The Muscular System
3 Types of Muscles
A Muscle is Composed of a Variety Of Tissues
Sarcomere – the structural and functional unit of a myofibril
The Sarcomere Thin and Thick Filaments
Muscular Responses Twitch – a brief period of contraction followed by a period of relaxation Phases 1. Latent Period – muscle tension is beginning 2. Period of Contraction Muscle fibers shortening 3. Period of Relaxation Ca 2+ renters the sarcoplasmic reticulum Relaxation – 1.acetylcholinesterase decomposes ACh in the synapse 2. Ca 2+ pump quickly moves Ca 2+ back into sarcoplasmic reticulum
Figure 9.14b Latent period Extraocular muscle (lateral rectus) Gastrocnemius Soleus Single stimulus (b) Comparison of the relative duration of twitch responses of three muscles
Summation – The force of individual twitches combines Incomplete tetanus – Ca 2+ increases in sarcoplasm results in quivering response Complete Tetanus – no period of relaxation
Treppe
The force that a muscle can generate is dependent on the length that it is stretched before stimulation
Muscle Fiber Type
The force that a muscle develops depends on: 1.The frequency at which individual muscle fibers are stimulated 2.How many fibers take part in the overall contraction - RECRUITMENT
Types of Contractions Isotonic Contraction – muscle changes length and moves a load – Concentric contraction – a muscle shortening contraction – Eccentric contraction – a muscle lengthening contraction Isometric contraction – tension in muscle increases but the muscle does not lengthen or shorten
Muscle Fatigue Exercise for a long period of time may cause a muscle to lose the ability to contract - FATIGUE Why? 1. decreased blood flow 2. ion imbalances across sarcolemma from repeated stimulation 3. psychological loss of the desire to exercise 4. increase in lactic acid = lowered pH which prevents muscles from responding to stimulation
What is a Cramp? A sustained, painful, involuntary muscle contraction Result from decreased electrolyte concentration in extracellular fluid which triggers uncontrolled muscle stimulation
Sliding Filament Theory ws/myosin.html ws/myosin.html l/Esp/folder_structure/su/m4/s11/sum4s11_9.htm