This is how muscles and tendons work

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Last Medical Review: April 1, 2020
Medically Reviewed by Dr. Elisabeth Vincent Hamelin
Muscles and Tendons (April 1, 2020)
The musculoskeletal system (April 1, 2020)

Our muscles and tendons allow us to move and important organs in the body can function. The muscles provide support to the skeleton and protect internal organs. In the muscles, heat is also generated which helps to keep the body temperature at a reasonable level.

In this text you can read about different types of muscles that are in the body. Most of the text is about skeletal muscles.

Different types of muscles

We have three different types of muscles in the body:

  • The heart muscles are in the heart. They are durable and fast. The heart muscles cannot be controlled by the will.
  • The skeletal muscles are found in, for example, arms and legs. They work fast but are not so durable. They can be controlled by the will. The skeletal muscles allow us to move, speak, swallow, chew and express emotions through the faces in the face. They also provide stability to the skeleton and protect our internal organs.
  • Smooth muscles are found, for example, in the walls of the blood vessels, the trachea, the bladder and the gastrointestinal tract. They cannot be controlled by the will. Smooth muscles are enduring but work slowly. The contractions of smooth muscles affect how the blood flows in the blood vessels and how the air flows through the trachea. Smooth muscles also push the urine and gastrointestinal contents against the urethra or rectum opening.

This is how skeletal muscles are built up

Skeletal muscle cells consist of several cells that have grown together. Each cell therefore contains several cell nuclei. The muscle cells are in bundles that are held together by connective tissue. Several bundles together form a muscle. There is also a membrane of connective tissue around the entire muscle. In the connective tissue there are nerves that send information to and from the muscle.

The skeletal muscles are controlled by the will

The contractions of the skeletal muscles are guided by our will. When you want to move, a nerve signal from the brain passes through the spinal cord. The nerve signal then passes to the muscle through various nerve fibers. The signal causes the muscle to contract.

The blood provides the muscles with oxygen and nutrition

The muscles get oxygen and nutrition from blood vessels that go into the muscle. As the muscle works, more blood flows to the muscle.

Muscles need a lot of energy when they work

Muscles consume a lot of energy when contracted. Therefore, the muscle cells contain many so-called mitochondria that produce the energy needed. The energy comes from the nutrition in the food we eat.

Lactic acid can be formed if the muscle does not get enough oxygen

A working muscle also needs oxygen. Sometimes the muscle does not get enough oxygen. This means that the nutrients in the muscle are not completely broken down. Then lactic acid is formed. It may feel like you are getting tired and getting muscle aches.

After birth, no more skeletal muscle cells are formed

The skeletal muscle cells are formed in the fetus. After birth, no more skeletal muscle cells are formed. As we grow, the size of the muscle cells increases instead. Some muscle cells can be up to 30 centimeters long.

Tendons attach the muscles to the skeleton

Each skeletal muscle is surrounded by a membrane of connective tissue. Where the muscle runs out, the connective tissue passes into a tendon that attaches to the skeleton. The tendons consist of tight connective tissue. The shortest tendons are only a few millimeters long and the longest ones are about 30 centimeters.

The tendons are protected by late skis and mucus sacks

Connective tissue is a type of tissue that is very strong and elastic. The tendon is therefore very tight. Some of the body’s tendons are protected in so-called late skis. A latex ski is a channel of connective tissue. For example, some of the tendons of the hand and foot are in late skis.

Even so-called mucus bags protect certain tendons. A mucus is like a fluid-filled bladder.

Late skis and mucus bags are especially needed where the tendons are subjected to great forces and where the tendon slides over a hard leg edge. Both tendon skis and mucus sacs contain fluid that causes the tendon to slide well against the tissue that is around the tendon.

The body’s bigger muscles

There are over 600 skeletal muscles in the body. The different muscle groups work together as you move. This makes the movements smooth.

Below are some of the body’s most important skeletal muscles.

The muscles of the head

On the face are several small superficial muscles that, for example, open and close the eyes and mouth. With the help of these muscles we can, for example, wrinkle the forehead, smile, blink and shape the lips in different ways. The muscles allow us to show other people how we feel and how we react to different things through different facial expressions.
We have four chewing muscles next to the two jaw joints. When we chew, these muscles contract. There are other muscles that handle the movements of the tongue and throat.

Muscles of the neck and neck

The neck has several important muscles. Among other things, the oblique neck muscle that allows you to bend and twist your head. It starts from the sternum and the clavicle and attaches to the temporal bone behind the ear.

The muscles of the neck are used when we move our heads. The muscles also help to keep the head and upper neck vertebrae stable.

The muscles of the shoulder

There are several muscles around the shoulders. They stabilize the shoulder joint and make it possible to move both the shoulder and the arm.

Here are some of the most important muscles:

  • The scalp muscle extends from the neck bone and the projections into the cervical and thoracic vertebrae. It attaches to the shoulder blade and the clavicle. The cutting muscle allows you to raise your arm over your head. It also holds the shoulder blade in place.
  • The wide back muscle sits on the side of the back. It goes from the spine and pelvis to the upper arm. When the muscle is tightened, the arm is pulled down and turned inward.
  • Large chest muscle starts from the clavicle, sternum and ribs to the upper arm bone. The muscle pulls the arm down and turns it inward.
  • The deltoid muscle goes between the clavicle, shoulder blade and upper arm. It gives the shaft its rounded shape. When the muscle is tightened, the arm is lifted to the horizontal position.
  • The rotator cuff is a group of four small muscles that surround the shoulder joint. The muscles are important for arm movements. They allow us to lift and turn our arm. They are also important for keeping the shaft stable.

Arm muscles

The upper arm has two large muscles:

  • The biceps muscle is in the front of the upper arm. It goes from the shoulder blade to the beam bone at the elbow. The muscle bends the elbow joint. In addition, it rotates the forearm outwards so that the palm comes up.
  • The triceps muscle is in the back of the upper arm. It extends from the shoulder blade to the elbow and extends the elbow joint.

Forearm muscles

In the forearm there are about twenty different muscles. Several muscles work together in groups. They can, for example, bend or stretch the wrist and fingers. They can also twist the forearm and hand outwards or inwards.

The forearm muscles extend between the legs of the forearm, hand and fingers. Some muscles start from the lower part of the upper leg and therefore also affect the elbow joint.

The muscles of the hand

The rough movements and power of the hand and fingers are handled by the forearm muscles. Minor movement of the fingers is called fine motor. Fine motoring is done with the help of several small muscles in the hand.

The fine motor of the hand is also dependent on the brain coordinating and controlling the movements. The area of ​​the brain that handles the movements of the hand is as large as the area that controls all the muscles of the chest, back and abdomen.

The muscles in the hand start from the legs of the wrist and the middle hand, and attach to the legs of the middle or fingers. The thumb and little finger are more moving and have their own muscles. Four muscles affect the movements of the thumb and three muscles affect the little finger. In the middle hand there are small muscles that allow you to spread your fingers, stretch your fingers and bend at the knuckles.

Back muscles

There are many muscles in the back. Some are located superficially when the skin. This applies, for example, to the capillary muscle and the broad back muscle. They affect the movements of the shoulder and arm.
Other muscles are deeper, such as the long muscles that go along the entire spine. Those muscles stretch the spine, twist the body and help with our posture.

Chest muscles

The chest muscles can be divided into superficial and deep muscles. The superficial are important for arm movements. This applies, for example, to the large chest muscle and small chest muscle. The deep muscles of the chest include the intercostal muscles and the midbrain.

The intercostal muscles are located between the ribs

The intercostal muscles are small muscles that sit between the ribs. As they work, the ribs are lifted and lowered. The intercostal muscles are therefore important in breathing, especially when we breathe in and breathe quickly. Calm exhalation does not occur with the help of muscles but only by the chest collapsing to its original position.

The middle nerve is an important muscle for breathing

The middle nerve is a muscle plate that separates the thorax from the abdominal cavity. The esophagus and large blood vessels pass through holes in the diaphragm. The air is sucked into the lungs when the diaphragm is tensioned. Then the middle fence pulls together and is lowered down. This makes the space in the chest cavity larger and the lungs more room. You exhale as the middle ground relaxes. Then the space in the chest cavity decreases again.

Abdominal muscles

The abdominal muscles are in several layers and protect the abdominal organs. The straight abdominal muscles are on both sides of the stomach. Further out to the sides are the oblique abdominal muscles and the transverse abdominal muscle. The abdominal muscles move between the lower ribs, hip bones and pubic bones.
The pressure inside the abdominal cavity increases as the abdominal muscles are tightened. You can use this for example when lifting heavy or peeing. The increased pressure also spreads to the chest and can help to exhale the air as you exhale. Increased abdominal pressure also reduces the strain on the spine when lifting something heavy.

Pelvic muscles

In the lower pelvis there is the so-called pelvic floor. It is a muscle plate that consists of several muscles. The pelvic floor prevents the pelvic internal organs from being pushed down as the pressure increases in the abdomen. Examples of when the pressure increases are when you jump, lift heavy, cough, sneeze, pee or poop. Annular muscles of the pelvic floor sit around the vagina, rectum and urethra. The vagina, rectum and urethra are squeezed together as these muscles contract.

The muscles of the seat

There are several muscles in the seat. Here are two of the most important:

  • Large seat muscle forms the contour of the buttocks. It extends into the hip joint and turns the leg outwards as well as the leg sideways.
  • The middle seat muscle sits inside the large seat muscle. It runs between the outside of the intestinal bone and the femur. The middle seat muscle extends the hip joint and turns it outward.

Thigh muscles

In the thigh there are several large muscles:

  • On the front of the thigh are the outer broad thigh muscle, the middle broad thigh muscle, the inner broad thigh muscle and the straight thigh muscle. These four muscles together form the quadriceps thigh muscle. The muscles bend the hip joint and stretch the knee joint and allow us to rise from a sitting position.
  • The tail muscle goes obliquely across the thigh from the outside of the hip to the inside of the tibia. The muscle is used when sitting with crossed legs in a so-called tailoring position. The hip joints are bent and the thighs are turned outwards when the tail muscles are contracted. At the same time, the knee joints are bent and the lower legs are turned inwards.
  • On the back of the thigh are three muscles that together stretch the hip joint and bend and twist the leg in the knee joint. Those muscles are usually called the hamstring muscles.
  • On the inside of the thigh are five muscles, all of which move the leg inwards towards the center of the body. The largest muscle is called the large inward driver muscle.

The muscles of the wad

On the lower leg there are several muscles gathered in groups. Here are some of the most important muscles:

  • In front of the tibia lies the anterior tibia. It starts from the tibia and calf bone and attaches to the ankle and toes. When you tighten the muscle, the ankle and toes are bent upwards.
  • The outer calf muscle and the inner calf muscle are located on the back of the lower leg. These muscles are based on the femur, tibia and calf bone. They attach to the Achilles tendon at the heel bone. Achilles tendon is the strongest tendon of the body. When the muscle is tightened, the knee joint bends and the ankle is stretched. The outer and inner calf muscles make the stump possible as you walk and run.

Foot muscles

The most important task for the foot muscles is to support the arches together with strong ligaments. Small muscles on the underside of the foot can bend and spread the toes. Small muscles on the top of the foot help stretch the toes.

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