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Muscle Physiology Lab #9.

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Presentation on theme: "Muscle Physiology Lab #9."— Presentation transcript:

1 Muscle Physiology Lab #9

2 Skeletal Muscle Organization
Muscle fibers (cells) elongate cells, parallel arrangement sarcolemma – cell membrane sarcoplasmic reticulum (SR) Internal membraneous network Stores Ca2+ transverse tubules Connect SR to sarcolemma myofibrils – protein bundles composed of: thick filaments thin filaments Lecture Text Figs. 12.1,12.5, 12.15

3 Myofibril Structure Lecture Text Fig. 12.6 Composed of sarcomeres
smallest functional unit of muscle repeating units of thin and thick protein filaments Thick Filament = Myosin Thin Filament = Actin, Troponin, Tropomyosin Lecture Text Fig. 12.6

4 Thick Filament Structure
Bundles of several hundred myosin molecules intertwining tails + globular heads heads contain: actin binding sites ATP-hydrolyzing sites project outward towards actin form crossbridges bonds with actin Important during contraction Lecture Text Fig

5 Thin Filament Structure
Actin primary structural protein spherical protein subunits connected in long, double strand Contains myosin binding site Tropomyosin threadlike proteins normally cover myosin binding sites Troponin Ca2+ Binding Protein holds tropomyosin in place Lecture Text Fig

6 Skeletal Muscle Contraction
Somatic motor neuron induces action potential in muscle fiber AP travels down sarcolemma Induces depolarization in the T-tubules Depolarization conducted to the SR Voltage-gated Ca2+ channels open in the SR releasing Ca2+ into the cytosol Lecture Text Fig

7 Skeletal Muscle Contraction
Ca2+ binds to troponin Troponin undergoes shape change pulls on tropomyosin tropomyosin shifts position uncovers myosin binding sites on the actin filaments Lecture Text Fig

8 Skeletal Muscle Contraction
myosin head binds to actin crossbridge bends power stroke pulls thin filaments toward center of the sarcomere crossbridge link breaks myosin head returns to original configuration binds to next actin molecule Lecture Text Figs , 12.12

9 Skeletal Muscle Contraction
Movement of thin filaments over thick sarcomere shortening length of the filaments do not change Lecture Text Fig. 12.9

10 Muscle Relaxation Ca2+ pumped back into the SR by active carrier-mediated transport troponin releases Ca2+ tropomyosin covers myosin binding sites on the actin molecules Membrane-bound enzyme (acetylcholinesterase) breaks down ACh released at the NMJ

11 All or None Individual muscle fibers respond to a single stimulus in an all or none fashion undergo action potential action potential triggers contraction subthreshold stimulus = no contraction superthreshold stimulus = maximal contraction

12 Motor Units Lecture Text Fig. 12.4
Multiple muscle fibers are enervated by a single motor neuron Motor Unit motor neuron + all muscle fibers it innervates muscle fibers in a motor unit contract as a single unit Lecture Text Fig. 12.4

13 Motor Unit Recruitment
Individual motor units contract in an all-or-none fashion Differences in contractile strength are due to differences in the number of contracting motor units Motor Unit Recruitment increasing the number of contracting motor units to increase the overall strength of contraction

14 Muscle Mechanics Twitch Tetany (Tetanus)
single contraction and relaxation of muscle in response to a single action potential Tetany (Tetanus) sustained tension exerted by a muscle due to continuous contraction

15 Twitch Properties Shortening of muscle Latent Period
Time btw AP production and development of tension. Excitation-contraction coupling Contraction Time Time btw beginning of contraction and peak tension Shortening of muscle Relaxation Time Time btw peak tension and return to resting tension Ca2+ re-uptake and stretching of muscle back to resting length Latent Period Contraction Time Relaxation Time

16 Temporal Summation AP duration much shorter than contraction duration
several APs can occur in a muscle fiber during the course of a contraction Multiple APs can have a summation effect on tension generation induce release of Ca2+ from SR before muscle is fully relaxed increase tension Muscle contraction Action potentials

17 Tetany Lecture Text Fig. 12.18 High rate of AP generation in fibers
no time for muscle to relax sustained level of tension Lecture Text Fig

18 Experiments: Frog gastrocnemius recordings
Follow instructions in manual CAREFULLY!!! Threshold Recruitment in muscle organs Twitch time measures Latent period, contraction time, relaxation time Repeated stimulation and stimulus frequency

19 Electromyograms (EMGs)
Muscles undergo action potentials Electrical signals conducted through body fluids Can be measured from the surface of the body EMGs can indicate muscle activity

20 Types of Muscle Contractions
Isotonic Contractions Muscle shortens in length Generated same strength for a given load throughout the contraction process Isometric Contractions Muscle does not shorten, remains at the same length Load = strength of contraction Lab Manual Fig. 5.16

21 Experiment: EMGs Motor unit recruitment on forearm
Isotonic vs. Isometric contractions

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