Membrane is more permeable to potassium than sodium. There are also large, negatively charged proteins inside axoplasm. A rapid polarity change in membrane of a neuron results from physical stimulus, electrical shock, pH change, etc. Transmission Across a Synapse . Axon membrane at synapse is presynaptic membrane, dendrite provides postsynaptic membrane and gap is synaptic cleft.
Neurotransmitters are chemicals stored in synaptic vesicles of axon.
Nerve impulse causes presynaptic membrane to open channels to calcium ions that interact with actin filaments that pull synaptic vesicles to membrane. Neurotransmitter in vesicles is released into synaptic cleft and diffuses across to postsynaptic membrane. If excitatory, the postsynaptic membrane potential is decreased, sodium ion channels open, and likelihood of neuron firing is increased. Neurotransmitters Are Varied a. Twenty-five different types of neurotransmitters include gases CO and NO, and neuropeptides or amino acids and derivatives. Failure to repackage or eliminate neurotransmitters in synapse causes continuous stimulation or inhibition.