Model Essay Paragraphs

A nitrogen containing compound that is essential in organisms is the sodium ion channels on the membrane of the post synaptic neurone. When an action potential travels down the axon and reaches the synaptic knob it stimulates the calcium ion channels to open, causing calcium ions to flood in. This influx of calcium ions into the synaptic knob via facilitated diffusion stimulates the release of vesicles containing the neurotransmitter, acetylcholine in cholinergic synapses, to move towards the membrane of the synaptic knob where it is released into the synaptic cleft via exocytosis. When this has happened the neurotransmitter diffuses across the cleft and binds to specific receptors on the post synaptic neurone of sodium ion channels, allowing them to open and cause an influx of sodium ions into the neurone, causing depolarisation and an action potential if the threshold is exceeded. Acetylcholinesterase breaks down acetyl/ethanoic acid and choline to close the sodium ion channels and these two molecules re-enter the synaptic knob and recombine to form acetylcholine using ATP, ready for a new action potential to arrive. The importance of the sodium ion channels on the post synaptic neurone is that it ensures an action potential can be created and continued from the previous neurone, allowing our body to respond to stimuli that may need us to move away from something, needing muscle contraction following the sliding filament theory where ATP is used to produce a power stroke using the myosin heads and actin filaments. ;