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 SarcomereThin and Thick Filaments

Muscular Responses

• Twitch – a brief period of contraction followed by a period of relaxation

• Phases 1. Latent Period – muscle tension is beginning2. Period of ContractionMuscle fibers shortening3. Period of RelaxationCa2+ renters the sarcoplasmic reticulum

Relaxation –1.acetylcholinesterase decomposes ACh in the synapse

2. Ca2+ pump quickly moves Ca2+ back into sarcoplasmic reticulum

Figure 9.14b

Latent period

Extraocular muscle (lateral rectus)

Gastrocnemius

Soleus

Singlestimulus

(b) Comparison of the relative duration of twitch responses of three muscles

• Summation – The force of individual twitches combines• Incomplete tetanus – Ca2+ 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 muscleincreases but the muscle does not lengthenor 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 flow2. ion imbalances across sarcolemma from repeated

stimulation3. psychological loss of the desire to exercise4. 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

• http://www.blackwellpublishing.com/matthews/myosin.html

http://www.mhhe.com/biosci/esp/2002_general/Esp/folder_structure/su/m4/s11/sum4s11_9.htm