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Neuroscience > Chapter 2 - Communication Within the Nervous System > Flashcards

Chapter 2 - Communication Within the Nervous System Flashcards

1
Q

What are neurons (3)?

A

Specialized cells that convey sensory information into the brain; carry out the operations involved in thought, feeling, and action; and transmit commands out into the body to control muscles and organs.

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2
Q

How many neurons are estimated to be in the human brain?

A

86 Billion

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3
Q

What types of cells each contain about 50% of the brain’s total cells?

A

Neurons and Glial cells

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4
Q

What are 4 things neurons are responsible for?

A

Movements, thoughts, memories, emotions.

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5
Q

How many neurons does the higher brain contain?

A

17 billion.

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6
Q

How many neurons does the cerebellum contain?

A

69 billion.

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7
Q

How many neurons does the spinal cord contain?

A

1 billion.

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8
Q

What is the most prominent part of the neuron?

A

The cell body/soma.

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9
Q

What is the cell body filled with?

A

Cytoplasm and organelles.

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10
Q

What is the largest organelle in the cell body?

A

The nucleus.

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11
Q

What does the nucleus contain?

A

The cell’s chromosomes.

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12
Q

What are the 3 major kinds of neurons?

A

Motor neurons, sensory neurons, and interneurons.

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13
Q

What is the main purpose of a motor neuron?

A

To carry commands to the muscles and organs.

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14
Q

What are dendrites?

A

Extension that branch out from the cell body and carries information to other locations.

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15
Q

Where is the myelin sheath located?

A

Wrapped around the axon.

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16
Q

What are axon terminals?

A

Swellings at the end of the axon branches that contain neurotransmitters.

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17
Q

What do neurotransmitters do?

A

Chemicals the neuron releases to communicate with a muscle, an organ or the next neuron in a chain.

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18
Q

What is the largest part of the neuron?

A

The cell body/soma.

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19
Q

What do sensory neurons do?

A

Carry information from the body and from the outside world into the brain and spinal cord.

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20
Q

Which type of neuron’s axon and dendrites extend in several directions form the cell body?

A

Motor neurons.

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21
Q

What type of neuron is multipolar?

A

Motor neurons.

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22
Q

What type of neurons can be either unipolar or bipolar?

A

Sensory neurons.

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23
Q

Which type of neuron has a single short stalk that divides into two brances?

A

Unipolar sensory neurons.

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24
Q

Which type of neuron has an axon on one side of the cell body and a dendritic process on the other?

A

Bipolar sensory neurons.

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25
Q

Which 2 types of neurons are specialized for transmission over long distances?

A

Motor and sensory neurons.

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26
Q

What is the main purpose of interneurons?

A

To connect one neuron to another in the same part of the brain or spinal cord.

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27
Q

Why don’t interneurons need long axons?

A

They make connections over very short distances.

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28
Q

What do interneurons do in the spinal cord?

A

They bridge between sensory neurons and motor neurons to produce a reflex.

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29
Q

What do interneurons do in the brain?

A

They connect adjacent neurons to carry out complex processing.

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30
Q

What is the most numerous type of neurons?

A

Interneurons.

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31
Q

What allows the neuron’s ability to communicate?

A

The neural membrane.

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32
Q

What is the neural membrane made of?

A

Lipid and protein.

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33
Q

What feature of the neural membrane allows for polarization?

A

Selective permeability.

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34
Q

What is polarization?

A

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

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35
Q

What is a voltage?

A

A difference in electrical charge between two points.

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36
Q

How is voltage expressed?

A

As a comparison of the inside of the neuron with the outside.

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37
Q

What is the resting potential?

A

The difference in charge between the inside and outside of the membrane of a neuron at rest.

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38
Q

What is the typical resting potential of a neuron?

A

Around -70mV.

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39
Q

What are ions?

A

Atoms that are charged because they have lost or gained one or more electrons.

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40
Q

What causes the resting potential?

A

Unequal distribution of electrical charges on the two sides of the neural membrane.

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41
Q

What causes neurons to move through the membrane to the side where they are less concentrated?

A

Force of diffusion.

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42
Q

What causes ions to be repelled from the side that is similarly charges and attracted to the side that is oppositely charges?

A

Electrostatic pressure.

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43
Q

What is the sodium-potassium pump made of?

A

Large protein molecules that move sodium ions through the cell membrane to the outside and potassium ions back inside.

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44
Q

What is the exchange rate of the sodium-potassium pump?

A

3 sodium ions to every 2 potassium ions.

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45
Q

What accounts for an estimated 40% of the neuron’s energy expenditure?

A

The sodium-potassium pump.

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46
Q

What stores the energy to power the action potential?

A

The resting potential.

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47
Q

What are ion channels?

A

Pores in the membrane formed by proteins that gate the flow of ions between the extracellular and intracellular fluids.

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48
Q

How are chemically gated channels opened?

A

By ligands (neurotransmitters or hormones).

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49
Q

How are electrically gated channels opened?

A

By a change in the electrical potential of the membrane.

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50
Q

How is a neuron usually stimulated (2)?

A

By inputs that arrive on the neuron’s dendrites and/or cell body from another neuron for from a sensory receptor.

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51
Q

What does an excitatory cause?

A

A slight partial depolarization.

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52
Q

What happens when an excitatory signal causes a slight partial depolarization?

A

The polarity in a small area of the membrane is shifted towards zero which disturbs the ion balance in the adjacent membrane so the disturbance flows down the dendrites and across the cell membrane.

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53
Q

What does it mean that a partial depolarization is decremental?

A

It is effective over only very short distances.

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54
Q

What is another term for partial depolarization?

A

Local potential.

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55
Q

How are ion channels in the axon gated?

A

Electrically.

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56
Q

What is the typical threshold for activating an ion channel?

A

About 10mV more positive than the resting potential.

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57
Q

What happens when an ion channel is activated?

A

It initiates an action potential.

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58
Q

What is an action potential?

A

An abrupt depolarization of the the membrane that allows the neuron to communicate over long distance.

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59
Q

At what rate to sodium ions rush into the axon when the channels open?

A

500 times greater than normal.

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60
Q

What does the term resting potential imply?

A

That the voltage across the resting neuron membrane is stored energy.

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61
Q

What happens when sodium channels open (2)?

A

A small area inside the membrane becomes fully depolarized to zero; the potential overshoots to around +30 or 40mV making the interior at that location temporarily positive.

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62
Q

What happens at the peak of the action potential?

A

Voltage sensors in the sodium channels detect the depolarization and close a gate which inactivates the channel and prevents further sodium ion influx.

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63
Q

What happens to voltage-gated potassium ion channels at depolarization?

A

They open and the positive charge + the concentration of potassium ions inside the membrane combine to force potassium ions out.

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64
Q

How long does the action potential last?

A

About 1 millisecond.

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65
Q

Which ions have participated in the action potential?

A

Only those in a very thin layer on either side of the membrane.

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66
Q

What happens to nearby sodium channels when depolarization occurs?

A

It causes a new action potential to be triggered right next to the first one creating a chain of action potentials that move through the axon.

67
Q

Does anything physically move down the axon during an action potential?

A

No.

68
Q

What happens when the action potential reaches the terminal?

A

They pass the signal on to the next neuron in the chain (or to an organ or a muscle).

69
Q

What are two ways that the action potential differs from the local potential that initiates it?

A

The action potential is ungraded and is nondecremental.

70
Q

What does it mean that the local potential is a graded potential?

A

It varies in magnitude with the strength of the stimulus that produced it.

71
Q

What does it mean that the action potential is ungraded?

A

It operates according to the all-or-none law.

72
Q

What is the all-or-none law?

A

An action potential occurs at full strength or does not occur at all.

73
Q

Does a larger graded potential produce a larger action potential?

A

No - due to the all-or-none law.

74
Q

What does it mean that the action potential is nondecremental?

A

It travels down the axon without any decrease in size, propagated anew and at full strength at each successive point along the way.

75
Q

What is a consequence of the action potential being ungraded?

A

Its size cannot carry information about the intensity of the initiating stimulus.

76
Q

What is one way stimulus intensity is represented?

A

By the number of neurons firing - a more intense stimulus will recruit firing in neurons with higher thresholds and therefore in more neurons.

77
Q

What is optogenetics?

A

A new research that allows researchers to create light-responsive channels (and receptors) in neurons so that they can be controlled by light.

78
Q

What is the relative refractory period?

A

When the potassium channels remain open for a few milliseconds following the absolute refractory period.

79
Q

What is the absolute refractory period?

A

When the neuron cannot generate another impulse for a millisecond or so with the sodium channels inactivated at the end of the action potential.

80
Q

What does the absolute refractory period do?

A

It limits how frequently the neuron can generate new action potentials.

81
Q

What is a second effect of the absolute refractory period?

A

Action potentials can only initiate new potentials in the forward direction, not behind them.

82
Q

What happens during the relative refractory period?

A

Another action potential can be generated but only by a stronger-than-threshold stimulus.

83
Q

What is the rate law?

A

The axon encodes stimulus intensity not in the size of its action potential but in its firing rate.

84
Q

What are glial cells?

A

Nonneural cells that provide a number of supporting functions to neurons.

85
Q

What is glia derived from?

A

The Greek word for glue.

86
Q

What is one of the most important functions of glial cells?

A

To increase the speed of conduction in neurons.

87
Q

Does conduction speed increase in direct proportion to axon size?

A

No - to reach 4 times the conduction speed size would need to increase by 4-square.

88
Q

How have vertebrates developed a way for faster conduction speed in neurons?

A

Myelination.

89
Q

What is myelin?

A

A fatty tissue produced by myelin that wraps around the axon to insulate it from the surrounding fluid and from other neurons.

90
Q

What does myelin cover?

A

Just the axon, not the cell body.

91
Q

What type of glial cell produces myelin in the brain and spinal cord?

A

Oligodendrocytes.

92
Q

What type of glial cell produces myelin in the rest of the nervous system (not brain and spinal cord)?

A

Schwann cells.

93
Q

What do almost 75% of the glial cells in the brain do?

A

Produce myelin - oligodendrocytes.

94
Q

Why can’t action potentials occur under the myelin sheath?

A

There are very few sodium channels under it.

95
Q

What are the gaps in the myelin sheath called?

A

Nodes of Ranvier.

96
Q

How do action potentials jump from node to node?

A

By saltatory conduction.

97
Q

What is saltatory conduction?

A

How action potentials jump from node to node along the axon.

98
Q

What are 3 benefits of having myelination and nodes of Ranvier?

A

The myelin insulates and reduces capacitance; breaks in myelination causes the signal to regenerate by an action potential at every node; myelination causes neurons to use less energy because there is less work for the sodium-potassium pumps.

99
Q

What is capacitance?

A

An electrical effect on the membrane that causes movement of ions down the axon to slow down.

100
Q

What do glial cells do during fetal development?

A

They form radial glial scaffolds that guide new new neurons to their destinations.

101
Q

What are 2 functions of microglia?

A

They provide energy to neurons and respond to injury and disease by removing cellular debris.

102
Q

What happens to myelin in diseases like multiple sclerosis?

A

Myelin is destroyed which increases capacitance and reduces the distance that graded potentials can travel before dying out. Conduction slows or stops in affected neurons.

103
Q

What are 2 functions of astrocytes?

A

Neurons form 7 times as many connections in their presence and play a key role in learning.

104
Q

What is the connection between two neurons called?

A

A synapse.

105
Q

What is the origin of the word synapse?

A

Latin “to grasp”

106
Q

Are neurons in direct physical contact at the synapse?

A

No - separated by synaptic cleft.

107
Q

What is the synaptic cleft?

A

The small gap that neurons are separated by.

108
Q

What is the presynaptic neuron?

A

The neuron that is transmitting to another.

109
Q

What is the postsynaptic neuron?

A

The receiving neuron.

110
Q

How did physiologists assume neurons communicated up until the 1920s?

A

By an electrical current.

111
Q

Who demonstrated that synaptic transmission is (mostly) chemical?

A

Otto Loewi.

112
Q

What did Otto’s Loewi’s experiments on frogs demonstrate (2)?

A

That synaptic transmission is (mostly) chemical and that neurons release at least 2 difference chemicals that have opposite effects.

113
Q

Where are neurotransmitters stored?

A

In the terminals in membrane-enclosed containers called vesicles.

114
Q

What are vesicles?

A

Membrane-enclosed containers in the terminals that store neurotransmitters.

115
Q

What is exocytosis?

A

When calcium ions enter the terminals and cause the vesicles nearest the membrane to fuse with it and release neurotransmitters to diffuse across the synaptic cleft.

116
Q

What ion triggers exocytosis?

A

Calcium.

117
Q

What type of channels does the action potential open when it arrives at the terminals?

A

Calcium channels.

118
Q

What happens with the neurotransmitter reaches the postsynaptic neuron?

A

It docks with protein receptors that match the molecular shape of the transmitter molecules (like a key in a lock). This activation causes ion channels in the membrane to open.

119
Q

What do ionotropic receptors do?

A

They open the channels directly to produce the immediate reactions required for muscle activity and sensory processing.

120
Q

What do metabotropic receptors do?

A

They open channels indirectly and slowly to produce longer-lasting effects.

121
Q

What happens when neurotransmitters open the channels at the postsynaptic neuron?

A

It sets off the graded potential that initiates the action potential.

122
Q

How long does the chemical jump across the synapse take?

A

A couple of milliseconds.

123
Q

What are the 2 effects that opening ion channels on the dendrites and cell body have?

A

It causes partial depolarization or increased polarization.

124
Q

What is partial depolarization?

A

Excitatory and facilitates the occurrence of an action potential.

125
Q

What is increased polarization?

A

Inhibitory and makes an action potential less likely to occur.

126
Q

What is another term for partial depolarization?

A

Hypopolarization.

127
Q

What is another term for increased polarization?

A

Hyperpolarization.

128
Q

What is hypopolarization?

A

Excitatory and facilitates the occurrence of an action potential.

129
Q

What is hyperpolarization?

A

Inhibitory and makes an action potential less likely to occur.

130
Q

What helps to prevent runaway excitation?

A

Inhibition.

131
Q

What is one cause of uncontrolled neural storms that sweep across the brain during an epileptic seizure?

A

A deficiency in receptors for an inhibitory transmitter.

132
Q

What determines whether the effect on the postsynaptic neuron if facilitating or inhibiting (2)?

A

A combination of which transmitter is released and the type of receptors on the postsynaptic neuron.

133
Q

What is an excitatory postsynaptic potential (EPSP)?

A

When receptors open sodium channels producing hypopolarization of the dendrites and cell body.

134
Q

What is an inhibitory postsynaptic potential (IPSP)?

A

When receptors open potassium, chloride, or both channels and produces a hyperpolarization of the dendrites and cell body.

135
Q

Where is the axon hillock?

A

Where the axon joins the cell body.

136
Q

How many inputs does a typical neuron receive from other neurons?

A

Approx. 1,000

137
Q

How many synaptic connections can a neuron have in most parts of the brain?

A

10,000

138
Q

How many synaptic connections can a neuron have in the cerebellum?

A

100,000

139
Q

What are 2 advantages of a single neuron not being able to cause a postsynaptic neuron to fire/prevent it from firing?

A

It ensure that a neuron will not be fired by the spontaneous activity of a single presynaptic neuron and it allows the neuron to combine multiple inputs into a more complex message.

140
Q

What are the 2 ways that potentials are combined at the axon hillock?

A

Spatial summation and temporal summation.

141
Q

What is spatial summation?

A

Combines potentials occurring simultaneously at different locations on the dendrites and cell body.

142
Q

What is temporal summation?

A

Combines potentials arriving a short time apart from either the same or separate inputs.

143
Q

What is the effect of summation combining EPSPs?

A

It makes an action potential more likely to occur.

144
Q

What is the effect of summation combining IPSPs?

A

It makes it more difficult for incoming EPSPs to trigger an action potential by making the interior even more negative.

145
Q

What are 2 effects of a neuron being able to summate inputs from multiple sources?

A

It becomes and information integrator and can function as a decision maker.

146
Q

What happens in the reuptake process?

A

Transmitters are taken back in to the terminals by membrane proteins called transporters and are repackaged in vesicles and used again.

147
Q

What are 3 ways neurotransmitters are recycled?

A

Reuptake, absorbed by astrocytes, or broken down through inactivation.

148
Q

What are synapses called that target dendrites?

A

Axodendritic.

149
Q

What are synapses called that target cell bodies?

A

Axosomatic.

150
Q

What happens at axoaxonic synapses?

A

A third neuron releases transmitter onto the terminals of the presynaptic neuron.

151
Q

What happens in presynaptic excitation or presynaptic inhibition?

A

It increases or decreases the presynaptic neuron’s release of neurotransmitter onto the postsynaptic neuron.

152
Q

What is one way that an axoaxonic synapse adjusts a presynaptic terminal’s activity?

A

By regulating the amount of calcium entering the terminal.

153
Q

What are 2 ways that neurons regulate their own synaptic activity?

A

Through autoreceptors and glial cells.

154
Q

How do autoreceptors contribute to neurons regulating their own synaptic activity?

A

Autoreceptors on the presynaptic terminals sense the amount of transmitter in the cleft; if the amount is excessive the presynaptic neuron reduces its output.

155
Q

How do glial cells contribute to neurons regulating their own synaptic activity?

A

They surround the synapse and prevent neurotransmitter from spreading to other synapses and some can remove neurotransmitter form the synaptic cleft and recycle it for the neuron’s reuse.

156
Q

What 2 types of receptors detect acetylcholine?

A

The nicotinic receptor and the muscarinic receptor.

157
Q

What is Dale’s principle?

A

The idea that a neuron is capable of releasing only one transmitter.

158
Q

What are the 3 ways a neuron can release multiple neurotransmitters at once?

A

Corelease, cotransmission, and releasing different transmitters for its various terminals.

159
Q

What is corelease?

A

When transmitters are packaged in the same vesicles.

160
Q

What is cotransmission?

A

When vesicles containing different transmitters in the same terminal are triggered to release at the same time.

161
Q

What provides an opportunity for coding to carry complex information involved in brain communication?

A

That neuron information often travels over specialized pathways.

162
Q

What are neural networks?

A

Groups of neurons that function together to carry out a process.

163
Q

What is an antagonist?

A

Any substance that reduces the effect of a neurotransmitter.

164
Q

What is the Human Connectome Project?

A

A large-scale, multi-university effort to map the brain’s circuits.

Neuroscience (6 decks)

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