Section 6: Skeletal Muscles Flashcards
How do muscles work as antagonistic pairs and name an example?
- 1 muscle contracts (agonist) - pulls on bone produces force
- 1 muscle relaxes (antagonist)
- Examples biceps and triceps on the arm
How are muscles attached to bones?
- By tendons
What attaches bones to bones?
- Ligaments
What are the advantages of skeletal muscles being arranged in antagonistic pairs?
- Muscles can only contract/ pull
- 2nd muscle required to reverse the movement of 1st muscle
- Help maintain posture - contraction of both muscles
What is the structure of the skeletal muscle?
- Muscle made up of bundles of muscle fibres packaged together
- Cell membrane = sarcolemma
- Cytoplasm = sarcoplasm
- Myofibrils made of 2 proteins, actin and myosin
- Shared nuclei
- Lots of endoplasmic reticulum
What does a sarcomere consist of?
- Ends - Z line
- Middle - M line
- H zone - around M line which contains only myosin
What causes the banding patterns and what are they called?
- Myosin filaments are thicker than actin filaments
- I bands - light bands only containing actin
- A bands - dark bands containing thick myosin filaments and some overlapping actin
What happens when muscles contract?
- Myosin heads slide actin past/ along myosin causing the sarcomere to contract
- Simultaneous contraction of lots of sarcomeres causes myofibrils and muscle fibres to contract
- When sarcomeres contract
- H zones = shorter
- I band = shorter
- A band = same
- Z lines closer
What is the sliding filament theory of muscle contraction?
- Action potential/ depolarisation spreads down T-tubules causing the release of calcium ions from sarcoplasmic reticulum which diffuse through the sarcoplasm to the myofibril
- Calcium binds to tropomyosin, causing it to move - changes shape exposing the myosin binding site to actin
- Myosin heads with ADP attached attach to binding sites forming actin myosin cross bridge
- Myosin heads move/change angles - pulling actin along myosin
- ATP binds to myosin head causing it to detach from actin binding site/ break cross bridge
- The hydrolysis of ATP by ATPase releases energy for myosin heads to move back to original position
- Myosin reattaches to a different binding site further along actin
Exam Question: Muscle disease by a mutated allele leads to myosin molecules being unable to bind to other myosin molecules. This means they can’t contract why? (3)
- Can not form myosin/ thick filaments
- Cant pull/ cant move actin
- Myosin moves/ if attached doesn’t move
- Cant move actin towards each other/ can not shorten sarcomere
What is the function and location of slow twitch fibres?
- Specialised for slow, sustained contractions
- Endurance activities e.g maintaining podture, long distance running
- Located in muscles that give posture and in leg muscles of long distance runners for aerobic respiration
What are the adaptations of slow twitch fibres?
- High levels of myoglobin (red coloured protein that stores oxygen) making them reddish colour
- Store large amounts of oxygen for aerobic respiration
- Many mitochondria - high rate of respiration
- Many capillaries - short diffusion pathway/ large surface area - supply high conc of oxygen/ glucose for respiration and to prevent build up of lactic acid causing muscle fatigue
What is the function and location of fast switch fibres?
- Specialised for producing rapid, intense contractions of short duration
- Short bursts of speed and power
- Located in legs of sprinters - anaerobic respiration produces energy quickly
What are the adaptations of fast switch fibres?
- Low levels of myoglobin - whitish colour - anaerobic respiration does not need oxygen
- Lots of glycogen - hydrolysed to lots of glucose - for glycolysis
- Higher conc of enzymes involved in anaerobic respiration - higher rate of respiration
- Store phosphocreatine which rapidly generates ATP from ADP by providing phosphate
What is the role of phosphocreatine in muscle contraction?
- Phosphocreatine stored inside cells
- Rapidly makes ATP by phosphorylating ADP (adding a phosphate group from PCr)
- PCr runs out after a few seconds so used in short bursts of vigorous exercise
- Used for anaerobic respiration.
