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Foundations of health and disease > neurones > Flashcards

neurones Flashcards

1
Q

what is voltage

A

the difference in electric potential energy per unit charge between two points

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2
Q

what is current

A

a flow of electric charge through a medium (through a surface)

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3
Q

what is a resistance

A

the opposition to the passage of an electric current; the inverse quantity is electrical conductance (g), measuring how easily electricity flows along a certain path

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4
Q

what is conductance

A

1/R – ability to conduct electric current

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5
Q

what is ohms law

A

V = I x R
I = V x g
(if you multiply the force on an ionic species (voltage) by the ability of it to be conducted forward (conductance = g), the result is the current that actually can flow per second

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6
Q

what is membrane potential

A

A measurement of the overall electrical potential energy across the membrane

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7
Q

what does membrane potential depend on

A

Vm depends on the relative electrical current and conductance of different ions

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8
Q

what happens when ion channels open- neurones

A

[Na+] is higher outside the cell so when the channels open, Na+ flows inside the cell and the membrane tends to become positive (inside)
[K+] is higher inside the cell so when the channels open, K+ flows to outside and the membrane becomes negative (inside)

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9
Q

what is equilibrium potential

A

whenever ion channels for that ion open, the membrane potential moves toward that ion’s equilibrium potential

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10
Q

what is Ena

A

+60mV

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11
Q

what is Ek

A

-90mV

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12
Q

what is Eca

A

+123mV

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13
Q

what is ECl

A

-40mV (-65mV neurones)

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14
Q

what is action potential

A

rapid changes in the membrane potential that spread rapidly along the nerve fibre membrane

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15
Q

at rest what is the membrane potential and what is the membrane more permeable to

A

-70 to -90 mV
membrane more permeable to K+

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16
Q

at action potential what is the membrane potential and what is the membrane more permeable to

A

+20 to +40mV
membrane temporarily more permabe to Na+, Ca2+ or both

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17
Q

what are the stages of action potential

A

stimulus reaches threshold
depolarisation
repolarisation
refactory period-hyperpolarisation
resting

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18
Q

what is the resting stage

A

: K+ that is going out of cell clamps the membrane potential negative

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19
Q

what is the initial depolarisation

A

Depolarisation: inside the cell the voltage becomes less negative (or more positive)
Could be a nearby cell depolarising
Could be synaptic transmission where a neurotransmitter opens a ligand-gated channel

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20
Q

what happens if the stimulus is below the threshold

A

Background K+ permeability pulls Vm back resting stage
This is a “failed initiation”

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21
Q

what is the positive feedback of depolarisation

A

The initial depolarisation causes a few of the Na+ channels to open
The additional current of Na+ going into the cell
more depolarisation
This acts as a positive feedback loop
When the voltage goes above the threshold voltage the cell is committed to an AP

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22
Q

what is repolarisation

A

Na+ channel inactivation decreased Na+ current going in
Delayed rectifier K+ channels open increased K+ going out
These cause the membrane to be less positive and more negative inside

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23
Q

what is hyperpolarisation

A

the voltage inside temporarily becomes slightly more negative than at rest
increased K+ permeability and decreased Na+ permeability
the membrane potential becomes even more negative
causes refractory period

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24
Q

what happens to the synapse when an action potential is caused

A

When Vm becomes positive inside during action potential, calcium channels open
Increase influx of Ca2+

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25
Q

what is a neurotransmitter

A

Endogenous chemical
Released extracellularly by a neuron
Used to signal to other neurons, myocytes, endocrine cells,…
Under physiological conditions

26
Q

what is the life cycle of a neurotransmitter in the presynaptic neurone

A

Synthesis
In the soma (cell body) or locally in the axon terminal
Sometimes instead of synthesis it is recycled (after use)
Storage
Transported into a vesicle for storage (synaptic vesicle)
Membrane depolarisation and activation of voltage-gated Ca2+ channels
Vesicle Transport and Fusion with the membrane
Release

27
Q

what is the life of a neurotransmitter at the post synaptic neurone

A

Diffusion across the synaptic cleft
Action on post-synaptic cell
Activation of specific receptors
Excitatory or inhibitory inputs
Open ion channel – if Na+, will cause depolarisation in the post-synaptic cell
Any of the different types of receptors
Signal termination
Removal of transmitter from synaptic cleft
Degradation by enzymes
Recycled into the presynaptic cells - reuptake

28
Q

when does synthesis of neurotransmitters stop

A

Synthesis stops depending the enzymes present in the neuron / cell

29
Q

what is noradrenaline secreted by

A

sympathetic nerve terminals

30
Q

what is adrenaline secreted by

A

secreted by chromaffin cells in the adrenal medulla

31
Q

what are types of adrenoreceptors

A

a and b

32
Q

what are features of α-adrenoceptors

A

α1, α2 (post-/pre-synaptic)
Blood vessels of organs and tissues except skeletal muscle vessels
Agonists: NA, Adr, isoprenaline
Antagonist: phentolamine

33
Q

what are features of β-adrenoceptors

A

β1 (myocardium), β2 (bronchi, uterus, muscle and coronary vessels), β3 (adipose tissue, bladder, gallbladder)
Agonists: Isoprenaline, Adr, NA
Antagonist: propranolol
Sensitive to up/down regulation

34
Q

what is the 2nd messenger system of a1 receptors

A

Gaq

35
Q

what is the 2nd messenger system of a2 receptors

A

Gai

36
Q

what is the 2nd messenger system of B1/2/3

A

Gas

37
Q

which adrenoreceptor causes smooth muscle contraction/ vasoconstriction

A

A1- in blood vessels

38
Q

which adrenoreceptor causes GI smooth muscle relaxation

A

A1

39
Q

which adrenoreceptor causes GI sphincteric muscle / bladder sphincter contraction

A

a1

40
Q

which adrenoreceptor causes glycogenolysis in the liver

A

a1/b1

41
Q

which adrenoreceptor causes decreased neurotransmitter release in the presynaptic sympathetic neurones

A

a2

42
Q

which adrenoreceptor causes increased heart rate and force of contraction

A

B1

43
Q

which adrenoreceptor causes dilation/relaxation in the bronchi and blood vessels

A

b2

44
Q

which adrenoreceptor causes tremor and glycogenesis in skeletal muscle

A

b2

45
Q

which adrenoreceptor causes lipolysis, thermogenesis in adipose tissue and skeletal muscle

A

b3

46
Q

which adrenoreceptor causes relaxation - preventing urination in the bladder

A

b3

47
Q

what is the pathway of ACH

A

Synthesis in the cytosol
Storage
Vesicle Transport and Fusion with the membrane
Release
Diffusion across the synaptic cleft
Action on post-synaptic cell – receptors
Signal termination
Metabolism by cholinesterase:

48
Q

what are metabotropic receptors (GPCR)

A

Metabotropic (GPCR)
Located postsynaptically in the smooth muscle, cardiac muscle, glands
Agonists: ACh, muscarine
Antagonist: atropine

49
Q

what are ionotropic receptors

A

Ionotropic (pentameric cations channel)
Autonomic ganglia, motor endplate, CNS
Agonists: ACh, nicotine
Antagonist: curare (tubocurarine)

50
Q

what is the 2nd messenger system for nicotinic receptors

A

ion channel

51
Q

what is the 2nd messenger system for muscarinic M1 (neural)

A

Gaq

52
Q

what is the 2nd messenger system for Muscarinic m2 (cardiac)

A

Gai

53
Q

what is the 2nd messenger system for muscarinic M3 (glandular/ smooth muscle)

A

Gaq

54
Q

what do muscarinic receptors do in the airway smooth muscle

A

bronchoconstriction

55
Q

what do muscarinic receptors do in the gut smooth muscle

A

constraction

56
Q

what do muscarinic receptors do in salivary glands

A

increased salivation

57
Q

what do muscarinic receptors do in the bladder smooth muscle

A

contraction

58
Q

what are features of preganglionic neurones

A

Cell bodies in the grey matter of the brain stem OR in the lateral horn of spinal cord grey matter
Long, synapse with postganglionic neurons at or near organ
Release ACh to activate nicotinic receptors on postganglionic neurons

59
Q

what are features of post-ganglionic neurones

A

Cell bodies are in indistinct ganglia near or on their final target organ (further away from the spinal cord)
Short, synapse on the target organ
Release ACh to activate muscarinic receptors on the target organ

60
Q

what are the effects of the sympathetic nervous system on sweat glands mediated by

A

muscarinic receptors because in this special case the postganglionic neurones are also cholinergic

61
Q

what are drugs effect on the autonomic nervous system

A

Drugs enhance or mimic the autonomic nervous system or block the effects of theneurotransmitters at their receptor sites

Foundations of health and disease (21 decks)

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