muscle can also be a clue to its etymology. For example, "flexor" decreases the angle at a joint, while "extensor" increases the angle. "Abductor" moves a bone away from the midline, while "adductor" moves it towards the midline. The sartorius muscle, for instance, externally rotates the hip and flexes/internally rotates the knee, as required when sitting cross-legged to sew, hence its name, derived from "sartor" (tailor).
In summary, understanding the etymology of muscle names can be a helpful tool for learning human anatomy, providing clues about a muscle's shape, size, location, and function.
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Muscle attachments and insertions
The muscles of the upper and lower extremities are a good place to start when learning about muscle attachments and insertions. For instance, the biceps brachii, located on the front of the upper arm between the shoulder and elbow, has two origins on the scapula and attaches to the upper part of the radius. The triceps brachii, located on the back of the upper arm, has three origins where it attaches to the scapula and inserts at the ulna at the back of the elbow. The brachialis, another upper arm muscle, runs from the humerus to the ulna. The coracobrachialis is the only upper arm muscle that does not connect to the forearm bones; instead, it attaches to the humerus.
The lower arm also contains several muscles with distinct attachments and insertions. The flexor digitorum profundus, for instance, originates at the top of the ulna and separates into four tendons that attach to the phalange bones of the index, middle, ring, and pinky fingers. The flexor pollicis longus, on the other hand, originates at the middle of the radius and has one long tendon that attaches to the base of the thumb. The pronator quadratus is a square-shaped muscle that connects the lower end of the ulna to the lower end of the radius near the wrist. The brachioradialis starts at the end of the humerus and runs to the radial styloid process at the wrist.
Understanding muscle attachments and insertions is crucial for comprehending body movement and the actions of various muscles. It is also important to note that the terms "origin" and "insertion" are usually described from an anatomical position, but they are not fixed and can vary depending on the position of the body.
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Muscle shape and location
Muscle diagrams are a great way to visualise the shape and location of muscles within a body region. There are over 600 muscles in the human body, with some sources estimating around 700 named muscles. These muscles are located almost everywhere throughout your body, and they are responsible for movement. They can be grouped by their location, such as chest, leg, or back muscles, or by the type of movement they perform, like abductors or flexors.
The shape of a muscle often determines its name. For example, the deltoid muscle is triangular, the rhomboid major muscle is shaped like a rhombus or diamond, and the teres muscle is round. The size of a muscle can also be used to distinguish between two muscles in the same region. For instance, the gluteal region contains three muscles differentiated by size: the gluteus maximus (large), gluteus medius (medium), and gluteus minimus (smallest). The direction in which the muscle fibres run can also be used to identify a muscle. In the abdominal region, the rectus abdominis runs straight up and down, the transverse abdominis runs transversely (left to right), and the obliques run at an angle.
Skeletal muscles, which are under voluntary control, are attached to bones by tendons. They are responsible for movement, posture, and balance. Most skeletal muscles are attached to two bones across a joint through tendons, which are tough bands of dense connective tissue. When muscles shorten in length, they pull on tendons, moving bones closer to each other. Skeletal muscles are striated, appearing to have light and dark stripes when viewed under a light microscope.
Cardiac muscle, on the other hand, is found only in the heart and is responsible for pumping blood throughout the body. Cardiac muscle is branched X or Y-shaped and is also striated. It is an involuntary muscle, contracting automatically without conscious control.
Visceral muscle, also known as smooth muscle, is found inside organs like the stomach, intestines, and blood vessels. It is the weakest of all muscle tissues and is also under involuntary control.
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Muscle innervations and functions
Muscle innervation refers to the process by which motor neurons supply nerves to muscle fibres, allowing them to contract and perform movements. Each muscle is connected to a specific motor neuron that sends electrical signals from the central nervous system, executing precise and coordinated actions. The pattern of muscle innervation varies across species and muscles. In some cases, multiple axons innervate each muscle fibre. However, in most higher vertebrates, particularly mammals, each AP in a motor neuron causes the contraction of every muscle fibre that its axon innervates.
The muscular system is responsible for the movement of the human body. There are about 700 named muscles that make up roughly half of a person's body weight. Each of these muscles is a discrete organ constructed of skeletal muscle tissue, blood vessels, tendons, and nerves. Muscle tissue is also found inside the heart, digestive organs, and blood vessels. There are three types of muscle tissue: visceral, cardiac, and skeletal.
Visceral muscle, also known as smooth muscle, is the weakest of all muscle tissues. It is found inside organs like the stomach, intestines, and blood vessels. Smooth muscle is under involuntary control and contracts to move substances through the organ. Cardiac muscle, on the other hand, is responsible for the rhythmic contractions of the heart and is also under involuntary control. Cardiac muscle tissue stimulates itself to contract and is considered intrinsically controlled.
Skeletal muscle, the only voluntary muscle tissue in the human body, is controlled consciously. It is attached to the bones of the skeletal system by tendons and works in a coordinated fashion to control body movements. Skeletal muscles are responsible for every physical action that a person consciously performs, such as speaking, walking, or writing. They contract to move parts of the bones closer to each other.
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