Skeletal Muscle Flashcards
Name the parts of the skeletal muscle structure?
-muscle fibre
-endomysium
-fascicles
-perimysium
-Epimysium
-deep fascia
What are skeletal muscle fibres?
-are individual cells- are around 50 microns in diameter and multinucleate
What sort if structure does muscle have and describe it?
-has hierarchical structure:
-lowest level of structure there are filaments of myosin and actin arranged into myofibrils
-One muscle fibre contains many myofibrils
-Fibres are arranged into bundles called fascicles
-Fascicles are arranged into whole muscles
-Myofibrils are composed of many sarcomeres joined together- these provide the striated microscopic appearance of skeletal and cardiac muscle
-mitochondira is found in muscle fibre just below the sarcolemma or between the myofibril
Describe the structure of myosin?
-long alpha-helical tail and 2 globular heads
-head is an ATP-ase, an actin binding molecule and a molecular motor
how are actin filaments formed?
by polymerisation of globular actin
How does movement in muscles occur?
by sliding movement between myosin and actin, not by changes in filament length
What is the Cross-bridge hypothesis of muscle contraction?
-That the Sliding of thin and thick filaments is caused by cross-bridges that extend from myosin filament
-These attach to actin and pull thin filaments towards centre of sarcomere and detach
-This process is also paired with the hydrolysis of ATP
How is muscular contraction controlled?
-has specialised system of tubular structures:
Transverse tubules and sarcoplasmic reticulum control concentration of calcium ions within cytoplasm
-Level of calcium ion concentration determines whether muscle is contracting (calcium high) or relaxing (calcium low)
How do molecular components of muscle come together to form sarcomeres?
-Myoblasts proliferate and fuse together in limb buds forming myotubes
-Allows sarcomeres to be detected
-Myotubes grow by subsequent waves of migration and fusion which are then targeted by components of motor nervous system
Describe the features of mature muscle fibres?
-can’t divide- known as terminally differentiated
-However a few myoblasts remain and can be activated for regeneration and repair after muscle damage
Describe the difference between fast and slow muscle fibre types within muscle?
-Fast fibre types have a fast isoform of myosin and little mitochondria so they are able to produce high forces quickly
-Slow fibre types have a slow isoform of myosin and many mitochondria for a lower force but sustained contractions
Describe how perfusion is controlled during muscle contraction?
-Low intensity contraction means only terminal arterioles supplying capillaries are dilated
-This dilation increases perfusion of capillary bed and increases SA available for oxygen and nutrient exchange
-High intensity exercise and contraction caused total blood flow to increase by dilation of feed arteries
-This increases delivery of oxygen and nutrients by increased bulk flow
Describe the structure of motor units?
-1 motor neuron and all muscle fibres it innervates make up a motor unit
-All fibres of 1 motor unit are the same fibre type
Describe the order in which muscle units are fired and why is this?
-Smallest motor unit is fired first, then medium then large.
-Due to henneman’s size principle: motor units are stimulated from smallest to largest because the excitation threshold is lower in neurons with smaller bodies
What is Asynchronous recruitment
and why is it used?
-Is the switching between different motor units during submaximal contraction
-Is used to avoid fatigue as it switches different motor units on and off to maintain the same force
