What are Muscles? Many multicellular animals have evolved specialized cells for movement. These cells contain numerous filaments of special proteins, action, and myosin. let’s discuss in detail various types of muscles are as under;
TYPES OF MUSCLES
The vertebrates possess three types of muscle cells.
- Smooth muscles
- Cardiac muscles
- Skeletal muscles.
Smooth muscles were the earliest form of muscle to evolve and it is found throughout the animal kingdom. Smooth muscles are long and spindle-shaped with each containing a single nucleus. It has no striations. It is not under the voluntary control. We describe smooth muscle, tissue most precisely as visceral, non-striated and involuntary. These muscles are found in the blood vessels, digestive tract and many other organs.
These are muscles of the heart. They constitute most of the mass of the heart walls. Heart muscle is composed of chains of a single cell, each with its own nucleus. The chain of cells is organized into fibres that are branched and interconnected. The Cardiac are striated and involuntary.
The muscles that are attached with the skeleton and associated with the movement of bones are called skeletal muscles. The skeletal muscles are consciously controlled and therefore is called voluntary muscle. Skeleton muscle is also called striped or striated muscle because they show alternate light and dark bands e.g., triceps and biceps. Generally, each end of the entire muscle is bone by a bundle of collagen, non-elastic fibres known as tendons.
Muscle fatigue is a state of physiological inability to contract. Muscle fatigue results from a relative deficit of ATP. When no ATP is available, contractures or states of continuous contractions result because the cross bridges are unable to detach. Excess accumulation of lactic acid and ionic imbalances also contribute to muscle fatigue. Lactic acid, which causes muscle pH to drop (and the muscle to ache), causes extreme fatigues by breaking glucose.
Tetany is the disease caused by low calcium in the blood. It increases the excitability of neurons and results in loss of sensations. Muscle twitches and convulsion occur. If untreated the system progresses to spasm of larynx respiratory paralysis, and ultimately death occurs.
Effect of exercise on muscle; The amount of work a muscle does is reflected in changes in the muscle itself. When muscles are used actively they increase in size or strength and become more efficient and fatigue resistant. Aerobic exercise such as swimming, joggings, and fast walking ‘results in several changes in skeletal muscle. Capillary surrounding the muscle fibers, as well as mitochondria with them, increase in number and fiber synthesizes more myoglobin. These changes result in more efficient muscle metabolism and resistance to fatigue. Complete immobilization of muscle leads to muscle weakness and severe atrophy.
It is also known as the titanic contraction of entire muscle:’ It lasts for just a few seconds or several hours, causing the muscle to become taut (stretched, tight) and painful. It is most common in the thigh and hip muscle it usually occurs at night or after exercise. It reflects low blood sugar level, electrolyte depletion, dehydration irritability of spinal cord and neurons.
Tetanus: The term tetanus is also used for an acute infectious disease caused by anaerobic bacterium, Clostridium tetani resulting in persistent painful spasms of some skeletal muscles typically begins gradually with stiffness of laws and neck muscle and progresses to fixed rigidity of jaws (lockjaw) and spasms of and limb muscle, usually fatal due to respiratory failure though rare in developed countries the tetanus is the major killer develop in countries where the mortality rate is 40 percent.
ARRANGEMENT OF SKELETAL MUSCLE FOR SKELETON MOVEMENT
Skeletal muscle has three parts:
1. Origin: It is the end of a muscle which remains fixed when muscle contracts,
2. Insertion: The end of a muscle that moves, and
3. Belly: It is thick part between origin and Insertion which contracts.
Connective tissue: Connective tissue binds other tissue and help to maintain body form by holding the various organs together. Connective tissue fibrils have two specialized kinds.
i) Ligament: They attach bone to bone and are slightly elastic.
ii) Tendons: They attach muscles to bones and are non-elastic.
Movement of Bones
The majority of muscle tissue in human- body is skeletal muscle. The skeletal muscles produce movements by pulling on tendons through cords of connective tissues that anchor muscle to the bones. The tendons then pull on bones. Most muscles pass across a joint and are attached to the bones that form joints. When such muscle contracts, it draws one bone towards or away from the bone with which it articulates. There are 650 muscles (n human body; most of which occurs in pairs. At joint, these muscles work against each other by contraction. This relationship is called antagonistic arrangement.
Movement of elbow joint
The movement of elbow joint by biceps and triceps is the best example of antagonism. The biceps (flexor) bend the arm at the elbow joint, and triceps (extensor) straightens it.
Levered movement. Rigid external or internal skeletons are attached to muscles, which move parts of the skeleton at movable joints. Each bony “lever” is moved by an antagonistic muscle pair. One muscle reverses the action of the other so that the lever can return to its original position.
Biceps brachii: The biceps brachii muscle arises from the two heads of a scapula and is inserted into the medial surface of the radius-bone.
Brachialis and brachioradialis: These muscles lie below the biceps brachii. The brachialis is inserted in the ulna, while brachioradialis is inserted in the radius. When these muscles contract they lift ulna and radius and bend the arm at the elbow.
Triceps brachii: The triceps brachii is the only big and powerful muscle that causes extension. It has three heads:
- A long head that arises from the scapula below the shoulder joint.
- A lateral head that arises from the lateral surface of the humerus.
3. A medial head that arises from the medial and posterior surface of the humerus.
All these heads fuse at their lower end and insert through a common tendon on the ulna. When triceps contracts it straightens arm at the elbow. In the antagonistic pairs, one muscle reverses the effect of the other but do not contract simultaneously.