Meet Your Muscles: Muscular System Anatomy
You need your muscles for almost everything you do. So it’s not surprising that you have hundreds of them. There are about 700 named skeletal muscles in the human body, including roughly 400 that no one cares about except specialists. On the other hand, there is just one important cardiac muscle. And there are literally countless smooth muscles. All these muscles make up your muscular system. The muscular system works with other body systems to keep you alive and healthy. It helps you do all the things you do. Together with the skeletal system, it forms the musculoskeletal system, which is responsible for movement of the human body.
What are muscles?
The human body consists of various tissues, including the skin, connective tissues, organs, nervous system, body fluids, bones, and muscles. Muscles are soft tissues made up of muscle cells that have the ability to contract and extend. Muscles produce force and the movement of our body.
The muscular system is made up of three different kinds of muscles: skeletal muscles, smooth muscle, and heart muscle. But what does each kind of muscle do? And where in the body are they located? Explore the muscular system in this engaging and informative post.
What are the three types of muscles of a human body?
We have three types of muscles: cardiac muscle, smooth muscles, and skeletal muscles.
- Cardiac muscle is found in the heart (forms the heart walls) only and is responsible for the beating of the heart. Cardiac muscle is involuntary, as it is not controlled by the brain.
- Smooth muscles are located in the walls of our organs such as stomach, esophagus, blood vessels, urethra, uterus, intestines, bladder, and bronchi. Smooth muscles are also found in the skin where they control the erection of body hair. Like cardiac muscle, smooth muscles are not controlled by the brain.
- Skeletal muscles are the biggest type of muscles and are responsible for producing movements of the human body. Your muscular system contains more than 600 skeletal muscles varying in size, shape, and use. Attached mainly to skeletal bones, skeletal muscles control every action that we consciously perform such as walking, sitting, eating, working, running, and exercising. In other words, the major purpose of skeletal muscles is to provide force to move the joints of the body in the different directions or planes that they are designed to move in. Most skeletal muscles are voluntary and are controlled by the brain. When we work on bodybuilding, we are trying to make our skeletal muscles stronger and bigger. This has many health benefits, as already discussed in detail (The benefits of weight training – countless reasons to lift weights).
Muscle control: voluntary and involuntary muscles
You can control some muscles – mainly skeletal muscles. The muscles involved in weightlifting fall into the category of skeletal muscle. You can make them move just by thinking. Suppose you want to pick an apple. You reach out and curl your fingers around the apple. You pull it down. Only you decide you want to do this. And your muscles make it happen. Walking around, lifting weights, sitting down, jumping, running, … the list could go on for a long time.
There are other muscles that you cannot control, no matter how hard you try. You can’t make food travel to your stomach more quickly. You can’t make your heart beat more slowly. These kinds of muscles do their work automatically. You would not be alive for long if you did not breathe and if your heart did not keep pumping. You do not even have to think about doing those things thanks to your involuntary muscles (cardiac muscle and smooth muscles).
Most important skeletal muscles of your body
As you already know, skeletal muscles are the ones you check out in the mirror. Physical training alters the appearance of skeletal muscles and can produce changes in muscle performance. Conversely, a lack of use can result in decreased performance and muscle appearance.
The muscles of your body which you can work out can broadly be divided into two categories – upper body and lower body muscles.
Most important upper body skeletal muscles
If your strength training program doesn’t include these eight upper body muscle groups, you’re missing out on major gains.
- Deltoids. Triangular muscle split into three sections: front (anterior deltoid), middle (lateral deltoid), and back (rear or posterior deltoid). Causes abduction, flexion, extension, and rotation of the shoulder, depending on which section is shortened.
- Trapezius. Elevates (raises) the shoulder girdle when shortened.
- Pectorals. Acts upon the shoulder joint, causing flexion, adduction and rotation.
- Latissimus dorsi. Also acts upon the shoulder joint, but causes extension, adduction and rotation.
- Biceps. These muscles have two heads at one end, which are attached to the humerus and scapula. When shortened, the biceps cause flexion at the elbow.
- Triceps. This muscle has three heads at one end, two attached to the humerus and one attached to the scapula. It mainly causes extension of the elbow joint, but also helps with extension and abduction of the shoulder joint.
- Abdominals. A group of muscles providing support for the front of the abdominal wall, and for flexing the spine. Also known as the rectus abdominis.
- Obliques. These muscles run diagonally, causing rotation and lateral (sideways) flexion of the spine.
Most important lower body skeletal muscles
If your strength training program doesn’t include these four lower body muscle groups, you’re missing out on major gains.
- Quadriceps. Group made up of four muscles (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis) which all meet at the patella. Responsible for flexion of the hip and extension of the knee.
- Gluteals. This muscle group has three main sections. The gluteus maximus is the largest part of the buttocks, and is the strongest muscle in the body. It mainly causes extension of the hip joint. The gluteus medius and gluteus minimus help with hip adduction and rotation.
- Hamstrings. Group made up of three muscles which extend the hip and flex the knee. Biceps femoris, semimembranous, and semitendinosus.
- Calf. Formed by two muscles, the gastrocnemius and soleus. These muscles cause plantar flexton (pointing the toes) of the ankle joint.
What are the main functions of the muscular system?
The main functions of the muscular system are as follows:
- generating movement
- maintaining posture
- stabilizing joints
- generating heat
- blood circulation
- organ protection
Skeletal muscle structure
Muscles make up about 45 per cent of the average person’s weight. They are 80 per cent water; the rest is mostly protein. Each muscle is made up of cylindrical fibres (sometimes called muscle cells), which are about 50–100 micrometres in diameter (the width of a human hair). They range from a few centimetres in length to 1 m, and can run the entire length of the muscle. These fibres are grouped in bundles called fasciculi, each separately wrapped in a sheath (perimysium) that holds them together.
Each muscle fibre comprises thread-like strands called myofibrils, each of which is about 1 micrometre in diameter, or 1⁄100th the diameter of a human hair. These hold myofilaments containing the contractile proteins myosin (thick filaments) and actin (thin filaments), whose actions are responsible for muscle contraction. To a large extent, your muscle’s cross-sectional area, together with the number and length of its fibres, determine its strength. You cannot change the number of fibres in your muscle, but you can increase both its cross-sectional areas through strength training, and the number of muscle fibres recruited when executing any given movement.
How do muscles generate force? How muscles work?
Muscles cells express two filament proteins called actin and myosin, which together form actomyosin filaments. The actomyosin filaments are flexible, and can contract and change in length and shape. The contraction of these filaments leads to force generation and the movements of muscles, leading to the movements of the body parts that are attached to the muscles.
Is there a difference between female and male muscles?
Generally, the muscles of men and women are the same and will perform and respond in a similar manner. However, men can develop more muscle mass than women.
Basic measures of body strength show that females generally have 30–50 per cent less strength than males. This is mainly in the upper body, where men are about 40 per cent stronger. Women typically have less muscle mass and more body fat. Additionally, a man’s taller and wider skeletal frame provides a leverage advantage. However, “female muscle” and “male muscle” are exactly the same.
There are no inherent gender differences in muscle quality or capacity, and women can generally generate the same force per unit of muscle as men. Furthermore, with training they make the same relative strength improvements. In certain sports, such as climbing, dance and aspects of gymnastics, the lower centre of gravity, flexibility, strength-to-weight ratio, and shorter levers give a woman a better relative strength ratio.
Connections & muscle attachments
As we’ve said, muscles and bones and joints form one integrated system, and no one component is more important than another. Without muscles, you would be a motionless pile of bones; without a skeleton, you’d look and move more like a jellyfish; and without joints to control and stabilize the bones, you’d stumble around like the scarecrow from the Wizard of Oz.
Therefore, muscles attach to bone via tendons. The attachment points are referred to as the origin and the insertion. The origin is the point of attachment that is proximal (closest to the root of a limb) or closest to the midline, or centre of the body. It is usually the least moveable point, acting as the anchor in muscle contraction. The insertion is the point of attachment that is distal (furthest from the root of a limb) or furthest from the midline or centre of the body. The insertion is usually the most moveable part, and can be drawn towards the origin. Knowing the origin and insertion of a muscle, which joint or joints the muscle crosses and what movement is caused at that joint or joints is a key element of exercise analysis.
Five fun facts about the muscular system
- Muscles make up approximately 40 percent of total weight.
- The heart is the hardest-working muscle in the body. It pumps 5 quarts of blood per minute and 2,000 gallons daily.
- The gluteus maximus is the body’s largest muscle. It is in the buttocks and helps humans maintain an upright posture.
- The ear contains the smallest muscles in the body alongside the smallest bones. These muscles hold the inner ear together and are connected to the eardrum.
- A muscle called the masseter in the jaw is the strongest muscle by weight. It allows the teeth to close with a force of up to 55 pounds on the incisors or 200 pounds on the molars.
To build your muscles, you need to know your muscles. There is no way of getting around the fact that you need to know your muscular system anatomy. Strength training isn’t a mindless jock activity. Athletes, trainers, bodybuilders and even regular gym-goers need to understand exactly how the muscles in their body function. That way they can work them properly to make them stronger and bigger. Each muscle serves a different purpose. Therefore the aim of exercising shouldn’t simply be to make them aesthetically pleasing but to make sure each and every muscle in your body is strong.