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PLE Physiology > Membrane Physiology, Nerve, and Muscle > Flashcards

Membrane Physiology, Nerve, and Muscle Flashcards

1
Q

Fick’s law of diffusion states that flux is proportional to?

A

(Surface area x Concentration difference) / Membrane Thickness

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2
Q

Three factors affecting rate of diffusion and how?

A

Concentration difference - proportional to rate accdg to fick law
Potential difference - electric forces
Pressure difference - higher pressure means faster diffusion

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3
Q

Define osmotic presssure

A

Amount of pressure required to stop osmosis

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4
Q

What is an osmole?

A

1 gram molecular weight of osmotically active substance

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5
Q

Osmolality vs osmolarity?

A

Osmolality - osmoles per kg water
Osmolarity - osmoles per liter solution

Osmolality determines osmotic presure, osmolarity is easier measured

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6
Q

Calcium channel and sodium channels play a role in depolarizing phase of the action potential. How to they differ?

A

Calcium - slow channel, sustained depolarization

Sodium - fast channel, initiation of action potential

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7
Q

Opening of the fast channels in cardiac muscle cause what?

A

Spike portion of action potenntial

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8
Q

Opening of the slow channels in cardiac muscle cause what?

A

Plateau of action potential - sustains contraction

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9
Q

How does the voltage gated potassium channel contribute to the plateau in action potential

A

Channels are slower to open, usually when plateau ends and Na and Ca channels close

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10
Q

Muscle type with no troponin

A

Smooth muscle

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11
Q

Regulatory protein in smooth musckle which initiates contraction

A

Calmodulin

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12
Q

Small invaginations of cell membrane about the surface of the sarcoplasmic tubules

A

Caveolae

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13
Q

Membrane spanning protein used to create gap junctions in cells

A

Connexin

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14
Q

Activator and inhibitor of NMDA receptor

A

Glutamate - activate

Magnesium ion - inhibit

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15
Q

Unphosphorylated myosin bridges bound to actin

A

Latch bridges

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16
Q

Composition of water in the body, in percentage

A

60% water (40% ICF 20% ECF)

out of 20% (80% interstitial fluid 20% plasma)

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17
Q

Logic behind membrane potential (in terms of diffusion and physics)

A

Na higher concentratin outside, K higher inside. Diffusion from higher to lower concentration creates difference in net charge, hence membrane potential

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18
Q

Resting membrane potential of a normal nerve fiber

A

-90 mV

potential inside is more negative

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19
Q

Function of the Na-K pump (ions and direction)

A

3 Na ions pumped outside

2 K ions pumped inside

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20
Q

Contributory factors for resting membrane potential

A

Diffusion potential of K (most impt)
Diffusion potential of Na (goldmann equation)
Na-K pump (extra -4mV due to more + ions going out)

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21
Q

Mechanics of the voltage gated sodium channel

A

Resting state -entry gate closed, exit gate open
Depolarization to a voltage of -70 to -50 causes conformational change, opening entry channel, causing more sodium to go inside
Same conformational change closes the exit channel but more slowly, When it closes, depolarization ends
When resting membrane potental returns to original, exit gate will reopen

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22
Q

Mechanics of the voltage gated potassium channel

A

Closed at rest
Opens slowly when potential rises toward zero, around time when sodium channel closes
Potassium exits cell, causing repolarization

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23
Q

Toxin that blocks sodium channels`

A

Tetrodotoxin

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24
Q

Toxin that blocks potassium channels

A

Tetraethylammonium

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25
Q

Why is potassium conductance greater than sodium conductance at resting state

A

Potassium leak channels make membrane more permeable to K

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26
Q

Effect of hypocalcemia on sodium channels

A

Na channels opened by a lower increase in membrane potential - making it more excitable. In muscles, it causes muscle tetany

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27
Q

What is the threshold for stimulation (quantity and logic)

A

-65 mV - membrane potential required to start action potential
when sodium entering is more than potassium exiting

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28
Q

Mechanism of propagation of action potential

A

Inward diffusing sodium ions in a depolarizing segment also increase voltage in adjacent membrane, causing that to depolarize too. It traves in all directions until entire membrane is depolarized

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29
Q

Mechanics of Na-K pump

A

Active transport - ATP requiring
3 Na out of cell for 2 K into cell.
Returns Na and K to original positions

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30
Q

How does automatic membrane depolarizaition work (i.e pacemaker cells)

A

More permeable to Na or Ca, Resting membrane potential is equal or higher than threshold for excitation

31
Q

What prevents self re-excitation in pacemaker cells?

A

Increased potassium conductance after repolarization causes hyperpolarization, bringing membrane potential closer to K Nernst potential (-94)

32
Q

What substance in the Schwann cell membrane insulates the nerve membrane of theaxons

A

Sphingomyelin

33
Q

Two advantages of saltatory conduction

A
  1. Faster velocity of nerve transmission

2. Less ions transferred = less energy required

34
Q

Period during which a second action potential cannot be elicited even with a strong stimulus

A

Absolute refractory period

35
Q

Effect of high extracellular fluid calcium on sodium permeability

A

Decreases Na permeability

36
Q

Thin membrane enclosing muscle fiber

A

Sarcolemma

37
Q

Components of myofibril? Which is thin which is thick

A

Actin - thin filament (acthin)

Myosin - thick filament

38
Q

A band vs I band? Components and structure at middle

A

A band - anisotropic to polarized light - myosin and actin overlap. Mid is M line

I band - isotropic -actin only. Mid is z disk

39
Q

Define a sarcomere

A

Portion of myofibril between two z disks

40
Q

Molecule which keeps actin and myosin in place

A

Titin

41
Q

Mechanism of muscle contraction - role of action potential, Ach, Na and Ca

A

Action potential to nerve ending,
acetylcholine release,
Acetylcholine gated Na channels in fiber open
Na diffuses, opening voltage gated Na channels
Action potential travels in fiber
Depolarization causes sarcoplasmic reticulum to release Ca
Ca initiates actin and myosin contraction
Ca is pumped back to SR and stops contraction

42
Q

What structure generates force of muscle contraction

A

Cross bridges of myosin, and actin

43
Q

Function of tropomyosin

A

Attached to active site of actin strand at resting state, inhubiting contraction

44
Q

Difference bet Trop I, Trop T and Trop C

A

Troponin is believed to attach tropomyosin to actin
I - strong affinty for actin
T - for tropomyosin
C - for Ca

45
Q

What initiates activation of actin active sites

A

Calcium

46
Q

Mechanism of the sliding filament theory of contraction

A

Cross bridge head binds with ATP and cleaves it to ADP and P, releasing energy
Calcium exposes actin active sites
Myosin binds to actin and pulls actin
Bound ADP and P is released, allowing new ATP to bind

47
Q

What is the Fenn Effect

A

The greater work performed by muscle, greater ATP is cleaved.

48
Q

Sarcomere length which provides maximal tension

A

2.2 um

49
Q

Sources of energy for muscle contraction

A

Phosphocreatine - cleavage of high energy phosphate bond
Glycolysis of glycogen stores (anaerobic)
Oxidative metabolism

50
Q

Energy requiring processess in muscle contraction

A

Walk along mechannism of actin and myosin
Pumping Ca from sarcoplasm back to sarcoplasmic reticulum
Pumping Na and K in pumps

51
Q

Differences bet fast and slow fibers based on

Type, color, size, innervation, blood vessel and mitochondria amount

A

Slow / Type 1 / Red Muscle
Small, for endurance, smaller nerve fibers, more extensive blood supply, increased mitochondria, lot of myoglobin

Fast /Type II / White Muscle
Large, for strength, extensive SR and large glycolytic enzymes for.rapid release, less extensive blood supply, fewer mitohondria, no myoglobin

52
Q

Function of myoglobin

A

Combines with oxygen and stores it in red muscle until needed

53
Q

Events starting from action potential speading to presynaptic terminal that lead to acetylcholine release in the NMJ

A
  1. Action potential spreads on terminal
  2. Voltage gated calcium channels open and allow Ca to move from synaptic space to interior
  3. Ca-calmodulin dependent kinase is activated and phosphorylates synapsin
  4. Synapsin anchoring Ach to cytoskeleton is freed. Vesicle moves to active zone
  5. Exocytosis and Ach release
54
Q

Acetylcholine receptor complex subunits in fetal and adult?

A

Fetal - 2 alpha 1 beta delta and gamma

Adult - 2 alpha 1 beta delta ans epsilon

55
Q

Acetylcholine attached to which subunit, causing thr conformational change

A

Alpha

56
Q

What ions pass through the activated acetylcholine gated channel

A

Na, K, Ca

But mostly Na in motor end plate

57
Q

What is end plate potential

A

Positive potential change after sodium influx in opened ach gated channel

58
Q

Two mechanisms of removal of acetylcholine in the synaptic cleft

A

Destruction by acetylcholinesterase

Diffusion out of synaptic space

59
Q

Effect of curare on motor end plate

A

Blocks ach channel attachment site

60
Q

Effect of botulinum toxin on motor end plate

A

Decrease quantity of ach release by nerve terminal

61
Q

Difference of nerve fiber and skeletal fiber in terms of

  1. Resting membrane potential
  2. Duration of action potential
  3. Velocity of conduction
A
  1. Resting membrane potential is almost the same
  2. Duration is longer in skeletal muscle by 5 times
  3. Velocity is slower in muscle fiber
62
Q

Function of T tubules

A

Penetratr the interior of muscle fiber and transmits current to inside, causing Ca release and muscle contraction

63
Q

Large chambers of sarcoplasmic reticulum abutting the T tubules

A

Terminal cisternae

64
Q

Receptors linked to calcium release channels in the T tubule which sense voltage change and causes release of calcium in terminal cisternae

A

Dihydropyridine receptor or Ryanodine receptor

65
Q

What maintains high calcium concentration in sarcoplasmic reticulum?

A

Calcium pump causes active transport back to SR

Calsequestrin binds to Ca in reticulum

66
Q

Multi unit vs unitary smooth muscle

A

Multi unit - fibers contract independently of each other, controllef by nerve stimuli
Ex: ciliary muscles of eye, iris, arrector pili

Unitary - (syncytial or visceral smooth muscle) - gap junctions allow contraction as a unit.

67
Q

In smooth muscle, actin is attached to which structure? (Counterpart of Z disk)

A

Dense bodies

68
Q

Which muscles can contract a higher percentage of length? Smooth or skeletal

A

Smooth

69
Q

Smooth muscle vs skeletal in terms of speed of myosin cross bridge cycling, energy requirement, and maximal force of contraction

A

Slower cycling, lower energy reqt, higher max force

70
Q

Latch mechanism of smooth muscle and importance

A

Energy required to maintain contraction is less, allowing prolonged tonic contraction

71
Q

How does calcium initiate contraction in the smooth muscle?

A
  1. Calcium entry
  2. Reversible binding with calmodulin
  3. Ca-calmodulin conplex activates myosin light chain kinase
  4. Kinase phosphorylates regulatory chain and activates myosin head
  5. Myosin head can bind with actin filament and proceed contraction
72
Q

Source of majority of Ca for smooth muscle

A

ECF. SR only contributes some since some smooth muscle have no SR

73
Q

Enzyme required for relaxation of smooth muscle -this deactivates myosin head

A

Myosin phosphatase - removes phosphate

74
Q

Stereospecificity is characteristic of what type of diffusion

A

Carrier-mediated diffusion

PLE Physiology (7 decks)

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