Circuit Elements Required for Neural Systems - Brain Theory from a Circuits and Systems Perspective - page 39

Fig. 3.6 Idealized synapse
(not drawn to scale)
Closer to the soma (the body of a neuron), inhibitory neurotransmitter ions may
contact and possibly surround a short segment of a branch, with the effect that they
deactivate portions of the membrane. Converting the membrane from active to
passive would soon attenuate a propagating pulse. An alternative possible mecha-
nism is that inhibitory neurotransmitters may provide internal electrons that tend to
discharge neural pulses. For either mechanism, the result is a significant attenuation
of propagating dendritic pulses.
There are many varieties of neurotransmitter-receptor combinations, some fast-
acting, some slower. A majority of neurotransmitters for neural communications
seem to be entities similar to those of glutamate (GLU) associated with excitatory
molecules and gamma amino butyric acid (GABA) associated with inhibitory
molecules.
Excitatory Ions
An intuitive way to visualize an excitory receptor is suggested in Fig. 3.7 . Initially,
sensitive particles within the membrane are held together by the strong intrinsic
electric field within the membrane. But as neurotransmitter ions randomly approach
a receiver they disrupt the alignment of membrane molecules. This triggers the
membrane and permit sodium ions to begin an action potential, energized in the
usual way by sodium, potassium, and other ions.