Muscles Flashcards
What are the alternative names for each type of muscle?
smooth - unstriped/involuntary
skeletal - striped/voluntary
cardiac - heart
What are the three types of muscle?
smooth, cardiac, skeletal
Describe the contractions of each type of muscle
smooth - slow
skeletal - rapid
cardiac - rapid/myogenic
Describe the speed of the fatigue of the muscle types
smooth - slow
skeletal - rapid
cardiac - never/very slow
Describe the distribution of the different types of muscle
smooth - tubular organs
skeletal - attached to skeleton/bones
cardiac - heart
What is antagonistic muscle action?
muscle pairs that act in opposite directions, one contracts and the other relaxes
Give an example of antagonistic muscles?
bicep and tricep
How is skeletal muscle controlled?
-by the voluntary nervous system
-each muscle is controlled by a motor neurone
How do motor neurones interact with muscles?
at a neuromuscular junction (specialised synapse between a motor neurone and muscle fibre)
Explain the process at a neuromuscular junction
-an action potential arrives at the neuromuscular junction causing Ca2+ channels to open
-Ca+ diffuses into neurone
-this causes vesicles containing acetylcholine to fuse with the pre-synaptic membrane
-acetylcholine diffuses across the synaptic cleft and binds to sarcolemma receptor proteins on the post-synaptic membrane
-this causes Na+ to diffuse into the sarcolemma
-post-synaptic membrane depolarises and sends the an action potential along the sarcolemma and down T-tubules
-T-tubules channel the action potential towards the sarcoplasmic reticulum which releases Ca2+ ions into the cytoplasm
-increase in Ca2+ ions causes the muscle cell to contract
Compare the neurotransmitter, post synaptic membrane, type of movement, effect, number of receptors, type of response of cholinergic synapse and NMJ
neurotransmitter - CS is acetylcholine, NMJ is acetylcholine
post synaptic membrane - CS is a neurone, NMJ is the sarcolemma in a muscle cell
type of movement - diffusion
effect - CS - action potential, NMJ - muscle contraction
number of receptors - CS - fewer, NMJ - more
type of response - CS - excitatory or inhibitory, NMJ - excitatory
What are muscle fibres joined by?
tendons
What is a sarcomere?
the basic contractile unit
What is a muscle fibre?
a single muscle cell
How do myofibrils appear under a microscope?
banded structures
How are the insides of the myofibrils structured?
parallel filaments
What are the two types of filament in a myofibril?
thick - myosin
thin - actin
How are the two filaments linked?
intervals called crossbridges
Describe the structure of myosin
-two heads called myosin heads
-each head contains an ATPase
-the heads stick out from the crossbridge
Describe the structure of actin
contains a binding site for myosin heads
Name the two proteins attached to actin
tropomyosin - wound around the actin
troponin - mound to the tropomyosin and contain calcium ion binding sites
What are the repeating units of a myofibril?
sarcomeres
The ends of each sarcomere are joined by…
Z-lines
What is the dark A-band?
thick myosin filaments
What is the light I-band?
where thin filaments do not overlap with thick filaments
What is the H-zone?
the portion of the A-band where the thick and thin filaments do not overlap
When a muscle contracts what happens to the length of the sarcomere?
reduces as thick and thin filaments slide past each other
What happens to the dark and light bands during contraction?
dark bands - stay the same length
light bands - reduce in length
Where does the energy supply for muscle contraction come from?
hydrolysis of ATP - movement of myosin heads and reabsorption of Ca2+ ions into the sarcoplasmic reticulum by active transport
What is the number of energy released by hydrolysis of ATP?
+33Kjmol-1
Name three ways ATP is obtained?
-ATP phosphocreatine system
-aerobic respiration
-anaerobic respiration
What does phosphocreatine do?
phosphorylates ADP to ATP to maintain the supply of ATP
Describe the phosphocreatine system
-acts a reserve supply of phosphate
-generates ATP very quickly
-used during short bursts of energy and runs out after a few seconds
-anaerobic
-no lactic acid made
How is the phosphocreatine store replenished?
with rest - uses the phosphate from ATP when the muscle is relaxed
Describe anaerobic respiration when replenishing ATP
-generates small amounts of ATP rapidly
-used during short periods of hard exercise
-lactic acid builds up which causes muscle fatigue
Describe aerobic respiration when replenishing ATP
-most ATP is produced this way
-only possible when oxygen is available
-good for long periods of low-intensity exercise
Describe myoglobin
-picks up oxygen very readily and is saturated at relatively low pO2
-if the pO2 falls to very low levels it will release all its oxygen
Name the two types of muscle fibre
fast twitch and slow twitch
Describe fast twitch muscle fibre (use/speed, thickness, by-product, ATP source, mitochondria/myoglobin)
-used for fast movements due to powerful and quick contractions
-thicker more numerous myosin filaments
-lactate produced cause them to become fatigued quickly
-anaerobic respiration and store a lot of phosphocreatine
-few mitochondria and little myoglobin
Describe slow twitch muscle fibre (use/speed, thickness, by-product, ATP source, mitochondria/myoglobin)
-endurance activities as they contract slowly and can work for long periods of time, like maintaining posture
-thinner/weaker contractions
-no lactate
-aerobic respiration - have a supply of glycogen and an excellent blood supply to deliver oxygen and glucose
-large number of mitochondria and high conc of myoglobin
Fibres run…
the whole length of the muscle
Describe the nuclei in a myofibril
they have many nuclei
When given a cross section of myofibrils, when it only has one type of thick dots what does this mean?
H-Zone - just thick filament
When given a cross section of myofibrils, when it has two types of dots what does this mean?
dark band - overlap of thick and thin filament
Compare fast vs slow twitch in terms of ATPase activity
slow - low , fast - high
Compare fast vs slow twitch in terms of capillary density
slow - high , fast - low
Compare fast vs slow twitch in terms of fibre colour
slow - dark red , fast - white
Compare fast vs slow twitch in terms of glycolytic enzymes
slow - low , fast - high
Explain the sliding filament theory
-when a nerve impulse arrives at a neuromuscular junction, calcium ions are released from the sarcoplasmic reticulum
-the calcium ions diffuse and then bind to the troponin molecules causing them to move/change shape
-the troponin displaces the tropomyosin on thin filaments and exposes the myosin binding sites
-myosin heads bind to the myosin binding sites, forming cross bridges and causing ADP and Pi to be released
-the myosin changes shape, causing the myosin head to nod forwards, sliding the actin over the myosin filament over each other
-then ATP binds to myosin heads, causing the head to detach
-ATP is then hydrolysed by ATPase, providing the energy to recock the heads to their normal position
-cycle repeats
What happens when a muscle stops being stimulated?
-calcium ions are actively reabsorbed into the sarcoplasmic reticulum
-troponin reverts back to its normal shape and tropomyosin moves back to block the myosin binding sites
