Neural Signalling

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7 Terms

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Neurons

  • transmit nerve impulses

  • make up the nervous system

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Structure of neurons

  • Dendrites: short branched fibres that convert chemical information from other neurons or receptor cells into chemical signals

  • Axon - elongated fibre that transmits electrical signals to terminal regions for communication with other neurons/effectors

  • Soma - cell body containing nucleus and organelles

  • Myelin sheath - insulates

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Nerouns at resting potential

  • sodium-potassium pump which maintains this - pumps 3 Na+ ions out, 2 K+ ions in

  • inside of cell = negative - higher Na+ concentration on outside, higher K+ on inside

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Neve impulse transmissions

  1. Resting potential

  2. Threshold potential - stimuli must cross it to activate neuron

  3. Depolarisation - stimulus depolarizes membrane, reaches potential around -55mV which triggers opening of voltage gated sodium channels - Na+ ions rush in due to gradient + attraction - influx makes neuron more positive - depolarizes to +30 mV

  4. Repolarization - voltage gated K+ channels open, allows K+ to leave neuron which makes cell more negative - returns to resting potential

  5. Hyperpolarization - too negative through efflux of K+ ions

  6. Return to resting state - sodium potassium pump returns neuron to resting state at approx. -70mv

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Variation in velocity of nerve impulses

  1. Myelination - nodes of Ranvier - jump = increase speed

  2. diameter of axon → smaller = slower, bigger = fast

    1. e.g., squids = giant axon which reduces resistance and faster conduction speed

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Synaptic Transmission (definition)

  • Occurs btw. arrival of an impulse at the presynaptic membrane and initiation of an impulse in the postsynaptic membrane

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Synaptic Transmission (process)

  1. release of neurotransmitter - arrival causes depolarization in the presynaptic membrane

  2. influx of Ca2+ causes vesicles (w neurotransmitters) to move to presynaptic membrane - due to voltage-gated calcium channel which open

  3. release of neurotransmitters into the synaptic gap by exocytosis

  4. new vesicles are formedw ith neurotransmitters - pumped back from synaptic gap

  5. depolarization occurs in post-synaptic neuron - action potential occurs