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Locomotor > Muscle function and muscle contraction > Flashcards

Muscle function and muscle contraction Flashcards

1
Q

what is the function of skeletal muscle

A
  • Movement - result of muscle contraction
  • Maintains posture – paraspinals contract to maintain posture
  • Stabilises joints
  • Generates heat – uses energy to contract therefore the breakdown of ATP produces heat
  • Acts as a store of intracellular calcium
  • Soaks up excess glucose – glucose is taken up into muscle and is used as a energy source of generate heat
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2
Q

describe the nerve and blood supply of skeletal muscle

A

– Enter or leave near the centre of the muscle then branch to all fibres

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3
Q

describe how muscle attaches to bone

A

– Most muscles cross a joint and attach to bones in at least 2 places in order for muscle to work, this is usually via the tendon

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4
Q

what type of tissue is bone

A

dense regular fibrocollagenous tissue

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5
Q

describe the connective tissue of the skeletal muscle

A
  • Epimysium surrounds the whole of an individual muscle
  • inside the muscle fibres are grouped together into fasiciles these are wrapped via the perimysium
  • In the muscle fibres in the fascicles these are wrapped with the endomysium
  • Goes endomysium, perimysium, epimysium
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6
Q

what is the myofibril

A
  • Mixture of actin and myosin that are arranged into the functional unit which is the sarcomere
  • These help the muscles contract
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7
Q

describe the myotendinous junction (junction between the muscle and the tendons)

A
  • All the connective tissue - endomysium, perimysium, epimysium – congregates at the tendon and becomes the dense continuous fibrocollagenous tendon itself
  • Muscle cells fuse into a single muscle fibre
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8
Q

where are the nuclei located in skeletal muscle

A

peripheral located around the edge of muscle fibres

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9
Q

what is a tendon bone attachment called

A

enthuses

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10
Q

describe how tendons are attached to bones

A
  • it is a transition tissue modification
  • goes from dense regular fibrocollagenous tissue to fibrocartilage to bone
  • fibrocartiallge is very strong and gives you flexibility with strength
    • As bones grow the attachment points also need to adapt – having fibrocartilage allows slippage or attachment allowing the bones to be able to grow and change
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11
Q

describe the micro anatomy of a muscle fibre

A
  • Sarcolemma – plasma membrane
  • Multinucleate – fusion of many cells into one
  • Sarcoplasm – cytoplasm contains myoglobin to store oxygen gives aerobic metabolism for skeletal muscle heat generation and energy generation
    • Sarcoplasmic reticulum = smooth endoplasmic reticulum
    – interconnecting tubules surround each myofibril
    – terminal cisternae (“end sacs”) store Ca2+
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12
Q

what proteins are in the muscles

A
  • Actin
  • Myosin
  • Accessory proteins, tropomyosin, troponin, titin, dystrophin
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13
Q

what are the main muscle proteins

A
  • Actin and myosin are the main muscle proteins
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14
Q

what does the fibrocartilage allow in the tendon and bone attachment

A

– having fibrocartilage allows slippage or attachment allowing the bones to be able to grow and change

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15
Q

describe the structure of skeletal muscles

A
  • Stripy appearance
  • They are peripherally located
  • Tear muscle fibres a little bit
  • The muscles are constantly repairing themselves and the damage that you have done to them
  • Stem cells in the muscles that repair large parts of damage
  • In between each muscle there is a white hap and this is the endomysium
  • A-bands
  • I-bands (arrow head = Z-line)
  • Sarcomere Z-line to Z-line
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16
Q

what is the definition of the sarcomere

A
  • this is from Z disc to Z disc, between the Z discs
17
Q

describe the sarcomere

A
  • actin and myosin overlap
  • where myosin and actin is is the M band
  • where actin only is is the I band
    when myosin only is is the H band
18
Q

what happens to the sarcomere when it contracts

A

– Z line gets closer together,

  • H band decreases,
  • I band decreases
  • A band remains the same
19
Q

what are T tubules

A
  • T tubules are tubes of plasma membrane that go deep into the muscle fibre and are associated with the sarcoplasmic reticulum
20
Q

what is the sarcoplasmic reticulum

A

store of calcium

21
Q

describe the structure of T tubules

A
  • T-tubule network = invaginations of the sarcolemma deep into muscle fibre
  • runs between the paired terminal cisternae of the SR
  • forms a triad, this is because the T tubules run and on either side there is a sarcoplasmic reticulum
22
Q

what is the A band and I band junction

A
  • A band – I band junction (starts of actin myosin overlap)
23
Q

what is the skeletal muscle innervated by

A
  • innervated by motor neurones
24
Q

how is the skeletal muscle innervated by motor neurones

A

– Axons enter muscle and each axon branches to make contact with several muscle fibres

25
Q

one muscle fibre for

A

– General rule one muscle fibre one neuromuscular junction

26
Q

is skeletal muscle voluntary or not

A

voluntary

27
Q

describe the skeletal motor neurones

A

• Lower motor neurones – live in the ventral horn of the spinal cord, exit through the ventral root and go through the muscle fibres and have a specialised synapse called the neuromuscular junction to depolarise and cause the muscle to contract

28
Q

where is the neuromuscular junction in the muscle fibre

A

in the centre

29
Q

how big is the synaptic cleft

A

• Axon terminal separated from the muscle fibre by a 1-2 nm synaptic cleft

30
Q

why is the muscle sarcolemma folded into ridges

A

• Muscle sarcolemma folded into ridges

– Has millions of ACh receptors

31
Q

describe how muscle contraction is caused

A

• Axon terminal contains synaptic vesicles
– Acetylcholine (Ach)
• Muscle sarcolemma folded into ridges
– Has millions of ACh receptors
• When action potential reaches terminal ACh released into cleft and binds to nicotinic ACh receptor
• Sodium enters
• Action potential once initiated conveyed down the T tubule network this causes calcium released from the sarcoplasmic reticulum into the sarcoplasm, close to the AI junction of the sarcomere
• Ca2+ binds to the calcium binding protein troponin (troponin is attached to tropomyosin)
– Causes conformational change that pulls tropomyosin away from myosin binding site on actin filament
– 3 troponin complex binding to the calcium
• Ca2+ taken back into sarcoplasmic reticulum = relaxation, troponin and tropmysoin will just go back onto the myosin binding site on actin
• Myosin hydrolyses ATP
– Stored energy produced by formation of ADP and inorganic phosphate
• Head binds to actin and neck bends
– Muscle contracts
– Releases ADP
• Myosin releases actin as new ATP attaches
– muscle relaxation

32
Q

what is a motor unit

A
  • a motor neurone and all the muscle fibres that are supplied by it
33
Q

describe type of movements that motor units can cause

A

• When that motor neuron fires all muscle fibres innervated by it will contract
– Leg muscles several hundred fibres in a motor unit don’t need precision movements
– Eye muscles as few as 4 – need precision movements

34
Q

all muscle fibres contract….

A

if there is an action potentail

35
Q

describe the sensory nerve work

A
  • Sensory nerve is wrapped around the centre and around the myofibrils, no contractile proteins in the centre, this is called the bag region as it is just empty
  • As the muscle is stretched or contracted, those wrapped around sensory nerve endings will sense the amount of stretch or contraction
  • The muscle spindle is fired more rapidly if it is stretched, this is sent back to the afferent axons to the spinal cord and the motor neurones saying that the muscle is being stretched and therefore it needed to contract
  • The motor axons efferent sense the information that they needed to contract and this shuts of it
36
Q

what are mechanosenstiive proprioceptors

A
  • they are sensitivity units within the muscle
  • specialised intramural muscle fibres between ordinary muscle fibres
  • when muscle stretched, muscle spindle fibres are stretched, sensory nerves stimulated and length changes detected
37
Q

what are the ATP stores

A
  • stored ATP enough for 2-3 seconds
    • Creatine phosphate – can use it to directly phosphorylate ADP to make it into ATP this gives us 15 seconds worth of movement
  • Anaerobic – uses glucose as glucose is taken in dosent need oxygen, makes lactic acid at the end of it and ATP is produced by glycolysis – gives us enough for about 2 minutes
  • Aerobic respiration is the majority of muscle movement - Uses oxygen to generate more ATPs out this can generate enough energy for hours
38
Q

why do we need a mixture of muscle fibrotypes

A
  • use different ATP stores
  • type 1 slow and type 2 fast twitch muscles
    then type 2 splits into type 2A and type 2B

Locomotor (22 decks)

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