What is a Tissue? 

A tissue is a group of similar cells that are organized to perform one or more specific functions. Tissues are classified into four different types based on their morphology and function: connective tissue, nervous tissue, muscle tissue, and epithelial tissue. A group of tissues forms the organs in the body such as the liver and heart. 

What is a Muscle Tissue? 

The muscle tissue is made of elongated cells called muscle fibers. These cells are specialized cells that can contract and expand. Various kinds of movements in the body are facilitated by muscles through contraction and expansion. Muscle is one of the four tissue types and it is combined with nerves, blood vessels, and many connective tissues that make the muscle organ. It is composed of three types of tissues which include: smooth muscle tissue, skeletal muscle tissue, and cardiac muscle tissue.  

Types of muscle tissue 

1. Smooth muscle tissue: It is a long spindle-shaped cell with a single nucleus that does not have striations and is poorly organized. It is present in the walls of the hollow organs like the stomach, intestine, blood vessels, and uterus. It is arranged in circular and longitudinal layers. The smooth muscle contraction is slow and sustained. It is involved in the involuntary movement of the internal organs. An example is the movement of the stomach and small intestine during the digestion of food. 

2. Cardiac muscle tissue: It is striated and appears short and thick, uninucleated, and has branching cells. The cells get fit together at a junction called intercalated discs. It is found only in the heart and involved in the involuntary movement (muscle movement controlled by the brain). It contracts to pump blood through blood vessels.  

3. Skeletal muscle tissue: It is a long (30 cm) cylindrical muscle that is striated (parallel stripes) and has a multinucleated cell. It is attached to the skeleton and involved in voluntary control. The skeletal muscles can contract rapidly with great force and during contraction, they pull on bones and skin and thereby control the movement of the body.  

What are the Characteristic Features of Muscle Tissue? 

• Excitability: It is the ability to receive and respond to a stimulus. An electrical impulse is generated that travels down the plasma membrane of the muscle cell.  
• Contractility: The ability to produce tension or shortening or both. There are two types of contractions: isotonic contraction and isometric contraction. During isotonic contraction, the tension is the same but a change in length of muscle fiber occurs. During an isometric contraction, the tension is increased and the length of muscle fiber remains the same.  
• Elasticity: Ability of a muscle to return to its original shape and length after extension or contractions. 
• Extensibility: It is the ability to be stretched without being damaged. 
• Muscle tone: The muscle fiber always remains at a state of slight contraction with a certain degree of vigor or tension and this state is a partial contraction of muscles. 

What are the Important Functions of Muscle Tissues?

Muscles account for most of the body weight. Some of their important functions are:  

• Help in body movements: It helps in whole-body movements like running and walking and localized movements like holding a book or nodding head. It depends on the integrated functioning of bones, joints, and skeletal muscles. 
• Stabilizing body positions: The skeletal muscle contraction stabilizes joints and helps in maintaining various body positions such as standing and sitting. 
• Thermogenic functions: When the muscles contract, it generates heat by thermogenesis. The generated heat helps in maintaining the normal body temperature. 
• Storing and moving substances within the body: The contractions of smooth muscles help in moving food and substances like bile or enzymes through the gastrointestinal tract. Similarly, skeletal muscle contractions promote the flow of lymph and help the return of blood to the heart. 

Nervous Tissue

The cells of the nervous tissue are called neurons and neuroglia which is the main component of the nervous system. It is located in the brain, spinal cord, and other nerves. The nerve cell neuron is the conducting cell that transmits impulses and the neuroglia is the non-conductive cell that provides support to the neurons. Another important function of the nerve cell is in controlling all the activities in the body.  

What is a Neuron and Describe its Structure?

The neuron is a specialized type of cell that is amitotic. It cannot be replaced as it does not undergo the process of mitosis. The structure of a neuron is like a branch of a tree which consists of three important parts: 

• Cell body (soma): The body of a neuron appears star-shaped that consists of a nucleus and a perinuclear cytoplasm. The nucleus is large and spherical to the ovoid. It is located centrally, having a single prominent nucleolus. The chromatin is finely dispersed. The cytoplasm contains polyribosomes, rough and smooth endoplasmic reticulum, Golgi complex, and Nissl bodies. The cell body lacks centrioles which are important for cell division. This is the amitotic feature of the cell. 
• Axon: It is the long part of the neuron which measures approximately 100 cm in length. It is originated from axon hillock and carries messages away from cyton and hence it is called an efferent process. The cytoplasm of the axon is known as axoplasm and the membrane is known as the axolemma. It is devoid of the ribosome and maintains axonal transport. Few axons have right-angled branches called axon collaterals. The axons are surrounded by segmented fatty substances called the myelin sheath. The myelinated fibers form the white matter of the central nervous system and unmyelinated fibers make the grey matter. The presence of unmyelinated regions between the myelin segments is called the nodes of Ranvier.  
• Dendrites: It is a short branch that is present as multiple elongated processes in the neuron. The number of dendrites in neurons varies and they are called afferent processes as they carry messages towards the cell body. The dendrites are also known as fibers and have a large surface area to receive a signal from other neurons. They are devoid of the Golgi complex.  

What is a Neuroglia?

Neuroglial cells undergo mitosis and help in providing support, nourishment, and protection to the neurons. They do not conduct nerve impulses but form the myelin sheath of axons. The neuroglia does not form synapses. It is found that every neuron contains at least ten neuroglial cells. There are four types of neuroglial cells based on their function and morphological features: 

1. Oligodendrocytes  
2. Astrocytes 
3. Microglia 
4. Ependymal cells 

Context and Applications: 

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for       

• Bachelor of Science in Biochemistry 
• Bachelor of Science in Anatomy and Physiology 
• Master of Science in Anatomy and Physiology