Chapter 2 - Communication Within the Nervous System Flashcards
(164 cards)
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.
2
Q
How many neurons are estimated to be in the human brain?
A
86 Billion
3
Q
What types of cells each contain about 50% of the brain’s total cells?
A
Neurons and Glial cells
4
Q
What are 4 things neurons are responsible for?
A
Movements, thoughts, memories, emotions.
5
Q
How many neurons does the higher brain contain?
A
17 billion.
6
Q
How many neurons does the cerebellum contain?
A
69 billion.
7
Q
How many neurons does the spinal cord contain?
A
1 billion.
8
Q
What is the most prominent part of the neuron?
A
The cell body/soma.
9
Q
What is the cell body filled with?
A
Cytoplasm and organelles.
10
Q
What is the largest organelle in the cell body?
A
The nucleus.
11
Q
What does the nucleus contain?
A
The cell’s chromosomes.
12
Q
What are the 3 major kinds of neurons?
A
Motor neurons, sensory neurons, and interneurons.
13
Q
What is the main purpose of a motor neuron?
A
To carry commands to the muscles and organs.
14
Q
What are dendrites?
A
Extension that branch out from the cell body and carries information to other locations.
15
Q
Where is the myelin sheath located?
A
Wrapped around the axon.
16
Q
What are axon terminals?
A
Swellings at the end of the axon branches that contain neurotransmitters.
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.
18
Q
What is the largest part of the neuron?
A
The cell body/soma.
19
Q
What do sensory neurons do?
A
Carry information from the body and from the outside world into the brain and spinal cord.
20
Q
Which type of neuron’s axon and dendrites extend in several directions form the cell body?
A
Motor neurons.
21
Q
What type of neuron is multipolar?
A
Motor neurons.
22
Q
What type of neurons can be either unipolar or bipolar?
A
Sensory neurons.
23
Q
Which type of neuron has a single short stalk that divides into two brances?
A
Unipolar sensory neurons.
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.
25
Which 2 types of neurons are specialized for transmission over long distances?
Motor and sensory neurons.
26
What is the main purpose of interneurons?
To connect one neuron to another in the same part of the brain or spinal cord.
27
Why don't interneurons need long axons?
They make connections over very short distances.
28
What do interneurons do in the spinal cord?
They bridge between sensory neurons and motor neurons to produce a reflex.
29
What do interneurons do in the brain?
They connect adjacent neurons to carry out complex processing.
30
What is the most numerous type of neurons?
Interneurons.
31
What allows the neuron's ability to communicate?
The neural membrane.
32
What is the neural membrane made of?
Lipid and protein.
33
What feature of the neural membrane allows for polarization?
Selective permeability.
34
What is polarization?
A difference in electrical charge between the inside and outside of the cell.
35
What is a voltage?
A difference in electrical charge between two points.
36
How is voltage expressed?
As a comparison of the inside of the neuron with the outside.
37
What is the resting potential?
The difference in charge between the inside and outside of the membrane of a neuron at rest.
38
What is the typical resting potential of a neuron?
Around -70mV.
39
What are ions?
Atoms that are charged because they have lost or gained one or more electrons.
40
What causes the resting potential?
Unequal distribution of electrical charges on the two sides of the neural membrane.
41
What causes neurons to move through the membrane to the side where they are less concentrated?
Force of diffusion.
42
What causes ions to be repelled from the side that is similarly charges and attracted to the side that is oppositely charges?
Electrostatic pressure.
43
What is the sodium-potassium pump made of?
Large protein molecules that move sodium ions through the cell membrane to the outside and potassium ions back inside.
44
What is the exchange rate of the sodium-potassium pump?
3 sodium ions to every 2 potassium ions.
45
What accounts for an estimated 40% of the neuron's energy expenditure?
The sodium-potassium pump.
46
What stores the energy to power the action potential?
The resting potential.
47
What are ion channels?
Pores in the membrane formed by proteins that gate the flow of ions between the extracellular and intracellular fluids.
48
How are chemically gated channels opened?
By ligands (neurotransmitters or hormones).
49
How are electrically gated channels opened?
By a change in the electrical potential of the membrane.
50
How is a neuron usually stimulated (2)?
By inputs that arrive on the neuron's dendrites and/or cell body from another neuron for from a sensory receptor.
51
What does an excitatory cause?
A slight partial depolarization.
52
What happens when an excitatory signal causes a slight partial depolarization?
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.
53
What does it mean that a partial depolarization is decremental?
It is effective over only very short distances.
54
What is another term for partial depolarization?
Local potential.
55
How are ion channels in the axon gated?
Electrically.
56
What is the typical threshold for activating an ion channel?
About 10mV more positive than the resting potential.
57
What happens when an ion channel is activated?
It initiates an action potential.
58
What is an action potential?
An abrupt depolarization of the the membrane that allows the neuron to communicate over long distance.
59
At what rate to sodium ions rush into the axon when the channels open?
500 times greater than normal.
60
What does the term resting potential imply?
That the voltage across the resting neuron membrane is stored energy.
61
What happens when sodium channels open (2)?
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.
62
What happens at the peak of the action potential?
Voltage sensors in the sodium channels detect the depolarization and close a gate which inactivates the channel and prevents further sodium ion influx.
63
What happens to voltage-gated potassium ion channels at depolarization?
They open and the positive charge + the concentration of potassium ions inside the membrane combine to force potassium ions out.
64
How long does the action potential last?
About 1 millisecond.
65
Which ions have participated in the action potential?
Only those in a very thin layer on either side of the membrane.
66
What happens to nearby sodium channels when depolarization occurs?
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
Does anything physically move down the axon during an action potential?
No.
68
What happens when the action potential reaches the terminal?
They pass the signal on to the next neuron in the chain (or to an organ or a muscle).
69
What are two ways that the action potential differs from the local potential that initiates it?
The action potential is ungraded and is nondecremental.
70
What does it mean that the local potential is a graded potential?
It varies in magnitude with the strength of the stimulus that produced it.
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What does it mean that the action potential is ungraded?
It operates according to the all-or-none law.
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What is the all-or-none law?
An action potential occurs at full strength or does not occur at all.
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Does a larger graded potential produce a larger action potential?
No - due to the all-or-none law.
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What does it mean that the action potential is nondecremental?
It travels down the axon without any decrease in size, propagated anew and at full strength at each successive point along the way.
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What is a consequence of the action potential being ungraded?
Its size cannot carry information about the intensity of the initiating stimulus.
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What is one way stimulus intensity is represented?
By the number of neurons firing - a more intense stimulus will recruit firing in neurons with higher thresholds and therefore in more neurons.
77
What is optogenetics?
A new research that allows researchers to create light-responsive channels (and receptors) in neurons so that they can be controlled by light.
78
What is the relative refractory period?
When the potassium channels remain open for a few milliseconds following the absolute refractory period.
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What is the absolute refractory period?
When the neuron cannot generate another impulse for a millisecond or so with the sodium channels inactivated at the end of the action potential.
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What does the absolute refractory period do?
It limits how frequently the neuron can generate new action potentials.
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What is a second effect of the absolute refractory period?
Action potentials can only initiate new potentials in the forward direction, not behind them.
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What happens during the relative refractory period?
Another action potential can be generated but only by a stronger-than-threshold stimulus.
83
What is the rate law?
The axon encodes stimulus intensity not in the size of its action potential but in its firing rate.
84
What are glial cells?
Nonneural cells that provide a number of supporting functions to neurons.
85
What is glia derived from?
The Greek word for glue.
86
What is one of the most important functions of glial cells?
To increase the speed of conduction in neurons.
87
Does conduction speed increase in direct proportion to axon size?
No - to reach 4 times the conduction speed size would need to increase by 4-square.
88
How have vertebrates developed a way for faster conduction speed in neurons?
Myelination.
89
What is myelin?
A fatty tissue produced by myelin that wraps around the axon to insulate it from the surrounding fluid and from other neurons.
90
What does myelin cover?
Just the axon, not the cell body.
91
What type of glial cell produces myelin in the brain and spinal cord?
Oligodendrocytes.
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What type of glial cell produces myelin in the rest of the nervous system (not brain and spinal cord)?
Schwann cells.
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What do almost 75% of the glial cells in the brain do?
Produce myelin - oligodendrocytes.
94
Why can't action potentials occur under the myelin sheath?
There are very few sodium channels under it.
95
What are the gaps in the myelin sheath called?
Nodes of Ranvier.
96
How do action potentials jump from node to node?
By saltatory conduction.
97
What is saltatory conduction?
How action potentials jump from node to node along the axon.
98
What are 3 benefits of having myelination and nodes of Ranvier?
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
What is capacitance?
An electrical effect on the membrane that causes movement of ions down the axon to slow down.
100
What do glial cells do during fetal development?
They form radial glial scaffolds that guide new new neurons to their destinations.
101
What are 2 functions of microglia?
They provide energy to neurons and respond to injury and disease by removing cellular debris.
102
What happens to myelin in diseases like multiple sclerosis?
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
What are 2 functions of astrocytes?
Neurons form 7 times as many connections in their presence and play a key role in learning.
104
What is the connection between two neurons called?
A synapse.
105
What is the origin of the word synapse?
Latin "to grasp"
106
Are neurons in direct physical contact at the synapse?
No - separated by synaptic cleft.
107
What is the synaptic cleft?
The small gap that neurons are separated by.
108
What is the presynaptic neuron?
The neuron that is transmitting to another.
109
What is the postsynaptic neuron?
The receiving neuron.
110
How did physiologists assume neurons communicated up until the 1920s?
By an electrical current.
111
Who demonstrated that synaptic transmission is (mostly) chemical?
Otto Loewi.
112
What did Otto's Loewi's experiments on frogs demonstrate (2)?
That synaptic transmission is (mostly) chemical and that neurons release at least 2 difference chemicals that have opposite effects.
113
Where are neurotransmitters stored?
In the terminals in membrane-enclosed containers called vesicles.
114
What are vesicles?
Membrane-enclosed containers in the terminals that store neurotransmitters.
115
What is exocytosis?
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
What ion triggers exocytosis?
Calcium.
117
What type of channels does the action potential open when it arrives at the terminals?
Calcium channels.
118
What happens with the neurotransmitter reaches the postsynaptic neuron?
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
What do ionotropic receptors do?
They open the channels directly to produce the immediate reactions required for muscle activity and sensory processing.
120
What do metabotropic receptors do?
They open channels indirectly and slowly to produce longer-lasting effects.
121
What happens when neurotransmitters open the channels at the postsynaptic neuron?
It sets off the graded potential that initiates the action potential.
122
How long does the chemical jump across the synapse take?
A couple of milliseconds.
123
What are the 2 effects that opening ion channels on the dendrites and cell body have?
It causes partial depolarization or increased polarization.
124
What is partial depolarization?
Excitatory and facilitates the occurrence of an action potential.
125
What is increased polarization?
Inhibitory and makes an action potential less likely to occur.
126
What is another term for partial depolarization?
Hypopolarization.
127
What is another term for increased polarization?
Hyperpolarization.
128
What is hypopolarization?
Excitatory and facilitates the occurrence of an action potential.
129
What is hyperpolarization?
Inhibitory and makes an action potential less likely to occur.
130
What helps to prevent runaway excitation?
Inhibition.
131
What is one cause of uncontrolled neural storms that sweep across the brain during an epileptic seizure?
A deficiency in receptors for an inhibitory transmitter.
132
What determines whether the effect on the postsynaptic neuron if facilitating or inhibiting (2)?
A combination of which transmitter is released and the type of receptors on the postsynaptic neuron.
133
What is an excitatory postsynaptic potential (EPSP)?
When receptors open sodium channels producing hypopolarization of the dendrites and cell body.
134
What is an inhibitory postsynaptic potential (IPSP)?
When receptors open potassium, chloride, or both channels and produces a hyperpolarization of the dendrites and cell body.
135
Where is the axon hillock?
Where the axon joins the cell body.
136
How many inputs does a typical neuron receive from other neurons?
Approx. 1,000
137
How many synaptic connections can a neuron have in most parts of the brain?
10,000
138
How many synaptic connections can a neuron have in the cerebellum?
100,000
139
What are 2 advantages of a single neuron not being able to cause a postsynaptic neuron to fire/prevent it from firing?
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
What are the 2 ways that potentials are combined at the axon hillock?
Spatial summation and temporal summation.
141
What is spatial summation?
Combines potentials occurring simultaneously at different locations on the dendrites and cell body.
142
What is temporal summation?
Combines potentials arriving a short time apart from either the same or separate inputs.
143
What is the effect of summation combining EPSPs?
It makes an action potential more likely to occur.
144
What is the effect of summation combining IPSPs?
It makes it more difficult for incoming EPSPs to trigger an action potential by making the interior even more negative.
145
What are 2 effects of a neuron being able to summate inputs from multiple sources?
It becomes and information integrator and can function as a decision maker.
146
What happens in the reuptake process?
Transmitters are taken back in to the terminals by membrane proteins called transporters and are repackaged in vesicles and used again.
147
What are 3 ways neurotransmitters are recycled?
Reuptake, absorbed by astrocytes, or broken down through inactivation.
148
What are synapses called that target dendrites?
Axodendritic.
149
What are synapses called that target cell bodies?
Axosomatic.
150
What happens at axoaxonic synapses?
A third neuron releases transmitter onto the terminals of the presynaptic neuron.
151
What happens in presynaptic excitation or presynaptic inhibition?
It increases or decreases the presynaptic neuron's release of neurotransmitter onto the postsynaptic neuron.
152
What is one way that an axoaxonic synapse adjusts a presynaptic terminal's activity?
By regulating the amount of calcium entering the terminal.
153
What are 2 ways that neurons regulate their own synaptic activity?
Through autoreceptors and glial cells.
154
How do autoreceptors contribute to neurons regulating their own synaptic activity?
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
How do glial cells contribute to neurons regulating their own synaptic activity?
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
What 2 types of receptors detect acetylcholine?
The nicotinic receptor and the muscarinic receptor.
157
What is Dale's principle?
The idea that a neuron is capable of releasing only one transmitter.
158
What are the 3 ways a neuron can release multiple neurotransmitters at once?
Corelease, cotransmission, and releasing different transmitters for its various terminals.
159
What is corelease?
When transmitters are packaged in the same vesicles.
160
What is cotransmission?
When vesicles containing different transmitters in the same terminal are triggered to release at the same time.
161
What provides an opportunity for coding to carry complex information involved in brain communication?
That neuron information often travels over specialized pathways.
162
What are neural networks?
Groups of neurons that function together to carry out a process.
163
What is an antagonist?
Any substance that reduces the effect of a neurotransmitter.
164
What is the Human Connectome Project?
A large-scale, multi-university effort to map the brain's circuits.
