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Guyton - unit questions > Unit II (4-8) - Membrane Physiology, Nerve and Muscle > Flashcards

Unit II (4-8) - Membrane Physiology, Nerve and Muscle Flashcards

1
Q

The resting membrane potential is

A

-90mv

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2
Q

During the depolarization stage there is increased permeability to what electrolyte

A

Na+

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3
Q

During the depolarization stage ____ channels close and ___ channels open

A

Na+

K+

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4
Q

_____ is responsible for establishing the action potential gradient

A

Na/K ATPase pump

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5
Q

The plateau in some action potentials is caused by

A

opening of slow Ca channels

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6
Q

What is the difference between an absolute and a relative refractory period?

A

Absolute - no action potential can occur when with strong stimulus
Relative - follows an absolute refractory period, action potential can be generated with a large enough stimulus

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7
Q

What is the difference between the I bend and the A band?

A

I band - light band - contains actin only

A band - dark band - contains actin and myosin

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8
Q

The ___ band in skeletal muscle decreases in length with muscle contraction

A

I band

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9
Q

The troponin complex is composed of what 3 subunits? and what does each subunit have strong affinity for

A

Troponin I (inhibitory) - strong affinity for actin
Troponin T - strong affinity for Tropomyosin
Troponin C - strong affinity for Calcium ions

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10
Q

Describe the general mechanism of skeletal muscle contraction

A
  1. AP travels along nerve cell to muscle fiber
  2. ACh secreted and opens ACh gated channels
  3. Na goes into muscle fiber
  4. AP travels along muscle fiber causing release of Ca from sarcoplasmic reticulum
  5. Ca binds troponin complex and allows for interaction between actin and myosin = contraction
  6. Ca goes back into sarcoplasmic reticulum and out of the cell = relaxation
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11
Q

What is the difference between Type I and Type II muscle fibers?

A

Type I - red muscle, smaller fibers with large amounts of myoglobin because it needs to store O2, fibers react slowly but with prolonged contraction
Type II - white muscle, larger fibers with no myoglobin, react rapidly

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12
Q

Why does rigor mortis occur?

A

Muscles become rigid due to loss of ATP (ATP is required to cause separation of cross bridges)

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13
Q

What is responsible for initiation of contraction of smooth muscle?

A

Ca -Calmodulin complex

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14
Q

What is responsible for relaxation of smooth muscle?

A

Decrease in the intracellular Ca concentration and myosin phosphatase removes phosphate from the myosin light chain, causing detachment of myosin from actin therefore relaxation

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15
Q

By what mechanisms can hormone or local tissue factors mediate smooth muscle excitation

A

Opening of Na or Ca channels = depolarization of membrane
Stimulation of action potential
Depolarization w/o AP - promoting Ca entry into the cell
Stimulation of Ca release from SR

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16
Q

By what mechanism can hormones or local tissue factors mediate smooth muscle relaxation

A

Close Na and Ca channels = prevent influx of ions
Opening K channels which = allowing efflux
Through second messengers = cAMP, cGMP - activates Ca pumps making it go into SR or out of muscle fiber

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17
Q

What is the source of energy in primary active transport?

A

ATP

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18
Q

What is the source of energy in secondary active transport?

A

ionic concentration gradient

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19
Q

Examples of primary active transport include

A

Na-K ATPase pump
Calcium pump
Hydrogen pump

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20
Q

What are the functions of the Na-K ATPase pump?

A
  1. maintain the electrical gradient in the cell
  2. controls cell volume
  3. makes ATP (only when working in reverse)
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21
Q

Examples of secondary active transport include

A 
Co transport (Na-Glu and Na-aa)
Counter transport (Na-Ca and Na-H) - Na into cell, Ca and H out of cell
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22
Q

Higher intra/extracellular?
Sodium, potassium, chloride, phosphate, protein

A

Intra - potassium, phosphate, protein
Extra - Sodium, chloride

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23
Q

What type of molecules can diffuse freely through the cell membrane?

A

Lipid

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24
Q

Name examples of substances that dissolve directly through the lipid bilayer (4)

A

Oxygen, nitrogen, C02 and alcohols

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25
Q

How do simple and facilitated diffusion compare/contrast?

A

Simple diffusion dependent on lipid solubility of substance, linear relationship with concentration
Facilitated diffusion depends on Vmax of substance, normally faster initially, then plateaus - limited by maximum rate of conformational change of carrier protein

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26
Q

What is the formula for net diffusion?

A

Net diffusion is proportional to the concentration of a substance outside a membrane, minus the concentration of the substance inside the membrane

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27
Q

What is the Nernst potential?

A

The electrical difference that will balance a given concentration difference of univalent ions at normal body temperature

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28
Q

What is the Nernst equation?

A

EMF(mV) = +/-(61/z) x (logC1/C2)
z = electrical charge of ion

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29
Q

What factors effect net diffusion?

A

Concentration, electrical potential, pressure

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30
Q

What determines osmotic pressure?

A

The number of particles per unit volume

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31
Q

How does the Na-K pump work? What is it’s main function?

A

3xNa+ pumped out of cell in exchange for 2xK+
Regulates cell volume

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32
Q

Describe the electrogenic nature of the Na-K pump

A

Because 3 Na and removed from the cell in exchange for 2 K+, there is a net positivity outside the cell and negativity inside the cell

33
Q

How does calcium concentration compare inside/outside the cell? How is it maintained?

A

Intracellular calcium concentration very low
2 calcium pumps, one pumps calcium outside the cell, the other pumps into intracellular organelles (SR in muscle, mitochondria other cells)

34
Q

Name 2 examples of primary active transport of hydrogen ions?

A

Gastric glands of the stomach
Late distal tubules and cortical collecting ducts in kidneys (intercalated cells)

35
Q

If it takes 1400 calories to concentrate 1 osmole of a substance 10-fold, how much would be needed to concentrate it to (a) 100-fold and (b) 1000-fold?

A

a) 2800
b) 4200

36
Q

What is the resting membrane potential of large nerves?

A

-70mV

37
Q

What factors contribute to the negative resting potential of cells?

A

Increased permeability of cell membrane to K+, allows K+ to leak out - main contributor
The 3Na-2K pump - more sodium removed from cell than potassium in

38
Q

What are the stages of a neutron action potential?

A

Resting stage
Depolarisation - voltage-gated sodium channels open, membrane becomes permeable to sodium ions, flood in and depolarisation
Repolarisation - sodium channels close, voltage-gated potassium channels open, potassium moves out, repolarisation

39
Q

Describe the opening, closing and re-opening of voltage-gated Na channels

A

When resting membrane potential becomes less negative, channel is activated. The same increase in voltage causes inactivation a few seconds later
Channel will not re-open until membrane potential returns to near the original level

40
Q

Describe the opening of the voltage-gated potassium channels

A

Activated when membrane potential rises, however, slight delay so open as sodium channels close

41
Q

What is the role of calcium in the generation of an action potential?

A

Voltage-gated slow calcium channels - contribute to depolarisation, produce more sustained depolarisation

42
Q

Where are calcium channels most numerous?

A

Smooth muscle and cardiac muscle

43
Q

How does the concentration of calcium ions in the ECF effect depolarisation?

A

When there is a deficit of Ca++, sodium channels are opened by smaller increase in membrane potential

44
Q

Which cells produce myelin?

A

Schwann cells

45
Q

What is the name for the notches in myelin?

A

Nodes on Ranvier

46
Q

What is the function of the nodes of Ranvier and what are the benefits (2)?

A

Allow saltatory conduction
1 - increased velocity of nerve transmission
2 - requires less energy

47
Q

Describe the microscopic structure of skeletal muscle

A

Light bands - actin only - I bands
Dark bands - actin and myosin - A bands
Z disks - actin attach
Region between Z disks = sarcomere
Titin - maintains side-by side relationship of actin/myosin
Space between myofibrils filled with sarcoplasm

48
Q

What is the content of the sarcoplasm?

A

K+, Mg++, PO4-, mitochondria

49
Q

Describe the general mechanism of muscle contraction

A

Action potential travels along motor nerve
ACh secreted
ACh acts on muscle fibre membrane - opens ACh-gated cation channels - Na influx => action potential
Action potential causes sarcoplasmic reticulum to release Ca++

50
Q

Describe the structure of myosin

A

6 polypeptide chains, 2 heavy, 4 light
Heavy chains wrap around each other to form helix, ends folded into head
Light chains form part of head
Myosin molecules bundled together with a twisted axis

51
Q

Describe the structure of actin

A

Backbone - double stranded F-actin, each strand polymerised G-actin
Each G actin molecule has ADP attached - active site for cross bridge interaction
Tropomyosin - wrapped around F actin - lie on top of binding sites in resting state
Troponin - TI - affinity for actin
- TT - affinity for tropomyosin
- TC - affinity for Ca++

52
Q

What activates actin?

A

Ca++

53
Q

Describe the relationship of ATP/ADP and the power stroke of the myosin head

A

ATP binds myosin head - ATPase - ADP + PO4
Binds exposed actin site - power stroke, ADP released
ATP binding causes myosin head detachment
ATP cleaved - head re-cocked

54
Q

What are the 3 sources of energy for muscle contraction?
Which of them need O2
Which is the main contributor to long term muscle contraction?

A

1 - phosphocreatine (O2)
2 - glycolysis
3 - oxidative metabolism (O2) (MAIN CONTRIBUTOR)

55
Q

What are the features of slow muscle fibres?

A

Small, small nerve fibres, extensive blood supply, lots of mitochondria, large amounts of myoglobin

56
Q

Describe ACh secretion in the NMJ

A

Action potential
Voltage-gated Ca++ channels open
Ca++ influx
Ca-calmodulin-dependent protein kinase activation
Phosphorylation of synapsin proteins (anchor ACh vesicles)
Free ACh vesicles dock at release sites and empty via exocytosis

57
Q

What ions are transmitted through ACh channels?

A

Positive only (strong negative charge in channel)
Sodium flows most - negative charge inside cell pulls in

58
Q

How/where is ACh formed?

A

Vesicles formed in Golgi
ACh formed in cytoplasm, immediately transported into vesicles

59
Q

What is ACh split to by acetylcholinesterase? What happens to the substances?

A

Acetate + choline
Choline actively reabsorbed to form more ACh

60
Q

How are vesicles formed for repeated NMJ transmission?

A

After each action potential coated pits appear (formed by contractile proteins - clarithrin) and break away to form new vesicles

61
Q

What is the MOA of neostigmine?

A

Inactivates acetylcholinesterase

62
Q

What is the pathophysiology of myasthenia gravis?

A

Autoantibodies produced that block or destroy ACh-r

63
Q

In what 3 ways do action potentials in skeletal muscle differ from in neurone?

A

Lower resting potential (-80-90mV)
Longer duration
Slower velocity of conduction

64
Q

How do action potentials spread across muscle fibres?

A

Across surface, penetration through transverse (T) tubules

65
Q

How does an action potential lead to calcium release in a muscle fibre?

A

Action potential sensed by dihydropyridine receptor, linked to calcium release channel (ryanodine receptor channel) in the sarcoplasmic reticulum

66
Q

How is calcium concentration in the sarcoplasmic reticulum achieved?

A

SERCA pump - constantly active
Calcium-binding protein in SR - calsequestrin

67
Q

What is the MOA of dantrolene?

A

Antagonises ryanodine receptor, inhibits calcium release from the SR

68
Q

What are the two types of smooth muscle?

A

Multi-unit - eg cilia/iris
Unitary - most viscera in body

69
Q

What is the main difference between smooth and skeletal muscle?

A

No troponin complex in smooth

70
Q

Briefly, how are smooth muscle fibres organised?

A

Actin filaments connected to dense bodies, with myosin fibres interspersed between

71
Q

What are 6 differences between smooth muscle contraction and skeletal?

A

Slow cycling of myosin cross-bridges
Low energy requirement
Slow onset
Greater force of contraction
Latch mechanism
Stress-relaxation

72
Q

How is smooth muscle activated?

A

Smooth muscle contains calmodulin rather than troponin
Ca++ binds to calmodulin
Ca-calmodulin activates myosin light chain kinase
Phosphorylates regulatory myosin head - while phosphorylated capable of repeated binding

73
Q

What is the source of calcium for SM contraction?

A

Extracellular (poorly developed sarcoplasmic reticulum)

74
Q

What regulates the force of SM contraction?

A

Extracellular calcium

75
Q

What causes SM relaxation?

A

Ca pump removes calcium, myosin phosphatase reverses phosphorylation of myosin head

76
Q

What is the action potential of SM?

A

-50-60mV

77
Q

What are the two types of action potential in unitary smooth muscle?

A

Spike potentials
Action potential with plateau

78
Q

How do smooth muscle action potentials differ from skeletal muscle?

A

Far more voltage-gated calcium channels, fewer sodium
Mainly generated by Ca influx, slower to open and remain open longer than Na channels

Guyton - unit questions (14 decks)

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