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Unit 2 Flashcards

1
Q

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

A

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

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2
Q

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

A

Lipid

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3
Q

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

A

Oxygen, nitrogen, C02 and alcohols

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4
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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5
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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6
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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7
Q

What is the Nernst equation?

A

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

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8
Q

What factors effect net diffusion?

A

Concentration, electrical potential, pressure

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9
Q

What determines osmotic pressure?

A

The number of particles per unit volume

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10
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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11
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

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12
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)

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13
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)

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14
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

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15
Q

What is the resting membrane potential of large nerves?

A

-70mV

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16
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

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17
Q

What are the stages of a neuron 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

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18
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

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19
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

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20
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

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21
Q

Where are calcium channels most numerous?

A

Smooth muscle and cardiac muscle

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22
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

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23
Q

Which cells produce myelin?

A

Schwann cells

24
Q

What is the name for the notches in myelin?

A

Nodes on Ranvier

25
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
26
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
27
What is the content of the sarcoplasm?
K+, Mg++, PO4-, mitochondria
28
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++
29
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
30
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++
31
What activates actin?
Ca++
32
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
33
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)
34
What are the features of slow muscle fibres?
Small, small nerve fibres, extensive blood supply, lots of mitochondria, large amounts of myoglobin
35
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
36
What ions are transmitted through ACh channels?
Positive only (strong negative charge in channel) Sodium flows most - negative charge inside cell pulls in
37
How/where is ACh formed?
Vesicles formed in Golgi ACh formed in cytoplasm, immediately transported into vesicles
38
What is ACh split to by acetylcholinesterase? What happens to the substances?
Acetate + choline Choline actively reabsorbed to form more ACh
39
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
40
What is the MOA of neostigmine?
Inactivates acetylcholinesterase
41
What is the pathophysiology of myasthenia gravis?
Autoantibodies produced that block or destroy ACh-r
42
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
43
How do action potentials spread across muscle fibres?
Across surface, penetration through transverse (T) tubules
44
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
45
How is calcium concentration in the sarcoplasmic reticulum achieved?
SERCA pump - constantly active Calcium-binding protein in SR - calsequestrin
46
What is the MOA of dantrolene?
Antagonises ryanodine receptor, inhibits calcium release from the SR
47
What are the two types of smooth muscle?
Multi-unit - eg cilia/iris Unitary - most viscera in body
48
What is the main difference between smooth and skeletal muscle?
No troponin complex in smooth
49
Briefly, how are smooth muscle fibres organised?
Actin filaments connected to dense bodies, with myosin fibres interspersed between
50
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
51
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
52
What is the source of calcium for SM contraction?
Extracellular (poorly developed sarcoplasmic reticulum)
53
What regulates the force of SM contraction?
Extracellular calcium
54
What causes SM relaxation?
Ca pump removes calcium, myosin phosphatase reverses phosphorylation of myosin head
55
What is the action potential of SM?
-50-60mV
56
What are the two types of action potential in unitary smooth muscle?
Spike potentials Action potential with plateau
57
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 (10 decks)

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