Usually, an individual has more than 600 muscles in their body that helps to move, breathe, see, lift, or stay still. For example, the heart is a muscle that pumps blood to the body.
Muscle is a soft tissue that is made up of highly specialized thin and elongated cells called muscle fibers that work for motion and other functions. There are different muscles that have different functions like running, jumping, digesting food, or beating thousands of times a day (heart). The sarcolemma is the membrane that may bind the muscle fiber, and this muscle fiber contains sarcoplasm which is composed of the network-like membrane called the sarcoplasmic reticulum. Numbers of longitudinal fibrils called myofibrils are present in each muscle fiber.
Similarly, muscles can be affected by injuries, disorders, or diseases associated with them. These conditions can cause muscle pain, muscle spasms, or muscle weakness.
Physiological properties of muscle tissue
- Contractibility
- Excitability
- Extensibility
- Elasticity
Types of Muscle Tissue
There are different muscles that are controlled by our will with the help of the nervous system called voluntary muscles, whereas there are other muscles that are not controlled according to our will, called involuntary muscles. Some voluntary muscles are moving, jumping, or dancing, whereas involuntary muscle is breathing or food digestion.
There are mainly three types of muscle tissue in the body.
Skeletal Muscles
- Skeletal muscles are those muscles that are attached to the bones, tendons, and ligaments. Skeletal muscles are attached to the bones with the help of tendons.
- They help to support the body weight and help in the movement of the body.
- Skeletal muscle is also called the voluntary muscle.
- As its cell fibers are composed of alternate light and dark band strips, it is also known as striated muscle.
- Compared to other cells, skeletal muscle fibers are quite larger and are also referred to as muscle fibers or myofibers.
- The length of each fiber is 1.2 inches, and the diameter is 0.004 inches.
- The longest fiber is found in the Sartorius muscle (12 inches) and the shortest fiber in the stapedius muscle (0.04 inches).
- Skeletal muscle consists of myofilament, where thick myofilament is composed of larger proteins called myosin, and thin myofilament is composed of small proteins called actin.
- Skeletal tissue consists of alternating light and dark bands when observed through the microscope.
- Dark A band (anisotropic band) is produced by overlapping the thick myosin and actin myofilament and does not allow the light to pass.
- Light I band (isotropic band) is produced by the thin actin myofilament and allows light to pass through it.
- Across the I band, there is a dark z line.
- Light H zone (Hensen’s disc) consists of only myosin myofilament in the A band.
- The sarcomere is the area between two Z lines.
- Skeletal muscles are found to be attached head, trunk, limbs, tongue, pharynx, body wall, esophagus, and other parts.
Functions of skeletal muscle
- Skeletal muscle plays an important role in chewing and swallowing the food
- It helps in breathing, that is, expansion and contraction of the chest cavity
- Maintain the body posture
- Movement of different parts and bones located in different body areas.
- Joints projection and holding at a single place.
- Bring the movement of the organs and locomotion of the body.
Smooth muscles
- Smooth muscle is also called the involuntary muscle because it is controlled by Autonomic Nervous System.
- It is non-striated and appears to be smooth when observed under the microscope.
- Smooth muscle cells consist of single elongated nuclei; their muscle fiber is long, spindle-shaped, and slender.
- A smooth muscle fiber is long but not as long of that as skeletal muscle fiber.
- It contains a large number of longitudinal myofibrils and is mostly enclosed by sarcolemma.
- There are no stipes in smooth muscle as the actin and myosin myofilaments are arranged more randomly, and these myofibrils are thinner.
- Smooth muscle is mainly found in the digestive system and the internal organs.
- Although its actions are rhythmical, contraction and relaxation are quite slower.
- The smooth muscle’s thin myofilament is mostly found in the cytoplasm.
Functions of smooth muscle
- Like other muscle systems, the function of the smooth muscle is to contract.
- Smooth muscle present in the digestive system is to help in the digestion of food.
- Similarly, it also helps in urination as these muscles are present in the body’s urinary system.
- It helps to push the food through the intestine by the peristalsis mechanism.
- Involuntary movement.
Cardiac muscles
- Cardiac muscles are those muscles that are present in the heart.
- It is similar to that of the skeletal muscle, and when observed under the microscope, they have similar striation.
- Each cardiac muscle cell is tightly packed, nucleated, and separated from the other.
- The intercalated disc is the specialized cell that joins one end of the cell with the other end with the help of desmosomes.
- An intercalated disc also helps to connect the myofibril filaments and helps in the contraction of the cardiac muscles.
- The cardiac muscle’s contraction occurs through the transmission of the impulse from one cell to another.
- An intercalated disc occurs at the location of the z-line.
- Cardiac muscle contains the light I and the dark A band.
- They are equipped with the central and autonomous nervous system for the heart’s regular contraction and blood pump.
- They are called the fatigue-less muscle as they don’t get fatigued.
Function of cardiac muscle
- It helps to keep the heart beating and pumping through involuntary movements.
- Maintains the coordination of the heart.
Muscles disorders
These muscles are affected for different reasons; when they get affected, they stop functioning properly. A wide range of diseased, drugs, disorders, and injuries causes problems with the working mechanism of muscles. So some of the conditions or disorders that affect the muscles include:
- Cancer and other diseases:
There are multiple types of cancers and diseases that lead to improper function of the muscles. These include cancer like sarcoma, neuromuscular diseases like amyotrophic lateral sclerosis (ALS), an autoimmune disorder such as myasthenia gravis (MG), and many other types of muscle diseases. Inflammation of the muscles is caused by a disease called polymyositis and leads to weakness of the muscle.
- Cardiovascular diseases:
Several kinds of diseases related to the heart can cause the failure of the cardiac muscles. Cardiovascular diseases such as coronary artery diseases and other venous diseases can cause problems with the blood vessel and the heart. When the blood vessel muscles weaken, it may lead to a heart attack.
- Chronic pain disorder:
The muscle pain and the disorders are caused by fibromyalgia. Fibromyalgia is a condition that causes pain all over the body and also leads to sleep problems. Fibromyalgia is mostly triggered by stress, including physical and mental stress.
- Genetic disorder:
There are some genetic problems that lead to the disorder of the muscles. Individuals mostly acquire these disorders from their family members. One of the inherited disorders is muscular dystrophy; because of this, the muscle’s weakness is permanent in the offspring. There are more than thirty different types of muscular dystrophy.
- Infections:
Muscle fibers are also infected by different infections like bacterial and viral infections. Infections like Lyme diseases, Rocky Mountain spotted fever, and malaria can cause muscle disorders.
- Injuries:
Sometimes muscles get torn or stretched due to the injury, and one of the common examples is Brain strains. Accidents, trauma, and other injuries can cause muscle cramps or muscle spasms. Also, paralysis can be seen because of severe cases.
- Medications:
Some of the medications can also lead to a muscle disorder. Drugs like chemotherapy medication can lead to muscle pain. Some of the drugs used for the treatment of blood pressure can result in muscle soreness. Some individuals develop muscle weakness after an allergic reaction to toxic substances or medication.
Many people have sore muscles after having a heavy exercise or workout. When people have muscle tears, they sometimes put more pressure on themselves by performing extra work or heavy exercise, which leads to the soreness of muscles. Usually, muscle soreness occurs after 2 to 3 days of heavy exercise, which is why it is called delayed onset muscle soreness (DOMS). Similarly, the torn muscle starts to heal after some time through the recovery of the small muscle tears. With the muscle tear and repair mechanism, the muscle gets bigger and bigger, and this phenomenon is mostly followed by athletes and individuals at the gym.
References
- https://my.clevelandclinic.org/health/body/21887-muscle
- https://www.britannica.com/science/muscle
- https://www.britannica.com/science/skeletal-muscle
- https://open.oregonstate.education/aandp/chapter/10-2-skeletal-muscle/
- https://my.clevelandclinic.org/health/body/21787-skeletal-muscle
- https://www.britannica.com/science/gastrocnemius-muscle
- https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/smooth-muscle
- https://www.britannica.com/science/trapezius-muscle
- https://www.ncbi.nlm.nih.gov/books/NBK526125/
- https://www.kenhub.com/en/library/anatomy/smooth-musculature
- https://biologydictionary.net/smooth-muscle/
- https://www.healthline.com/health/cardiac-muscle-tissue#function
- https://www.medicalnewstoday.com/articles/325530
- https://www.sciencedirect.com/topics/immunology-and-microbiology/cardiac-muscle
- https://www.nhs.uk/conditions/fibromyalgia/causes/
- https://my.clevelandclinic.org/health/body/21887-muscle
- https://www.britannica.com/science/muscle
