Skeletal muscle and Force Generation Mechanism Flashcards

1
Q

what are the three types of muscle

A

skeletal, smooth, cardiac

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2
Q

what is the classification of skeletal muscle

A

striated, voluntary

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3
Q

what is the sarcolemma

A

the cell membrane that encloses each muscle cell

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4
Q

what is the endomysium

A

the connective tissue that wraps each individual muscle fibre

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5
Q

what is the perimysium

A

connective tissue that wraps bundles of muscle fibres

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6
Q

what is the epimysium

A

connective tissue that wraps the whole muscle.

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7
Q

what is the fascia

A

a layer of thickened connective tissue that covers the entire muscle

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8
Q

what are the layers of musscle tissue

A

sarcolemma
endomysium
perimysium
epimysium
fascia

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9
Q

what happens when a nerve impulse reaches the neuromuscular junction

A

causes chemical transmitter (acetylcholine) to be released
Triggers muscle contraction

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10
Q

what is skeletal muscle supplied by

A

the efferent arm of the somatic nervous system

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11
Q

where are lower motor neuron cell bodies

A

in the ventral horn of the spinal cord

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12
Q

what is the motor end plate

A

The specialized postsynaptic region of a muscle cell. The motor endplate is immediately across the synaptic cleft from the presynaptic axon terminal

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13
Q

Excitatory signal sent from the terminal button to the motor end
plate using ACh via ________

A

the nicotinic receptor

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14
Q

what is muscle fibre composed of

A

myofibrils which are composed of sarcomeres which is composed of filaments

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15
Q

what causes striations

A

thick and thin filaments which run parallel

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16
Q

what is in the H zone of a sarcomere

A

think filaments (myosin) only

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17
Q

what is in the A band of a sarcomere

A

thick filamants and overlapping thin filaments (actin)

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18
Q

what is in the I band of a sarcomere

A

thin filaments only

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19
Q

name the proteins of a sarcomere

A

Contractile Proteins e.g. actin and myosin
Structural Proteins e.g. titin, dystrophin
Regulatory Proteins e.g. troponin-Complex, tropomysoin

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20
Q

how is a thin myofilament formed

A
  1. Small actin molecules (G-actin) link together to form long, twisted strands called F-actin.
  2. Tropomyosin wraps around actin, blocking binding sites, while troponin attaches to tropomyosin and controls muscle contraction.
  3. Together, these proteins form the thin myofilament, which plays a key role in muscle contraction by interacting with thick myofilaments (myosin).
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21
Q

describe the formation of a thick myofilament

A
  1. Many myosin proteins come together. Each myosin has a long tail and a head that sticks out.
  2. The tails of the myosin molecules bundle together in the center, while the heads extend outward.
  3. The myosin heads are arranged at both ends of the filament, allowing them to interact with thin filaments during muscle contraction.
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22
Q

what is in the head of a myosin

A

actin-binding site
Nucleotide binding site for ATP and ATPase

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23
Q

what is the function of titin

A

Anchors thick filaments between M-line and Z-line
Provides structural support and elasticity - helps prevent sarcomere popping and Z-line streaming

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24
Q

what is Excitation-contraction coupling

A

how muscle contractions are turned on and off

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25
Q

what is Muscle cell metabolism

A

how muscle cells provide ATP to drive the crossbridge cycle

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26
Q

what happens to a Thin Myofilament when muscle is contracting

A

when calcium ions bind to troponin, this causes troponin to change shape.
tropomyosin moves away from mysoin binding sites on actin, allowing myosin head to bind to actin. forming crossbridge

27
Q

what is a tropomyosin

A

Spans 7 G-actin monomers
Overlaps binding sites on actin for myosin

28
Q

what is a troponin complex

A

1 per tropomyosin
Complex of three proteins (T,I & C)
(regulates skeletal muscle contraction)

29
Q

what is the steric blocking model

A

At rest
– myosin binding sites on actin blocked by tropomyosin

30
Q

what is the function of troponin C in a Troponin Complex

A

binds to calcium ions to produce a conformational change in Troponin I.

31
Q

what is the function of troponin I in a Troponin Complex

A

binds to actin to hold the troponin-tropomyosin complex in place.

32
Q

what is the function of troponin T in a Troponin Complex

A

binds to tropomyosin, interlocking them to form a troponin-tropomyosin complex.

33
Q

how are mysoin heads activated

A

when ATP binds to myosin head and is hydrolized to ADP and a phospate. the energy from the hydrolysis, activates the mysoin head

head must be activated for crossbridge to form

34
Q

what are the four steps of the cross bridge cycle

A
  1. cross bridge formation
  2. the power stroke
  3. cross bridge detachment
  4. Reactivation of myosin head
35
Q

what is step 2 of the cross bridge cycle (the power stroke)

A

ADP is released from mysoin head and the activated myosin head pivots, sliding the thin myofilament towards the centre of the sacromere

36
Q

describe stage 3 of the cross bridge cycle (cross bridge detachment)

A

when another ATP binds to the myosin head, the link between the myosin head and actin weakens, and the myosin head detaches

37
Q

what is the importance of the cross bridge cycle

A

causes thin myofilaments to be pulled toward each other and the sarcomere shortens. this shortening causes the whole muscle to contract

sarcomere shortens by pulling in of the Z line at each end

38
Q

when does the cross bridge cycle end (muscle stops contracting)

A

when calcium ions are actively transported back to the sarcoplasmic reticulum.
troponin returns to its original shpe allowing tropomyosin covers binding site again

39
Q

what happens within a sarcomere during contraction

A
  • A band stays same length
  • I band shortens
  • H zone shortens
40
Q

how is calcium rleased from thesacrcoplasmic reticulum

A

action potential runs deep into muscle fibre vis T tubles, activating voltage-gated calcium channels ( Dihydropyridine receptors), releasing the calcium

41
Q

where is ATP used by muscles

A
  1. Crossbridge cycle
    * Splitting of ATP by myosin (for power stroke)
    * Binding of fresh ATP to myosin to cause dissociation
  2. Active transport of calcium back into sarcoplasmic reticulum
    * Relaxation
42
Q

what are the 3 pathways of sources for ATP

A

Creathine Phosphate
Glycolysis
Oxidative Phosphorylation

43
Q

what is the creatine phosphate system

A

Creatine phosphate + ADP <——> (creatine kinase) Creatine + ATP

44
Q

what is Non-Oxidative Glycolysis

A

glucose is broken down into 2 lactic acids and 2 ATP

45
Q

what is a twitch contraction

A

Contraction produced in a muscle fiber in
response to a Single Action Potential

46
Q

what are the phases of a muscle twitch

A
  1. latent period
  2. contraction phase
  3. relaxation phase
47
Q

what is the latent period of a muscle twitch

A

Time from action potential in muscle
cell to onset of contraction

48
Q

what is the contraction phase of a mucsle twitch

A

Crossbridge cycles take place
repeatedly

49
Q

what is the relaxation phase of a muscle twitch

A

Tension is decreasing back to zero
(longer than contraction phase)
Calcium reuptake

50
Q

what is a isotonic contraction

A

tension remains the same, whilst the muscle’s length changes.

51
Q

what is an isometric contraction

A

contractions in which there is no change in the length of the muscle.

52
Q

what are the differences between an isotonic ans isometric contraction

A

Isometric Twitch Contraction
– Length constant
– Contractile elements generating tension
– Muscle does NOT shorten, load not lifted
- can occur daily

Isotonic Twitch Contraction
– Constant tension
– Load is lifted as muscle shortens
– rarer

53
Q

Increases in frequency of action potentials in muscle fibers increases tension in two ways _____ and _______

A

treppe and summation and tetanus

54
Q

what is treppe

A

Independent twitches follow one another closely

the graduated series of increasingly vigorous contractions that results when a corresponding series of identical stimuli is applied to a rested muscle

55
Q

what is a cause of treppe

A

Increase cytosolic calcium

56
Q

what are causes of summation and tetanus

A
  • Amount of tension developed depends on amount of calcium bound to troponin
  • Crossbridge cycles max out
  • Maximum tetanic contraction
57
Q

what is summation and tetanus

A

to the ways muscle fibers respond to repeated stimulation.

58
Q

Small motor units are recruited _____

59
Q

Large motor units are recruited _____

60
Q

Force-generating capacity depends on _____

A

number of crossbridges in each sarcomere and geometrical arrangement of sarcomeres

More crossbridges/sarcomere → more force
More sarcomeres in PARALLEL→ more force

61
Q

What is summation

A

Summation: When a muscle is stimulated repeatedly before it has fully relaxed from a previous contraction, the force of each subsequent contraction adds to the previous one.
This occurs because calcium ions remain in the muscle fibers, enhancing contraction strength

62
Q

What is tetanus

A

When a muscle is stimulated so rapidly that it does not have time to relax between stimuli, it reaches a sustained, maximal contraction.