Muscle structure and functions Flashcards
What do muscles do
produce movement
maintain postures and positions
also, protection, heat production (themogenesis) and drive the circulatory system (vascular pump)
what type of muscle do we have
smooth (visceral) muscle
cardiac muscle
skeletal muscle
how muscle contracts (balloonist theory)
contracting muscles swell
volume of the muscles increases when contracting
Jan Swammerdam theory of muscle contraction
upon contraction volume does not increase in fact it decreases slightly
disproving balloonist theory
Muscle fibres
Muscle consists of bundles of fibres (fascicles) and each fibre can individually contract
each contractile fibre generates tension, which applies force to both ends
Tendon
Attaches muscles to bone
Forces generated by individual fibres are gathered together in tendons and the resultant force pulls the bone
Muscle fibre architecture
In some muscles fibres are packed in different direction
Muscle fibres are organised to optimise the trade-off between strength and speed dependent on their functional needs.
parallel vs pennate muscles
parallel- straight fibres
less muscles fibres between tendon in this way so is weaker
pennate- diagonal fibres
higher number of fibres therefore is stronger having greater PCSA
PCSA- Physiological cross-section Area
Area of the cross section of a muscle perpendicular to its fibres
Parallel vs pennate muscle: speed
parallel-has a shorter shortening distance so will be faster
pennate- has a larger distance to shorten and will be slower
Muscle contraction
Contraction does not always mean shortening
Lateral Raise
when external force=muscle force, muscle length will stay constant: isometric contraction (hold arm in abduction)
when external force< muscle force, muscle will shorten while contracting: concentric contraction (raise arm to abduction)
when external force> muscle force, muscle can be lengthened while contracting: eccentric contraction (lower arm in adduction)
agonist
antagonist
prime mover (agony)
muscle that has to relax
Structure of Muscle fibre
From microscopic view-
skeletal muscle fibres are striated
Muscle fibres are bundles of myofibrils
Myofibrils is striated made up of Sarcomere chains
Sarcomere- the most basic functional unit of muscle contraction
Inside the Sarcomere- myofilaments
A sarcomere consists of two ‘inter-digitated’ myofilamnets
actin (thin)
and
Myosin (thick) filaments
A band (darker area)
I band (lighter area)
Sliding filament model
Actin and myosin filaments slide towards each other
Myosins row (move along) in the sea of actins
the main source of the sliding comes from interactions between myosin heads and actin binding sites, called cross- bridges
terminology
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
