Textbook Notes (363,452)
Canada (158,372)
Biology (352)
BIOL 153 (6)

Muscle Physiology.doc

13 Pages
Unlock Document

University of British Columbia
BIOL 153
Robert Harris

Muscular System Based on the lecture and text material, you should be able to do the following: describe the microscopic structure of a striated muscle fibre describe the functional roles of myofibrils, sarcoplasmic reticulum and T-tubules give a detailed description of the sliding filament theory of muscle contraction explain the events leading from the arrival of neurotransmitter at the endplate of a neuromuscular junction, through contraction and on to relaxation of a muscle fibre explain what cross-bridge formation is explain whythick and thin filaments do not slip backwards during muscle fibre contraction when the cross-bridges break and reform between the actin and myosin molecules define muscle twitch and describe the events which occur during its three phases giventhatactionpotentialsinnervesandmusclesareall-or-noneevents,explainhowsmooth graded contractions of muscles are produced differentiate between isometric and isotonic contractions describe the sources of ATP used during muscle contraction listanddescribethefeatureswhichaffecttheforceandspeedofcontractionofamusclefibre define muscle fatigue and possible causes of it list the different types of muscles and their characteristics compare and contrast stretch, flexor and crossed extensor reflexes describe the mechanism of contraction in smooth muscles and compare that to striated muscle **Note that the prefixes myo- and sarco- both refer to muscle 1. Microscopic Anatomy A) Muscle fibers (single muscle cells): are very long organelle arrangement is similar to other cells except that: they have several nuclei (multinucleate) plasma membrane is called sarcolemma cytoplasm is called sarcoplasm endoplasmic reticulum (ER) is called sarcoplasmic reticulum (SR) sarcoplasm contains many, highly organized protein filaments B) Myofibrils: hundreds to thousands of long bundles per muscle fiber run in parallel down the entire length of the cell occupy ~ 80% of the volume of the cell C) Striations: on each myofibril, repeating bands of dark and light can be distinguished dark bands are called A bands light bands are called I bands A and I bands are almost perfectly aligned with one another and are visible through the sarcolemma striated appearance of the skeletal muscle D) Sarcomeres: there is a dark line (Z line or Z disc) that zigzags down the middle of the I band the region between two successive Z lines is called a sarcomere (there are many successive sarcomeres in a single myofibril) E) Myofilaments: myofibrils are composed of two types of protein filaments: I) Thick filaments ~ 16nm in diameter composed mainly of myosin (golf club- shaped protein) myosin tail is made of [email protected] polypeptide chains myosinhastwoglobularheadswhichhaveadditional light polypeptide chains the head is the functional unit of the myosin moleculeB b/c they link the thick and thin filaments during contraction(cross bridges) the heads have actin binding sites & ATP binding sites ~200myosinmoleculesbundletogether w/theirtailslinedup (parallel)toformthecentralpartofthefilamentBtheirheads protrude out from the central part at both ends (like a q-tip with long cotton ends thick filaments surround thin filaments 3:1 II) Thin filaments ~ 7-8nm in diameter composed mainly of actin in a helical structure globular actin (G actin) has binding sites for myosin cross bridges regulatory proteins B troponin and tropomyosin B help control the interaction between thick and thin filaments thin filaments surround thick filaments 6:1 a) Troponin 3 polypeptide complex: TnI inhibitory subunit that binds to actin during relaxed state of muscle TnT helps tropomyosin position itself properly on actin during contraction TnC binds calcium ions b) Tropomyosin rod-shapedproteinwhichwrapsaroundtheactincore of the thin filament to help stiffen it in a relaxed muscle fiber, it blocks the active site of the actin so that a myosin head cannot bind III) Elastic filaments made of the stretchy protein titin (aka connectin) attach thick filaments to the Z disc thoughttoplayamajorroleintheorganizationoftheAbands and the muscle cell as a whole the part of the titin that spans the I bands allows the muscle cell to spring back into shape after being stretched F) Integration of Bands and Filaments: thick and thin filaments overlap each other to form the dark or A band when a muscle cell is relaxed, theyonlyoverlap where the myosin heads are located (at the ends of the thick filament) in the middle of the A band, the filaments do not overlap (there is onlythick filament), therefore, this area appears slightly lighter this is called the H
More Less

Related notes for BIOL 153

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.