muscle structure Flashcards
what is a tendon?
connects bone to skeletal muscle
what is a ligament?
connect bones to bones
what is a cartilage?
between bones ‘shock absorbers’
what is a muscle?
bundles of fibres, different structures
what is a cardiac muscle?
present in the heart, acts involuntarily (myogenic)
what are skeletal muscles?
attached to bones, vast majority of muscles, discontinuous contraction, controlled voluntarily
what are smooth muscles?
involuntary muscle, found in the gut, blood vessel walls and in the iris of the eye, slow and weak contraction
what is the function of skeletal muscle?
receiving a nerve impulse and working in antagonistic pairs to pull bones
what are antagonistic pairs?
you cannot stimulate the contraction of two antagonistic muscles at the same time, prime mover contracts and antagonist relaxes e.g. bicep and tricep in flexion/extension at the elbow
describe the structure of a skeletal muscle
made up of large bundles of long cells called muscle fibres, the cell membrane is called the sarcolemma, bits of the sarcolemma fold inwards and stick to the sarcoplasm, called T (transverse) tubules which help spread electrical impulses throughout the sarcoplasm to reach all parts of the muscle fibre, internal membranes called the sarcoplasmic reticulum run through sarcoplasm which stores and releases calcium ions, contain lots of mitochondria, they are multinucleate, lots of long cylindrical organelles called myofibrils made up of proteins
how are muscle fibres grouped into fast or slow twitch?
resistance to fatigue, speed of contraction
what is the speed of contraction in fast twitch muscle fibres?
fast
what is the speed of contraction in slow twitch muscle fibres?
slow
what is the power of contraction in fast twitch muscle fibres?
strong
what is the power of contraction in slow twitch muscle fibres?
weaker
what is the type of activity in fast twitch muscle fibres?
sprinting
what is the type of activity in slow twitch muscle fibres?
long distance running
what is the type of respiration in fast twitch muscle fibres?
anaerobic
what is the type of respiration in slow twitch muscle fibres?
aerobic
what is an example of a fast twitch muscle?
quad, biceps
what is an example of a slow twitch muscle?
core
what are the key features of fast twitch muscle fibres?
thicker and more myosin filament, high concentration of enzymes for anaerobic respiration, a store of phosphocreatine (energy buffer/phosphate for ATP)
what are the negatives of fast twitch muscles?
fewer blood vessels, run out of oxygen more quickly, thicker so larger diffusion pathway
what are the key features of slow twitch muscles?
large amount of myoglobin, good supply of glycogen, good blood vessel network, many mitochondria, small diameter, darker in colour
why do slow twitch muscles need a large amount of myoglobin?
aerobic respiration (stores oxygen)
why do slow twitch muscles need a good supply of glycogen?
aerobic respiration (store of glucose)
why do slow twitch muscles need a good blood vessel network?
good blood supply to transport oxygen and remove CO2 for respiration
why do slow twitch muscles need many mitochondria?
the site of aerobic respiration, sustained respiration
why do slow twitch muscles have a small diameter?
easier diffusion on oxygen and CO2, short diffusion pathway
why are slow twitch muscles darker in colour?
because they have a greater blood supply
what does it mean that muscle fibres are fused together?
they are one cell which share a nucleus (multinucleated), cytoplasm (sarcoplasm) and cell membrane (sarcolemma)
why do nuclei have to be dotted all over the sarcoplasm?
transcription (growth and repair), all cells controlled
what organelle will be in large number in the sarcoplasm and why?
mitochondria - ATP for contraction and protein synthesis
RER- protein synthesis
what are myofibrils?
consist of two types of protein filaments (actin and myosin) multiple sarcomeres, banding pattern, causes myofibrils to appear striped
what is actin?
thinner, two strands coiled around each other
what is myosin?
thicker, rod shaped fibres with bulbed heads which project outward
what are A-bands? (Anisotropic)
dark bands where actin and myosin overlap, depends on myosin length
what are I bands? (Isotropic)
no overlap, actin only
what is the H zone?
only myosin
what is a sarcomere?
z line to z line, gets smaller when muscle contracts
what is the all or nothing principle?
the strength by which a nerve or muscle fibre responds to a stimulus is independent of the strength of the impulse
what is a neuromuscular junction?
where a motor neurone reaches skeletal muscle fibres, often multiple junctions to different fibres so multiple fibres stimulated, speeds up the response, contraction is quicker and more powerful, threshold is met
neuromuscular junctions follow the all or nothing principle but…
multiple neurones=one muscle unit, slight force = fewer fibres stimulated, large force = multiple stimulated
what type of synapse is a neuromuscular junction?
cholinergic synapse, using acetyl choline and acetyl choline sterase
explain the process of synaptic transmission at a neuromuscular junction
arrival of action potential from the presynaptic neurone depolarises the presynaptic knob causing calcium gated channels to open which changes the charge so vesicles move and fuse with the membrane and release the neurotransmitter acetylcholine. Acetyl choline diffuses across the synaptic cleft and binds to neuroreceptors on the muscle fibre causing a change in tertiary structure so sodium gated ion channels open, influx of sodium establishes an action potential if threshold is met
how do action potentials travel into the muscle fibre?
through T-tubules which branch through the sarcoplasm to the sarcoplasmic reticulum which releases calcium ions
what are the two other proteins found in muscle fibres (besides actin and myosin)?
troponin and tropomyosin
what is tropomyosin?
long and thin fibrous strands, wrap around the actin filaments
what is troponin?
globular protein involved in muscle contraction
describe the role of calcium ions in muscle contraction
calcium ions diffuse into the myofibrils from the sarcoplasmic reticulum changing the shape of the tropomyosin. This uncovers the binding site on the actin so a myosin head with an attached molecule of ADP can bind. The actin is pulled along and ADP released. The attachment of ATP to the myosin head then causes myosin head to detach. This ATP is later hydrolysed by ATPase releasing a small packet of energy. This energy causes the myosin head to return to it’s original form
when nervous stimulation stops what will happen?
calcium ions are actively transported back into SR using energy from ATP hydrolysis, troponin no longer changes shape of tropomyosin, tropomyosin blocks the actin filament, myosin heads are unable to bind
what does muscle contraction rely on energy for?
to move myosin heads, to reabsorb calcium ions into the SR
where does the energy come from for muscle contraction?
hydrolysis of ATP and then it’s regeneration, aerobically in oxidative phosphorylation in the mitochondria, anaerobically through phosphorylation using phosphocreatine
what is phosphocreatine?
a buffer supply of energy stored in the muscle used to restore ATP, reserve supply of phosphate, broken down when energy is needed, combines with ADP to reform ATP, is immediately available
