BIOSCI 107 ET: Neurons

Question 1

What is the Nervous System Comprised of?

Answer 1

CNS and PNS.

Question 2

What are Neurons (Nerve Cells)?

Answer 2

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

Question 3

What 2 Communication Types are used by Neurons?

Answer 3

Electrical signals, chemical signals.

Question 4

Where are Electrical Signals Used?

Answer 4

Dendrites, cell body, axon.

Question 5

Where are Chemical Signals Used?

Answer 5

Synapses.

Question 6

What is the Resting Membrane Potential?

Answer 6

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

Question 7

What is the Typical Resting Membrane Potential of Cells?

Answer 7

Almost all cells have a negative resting membrane potential.

Question 8

Which 3 Areas are Excitable?

Answer 8

Neurons, muscle fibres, some endocrine cells.

Question 9

What does Excitable Mean?

Answer 9

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

Question 10

Which 2 Techniques are used to Measure Intracellular Potentials Today?

Answer 10

Microelectrode recording technique, patch-clamp technique.

Question 11

What is an Important Convention to Remember about RMP?

Answer 11

The potential outside the cell is defined as zero.

Question 12

Which 3 Factors Cause the RMP?

Answer 12

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).

Question 13

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

Answer 13

K: 5 mM
Na: 150 mM

Question 14

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

Answer 14

K: 100 mM
Na: 15 mM

Question 15

How are the Concentration Gradients for K and Na Maintained?

Answer 15

By the Na/K pump.

Question 16

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

Answer 16

Non-gated channels, gated channels.

Question 17

What are Non-Gated Channels in Neurons?

Answer 17

‘Leak’ channels open at rest.

Question 18

What are Gated Channels in Neurons?

Answer 18

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

Question 19

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

Answer 19

At rest: Pk / PNa = 40 / 1.

P = membrane permeability.

Question 20

How can we Calculate Equilibrium Potential for Each Ion?

Answer 20

Using the Nernst Equation.

Question 21

What is an Equilibrium Potential?

Answer 21

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

Question 22

What is Unique about Glia Cells?

Answer 22

They only have leak channels for K.

Question 23

What is an Important Rule about Cell Membranes and Permeability?

Answer 23

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

Question 24

What is the Goldman Equation?

Answer 24

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

Question 25

When does Neuron Potential Change?

Answer 25

When membrane permeability or ion concentrations change.

Question 26

What is Hyperpolarisation?

Answer 26

When potential becomes more negative.

Question 27

What is Depolarisation?

Answer 27

When potential becomes less negative.

Question 28

What is the Action Potential?

Answer 28

A brief fluctuation in membrane potential.

Question 29

What causes the Action Potential?

Answer 29

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

Question 30

When do Action Potentials Occur?

Answer 30

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

Question 31

Why are Action Potentials Important?

Answer 31

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

Question 32

What are the 3 Stages of Action Potentials?

Answer 32

Fast depolarisation, repolarisation, after-hyperpolarisation.

Question 33

How do we Group the 3 Stages of Action Potentials?

Answer 33

1 + 2 are the absolute refractory period. | 3 is the relative refractory period.

Question 34

What can the Stimulus of an Action Potential be?

Answer 34

Physical or chemical.

Question 35

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

Answer 35

Electric current, light, stretch.

Question 36

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

Answer 36

A drug, synaptic excitation.

Question 37

What Happens when MP Reaches the Threshold?

Answer 37

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

Question 38

What Happens After MP Reaches the Threshold?

Answer 38

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

Question 39

What Happens After Overshoot?

Answer 39

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

Question 40

Why does MP Shift Towards Ek after Overshoot?

Answer 40

Since Pk / PNa becomes 100 : 1.

Question 41

What Happens when Voltage Threshold is Reached?

Answer 41

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

Question 42

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

Answer 42

When inside potential becomes positive, Na channels inactivate.

Question 43

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

Answer 43

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

Question 44

When does Hyperpolarisation occur in Electrical Currents?

Answer 44

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

Question 45

When does Depolarisation occur in Electrical Currents?

Answer 45

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

Question 46

Where are APs First Generated?

Answer 46

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

Question 47

What Evokes Depolarisation to Threshold?

Answer 47

Excitatory postsynaptic potentials, which spread passively from dendrites.

Question 48

Where do Generated APs go?

Answer 48

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

Question 49

What are the 2 Types of Axon?

Answer 49

Unmyelinated and myelinated.

Question 50

What are Unmyelinated Axons?

Answer 50

Small diameter, transmission of APs slow, continuous.

Question 51

What are Myelinated Axons?

Answer 51

Larger diameter, transmission of APs fast, saltatory.

Question 52

What are the 2 Stages of Actions Potential Transmission?

Answer 52

Passive spread, generation of action potentials.

Question 53

How is Local (Subthreshold) Depolarisation Induced?

Answer 53

By current injected into an axon by a glass microelectrode.

Question 54

Why is Conduction Velocity Slow in Unmyelinated Axons?

Answer 54

AP must be regenerated at every point on the membrane.

Question 55

Which 2 Components Form the Myelin Sheath?

Answer 55

Oligodendrocytes in the CNS, Schwann cells in the PNS.

Question 56

What is Myelination?

Answer 56

Discontinuous; interrupted at nodes of Ranvier.

Question 57

What is Important to Remember about Passive Conduction?

Answer 57

It occurs in both directions.

Question 58

Why is there Less Dissipation during Myelination?

Answer 58

Due to the insulating properties.

Question 59

How does Myelination increase Speed of SP Conduction?

Answer 59

By increasing efficiency of passive spread.

Question 60

Where in APs Generating in Myelinated Axons?

Answer 60

At nodes of Ranvier only - flowing passively between them.

Question 61

Why does AP Conduct in only One Direction?

Answer 61

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

Question 62

Where is Information about the Strength of the Stimulus Coded?

Answer 62

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

Question 63

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

Answer 63

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

Question 64

What is an Example of a Neurotransmitter?

Answer 64

Acetylecholine.

Question 65

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

Answer 65

Excitatory and inhibitory synapses.

Question 66

What is an Excitatory Synapse?

Answer 66

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

Question 67

What is an Inhibitory Synapse?

Answer 67

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

Question 68

What are the Neurotransmitters of Excitatory Synapses?

Answer 68

Glutamic acid or ACh.

Question 69

What are the Neurotransmitters of Inhibitory Synapses?

Answer 69

GABA or glycine.

Question 70

What is the Ionic Mechanism of EPSPs?

Answer 70

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

Question 71

What is the Ionic Mechanism of IPSPs?

Answer 71

Transient opening of K channels.

Question 72

What are the 2 Classifications of Neurotransmitters?

Answer 72

Small molecule neurotransmitters, neuropeptides.

Question 73

How do we Identify Small Molecule Neurotransmitters?

Answer 73

Fast action, direct on postsynaptic receptors.

Question 74

How do we Identify Neuropeptides?

Answer 74

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

Question 75

What are Some Examples of Small Molecule Neurotransmitters?

Answer 75

Amino acids, acetylcholine, amines.

Question 76

What are Some Examples of Neuropeptides?

Answer 76

NPY, substance P, kisspeptin, enkephaln.

Question 77

Which 3 Factors Determine Synaptic Action?

Answer 77

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

Question 78

What is Excitotoxicity?

Answer 78

Excessive Ca entry that damages neurons.

Question 79

What Happens if too much Glutamate is Released?

Answer 79

Excessive depolarisation and over-activation of neurons.

Question 80

Which 3 Factors can Cause Neurotransmitter Inactivation?

Answer 80

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

Question 81

What must Take Place for Depolarisation?

Answer 81

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