Biopsychology - Synaptic Transmission

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  • Created on: 24-06-22 09:27
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  • Synaptic Transmission
    • Key Words:
      • Excitation
        • When a neurotransmitter, such as adrenaline, increases the positive charge of the postsynaptic neuron.
          • This increases the likelihood that the neuron will fire and pass on the electrical impulse.
      • Neurotransmitter
        • Brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another.
        • Neurotransmitters can be broadly divided into those that perform an excitatory function and those that perform an inhibitory function.
      • Inhibition
        • When a neurotransmitter, such as serotonin, makes the charge of the postsynaptic neuron more negative.
          • This decreases the likelihood that the neuron will fire and pass on the electrical impulse.
      • Synaptic transmission
        • The process by which neighbouring neurons communicate with each other by sending chemical messages across the gap (the synaptic cleft) that separates them.
      • Synapse
        • The tiny gap between the end of the presynaptic neuron and the postsynaptic neuron.
    • Neurotransmitters
      • Neurotransmitters are chemicals that diffuse across the synapse to the next neuron in the chain.
      • Once the neurotransmitter crosses the gap, it is taken up by the postsynaptic receptor site - the dendrites of the next neuron.
      • Here, the chemical message is converted back into an electrical impulse and the process of transmission begins again in this other neuron.
      • There are many types of neurotransmitters which have been identified in the brain, as well as in the spinal cord and some glands.
      • Each neurotransmitter has its own specific molecular structure that fits perfectly into a postsynaptic receptor site (similar to the lock and key).
      • Neurotransmitters have specialist functions, e.g. acetylcholine (ACh) is found at each point where a motor neuron meets a muscle, upon its release - it will cause muscles to contract.
    • Chemical transmission - synapses
      • Neurons communicate with each other within groups known as neural networks.
      • Each neuron is separated from the next by a synapse.
        • The synapse includes the space between them (called the synaptic cleft) as well as the presynaptic terminal and postsynaptic receptor site.
      • Signals within neurons are transmitted electrically (known as action potential).
      • Signals between neurons are transmitted chemically by synaptic transmission.
      • When the electrical impulse reaches the end of the neuron (the presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles.
    • Summation
      • Whether a postsynaptic neuron does fire is decided by the process of summation.
      • The excitatory and inhibitory influences are summon:
        • If the net effect on the postsynaptic neuron is excitatory = postsynaptic neuron is more likely to fire - and, the inside of the synaptic neuron becomes positively charged.
        • If the net effect on the postsynaptic neuron is inhibitory = postsynaptic neuron is less likely to fire.
      • Once the electrical impulse is created it travels down the neuron.
      • The action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the threshold.
    • Excitation and Inhitibion
      • Neurotransmitters have either an excitatory or inhibitory effect on the neighbouring neuron.
        • The neurotransmitter serotonin causes inhibition in the receiving neuron = results in the neuron becoming more negatively charged and less likely to fire.
        • The neurotransmitter adrenaline (an element of the stress response and it is also a hormone) causes excitation of the postsynaptic neuron by increasing its positive charge and making it more likely to fire.


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