Synaptic Transmission

• Synaptic transmission is the process by which neighbouring neurons communicate with each other by sending chemical messages across the synapse that separates them.
• Neurotransmitters are brain chemicals released from the synaptic vesicles that relay signals across the synapse from one neuron to another. (can be divided into inhibitory or excitatory neurotransmitters).
• Excitation is when a neurotransmitter increases the + charge of the neuron making it more likely to fire and pass on the impulse. (Depolarisation)
• Inhibitory is when a neurotransmitter increases the - charge of the neuron making it less likely to fire and pass on the impulse. (Hyperpolarisation)
• Postsynaptic receptor site - the dendrites of the next neuron.
• Reflex arc: stimulus - receptor - SN - RN - MN - effector - response

  
• Process of reflex arc: Sensation detected in sensory neurone receptors. This results in electrical signals being pushed along dendrite then to axon then it reaches the axon terminal. Converts into chemical signal and crosses synaptic cleft by relay neurone, which is located in spine. This passed immediately to motor neurone. This signal reaches effector triggering movement response.
• 1ST STEP - action potential arrives at axon terminal. This causes vesicles to merge with membrane of presynaptic cell releasing neurotransmitters into synaptic cleft which diffuses to post-synaptic cleft.
• 2ND STEP - Summation is the effect of all inhibitory and excitory neurotransmitters influences on postsynaptic cell. Added/subtracted and if threshold is reached formation of new action potential likelihood is increased and often travels down to next axon.
• 3RD STEP - Once neurotransmitters detected by receptors they detach and are reabsorbed into presynaptic cell (Reuptake) of neurotransmitter neural impulse - happens at transport proteins.
• Selective serotonin reuptake inhibitors - blocks reabsorption of serotonin into presynaptic cell.
• Neural networks are the groups through which neurons communicate with each other.
• Signals within neurons are transmitted electrically but signals between neurons are transmitted chemically across the synapse.
• Serotonin causes inhibition in receiving neuron making it more negatively charged, therefore, less likely to fire.
• Adrenaline causes excitation in post synaptic neuron increasing its' positive charge, therefore making it more likely to fire.
• Multiple simultaneous inputs = spatial summation
• Repeated inputs = temporal summation