Muscular system

Ahmed Raza

It twists, it bends, it can cup, it helps suck. The tongue is an essential part of human anatomy. Many of us grew up believing the playful tongue is the strongest muscle in the body.

But, is it really?

There is no straightforward answer to this question. To understand the tongue’s strength and movement, it is necessary to first examine basic muscle anatomy, the muscular system’s relationship to the body, and disorders of the muscular system.

Balance of body systems

Every movement in the body involves each body system. Without the active cooperation of the nervous, circulatory, endocrine, respiratory, digestive, immune, skeletal, and muscular systems, just to name a few, the body cannot create movement. Every system of the body overlaps and is interdependent.

Without the nervous system, it is impossible to coordinate the muscles of the body or to modulate the dilation of the blood vessels that supply the brain, heart, bones, or muscles with oxygen-rich blood.

Without the medical scribe training online-circulatory system, other systems, such as the respiratory, digestive, and endocrine systems would not be able to distribute oxygen, nutrients, and hormones to the cells of the body.

The skeletal system and the muscular system, collectively known as the musculoskeletal system, are often treated separately when reviewing anatomy. When reviewing movement, however, it makes sense to think of the muscles and bones working together to negotiate the body’s relation to gravity and space.

The muscular system is made up of muscles, tendons, and nerve endings that orchestrate the precise sequencing and timing of muscle actions. The major muscles of the body are shown in figure 1.

Figure 1 Major Muscles of the Body

Figure 1. Major muscles of the body. (© User:CFCF/Wikimedia Commons/CC BY 4.0)

Basic muscle anatomy

A working muscle is an organ made up of at least four different tissues, as shown in figure 2:

Muscle tissue — contracts and creates movement, produces heat, and provides skeletal support.
Connective tissue — communicates the power of the contraction to whatever the muscle connects to, such as bones, organs, or skin (epithelial tissue).
Nervous tissue — tells the muscle when to fire, for how long, and at what intensity.
Blood vessels — provides the nourishment that allows the muscle tissue to be active. Connective tissue and several layers of smooth muscle cells make up the largest vessels (arteries and veins).

Figure-2 Types of Tissue

Figure 2. Types of tissue. (© User:OpenStax/Wikimedia Commons/CC-BY-SA-3.0)

There are three basic types of muscle tissue, as illustrated in figure 3:

Skeletal muscle — is attached to bones to create movement at the joints. It has alternating bands of light and dark transverse fibers that give the tissue a striated appearance. The peripheral portion of the central nervous system (CNS), also known as the somatic nervous system, controls the skeletal muscles. This allows many of these muscles to work under conscious (voluntary) control. The striated muscle fibers act independently of neighboring muscle fibers.
Smooth muscle — is found in the walls of hollow internal organs such as blood vessels, the gastrointestinal tract, bladder, and uterus. It is controlled by the autonomic nervous system, meaning it acts involuntarily (not under conscious control). The non-striated muscle cell is spindle-shaped containing one central nucleus. Smooth muscle contractions are slow and rhythmical.
Cardiac muscle — is found in the walls of the heart (myocardium) and is also under the control of the SA node and the autonomic nervous system. Cardiac muscle is rectangular and is striated, like skeletal muscle, but the muscle cell has only one central nucleus, like smooth muscle. The cardiac muscle contraction is involuntary, strong, and rhythmical.

Figure 3 Types of Muscle Tissue

Figure 3. Muscle tissue. (© User:Arcadian/Wikimedia Commons/CC-BY-SA-3.0)

The skeletal muscle that we see with the naked eye is made up of bundles of fascicles (illustrated in figure 4) enveloped by a thick connective tissue called the fascia (or deep fascia). The fascia should not be confused with the layers of tissue located within the structure of muscle.

Figure 4 Bundles of Fascicles

Figure 4. Bundles of fascicles.* (© User:OpenStax College/Wikimedia Commons/CC-BY-SA-4.0)

The fascicles consist of bundles of muscle fibers (muscle cells); inside the muscle cells are bundles of myofibrils (myofilaments). The myofibrils are made up of thick and thin twisted strands (filaments) that overlap and lie alongside each other.

Each of these bundles of fascicles, muscle fibers, and myofibrils are wrapped in a layer of connective tissue (epimysium, perimysium, endomysium, and sarcolemma). All of the layers of connective tissue come together—at the ends of the muscles—to create tendons that connect muscles to bones (see figure 5).

Figure 5 Tendon Muscle Structure

Figure 5. Tendon and muscle structure. (© User:Arcadian/Wikimedia Commons/CC-BY-SA-3.0)

Muscular system function

Muscles surround joints and wrap around bones in astonishingly sophisticated spiraling layers. The principal functions of the muscular system in the body are as follows.

Movement

Skeletal muscles assist in the voluntary actions of every human body part. Active contraction of these muscles transpires at the expense of energy, which creates a force that moves the body part. Muscles can be viewed as the motors of the body, which convert chemical energy, present in food, into mechanical work.

The muscles work collectively as a matrix of potential movement choices. This pattern affects every articulation in the body. Muscles do not function in isolation, and a single muscle never works without support and modulation from other muscles. Each muscle affects every other muscle, whether they are nearby or far away.

When a muscle contracts, molecules create and release bonds between the thick (myosin) and thin (actin) filaments of the sarcomere (a structural unit of a myofibril), as seen in figure 6, to create a sliding action that increases their overlap. This action draws the two ends of the myofibril toward each other. If enough myofibrils shorten, the whole muscle slides shorter.

Figure 6 Sarcomere Diagram

Figure 6. Sarcomere diagram. (© User:SlothMcCarty/Wikimedia Commons/CC-BY-SA-3.0)

Posture and stability

The human skeleton is composed of bones and the joints that are between them. Skeletal muscles play a significant role in stabilizing the human skeleton. They also help in maintaining proper posture. Muscular and connective tissue provide the joints with stability.

Heat production

Muscles use a substantial amount of the body’s total energy during an activity such as contraction. Because of this, the body’s metabolic rate is increased, producing a significant amount of heat in the body. This feature of muscles is of particular importance for individuals living in cold climates.

Temperature homeostasis regulation: Video tutorial

Circulation

Cardiac muscles are responsible for forcing the blood out of the heart and pumping it throughout the body. The blood is in constant movement with the regular pumping motion of the heart, thereby supplying oxygen and nutrients to every tissue in the body and also removing waste products.

Digestion promotion

Smooth muscles line the organs of the human digestive system, such as the esophagus, stomach, and intestine. These muscles contract and aid in the digestive system to digest food.

Nearly all movement in the body is the result of muscle contraction. Exclusions to this are the action of cilia, the flagellum of sperm, and amoeboid movement of some white blood cells.

Disorders of the muscular system

Many ailments can affect muscles. Muscle disorders can cause pain, weakness, or even paralysis (immobility).

Causes of muscle disorders

Injury or overuse, such as in strains or sprains, tendinitis, and cramps or spasms
Genetic disorder, such as muscular dystrophy
Inflammation, such as myositis
Diseases of nerves that affect muscles
Infections
Certain medications
Some cancers
Sometimes the cause is unknown

Muscular disorders

Diagnosis and tests

Treatments and therapies

Fact or fiction

Now, on to what you’ve been waiting for—is the tongue the strongest muscle in the body?

The short answer is no.

Just because the tongue doesn’t fatigue (that is if a person doesn’t have any disorders), doesn’t mean it is the strongest.

The question of whether the tongue is the strongest muscle in the body is itself misleading. The soft tongue is not just one muscle; it is a collection of eight separate muscles. There is a lot of redundancy in the muscle architecture of the tongue, which means the activation of different muscle fibers gets the same result.

The tongue also doesn’t win for having the most brute force (i.e., the quadriceps and glutes, which contain a large number of sarcomeres) or for having the most overall work done in the course of a lifetime. By the later measure, the hardest working muscle in the body is the one that is pumping and pumping 24/7 to keep the blood flowing: your heart.

This article is not all inclusive. Please contact us at PMT supportEmail to reach the author and recommend other facts or muscular disorders that interest you!