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Brain and behaviour > Lecture 4 > Flashcards

Lecture 4 Flashcards

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1
Q

Physical basis of electrical charge

A

Matter = molecules
Molecules = elements
Atoms are the smallest particle of an element that has the properties of an element.

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2
Q

What do atoms consist of

A
  • Protons (+) and neutrons (0): inside the centre of the atom.
  • Electrons (-) outside nucleus: orbit in electron shells.
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3
Q

What are ions

A

Ions are atoms that:

  • Have a surplus of electrons (anions, negative ions)
  • Have a shortage of electrons (cations, positively charged ions).
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4
Q

What is the voltage range of neurons

A

0-220 mV

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5
Q

Magnitude of potential differences

A
  • Microvolt (uV (looking like a u) - radio & television receivers, EEGs.
  • Millivolt (mV) - audio & video signals, nervous activity
  • Volt (V) - penlight battery, outlet, car battery
  • Kilovolt (kV) - distribution of electricity, trains, trolleys
  • Megavolt (MV) - powerlines, lightning.
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6
Q

Current (+ types)

A

An electrical charge that moves (unit = Ampere (A))

  • Electrons flow from - to + = electron current.
  • High concentration to a low concentration.
  • Alternating current (AC)
  • Direct current (DC)
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7
Q

Alternating current

A

Home appliances with motors (e.g., vacuum cleaner)

  • In the AC, the direction of current changes.
  • Advantage: more efficient transport and easier to change voltage
  • Disadvantage: human body is more sensitive to AC.
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8
Q

Direct current

A

Nervous system, batteries.

  • In DC, the positive and negative terminals are always positive and negative.
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9
Q

0.5-2 mA

A

Unharmful, gives a light tingling sensation

  • Electric flyswatter
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10
Q

5-20 mA

A

Muscle cramps in arm and hands. Impossible to let go over 20 mA

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11
Q

20-40 mA

A

Breathing is obstructed, nerve centres can be paralysed.

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12
Q

40-200 mA

A

Heart stops working, blood circulation halts

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13
Q

200-100 mA

A

Burns in tissue, muscles and nerves

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14
Q

> 1000 mA

A

Poisoning of kidneys

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15
Q

Key ions to remember (4)

A
  1. Na+ = sodium ion
  2. K+ = potassium ion
  3. Cl- = chloride ion
  4. Ca^2+ = calcium ion
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16
Q

Max m/s for ions and electrons

A

NB: ions do not carry the same kind of electrical current that powers your phone.

  • Ions = max 90 m/s (324 km/h)
  • Electrons = 270,000 km/s (90% speed of light)
17
Q

3 ways ion movement produces electrical charges

A
  1. Diffusion
  2. Concentration gradient
  3. Voltage gradient
18
Q

Diffusion

A

Is a passive process.

  • Na ^+ binds with negative poles (O).
  • Cl ^- binds with positive poles (H).
19
Q

Resting potential general info

A

Difference in charge between intracellular and extracellular side ~-70 mV = resting potential (potential energy)

20
Q

What ions are critical to resting potential?

A
  • Cations: Na+ (Sodium), K+ (Potassium)
  • Anions: Cl- (Chloride), A- (Large protein molecules)
  • Intracellular: more A- and K+
  • Extracellular: more Cl- and Na+.
  • NB: Sodium (Na+) and Potassium (K+) most ‘actively’ involved in neural communication.
21
Q

What ions have a higher concentration inside the axon?

A

A- and K+

22
Q

What ions are more concentrated outside the axon?

A

Cl- and Na+

23
Q

Maintaining resting potential

A

Channels allow K+ influx and efflux (passive transport) to balance intracellular A-.

Gates prevent influx of Na+.

Na+/K+ pump pumps Na+ out of the cell and K+ into the cell.

  • 3:2 costs energy!
24
Q

2 options for stimulating a neuron

A

Apply a negative charge (voltage)

Apply a positive charge (voltage)

  • Both options induce graded potentials
25
Q

Applying a positive charge to stimulate a neuron

A

Depolarisation –> Na+ influx

  • Potential difference decreases (e.g., -70mV to -65 mV)
26
Q

Applying a negative charge to stimulate a neuron

A

Hyperpolarisation –> K+ efflux or Cl- influx

  • Potential difference increases (e.g., -70mV to -73mV)
27
Q

Graded potentials

A

Small fluctuations across the cell membrane that extinguish with distance and can be summed.

  • Gated channels
  • On dendrites and cell body
28
Q

Action potential general

A

A brief (1ms) and large all or nothing potential that temporarily reverses the membranes polarity.

  • Refractory period: a neuron needs to wait until the action potential is over before it can generate another action potential
  • Voltage sensitive channels
  • On axon hillock and axon (in some neurons also on dendrites (back propagation))
29
Q

How action potential arises

A

When the potential difference over the membrane exceeds a certain level

  • Firing threshold (e.g., -50 mV).
30
Q

Absolutely refractory period

A

Depolarisation + repolarisation

  • It is absolutely impossible for the cell to fire.
31
Q

Relatively refractory period

A

Hyperpolarisation

  • The cell may fire, but it is more difficult.
32
Q

How does the action potential propagate along the axon (2 ways)?

A
  1. Continuous conduction
  2. Saltatory conduction
33
Q

Continuous conduction

A

Potential difference in one place activates nearby gates: domino effect

34
Q

Saltatory conduction

A

Axons are often wrapped in myelin (isolating layer).

  • There are small ‘gaps’ in this isolation –> nodes of Ranvier
  • The action potential can ‘jump’ from node to node

NB: Saltatory conduction is faster and costs less energy than normal propagation.

35
Q

Multiple sclerosis

A

Degradation of the myeline sheath in the CNS (oligodendroglia degeneration)

36
Q

How do neurons communicate?

A

Cell A = presynaptic
Cell B = postsynaptic

  • An action potential is generated by presynaptic Cell A
  • May cause graded potentials at postsynaptic Cell B.
37
Q

Excitation of Cell B (= turn on)

A

Excitatory postsynaptic potential (EPSP) may depolarise Cell B (bring it closer to firing threshold)

  • EPSPs produced at the same time, but on separate parts of he membrane do not influence each other.
  • EPSPs produced at the same time and close together add to form a larger EPSP.
38
Q

Inhibition of Cell B (= turn off)

A

Inhibitory postsynaptic potential (IPSP) may hyperpolarise Cell B (bring it further away from firing threshold).

39
Q

The net effect of all EPSP’s and IPSP’s determines whether a cell fires

A

If the potential difference at the initial segment on the axon hillock becomes smaller than the -50 mV threshold, an action potential is propagated along the axon.

Brain and behaviour (14 decks)

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