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Biology > Skeletal muscles > Flashcards

Skeletal muscles Flashcards

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1
Q

What are the 3 types of muscle and where are they found?

A
  • cardiac muscle - found in the heart
  • smooth muscle - found in the walls of blood vessels and the gut
  • skeletal muscle - attached to the bone and acts under voluntary, conscious control
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2
Q

What does antagonistic pairs mean?

A

Whilst one muscle contracts (agonist) the other relaxes (antagonist)

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3
Q

What is the gross structure of skeletal muscle?

A

the muscle is divided into bundles of muscle fibres (cells). Each muscle fibre consists of sarcoplasm, sarcoplasmic reticulum, mitochondria, sarcolemma, transverse T tubules, nucleus and myofibrils

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4
Q

What is the sarcolemma?

A
  • cell membrane of a muscle fibre - like an axon membrane because action potentials can pass along to cause contraction
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5
Q

What do transverse T tubules do?

A

Folded sarcolemma which stick into the sarcoplasm - this helps to spread impulses throughout the sarcoplasm to reach all parts of the muscle, to allow for simultaneous contraction

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6
Q

What is the role of the sarcoplasmic reticulum?

A

stores and releases calcium ions involve in muscle contraction

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7
Q

What are myofibrils?

A

bundles of protein filaments, consisting of actin and myosin, which cause contraction

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8
Q

What are thin and thick filaments?

A

actin = thin filament, lighter
myosin = thick filament, darker

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9
Q

What is the ultrastructure of skeletal muscle?

A
  • light bands are called I bands because they appear lighter as they consist of only thin filaments (actin)
  • dark bands are called A bands because the thick and thin filaments overlap in this region (actin and myosin)
  • at the centre of each A band is the H zone (consisting of just myosin), with an M line at the centre
  • the centre of each I band is called the Z line
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10
Q

What is a sarcomere?

A

the distance between adjacent Z lines - when the muscle contracts, the sarcomeres shorten

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11
Q

What happens to the distance between Z lines when the muscle contracts?

A

decreases

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12
Q

What happens to the width of the I band when the muscle contracts?

A

decreases

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13
Q

What happens to the width of the A band when the muscle contracts?

A

stays the same

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14
Q

What happens to the length of the myosin filaments when the muscle contracts?

A

stays the same

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15
Q

What is the siding filament theory?

A
  • when the muscle contracts, the sarcomeres become smaller
  • however the filaments do not change in length
  • instead they slide past each other (overlap)
  • so actin filaments slide between myosin filaments and the zone of overlap is larger
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16
Q

What is the difference between slow and fast twitch muscle fibres?

A
  • slow-twice fibres contract more slowly and provide less powerful contractions over a longer period
  • they are adapted to endurance work
  • fast-twitch fibres contract more rapidly and produce powerful contractions for a shorter period
  • adapted to intense exercise such as weightlifting
17
Q

How are slow-twitch muscle fibres adapted?

A
  • large stores of myoglobin - higher affinity for oxygen at lower partial pressures
  • rich supply of blood vessels - for glucose and oxygen
  • numerous mitochondria - aerobic respiration produces more ATP
18
Q

How are fast-twitch muscle fibres adapted?

A
  • thicker and more numerous myosin filaments
  • high concentration of enzymes involves in anaerobic respiration
  • high concentration of phosphocreatine to rapidly generate ATP from ADP
  • supply of glycogen
19
Q

What is a neuromuscular junction?

A

Where a motor neurone meets a skeletal muscle fibre

20
Q

How are impulses transmitted across a neuromuscular junction?

A
  • an action potential causes calcium ions to be released, vesicles fuse with the membrane causing AcH to diffuse across the synaptic cleft
  • binds to complementary receptors on Na+ channels in sarcolemma, Na+ ions enter and membrane is depolarised
  • causes actin and myosin bridge cycle
21
Q

What are the similarities between neuromuscular junctions and synapses?

A
  • both have neurotransmitters transported by diffusion
  • both have receptors, that on binding with a neurotransmitter cause an influx of sodium ions
  • both use a sodium potassium pump to repolarise the axon
  • both use enzymes to break down the neurotransmitter
22
Q

What are the differences between neuromuscular junctions and synapses?

A
  • neuromuscular junctions are only excitatory, whereas cholinergic synapses can be excitatory or inhibitory
  • neuromuscular junctions link neurones to muscles, whereas cholinergic synapses can link neurones to neurones, or neurones to other effectors
  • neuromuscular junctions only involve motor neurones, whereas cholinergic synapses can involve motor, sensory or intermediate neurones
  • the action potential ends at a neuromuscular junction, whereas at a cholinergic synapse a new action potential may be produced
  • at neuromuscular junctions acetylcholine binds to receptors on the sarcolemma of the muscle fibre, whereas at cholinergic synapses acetylcholine binds to receptors on the membrane of the postsynaptic neurone
23
Q

What is the evidence for the sliding filament theory?

A
  • I band narrows
  • Z lines move closer together
  • sarcomere shortens
  • H zone narrows
24
Q

How is the muscle stimulated during contraction?

A
  • action potential reaches many neuromuscular junctions, causing calcium ion channels to open and calcium ions diffuse into the synaptic knob
  • calcium ions cause the synaptic vesicles to fuse with the presynaptic membrane and release their acetylcholine into the synaptic cleft
  • acetylcholine diffuses across the synaptic cleft and binds with receptors on the sarcolemma, causing an influx of sodium ions and depolarisation
25
Q

How does muscle contraction occur?

A
  • tropomyosin molecule prevents myosin head from attaching to binding sites on the actin molecule
  • action potential travels through T tubules and causes calcium ions to be released from the sarcoplasmic reticulum and diffuse into myofibrils
  • calcium ions bind to troponin, which causes the tropomyosin to pull away from binding sites on actin, exposing them
  • myosin heads attach to the exposed binding sites on actin, forming an actinomyosin cross-bridge
  • once attached, the myosin heads change their angle, pulling along the actin filament “power stroke” and ADP is released
  • an ATP molecule attaches to the myosin head, causing it to detach from the actin filament
  • ATP is then hydrolysed by ATP hydrolase which provides energy for the myosin head to bend to its original position
  • myosin head attaches to a binding site further along the actin filament and the cycle repeats
26
Q

How does the muscle relax again?

A
  • calcium ions are actively transported back into the endoplasmic reticulum using energy from ATP hydrolysis
  • tropomyosin blocks binding sites on actin
  • myosin heads are unable to bind and contraction ceases
27
Q

What is energy needed for during muscle contraction?

A
  • movement of myosin heads
  • reabsorption of calcium ions into endoplasmic reticulum
28
Q

How is phosphocreatine used to supply energy during muscle contraction?

A
  • during very high intensity exercise
  • phosphocreatine is broken down into creatine and inorganic phosphate at rest
  • during exercise, ADP will combine with the inorganic phosphate to form ATP
  • phosphocreatine store is replenished using phosphate from ATP when the muscle is relaxed

Biology (28 decks)

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