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Muscle Physiology Notes.pdf - Muscle Physiology Dr John...

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1Muscle PhysiologyDr John LopesDivision of Medical PhysiologyDept of Biomedical SciencesOffice: Fisan building, room F510Email:[email protected]
2Introduction to MusclesMuscles play an important role in most of our daily body functions, eg. body postureand movement, eating, digestion, eye movement, breathing and speaking.It is therefore understandable that musclesmake up half of an adult’s body mass.Muscle cells are the only cells that can generate tension, which they do byshortening their length.Muscles can generate variable tension in a controlled manner through shortening(contraction) and lengthening (relaxation) muscle cells to:oMove the eyes and eyelids,oSupport and move the body,oExpand the ribcage to facilitate breathing,oRegulate blood flow to and from the various tissues (tissue perfusion) byincreasing or decreasing blood vessel diameters, which is respectively known asvasodilatation or vasoconstriction,oAllow biting, chewing and swallowing of food,oChurn food in the stomach to facilitate food digestion,oMove food waste products down the intestines to the anus for defecation,oKeep sphincters (like those controlling the outlet of the bladder and anus)closed for long periods of time.Types of Muscle TissueThe various muscle functions mentioned above (and more) differ in terms of theamount of tension generated, duration of contraction, rate of contraction andstimuli that induce contraction.For this reason your body containsdifferent types of muscles that can be classified(figure 1) into:o2 muscle types based on the stimulus that control contraction, ie. voluntarymuscles under somatic motor neural control and involuntary muscles underautonomic neural control.o3 muscle types based on their location in the body, ie. skeletal muscle,cardiac muscle and visceral muscle.o2 muscle types according to their histological appearance, ie. striated andunstriated.During this course we will mainly differentiate between muscle types based on theirlocation, unless stated otherwise.Muscle cells (also known as muscle fibers, myofibers & myocytes) generate moretension collectively than individually and therefore they always work together in agroup to do a specific function together.A group of muscle cells that function together in an organ are therefore always ofthe same type, eg. skeletal muscle cells for body movement, cardiac muscle cells forpumping blood from the heart through the entire body or smooth muscle cells forsphincter control & regulating blood flow through blood vessels.
3Each muscle type is adapted to suit its function and therefore each muscle typecan:oexert distinct amounts of tension, eg. the heart generates more force to pumpblood than what your eyelids require to blink,ocontract at a different rate, eg. your eyes can blink faster than what yourstomach has to churn food for digestion,oapply tension for different time durations, eg. contraction of the anal sphincterfor hours, which cannot be done by skeletal muscles that would fatigue morerapidly.

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