okay in this video going to talk about neural integration integration refers to neurons functioning together in groups and these groups can contribute to kind of broader neural functions so of the billions of neurons we find in our central nervous system a lot of these need to integrate information in ways that allow for a nice smooth and coordinated response so when we refer to neurons that function together in groups those are going to be pools so pools of neurons can receive and integrate incoming information from other neuron pulls and they basically process and forward this information along to other destinations so a simple neuronal pool is basically we have a single presynaptic fiber that branches and discharges on several different neurons within their pool now the discharge zone refers to neurons that are closer to the incoming fiber and are therefore more likely to generate an impulse the facilitated zone refers to neurons that are more on the periphery of the pool and because they're farther away from the incoming fiber they're usually not excited to threshold unless you have you know other neurons that are stimulating those cells as well so to see this represented pictorially we see that we've an axon coming down here and there's lots of axon collaterals here that are branching and those other Tullio dendrite here and essentially what we find is for those neurons that are in the center and kind of closest to the the axon here these ones are in the discharge zone they're more likely to fire action potentials because they get more inputs if you count up all the inputs here you see that you know there's neurons in the center here have a lot more synapses than those in the periphery and because of their many inputs they're more likely to fire and generate their own action potentials as well for the neurons that are off to the side because of their fewer inputs and they're farther away from the rest of the fibers these are much less likely to fire action potentials unless they're actually stealing about other cells as well now other types of neuronal processing include serial processing this is actually where we have input that travels along one pathway to a specific destination now one neuron can stimulate the next one which delays the next one and the system works in an all-or-none manner to produce very specific and anticipated responses in an exact this is like a spinal reflex where if you tap the patellar tendon you know there's a there's an impulse that goes back to your spinal cord then that activates a motor neuron that then stimulates the appropriate skeletal muscle to contract which then causes your leg to kick out now reflexes are rapid automatic responses to stimuli and they occur in an all-or-none process once you steam light a reflex it should complete now a particular stimulus always causes the same response so that's why we say that these reflexes are stereotypes because they were produced the same response every time now they occur over pathways which we call reflex arcs which have these five essential components we got receptors sensory neurons the integration Center motor neuron and the effector so to kind of look at what what a simple reflex arc would look like we'd have the receptor level which would be somewhere in the periphery that's going to generate action potentials that then travel along this you know unipolar neuron back towards a spinal cord where integration occurs and this is where you get communication with an inter neuron the intern neurons are multi polar neurons that receive many different inputs but in this case here is just a very simple input and this this in turn on them can synapse with a motor neuron and this motor neuron cannon can transmit action potentials out towards an effector to carry out the response so in the case of the patellar tendon reflex we see that if you tap the patellar tendon this activates stretch receptors in that tendon which then can generate action potentials that are transmitted towards the spinal cord you get a communication between the sensory neuron and your inter neuron inter neuron - motor neuron and then you get action potentials out towards your muscle which then causes your leg to kick out so with parallel processing we see that input travels along several different pathways in different parts of the circuitry deal simultaneously with information this is a little bit more complicated than than serial processing but with parallel processing this is important for kind of higher-level month mental functioning an example of this could be something like a smell that reminds you of an odor that could be associated with other experiences you know maybe there's a smell that reminded you of a fond memory from childhood in smelling that causes the you know sort of the memory to become conscious again now these circuits here can occur in a lot of her ways but there's four major types we have diverging converging reverberating in parallel after discharge and so we see here's a diverging circuit diverging circuits are essentially where one neuron could branch out and activate other neurons that then activate other ones which activate other ones so you see that that the signal that diverges so from one neuron you can get many different neurons that are activated and this is think of this as like amplifying information it's an example of diverging circuit where information can be amplified would be like in the spinal cord we could have one motor neuron that connects to many hundreds of muscle fibers or even thousands of muscle fibers and so that even though you have one neuron that's activated and go to lots of different outputs so a converging circuit is where you have many inputs but they all converge on one output neuron and you'd see here you have like three different neurons that are then synapsing on one output neuron here in that sense it's converging and you can think about this as basically an information consolidation where an example of like where this occurs in the body is like different sensory stimuli can elicit the same memory you know for instance this these neurons could be from like the odors of you know freshly cut grass and this neuron might be activated when you smell maybe like wet cement you know and this neuron might be when you see you know maybe like a bright sunny day and because of these converging information you know you get this output that then could potentially allow you to remember you know maybe just a summer evening that you had in the in the past so a reverberating circuit is essentially where a signal travels along this chain of neurons and there's actually feedback along the way and so what's interesting here is that these reverberating circuits create rhythms or oscillations so you might wonder well where in the body would you want to have neural networks that generate rhythms well it turns out that we actually have a lot of rhythms in our body you know there's asleep there's a sleep-wake rhythm we have breathing rhythms there's also a repetitive motor activities like walking we also have neurons in our brain that help keep time and they do this by generating a certain rhythm of action potentials and this gives us a sense of time like how much time has passed and so these reverberations create these frequencies and oscillating circuits that essentially allow us for you know rhythm generation and the parallel after discharge circuit is where a signal stimulates neurons that are related in parallel rays and they eventually can converge in a single output this is basically where an impulse reaches an output cell at different times and then causes a burst of impulses called an after discharge so if you look here we would find then that because this one motor neuron has an axon that been directly synapses on the output neuron this is going to be the fastest and then over here where you actually have two neurons in the path on the side here on the side here these are going to be slower it's gonna find in that although the action potential is going to get to this neuron quicker other action potentials from these pathways will also get to the output neuron and this creates kind of frequencies of action potentials that you know eventually stimulate an output neuron so with these parallel after discharge circuits you can get more kind of odd patterns of output an example of this would be things like exacting mental processes like mathematical calculations you know like understanding mathematical equations could rely on these sorts of parallel after discharge circuits so in terms of the developmental aspects of neurons we know that our nervous system originates from something called a neural tube and the neural tube actually comes from the layer of ectoderm embryologically and this tube is basically where the ectoderm folds and essentially makes the CNS so your central nervous system is the folding of this ectoderm from the neural tube and the neural epithelial cells of this narrow tube proliferate into cells that are needed for development neuroblasts become a mitotic and migrate in these neuroblasts can sprout axons and connect with targets to become neuron this occurs pretty early on in development now the way that that neurons can form connections is by something called a growth cone and the growth cones are kind of a prickly structure at the tip of the axon that allows it to interact with its environment through like cell surface adhesion proteins neurotrophins that attract or repel the growth cone we have nerve growth factors or NGS that can attract these growth cones which help keep these cells alive and then feel a podía which are growth current processes that follow the signal towards a target so think of the growth cone is like this sort of expending process that is guided by lots of different chemical factors until it reaches its target it can form a community communication point with a target cell so once the axon finds a target it must find the right place to form a synapse now it's cool here's a astrocytes that help guide the development and growth of neurons they actually provide the physical support and the cholesterol that's needed for the construction of the synapse so the astrocytes play that as a nice sort of intermediary role with helping to facilitate the communication between different cells because they essentially give the appropriate components for that synapse to form so about two-thirds of neurons to actually die before birth which is fascinating so you actually a lot more neurons in your body before birth then after and if these axons don't form with a target then they're triggered to undergo a Potosi switch is programmed cell death now many other cells also undergo a pitocin tsering development so what's interesting is that you know later on after birth what you're left with and what you develop with is actually a far fewer number of neurons than what you're born with or even what you had prenatally now these neurons are a mitotic before birth however there are a few special neuronal populations that can divide after birth you know especially in areas like your olfactory neurons you know in your in your olfactory bulbs for smell in your hippocampus which is involved with learning and memory these are some of the few areas that where you still have nerve cell division and you can actually can generate new ones to replenish maybe aging or damaged neurons so in terms of what the growth cone looks like you can see that there's the axon has expanded tip and all these kind of projections ice that hang off here now on these projections here in the growth cone you actually would find receptors for different chemicals and these the chemicals that these receptors pick up either guide or inhibit the growth of this cone in that direction so you can think about these little projections as being like a little nose that sniffs out the correct chemical scent trail for where this axon needs to connect and I think that's pretty amazing