Muscle structure and function (wk2) Flashcards
What do muscles do?
-Most of your influences to the external world are delivered through contracting muscles
-Physical interactions, voice production, emotional expressions, typing/writing
-Produce movement
-Maintains postures and positions
-Protection, heat production (thermogenesis) and driving circulatory system (vascular pump)
Name the 3 types of muscles tissues we have:
-Smooth (visceral) muscle -> involuntary
-Cardiac muscle -> involuntary
-Skeletal muscle
Describe the experiment by Swammerdam on muscle volume:
-Contracting muscle used to be seen as ‘swelling’, called the balloonist theory
-It was created by Erasistratus in 304-250 BC. The critical prediction was that the volume of the muscle increases when contracting
-Jan Swammerdam studied this theory using a frog leg in a jar of water and pinched the nerve, to see if the water height would increase from the enlarged muscle. He found that the volume actually decreased
Describe the basic structure of muscle:
-Muscle consists of bundles of fibres (fascicle) and each fibre individually contracts
-Muscle fibre contraction -> each contractile fibre generates tension, which applies force to both ends
-Tendon attaches muscle to bone (but some muscles attach directly to the bone)
-Musculo-tendon contraction -> forces generated by individual fibres are gathered in tendons and the resultant force pulls the bone
-Aponeurosis -> a flat sheet of tissue that connects muscles to bones
Describe/identify the main types of muscle fibre architecture
-Some muscles have fibres that are packed in different directions
-Examples of muscle fibre architecture types include; parallel, penniform, bipennate and strap
Describe parallel and pennate muscles and draw them out:
-Pennate muscles are stronger because more fibres are packed
-Pennate muscles have greater physiological cross-sectional area (PCSA) (the area of cross section of a muscle perpendicular to its fibres)
-Pennate muscles are slower because fibres have to shorten over a greater distance to shorten the muscle over the same distance
Describe the 3 types of muscle contraction:
-Isometric -> when there is no change in length
-Concentric -> where the muscle length shortens to produce force
-Eccentric -> where the muscle lengthens under tension
(agonist=prime mover + antagonist=muscle that has to relax)
Describe the muscle hierarchical structure and annotate a diagram:
-Muscle consists of a bundle of muscle fascicles
-Each fascicle is a bundle of muscle fibres
-Each bundle of muscle fibres is a bundle of myofibril’s
-Myofibril -> sarcomere chain (sarcomere is the most basic functional unit of muscle contraction)
-Each sarcomere has a mechanism that generates the tension
Describe the inside of a sarcomere:
-A single sarcomere consist of 2 ‘inter-digitated’ myofilaments, actin (thin) and myosin (thick) filaments
-These are in the molecular, darker level of the muscle
-Actin and myosin are types of protein
-The whole ‘unit’ is the sarcomere
-Actin -> I-band (lighter) + Z-line runs through
-Myosin -> A-band + M-line runs through
What is the sliding filament model?
-Actin and myosin filaments slide towards each other
-The main source of the sliding forces come from interactions between myosin heads and actin binding sites, called cross-bridges
-Binding sites -> positions on actin filaments where the myosin head can attach
-Cross bridges -> temporarily formed mechanical bridges between actin binding sites and myosin heads
-Power stroke -> a ‘nod’ of the myosin head that applies force to the actin filament via the cross-bridge
-ATP and calcium combines the actin and myosin together more. This creates a better cross-bridge which can create a better contraction of the muscle
-How to remember: Myosin’s row in the sea of actins
Describe the length-tension curve (use the diagram from the 09/10 for this)
- Optimal position for cross-bridge formation
- Muscle stretched. Unable to actively contract, passive resistance prevents being stretched further
- Muscle short and slack. No passive resistance, unable to actively contract. Titin filaments is anchoring the sarcomere from stretching anymore than should be allowed. Too much cross over, leads to a few binding sites, which leads to a small contraction
Describe what passive insufficiency is:
-When a muscle is lengthened to its full extent, but is limiting movement at one or more of the joints it crosses
-The absolute length at stretch possible for any muscle is limited by;
1. Number of sarcomeres + proteins with sarcomeres
-Passive insufficiency becomes a problem for large muscle which cross over one another e.g. hamstrings and quadriceps group
Describe what active insufficiency is:
-Decreased tension and inability to generate force in a multi-joint muscle when it is in a shortened position
-Unavailability of further actin binding sites, when filaments fully overlapping prevents muscle generating active tension
Describe the relationship between eccentric contractions and the sliding filament theory:
-Refer to the diagram (09/10)
-When a muscle is trying to resist lengthening, the long protein titin binds with actin, shortening its length and making it harder for the myosin to slide back away from the actin
-A = Passive strength
-B = Eccentric lengthening
