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Biological Psych > Bio Psych 2b: More neurons, action potentials, and synapses > Flashcards

Bio Psych 2b: More neurons, action potentials, and synapses Flashcards

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1
Q

What is the resting potential?

A

The difference in charge in electrical charge between the inside and the outside of a neuron

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2
Q

What are all parts of a neuron covered by?

A

A membrane

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3
Q

What is the membrane composed of?

A

Two layers of phospholipid molecules (also known as a phospholipid bilayer)

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4
Q

What are phospholipid molecules?

A

Chains of fatty acids linked to a phosphate group

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5
Q

What is embedded among the phospholipids?

A

Cylindrical proteins that let certain chemicals pass

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6
Q

What happens when the membrane is at rest?

A

It maintains an electrical gradient

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7
Q

What is an electrical gradient also known as?

A

Polarisation

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8
Q

What is polarisation?

A

A difference in electrical charge between the inside and outside of the cell

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9
Q

Why does the inside of the membrane have a slightly negative charge compared to the outside?

A

Mainly because of negatively charged proteins inside the cell

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10
Q

What is the difference in voltage called?

A

The resting potential

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11
Q

What is one key feature of the membrane?

A

That it is selectively permeable

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12
Q

What are the charged ions that cross through the channels that are sometimes open and sometimes closed?

A

Sodium, potassium, calcium, and chloride

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13
Q

What can open these channels in the membrane?

A

Stimulation

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14
Q

What is a sodium-potassium pump?

A

A protein complex

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15
Q

What does the sodium-potassium pump do?

A

Repeatedly transports three sodium ions out of the cell while drawing two potassium ions in

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16
Q

Describe the concentration of sodium outside and inside the membrane

A

Sodium ions are more than 10 times more concentrated outside the membrane than inside

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17
Q

Describe the concentration of potassium inside and outside the membrane

A

Potassium ions are more concentrated inside than outside

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18
Q

What happens to sodium ions when they are pumped out?

A

They stay out

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19
Q

What happens to potassium ions when sodium ions are pumped out?

A

Some of the potassium in the neuron slowly leaks out, carrying a positive charge

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20
Q

What does the potassium leakage cause?

A

An increase in the electrical gradient across the membrane

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21
Q

What is one force that tends to push sodium into the cell?

A

The electrical gradient

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22
Q

Explain how the electrical gradient pushes sodium into the cell

A

Sodium is positively charged, and the inside of the cell is negatively charged, mainly because of negatively charged proteins. Opposite electrical charges attract, so the electrical gradient attracts sodium into the cell

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23
Q

What is the other forces that pushes sodium into the cell?

A

The concentration gradient

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24
Q

What is the concentration gradient?

A

The difference in distribution of ions across the membrane

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25
Q

How does the concentration gradient lead to sodium being pushed into the cell?

A

Sodium is more concentrated outside than inside, so just by the laws of probability, it is more likely to enter the cell than to leave. It would enter rapidly if it could, but the sodium channels are closed

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26
Q

What is potassium subject to?

A

Competing forces

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27
Q

What does the electrical gradient cause potassium to do?

A

It tends to attract potassium into the cell

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28
Q

How does the electrical gradient attract potassium into the cell?

A

Potassium is positively charged, and inside the cell is negatively charged

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29
Q

True or false: potassium is more concentrated inside the cell than outside

A

True

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30
Q

Due to potassium being more concentrated inside the cell than outside it, what does the concentration gradient do to potassium?

A

Drive it out of the cell

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31
Q

Do the almost completely closed potassium channels allow a small amount of potassium to flow more outward than inward?

A

Yes

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32
Q

What does the sodium-potassium pump continue to do to potassium?

A

Pull it back into the cell

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33
Q

What does the resting potential prepare the neuron to do?

A

To respond rapidly

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34
Q

What does excitation of the neuron do?

A

Open up sodium channels, letting sodium enter rapidly

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35
Q

When does the resting potential remain stable until?

A

Until the neuron is stimulated

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36
Q

What are the messages axons send called?

A

Action potentials

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37
Q

What does hyperpolarisation mean?

A

Increased polarisation as a result of increasing negative charge

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38
Q

What happens when potential reaches the threshold?

A

The membrane opens its sodium channels and permits sodium ions to flow into the cell, driving the membrane potential upward

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39
Q

What does any subthreshold stimulation produce?

A

A small response that quickly delays

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40
Q

What does any stimulation beyond the threshold produce?

A

A big response

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41
Q

What does any depolarisation that reaches or passes the threshold produce?

A

An action potential

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42
Q

What is the all-or-none law?

A

That the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it, provided that the stimulus reaches the threshold

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43
Q

What are the three main principles of the chemical events behind an action potential?

A
  1. At the start, sodium ions are mostly outside the neuron, and potassium ions are mostly inside. 2. Depolarising the membrane opens the sodium and potassium channels. 3. At the peak of the action potential, the sodium channels close
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44
Q

What does a neuron’s membrane contain?

A

Cylindrical proteins

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45
Q

What is a protein that allows sodium to cross called?

A

A sodium channel

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46
Q

What is a protein that allows potassium to cross called?

A

A potassium channel

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47
Q

What are potassium and ion channels called?

A

Voltage-gated channels

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48
Q

What are potassium and ion channels called?

A

Voltage-gated channels

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49
Q

Why are they called voltage-gated channels?

A

Because they open or close depending on the voltage across the membrane

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50
Q

Are the sodium channels open or closed at the resting potential?

A

Fully closed

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51
Q

Are the potassium channels open or closed at the resting potential?

A

Almost fully closed

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52
Q

What happens to the channels as the membrane becomes depolarised?

A

Both types of channels begin to open, allowing freer flow

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53
Q

At first, does opening the potassium channels make much difference?

A

At first, opening the potassium channels makes little difference

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54
Q

At first, does opening the sodium channels make much of a difference?

A

At first, opening the sodium channels makes a big difference

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55
Q

Why, at first, does opening the sodium channels make a big difference?

A

Because both the electrical gradient and the concentration gradient tend to drive sodium ions into the neuron. Sodium ions enter the cell rapidly, and the electrical potential across the membrane quickly passes beyond zero to a reversed polarity

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56
Q

What happens to sodium channels at the peak of the action potential?

A

They snap shut

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57
Q

What does depolarising the membrane do?

A

Opens potassium channels

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58
Q

What happens to the charge inside the cell after so many sodium ions have crossed the membrane?

A

The inside of the cell has a slight positive charge instead its usual negative charge

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59
Q

Now that the inside of the cell has a slight positive charge, what does this mean for the concentration gradient and the electrical gradient?

A

They drive potassium ions out of the cell

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60
Q

What occurs as a result of potassium channels remaining open after the sodium channels close?

A

Enough potassium leaves to drive the membrane back to its original level and then slightly beyond it

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61
Q

What happens to the membrane at the end of this process?

A

The membrane has restarted to its resting potential

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62
Q

What is the state of the inside of the neuron at the end of the process?

A

The inside of the neuron has slightly more sodium ions and slightly fewer potassium ions than before

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63
Q

What does the sodium-potassium pump eventually do?

A

Eventually, the sodium-potassium pump restores the original distribution of ions

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64
Q

Propagation of the axon potential: what enters the axon during an action potential?

A

Sodium ions enter the axon during an action potential

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65
Q

What is the charge of the spot where they enter temporarily in comparison with neighbouring areas along the axon?

A

Temporarily, the spot where they enter is positively charged in comparison with neighbouring areas along the axon

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66
Q

Where does this positive charge go?

A

The positive charge flows to neighbouring regions of the axon

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67
Q

What is the result of the positive charge flowing to neighbouring regions of the axon?

A

The positive charge flowing to neighbouring regions of the axon slightly depolarise the next area of the membrane, causing it to reach its threshold and open its sodium channels

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68
Q

What happens at the point of the sodium channels opening as a result of the positive charge flowing to neighbouring areas along the axon?

A

The membrane regenerates the action potential

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69
Q

In other words, what is happening along the axon?

A

The action potential travels along the axon

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70
Q

What does the term ‘propagation of the action potential’ describe?

A

The transmission of an action potential down an axon

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71
Q

Where does an action potential start?

A

In an axon and propagates without loss from start to finish

72
Q

What happens to the action potential at the start in an axon?

A

It “back-propagates” into the cell body and dendrites

73
Q

Do the cell body and dendrites conduct action potentials?

A

The cell body and dendrites do not conduct action potentials, but they passively register the electrical event that started in the nearby axon

74
Q

What happens when an action potential back-propagates into a dendrite?

A

The dendrite becomes more susceptible to the structural changes responsible for learning

75
Q

Summarise the 6 steps of the action potential

A
  1. When an area of the axon membrane reaches its threshold, sodium channels and potassium channels open
  2. Opening sodium channels lets sodium ions rush into the axon. At first, opening the potassium channels produces little effect
  3. Positive charge flows down the axon and opens voltage-gated sodium channels at the next point
  4. At the peak of the action potential, the sodium gates snap shut
  5. Because voltage-gated potassium channels remain open, potassium ions flow out of the axon, returning the membrane toward its original depolarisation
  6. A few milliseconds later, the voltage-dependent potassium channels close
76
Q

What happens to the electrical potential across the membrane when the action potential is at its peak?

A

The electrical potential across the membrane is above the threshold

77
Q

Why doesn’t the cell produce another action potential when the electrical potential across the membrane is above the threshold when the action potential is at its peak?

A

At the peak of the action potential, the sodium channels shut tightly and remain tightly shut for approximately the next millisecond. This period is the absolute refractory period

78
Q

What is the absolute refractory period?

A

The time when the membrane cannot produce an action potential, regardless of the stimulation

79
Q

What happens after the absolute refractory period?

A

The relative refractory period. The sodium channels relax a bit, but the departure of potassium ions has driven the membrane potential farther into negative territory than usual. At this time, the membrane is in a relative refractory period.

80
Q

What is the relative refractory period?

A

When a stronger-than-usual stimulus is necessary to initiate an action potential

81
Q

What are the two facts that the refractory period depends on?

A

The sodium channels are closed, and potassium is flowing out of the cell

82
Q

Which way does electrical charge flow?

A

In both directions

83
Q

What are sheaths of myelin?

A

An insulating material composed of fats and proteins

84
Q

Why did vertebrate axons evolve myelin sheaths

A

To increase the speed of the action potential

85
Q

Where are myelinated axons present in only?

A

Vertebrates

86
Q

What are myelinated axons covered with?

A

Layers of fats and proteins

87
Q

What is the myelin sheath interrupted periodically by?

A

Short sections called nodes of ranvier

88
Q

Where does the action potential start at in myelinated axons?

A

In myelinated axons, the action potential starts at the first node of ranvier

89
Q

At the first myelin segment, why can’t the action potential regenerate along the membrane between nodes?

A

The action potential cannot regenerate along the membrane between nodes because the axon has few if any sodium channels between nodes

90
Q

What happens after an action potential occurs at a node?

A

Sodium ions enter the axon and diffuse, pushing a chain of positive charge along the axon to the next node, where they quickly regenerate the action potential

91
Q

What is saltatory conduction?

A

The jumping of action potentials from node to node

92
Q

What does saltatory conduction do?

A

Provides rapid conduction of impulses

93
Q

In terms of energy, what does saltatory conduction do?

A

Conserves energy

94
Q

How does saltatory conduction conserve energy?

A

Instead of admitting sodium ions at every point along the axon and pumping them out, a myelinated axon admits sodium only at its nodes

95
Q

What are tiny neurons called?

A

Local neurons

96
Q

What do local neurons do?

A

They have no axon and communicate with their immediate neighbours

97
Q

Do local neurons produce action potentials?

A

They do not produce action potentials because they do not have an axon and they do not follow the all-or-none law

98
Q

In cells where there are no action potential produced, what happens?

A

Greater amounts of stimulation produce greater depolarisation, known as a graded potential. The graded potential spreads over the surface of the tiny neuron, declining in strength over distance

99
Q

What kind of effect do local neurons have on neighbouring cells?

A

Inhibitory effects

100
Q

Why are local neurons hard to study?

A

It is almost impossible to insert an electrode into a tiny cell without damaging it

101
Q

What are reflexes?

A

Automatic muscular responses to stimuli

102
Q

What is the reflex arc?

A

The circuit from sensory neuron to muscle response

103
Q

What must a reflex require because neurons are separate from one another?

A

Communication between neurons

104
Q

What properties of reflexes that suggest special processes at the junctions between neurons did Sherrington observe?

A
  1. Reflexes are slower than conduction along an axon
  2. Several weak stimuli presented at nearby places or times combine their effects
  3. When one set of muscles becomes excited, a different set becomes relaxed
105
Q

What did Sherrington find in terms of stimuli and what did he call this phenomenon?

A

Repeated stimuli within a brief time combine their effects. He called this phenomenon temporal summation, meaning summation over time

106
Q

Which neuron delivers transmission?

A

The presynaptic neuron

107
Q

Which neuron receives transmission?

A

The postsynaptic neuron

108
Q

What are action potentials always?

A

Depolarisations

109
Q

What can graded potentials be either of?

A

Graded potentials can be either depolarisations (excitatory) or hyperpolarisations (inhibitory) and they decay over both time and distance

110
Q

What is a graded depolarisation and what does it result from?

A

A graded depolarisation is an excitatory postsynaptic potential (EPSP) which results from sodium ions entering the neuron

111
Q

What is a graded hyperpolarisation and what is it produced by?

A

A graded hyperpolarisation is an inhibitory postsynaptic potential (IPSP), produced by a flow of negatively charged chloride ions into the cell

112
Q

In terms of summation, what do synapses have the property of and who found this?

A

Sherrington found that synapses have the property of spatial summation- summation over space

113
Q

When does temporal summation and spatial summation occur together?

A

Temporal summation and spatial summation occur together when a neuron receives input from several axons in succession

114
Q

State Sherrington’s explanation that assumes certain connections in the spinal cord

A

A pinch on the foot sends a message along a sensory neuron to an interneuron in the spinal cord that excites the motor neurons connected to the flexor muscles of that leg and the extensor muscles of the other legs. The interneuron also sends messages to inhibit the extensor muscles in that leg and the flexor muscles of the three other legs

115
Q

What happens at these synapses?

A

Input from an axon hyperpolarises the potsynaptic cell, moving the cell’s charge farther from the threshold and decreasing the probability of an action potential

116
Q

What do most neurons have in terms of firing rate?

A

Most neurons have a spontaneous firing rate

117
Q

What is a spontaneous firing rate?

A

A periodic production of action potentials even without synaptic input

118
Q

In such cases of a spontaneous firing rate, what do EPSPs do?

A

EPSPs increase the frequency of action potentials above the spontaneous rate

119
Q

In the case of a spontaneous firing rate, what do IPSPs do?

A

IPSPs decrease the frequency of action potentials below the spontaneous rate

120
Q

What were the overall findings from Loewi?

A

Stimulating one nerve released something that inhibited heart rate, and stimulating a different nerve released something that increased heart rate. Loewi concluded that nerves send messages by releasing chemicals

121
Q

Summarise the chemical events at a synapse

A
  1. The neuron synthesises chemicals that serve as neurotransmitters, either in the cell body or at the end of the axon
  2. Action potentials travel down the axon. At the presynaptic terminal, the depolarisation enables calcium to enter the cell. Calcium releases neurotransmitters from the terminals and into the synaptic cleft, the space between the presynaptic and postsynaptic neurons
  3. The released molecules diffuse across the narrow cleft, attach to receptors, and alter the activity of the postsynaptic neuron in any of several ways
  4. The neurotransmitter molecules separate from their receptors
  5. The neurotransmitter molecules may be taken back into the presynaptic neuron for recycling, or they may diffuse away
  6. Some postsynaptic cells send reverse messages to control the further release of neurotransmitter by presynaptic cells
122
Q

What are the chemicals that a neurone releases at a synapse?

A

Neurotransmitters or neuromodulators

123
Q

How do several drugs act?

A

By altering the synthesis of transmitters

124
Q

What helps increase the supply of dopamine?

A

L-dopa, a precursor to dopamine

125
Q

Describe the synthesis of acetylcholine

A

Acetyl coenzyme A (from metabolism) + choline (from metabolism or diet) -> acetylcholine

126
Q

Describe the synthesis of dopamine

A

Phenylalanine (from diet) -> tyrosine -> dopa -> dopamine

127
Q

Describe the synthesis of norepinephrine

A

Phenylalanine (from diet) -> tyrosine -> dopa -> dopamine -> norepinephrine

128
Q

Describe the synthesis of epinephrine

A

Phenylalanine (from diet) -> tyrosine -> dopa -> dopamine -> norepinephrine -> epinephrine

129
Q

Describe the synthesis of serotonin

A

Tryptophan (from diet) -> 5-hydroxytryptophan -> serotonin (5-hydroxytryptamine)

130
Q

Where are most neurotransmitters synthesised?

A

Most neurotransmitters are synthesised in the presynaptic terminal, near the point of release

131
Q

How and what does the presynaptic terminal store high concentrations of?

A

The presynaptic terminal stores high concentrations of neurotransmitter molecules in vesicles, tiny nearly spherical packets

132
Q

What and where does the presynaptic terminal also hold?

A

The presynaptic terminal also holds much neurotransmitter outside the vesicles

133
Q

Does an action potential by itself release the neurotransmitter at the end of the axon?

A

An action potential by itself does not release the neurotransmitter at the end of the axon

134
Q

How is the neurotransmitter released at the end of the axon?

A

Depolarisation opens voltage-dependent calcium channels in the presynaptic terminal,. The calcium entry causes exocytosis- a burst of release of neurotransmitter from the presynaptic neuron. The released neurotransmitter diffuses across the synaptic cleft to the postsynaptic membrane, where is attaches to a receptor

135
Q

How many transmitters do neurons release?

A

Neurons release a combination of two or more transmitters

136
Q

What does the effect of a neurotransmitter depend on?

A

the effect of a neurotransmitter depends on how it affects its receptor

137
Q

What may happen when a neurotransmitter attaches to its receptor?

A

When the neurotransmitter attaches to its receptor, the receptor may open a channel—exerting an ionotropic effect—or it may produce a slower but longer effect—metabotropic effect

138
Q

What happens when a neurotransmitter binds to an ionotropic receptor?

A

When the neurotransmitter binds to an ionotropic receptor, it twists the receptor just enough to open its central channel, which has a size and shape that lets one type of ion pass-through

139
Q

What is different about the channels controlled by a neurotransmitter?

A

In contrast to the voltage-gated channels along an axon, the channels controlled by a neurotransmitter are transmitter-gated or ligand-gated.

140
Q

What does Glutamate do and what do most of the inhibitory ionotropic synapses use?

A

Glutamate opens sodium channels. Most of the inhibitory ionotropic synapses use GABA (gamma-aminobutyric acid), which opens chloride channels

141
Q

What happens to the inner portion when the receptor is at rest?

A

When the receptor is at rest, the inner portion coils together tightly enough to block sodium passage.

142
Q

What are neuromodulators?

A

chemicals that affect receptors which control metabotropic effects

143
Q

What happens when a neurotransmitter attaches to a metabotropic receptor?

A

it bends the receptor protein that goes through the membrane of the cell. The other side of that receptor is attached to a G protein—a protein coupled to guanosine triphosphate(GTP), an energy-storing molecule. Bending the receptor protein detaches that G protein, which is then free to take its energy elsewhere in the cell

144
Q

What is the result of that G protein?

A

increased concentration of a second messenger, such as cyclic adenosine monophosphate (cyclic AMP), inside the cell

145
Q

What is the difference between the ionotropic synapse effect location vs the metabotropic synapse location?

A

An ionotropic synapse has effects localised to one point on the membrane, whereas a metabotropic synapse, by way of its second messenger, influences activity in much or all of the cell and over a longer time

146
Q

What can neuromodulators be released by and where do they diffuse to?

A

neuromodulators can be released by dendrites, by the cell body, or by the sides of the axon, and they diffuse to receptors in a wider area, not just a receptor immediately next to the point of release

147
Q

What are neurotransmitters released by?

A

Axon terminal

148
Q

Where are neurotransmitter receptors?

A

immediately adjacent

149
Q

When are the onset of effects?

A

Sudden

150
Q

How long are the duration of effects of neurotransmitters?

A

a few milliseconds

151
Q

what are neuromodulators released by?

A

cell body, dendrites, and side of axon

152
Q

where are neuromodulator receptors?

A

they are spread out

153
Q

How long are the duration of effects of neuromodulators?

A

seconds to minutes

154
Q

What can a drug that chemically resembles a neurotransmitter do?

A

it can bind to its receptor

155
Q

What is the reuptake process?

A

After the release of glutamate or GABA, specialised transporter proteins quickly move the molecules back into the presynaptic cell.

156
Q

What are the two purposes of reuptake?

A

This process, called reuptake, serves two purposes. One is recycling so that the presynaptic neuron has transmitters available for release again. The other is to halt the effect on the postsynaptic cell.

157
Q

When does acetylcholine undergo reuptake?

A

Acetylcholine undergoes reuptake only after the enzyme acetylcholinesterase breaks it into two fragments: acetate and choline

158
Q

What does the new choline do?

A

The choline diffuses back to the presynaptic neuron, which reattaches it to form acetylcholine again

159
Q

How can action potentials at a synapse impair transmission?

A

Rapid series of action potentials at a synapse can deplete the neurotransmitter faster than the presynaptic cell replenishes it, impairing transmission

160
Q

What happens after serotonin, epinephrine, norepinephrine, and dopamine activate a receptor?

A

The presynaptic neuron takes up much or most of the released neurotransmitter molecules for reuse

161
Q

Why is slow reuptake beneficial?

A

slow reuptake is a benefit because it enables the chemicals to build up enough concentration to have significant effects on their receptors

162
Q

What do stimulant drugs do to transporters?

A

Stimulant drugs inhibit the transporters for dopamine, serotonin, and norepinephrine, decreasing reuptake and prolonging the effects of the neurotransmitters

163
Q

What happens when stimulant drugs prevent the usual amount of dopamine reuptake?

A

enzymes break down much of the extra dopamine that stays in the synaptic cleft

164
Q

Why does a withdrawal state occur after stimulant drugs are taken?

A

The pre-synaptic cell needs extra time to replenish its supply. A few hours after taking a stimulant drug, a user has less than usual dopamine and enters a withdrawal state

165
Q

What are autoreceptors?

A

receptors sensitive to the same transmitter they release.

166
Q

What do they do?

A

These respond to the released transmitter by inhibiting further synthesis and release. That is, they provide negative feedback

167
Q

What are reverse transmitters and what do they do?

A

they are postsynaptic neurons that respond to stimulation by releasing chemicals that travel back to the presynaptic terminal to inhibit further release of transmitter

168
Q

What are the main synaptic effects of amphetamines

A

Blocks reuptake of dopamine and several other transmitters

169
Q

What are the main synaptic effects of cocaine?

A

Blocks reuptake of dopamine and several other transmitters

170
Q

What are the main synaptic effects of methylphenidate?

A

Blocks reuptake of dopamine and others, but gradually

171
Q

What are the main synaptic effects of MDMA?

A

Releases dopamine, serotonin, and norepinephrine

172
Q

What are the main synaptic effects of Nicotine?

A

Stimulates nicotinic-type acetylcholine receptor, which increases dopamine release

173
Q

What are the main synaptic effects of opiates?

A

Stimulates endorphin receptors

174
Q

What are the main synaptic effects of cannabinoids?

A

Excites negative feedback receptors on presynaptic cells

175
Q

What are the main synaptic effects of hallucinogens?

A

Stimulates serotonin type 2A receptors

176
Q

What is a gap junction?

A

When the membrane of one neurone makes direct contact with another at an electrical synapse (the contact is the gap junction)

177
Q

What happens during a gap junction?

A

Large pores of the membrane of one neuron line up precisely with pores in the membrane of the other cell. These pores are large enough for sodium and other ions to pass readily, and the pores are always open. Whenever one of the neurons is depolarized, sodium ions from that cell pass immediately into the other neuron and depolarize it, too

Biological Psych (6 decks)

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