Unit 6: Muscles Flashcards
What are skeletal muscles
striped/striated muscle
consists if numerous long muscle fibres/cells
What are properties of muscle fibres
- cylindrical in shape and enclosed by a cell surface membrane (sarcolemma)
- many nuclei (multinucleate)
- contain many microfibris with cross-striations
- arranged in parallel to give striped appearance
Which microscope can see muscle
electron microscope
What are the repeating bands in a muscle called
sarcomere
What is actin
thin filaments which possess binding sites for myosin heads
What is myosin
thick filaments composed of many myosin molecules bundled together
myosin heads have ATP hydrolyse activity to provide energy for contraction
What does the A band represent
dark band
length of myosin filaments
What does the outer region of the A band represent?
overlapping myosin and actin filaments
- these are darker
What is the H zone
only contains myosin filaments
- not as dark and at the centre of the A band
What is the M line?
connects myosin filaments in the A band
What is the I band
light band
contains only thin actin filaments
What is the Z line?
connects actin filaments and is the boundary of the sarcomere
Outline the sliding hypothesis
during contraction actin filaments are pulled between myosin filaments resulting in the shortening of the muscle fibre and changes in banding pattern
What happens to the H zone during contraction?
Narrows
What happens to the outer regions during contraction
become wider
What happens to the A band during contraction?
stays the same length of myosin filaments dont change
What happens to the I band during contraction
narrows the non overlapping actin filaments
What happens to the Z band during contraction
move closer together
What happens to the length of the sarcomere during contraction
decrease
What is tropomyosim
a protein that covers the binding site of actin
How do mucles contract
by the formation of cross bridges between actin and myosin filaments
Outline the mechanism of muscle contraction
- contraction is activated by Ca2+ ions released from the sarcoplasmic reticulum
- when released Ca2+ binds to tropomyosin causing it to change shape and move from the binding site
- enables actinomyosin bridges to form as myosin heads attach to actin filaments
- Ca2+ stimulate ATP hydrolase to hydrolyse ATP providing energy to move the myosin head which pulls the actin filament and to detach the myosin head which breaks actinomyosin bridges
- Bridges rapidly break and reform as the myosin heads attach further along the filaments pulling past the myosin filaments causing shortening of each sarcomere
- mitochondria in muscle fibres supply ATP via aerobic respiration
- when the muscle is no longer stimulated the Ca2+ ions are actively moved back into the sarcoplasmic reticulum
What is a Neuromuscular junction?
a specialised synapse between a motor neurone and the sarcolemma
- synapses with a muscle fibre & sarcolemma represents postSM
Outline transmission across a Neuromuscular junction
- action potential arrives and synaptic know stimulating depolarisation of preSM
- stimulates Ca+ channels to open in the preSM and diffuse into the synaptic knob
- cause synaptic vesicles to fuse with preSM and break open
- acetylcholine is released and diffuse across synaptic cleft
- acetylcholine attach to specific receptor sites on the sarcolemma
- stimulates entry of Na+ causing depolarisation
- results in action potential along sarcolemma into muscle fibres stimulating release of Ca2+ which initiate muscle contraction
- acetylcholine is broken down by cholinesterase
- choline and acetyl is taken up by active transport into synaptic knob and acetylcholine is resynthesised using ATP
What are the two muscle fibres skeletal muscles are made up of
slow and fast fibres
What are the properties of slow fibres?
- contract slowly
- many mitochondria
- energy released slowly thru aerobic respiration
- high resistance to fatigue (work for long time without tiring)
- good for endurance events
- low concentration of glycogen as lots of energy released per glucose molecule
- red in colour due to myglobin
- low conc of phospocreatine
What are the properties of fast fibres
- contract quickly
- few mitochondria
- energy released quickly thru anaerobic respiration
- low resistance to fatigue (tire easily)
- good for short bursts of speed/power
- high concentration of glycogen to provide lots of glucose as less energy is released per glucose
- white due to no myglobin
- high conc of phospocreatine
Why is ATP required during muscle contraction
- to move myosin head which pulls actin filament
- to detach myosin head which breaks actin-myosin bridges
- for reabsorption of Ca2+ into sarcoplasmic
How is ATP produced by the phosphocreatine system
phosphocreatine is stored in muscle and used as a reserve for the supply of phosphate to combine with ADP to form ATP
- helps produce ATP quickly in anaerobic conditions
Why is the phosphocreatine system used during short periods of vigorous exercise
it generates ATP but phosphocreatine is used up after a few seconds
the process is anaerobic but doesn’t produce lactic acid
How is phosphocreatine reformed?
using phosphate from ATP when the muscle is relaxed
How can ATP be produced?
- phosphocreatine system
- anaerobic respiration
- aerobic respiration
How is ATP produced by Anaerobic respiration
by glycolysis which produces pyruvate
when O2 is in short supply pyruvate is converted to lactate which builds up in muscle causing fatigue
How is ATP produced by Aerobic respiration?
produced during oxidative respiration in mitochondria
this process is rapidly uded up
How do skeletal muscles attatch to bones
By inelastic tendons
How do the biceps and triceps work antagonistically?
- bicep muscle contracts pulling lower arm up
- simultaneously the triceps muscle relaxes and lengthens
- triceps muscle contracts to return lower arm to its original position
- at same time biceps muscle relaxes and lengthens
