lesson 12 Flashcards
(89 cards)
1
Q
What are neurons?
A
The cells that do the primary work in the brain.
2
Q
What is the approximate diameter of an average neuron’s cell body?
A
10-20 μm (micrometers), about 1/5 the thickness of a sheet of paper.
3
Q
How fast does a neuron fire an action potential?
A
In about 1-2 ms (one to two thousandths of a second).
4
Q
Approximately how many neurons are in the average human brain?
A
About 80 billion.
5
Q
What is a synapse?
A
The point where neurons connect and exchange information.
6
Q
Approximately how many synapses are in the average human brain?
A
About 1000 trillion.
7
Q
What are behavioral neuroscientists?
A
People who study how the brain creates behavior.
8
Q
Besides neurons, what other type of cell is found in the brain?
A
Glia.
9
Q
What are the three main steps in brain function related to learning?
A
Acquiring new information, remembering it, and using it to drive behavior.
10
Q
How does information enter the brain from the world?
A
hrough our senses (vision, hearing, etc.) using specialized organs like eyes or ears, which send information via sensory neurons.
11
Q
What are sensory neurons?
A
Neurons that send information from sensory organs to the brain and spinal cord.
12
Q
What are motor neurons?
A
Neurons that carry signals from the brain and spinal cord to muscles to produce movement.
13
Q
What are dendrites?
A
The parts of a neuron that receive information.
14
Q
What is the soma?
A
The body of the neuron cell.
15
Q
What is the axon?
A
The long, slender projection of a neuron that conducts electrical impulses away from the cell body.
16
Q
What is the axon hillock?
A
The point where the axon connects to the soma.
17
Q
What is myelin?
A
sheath made from glial cells that covers most axons and helps them transmit information faster.
18
Q
What is the axon terminal?
A
The end of the axon, where it splits into smaller processes that form synapses with other neurons.
19
Q
: What is the synapse?
A
The location where the axon terminal of one neuron contacts a dendrite of another neuron, allowing for information exchange.
20
Q
What are presynaptic and postsynaptic cells?
A
The presynaptic cell is the sending neuron at a synapse, and the postsynaptic cell is the receiving neuron.
21
Q
: What is an action potential?
A
An electrical signal that travels down the axon of a neuron, transmitting information.
22
Q
What is the all-or-none principle of action potentials?
A
Neurons either generate a full-strength action potential or none at all; there are no partial activations.
23
Q
What is membrane potential?
A
: The electrical charge difference between the inside and outside of a neuron.
24
Q
What is a neuron’s threshold?
A
The level of membrane potential that must be exceeded for a neuron to fire an action potential.
25
What is the refractory period?
The period after a neuron has fired an action potential during which it cannot fire again.
26
What is the synaptic cleft?
The gap between the presynaptic and postsynaptic neurons at a synapse.
27
How do neurons communicate at the synapse?
: Through the release of neurotransmitters, which are chemicals that transmit information between neurons.
28
What are synaptic vesicles?
Small bubbles of membrane that contain neurotransmitter molecules and cluster at the axon terminal.
29
What are receptors in the synapse?
Proteins on the membrane of the postsynaptic neuron's dendrite that bind neurotransmitters and trigger changes in the cell.
30
What is the significance of neurons having many dendrites?
It allows neurons to sum up stimulations received at different dendrites, potentially reaching the firing threshold.
31
What is an excitatory neurotransmitter? Give an example.
A neurotransmitter that increases the membrane potential of the postsynaptic cell, making it more likely to fire. Example: glutamate.
32
What is an inhibitory neurotransmitter? Give an example.
A neurotransmitter that decreases the membrane potential of the postsynaptic cell, making it less likely to fire. Example: GABA.
33
What is a reflex arc?
A simple neural circuit that controls reflex responses, like the knee-jerk refle
34
What is an interneuron?
A neuron that is entirely contained within one structure, such as the spinal cord.
35
What is a neuromuscular junction?
The connection between a motor neuron and a muscle fiber.
36
Material that helps the axon transmit information faster
myelin
37
the neruon on the receiving end of the synapse
post synaptic cell
38
where the axon terminal connects with a dendrite of another neuron
synapse
39
where the axon connects to the soma
axon hillock
40
the body of the neuron
soma
41
the part of teh neuron that receivesinfo
dendrite
42
place whewre the axon may split into many smaller processes
axon terminal
43
part of the neuron that info flows down
axon
44
process of communication at the synapse works in 5 steps
1. An action potential arrives, coming down the axon of the presynaptic neuron
2. When it reaches the axon terminal, the action potential causes a change in the membrane there which leads to some vesicles fusing with the cell membrane, thus spilling their neurotransmitter into the synaptic cleft
3. The neurotransmitter diffuses across the synaptic cleft and arrives at the other side, at the postsynaptic neuron’s dendrite.
4. On the membrane of the dendrite are receptors – proteins that can bind the neurotransmitter. When they detect that a molecule of neurotransmitter has bound to them, they change shape (or do other things), leading to ions moving in or out of the cell, and changing their membrane potential.
5. If the potential changes enough to exceed the postsynaptic cell’s firing threshold, a new action potential will be formed, and start moving down the axon... and the entire process repeats from #1.
45
How is learning expressed in the brain at the neuronal level?
By a change in how neurons communicate.
46
What is one of the main mechanisms by which neurons change their communication to learn?
Changing the strength of the synapse.
47
What is Hebbian learning?
The idea that learning consists of changing the connections between ne
48
What does "strength" mean in the context of a synapse?
How likely it is that the postsynaptic neuron will reach its firing threshold based on just one stimulation.
49
What is long-term potentiation (LTP)?
The process by which the strength of a synapse is increased (potentiated).
50
In what type of synapse does LTP primarily occur?
: Synapses where glutamate is the neurotransmitter and the postsynaptic cell has both AMPA and NMDA receptors.
51
How do AMPA receptors function?
When glutamate binds to them, they allow ions into the cell, increasing its polarization and making it more likely to fire an action potential.
52
What makes NMDA receptors different from AMPA receptors?
They require both glutamate binding and the postsynaptic cell to already be highly polarized to open and allow ions into the cell.
53
What are NMDA receptors sometimes called, and why?
"Coincidence detectors," because they require two events to coincide (glutamate binding and high polarization) to open.
54
What happens when NMDA receptors open?
They cause changes inside the cell that strengthen the synapse, such as increasing the number and sensitivity of receptors.
55
In the three-neuron circuit (A, B, and C), what happens if neuron A fires alone?
It activates AMPA receptors in neuron C, increasing its potential, but probably not enough to activate NMDA receptors, so there's no change to the synapse.
56
In the same circuit, what happens if neurons A and B fire at the same time or very shortly after each other?
The combined stimulation might be enough to raise neuron C's potential to activate NMDA receptors, strengthening both the A-C and B-C synapses.
57
How can LTP in this circuit explain Pavlov's experiment (buzzer - CS, food - US, salivation - CR)?
Neuron A fires to the buzzer, neuron B to the food. If they fire close in time, NMDA receptors in neuron C (controlling salivation) strengthen the synapse. After repeated pairings, the buzzer alone (A firing) can trigger C to fire, causing salivation.
58
Does the text suggest that the three-neuron circuit is exactly how the brain performs Pavlovian conditioning?
No, it's a simplification. Real brain circuits are much more complex, but this shows how simple neurons and rules can create learning.
59
(Reflection point) Briefly describe how Pavlov's experimental results can be explained using the mechanisms of LTP.
In Pavlov's experiment, the CS (e.g., a bell) and the US (e.g., food) are represented by the activation of different sets of neurons. When the CS and US are presented close together in time, the neurons representing them fire in close succession. This coincident firing leads to the activation of NMDA receptors in the postsynaptic neurons involved in the conditioned response (CR, e.g., salivation). The activation of NMDA receptors triggers LTP, strengthening the synaptic connections between the neurons representing the CS and the neurons controlling the CR. As a result, the CS alone becomes capable of eliciting the CR, even in the absence of the US.
60
events at the synapse in order:
1. An action potential arrives, coming down the axon of the presynaptic neuron
2. At the axon terminal, the action potential causes vesicles to fuse with the cell membrane, spilling neurotransmitter into the synaptic cleft
3. The neurotransmitter diffuses across the synaptic cleft and arrives at the postsynaptic neuron’s dendrite
4. Neurotransmitter binds to receptors, leading to ions moving in or out of the postsynaptic neuron, changing its membrane potential
5. The postsynaptic cell’s firing threshold is exceed, causing a new action potential to be formed and start moving down the axon
61
Equipotentiality Versus Phrenology
Gall proposed iliat particular mental abilities are associated
witl1 specific cortical regions. Lashley proposed iliat mental
abilities are not associated with specific cortical regions but
instead can be pe1formed by any sufficiently large region
of cortex. Gall used correlations between skull features and
individual variations in humans to support his ideas. Lashley
used differences in tl1e capacity of rats to learn mazes after
undergoing cortical lesion to support his tl1eory
62
Synaptic plasticity is one of the most researched phenomena in the field of neuroscience, yet many
of its features remain poorly understood. Identify which, if any, of the fo ll owing statements accu-
rately describe(s) what is known about synapt ic plasticity. (Answers appear at the end of the chapter.}
1. Synaptic change can be produced through electrica l stimulation.
2. Whenever firing patterns change in a neural circuit. synaptic change has occurred somewhere
in the circuit.
3. Synaptic plasticity can weaken or strengthen connections between neurons.
4. Synaptic plasticity can be measured in humans us ing fMRI.
5. LTP is observed on ly in an im als that have recently been learning
l. True. This is what happened in the original
LTP studies: the researchers stimulated one
ANSWERS TO TEST YOUR KNOWLEDGE I 73
absence of these LTP effects. What does this tell us
about the relationship between LTP and learning?
4. Carbon monoxide poisoning can damage many dif-
ferent parts of the brain, resulting in many different
kinds of deficits-for example , severe impairments
in language or an inability to recognize objects.
Describe one way a neuropsychologist could deter-
mine what part(s) of tl1e brain might have been
damaged.
5. Lashle y's findings from lesion experiments in rats
suggest that the brain can function when only part
of the cerebral cortex is available. In addition, inver-
tebrates have been learning successfully for millions
of years with very different sorts of nervous systems
and less than 1% of ilie total neurons mammals
have. What does this information imply about the
role of the cerebral cortex in learning and memory?
neuron and observed LTP in the postsynaptic
neuron, indicating that the synapse had been
strengthened.
2. Fa lse. A neuron changes its firing pattern when its
inputs change, whether or not any synaptic change
takes place.
3. True.
4. False. £MRI does not measure neural activity and
cannot detect synapses; it measures changes in
blood oxygenation, which is an indirect measure of
neural activity.
5. False. LTP has only occasionally been observed in
animals that are learning. It is commonly measured
independent of any observable behavior.
63
In addition to learning to salivate whenever they
heard a bell, some of Pavlov's dogs learned to sali-
vate whenever Pavlov walked into the room. Use the
concepts of synaptic plasticity and Hebbian learning
to explain why this might have occurred. What
region(s) of a clog's cortex might have changed as a
result of this learning?
Because of Hebbian learning — Pavlov’s presence was repeatedly paired with food, strengthening synapses (synaptic plasticity) between visual cues and salivation.
Brain regions that changed?
Visual cortex, amygdala, insula, and prefrontal cortex.
64
Neuroimages (such as £MRI brain scans) of differ-
ent individuals performing the same task often differ
greatly in tl1e brain regions shown to be activated.
Does this mean that the brains of these individuals
function differently? If not, why not?
Not necessarily — people may use different strategies or have different brain anatomies for the same task.
65
Drugs tl1at block LTP in the hippocampus impair
learning in some tasks but facilitate learning in
otl1er tasks. Similarly, some researchers have corre-
lated LTP-like effects witl1 learning in a variety of
tasks, whereas others have observed learning in the absence of these LTP effects. What does this tell us
about the relationship between LTP and learning?
LTP is one mechanism for learning, but not the only one. Learning can occur with or without LTP.
66
Carbon monoxide poisoning can damage many dif-
ferent parts of the brain, resulting in many different
kinds of deficits-for example , severe impairments
in language or an inability to recognize objects.
Describe one way a neuropsychologist could deter-
mine what part(s) of tl1e brain might have been
damaged.
By giving cognitive and behavioral tests to link specific deficits to known brain region functions.
67
Lashle y's findings from lesion experiments in rats
suggest that the brain can function when only part
of the cerebral cortex is available. In addition, inver-
tebrates have been learning successfully for millions
of years with very different sorts of nervous systems
and less than 1% of ilie total neurons mammals
have. What does this information imply about the
role of the cerebral cortex in learning and memory?
The cortex helps learning, but it’s not essential. Other brain areas or simpler systems can support learning too.
68
What structures make up the vertebrate central nervous system (CNS)?
brian and spinal cord
69
How does the brain control behavior?
Through connections with the peripheral nervous system (PNS), which includes sensory neurons from receptors and motor neurons to muscles.
70
Which brain regions contribute to learning and memory?
The cerebral cortex, cerebellum, hippocampus, basal ganglia, and amygdala.
71
What are neurons, and what is special about them?
Neurons are the building blocks of the nervous system, capable of changing their function and modifying how they process inputs.
72
What do MRI and DTI brain imaging techniques do?
They measure variations in brain structure in living humans without harm.
73
What can structural brain imaging tell us about learning?
It allows researchers to collect detailed information about neural changes that occur during learning.
74
What have enriched environment studies shown about learning?
Learning experiences can significantly impact brain structure and an individual’s learning and memory abilities.
75
What is structural plasticity?
The brain’s ability to change with experience, often through strengthening or weakening connections between neurons.
76
What are reflexes?
Natural, automatic responses to stimuli.
77
What did early neuroscientists like Sherrington believe about learning?
That complex learning involved combining simple spinal reflexes.
78
How are sensory signals processed in the brain?
They are initially processed in cortical regions specialized for the signals, then lead to activity in other regions like the motor cortex.
79
What does functional neuroimaging (like fMRI) allow researchers to do?
Track brain activity during memory tasks by measuring changes in activity in different brain regions.
80
What does electroencephalography (EEG) allow researchers to do?
Track the activity of large populations of neurons over time and monitor changes as learning occurs.
81
What do single-cell recordings measure?
The electrical activity ("firing") of individual neurons, and how their firing patterns change during learning or memory recall.
82
What have brain-imaging studies of memory savants shown?
Remembering experienced events involves a broad network of brain regions.
83
What have brain lesion studies revealed?
How different brain regions contribute to learning and memory.
84
What are synapses?
Tiny gaps between neurons where neurotransmitters are released to activate receptors on the next neuron.
85
What is long-term potentiation (LTP)?
A process where synaptic transmission becomes more effective after strong electrical stimulation.
86
What is long-term depression (LTD)?
A process where synaptic transmission becomes less effective when neurons do not fire together.
87
What can implanted electrodes be used for in research?
To stimulate neurons and observe the resulting sensations or responses.
88
How can brain stimulation affect memory?
It can sometimes enhance memory, just as lesions can impair it.
89
How do drugs that affect the brain work?
y altering neural activity, often interfering with synaptic transmission.
