Structure of skeletal muscle Flashcards
What are muscles?
Muscles are effector organs that respond to nervous stimulation by contacting and producing movement
What are the three types of muscle? Describe them and where they are found too
1) Cardiac muscle: found in the heart only
2) Smooth muscle: found in the walls of blood vessels and the gut
3) Skeletal muscles: make up bulk of body muscle in vertebrates
What type of muscle is under voluntary control?
Skeletal muscle, which are responsible for conscious movement
What types of muscle are under involuntary control?
Cardiac and smooth muscle, they contract without conscious control
What are muscles made up of?
Muscles are made up of tiny muscle fibres called myofibrils
What are myofibrils?
Tiny muscle fibres that work together to generate powerful contractions
What are myofibrils made up of?
Myofibrils are made up of fused cells that share nuclei and cytoplasm (called sarcoplasm)
There is also a higher number of mitochondria because a high amount of ATO needs to be produced
Why are muscle fibres not made up of individual cells joined end to end?
The junctions between cells would be weak points, reducing the overall strength of muscle contraction
How is muscle structure adapted to be more efficient for contraction?
Individual cells fuse together to form muscle fibres, which provide greater strength
What is the sarcoplasm?
The shared cytoplasm within a muscle fibre, mainly found around the fibre’s circumference
What organelles are found in high concentrations in the sarcoplasm?
Mitochondria (for ATP production) and endoplasmic reticulum
What two protein filaments make up myofibrils? What do these two protein filaments form?
Myosin and actin are protein filaments that form a sarcomere.
Actin is a thinner protein which consists of two strands twisted around one another
Myosin is a thicker protein which consists of long rod - shaped tails with bulbous heads that project to the side
What is the function of actin and myosin in muscle contraction?
They interact to form cross - bridges, allowing the muscle to contract
Why do myofibrils appear striped?
Myofibrils appear striped due to their alternating light and dark coloured bands
What are I bands? (isotropic bands)
Light bands where thick (myosin) and thin (actin) filaments do not overlap
What are A bands? (anisotropic bands)
Dark bands where thick (myosin) and thin (actin) filaments overlap
What is the Z-line?
A line in the centre of the I band that marks the boundary of a sarcomere
What is the H-zone?
A lighter region in the centre of the A band where only myosin filaments are present
What is the sarcomere?
The functional unit of muscle contraction defined as the distance between adjacent Z lines is called the sarcomere
What happens to the sarcomere when muscles contract?
The sarcomere shortens and the pattern of light bands (I bands) and dark bands (A bands) change
What is tropomyosin?
A fibrous protein that wraps around the actin filament in muscle fibres
What is the function of tropomyosin in muscle contraction?
It helps regulate muscle contraction by blocking the myosin - binding sites on actin when the muscle is relaxed
