Organisms Response to Change - Skeletal Muscles Flashcards
what is the function of skeletal muscles?
voluntary movements
what is the structure of a skeletal muscle?
consists of bundles of muscle fibres
what is the structure of muscle fibres?
formed from many cells fused together
what is a sarcolemma?
the cell membrane of a muscle fibre
what is a sarcoplasm?
the cytoplasm of a muscle fibre
what is a sarcoplasmic reticulum?
the endoplasmic reticulum of a muscle fibre
why do muscle fibres have a banded appearance?
myofibrils
what are myofibrils made up of?
protein filaments, which consist of thin and thick myofilaments
what is actin?
thin myofilaments
what is myosin?
thick myofilaments
what does tropomyosin form?
long thin threads that are wound around actin filaments
what is a sarcomere?
a section of a muscle fibre, specifically the distance between one Z disc to the next
what is the Z disc?
the section of the sarcomere that actin is attached to
what is the A band?
section of the sarcomere where myosin and actin is found
what is the I band?
section of the sarcomere containing only actin
what is the M line?
where myosin is attached
what is the H band?
section of the sarcomere containing only myosin
what happens to a sarcomere when the muscle contracts?
it gets shorter because the I band slides into the H band
what happens to the length of the A, I and H bands during muscle contraction?
A band - stays same
I band - shorter
H band - shorter
what does the motor unit do?
supplies all the muscle fibres from a single motor neuron
what is released when the action potential reaches the end of a motor neurone?
acetylcholine
are neuromuscular junctions excitatory or inhibitory?
excitatory only
what is a neuromuscular junction?
point where a motor joint meets a skeletal muscle fibre
what are t-tubules?
extensions of the cell surface membrane
what is the function of t-tubules?
carry the wave of excitation to the sarcoplasmic reticulum
when the wave of excitation reaches the sarcoplasmic reticulum, what occurs?
Calcium ions are activated in the sarcoplasmic reticulum, which then diffuse into the sarcoplasm
what are the similarities between neuromuscular junctions and cholinergic synapses?
neurotransmitters transported by diffusion
receptors cause influx of sodium ions
use a sodium potassium pump to repolarise axons
use enzymes to break down neurotransmitters
what are the differences between neuromuscular junctions and cholinergic synapses?
neuromuscular only excitatory, cholinergic can be inhibitory too
neuromuscular links neurons to muscles only, cholinergic also links neurons to other organs/effectors
action potential ends at neuromuscular, cholinergic may produce a new one
acetylcholine binds to receptors on muscle fiber in neuromuscular, binds to receptors on membrane of post-synaptic neuron in cholinergic
describe the sliding filament theory of muscle contraction
calcium ions cause tropomyosin to move away from actin binding sites, allowing a myosin head to attach and form a cross bridge
myosin head changes angle, pulling actin filament along and releasing ADP
ATP attaches to myosin head, allowing it to detach
ATP hydrolysed allowing myosin head to return to original position
what is myosin made up of?
fibrous protein
globular protein
what is the structure of the fibrous protein in myosin?
protein arranged into a tail-shaped filament
what is the structure of the globular protein in myosin?
two bulbous structures at the end of the protein
how is muscle contraction stimulated?
action potential reaches neuromuscular junctions, causing calcium ions to diffuse into the synaptic knob
this causes synaptic vesicles to fuse with the presynaptic membrane and release acetylcholine, which diffuses across
acetylcholine binds to receptors of muscle cell membrane, causing it to depolarise
what type of exercise are slow twitch muscle fibres adapted for?
endurance over a long period of time
what are the adaptations of slow twitch muscle fibres?
contracts slowly and less powerfully
lots of mitochondria for aerobic respiration
rich supply of blood vessels and myoglobin
what is myoglobin?
red molecule that stores oxygen for respiration
what type of exercise are fast twitch muscle fibres adapted for?
short and intensive exercise
what are the adaptations of fast twitch muscle fibres?
contract rapidly and powerfully
lots of thick myosin filaments
high conc of glycogen as well as enzymes needed for anaerobic respiration
stores of phosphocreatine
what is phosphocreatine?
a molecule that can rapidly produce ADP in anaerobic conditions by donating a phosphate group
