How does the human body work? - Class 11
Let's learn the mechanism of reflex actions. Created by Mahesh Shenoy.
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- How does the relay neuron know exactly to which motor neuron it should send ?(5 votes)
- the junctions between neurons through which the signals can be sent are called the chemical synapses. they produce some chemicals when electrical signals reach them. these chemicals are neurotransmitters that can bind to the receptors on the motor neuron. this is like an electrochemical circuit which generate electrical signals in the motor neuron that leads to exactly what reaction is required. these reach the muscles cells in which the reflex action take place(9 votes)
- is reflex action only in humans or all animals? are there any examples?(4 votes)
- Yes animals are having reflex actions. And the thing is as animals are not having a fast thinking or that much of a well developed brain there is more reflex arcs present in them so that they do not get hurt or they are able to react quickly to a stimulus.(2 votes)
- How does the relay neuron send the signal to both the brain and the motor neuron? There's only one signal right?(5 votes)
- Well, the relay neuron splits the signals in two, the first goes to brain, the second goes to motor neuron.(3 votes)
- Can we suppress reflex reactions? (For example, if we intentionally keep a finger near the flame of the candle, we can hold it there in spite of feeling the heat)
Stay Home Stay Safe...(4 votes)
Reflexes are actions we can't control. Most reflexes protect the body. They are coordinated by nerves that go to and from the spinal cord without the brain's direct involvement
So, never try to control reflex actions, as it can harm the the nerves system, which ultimately harms the brain.(3 votes)
- When we touch a hot surface, reflex action takes place and we move our hand. The doubt I have is that how did we know that that action we did was dangerous and that we knew that we need to remove our hand from the hot surface because we already know that during a reflex action, the message is not received by the brain. So how is it that without thinking, the muscle responds to the stimulus in the form of a reflex action.
Basically, how do the muscles know that the action we did calls for a reflex action rather than a normal one?(4 votes)
- As we got to know the reflex actions are the ones which reacts to a stimulus. These are the actions which can cause any type of damage or harm to our body and this we get to know by our past experiences or what we might have suffered from and the information gets stored in our subconscious mind. Basically reflex actions reacts to physically harming actions. When we touch a hot cup we do know that it can hurt us because we have got hurt the first time we did the same thing and the same goes to hurting our knees with an object and also too much amount of light entering in our eyes because it does causes harm. If the whole process takes place in the normal way sending the signals to brain first then it will take too much time and we already would have got burnt which is what we don’t want and fir which the reflex arc are present in our body. Our brains know that these are the actions which needs to be responded to as quickly as possible as we have experienced pain or an uncomfortable feeling because of these actions in the past .
Hope this helps.(3 votes)
- How does the leg come up work? (0:17)(4 votes)
- The best known of the reflexes is the patellar, or knee-jerk, reflex. The DTR exam involves a healthcare provider tapping your knee with a rubber hammer (it shouldn't hurt). This tap stretches your patellar tendon and the muscle in your thigh that connects to it.
That's how the leg moved on its own.(1 vote)
- can a single motor neuron move my whole bicep muscle?
or we need more than 1 motor neuron to move my bicep muscle so there is a ganglion present in the reflex arch?(2 votes)
- NO a single motor neurone would not be able to move the bicep, it needs multiple other neurones connecting to each other to be able to pass the electrical current through. After the brain sends a signal, the current travels through multiple neurones, then those neurones pass the electrical current to the skeletal muscle through a synaptic gap.(3 votes)
- can a single motor neuron make my whole bicep muscle move??(1 vote)
- NO a single motor neurone would not be able to move the bicep, it needs multiple other neurones connecting to each other to be able to pass the electrical current through. After the brain sends a signal, the current travels through multiple neurones, then those neurones pass the electrical current to the skeletal muscle through a synaptic gap. This answer is by joshna.rhea to answered to a similar question.(1 vote)
- Is it correct to say that the brain is not involved in producing reflex actions since before the neuron can send the message to the brain, another neuron takes it and produces the reflex action, like in the example given in this video about flinching away when your hand is above fire?(1 vote)
- Yes, the brain is not involved in reflex actions. The neuron just carried the information to the brain so that we know what happened.(1 vote)
- Can someone elaborate to me about the spinal cord?(1 vote)
- The spinal cord is part of the Central nervous system (CNS). Spinal nerves arise from it. It is responsible for reflex actions. It is also a part of the reflex arc. It is protected by a bony cage called the Vertebral column(1 vote)
check out these four videos in the second one look at that black pupil at the at the center see what happens to it has a shine light okay and over here my leg is coming up automatically I'm not doing this on purpose the moment I hit it the leg comes up automatically so the question is what did you find common in all the four videos well besides the fact that I'm torturing myself at least my idly one thing common you can find is that in all four cases there is a stimulus what's a stimulus you ask stimulus is some kind of a change in the environment of a body for example over here the temperature of the finger changes that's a stimulus over here the light the amount of light entering my eye changes stimulus here before I sneezed I sniffed something so the environment inside my nose changed stimulus and over here I'm hitting myself somewhere at the knee so the pressure changed again a stimulus okay what else is common well I am responding to that stimulus in all the four cases but here I move my hand away here my pupils become smaller over here I sneeze trying to get that you know get something out and over here my leg raises so there's a response to the stimulus great there's one more thing that's common in all the four what's that the thing is these responses are all involuntary meaning I am NOT consciously deciding to do that it's happening automatically right so it's an involuntary response to a stimulus that my dear friend is what we call a reflex action so let's write that down what's a reflex action reflex action what is that well it's it's an involuntary response in voluntary response to a stimulus now what's so interesting about reflex actions is that it's different than other involuntary processes like your heart beating and your breathing or maybe digestion those are also involuntary processes but over here it requires a stimulus only then the reflex action happens that's what's different over here so I guess the question is how does this work I mean how can you respond to something without being conscious about it without even thinking about it I mean look at these cases I'm not even thinking about it and it's just happening so how does it work well turns out some of the reflex actions are more complicated than the others so we will only study the one that is most commonly found in our body okay and so it turns out that the mechanism of this one the mechanism of this reflex action is the most common so let's look at this one in detail so here is my arm I have shown the bicep muscle over here because that'll be important for us so in such reflex action it turns out that there are only three neurons involved only three cells are involved and it involves our spinal cord so let me just draw that as well so this is a section of the spinal cord if I were to show you a little bit more of my spinal cord here it is this is the down part so you can kind of see right what is what I mean by a section and these are the nerves that are coming out the bundle of nerves that are coming out from the spinal cord okay so let's see what happens so the moment the temperature of my finger increases that is detected by a neuron which is present over here that neuron converts that heat into electrical signal and that electrical signal is sent to the spinal cord so this is a neuron and if you're wondering why am i moving it over here I'll tell you in a second but anyways this single neuron and if you're wondering are can a cell be as long the answer is yes neural neurons are the longest cells in our body neurons can be really really long okay so that single neuron takes that electrical signal and sends it to the spinal cord what happens after that well then that signal is taken by another neuron so the signal goes to another neuron over here another neuron over here and then that signal goes to the brain the neuron sends that signal to the brain so it's going like this goes this way and then from here that signal goes to the brain okay and this is what happens all the time so there's nothing different over here but what's different in reflex action what happens next is that it will not wait for the brain to give command okay usually once the signal is sent to the brain the brain is the one that processes the signal then it decides what to do but in reflex action that in this reflex action at least that's not what happens what happens is it does not wait for the brain to give the command the signal from this neuron is immediately sent to yet another neuron and that's what's that's what's different over here it's sent to yet another neuron which sends that signal directly to my bicep muscle in this case it sends it directly to that bicep muscle so the electricity gets directly sent to the bicep the bicep contracts pulling my you know my hand and as a result my hand moves away from the fire and so the speciality of the reflex action is that it does not wait for your brain to process that information and then to give you come out it immediately redirects it to the muscle and the reflex action is carried out and this is why even without thinking about it even if you're not thinking about it even if this haxon happens accidentally automatically the hand moves away that's the speciality of reflex action okay so the obvious question might be why is this happening why are we not waiting for the brain to process the information and then give the command can you think about this I want you to pause the video and think about I the information is directly sent to the muscle why not why aren't we waiting for the brain can you answer that pause the video and think about it well I'm pretty sure you guessed it if we had to wait for the brain to think about it and then decide what to do in that time the damage would have already been done right because this is a dangerous situation for our survival we need immediate action and in such cases it does not wait for your brain that's the speciality of this reflex action and so you see since the reflex actions are super important for our survival we still have them even though we have a complex brain in fact would you be surprised if I told you that reflex actions were first evolved before a complex brain right before complex intelligence evolve reflex actions evolve first because they are the ones that will ensure your survival so the last thing to do is just go ahead and label this diagram and I'll also tell you a couple of things to remember while drawing this so this big neuron that senses the stimulus we call it no surprise the sensory neuron so this is called the sensory neuron and this neuron that acts on the muscle and makes it contract and makes your hand move this one is called the motor neuron motor neuron it's called so because it's causing motion it's because of this neuron motion is happening that's why it's called motor neuron and the neuron that transfers the information from the sensory neuron to the motor neuron in the in the spinal cord this one is called this one is called the relay neuron really means transfer of information over here so this is called the relay neuron and of course this is our spinal cord this is our spinal cord and lastly this entire pathway which consists of sensory neuron the relay neuron and the motor neuron an entire pathway is also given a name it's called the reflex arc reflex arc okay so in our example the reflex arc consists of one sensory neuron one really neuron and one motor neuron of course some other reflex arcs might have more neurons in them some reflex arcs can have fewer neurons in them that's right for example that knee reflex that we saw it turns out it only has sensory and motor it does not contain really so some reflex arcs can have only two neurons but the most common ones will have three neurons in them okay now a couple of things to remember while drawing this first of all why do I draw a loop over here in the sensory neuron well that's because most of the time when we see a neuron this is the picture that comes to our head right but neurons don't have to look like this neutrons can have a variety of shapes and one of the shapes that neurons can have is like this any ones can also look like this and sensory neurons do look like this all sensitive neurons look like this and so this thing that I've drawn this loop I've drawn is actually the body of the neuron over here all right that's why sensory neurons are drawn that way so keep that in mind it's let me get rid of that and the second thing you may want to remember is that sensory neurons always go to the back side of our spinal cord so this is the back side and the motor neurons will always come out of the front side of the spinal cord just something to remember while drawing the diagram that's it time to now recall recall what we just learned so can you define what reflex action is what is a reflex arc can you tell what sensory neurons relay neurons which are also called inter neurons by the way I forgot to mention that and motor neurons what do they do and finally can you try drawing the entire reflex arc drawing see if you try to recall this now you will be able to remember this much longer okay so please try and recall and of course if you are stuck anywhere you can always go back and watch the video