Topic 6—B: Nervous coordination-3. Muscle structure Flashcards
What are muscles?
- They are effectors so they contract in response to nervous impulses
What are the 3 different types of muscle?
- Smooth muscle
- Cardiac muscle
- Skeletal muscle
Smooth muscle
- contracts without conscious control
- found in walls of internal organs (apart from the heart), e.g. stomach, intestine, and blood vessels
Cardiac muscle
- contracts without conscious control (like smooth muscle) but it’s only found in the heart
Skeletal muscle
- also called striated, striped or voluntary muscle
- type of muscle you use to move e.g. the biceps and triceps move the lower arm
Role of skeletal muscle
- Skeletal muscles are attached to bones by tendons
- Ligaments attach bones to other bones to hold them together
- Pairs of skeletal muscles contract and relax to move bones at a joint- the bones of the skeleton are incompressible (rigid) so they act as levers, giving the muscles something to pull against.
Antagonistic pairs
- Muscles that work together to move a bone are called antagonistic pairs
- The contracting muscle is called the agonist and the relaxing muscle is called the antagonist
Structure of skeletal muscle
- Skeletal muscle is made up of large bundles of long cells called muscle fibres
- The cell membrane of muscle fibre is called the sarcolemma
- Bits of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm (a muscle cell’s cytoplasm)
- These folds are called transverse T tubules and they help. To spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre
- A network of internal membranes called the sarcoplasmic reticulum runs throughout the sarcoplasm
- Sarcoplasmic reticulum stores and releases calcium ions that are needed for muscle contraction
- Muscle fibres have lots of mitochondria to provide the ATP that’s needed for muscle contraction
- They contain many nuclei and have lots f long cylindrical organelles called myofibrils
- Myofibrils are made up of proteins and are highly specialised for contraction
What is skeletal muscle also known as?
Striated muscle
How is the muscle attached to the skeleton?
By tendons under voluntary control
What is the muscle composed of?
A series of bundles
What are bundles?
These are a group of uncle fibres which are surrounded by connective tissue containing blood vessels and nerves
What happens in a muscle fibre?
- The cells fuse during development to form a very long, strong, multicucleated cell. Can withstand very high tension
What does each fibre contain a large number of?
- Myofibrils within the cytoplasm (sarcoplasm in muscle cells)
- They exhibit a distinctive striated pattern under the microscope
What is the pattern of banding on a Myofibrils caused by?
- The sarcomeres
What is a sarcomere?
- Smallest contractile units in a muscle, which are arranged end-to-end for the entire length of each myofibril
How is each sarcomere formed?
- From thousands of protein filaments
- These proteins can slide together, shortening the sarcomere
What does myofibril contain?
- Bundles of thick and thin myofilaments that move past eachother to make muscles contract
What are the thick myofilaments made of?
- The protein myosin
What are the thin myofilaments made of?
- The protein actin
What will you see if you look at a myofibril under an electron microscope?
- A pattern of alternating dark and light bands
A bands
- Dark bands contain the thick myosin filaments and some overlapping thin actin filaments
I bands
- Light bands contain thin actin filaments only
What is a myofibril made up of?
- Many short units called sarcomeres
What is the end of each sarcomere marked with?
- Z line
What is in the middle of each sarcomere?
An m line
What is the m line?
- The middle of the myosin filaments
What is around the M line?
- The H zone
H zone
Only consists of myosin filaments
What is muscle contraction explained by?
- The sliding filament theory
What happens in the sliding filament theory?
- Myosin and actin filaments slide over one another to make the sarcomeres contract
- Myofilaments themselves don’t contract
- Simulataneous contraction of lots of sarcomeres means the Myofibrils and muscle fibres contract
- Sarcomeres return to their original length as the muscle relaxes
What happens to the A band during contraction?
- It remains the same length
What happens to the I band during contraction?
- It gets shorter
What happens to the H zone during contraction?
- It gets shorter
