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Science for Medicine > muscle > Flashcards

muscle Flashcards

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1
Q

muscles allow us to

A

Generate force & movement

Allow us to express & regulate ourselves

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2
Q

types of muscle

A

smooth
skeletal
cardiac

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3
Q

what muscles are striated

A

skeletal (voluntary muscles diaphragm)

cardiac (heart)

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4
Q

Smooth muscle is found in

A 
blood vessels
vas deferens
airways
uterus
GI tract
bladder etc.
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5
Q

in skeletal muscle the nucleus

A

is on the top of striations (many nucleus)

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6
Q

in cardiac muscle the nucleus is

A

in the middle of striations

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7
Q

in smooth muscle the nucleus is

A

in teh middle of a cell and looks like an eye

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8
Q

Skeletal muscle cell =

A

muscle fibre

- Multinucleate

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9
Q

skeletal muscle is formed in

A

utero from mononucleate myoblasts
Increase fibre size during growth
- Myoblasts do not replace cells if damaged

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10
Q

Muscles are bundles of

A

fibres encased in connective tissue sheaths.

- Attached to bones by tendons

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11
Q

if muscle cells are injured they are replaced by

A

satellite cells
Satellite cells differentiate to form new muscle fibres

  • Other fibres undergo hypertrophy to compensate
  • Muscle will never completely recover
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12
Q

the cross bridge cycle

A
  • cross bridge binds to actin (Ca2+ rises)
  • crossbridge moves
  • ATP binds to myosin causing cross bridge to detach
  • hydrolysis of ATP energises cross bridges.
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13
Q

roponin, tropomyosin + Ca2+

A

Tropomyosin partially covers myosin binding site (like wire)
- Held in blocking position by troponin
- Co-operative block
Calcium binds to troponin
Troponin alters shape – pulls tropomyosin away
Remove calcium – blocks sites again

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14
Q

relaxed muscle =

A

less calcium

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15
Q

muscle is energy hungry that why so much

A

mitochondria is spread out across it

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16
Q

muscles have double membrane so that

A

if the first one is damaged then the second one will protect the contents from leaking out as contents have potential to do harm

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17
Q

muscles contain loads of capiliries as

A

then its easier for oxygen to reach the muscle and also to get rid of waste products easily

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18
Q

muscle contains

A 
sarcoplasmic reticulum - mesh like
myofibrils
cytosol
plasma membrane
mitochondria (lots)
lateral sacs 
transverse tubules (between lateral sacs)
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19
Q

tropomyocin contains

A

troponin (calcium binding site)

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20
Q

in contraction and relaxation of skeletal muscle

A
  • muscle action potential propogated
  • DHP receptor and Ryanodine receptor cause release of Ca2+ from lateral sac
  • Ca2+ binding to troponin removes blocking action of tropomyosin
  • cross bridge move using ATP
  • Ca2+ removal from troponin restores tropomyosin blocking action
  • ATP used to take up Ca2+ into lateral sac
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21
Q

Motor Units is made up of

A

Motor neurons + muscle fibres

  • Muscle fibres within a unit may be scattered throughout muscle
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22
Q

Muscle Mechanics:

TENSION

A

Force exerted by muscle

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23
Q

Muscle Mechanics:

LOAD

A

Force exerted on muscle

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24
Q

Muscle Mechanics:

ISOMETRIC

A

Contraction with constant length

e.g. weightlifting

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25
Q

Muscle Mechanics:

ISOTONIC (or concentric)

A

Contraction with shortening length

e.g. running

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26
Q

Muscle Mechanics:

LENGTHENING

A

Contraction with increasing length

e.g. sitting down

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27
Q

Twitch Contractions

A

Single AP —> Muscle fibre —> TWITCH

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28
Q

Latent period =

A

time before excitation contraction starts

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29
Q

Contraction time occurs

A

between start of tension and time when we have peak tension

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30
Q

Muscle fibres have different

A

contraction times.

Contraction time depends on [Ca2+]

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31
Q

Isometric has shorter

A

latent period, but longer contraction event

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32
Q

As load increases,

A

contraction velocity and distance shortened decreases,

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33
Q

Tetanus

A
  • AP is 1-2ms long, but twitch may last up to 100ms
  • May get more AP’s during contraction

These add up = SUMMATION

34
Q

Tetanic tension greater than

A

twitch tension since [Ca2+] never gets low enough to allow troponin/tropomyosin to re-block myosin binding sites

35
Q

Length-Tension Relationship

Less overlap of filaments =

A

less tension

36
Q

Length-Tension Relationship

Too much overlap =

A

filaments interfere with each other

37
Q 
Length-Tension Relationship
OPTIMAL LENGTH (lo)
A

Muscle length for greatest isometric tension

38
Q

Flexors and Extensors

Movement around a limb requires

A

2 antagonistic groups of muscles – 1 flexes, the other extends(straightens)

39
Q

Flexors and Extensors

Muscles are arranged in

A

lever systems
- Muscles exert far more force than the load they support
Lever system amplifies muscle shortening velocity producing increased maneuverability

40
Q

Energy for Contraction - ATP:

Hydrolysis of ATP energises X-bridges

A

ATP binds to myosin
Dissociates bridges bound to actin
New cycle may begin

note- X bridge is the same as cross bridge

41
Q

Energy for Contraction - ATP:

ATP also powers Ca2+ - ATPase in SR

A

Ca2+ pumped back into SR

Contraction ends

42
Q

Fatigue is caused by

A 
Repeated muscle stimulus.
this depends on:
    - fibre type
    - length of contraction
    - fitness of individual

If muscle is rested, can contract again

43
Q

Fatigue prevents

A

muscles using up vast amounts of ATP which would cause rigor (ie muscles would not be able to activate new cross bridge cycles)

44
Q

Factors causing fatigue

During high intensity, short duration exercise:

A
  • Conduction failure due to increase in [K+] which leads to depolarisation
  • increase in [lactic acid] which acidifies proteins
  • increase in [ADP] and [Pi] inhibits X-bridge cycle, delaying myosin detachment from actin filaments
45
Q

Factors causing fatigue

During long-term, low intensity exercise:

A
  • decrease in muscle glycogen
  • decrease in blood glucose
  • dehydration

central command fatigue is when the cerebral cortex cannot excite motor neurons - there is no will to win.

46
Q

Skeletal Muscle Fibre Types

A

Characterised based on whether:

  • Fibres are fast or slow-shortening
  • The oxidative or glycolytic ATP forming pathways are used
47
Q

fast shortening skeletal muscle fibre means

A

myosin has high ATPase activity

48
Q

slow shortening skeletal muscle fibre means

A

it has low ATPase activity

49
Q

oxidative fibres

A
  • increased mitochondria leads to increased oxidative phosphorylation
  • increased vascularisation to deliver more O2 and nutrients
  • contain myoglobin which increases O2 delivery
  • fibres are red and have low diameters
50
Q

Glycolytic Fibres

A
  • few mitochondria
  • increased glycolytic enzymes and glycogen
  • lower blood supply
  • white fibres with larger diameteres
51
Q

what are the three types of muscle fibres and how do they react to fatigue

A

Slow Oxidative (I) resists fatigue

Fast Oxidative (IIa) has intermediate resistance to fatigue

Fast Glycolytic (IIb) fatigues quickly

52
Q

Muscle fibre recruitment

A
  • An increase in load means we have to increase the need to activate more motor neurons
53
Q

Muscle fibre recruitment =

A

increase in the number of active motor units
- An increase in load causes and increase in need to activate more motor neurons.

slow oxidative fibres are activated first followed by fast oxidative and lastly fast glycolytic fibres.

54
Q

neural control of muscle tension depends on

A
  • frequency of action potentials to motor units

- recruitment of motor units

55
Q

Denervation atrophy =

A

nerve is destroyed/ NMJ is destroyed

56
Q

disuse atrophy =

A

happens when muscle is not used

57
Q

muscle mass can be decreased by

A

denervation atrophy

disuse atrophy

58
Q

exercise causes

A

hypertrophy (increase in mass)

59
Q

aerobic exercise causes

A

increase in mitochondria which leads to increased vascularisation which causes increase in fibre diameter

60
Q

Anaerobic (strength) exercise causes

A

increased diameter and increased glycolysis

61
Q

the types of muscle fibres you have is determined by

A

the type of exercise you do

62
Q

smooth muscle unlike skeletal and cardiac muscles have

A

No striations

63
Q

smooth muscle is

A

innervated by autonomic nervous system not the somatic nervous system

64
Q

smooth muscle has a

A

X-bridge cycle and uses Ca2+

Filaments and excitation-contraction coupling are different

65
Q

smooth muscle exists in

A

hollow organs (e.g. GI tract, uterus, airways, ducts)

66
Q

Smooth muscle features

A
  • Spindle-shaped (2-10mm diameter)
  • Mononucleate and divide through life
  • Thick myosin and thin actin filaments, like skeletal muscle
67
Q

how are the filaments in smooth muscle different

A

filaments arranged diagonally across cells and are anchored to membranes and cell structures by dense bodies (like Z-lines)

  • Filaments still slide together to contract cell
68
Q

Smooth Muscle X-bridge cycle activation

A
  • increase in Ca2+
  • Ca2+ binds to calmodulin
  • Ca2+ calmodulin binds to myosin light chain kinase
  • kinase phosphorylates myosin cross bridges with ATP
  • phosphorylated cross bridges bind to actin filaments
  • contraction and tension occurs
69
Q

smooth muscle relaxed via the action of

A

myosin light chain phosphatase.

this dephosphorylates the cross bridges

70
Q

persistant stimulation and increase in Ca2+ in some smooth muscle means

A
  • Phosphorylated X-bridges may be dephosphorylated when still bound to actin
  • there is a decreased rate of ATP splitting
  • Slows X-bridge cycle
  • Means you can maintain tension for long time with low ATP consumption
  • Useful in blood vessel walls that have to stay open for long periods
71
Q

Sources of Cytosolic Ca2+

A 
Sarcoplasmic Reticulum (SR)
    - less sarcoplasmic reticulum in smooth muscle than in 
      skeletal, no T-tubules + randomly arranged

extracellular Ca2+
- voltage activated Ca2+ channels (VACC’s)

72
Q

Ca2+ is removed from cytosol by

A

pumping back into the sarcoplasmic reticulum and out of cells by Ca2+ ATPases (slower process than in skeletal muscle)

73
Q

In skeletal muscle:

1 action potential

A

releases enough Ca2+ to saturate all troponin sites

74
Q

in smooth muscle:

1 action potential

A

causes some sites to be activated

- you can grade contraction depending on the number of action potentials that reach the cells

75
Q

smooth muscle has tone.

this means

A

a basal level of Ca2+ in cells causes a constant of tension

76
Q

Factors affecting contractile activity

Dynamic balance of all the following:

A
  • Spontaneous electrical activity in muscle membranes = Pacemaker activity
  • Autonomic neurotransmitters from varicosities
  • Hormones (e.g. oxytocin)
  • Local factors (paracrine agents, pH, O2, osmolarity, ions, NO)
  • Stretch
77
Q

Smooth Muscle Types

A

single

multiunit

78
Q

single unit smooth muscle found in

A

gasto intestinal tract
uterus
small blood vessels

79
Q

single unit smooth muscle structure and function

A
  • many cells linked by gap functions
  • signals travel between cells
  • contract synchronously
  • may contain pacemaker cells
  • stretch evokes contraction
80
Q

multiunit smooth muscle found in

A

airways
large arteries
hairs

81
Q

multiunit smooth muscle structure and function

A
  • few or no gap junctions
  • richly innervated by the autonomic nervous system
  • don’t respond to stretch
82
Q

most smooth muscle in organs are

A

a mixture of single unit and multiunit population of cells.

this means that an organ can have a mixture of properties in different areas.

Science for Medicine (16 decks)

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