13.9-13.10 Muscles Flashcards
What are the three types of muscle in the body?
1) Skeletal muscle
2) Cardiac muscle
3) Involuntary muscle (also known as smooth muscle)
Where is skeletal muscle found?
- Skeletal muscles make up the bulk of body muscle tissue.
- These are the cells responsible for movement e.g biceps and triceps
Where is cardiac muscle found?
- Cardiac muscle cells are only found in the heart.
- These cells are myogenic, meaning they contract without the need for a nervous stimulus, causing the heart to beat in a regular rhythm.
Where is involuntary muscle found?
- Involuntary muscle cells are found in many parts of the body e.g the walls of hollow organs such as the stomach and bladder.
- They are also found in the walls of blood vessels and the digestive tract
What are skeletal muscles made up of?
Skeletal muscles are made up of bundles of muscle fibres.
What is the plasma membrane around the muscle fibres called?
Sarcolemma
What is the shared cytoplasm within a muscle fibre called?
Sarcoplasm
Why are muscle fibres formed from individual muscle cells fusing together?
This makes the muscle stronger, as the junction between adjacent cells would act as a point of weakness,
What is it called when parts of the sarcolemma fold inwards?
Transverse/T-tubules
Why do parts of the sarcolemma fold inwards?
- Parts of the sarcolemma fold inwards to help spread electrical impulses throughout the sarcoplasm.
- This ensures that the whole of the fibre receives the impulse to contract at the same time.
What else do muscles fibres contain and why?
1) Lots of mitochondria to provide the ATP that is needed for muscle contraction.
2) Sarcoplasmic reticulum which extends throughout the muscle fibre and contains calcium ions required for muscle contraction.
What are myofibrils?
Myofibrils are long cylindrical organelles found in muscle which are made of protein and specialised for contraction.
Which two types of protein filaments are myofibrils made up of?
1) Actin: The thinner filament and consists of two strands twisted around each other.
2) Myosin: The thicker filament and consists of long rod-shaped fibres that project to one side.
What is a sarcomere?
- A sarcomere is the functional unit of a myofibril.
- When a muscle contracts, the sarcomere contracts.
What are light bands?
Light bands are areas that appear light as they are the region where the actin and myosin filaments do not overlap. Known as I(isotopic)-bands
What are dark bands?
- Dark bands are areas that appear dark because of the presence of thick myosin filaments.
- The edges are particularly dark as the myosin is overlapped with actin.
- a bands
What is the Z-line?
- The Z line is a line found at the centre of each light band.
- The distance between adjacent Z-lines is called a sarcomere.
What is the H-zone?
- The H zone is a lighter coloured region found in the centre of each dark band.
- Only myosin filaments are present at this point.
What is the sliding filament model?
- During contraction the myosin filaments pull the actin filaments towards the centre of the sarcomere.
- This results in the light band (I band) and H-zone becoming narrower, and the Z lines moving closer together causing the sarcomere to shorten
- The dark band (A band) remains the same width, as the myosin filaments themselves have not shortened, but now overlap the actin filaments by a greater amount.
- The simultaneous contraction of lots of sarcomeres means that myofibrils and muscle fibres contract.
- This results in enough force to pull on a bone and cause movement.
- When sarcomeres return to their original length the muscle relaxes.
What is the structure of myosin?
- Myosin filaments have globular heads that are hinged which allows them to move back and forwards.
- On the head is a binding site for each of actin and ATP.
- The tails of several hundred myosin molecules are aligned together to form the myosin filament.
What are actin-myosin sites?
- Actin filaments have binding sites for myosin heads and these are called actin-myosin sites.
What are the actin-myosin sites blocked by?
Actin-myosin binds sites are blocked by the presence of TROPOMYOSIN which is held in place by TROPONIN.
When are the actin-myosin sites blocked by tropomyosin?
- When a muscle is in a resting state (relaxed) the actin-myosin sites are blocked by tropomyosin.
- The myosin heads can therefore not bind to the actin, and the filaments cannot slide past each other.
When a muscle is stimulated to contract what happens?
- myosin heads form bonds with actin filaments known as actin-myosin cross-bridges.
- The myosin heads then flex (change direction) in unison, pulling the actin filament along the myosin filament.
- The myosin detaches from the actin and its head returns to its original angle, using ATP.
- The myosin then reattaches further along the actin filament and the process occurs again.
