Clicker questions Clicker channel 70 Response Ware Session ID psio201 Which of the following has ATPase activity during cross bridge cycling 87 1 2 3 4 Actin Troponin Myosin Tropomyosin 3 1 5 2 4 3 4 When muscle action potentials travel down Ttubules they 97 A trigger attachment of myosin to titin B trigger detachment of tropomyosin from troponin C trigger release of Ca2 from the SR D trigger movement of Na out of the myofibrils 0 A 2 B 1 C D During relaxation calcium 1 is actively transported out of the sarcoplasmic reticulum SR 2 is actively transported into the SR 3 passively diffuses out of the SR 4 passively diffuses into the SR 88 5 2 1 2 3 5 4 Lecture 20 Muscle Mechanics Claudia Stanescu Ph D Office hours Tuesday and Thursday 1 2pm in Gittings 108 or by appointment Objectives pp 311 315 sec 10 5 1 List the three phases of a muscle twitch 2 Compare and contrast the characteristics of a muscle twitch and tetanic contraction Describe the development of tetanus in terms of temporal summation 3 Define a motor unit and discuss it in the context of spatial summation 4 Describe the size principle in the context of development of increased tension during a voluntary muscle contraction 5 Describe isometric and isotonic contractions 6 Describe the strategies used to increase force in the muscle including increasing motor unit recruitment frequency of activation and the length of muscle at the beginning of a contraction Muscle Mechanics 1 The Muscle Twitch contraction arising from a single electrical stimulus e g an action potential 3 Periods 1 Latent 2 Contraction 3 Relaxation 1 Latent Period 2 msec or less Action potential sweeps over the sarcolemma Calcium ions released from the sarcoplasmic reticulum No change in tension 2 Contraction Period 10 100 msec Calcium binds to troponin Myosin binding sites on actin are exposed Crossbridges form and swivel Peak tension develops 3 Relaxation Period 10 100 msec Calcium ions transported back into the sarcoplasmic reticulum Myosin binding sites on actin are covered by tropomyosin Myosin heads detach from actin Tension decreases The Time Course of a Twitch varies for different muscles fast twitch vs slow twitch Fast twitch gastroc Tension eye Slow twitch soleus Time Muscle Mechanics 2 Tetanus or tetanic contraction summation over time Temporal Summation of individual twitches Tetanus temporal summation is a mechanism for increasing tension Tension Production and the Motor Unit Motor Unit a motor neuron and all the muscle fibers cells it innervates Muscles typically contain many motor units by activating recruiting increasing numbers of motor units tension can be increased Spatial Summation Motor Units and the Size Principle The first motor units recruited are small innervate few fibers the result is fine carefully controlled increase in tension As more force is required larger motor units are recruited Small SO SO Slow Oxidative Medium FFR Large FF Small SO Intermediate FOG Large FF FOG Intermediate oxidative glycolytic fatigue resistant Small SO Medium FOG FG fast glycolytic fatiguable Large FG Exam 2 Grade Average vs SI Attendance 100 96 Average Grade on Exam 2 95 90 88 87 85 85 83 81 80 80 75 70 Class Average SI Average Non SI SI 1 SI 2 3 SI 4 5 SI 6 7 Clicker questions Clicker channel 70 Response Ware Session ID psio201 The muscle twitch takes place in response to a series of action potentials and can vary in duration based on the strength of these electrical signals 94 A True B False se Fa l Tr ue 6 The period during a muscle twitch when the action potential is travelling across the sarcolemma leading to calcium release from the SR and tension is zero is called the A Latent period B Contraction period C Relaxation period 93 1 A B 6 C Increasing the frequency of action potentials that stimulate a muscle can increase force production This is called A Size principle B Temporal summation C Spatial summation D Motor unit recruitment 71 18 10 2 A B C D Size Principle motor units are recruited in order from small to large 100 maximal force Jump Sprint 60 Run add fast motor units Walk 20 Stand add intermediate 25 50 75 100 of motor units recruited smallest motor units largest motor units Size Principle motor units are recruited in order from small to large Slow Intermediate Fast Isometric vs Isotonic Contractions 1 Isometric same length muscle generates tension but does not shorten every contraction begins isometrically 2 Isotonic same tension after sufficient tension is generated to move the load the muscle changes length Two types 1 concentric 2 eccentric Isometric vs Isotonic Contractions Silverthorn Human Physiology An Integrated Approach 6th ed page 422 Isometric vs Isotonic Contractions Silverthorn Human Physiology An Integrated Approach 6th ed page 422 Isotonic contractions Concentric vs Eccentric contractions 1 When developed tension is sufficient to move the load the muscle shortens concentric contraction Effort Load 2 As tension decreases and the load exceeds tension the muscle lengthens eccentric contraction Load Effort Note All muscle actions are based on the concentric contraction of a muscle Strategies to increase force 1 Increase motor unit recruitment spatial summation 2 Increase frequency of stimulation temporal summation 3 Optimal muscle fiber length at start of contraction see length tension relationship Nervous System Length Tension Relationship Optimal overlap more crossbridges Length Tension Relationship Tension generated is proportional to the number of cross bridges formed Peak tension is developed at an intermediate sarcomere length According to the length tension relationship muscle tension is proportional to muscle length 97 A True B False se Fa l Tr ue 3 Suggested Learning Activities Draw the a graph of the twitch in a slow twitch fiber label the three phases and explain each one How would this graph differ in a fast twitch fiber Draw the length tension relationship including a diagram of the sarcomere length