My picture displays that neuron cell.

 

 

Cell signaling through the use of G-protein-linked receptors occurs in a cyclic series of events. Before the ligand binds, the inactive G-protein can bind to a newly-revealed site on the receptor specific for its binding. Once the G-protein binds to the receptor, the resultant shape change activates the G-protein, which releases GDP and picks up GTP. The subunits of the G-protein then split into the α subunit and the β subunit. One or both of these G-protein fragments may be able to activate other proteins as a result. Later, the GTP on the active α subunit of the G-protein is hydrolyzed to GDP and the β subunit is deactivated. The subunits re-associate to form the inactive G-protein, and the cycle starts over.

The picture is just a representation of the process and part of the reason why I chose it.

1 - channel domains (typically four per channel), 2 - outer vestibule, 3 - selectivity filter, 4 - diameter of selectivity filter, 5 - phosphorylation site, 6 - cell membrane.

 

The largest family of cell surface receptors are the G-protein coupled receptors (GPCRs).  There are hundreds of different GPCR proteins, and nearly a third drugs target this type of receptor.  A diverse set of ligands bind to this type of receptor, including peptide hormones, neurotransmitters, and odor molecules.  These receptors all have a similar structure with seven transmembrane domains.  On the basis of their seven-transmembrane domain structure, many GPCRs have been identified in the human genome.  Proteins that were identified by sequence homology, but whose ligands are not known, are termed orphan receptors.

GPCRs associate with heterotrimeric G-proteins (green), that is, G-proteins composed of three different subunits:  alpha, beta, andgamma.  The subunits are tethered at the membrane surface by covalently attached lipid molecules.

When a ligand binds, the receptor activates the attached G-protein by causing the exchange of GTP (yellow) for GDP (red).  The activated G-protein then dissociates into an alpha (G-alpha) and a beta-gamma complex.   G-alpha bound to GTP is active, and can diffuse along the membrane surface to activate (and sometimes inhibit) target proteins, often enzymes that generate second messengers.  Likewise, the beta-gamma complex is also able to diffuse along the inner membrane surface and affect protein activity.

Inactivation occurs because G-alpha has intrinsic GTPase activity. After GTP hydrolysis, G-alpha bound to GDP will reassociate with a beta-gamma complex to form an inactive G-protein that can again associate with a receptor.

The GTPase activity of the G-alpha can be made faster by other proteins--sometimes the target protein, sometimes a separate regulatory protein. Cholera toxin causes a chemical modification that prevents GTP hydrolysis and leads to unregulated signaling.

 

 

Ion channel is used to restore the balance of ions across a membrane. It serves as a counterbalance to active transport, a process where a cell uses energy to actively pump ions and other charged molecules across a membrane in order to establish ion gradients or alter the pH of an organelle to activate enzymes. Ion channels are regionally located in the neuron.
An ion channel is usually equipped with four basic parts: a central conduction pathway (opening) for ions to pass through, an ion recognition site to allow passage of specific ions (selectivity filter), one or more gates that may open or close, and a sensor that senses the triggering signal and transmits it to the gate.
 

      Voltage-gated ion channels are a class of transmembrane proteins that are activated by changes in electrical potential difference across the cell membrane. Voltage-gated ion channels are generally composed of several subunits arranged in such a way that there is a central pore through which ions can travel down their electrochemical gradients. The channels tend to be ion-specific, although similarly sized and charged ions may sometimes travel through them. Voltage-gated ion channels that are selectively permeable to each of the major physiological ions—Na+, K+, Ca2+, and Cl-The functionality of voltage-gated ion channels is attributed to its three main discrete units: closed-activatable, activated (open and conducting), and closed-inactivatable. Na channels are made up of 1800 to 4000 amino acids with four transmembrane repeat domains. The molecules of the protein interact with each other and surrounding molecules to form a structure that defines its function. 
Each of the four transmembrane domains contains a voltage-sensitive alpha helix that is displaced in the open or conduction state. The linker between the III and IV repeat domains act as a ball and chain to fold up into the channel opening to block sodium ions (Na+) from moving through the channel in the inactivatable state. When a channel opens Na+ moves from outside the membrane, through the channel, to the inside following both a concentration gradient and a voltage gradient. Shortly after the channel opens it becomes energetically favorable for the linker between the III and IV repeat to move into the opening and block further Na+ movement. Voltage-gated sodium channels and calcium channels are made up of a single polypeptide with four homologous domains. Each domain contains 6 membrane-spanning alpha helices. One of these helices, S4, is the voltage sensing helix. The S4 segment contains many positive charges such that a high positive charge outside the cell repels the helix, keeping the channel in its closed state. In general, the voltage-sensing port. 
The picture shows a voltage-gated ion channel. At resting, the voltage-gated ion channel is closed and ions cannot pass. neuron stimulation -> the membrane potential will increase -> conformational change in the channel and allows ions to pass. The channel remains open briefly -> further conformational change -> inactivated by the so-called "ball and chain" portion of the protein. The channel will remain inactive and refractory for a brief period of time before returning to the active, but closed, resting position.