Synapse
- 1. Synapse Starter activity Draw a labelled graph explaining the process of the action potential
- 3. Synapse Learning objectives Describe the structure and function of a synapse Understand the role of acetylcholine as a transmitter substance Distinguish between the post-synaptic potentials
- 4. Synapse A synapse is a specialised junction between 2 neurones where the nerve impulse is passed from one neurone to another There are 2 types of synapse in the nervous system (electrical and chemical) An electrical synapse can only be effective when neurones are very close together (2nm)
- 6. Chemical synapse In the chemical synapses, is when an impulse from the (presynaptic) neurone triggers a chemical transmitter substance which is binds to the (postsynaptic) neurone. As the action potential reaches the synaptic knob, this allows the calcium channels to open allow the Ca+ to diffuse into the knob Increase of Ca+ concentrations stimulates the movements of vesicles containing the neurotransmitter (acetylcholine) to the presynaptic membrane The mitochondria will generate energy (ATP) which will contribute to the production of the transmitter substance and also assists in the movement of the vesicles The vesicles (contain 10,000 neurotransmitter molecules) then fuse with the membrane and release the neurotransmitter by exocytosis into the synaptic cleft The transmitter substance then quickly diffuses across the synaptic cleft and will then bind to the receptors on the postsynaptic membrane which then open certain ion channels in the membrane The movement of ions (Na+, K+, or Cl-) in or out of the postsynaptic neurone results in the generation of a (postsynaptic potential) Postsynaptic potential will depend upon the which ions are moving and the build up of ions There are 2 types of postsynaptic potentials Excitatory postsynaptic potential occurs when the membrane has been depolarised (building up of a positive charge from -70mV to the firing level -55mV) Inhibitory postsynaptic potentials occurs when the membrane has been hyperpolarised (building up of a negative charge so it is further away from the firing level) Finally the transmitter substance is quickly removed from the receptors by diffusion and by enzymes and make the transmitter substance into inactive products It is very important that the transmitters are removed so it can maintain the nerve impulse (if left in the neuromuscular junction the region would be kept at the postsynaptic potential and cause the loss of muscle control, rather than returning it to the resting potential)
- 10. Neurotransmitter The chemical compound acetylcholine ( Ach) , was the first neurotransmitter to be identified. It is a chemical transmitter in both the peripheral nervous system (neuromuscular junctions) and central nervous system (brain). Acetylcholine is one of many neurotransmitters in the autonomic nervous system (ANS) and the only neurotransmitter used in the somatic nervous system (SNS). Acetylcholine is the neurotransmitter in all autonomic ganglia