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Lecture 3

Lecture 3 _ Receptors BIO271.pdf

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Department
Biology
Course Code
BIO271H1
Professor
Melanie Woodin

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Lecture 3 January 21, 2017:58 PM 48:18 You still need to know about absolute refractory period and why the action potential wont start until a certain period. BIO271 Page 1 If you think about sensory input you realize much of it is happening in the brain is responding to the sensory input. What the brain is doing is processing it into a response. The general idea about sensory systems is there are some stimuli out in environemnt. olfactory, visual input auditory and within the receptor cell somewhere if we are going to receptor to the signal and we have to have receptor specialized for the sensory input. Dogs can hear the type we don’t haear because we don’t have the right type of auditory receptors. We can only detect the sensory inputs for what we have the right receptor for. We can have some aplification of the receptor. Eg: signal from the photorecptor is detected by the brain ebcause the visual system amplified the response. BIO271 Page 2 And as a general property of all of our sensory systems we can have an activation of the sensory preceptor. But within that receptor cell that signal is going to be amplified.so for example light on photoreceptor can be detected by brain, not because the brain can detect only the signal produced by the photons but because your visual system amplified the syignal. We will talk how dif receptor types amplify. Once it is amplifid it goes to the brain and decided what to do . When we are talking about sensory systems we are talking about transduction. We have chemical cue factory, we have sound waves in our auditory system, we have photon light these all are dif stimuli and the receptors need to transduce them into the energy of the AP. Transduction is the process by which see slide for definition. These are hair cells we will talk about in the auditory system. This cell waves come in it reveberate to the coclia. They are then going to hit across the hair cells and by moving the hair (Action potential) cells, you open ion channels that transduce it to an AP. All of the BIO271 Page 3 See Slide. There are receptor protein cells that can detect the stimulus and that is going to lead to the opening and closing of the ion channel. Which will change the Which can then lead to action potential firing. membrane potential and the membrane pot is going to be sent to the nervous system. This is a similar pattern you are going to see in all sensory receptors Each receptor is selective for dif kinds of energy. After it specializes and detects it amplifies. This is an example of what these receptors looks like. This is an overview. We will be talking about it more later. On the left it is a chemoreceptor. Chemoreceotrs are stimulated by multiple factors like molecules that bind to receptor proteins. once it is bound the protein doesn’t go inside the cell. It activates a Signal Transduction Pathway. Opens ion channels and change the membrane potential and someway the change in the memb pot signals to the brain. The amplification you are going to see which is not shown in this slide, would be the activation of one receptor protein shown here not only activates one ion channel but multiple ion channels so one moelcule bindds here and hundred binds here. Mechanoreceptor at work is the middle figure. Some examples are in skin. You apply pressure on the mechanorecotr is going to activate the mechanorector. Activates different STP and opens ion channels. Change of memb pot and sends signal to brain Photoreceptor in the corner figure. We have Light stimulus. So photons come in and activates photo recptors. With then creates a similar patheay. So regardless of the receptor type it has it leads to opening and closing of an action potential which changes the membrane potential and all these activates one of the receptors in the membrane. BIO271 Page 4 All these changes in the membrane potential we have ion channel opening and changes in membrane potential. Those are all graded potentials. We said the graded pot is a change in meb pot. They are proportional to the size of the input. you can imagine if you had one receptor protein activated in a chemoreceptor you will have smaller membrane potentials vs having 100 chemoreceptors you can have larger memb pots. Now just to confuse you there are two terms for these gradded potentials. Don’t know why but there are two terms and we have to learn them. Don’t get confused. Depending on how the graded pot happens we can call it generator potential and receptor potential. When the graded pot happens in the sensory receptor that has an axon this is going to take the information to the brain we call it generator pot. Eg: The term here is to verify __ when we talk about afferent neurons we are talking about a cell with afferent neurons that is sensing information and taking it through the axon into the spinal code in a vertebrate. Hearing information and sending it inwards, towards we call here the integration centre, we are taking the information in and it is a primary afferent neuron.when the receptor is actually on that cell that has an axon goig into the nervous system we call it a generator potential. We wil see some of these sensory receptors are not only afferent neurons themselves. There are ones that on epithelial thatsends signals to primary afferet neurons. We will see when the graded potential happens there we call it receptor potential. This is This is what it looks like We can call graded potentials two different things depending on the arrangement of the sensory system. So this is an example of a sensory neuron which is a primary afferent neuron. So you can imagine this case can be receptor protein here that can responds to the stimulus (photon of light etc), the receptor protein is on the neuron itself. Just like a synapse. The NT comes in and binds and it opens the receptor and you get a graded potential and the GP is large enough so when it reaches the trigger zone we get an action potential. This is actually very analogous to your synapse. But in this case it is not a chemical neurotransmitter. It is some type of stimulus on the receptor protein and we call is a generator potential. Versus In this example B) where the receptor is not directly on the neuron it is made on to another cell type and the most common one is epithelial cell and the activation, the graded potential we call it the receptor potential. The result is the activation of synaptic transmission. This is what looks like a presynaptic cell is actually an epithelial cell. So we activate the receptor potential and we get graded potential and in this case in the epithelial cell there is no action potential. The action pot is going to be unique to the neuron. But that receptor pot which is a depolarization is a depolarization not to open up the voltage gated calcium channels to release NT. So basically activates now the transmitter receptor and makes a graded potential to make an action potential. Spend a lil time and read the book. (remember- they both are graded potentials but with different terms depending on where you find them) BIO271 Page 5 So what do we call these dif receptors? Depends upon a number of things. Ive being referring to them based on the sensory system in whichh they are located. But in the book they’ve used all these other terms depending upon where the stimulus are located. If it detects distant stimuli we are going to call it telerecptors. Eg: light coming in or sound waves. If we are sensing things on our body, outside our body but directly impacting us here such as you are putting pressur eon the skin or temperature change. They are exteroreceptors. And of course we have lot of sensory receptors insid ethe bodyas well to detect things like blood pressure and oxygen But these don’t tell us how they work but where they are located. Where the info is coming from. You might be more familiar with the classification based on the sensory system itself. And of course some are obvious such as photorecptors, are activated by light in the visual system Chemreceotirs - activated by chemicals. In for example we got olfacotry in mouth and also taste receptors for taste. Mechanorecptrd are critical for pressure and movement (slide) This is things like touch but also hearing, balance (vestibular system) blood pressure Also electro receptors, magneto and thermorecptors Electroreceptors and magneto receptors are more specialized in other animal types. There are few terms you need to know in sensory stimuls 1) Adequate stimulus - this is really the stimulus the receptor responds to. So, photoreceptors in your eye its adequate stimulus it is going to be a photon unit. This is what the receptor is most sensitive for and responsds to. Mechano recptor - pressure So many types or so even though they have an adequate stimuls can also respond to other stimuli. But it is not going to be at the same level. When you are rubbing your eye, tired and studying you are actually activationg the photon receptors but not through light you are activating by pressure __) so some sort of receptors have adequate receptors they prefer to respond to and they respond to that but some of them respond to other things but that is not their preferred adequate stimulus. There are some polymodel receptos. Less common though. Tey are receptors that are sensitive to more than one stimulus modality. They don’t have one adequate stimulus. BIO271 Page 6 not their preferred adequate stimulus. There are some polymodel receptos. Less common though. Tey are receptors that are sensitive to more than one stimulus modality. They don’t have one adequate stimulus. They can have several. And for example nociceptors and they can detect different kinds of pain. There are dif ways to activate pain pathways and some polymodal receptors can detect it by things like chemical activation. Things like caspases which is an activator in pathways but also changes in temperature. So we've being talking about using this sensory input stimuli into an AP in the primary afferent neuron. So someties it happens directly but sometimes it happens via transmission through an epithileal cell. But how do you differentiate the incoming signal strength of the signal. How can the nerves system in the brain differnetiate between these. This is going to happen using a number of dif components of the stimulus. The type of modality. In the brain we have different regions of the brain that are dedicating to the dif sensory systems. Primary visual cortex, primary auditory cortex, primary_______etc. so those are where all the input is coming from, from that sensory system. So that would be stimulus modality. Within those locations we have a map to the stimulus loction. So within the brain if you are looking for the signals in the primary visuaal cortex there are map… but the brain knows if the input is coming from the periphery position of the system or the central position of the system. We also know about the intensity, we know the _______________ we also know information aout the
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