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Guyton - unit questions EW > 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
How do simple and facilitated diffusion compare/contrast?
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
26
What is the formula for net diffusion?
Net diffusion is proportional to the concentration of a substance outside a membrane, minus the concentration of the substance inside the membrane
27
What is the Nernst potential?
The electrical difference that will balance a given concentration difference of univalent ions at normal body temperature
28
What is the Nernst equation?
EMF(mV) = +/-(61/z) x (logC1/C2) z = electrical charge of ion
29
What factors effect net diffusion?
Concentration, electrical potential, pressure
30
What determines osmotic pressure?
The number of particles per unit volume
31
How does the Na-K pump work? What is it's main function?
3xNa+ pumped out of cell in exchange for 2xK+ Regulates cell volume
32
Describe the electrogenic nature of the Na-K pump
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
How does calcium concentration compare inside/outside the cell? How is it maintained?
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
Name 2 examples of primary active transport of hydrogen ions?
Gastric glands of the stomach Late distal tubules and cortical collecting ducts in kidneys (intercalated cells)
35
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) 2800 b) 4200
36
What is the resting membrane potential of large nerves?
-70mV
37
What factors contribute to the negative resting potential of cells?
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
What are the stages of a neutron action potential?
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
Describe the opening, closing and re-opening of voltage-gated Na channels
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
Describe the opening of the voltage-gated potassium channels
Activated when membrane potential rises, however, slight delay so open as sodium channels close
41
What is the role of calcium in the generation of an action potential?
Voltage-gated slow calcium channels - contribute to depolarisation, produce more sustained depolarisation
42
Where are calcium channels most numerous?
Smooth muscle and cardiac muscle
43
How does the concentration of calcium ions in the ECF effect depolarisation?
When there is a deficit of Ca++, sodium channels are opened by smaller increase in membrane potential
44
Which cells produce myelin?
Schwann cells
45
What is the name for the notches in myelin?
Nodes on Ranvier
46
What is the function of the nodes of Ranvier and what are the benefits (2)?
Allow saltatory conduction 1 - increased velocity of nerve transmission 2 - requires less energy
47
Describe the microscopic structure of skeletal muscle
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
What is the content of the sarcoplasm?
K+, Mg++, PO4-, mitochondria
49
Describe the general mechanism of muscle contraction
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
Describe the structure of myosin
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
Describe the structure of actin
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
What activates actin?
Ca++
53
Describe the relationship of ATP/ADP and the power stroke of the myosin head
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
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?
1 - phosphocreatine (O2) 2 - glycolysis 3 - oxidative metabolism (O2) (MAIN CONTRIBUTOR)
55
What are the features of slow muscle fibres?
Small, small nerve fibres, extensive blood supply, lots of mitochondria, large amounts of myoglobin
56
Describe ACh secretion in the NMJ
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
What ions are transmitted through ACh channels?
Positive only (strong negative charge in channel) Sodium flows most - negative charge inside cell pulls in
58
How/where is ACh formed?
Vesicles formed in Golgi ACh formed in cytoplasm, immediately transported into vesicles
59
What is ACh split to by acetylcholinesterase? What happens to the substances?
Acetate + choline Choline actively reabsorbed to form more ACh
60
How are vesicles formed for repeated NMJ transmission?
After each action potential coated pits appear (formed by contractile proteins - clarithrin) and break away to form new vesicles
61
What is the MOA of neostigmine?
Inactivates acetylcholinesterase
62
What is the pathophysiology of myasthenia gravis?
Autoantibodies produced that block or destroy ACh-r
63
In what 3 ways do action potentials in skeletal muscle differ from in neurone?
Lower resting potential (-80-90mV) Longer duration Slower velocity of conduction
64
How do action potentials spread across muscle fibres?
Across surface, penetration through transverse (T) tubules
65
How does an action potential lead to calcium release in a muscle fibre?
Action potential sensed by dihydropyridine receptor, linked to calcium release channel (ryanodine receptor channel) in the sarcoplasmic reticulum
66
How is calcium concentration in the sarcoplasmic reticulum achieved?
SERCA pump - constantly active Calcium-binding protein in SR - calsequestrin
67
What is the MOA of dantrolene?
Antagonises ryanodine receptor, inhibits calcium release from the SR
68
What are the two types of smooth muscle?
Multi-unit - eg cilia/iris Unitary - most viscera in body
69
What is the main difference between smooth and skeletal muscle?
No troponin complex in smooth
70
Briefly, how are smooth muscle fibres organised?
Actin filaments connected to dense bodies, with myosin fibres interspersed between
71
What are 6 differences between smooth muscle contraction and skeletal?
Slow cycling of myosin cross-bridges Low energy requirement Slow onset Greater force of contraction Latch mechanism Stress-relaxation
72
How is smooth muscle activated?
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
What is the source of calcium for SM contraction?
Extracellular (poorly developed sarcoplasmic reticulum)
74
What regulates the force of SM contraction?
Extracellular calcium
75
What causes SM relaxation?
Ca pump removes calcium, myosin phosphatase reverses phosphorylation of myosin head
76
What is the action potential of SM?
-50-60mV
77
What are the two types of action potential in unitary smooth muscle?
Spike potentials Action potential with plateau
78
How do smooth muscle action potentials differ from skeletal muscle?
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 EW (14 decks)

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