Problem
EPSPs (Excitatory Postsynaptic Potentials) and IPSPs (Inhibitory Postsynaptic Potentials) are the two types of electrical signals that can be transmitted along neuronal pathways. EPSPs are excitatory signals, meaning they tend to make a neuron more likely to fire an action potential. Meanwhile, IPSPs make a neuron less likely to fire-they inhibit it. A single neuron receives both excitatory and inhibitory signals at the same time, forming a balance of EPPSs and IPSPs for the nerve impulse to reach its destination.
EPSPs occur when the post-synaptic membrane is stimulated by an excitatory neurotransmitter, resulting in depolarization of the neuron. IPSPs are caused by inhibitory neurotransmitters and result in hyperpolarization or hyperpolarization of the post-synaptic membrane.
Tetanus is one example of how important IPSPs are to normal neuronal functioning. Tetanus is caused by an infective toxin known as tetanospasmin, which binds to inhibitory neurons causing them to fire constantly without inhibition. This leads to excessive muscle contractions due to their lack of inhibition from the motor neurons. In extreme cases, this can lead even lead to death due to respiratory failure or cardiac arrest as muscles become locked in spasm without any opportunity for relaxation due to the constant firing of IPSPs inhibiting motor neurons from sending out necessary motor signals for relaxation. This demonstrates just how important it is for there to be balanced transmission between both EPSP and IPSP signals; an excess or absence of either type can have dire consequences on neural functioning and overall health.
If toxin releases neurotransmitters that affect the motor neurons, why aren't other neurotransmitters affected (such as those that affect mental capabilities)?