Figure 1.

Anatomy of the neuron. The brain comprised functional units called neurons, which process information both through electrical and chemical signals. Communication between neurons occurs through release of chemical mediators called neurotransmitters from synaptic boutons located distally on presynaptic inputs, which diffuses through a microscopic gap (the synapse) to receptors on the receiving (postsynaptic) neuron. Neurons display both functional and spatial polarity, with multiple dendrites receiving signals and typically a single axon for sending signals, both emerging from a central soma or cell body. In contrast, communication within a neuron occurs through transient changes in membrane voltages (the action potential), which are generated primarily through movement of ions through voltage-gated sodium (Nav) and potassium (Kv) channels. These channels are highly enriched at the axonal initial segment (AIS), a protein-dense region that functions as the site of action potential initiation. Ion channels are also found in high concentrations at the nodes of Ranvier, gaps in the insulating myelin sheath surrounding the axon that allow for rapid, or salutatory propagation of action potentials. (A) Schematic of the neuron. Excitatory postsynaptic potential (EPSP) and action potential (AP) shown in red, at the synaptic bouton and the axon initial segment, respectively. (B) Confocal microscopy of a primary rat hippocampal neuron, labeled with anti-PanNav (red) and anti-MAP2 (blue) antibody visualizing axonal and somatodendritic compartments, respectively.