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Electricity and Nerves By Nihal Sogandji, Aaron Williams and Mohammed AliElectricity, Nerves and the Nervous System Nihal SogandjiThe Nervous SystemCells of the Nervous System 1.Neurones 2.Glial CellsReflex ArcCharge (Q): ‘Amount’ of electricity - Net charge arises from an imbalance of positive and negative ions. Measured in Coulombs, C. Voltage (V): Amount of potential work that can be done per unit charge, V=W/Q measured in Volts (V). This value is always relative and requires a reference region. Current (I): Rate of movement of charge past a point in a net direction measured in Amperes (A) Resistance (R) = V/I = constant for Ohmic conductors. The inverse of resistance is conductance g = 1/R Capacitance: Simplest capacitors are made of two conductors separated by an insulator that allows differential charges to build up on either side. Capacitance is the amount of charge stored per voltage. Measured in Farads (F).The Equivalent CircuitThe Structure of the Plasma MembraneAction potentials and Conduction Aaron WilliamsHow is the signal carried down the axon? • As transient depolarisation – Membrane is polarised – This polarisation changes at a point on the membrane –depolarisations to occur alongside itequentThe all or nothing nature of action potentials • “In an excitable tissue, the magnitude of the response is independent of stimulus strength, provided the stimulus is above threshold” • This is due to voltage gated channels● Stimulus above threshold ● Voltage gated sodium channels open, allowing sodium cations to enter the cell ● Voltage gated sodium channels inactivate ● Voltage gated potassium channels open, allowing potassium ions to flow out of the cell ● Return to resting potentialPropagation of the Action Potential ● Electrostatic attraction causes cations to move down the axon, stimulating other action potentials ● Unidirectional, as upstream regions of the membrane are hyperpolarised ● Speed of propagation dependent on many factorsFactors affecting conduction speed ● Temperature ● Myelination Mohammed Ali The axon terminal and the synapse passes from one neuron to another.on between two neurons through whichg an impulse Two types olf junctions: ● Gap junctions - electrical impulse passes directly from axon to dendrites ● Chemical transmission via synapse Gap junctions Flow of ions allows for the sodium ios to carry on the local circuit current to the next neuron to trigger an action potential in the same way as described before Gap junction = two connexons one connexon = 6 connexin protein subunits Quicker than chemical transmissionChemical transmission - synapse Allows for greater specificity and the ability for summation (will discuss further) Use “presynpatic” and “postsynpatic” instead proportional to the square of that distance. thus (because the synaptic cleft is only 20 to 40 nm, the delay is still tinySNARE Complex Presynaptic vesicles containing neurotransmitter is located to the presynaptic neurone membrane by SNARE complexes. Allows quick fusion and release of neurotransmitter into the synaptic cleft Don’t need to know specifics- simply just that binding of calcium causes increased coiling (zippering) of SNARE proteins, causing formation of a fusion pore allowing release of neurotransmitter throguh the pore, and then the vesicle is reformed (Please feel free to ask questions about the process though if you would like) Process of chemical synaptic transmission and 2. Voltage-gated calcium ion channels open (they close due to a calcium sensor) 3. Calcium binds to synaptotagmin, causing pore formation described earlier 4. Release of acetylcholine into synaptic cleft summation 5. receptordiffuses across to post-synaptic membrane and binds to acetylcholine 6. After two ACh bind, the acetylcholine receptor opens and allows passage of 7. Sodium ions causes a small depolarisation called an excitatory post synaptic IPSP is (sometimes) caused by flow of negatively potenital (EPSP) cytoplasm and can affect whether an actione potential occurs - allows integration of EPSP =/= ACTION POTENTIAL information Multiple EPSP arestimulatedand they sum up to surpass threshold and stimulate action potential. This process allows for summation.https://www.kenhub.com/en/library/anatomy/the-nervous-system https://serendipstudio.org/exchange/brains/structures https://www.kenhub.com/en/library/anatomy/the-nervous-system https://www.researchgate.net/figure/Reflex-arc-It-consists-of-a-receptor-a- sensory-neuron-a-reflex-center-spinal-cord-a_fig1_263858109 https://itectec.com/electrical/electronic-is-the-50-loss-of-energy-when-charging-a-cap- from-a-battery-a-set-rule-in-stone/ https://www.researchgate.net/figure/Equivalent-electrical-circuit-for-the-cells- membrane-4_fig1_3132006 https://www.khanacademy.org/science/ap-biology/cell-structure-and- function/plasma-membranes/a/structure-of-the-plasma-membrane https://www.kenhub.com/en/library/anatomy/action-potentialfeedback form QR CODE HERE