Week 1 Lecture 5 Flashcards
What is receptor potential?
Change in membrane potential as a result of the receipt of signal from exterior sensory cue
Which sensory receptors do not depolarize?
Photoreceptors (hyperpolarize)
Where are receptor proteins located and what happen when they receive signals?
In the sensory cell membrane and they change shape when specific energy is received
What are the two results of receptor protein changing shape?
- Directly open ion channels
- Activation of enzymes that produce 2nd messengers that amplify the signal
What are the two stages of amplification?
- G-coupled protein can activate a number of different enzymes molecules
- Each of these enzymes will produce a lot of secondary messengers
How do odorants interact with olfactory receptors?
Specific odorants interact with specific olfactory receptors
What is the signalling cascade associated with odorant binding to olfactory receptor? (5)
- activation of G-protein
- activation of adenyl cyclase
- production of cAMP
- cAMP binding directly to cation channels (Na+ and Ca++) and opening them
- the depolarization of the membrane
What happens to the depolarizing current that resulted from olfactory receptor cascade?
The depolarizing current travels down the membrane via passive conduction to the trigger zone of the axon
What are the two categories of sensory cell transmission? (2)
- Sensory cell generates action potential at spike generating zone e.g. mechanoreceptors
- Sensory cell releases vesicles by impulses generated by post-synaptic neuron when depolarized e.g. taste receptors
How are signals transmitted via vesicles? (5)
- Binding of taste molecule to taste receptor produces depolarizing current
- Depolarizing current moves passively to the other end of the cell
- At the other end of the cell, depolarizing current activates voltage-gated calcium channels
- Voltage-gated Ca++ channels open resulting in influx of Ca++
- Ca++ promote exocytosis and the release of vesicles
What is adaption?
The decay in membrane potential over time in which the original voltage is not sustained despite the stimulus being constant
What are the two types of adaption?
Slow adapting and rapidly adapting
What is slow adaption?
Receptor potential is sustained fro duration of stimulus
What is rapid adaptation?
Receptor potential is a result of the change in stimulus energy, decay occurs when stimulus is constant
What is of interest in slow and rapid adaptation?
In slow adaptation, the magnitude of the stimulus is of interest while with rapid adaptation the delivery and velocity of the stimulus is of interest
What is habituation?
The response to successive stimuli becomes progressively weaker over time
Do all cells show habituation response?
Habituation response depends on the cell the cell, some show large degree of habituation some don’t
What is the receptor potential directly proportional to?
The intensity of the stimulus, the greater the intensity of the stimulus, the greater the depolarization
What happens as stimulus intensity increases?
Higher threshold sensory neurons are recruited because refractory period limits impulse frequency
What are strategies used to code for the strength of stimulus? (2)
- Increase frequency of AP at excitable membrane
- Recruiting addition receptors with higher threshold
What strategy is used to distinguish differences in the modality of stimulus?
The ‘labeled line’ strategy
What is the labeled line strategy?
The activity in one pathway is indicative of a particular stimulus quality and nothing else
What is population coding?
Using the ratio of activity from a restricted number of receptor types to code information e.g. how colours are processed
Why is population coding significant?
It is more efficient to use ratio of a restricted amount of receptor proteins for all qualities than a receptor for each quality.
