15.7- Structure of skeletal muscle

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  • Created by: Megan2413
  • Created on: 28-11-17 19:03
What are the three types of muscle in the body?
- Skeletal - Cardiac - Smooth
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Where is each type of muscle found?
- Skeletal muscle is attached to the skeleton - Cardiac muscle is found in the heart - Smooth muscle is found in the walls of blood vessels and gut
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Which type(s) of muscle are under voluntary control?
Skeletal muscle
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Which type(s) of muscle are under involuntary control?
Cardiac muscle and smooth muscle
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What are myofibrils?
They are tiny muscle fibres running the whole length of the muscle
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What are myofibrils made up of?
Many muscle cells fused together to share nuclei and sarcoplasm
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What is sarcoplasm?
Muscle cell cytoplasm
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What is the membrane surrounding myofibrils called?
Sarcolemma
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What organelles do myofibrils contain in abundance?
Mitochondria and endoplasmic reticulum
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What are the two main muscle protein filaments?
Actin and myosin
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What is actin?
It is thin and consists of two strands twisted around each other . It is attached to the z line on a sarcomere and associated with tropomyosin and troponin
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What is myosin?
A long rod shaped fibrous protein with 'head' that project to the side and 'tails' which are attached to the centre of the sarcomere
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What are the two bands called in a sarcomere?
Anisotropic (A) band and isotropic (I) band
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Which band is darker in colour and why?
The A band is darker because it is an overlap of actin and myosin whereas the I band is just actin filaments
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What zone is in the centre of the A band? What filament(s) does it contain?
H zone containing just myosin filaments
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Where is the M line situated?
In the centre of the H zone
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Where are the z lines found?
At the start and end of a sarcomere
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What are striation?
The stripes found on a single muscle fibre
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What other things can be found running the length of a bundle of muscle fibres?
Nerves and blood capillaries
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What are the two types of muscle fibre?
Fast twitch and slow twitch
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Which fibre contracts slower?
Slow twitch
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What is the power of contraction like in each fibre?
Fast twitch muscles have more powerful contractions over a short period of time and slow twitch muscles have large amounts of energy over a longer period of time
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Which muscle fibre fatigues more easily?
Fast twitch
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What type of work is each muscle fibre adapted to?
Fast twitch muscles are adapted to intense exercise whereas slow twitch muscles are more adapted to endurance work
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Where can each muscle fibre be found?
Fast twitch muscles are can be found in biceps whereas slow twitch muscles canbbe found in the calf muscles
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What type of respiration is used for each type of muscle fibre?
Fast twitch muscles use anaerobic and slow twitch muscles use aerobic
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Give three adaptations of a slow twitch muscle fibre
- Stores lots of oxygen storing molecules (myoglobin) - Has a rich supply of blood vessels to deliver oxygen and glucose for aerobic respiration - Many mitochondria for ATP production
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Give four adaptations for fast twitch muscle fibres
- High concentration of glycogen - High concentration of enzymes involved in anaerobic respiration - Thicker and more myosin filaments - Store lots of phosphocreatine
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What is phosphocreatine used for?
To quickly regenerate ATP from ADP in anaerobic conditions
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What is a neuromuscular junction?
The point at which a motor neurone meets a skeletal muscle fibre
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What is a motor unit?
A muscle fibre and motor neurone
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What controls the force of a muscle contraction?
The number of motor units stimulated
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What happens when an action potential arrives at a neuromuscular junction?
Calcium channels are opened at the presynaptic membrane, allowing calcium ions to enter the motor neurone
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What do the calcium ions stimulate?
The vesicles in the motor neurone containing acetylcholine to fuse with the presynaptic membrane, releasing acetylcholine molecules into the synapse
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What then happens to acetycholine?
It diffuses across and binds to receptor sites on the myofibril (postsynaptic) membrane
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What does the binding of acetylcholine to receptor sites on the myofibril membrane allow?
It opens the sodium ion channels to open and enter the muscle fibre causing a depolarisation of the membrane and a subsequent muscle contraction
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How is acetylcholine broken down?
By acetylcholinesterase into ethanoic acid and choline
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What is the difference between the type of synapse of a neuromuscular junction and cholinergic synapse?
Neuromuscular junctions are only excitatory but cholinergic synapses can be either excitatory or inhibitory
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What do neuromuscular junctions link together?
Motor neurones to muscles
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What do cholinergic synapses link together?
Neurones to neurones or neurones to effectors
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Is there a new action potential created at a neuromuscualr junction?
No the action potential ends here
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Is there a new action potential created at a cholinergic synapse?
A new action potential may be created in the postsynaptic neurone
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The insecticide DFP combines with the active site of the enzymes acteylcholinesterase- why do muscles stay contracted until the insecticide is lost from the neuromuscular junction?
Acetylcholinesterase is unable to breakdown acetylcholine hence it is still available to depolarise the membrane and generate action potentials continuously causing the muscle to contract
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Other cards in this set

Card 2

Front

Where is each type of muscle found?

Back

- Skeletal muscle is attached to the skeleton - Cardiac muscle is found in the heart - Smooth muscle is found in the walls of blood vessels and gut

Card 3

Front

Which type(s) of muscle are under voluntary control?

Back

Preview of the front of card 3

Card 4

Front

Which type(s) of muscle are under involuntary control?

Back

Preview of the front of card 4

Card 5

Front

What are myofibrils?

Back

Preview of the front of card 5
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