Muscle (3.6.3) Flashcards
What is a Skeletal Muscle also known as?
Striped / Striated Muscle
Why is a Skeletal Muscle also known as a Striped / Striated Muscle?
Due to its striped appearance when viewed under a microscope due to alternate light bands of protein filaments
What is a muscle attached to?
Bone
What stimulates a muscle to contract?
Nerves
What does a muscle act as?
Effector
What are 2 features of muscle fibres?
- Multinucleate
* Many Mitochondria
Explain the Structure of Muscles:
- Consists of cells, muscle fibres that are multinucleate and contain many mitochondria
- Elongated with bundles of myofibrils
- Sarcolemma = cell surface membrane, folded deeply into muscle fibre (t – tubules)
- Sarcoplasm
- Sarcoplasmic Reticulum containing Ca2+
What are the 2 protein filaments in Myofibrils?
1) Thick Filaments – Myosin
2) Thin Filaments - Actin
What line is Actin attracted to?
Z – Line
What is the part of the myofibril between 2 Z – lines called?
Sarcomere
What line is Myosin attracted to?
M – Line
What does the A – Band include?
This is where Myosin Filaments + Actin Filaments
What does the I – Band include?
Only Actin Filaments
What does the H – Band include?
Only Myosin Filaments
What Theory explains Muscle Contraction
Sliding Filament Theory
How are the Bands affected when a muscle contracts?
- I Band is reduced as Actin slides between myosin
- A Band remains the same as Myosin length is unchanged
- H Zone is reduced as overlap between Actin + Myosin increases
- Sarcomere is reduced in length
What stops myosin heads from binding to Actin in a resting muscle?
The binding sites, in a resting muscle, will be blocked by a protein called Tropomyosin
What causes the unblocking of myosin binding sites?
The release of Calcium ions as they cause Tropomysoin to change shape and expose the myosin binding sites on the Actin filament
What causes the release of Calcium ions?
When an action potential spreads along the t-tubules
Events for Each Myosin Head:
- Myosin Head attaches to myosin binding site on Actin filaments forming actinomyosin bridge
- Myosin head tilts in a rowing action, sliding actin filaments iver myosin filaments towards the centre of Sarcomere
- ATP binds to the myosin head and causes it to release the actin filament
- ATP hydrolase (in the head) hydrolyses ATP releasing energy which causes the myosin head to flip back into its original position
- Cycle Repeats
What happens when the action potentials stop arriving?
- Calcium ions actively pumped back into Sarcoplasmic reticulum via Active transport – ATP needed)
- Tropomyosin returns to original shape + myosin heads no longer attach to Acton filaments
- The muscle remains in its contracted state as Action filaments only slide in 1 direction towards centre of Sarcomere.
Why are the muscles described to work in antagonistic pairs?
As they work against an incompressible skeleton which means when 1 contracts, the other muscle in the pair relaxes
When is energy needed in muscle contraction?
- Movement of myosin heads (detach + return to original position)
- Return of Ca2+ ions into Sarcoplasmic reticulum by active transport
State 2 sources where Energy is supplied from?
- ATP
* Phosphocreatine
Why must energy be supplied by another source?
This is because hydrolysis of ATP releases energy + ADP + Pi. Muscle fibres only store small quantities enough for 3-4 secs of muscle contractions and it takes 10 secs to generate ATP from anaerobic respiration, so it must be supplied by another source
Why is Phosphocreatine useful?
This is because Muscle fibres can store it; producing ATP rapidly
What is the formula to produce ATP using Phosphocreatine?
ADP + Phosphocreatine ATP + Creatine
What happens with Phosphocreatine when muscle fibre stops contracting?
It is resynthesised
What are the 2 types of Muscle Fibre?
- Slow Twitch Fibres
* Fast Twitch Fibres
Explain the basic function of Slow twitch fibres
- Rely on ATP generated by aerobic respiration
* Contract slowly over long periods of time (standing, walking, balancing etc.)
