lecture 2 physio ppt.pptx
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The document summarizes the structure and components of muscle cells and their myofibrils. It describes that muscles are made of long cylindrical cells called myofibers which contain protein filaments for contraction. Each myofiber contains many myofibrils which are made of repeating contractile units called sarcomeres. Sarcomeres contain thick and thin filaments of myosin and actin that slide during muscle contraction and relaxation.
lecture 2 physio ppt.pptx
- 1. Physiology - HND Khawaja Taimoor Shahid
- 2. Skin as Mechanoreceptor Structure Topic # 5 • The simplest mechanoreceptors consist of morphologically undifferentiated nerve endings found in the connective tissue of skin. • More complex mechanoreceptors have accessory structures that transfer mechanical energy to the receptive membrane.
- 3. Mechanoreceptors for Touch, Vibration and Pressure • Multiple receptors for these senses are embedded in the skin. These include: • Hair end organs: Situated at the base of hairs and receive gentle touch stimulus due to displacement of hairs. • Meissner’s Corpuscles: are the touch receptors. They have encapsulated nerve endings which lie in papillae which extend into the ridges of fingertips. • Pacinian corpuscles: are situated quite deep in the skin. They have encapsulated nerve endings and receive deep pressure stimulus. • Merkel’s Disks: are associated with the reception of vibration.
- 5. Stretch Mechanoreceptors • The stretch receptors of various kinds are found in muscles of arthropods and vertebrates. Most common of these are proprioceptors that detect muscle movements. • They consist of mechanically sensitive sensory endings (dendrites of sensory neurons) which are associated with specialized muscle fibers. • When the muscle is stretched, dendrites receive this stimulus and action potentials are triggered in the sensory neuron and transmitted to the spinal cord. • Skin provides strechibility and elasticity to skin.
- 6. Sound and Equilibrium Receptors • Hearing and the perception of body equilibrium are related in most animals. • For both senses, mechanoreceptor cells produce receptor potentials when settling particles or moving fluid cause deflection of cell surface structures. • The receptors for sound and equilibrium are found in the vertebrate middle and inner ear and in the vestibular system.
- 7. Skin Diseases • Topic # 6 • See pathology notes
- 8. Topic-7 Types of Glands • Glands are broadly classified into two types: • Endocrine glands AND Exocrine glands • Endocrine Glands • Endocrine glands are the ductless glands that secrete their products i.e. hormones directly into the circulatory system. • Various endocrine tissues are structurally and chemically diverse. They do not exhibit a common morphologic plan or distinctive gross morphologic feature except that such tissues are richly vascularized. For this reason, identifying and locating the endocrine tissues has been a difficult task in some cases. • Some endocrine glands contain more than one type of secretory cells, each producing a different hormone. • The endocrine glands belong to the body's control system. The endocrine secretions play role in chemical coordination of the body and modulate short-term and long-term physiological processes. • Examples • Pituitary, thyroid and adrenal glands.
- 10. Exocrine glands • Exocrine glands produce fluid secretions that are delivered through ducts onto the epithelial surfaces of the body. • Exocrine glands are more easily identified than endocrine glands because of their duct leading to the body surface. • The fluid secretions may be either proteins (enzymes) or mucous or both. • Examples: • Salivary glands produce saliva that is delivered to the oral cavity for partial digestion of food through parotid and submandibular ducts. • Pancreas produces enzyme-containing pancreatic juice that is delivered to the small intestine through pancreatic duct. • Lacrimal glands produce tears that is delivered through lacrimal duct on the surface of eye to provide lubrication. • Mammary glands produce milk that is delivered through lactiferous ducts to the nipples for nourishing the young.
- 11. Topic-08 Thermoreception • Thermoreception is the sense by which an organism perceives hot or cold temperatures. • Thermoreceptors are located in the skin, upper surface of the tongue and anterior hypothalamus. • Skin thermoreceptors detect changes in environmental temperature while thermoreceptors in anterior hypothalamus detect changes in body core temperature. • Thermoreceptors are phasic-type receptors i.e. they respond very rapidly to minute changes in temperature but adapt and quit firing quickly, if the stimulus persists.
- 12. Warmth and Cold Receptors • There are two kinds of thermoreceptors in the external skin and upper surface of the tongue: • Cold receptors AND Warmth receptors • Cold Receptors • The cold thermoreceptors are 3.5 times more common in skin than heat receptors. • They consist of free nerve endings of neurons that have thin myelinated Aδ fibers having faster conduction velocity (19m/s). • They increase their firing rate when the skin is cooled below body temperature.
- 13. Warmth Receptors • Warmth Receptors increase their firing rate in response to temperatures above body temperature. • They consist of free nerve endings of neurons that have unmyelinated C fibers with low conduction speed (0.8m/s). • Both these receptors are quite sensitive which enable human beings to detect a change in skin temperature of as little as 0.01°C.
- 14. TRP Proteins in Thermoreceptors • The membranes of thermoreceptors have ion channel proteins belonging to the family of transient receptor potential (TRP) proteins. • There are many subfamilies within the TRP family of ion channels, which form many different types of receptors. The TRP’s involved in thermoreception are TRPA, TRPM and TRPV. • The transduction of temperature in cold receptors is mediated by the TRPA and TRPM while TRPV are involved in warmth reception. • TRP ion channels allow an influx of many cations which tends to be dominated by Ca2+. The increase in ion concentration depolarizes the membrane, and causes action potentials to fire.
- 15. Neural Pathway of Temperature Sensation • Both warm and cool stimuli transduce information along the same neural pathway. • Cell bodies of neurons of cutaneous thermoreceptors reside in the dorsal root ganglion (DRG) or the trigeminal ganglion on the dorsal horn of the spinal cord. The neurons of dorsal horn of the spinal cord communicate via synapses to the thalamus and then to the hypothalamus. The hypothalamus then elicits action potentials to induce the proper thermoregulatory responses.
- 17. Topic-09 The Structure of Muscle • The Muscle Cells (Myofibers) • Each muscle consists of hundreds to thousands of long, cylindrical, multinucleated cells called muscle fibers or myofibers, which are arranged in bundles called fascicles. • Skeletal muscle fibers range from 5 to 100 μm in diameter, and may be many centimeters in length.
- 19. The membrane of the cell is called sarcolemma, its cytoplasm is called sarcoplasm and its endoplasmic reticulum is known as sarcoplasmic reticulum.
- 20. Myofibrils: Within each muscle fiber, numerous myofibrils run in parallel fashion. Myofibrils are 1-2 μm in diameter and extend the entire length of the cell.
- 21. Myofilaments: Each myofibril is composed of myofilaments. Myofilaments are of two types, thin filaments and thick filaments. Thin filaments are composed of actin while the thick filaments are composed of myosin molecules.
- 22. Sarcomere: The regular arrangement of the thick and thin filaments creates a pattern of repeating light and dark bands. This pattern gives a striped appearance to the muscle cell. Each repeating unit is called a sarcomere and is the basic functional contractile unit of the muscle.
- 23. Structure of Sarcomere • Each dark band in a sarcomere is called A band. This band is anisotropic i.e. it polarizes visible light. • Each A band has a lighter stripe in its center which is called H-zone. • The H-zone is bisected by a dark line called M-line. • The light band is called I band. It is isotropic i.e. non- polarizing. • The I band has a mid-line called Z-line. • A sarcomere is the region of a myofibril between two successive Z-lines.
- 25. Topic-10 Myofilament Substructure • Myofilament is made up of thick and thin filaments. • Thick Filaments • Thick filaments extend the entire length of A band. • These filaments are about 16 nm in diameter and are composed of about 300 myosin molecules.
- 27. • Myosin Molecule • Each myosin molecule consists of two identical heavy chains which are coiled together to form a long tail. It also has two globular heads which are made from two heavy chains plus three or four calcium-binding light chains. • The heads form cross bridges between the thick and the thin myofilaments during contraction.
- 28. Thin Filaments • The thin filaments are 7-8 nm thick and extend across the I band. • They are composed chiefly of actin molecules. • • Thin filaments also overlap myosin filaments in the peripheral darker regions of the A band. In these regions, six actin filaments surround each myosin filament while each actin filament is surrounded by three myosin filaments. • In thin filaments, actin molecules are arranged in two chains which twist around each other. • Two strands of another protein tropomyosin twist around the actin and help to stiffen it. In a relaxed muscle fiber, they block myosin binding so that the myosin heads can not bind to the thin filaments.
- 29. • Thin filaments also have a three polypeptide complex troponin at intervals of about 40nm along the thin filament. • One of the troponin polypeptides (TnI) is an inhibitory subunit that binds to actin, other (TnT) binds to tropomyosin and helps position it on actin while third (TnC) binds the calcium ions. • Both troponin and tropomyosin help control the myosin-actin interactions involved in contractions.
- 30. The H Zone • The center of A band appears lighter than the other regions in a relaxed sarcomere. • This region is called H zone and contains only thick filaments. There are no overlaps between the actin and myosin in this region. • The H zone is bisected by a dark line, the M line which contains enzymes important in energy metabolism.