L5 Flashcards
(107 cards)
1
Q
What is a receptor potential?
A
A change in membrane potential due to receipt of signal from exterior sensory cue
2
Q
How does receptor potential differ from post-synaptic potential?
A
Input comes from external environment rather than from another neuron
3
Q
What typically happens to sensory receptors when they receive specific energy?
A
They generally depolarize, with photoreceptors being an exception
4
Q
What is the exception to depolarization in sensory receptors?
A
Photoreceptors hyperpolarize in response to light
5
Q
Where are receptor proteins located?
A
Embedded in the sensory cell membrane
6
Q
What happens to receptor proteins when they receive specific energy?
A
They change shape, leading to membrane depolarization
7
Q
What are the two main pathways when a receptor protein changes shape?
A
Direct ion channel opening or enzyme activation via G-protein coupling
8
Q
What happens in the ionotropic pathway of receptor proteins?
A
Directly opens ion channels (e.g., cation channels), leading to membrane depolarization
9
Q
What happens in the metabotropic pathway of receptor proteins?
A
Enzyme activation via G-protein coupling leads to second messenger production
10
Q
What is the advantage of the metabotropic receptor pathway?
A
Signal amplification through multiple stages
11
Q
What are the stages of amplification in metabotropic signaling?
A
G-protein activates multiple enzymes, each producing many second messengers
12
Q
How many stages of amplification occur in metabotropic receptor signaling?
A
2 stages
13
Q
What happens in the first stage of amplification?
A
G-protein activates multiple enzyme molecules
14
Q
What happens in the second stage of amplification?
A
Each enzyme molecule produces lots of second messengers (cAMP)
15
Q
What is the overall result of the two-stage amplification process?
A
One stimulus molecule can produce lots of second messengers
16
Q
Why is amplification important in sensory reception?
A
It allows detection of very weak stimuli by magnifying the signal
17
Q
Where are olfactory neurons located?
A
Inside the nasal passage
18
Q
How are olfactory receptor cells positioned in the nasal cavity?
A
They line the mucus layer and are embedded in the mucus
19
Q
What is the shape of olfactory neurons?
A
Finger-like projections
20
Q
What is the first step in olfactory transduction?
A
Specific receptor proteins bind specific odorants
21
Q
What happens after an odorant binds to its receptor?
A
G-protein activation → adenylyl cyclase activation → cAMP production
22
Q
How does cAMP affect ion channels in olfactory neurons?
A
cAMP directly binds to ion channels, allowing cations (Na+ and Ca++) to enter
23
Q
What is the result of cation influx in olfactory neurons?
A
Membrane depolarization, which may lead to firing action potentials
24
Q
What bone separates the nasal cavity from the brain?
A
The ethmoid bone
25
What happens if the ethmoid bone is damaged in a certain way?
Olfactory neuron axons can be cut, resulting in loss of smell
26
What makes the olfactory system anatomically unique?
Direct connection from nose to brain through the ethmoid bone
27
What must happen for an olfactory neuron to trigger an action potential?
The depolarizing current must be strong enough to bring the trigger zone to threshold
28
What advantage does the metabotropic mechanism provide in olfactory reception?
Signal amplification, making cells sensitive to as few as 1-2 molecules in the air
29
Why would olfactory reception fail if odorants bound directly to ion channels?
Only 1-2 ion channels would open, producing insufficient depolarization to detect the odorant
30
What makes the olfactory pathway unique compared to other sensory systems?
It bypasses the thalamus, going directly from olfactory bulb to olfactory cortex
31
What is the pathway of olfactory signal transduction?
Odorant → G-protein activation → adenylyl cyclase → cAMP production → cation channel opening → depolarization
32
What are the two categories of sensory cell transmission?
1) Sensory cell generates an action potential at a spike-generating zone
2) Sensory cell releases vesicles when depolarized
33
Where is the trigger zone typically located in olfactory neurons?
At the branch point where the axon connects to the cell body
34
Where is the first patch of excitable membrane typically located in sensory neurons?
At the branch point of the axon
35
What must happen for a receptor potential to generate an action potential?
It must travel to the trigger zone and summate enough to reach threshold
36
What type of spread occurs when receptor potentials travel to the trigger zone?
Passive spread
37
What cellular structures are concentrated at the branch point?
Voltage-gated sodium channels
38
How do skin receptors initially respond to pressure?
Pressure opens ion channels in the membrane, generating a depolarizing current
39
What type of potential is a receptor potential?
A graded potential
40
What is the relationship between summation and action potential generation?
Multiple receptor potentials must summate at the trigger zone to reach threshold for an AP
41
Why is the branch point important for sensory signal transmission?
It contains many voltage-gated sodium channels and is where APs are generated
42
What happens in sensory cells that use vesicle transmission instead of APs?
The depolarizing current travels through the membrane, triggers Ca²⁺ influx, and causes vesicle exocytosis
43
Which cell generates the action potential in vesicle-based sensory transmission?
The post-synaptic neuron (next cell in line)
44
What ion is crucial for vesicle release in sensory cells?
Calcium (Ca²⁺)
45
Why don't taste receptor cells generate action potentials?
They are very small cells that lack axons
46
How do taste receptors respond to chemical stimuli?
They bind chemicals, produce a depolarizing current, and release neurotransmitters
47
How does the depolarizing current travel in taste receptor cells?
It travels passively through the membrane to the other end of the cell
48
What is the sequence of events in taste receptor signaling?
Chemical binding → depolarization → Ca²⁺ influx → neurotransmitter release
49
What is sensory adaptation?
The decay of membrane potential over time despite constant stimulus
50
What are the two types of adaptation?
Slowly adapting and rapidly adapting
51
What happens to the original voltage during adaptation?
It's not sustained and drops over time, even with constant stimulus
52
What is the main characteristic of slowly adapting receptors?
Receptor potential is sustained for the duration of stimulus with slow decay
53
What aspect of a stimulus are slowly adapting receptors primarily interested in?
The overall magnitude of the stimulus
54
What happens to the receptor potential in slowly adapting receptors during constant stimulation?
There is always some receptor potential maintained as long as the stimulus is present
55
What triggers a receptor potential in rapidly adapting receptors?
Changes in stimulus energy (upwards or downwards), not constant stimuli
56
What happens to the receptor potential in rapidly adapting receptors when a stimulus remains constant?
It decays to zero
57
What aspect of a stimulus do rapidly adapting receptors primarily detect?
How quickly the stimulus is being delivered (velocity of stimulus)
58
How quickly the stimulus is being delivered (velocity of stimulus)
Deep layers of the skin for sensing vibration, pressure, and touch
59
What unique response can rapidly adapting receptors show when a stimulus is removed?
Hyperpolarization (response in the opposite direction)
60
How well do pain receptors adapt?
Pain receptors do not adapt very well
61
How does habituation differ from adaptation?
Habituation is a response to successive stimuli over time, not a single continuous stimulus
62
What happens to response strength during habituation?
Repeated identical stimuli elicit progressively weaker responses
63
Is habituation subject to conscious control?
No, sensory cells do this on their own
64
What happens if there's a long interval between identical stimuli?
Habituation won't occur if you wait too long (e.g., an hour) between stimuli
65
How does habituation affect our attention to stimuli?
We become accustomed to stimuli and pay less attention to them
66
How does receptor potential vary with stimulus intensity?
Directly proportional - greater stimulus intensity causes greater receptor potential
67
What happens to action potential frequency as stimulus intensity increases?
It increases - greater stimulus intensity leads to higher AP frequency
68
What happens to the membrane when there's greater depolarization?
It reaches threshold faster, generating a spike train
69
What limits the maximum frequency of action potentials?
The refractory period
70
What is the approximate maximum number of action potentials possible in one second?
About 1000 APs per second
71
Why is there a limit to the number of action potentials in one minute?
Due to the refractory period needed to restore voltage-gated sodium channels
72
If it takes 1 ms to restore voltage-gated sodium channels, what is the maximum firing rate?
1000 action potentials per second
73
What happens when you reach the ceiling of action potential frequency?
You hit a maximum rate (plateau) due to refractory period limitations
74
What strategy does the nervous system use to code stimulus intensities beyond the frequency ceiling?
Recruitment of additional neurons with higher thresholds
75
What are "higher threshold sensory neurons"?
Neurons that require greater stimulus intensity before generating a receptor potential
76
How does the nervous system encode increasing stimulus intensity beyond 1000 APs/second?
By recruiting additional neurons with higher thresholds
77
What happens to the population of active neurons as stimulus intensity increases?
More neurons with higher thresholds are recruited to the active population
78
What are the two main strategies to code for stimulus strength?
1) Increase AP frequency
2) Recruit additional receptors with higher thresholds
79
What happens to action potential frequency as stimulus strength increases?
It increases until reaching a maximum discharge rate
80
What happens when AP frequency reaches its maximum?
It plateaus and cannot increase further (frequency doesn't go any higher)
81
How does the nervous system code for stimulus strengths beyond the maximum AP frequency?
By recruiting additional receptors (Receptor B) with higher thresholds
82
What is meant by "the curve has shifted" when referring to Receptor B?
Receptor B's activation curve is shifted to the right, requiring stronger stimuli to activate
83
How is stimulus strength coded across different neurons?
By looking at total activity across different populations of neurons instead of just one
84
What is the range of receptor sensitivities in the sensory system?
Some receptors are very sensitive while others require very strong stimuli before activating
85
What is meant by "modality" in sensory physiology?
Different types or qualities of stimuli (like light, sound, touch)
86
What strategy does the nervous system use to distinguish different modalities?
The "Labeled Line" strategy
87
What does the "Labeled Line" strategy mean?
Activity in one pathway means a particular stimulus quality and nothing else
88
How are different sensory qualities (like light and sound) processed?
Each has a completely separate system devoted to it
89
What are sub-modalities?
Varieties of stimulus qualities within a modality (e.g., different colors, smooth vs. rough touch)
90
Why would having separate receptor proteins for all stimulus qualities be inefficient?
There wouldn't be enough space in the brain for all these different receptors
91
What is population coding?
Coding using the ratio of activity from a restricted number of different receptor types
92
Why is population coding more efficient than having individual receptors for each stimulus quality?
It requires fewer receptor types while still allowing discrimination between many stimuli
93
How are specific stimuli coded in population coding?
By the ratio of activity across the population of receptors
94
What's an example of where population coding is used in sensory systems?
Color vision - using three cone types instead of separate receptors for every color
95
How does a single receptor type respond to stimuli in population coding?
It responds to a wide range of stimuli but has a specific peak sensitivity
96
In the example with receptors A, B, and C, how would a specific stimulus be encoded?
One receptor (e.g., C) might be activated strongly while others (A, B) are activated more weakly
97
What creates the unique "signature" for a specific stimulus in population coding?
The ratio of activation across different receptor types
98
Why is population coding described as "very efficient"?
A small number of receptor types can encode a vast range of stimulus qualities
99
How does the brain interpret which specific stimulus is present using population coding?
By analyzing the relative activation pattern across all receptor types
100
What is a receptive field?
The specific spatial area (territory) to which a sensory neuron responds when stimulated
101
What is the typical size of a receptive field in cutaneous sensory neurons?
Generally 10-20 mm across, but can be as small as 1 mm in fingertips
102
Why do fingertips have smaller receptive fields than other body areas?
To provide greater sensitivity through denser neuron distribution
103
What happens when multiple primary sensory neurons converge on a single secondary neuron?
They create a larger receptive field with less precise discrimination
104
How does the size of receptive fields relate to two-point discrimination?
Smaller receptive fields allow better two-point discrimination; larger fields result in poorer discrimination
105
Why is each sensory neuron's receptive field unique?
Each neuron responds to stimulation in a different specific territory of skin
106
What's the relationship between neuron density and receptive field size?
Higher neuron density = smaller receptive fields = greater sensitivity
107
What happens when two stimuli fall within the same secondary receptive field?
They're perceived as a single point because they send only one signal to the brain
