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Lecture Nine : Muscle II - Skeletal muscle function

Q: Explain the Process of Excitation Coupling

Action Potential depolarises the membrane It triggers the voltage sensor of the t-tubules , which is coupled with the voltage gated channels of the sarcoplasmic reticulum This triggers the voltage gated channels to open which releases Ca2+ ions

Q: Explain How sarcomere length influences muscle tension?

Length of muscle fibres : Longer fibres can contract more (greater range of movement). Fibres can shorten up to 50% of their resting length during contraction. Maximum tension is achieved at optimal length, with optimal actin-myosin overlap. Too much, or too little overlap will not result in optimal contractile force/tension being produced.

Q: Explain How the rate of stimulation influences muscle tension ?

TWITCH : A single action potential will result in a pulse of Ca2+ release into the cytoplasm and a short period of tension development. TETANUS : Many action potentials fired in rapid sequence results in a sustained release of Ca2+ from the SR. A sustained period of actin-myosin interaction and a sustained period of contraction.

6 important questions on Lecture Nine : Muscle II - Skeletal muscle function

Explain the Process of Excitation Coupling

Action Potential depolarises the membrane
It triggers the voltage sensor of the t-tubules , which is coupled with the voltage gated channels of the sarcoplasmic reticulum
This triggers the voltage gated channels to open which releases Ca2+ ions

Explain the Process of Contraction Coupling

Action potential travels over sarcolemma and T-tubules, triggering release of Ca2+ ions from the sarcoplasmic reticulum (SR)
Ca2+ binds to troponin (on thin filaments) causing tropomyosin to expose myosin binding sites on actin.
Myosin heads prop up into their binding sites on Actin - forming a Cross bridge

Explain What a Cross Bridge Cycle is ?

ATP binds to myosin heads causing actin and myosin to separate ; and is also hydrolysed into ADP+Pi
For the myosin heads to bind to the actin site , ADP+Pi must be released

This cycle continues as long as Ca2+ and ATP are available.

Explain How sarcomere length influences muscle tension?

Length of muscle fibres : Longer fibres can contract more (greater range of movement). Fibres can shorten up to 50% of their resting length during contraction. Maximum tension is achieved at optimal length, with optimal actin-myosin overlap. Too much, or too little overlap will not result in optimal contractile force/tension being produced.

Explain How the rate of stimulation influences muscle tension ?

TWITCH : A single action potential will result in a pulse of Ca2+ release into the cytoplasm and a short period of tension development.
TETANUS : Many action potentials fired in rapid sequence results in a sustained release of Ca2+ from the SR. A sustained period of actin-myosin interaction and a sustained period of contraction.

Explain How the number of active fibres influences muscle tension ?

The number of fibres activated is regulated by how many neurons are active at one time • A small number of active neurons tends to produce low force from the muscle, with the amount of force generally increasing as more motor units are activated. This is called recruitment.
By increasing the number of muscle fibres, you increase the cross-sectional area of muscle which is directly proportional to tension (can produce more contractile force).

The question on the page originate from the summary of the following study material:

HUBS191

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