Smooth Muscle Physiology PDF - Istanbul Atlas University - Oct. 2024

Smooth Muscle Physiology Fac. of Health Sciences Istanbul Atlas University Istanbul Oct. 2024  Learning Outcomes General Functions of Smooth Muscle Its functional Anatomy Physiology of Smooth muscle Smooth muscle types ...

Smooth Muscle Physiology Fac. of Health Sciences Istanbul Atlas University Istanbul Oct. 2024  Learning Outcomes General Functions of Smooth Muscle Its functional Anatomy Physiology of Smooth muscle Smooth muscle types  Introduction Fusiform, non-striated cells Single, centrally-placed nucleus Contraction is non-voluntary Contraction is modulated in a neuroendocrine manner Found in blood vessels, GI and urogenital organ walls, dermis of skin  Microscopic Anatomy of Smooth Muscle ❑ Smooth muscle Cell has 3 types of filaments: Thick myosin filaments Longer than those in skeletal muscle Thin actin filaments Contain tropomyosin Calmodulin ( but no troponin) Filaments of intermediate size ( Intermediate Filaments ) Do not directly participate in contraction Form part of cytoskeletal framework that supports cell shape ❑ No striations Although smooth muscle fibers do contain actin and myosin, the filaments are thin and randomly arranged so that it lacks striations Dense bodies are analogous to Z lines (plaques into which actin filaments insert) Contraction pulls dense bodies together Contraction is slow and sustained. No T-tubules A poorly developed sarcoplasmic reticulum  Functional anatomy of Smooth muscle Actin has no troponin (the protein that binds to myosin in skeletal muscle) rather smooth muscle has a calcium binding protein called calmodulin. ▪ This protein activities the actin and myosin cross bridge formation. Most of the calcium required for contraction comes into the cell by diffusion from the extracellular fluid. Calcium-Calmodulin activation of Myosin Cross Bridge in Smooth Muscle  Cont. Smooth muscle is more resistant to fatigue and produces a slower, longer lasting contraction than skeletal muscle. It is more energy efficient than skeletal muscle in that it can maintain a more forceful contraction for a longer period of time with the same amount of ATP.  Cont. Smooth muscle can be stimulated to contract by multiple types of signals: by nervous signals, by hormonal stimulation, by stretch of the muscle, and in several other ways. Smooth muscle membrane contains many types of receptor proteins that can initiate the contractile process.  Autonomic nervous system control ❑ Unconscious control of smooth muscle contraction Neurotransmitters: Acetylcholine (as in skeletal muscle) Norepinephrine ❖ Neurotransmitters for smooth muscle can be either excitatory (cause muscle contraction), or inhibitory (prevent muscle contraction) depending on the receptor on the smooth muscle cell membrane (Whereas the neurotransmitter for skeletal muscle is always excitatory).  Types of Smooth muscle ❑ Single Unit Smooth Muscle Also called visceral smooth muscle because it is found in the walls of the hollow visceral organs such as the stomach, intestines, urinary bladder and uterus. ❑ Multiunit smooth muscle  Single Unit Smooth Muscle More common of the two types of smooth muscle. The muscle fibers are organized into sheets of cells held in close contact by gap junctions. Self-excitable (does not require nervous stimulation for contraction) Fibers become excited and contract as single unit. Cells electrically linked by gap junctions.  Multiunit smooth muscle Fibers are not very well organized Occur as separate fibers scattered throughout the sarcoplasm rather than in sheets. Requires stimulation by a motor nerve impulse from the autonomic nervous system. This type of smooth muscle is found in the irises of the eyes, arrector pili muscles, blood vessels, and large airways of the lungs  Intrinsic Control of Smooth Muscle Contraction ❑ Myogenic Response Smooth muscle is stimulated to contract when it is stretched Smooth muscle is able to distend, or stretch, without great increases in tension or tightness Allows hollow organs to be filled When the smooth muscle reaches is stretching capacity, it will contract and force the contents out Such as occurs in the intestines or urinary bladder.  Functional Properties of Smooth muscle Some visceral muscle exhibits autorhythmic contractions. Tends to contract in response to sudden stretch but no to slow increase in length. Exhibits relatively constant tension: Smooth muscle tone Amplitude of contraction remains constant although muscle length varies. Electrical Properties of Smooth muscle  Smooth muscle Regeneration and Growth Increase in size (hypertrophy) Increase in number (regeneration/proliferation) Smooth muscle cells are proliferative (e.g. uterine myometrium and vascular smooth muscle) Vascular pericytes can also provide source of smooth muscle THANK YOU