PHYSIOLOGY OF SMOOTH MUSCLE (INVOLUNTARY MUSCLES)

This presentation provides a detailed overview of the physiology of smooth muscles, highlighting their structure, unique properties, and functional roles in the human body. It covers key topics such as the types of smooth muscles, excitation–contraction coupling, role of calcium ions, regulation of contraction, and comparison with skeletal and cardiac muscles. Special emphasis is given to the mechanisms of innervation, neurotransmitters, and the importance of smooth muscle activity in vital processes like digestion, circulation, and respiration.
Designed for students, researchers, and educators in physiology, biochemistry, and medical sciences, this PPT serves as a concise learning resource to understand the fundamental and clinical significance of smooth muscle physiology.

1. Physiology of Smooth Muscle SANJIDH SAJ A S

2. SMOOTH MUSCLES Smooth muscles is also known as the plain, non striated, smooth involuntary muscles. It is called non striated because it has got no cross striations. The contraction of this muscle is not controlled by will The smooth muscles are mesenchymal in origin. The mesenchymal cells first starts to stretch out. The nucleus becomes elongate and myofilaments appear in the cytoplasm. In the case of blood vessels, the mesenchymal cells are arranged along the walls of the tube at regular intervals and developed in the same fashion As already mentioned and ultimately forming the continuous circular and longitudinal muscle layers of the blood vessels. The smooth muscle fibres can increase in size and also in bulk during physiological requirement (e.g.: uterus in pregnancy)and in pathological stimuli(e.g.: arterioles in hypertension) There is also evidences that smooth muscle cells themselves can divide by mitosis.

3. Structure of Smooth Muscle Structure Smooth muscle cells are small and spindle-shaped, with a single nucleus. They lack the sarcomeres found in skeletal muscle, which gives them a smooth appearance. Organization Smooth muscle cells are arranged in sheets or bundles, allowing for coordinated contractions. The arrangement of the cells can be either circular or longitudinal, depending on the organ.

4. Functions of Smooth Muscle Smooth muscle plays a vital role in various physiological processes, allowing for controlled movement and regulation of internal organs. Peristalsis Smooth muscle contractions in the digestive tract propel food through the esophagus, stomach, and intestines. Blood Pressure Regulation Smooth muscle in blood vessels controls blood flow and blood pressure by contracting or relaxing. Urination Smooth muscle in the bladder wall helps control urination by contracting to expel urine. Reproductive system Facilitate movement of sperms in males and in females ,it accelerates the movement of ovum into the uterus through fallopian tube Respiratory system Contraction and relaxation of smooth muscles of air passage regulate inflow and outflow of air.

5. Gastrointestinal Tract and Smooth Muscle Smooth muscle in the gastrointestinal tract plays a critical role in digestion, propelling food along the digestive tract, mixing it with digestive juices, and controlling the rate of digestion. 1 Peristalsis The rhythmic contractions of smooth muscle in the digestive tract propel food along the esophagus, stomach, and intestines. 2 Segmentation Circular smooth muscle contractions in the small intestine mix food with digestive juices, enhancing absorption. 3 Sphincter Control Smooth muscle sphincters control the movement of food between different parts of the digestive tract.

6. Cardiovascular System and Smooth Muscle Smooth muscle in the cardiovascular system plays a crucial role in regulating blood pressure, blood flow, and oxygen delivery to tissues. Vasoconstriction Contraction of smooth muscle in blood vessels reduces the diameter of the vessel, increasing blood pressure. Vasodilation Relaxation of smooth muscle in blood vessels increases the diameter of the vessel, decreasing blood pressure.

7. Respiratory System and Smooth Muscle Smooth muscle in the respiratory system controls airflow to the lungs, ensuring efficient gas exchange and maintaining respiratory function. 1 Bronchodilation Relaxation of smooth muscle in the bronchioles increases airflow to the lungs. 2 Bronchoconstriction Contraction of smooth muscle in the bronchioles restricts airflow to the lungs. 3 Coughing and Sneezing Smooth muscle contractions in the airways aid in expelling irritants or foreign substances.

8. Urinary Tract and Smooth Muscle Smooth muscle in the urinary system controls urine storage and elimination, playing a critical role in maintaining urinary function. Bladder Smooth muscle in the bladder wall contracts to expel urine during urination. Ureters Smooth muscle in the ureter walls propels urine from the kidneys to the bladder. Urethra Smooth muscle in the urethra controls the flow of urine from the bladder to the outside.

9. Regulation of Smooth Muscle Contraction Smooth muscle contraction is regulated by a complex interplay of factors, including calcium ions, calmodulin, myosin light-chain kinase, and phosphorylation. Calcium Influx Calcium ions enter the smooth muscle cell through voltage-gated or ligand-gated calcium channels. Calmodulin Activation Calcium ions bind to calmodulin, a calcium-binding protein. Myosin Light-Chain Kinase Activation The calcium-calmodulin complex activates myosin light-chain kinase, an enzyme that phosphorylates myosin. Myosin Phosphorylation Phosphorylation of myosin allows it to bind to actin and initiate the sliding filament mechanism, resulting in muscle contraction.

10. REFERENCES CC Chatterjee’s Human Physiology Vol 1, 12th edition, CBS Publishers (page no-186-191) Guyton and Hall Textbook of Medical Physiology, 12 th edition (page no-91-98)

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