Neurons and Synaptic Transmission

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  • Neuron and Synaptic Transmission
    • Structure and Function of Neurons
      • Neurons = specialised cells that carry neural information throughout the body
      • Dendrites receive signals from other neurons or from sensory receptors
      • Cell body is the control centre of the neuron. From here the impulses are carried along the axon
      • Axon is where the impulses are terminated at the axon terminal
        • Myelin sheath is an insulating layer around the axon if it is damaged the impulses slow down
      • Sensory neurons:
        • Carry nerve impulses from sensory receptors the spinal cord and the brain
          • When they reach the brain they are converted into sensations so the organism can react accordingly
          • Impulses terminated in the spinal cord allows for reflexes occur quickly with out delay
      • Relay neurons:
        • Allow sensory and motor neurons to communicate
        • Lie within the brain and the spinal cord
      • Motor neurons:
        • Form synapses with muscles and control their contractions
        • Release  neurotransmitters that trigger a response and lead to muscle movement
          • Strength of muscle contraction depends on the rate of the firing of axons of motor neurons that control
    • Synaptic Transmission
      • 1) An action potential arrives at the terminal button at the end of the axon
      • 2) For it to be transferred it must cross a synapse between the presynaptic neuron and the postsynaptic neuron
      • 3) End of the axon there are a number of synaptic vesicles that contain neurotransmitters
      • 4)  Once the AP reaches the vesicles they release their contents through exocytosis
      • 5)  The neurotransmitters diffuses across the gap between the pre and post cell where it binds to receptors
      • 6) Once the y are activated the receptors produce excitatory or inhibitory effects on the postsynaptic neuron
    • Excitatory and Inhibitory Neurotransmitters
      • Excitatory neurotransmitters e.g noradrenaline increase the likelihood that an excitatory signal is sent to the postsynaptic cell which is then more likely to fire
        • Nervous systems on switches
        • When binding with a postsynaptic cell causes an electrical change in the membrane resulting in an EPSP
      • Inhibitory neurotransmitters e.g serotonin decrease the likelihood of the neuron firing. They are generally responsible for calming the mind and bodying filtering out unnecessary excitatory neurons
        • Nervous systems off switches
        • When bonded with a postsynaptic receptor results in an IPSP
      • Nerve cells can receive both IPSP and EPSP at the same time the likelihood of the cell firing is determined  by adding up the synaptic input
        • The strength of an EPSP can be increased by spacial summation and temporal summation
          • Spacial summation is where a large number of EPSPs are generated at many different synapses on the same postsynaptic neuron at the same time
          • Temporal summation is when a large number of EPSPs are generated at the same synapse by high frequency action potentials on the presynaptic nerve


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