In addition to movement, muscle contraction also fulfills some other important functions in the body, such as posture, joint stability, and heat production. Posture, such as sitting and standing, is maintained as a result of muscle contraction. The skeletal muscles are continually making fine adjustments that hold the body in stationary positions. Smooth muscles are also present within the walls of the bladder and the bronchi.
The arrector pili muscles in the skin, which make the hair stand up, also comprise smooth muscle fibers. Cardiac muscles are responsible for the heartbeat and only exist in the heart. These muscles work automatically without stopping, day and night. They are similar in structure to the skeletal muscles, so doctors sometimes classify them as striated muscles.
The cardiac muscles contract so that the heart can squeeze out blood and then relax so that it can fill up with blood again. Muscle weakness can affect people with upper or lower motor neuron dysfunction or conditions such as myasthenia gravis that affect the area where the nerves join the muscle. Stroke , spinal cord compression, and multiple sclerosis can all also lead to muscle weakness. They are likely to use the universal scale for testing muscle strength:.
If a doctor finds evidence of muscle weakness, they may order tests to identify the underlying problem. The treatment will depend on the cause. A person can often relieve the symptoms of a muscle injury using the RICE method :. If a person experiences extreme and unexplained muscle pain or muscle weakness, especially if they also have difficulty breathing, they should see a doctor as soon as possible. Developing muscles through exercise can improve balance, bone health, and flexibility, and it can enhance strength and stamina.
People can choose from a wide range of physical activity options, but there are two main types of exercise: aerobic and anaerobic. Aerobic exercise sessions are typically of long duration and require medium-to-low levels of exertion. This type of exercise requires the body to use the muscles at well below their maximum strength capacity.
A marathon is an example of an aerobic activity with a very long duration. They use a higher proportion of the slow-twitch muscle fibers. Energy consumption comes from carbohydrates, fat, and protein, and the body produces high quantities of oxygen and very little lactic acid.
During anaerobic exercise, the muscles contract intensely at a level nearer to their maximum strength. Athletes who aim to improve their strength, speed, and power will focus more on this type of exercise.
A single anaerobic activity lasts from a few seconds to a maximum of 2 minutes. Examples include weightlifting, sprinting, climbing, and jumping rope. Anaerobic exercise uses more fast-twitch muscle fibers. There are other muscles throughout the body named by their shape or location. The deltoid is a large, triangular-shaped muscle that covers the shoulder.
It is so-named because the Greek letter delta looks like a triangle. When a muscle has a widespread expansion over a sizable area, but then the fascicles come to a single, common attachment point, the muscle is called convergent. The attachment point for a convergent muscle could be a tendon, an aponeurosis a flat, broad tendon , or a raphe a very slender tendon.
The large muscle on the chest, the pectoralis major, is an example of a convergent muscle because it converges on the greater tubercle of the humerus via a tendon. The temporalis muscle of the cranium is another. Due to this design, the muscle fibers in a pennate muscle can only pull at an angle, and as a result, contracting pennate muscles do not move their tendons very far. However, because a pennate muscle generally can hold more muscle fibers within it, it can produce relatively more tension for its size.
There are three subtypes of pennate muscles. In a unipennate muscle, the fascicles are located on one side of the tendon. The extensor digitorum of the forearm is an example of a unipennate muscle.
A bipennate muscle has fascicles on both sides of the tendon. In some pennate muscles, the muscle fibers wrap around the tendon, sometimes forming individual fascicles in the process. This arrangement is referred to as multipennate.
A common example is the deltoid muscle of the shoulder, which covers the shoulder but has a single tendon that inserts on the deltoid tuberosity of the humerus. Because of fascicles, a portion of a multipennate muscle like the deltoid can be stimulated by the nervous system to change the direction of the pull.
For example, when the deltoid muscle contracts, the arm abducts moves away from midline in the sagittal plane , but when only the anterior fascicle is stimulated, the arm will abduct and flex move anteriorly at the shoulder joint. Skeletal muscles do not work by themselves.
Muscles are arranged in pairs based on their functions. For muscles attached to the bones of the skeleton, the connection determines the force, speed, and range of movement. These characteristics depend on each other and can explain the general organization of the muscular and skeletal systems.
The skeleton and muscles act together to move the body. Have you ever used the back of a hammer to remove a nail from wood? This allows you to contract your facial muscles just a tiny bit and make dozens of different kinds of faces. Even the smallest movement can turn a smile into a frown. You can raise your eyebrow to look surprised or wiggle your nose. And while you're looking at your face, don't pass over your tongue — a muscle that's attached only at one end!
Your tongue is actually made of a group of muscles that work together to allow you to talk and help you chew food. Stick out your tongue and wiggle it around to see those muscles at work. Because there are so many skeletal muscles in your body, we can't list them all here. But here are a few of the major ones:.
Reviewed by: KidsHealth Medical Experts. Larger text size Large text size Regular text size. Smooth Muscles Smooth muscles — sometimes also called involuntary muscles — are usually in sheets, or layers, with one layer of muscle behind the other. Page 1 A Hearty Muscle The muscle that makes up the heart is called cardiac muscle. Skeletal Muscle. Face Muscles You may not think of it as a muscular body part, but your face has plenty of muscles.
Major Muscles Because there are so many skeletal muscles in your body, we can't list them all here. But here are a few of the major ones: In each of your shoulders is a deltoid say: DEL-toyd muscle. Your deltoid muscles help you move your shoulders every which way — from swinging a softball bat to shrugging your shoulders when you're not sure of an answer.
The pectoralis say: pek-tuh-RAH-lus muscles are found on each side of your upper chest.
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