Neural signaling

• Membrane resting potential is =70mV
• During depolarization, Na+ voltage and ligand gated channels open, allowing Na+ to flow into the cell and make potential "more" positive (+30 mV)
• Depolarization starts when membrane potential crosses the threshold of -55mV
• There is a positive overshoot as Na+ keeps flowing in and in the presence of a + charge, the K+ voltage gate opens and K+ flows out of the cell t make it less positive for repolarization
• The K+ channel is slow to close, meaning it overshoots the negative potential as it goes below resting potential, this leads to the absolute refractory period when the K+ and Na+ pump opens
• The K+ and Na+ pump actively transports Na+ out of the cell and K+ into to restore Na+ concentration (high outside) and K+ concentration (high inside) to allow for the cycle to repeat
• The electrical signals flow from the dendrites attached to the cell body (with nucleus), through the axon and to the synaptic knobs
• Impulse works to change membrane potientials
• The action potential is a response to pressure/activity that causes electrical impulses to pass
• There is negatively charged proteins inside nerve fibres
• Passive/facilitated transport of ions helps to balance them across its the membrane. Due to K+ permeability of the membrane, it flows through the channels faster than Na+
• The resting is negative because of the negatively charged proteins inside the axon fibre so inside is more negatively charged compared to the outside
• During the absolute refractory period, no other stimulus can be collected
• Depolarization happens in response to a stimulus that causes Na+ to flow into cytoplasm of axon to reverse its polarity
• Electrical signal transmissions often occur at about 1m per second due to the small diameter of the axons- bigger diameters = increased speed due to reduced resistance
• With larger diameter of axons (500 um), squids are allowed to respond quickly to danger with faster movements due to faster transmission
• Schwann cells in the PNS make myelin
• Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's electrical wires) to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon.
• Myelinated axons speed up signal transmissions in nerve cells through resisting the electron transmission and preventing the depolarization of the nodes and acts as an insulator instead of a conductor. This forces the signals to jump between nodes of Ranvier in between, speeding up the rate of transmission (saltatory conduction)
• Myelinated axon

  A) Nodes of Ranvier

  B) Nucleus of Schwann cells

  C) Myelin shealth

  D) Neurofibrils

  E) Axon membrane

  F) Neurilemma

  
• The axons of the CNS are all myelinated but those of the PNS are not because the Schwann cells take up too much space that is not available in the PNS where a lot of neurons are packed into a small area. Additionally, speeding up the rate of transmission means more things are felt and if this was done for the PNS we would feel EVERYTHING which is not wanted
• Myelin sheaths also provide the axon with protection and nutrition
• Demyelinating diseases include multiple sclerosis where your immune system mistakes healthy nerve cells for harmful ones by identifying the myelin as "non-self"
• Demyelinating diseases causes inflammation and damages the sheath that can weaken muscles, cause double vision, numbness or tingling or others
• Signals only travel in one way due to there only being 1 transmission site and receptors only receiving in one direction
• synapse


  the meeting point between two neurons.
• There are two types of Synapses: Some of your synapses are electrical -- that would be like an immediate group text. Others are chemical synapses -- they take more time to be received and read, but they're used more often and are much easier to control, sending signals to only certain recipients.
• Your super fast electrical synapses send an: ion current flowing directly from the cytoplasm of one nerve cell to another, through small windows called gap junctions. They're super fast because the signal is never converted from its pure electrical state to any other kind of signal, the way it is in a chemical synapse. Instead, one cell and one synapse can trigger thousands of other cells that can all act in synchrony.
• The main advantage chemical synapses have over electrical ones is that they can effectively: convert the signal in steps -- from electrical to chemical back to electrical -- which allows for different ways to control that impulse.
• At the synapse, that signal can be: modified, amplified, inhibited, or split, either immediately or over longer periods of time.
• This set-up has two principal parts: The cell that's sending the signal is the presynaptic neuron, and it transmits through a knob-like structure called the presynaptic terminal, usually the axon terminal.
• This terminal holds a whole bunch of tiny: synaptic vesicle sacs, each loaded with thousands of molecules of a given neurotransmitter.
• The receiving cell, meanwhile, is, yes, thankfully the postsynaptic neuron, and it accepts the: the neurotransmitters in its receptor region, which is usually on the dendrite or just on the cell body itself.
• And these two neurons communicate even though they never actually touch. Instead, there's a tiny gap called a: synaptic cleft between them -- less than five millionths of a centimeter apart.
• When an action potential races along the axon of a neuron, activating sodium and potassium channels in a wave, it eventually comes down to the presynaptic terminal, and activates the voltage-gated calcium (Ca2+) channels there to open and release the calcium into the neuron's cytoplasm. This flow of positively-charged calcium ions causes all those tiny synaptic vesicles to fuse with the cell membrane and purge their chemical messengers. And it's these neurotransmitters that act like couriers diffusing across the synaptic gap, and binding to receptor sites on the postsynaptic neuron.: So, the first neuron has managed to convert the electrical signal into a chemical one. But in order for it to become an action potential again in the receiving neuron, it has to be converted back to electrical. And that happens once a neurotransmitter binds to a receptor. Because, that's what causes the ion channels to open. And depending on which particular neurotransmitter binds to which receptor, the neuron might either get excited or inhibited. The neurotransmitter tells it what to do. Excitatory neurotransmitters depolarize the postsynaptic neuron by making the inside of it more positive and bringing it closer to its action potential threshold, making it more likely to fire that message on to the next neuron. But an inhibitory neurotransmitter hyperpolarizes the postsynaptic neuron by making the inside more negative, driving its charge down -- away from its threshold. So, not only does the message not get passed along, it's now even harder to excite that portion of the neuron.
• Any region of a single neuron may have hundreds of synapses, each with different inhibitory or excitatory neurotransmitters. So the likelihood of that post-synaptic neuron developing an action potential depends on: the sum of all of the excitations and inhibitions in that area.
• Now, we have over a hundred different kinds of naturally-occurring neurotransmitters in our bodies that serve different functions. They help us: move around, and keep our vital organs humming along, amp us up, calm us down, make us hungry, sleepy, or more alert, or simply just make us feel good.
• neurotransmitters don't stay bonded to their receptors for more than a few milliseconds. After they deliver their message, they just sort of pop back out, and then either: degrade or get recycled. Some kinds diffuse back across the synapse and are immediately re-absorbed by the sending neuron, in a process called reuptake. Others are broken down by enzymes in the synaptic cleft, or sent away from the synapse by diffusion.
• And this mechanism is what many drugs -- both legal and illegal -- so successfully exploit, in order to create their desired effects.: These drugs can either excite or inhibit the production, release, and reuptake of neurotransmitters. And sometimes they can simply mimic neurotransmitters, tricking a neuron into thinking it's getting a natural chemical signal, when really it's anything but.
• Take cocaine, for example. Once it hits your bloodstream, it targets three major neurotransmitters -- serotonin, dopamine, and norepinephrine.