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Biology > BIOSCI 107 ET: Neurons > Flashcards

BIOSCI 107 ET: Neurons Flashcards

1
Q

What is the Nervous System Comprised of?

A

CNS and PNS.

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2
Q

What are Neurons (Nerve Cells)?

A

The principal building blocks and instruments of communication in the brain.

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3
Q

What 2 Communication Types are used by Neurons?

A

Electrical signals, chemical signals.

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4
Q

Where are Electrical Signals Used?

A

Dendrites, cell body, axon.

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5
Q

Where are Chemical Signals Used?

A

Synapses.

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6
Q

What is the Resting Membrane Potential?

A

Electrical potential difference (50 to 70 mV) across the cell membrane which results from separation of charge.

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7
Q

What is the Typical Resting Membrane Potential of Cells?

A

Almost all cells have a negative resting membrane potential.

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8
Q

Which 3 Areas are Excitable?

A

Neurons, muscle fibres, some endocrine cells.

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9
Q

What does Excitable Mean?

A

Ability to suddenly respond with a transient change of the resting membrane potential in response to a stimulus.

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10
Q

Which 2 Techniques are used to Measure Intracellular Potentials Today?

A

Microelectrode recording technique, patch-clamp technique.

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11
Q

What is an Important Convention to Remember about RMP?

A

The potential outside the cell is defined as zero.

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12
Q

Which 3 Factors Cause the RMP?

A

Unequal concentrations of Na and K inside/outside the cell, unequal permeability of cell membrane to these ions, electrogenic action of Na/K pump (minor).

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13
Q

What are the Approximate Concentrations of K and Na Outside the Cell?

A

K: 5 mM
Na: 150 mM

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14
Q

What are the Approximate Concentrations of K and Na Inside the Cell?

A

K: 100 mM
Na: 15 mM

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15
Q

How are the Concentration Gradients for K and Na Maintained?

A

By the Na/K pump.

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16
Q

What are the 2 Main Types of Ion Channel in Ions?

A

Non-gated channels, gated channels.

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17
Q

What are Non-Gated Channels in Neurons?

A

‘Leak’ channels open at rest.

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18
Q

What are Gated Channels in Neurons?

A

Voltage/ligand (chemical)/mechanically gated - closed at rest.

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19
Q

How do the Numbers of K Channels compare to those of Na?

A

At rest: Pk / PNa = 40 / 1.

P = membrane permeability.

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20
Q

How can we Calculate Equilibrium Potential for Each Ion?

A

Using the Nernst Equation.

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21
Q

What is an Equilibrium Potential?

A

An intracellular potential at which the net flow of ions is zero, in spite of a concentration gradient and permeability.

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22
Q

What is Unique about Glia Cells?

A

They only have leak channels for K.

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23
Q

What is an Important Rule about Cell Membranes and Permeability?

A

Higher the permeability of the cell membrane to an ion, the more this ion can shift RMP towards its equilibrium potential.

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24
Q

What is the Goldman Equation?

A

Calculates value of RMP, including both concentration gradients and relative permeability to K and Na ions.

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25
Q

When does Neuron Potential Change?

A

When membrane permeability or ion concentrations change.

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26
Q

What is Hyperpolarisation?

A

When potential becomes more negative.

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27
Q

What is Depolarisation?

A

When potential becomes less negative.

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28
Q

What is the Action Potential?

A

A brief fluctuation in membrane potential.

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29
Q

What causes the Action Potential?

A

A transient opening of voltage-gated ion channels, which spreads like a wave, along axon.

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30
Q

When do Action Potentials Occur?

A

After the membrane potential reaches certain voltage - threshold (55 mV).

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31
Q

Why are Action Potentials Important?

A

Information coded in their frequency - language, also a key element of signal transmission along axons.

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32
Q

What are the 3 Stages of Action Potentials?

A

Fast depolarisation, repolarisation, after-hyperpolarisation.

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33
Q

How do we Group the 3 Stages of Action Potentials?

A

1 + 2 are the absolute refractory period.

3 is the relative refractory period.

34
Q

What can the Stimulus of an Action Potential be?

A

Physical or chemical.

35
Q

What are some Examples of Physical Stimuli for the Action Potential?

A

Electric current, light, stretch.

36
Q

What are some Examples of a Chemical Stimuli for the Action Potential?

A

A drug, synaptic excitation.

37
Q

What Happens when MP Reaches the Threshold?

A

A sudden activation (opening) of voltage-gated Na channels (increased permeability).

38
Q

What Happens After MP Reaches the Threshold?

A

Pk / PNa is 1:20 instead of 40:1, so MP shifts towards ENa causing overshoot.

39
Q

What Happens After Overshoot?

A

Transient opening of voltage-gated K channels - repolarisation and AHP.

40
Q

Why does MP Shift Towards Ek after Overshoot?

A

Since Pk / PNa becomes 100 : 1.

41
Q

What Happens when Voltage Threshold is Reached?

A

Sodium channels open and Na ions move into cell (both gradients).

42
Q

When does Influx of Na Slow Down in a Voltage-Gated Channel?

A

When inside potential becomes positive, Na channels inactivate.

43
Q

What is Important to Remember about the Amplitude of Action Potentials?

A

It is usually constant and doesn’t depend on stimulus intensity.

44
Q

When does Hyperpolarisation occur in Electrical Currents?

A

When the current generated by an outside source flows through membrane from outside to inside.

45
Q

When does Depolarisation occur in Electrical Currents?

A

When the current generated by an outside source flows through membrane from inside to outside.

46
Q

Where are APs First Generated?

A

In the axon initial segment which has the lowest threshold - trigger zone.

47
Q

What Evokes Depolarisation to Threshold?

A

Excitatory postsynaptic potentials, which spread passively from dendrites.

48
Q

Where do Generated APs go?

A

Transmitted actively along the axon, away from the cell body.

49
Q

What are the 2 Types of Axon?

A

Unmyelinated and myelinated.

50
Q

What are Unmyelinated Axons?

A

Small diameter, transmission of APs slow, continuous.

51
Q

What are Myelinated Axons?

A

Larger diameter, transmission of APs fast, saltatory.

52
Q

What are the 2 Stages of Actions Potential Transmission?

A

Passive spread, generation of action potentials.

53
Q

How is Local (Subthreshold) Depolarisation Induced?

A

By current injected into an axon by a glass microelectrode.

54
Q

Why is Conduction Velocity Slow in Unmyelinated Axons?

A

AP must be regenerated at every point on the membrane.

55
Q

Which 2 Components Form the Myelin Sheath?

A

Oligodendrocytes in the CNS, Schwann cells in the PNS.

56
Q

What is Myelination?

A

Discontinuous; interrupted at nodes of Ranvier.

57
Q

What is Important to Remember about Passive Conduction?

A

It occurs in both directions.

58
Q

Why is there Less Dissipation during Myelination?

A

Due to the insulating properties.

59
Q

How does Myelination increase Speed of SP Conduction?

A

By increasing efficiency of passive spread.

60
Q

Where in APs Generating in Myelinated Axons?

A

At nodes of Ranvier only - flowing passively between them.

61
Q

Why does AP Conduct in only One Direction?

A

Due to absolute refractory period - once this is over, AP has already moved down the axon.

62
Q

Where is Information about the Strength of the Stimulus Coded?

A

In the amplitude of the receptor potential and the frequency of APs.

63
Q

What are the 2 Ways Messages can be Transmitted between Excitable Tissues?

A

Synaptic transmission between neurons or between a neuron and a muscle fiber.

64
Q

What is an Example of a Neurotransmitter?

A

Acetylecholine.

65
Q

What are the 2 Main Types of Chemical Synapses in the CNS?

A

Excitatory and inhibitory synapses.

66
Q

What is an Excitatory Synapse?

A

Depolarisation of the postsynaptic membrane, called the Excitatory Postsynaptic Potential.

67
Q

What is an Inhibitory Synapse?

A

Hyperpolarisation of the postsynaptic membrane, called the Inhibitory Postsynaptic Potential.

68
Q

What are the Neurotransmitters of Excitatory Synapses?

A

Glutamic acid or ACh.

69
Q

What are the Neurotransmitters of Inhibitory Synapses?

A

GABA or glycine.

70
Q

What is the Ionic Mechanism of EPSPs?

A

Transient opening of channels for Na, K and Ca (sometimes).

71
Q

What is the Ionic Mechanism of IPSPs?

A

Transient opening of K channels.

72
Q

What are the 2 Classifications of Neurotransmitters?

A

Small molecule neurotransmitters, neuropeptides.

73
Q

How do we Identify Small Molecule Neurotransmitters?

A

Fast action, direct on postsynaptic receptors.

74
Q

How do we Identify Neuropeptides?

A

Large, have an indirect action on postsynaptic receptors, or modulatory action on effects of other neurotransmitters.

75
Q

What are Some Examples of Small Molecule Neurotransmitters?

A

Amino acids, acetylcholine, amines.

76
Q

What are Some Examples of Neuropeptides?

A

NPY, substance P, kisspeptin, enkephaln.

77
Q

Which 3 Factors Determine Synaptic Action?

A

Type of neurotransmitter/modulator, type of receptor, amount of receptor.

78
Q

What is Excitotoxicity?

A

Excessive Ca entry that damages neurons.

79
Q

What Happens if too much Glutamate is Released?

A

Excessive depolarisation and over-activation of neurons.

80
Q

Which 3 Factors can Cause Neurotransmitter Inactivation?

A

Diffusion from synapse, enzymatic degradation in synaptic cleft, re-uptake/recycling.

81
Q

What must Take Place for Depolarisation?

A

To depolarise initial segment to threshold, EPSPs need to be enhanced.

Biology (15 decks)

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