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Biology - Nervous coordination and muscle, Synapse, Nerve cells pass…

- - - - The nervous system uses nuerons to pass electrical impulses along. The process is rapid and quick. Everything is localised
        
        What are the 3 types of nuerons
        
        Sensory nuerone
        
        What dies it do?
        
        It transmits nerve impulses from the receptor to the relay nuerone.
        
        How is it structured? (just need to know basic shape)
        
        I know it's a sensory nuerone becaause the nerve endings are on both sides and the cell body is at the top
        
        Relay nuerone
        
        What do they do?
        
        transmit impulses from the sensory nuerone to the relay nuerine
        
        How are they structured? (just need to know basic shape)
        
        Motor nuerone
        
        What do they look like?
        
        What are the schwann cells?
        
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        What are the nodes of randvier?
        
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        What do they do?
        
        They are connected to the effecor (a muscle or a gland) - That is how the nervous system (like seeing someone you hate) can trigger the horemonal system
        
        How do nerve cells work?
        
        Resting potential
        
        What is the process of a nerve cell staying at -70mv?
        
        3 sodium ions are actively transported out of the axon whereas 2 potassium iona are actively transported in via facilitated diffusion
        
        The sodium ions naturally diffuses back into the axon whereas the potassium begins to diffuse out
        
        However, the axon is extremely permeable to potassium and not permeable to sodium (K+ gated channels = open, most of the Na+ channels = closed), This creates an electrochemical gradient of sodium and pootassium ions. This is what decreases the pd to -70mv
        
        What is meant by an electrochemical gradient?
        
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        What is resting potential?
        
        Resting potential is when there is a constant potential difference of -70 mv inside the axon as opposed tho the outside of the axon. The axon is polarised :red_flag:
        It's when the nuerone is unstimulated
        
        What is meant by a potential difference of - 70 mv
        
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  - - - Glands produce chemicals that are transported in the blood. The response is long-lasting and the process is reletivelly slow
- - - - Apart from being recycled why else is it good that ACh breaks down
        
        It prevents constantly generating an action potential in the post synaptic nueone (cos AChE is breaking ACh down, so the sodium channels close)
  - - - Synapses that produce a new action potential in the postsynaptic nuerone
- - - - How is this possible?
        
        The nuerotransmitter is only made in the presynaptic nuerone
        
        The specific receptor proteins that the nuerotransmitter binds to are only found in postsyaptic nuerones
  - - - If there is a small stimuli (low frequency action potentials), the concentration of nuerotransmitter released may not be high enough to trigger an action potential in the postsynaptic nuerone. However a process called summation happens to allow this, but there are 2 types
        
        What are the 2 types of summation?
        
        Spatial summation
        
        What is it?
        
        When there are many different presynaptic nuerones, each realeasing (a small amount of) nuerotransmitter. Together they will exceed the threshold value and trigger an action potential in the postsynaptic nuerone
        
        Temporal summation
        
        What is it?
        
        When a single presynaptic nuerone releases (a small conc.) nuerotransmitter many times over a shorth period of time
  - - - These are synapses that make it less likely for an action potential to be triggered in the postsynaptic nuerone
    - - A presynaptic nuerone releases a type of nuerotransmitter that binds to chloride ion protein channels in the post synaptic nuerone
      - This causes the chloride ion protein channe to open.
      - This also causes nearby potassium ion channels to open
      - There is an influx of Cl- and an outflux of K+ via FD
      - This causes the membrane potential to be less than -70mv (it would be like -90mv) (hyperpolarisation)
      - This makes it less likely for an action potential to be created as a larger influx of Na+ ions are needed to produce one.
- - - - What is an electrochemial gradient?
        
        https://youtu.be/Ba02v7eoVWQ
        It's not 1 arrow but rather 2 arrows, an electrical gradient and a chemical gradient.
        The sodium is going from a high conc. to a low conc. despite there being a positive charge (an electrical gradient)
- - - - Reepolarisation
        
        How does it work
        
        After 40mv the sodium gated channels close and the potassium volatge gated channels open (Although some of them are opened at resting potential, most of them are triggered open at +40mv) . (the membrane is more permeable to potassium). This means that potassium ions diffuse out of the cell, due to their electrochemical gradient . (making the inside of the axon more negative)
        
        Hyperpolarisation
        
        The potassium gates are slow to close so there is a slight 'overshoot' where too many potassium ions diffuse out, this means the potential is lower than -70mv
        
        The axon is back at resting potential
        
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        What is repolarisation?
        
        When that paticular point of the axon goes back to -70mv, it has to do that or else it'll always be charged, and we'd always feel that stiumili
      - Refactory period
        
        What is it? :red_flag:
        
        The refactory period is the period which the membrane of the axon cannot be depolarised, so no new action potential can be initiated.
        (This is because after they have been depolarised, the sodium ions are shut and CANNOT be opened for a while)
        
        What is the point of the refactory period?
        
        It ensures the wave of depolrisation is only in one direction. Some Na+ ions might go to the left, but no depolarisation would happen there due to refactory period. so the wave of depolarisation only occurs to the right
        (an action potenial cannot be propagated in a reigon that is refactory)
        
        It ensures that action potentials pass along as discreate impulses.
        (this is cos a new action potential can't be formed behind the 1st one)
        
        It limits the frequency of impulses at the axon at a given time. This decreases the strength of the stimuli.
        (it stops us feeling immense pain)
    - - Diameter of the axon
        
        If you increase the diameter, there will be less resistance to the flow of ions. There will also be less leakage of ions from a large axon (Leakage makes the potentials harder to maintain)
      - Temperature :red_flag:
        
        If you increase the temperature, you increase the rate of diffusion of ions. This means there will be a faster impulse
        
        What happens if the temperature is too high?
        
        If the temperature is too high, the proteins in the plasma membrane would denature. (this means that channel proteins would stop working)
      - Weather the nuerone has a myelin sheath or not
        
        In a non-myelinated axon, the impulse travels like a wave along the whole length, each part has to go though depolarisation
        In a myelinated axon, the impulses just have to depolarise the next node as the nuerone's cytoplasm conducts enough electrical charge to depolarise the next node. The impulse 'jumps' from node to node. This is called Saltatory conduction