Maximus Gage
Voluntary muscles, also known as red muscles or striated muscles, are muscles whose contraction is controlled by the will of the individual. They are distinct from involuntary muscles, such as cardiac and smooth muscles, which are controlled by the autonomic nervous system. Voluntary muscles are divided into two categories: superficial and deep. Superficial muscles are mimic muscles, present only in the neck and head, and allow for facial expressions and eye movement. Deep muscles are further classified into skeletal muscles, which move bones under conscious control, and muscles attached to other organs, such as the tongue and pharynx. Skeletal muscles, the most common type of muscle in the body, are responsible for a wide range of movements and functions, including skilled, rapid movements like throwing a dart.
| Characteristics | Values |
|---|---|
| Type | Red muscles, striated muscles, superficial muscles, deep muscles, skeletal muscles, flexors, extensors, abductor muscles, adductor muscles, synergistic muscles |
| Controlled by | The will of the subject, voluntary brain activity, central nervous system, somatic nervous system |
| Functions | Enable the body to maintain posture and body position, stabilize and strengthen joints, produce heat to maintain normal body temperature, control facial expressions, enable movement of the tongue, eyes, hand, fingers, neck, etc. |
| Diseases | Hypotonia, hypertonia, amyotrophic lateral sclerosis (ALS) |
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What You'll Learn
Skeletal muscles
Each skeletal muscle is made up of thousands of individual muscle cells, called muscle fibers or muscle cells. These muscle fibers are specialized to generate force and movement. They contract to facilitate movements like bending an elbow or moving a limb toward or away from the midline of the body. When skeletal muscles contract, they work in coordination with other muscles and the nervous system. For example, bending the elbow involves the contraction of the biceps (a flexor) and the relaxation of the triceps (an extensor).
The movement of skeletal muscles is controlled by the central nervous system, specifically through the somatic nervous system, which is comprised of afferent and efferent nerves. Afferent nerves relay information to the central nervous system, while efferent nerves stimulate muscle contraction. Each muscle fiber is connected to a nerve ending that receives signals from the brain, triggering a series of chemical reactions and nerve stimuli that induce muscle contraction. These nerve stimuli are transmitted by motor nerve fibers, which can control multiple muscle fibers, forming a functional unit known as a motor unit. The link between the central nervous system and skeletal muscles is critical for voluntary movement.
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Flexors and extensors
Voluntary muscles, also known as "red muscles" or "striated muscles", are muscles whose contraction is controlled by voluntary brain activity. They are divided into two categories: superficial and deep muscles. Superficial muscles are mimic muscles and are present only at the neck and head. Deep muscles are further divided into skeletal muscles and muscles attached to other organs.
Skeletal muscles, which are controlled by the central nervous system, can be classified as flexors or extensors. Flexors are muscles that contract to bend a joint, bringing the bones closer together and decreasing the angle between them. For example, the biceps are a type of flexor that contracts when the elbow is bent. The flexor digitorum profundus, for instance, allows for complex movements of the arm, wrist, and fingers. Other flexors include the lumbrical muscle, rectus abdominis muscle, and longus capitis muscle.
Extensors, on the other hand, are muscles that straighten a joint, increasing the angle between the bones. For example, the triceps are an extensor that relaxes when the elbow is bent. The forearm's extensor compartment contains seven muscles, including the brachioradialis and extensor carpi radialis longus.
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Superficial and deep muscles
Voluntary muscles, also known as "red muscles" or "striated muscles", are muscles of the human body whose contraction is controlled by voluntary brain activity. They are divided into two categories: superficial and deep muscles.
Superficial Muscles
Superficial muscles, also known as mimic muscles, are present only at the neck and head. They include muscles such as the trapezius and the latissimus dorsi, which are the most superficial back muscles. The trapezius is a broad, flat, and triangular muscle, with the muscles on each side forming a trapezoid shape. The trapezius originates from the skull, ligamentum nuchae, and the spinous processes of C7-T12, with fibres attaching to the clavicle, acromion, and scapula spine. The upper fibres of the trapezius elevate the scapula and rotate it during arm abduction, while the middle fibres retract the scapula and the lower fibres pull it inferiorly. The latissimus dorsi originates from the lower back and covers a wide area. Its fibres converge into a tendon that attaches to the intertubercular sulcus of the humerus.
Deep Muscles
Deep muscles are further divided into skeletal muscle and muscles attached to other organs, such as the eyes, ears, tongue, and pharynx. Skeletal muscles are responsible for moving bones under conscious control. These include muscles like the flexors, which bend joints and bring bones closer together, and extensors, which straighten joints and increase the angle between bones. For example, bending the elbow involves the contraction of the biceps (a flexor) and the relaxation of the triceps (an extensor). The deep muscles of the back extend from the sacrum to the base of the skull and are associated with movements of the vertebral column and control of posture. They are covered by deep fascia, which plays a role in their organisation.
The Transversospinales muscle group is a deep group of back muscles that lie deep to the Erector Spinae and assist in bending the back when contracted bilaterally. The nervous supply to the deep back muscles arises from the dorsal rami of the spinal nerves, providing sensation to the skin of the back.
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Agonists and antagonists
Voluntary muscles, also known as "red muscles" or "striated muscles", are muscles whose contraction is controlled by the will of the subject. They are divided into two categories: superficial and deep muscles. Superficial muscles are mimic muscles, present only at the neck and head. Deep muscles are further divided into skeletal muscles (which move bones under conscious control) and muscles attached to other organs such as the eyes, ears, tongue, and pharynx.
Skeletal muscles create movement by pulling on our skeleton. A muscle is usually connected to two bones, and when the muscle contracts, it brings one bone closer to the other. When discussing movement at a joint, the muscle performing the action on one side of the joint is called the agonist, and the muscle on the other side of the joint with the potential to oppose the action is called the antagonist. In other words, the agonist muscle contracts to perform the motion, and the antagonist muscle can oppose that motion.
For example, when flexing the elbow, the biceps are the agonist because they cause the elbow to flex, while the triceps are the antagonist because they are on the opposite side of the elbow joint and have the potential to oppose the elbow flexion. However, when we talk about active elbow extension, the triceps are the agonist because they cause the action, and the biceps are the antagonist. This demonstrates how one muscle can be the agonist for one movement and the antagonist for another movement.
Understanding the roles of agonists and antagonists is important for injury prevention and maintaining a healthy balance in the body.
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Somatic nervous system
The somatic nervous system is a subdivision of the peripheral nervous system, which encompasses the entire nervous system except the brain and spinal cord. It is responsible for facilitating the organs and striated muscles of the central nervous system, enabling us to perform our daily tasks.
The somatic nervous system plays a crucial role in controlling voluntary muscular systems within the body and the process of voluntary reflex arcs. It allows us to move and control muscles throughout our bodies. This system receives signals from the brain and transmits them to the muscles, enabling movement. For example, when we want to bend our elbow, the biceps (a flexor) contract, while the triceps (an extensor) relax.
The somatic nervous system also includes 31 spinal nerves and 12 cranial nerves. The spinal nerves act as a bridge between the environment and the central nervous system, transferring autonomic, sensory, and motor impulses to and from the spinal cord. These impulses are then transmitted to the lower motor neurons in the spinal cord through axons known as the corticospinal tract. The cranial nerves, on the other hand, facilitate functions such as eye movement, chewing, swallowing, and facial expressions.
Additionally, the somatic nervous system is responsible for feeding information from four of our senses—smell, sound, taste, and touch—to the brain. It also plays a role in controlling breathing. While we usually breathe automatically, we can also manually control our inhalation and exhalation through the somatic nervous system.
This system is susceptible to various medical conditions, such as peripheral neuropathy, which can be congenital or acquired. Charcot-Marie-Tooth disease, Myasthenia gravis, and Guillain-Barré syndrome are examples of ailments that can affect the somatic nervous system.
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Frequently asked questions
Voluntary muscles, also known as "red muscles" or striated muscles, are muscles whose contraction is controlled by the will of the individual. They are divided into two categories: superficial and deep.
Skeletal muscles are a type of voluntary muscle, comprising 30-40% of your total body mass. Examples include shoulder muscles, hamstring muscles, and abdominal muscles. Superficial muscles are mimic muscles, found only in the neck and head.
Each voluntary muscle fibre is connected to a nerve ending that receives orders from the brain. This triggers a series of chemical reactions, causing nerve stimuli that induce muscle contraction.
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