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Science for Medicine > Muscle 2 > Flashcards

Muscle 2 Flashcards

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1
Q

Where does the energy for contraction come from?

A 
Hydrolysis of ATP energises cross bridges
-ATP binds to myosin
-Dissociates bridges bound to actin
-New cycle may begin
ATP also powers Ca ATPase in SR
-Ca pumped back into SR
-Contraction ends
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2
Q

Muscle fatigue

A

Repeated muscle stimulation

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3
Q

What is fatigue dependent on?

A
  • Fibre type
  • Length of individual contraction
  • Fitness of individual
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4
Q

What does fatigue prevent?

A

Prevents muscles using up vast amounts of ATP which would cause rigor

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5
Q

How does high intensity, short duration exercise cause fatigue?

A
  • Conduction fails due to increase in[K] leading to depolarisation
  • Increased [lactic acid] leads to acidified proteins
  • Increased [ADP] and [Pi] inhibits cross bridge cycle, delaying myosin detachment from actin filaments
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6
Q

How does long term, low intensity exercise cause fatigue?

A
  • Decrease in muscle glycogen
  • Decrease in blood glucose
  • Dehydration
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7
Q

What is central command fatigue?

A

Cerebral cortex cannot excite motor neurones

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8
Q

How are skeletal muscle fibres characterised?

A

Based on

  • Fibres are fast or slow shortening
  • The oxidative or glycotic ATP forming pathways are used
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9
Q

Describe ATPase activity in fast shortening skeletal muscle fibres.

A

Myosin has high ATPase activity

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10
Q

Describe ATPase activity in slow shortening skeletal muscle fibres.

A

Myosin has low ATPase activity

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11
Q

Describe oxidative fibres.

A
  • Increase in mitochondria leads to increase in oxidative phosphorylation
  • Increase in vascularisation to deliver more O2 and nutrients
  • Contain myoglobin which increases O2 delivery
  • fibres are red and have low diameters
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12
Q

Describe glycolytic fibres.

A

-Few mitochondria
-Increase in glycolytic enzymes and glycogen
-lower blood supply
White fibres with larger diameters

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13
Q

What are the 3 types of muscle fibres?

A
  • Slow oxidative (I) which resist fatigue
  • Fast oxidative (IIa) which have intermediate resistance to fatigue
  • Fast glycolytic (IIb) which fatigue quickly
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14
Q

Describe muscle fibre recruitment.

A
  • Increased load means and increased need to activate more motor units
  • Increased number of active motor units means recruitment
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15
Q

What is the order of muscle recruitment?

A
  • Slow oxidative
  • Fast oxidative
  • Fast glycolytic
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16
Q

What does neural control of muscle tension depend on?

A
  • Frequency of AP to motor units

- Recruitment of motor units

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17
Q

What causes denervation atrophy?

A

Destruction of nerve/NMJ

18
Q

What causes disuse atrophy?

A

Muscle not used

19
Q

What causes hypertrophy?

A

Exercise

20
Q

What does aerobic exercise cause?

A
  • Increase in mitochondria
  • Increase in vascularisation
  • Increase in fibre diameter
21
Q

What does anaerobic exercise cause?

A
  • Increase in diameter

- Increase in glycolysis

22
Q

How are smooth muscles identified?

A

Contain no striations

23
Q

What are smooth muscles innervated by?

A

Autonomic nervous system

24
Q

How are their mechanisms similar and different to skeletal muscle?

A
  • Similar: has a cross bridge cycle and uses Ca ions

- Different: filaments and excitation-contraction coupling are different

25
Q

What are the features of smooth muscle?

A
  • Spindle shaped
  • Mononucleate and divide throughout life
  • Thick myosin and thin actin filaments
26
Q

How are the filaments arranged in smooth muscle?

A

Diagonally across cells and are anchored to membranes and cell structure by dense bodies (like Z lines)

27
Q

Describe the cross bridge cycle in smooth muscle.

A
  • Increase in calcium
  • Calcium binds to calmodulin
  • Ca-calmodulin binds to myosin light chain kinase
  • Kinase phosphorylates myosin cross bridges with ATP
  • Phosphorylated cross bridges bind to actin filaments
  • Contraction and tension
28
Q

How does smooth muscle relax?

A

Via the action of myosin light chain phosphatase which dephosphorylates the cross bridges

29
Q

How can tension be maintained in smooth muscle for a long time with low ATP consumption?

A
  • Persistent stimulation and increased [Ca] in smooth muscle
  • Phosphorylated cross bridges may be dephosphorylate when still bound to actin
  • Decreases the rate of ATP splitting
  • Slows cross bridge cycle
30
Q

What are the 2 sources of cytosolic Ca ions?

A

Sarcoplasmic reticulum
-Less SR in smooth muscle than in skeletal, no T-tubules + randomly arranged
Extracellular Ca
-Voltage activated Ca channels

31
Q

How is Ca removed from the cytosol?

A

It is pumped back into the SR and out of the cell by Ca ATPase

32
Q

How much Ca is released by 1 AP in skeletal muscle?

A

Enough to saturate all troponin sites

33
Q

How is contraction graded in smooth muscle?

A

Dependent on the number of APs that reach the cells as only some sites are activated

34
Q

What is meant by smooth muscle having tone?

A

A basal level of Ca ions in cells causes a constant level of tension

35
Q

What factors affect contractile activity?

A
  • Spontaneous electrical activity in muscle membranes (Pacemaker activity)
  • Autonomic neurotransmitters from varicosities
  • Hormones
  • Local factor
  • Stretch
36
Q

What are the 2 types of smooth muscle?

A

Single or multiunit smooth muscle

37
Q

What are examples of single unit smooth muscles?

A
  • GIT
  • Uterus
  • Small blood vessels
38
Q

Describe single unit smooth muscles.

A
  • Many cells linked by gap junctions
  • Signals travel between cells
  • Contract synchronously
  • May contain pacemaker cells
  • Stretch evokes constriction
39
Q

What are examples of multiunit smooth muscles?

A
  • Heart
  • Large arteries
  • Hairs
40
Q

Describe multiunit smooth muscles.

A
  • Few or no gap junctions
  • Richly innervated by ANS
  • Don’t respond to stretch
41
Q

What are most smooth muscles in organs?

A

A mixture of single and multiunit populations of cells

Science for Medicine (50 decks)

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