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Week 4 signposts - Coggle Diagram
Week 4 signposts
. Briefly describe the features of the single muscle fiber that demonstrate it is specialised for contractile function
General chemical composition - 75% water, 20% protein (15% myofibrillar, 5% non-myofibrillar aka sarcoplasmic), 5% inorganic compounds
Nuclei/ ‘Myonuclei' - located on the periphery of the cell, in the space between the myofibrils and the sarcolemma. myonuclei are higher in density at the motor end plate.
Sarcolemma - specialised cell membrane of muscle fibers (can stretch). can be excited electrically by AP from motor neuron.
sarcoplasm - specialised cytoplasm, occupies around 9%. the aqueous medium suspends myofibrillar proteins and organelles.
mitochondria - around 5-6% of ICS, specialization includes increased number and size of mitochondrion. peripheral and intermyofibrillar mitochondria help provide energy for muscle contraction
Sarcoplasmic Reticulum (SR), and its Terminal Cisternae - the SR is a smooth ER, stores, releases & retirieves calcium ions, which is fundamental for contraction (excitation-contraction coupling)/ the terminal cisternae is a region of the SR in close proximity and surrounding the T-tubules.
T-Tubule Network - invaginations of the sarcolemma that extend inwards towards the center of the cell. communicate with the outside of the cell membrane, and deep in the muscle fiber
Myofibrils/ Myofibrillar Proteins - suspended in the sarcoplasm & run the length of the fiber. made up of sarcomeres connected end to end. there are hundreds to thousands of myofibrils in one mm fiber.
Basement Membrane/ Basal Lamina - immeditaely external to the sarcolemma, extracellular deposition of protein to form a membrane playing a role in mechanical support, supporting cell develepoment & regeneration, cell-matrix signaling (eg. mechanotransduction)
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State the Hierarchy of Structural Organisation of the Enwrapping Connective Tissues within Skeletal
Muscle
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perimysium - intermediate connective - wrapping fascicles. encases around 150 muscle fibers, to create discrete fascicles. organisation is important for function
enodmysium - wraps the individual mm fibres, surrounds and supports the cell ECM.
sarcolemma - specialised version of cell membrane, covers each muscle fiber - it has elastic properties so it is part of the CT framework
Briefly describe the structure and function of the Thick and Thin filaments, referring to the role of Titin
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Thin filament is made up of 2x actin chains (consecutive actin proteins). every actin monomer (single actin unit) has a binding site for myosin
tropomysosin - wrapped around actin covering the myosin-biding site when the muscle is not contracting, and its location is dictated by troponin
troponin - when a muscle is not contracting, tropomyosin is blocking myosin from attaching where it normally attaches to. is attatched to tropomyosin and has calcium-binding sites - with enough calcium the troponin will uncover the tropomysosin
titin is a protein that is very elastic and allows the skeletal muscle t return to its normal length after contraction or stretching
Describe what is meant by “Muscle Fiber Type”, and the characteristics of Slow- and Fast-Twitch
muscle fibers
Type 2a - Fast Oxidative (/glycolytic) - high mitochondria count, can be aerobic and anaerobic, and is fast in contracting
Type 2b/x - Fast Glycolytic - anaerobic, low mitochondria count, faster contractions, but easily fatigue able
Type 1 - Slow Oxidative twitch muscles - use aerobic systems to create energy, therefore high in mitochondria, red in colour, and have higher myoglobin and higher fatigue resistance
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Briefly describe where energy (in the form of ATP) is derived to power skeletal muscle contraction,
including the role of the enzyme Myosin ATPase
The enzyme Myosin ATPase is found in the cross-bridge heads, and when the cross bridges bind with the actin, ATP stored in the muscle binds and becomes hydrolysed by the enzyme, therefore producing ADP and a phophate group.
Describe the key structures within the Neuromuscular Junction, stating their roles in E-C Coupling
Motor nerve fiber carried down the nerve signal into the synaptic knob, and the action potential of the knob excretes (exocytosis) ACh to receptors in the synaptic cleft - causing the excitation of muscle fibre. the sction potential travels down t-tubule, and triggers the release of calcium
Describe the Sliding Filament Theory (SFT) of skeletal muscle, including reference to the “walk along” mechanism of myosin head engagement and the key molecular events that result in the “power stroke"
the acetylcholine creates a action potential that allows calcium to be released from the sarcoplasmic reticulum, therefore binding to troponin, and therefore moving tropomyosin, and exposing the active sites on the actin for the myosin heads to attach to
. Briefly describe how the SFT of skeletal muscle helps to explain the Length: Tension relationship of
skeletal muscle
The optimum length of the sarcomere is when the maximum amount of cross bridges are binding with active sites. therefore the right amount of tension will optimize this.
Briefly describe the Force: Velocity relationship of skeletal muscle, providing an introductory link to
how this ties in with Strength Qualities and exercise prescription
When the load is lighter, its contraction can be done more rapidly, and therefore when training strength qualities such as speed strength, it is more efficiently done with lighter weights.
describe how elements other than the contractile elements (e.g. the sarcomere), need to be considered - referring to what the stretch-shortening cycle is, and how the various parts of skeletal muscle structure help to carry out a stretch-shortening cycle
The muscle tendon, as a part of the muscle tendon unit. it allows the concentric phase (shortening) to be fast and explosive in movement, the muscle spindle cells (proprioceptors) are stimulated during ECC and can trigger a reflex to enhance contraction