Renshaw cells are interneurons in the spinal cord that release the inhibitory neurotransmitter glycine.

Competitive inhibitors directly compete with ligands for the same binding sites (active sites). Irreversible inhibitors are molecules that bind irreversible to the active site. Covalent modulators are molecules that bind covalently to proteins and changes their activity. pH and temperature may alter the 3D shape of the protein and can be irreversible, while ligand binding, and competitive inhibition is a reversible process that involves the formation of weak, not covalent, bonds.

Cholinergic neurons, whether in the sympathetic or parasympathetic nervous system, release acetylcholine as the neurotransmitter. Nonadrenergic, noncholinergic neurons include some postganglionic parasympathetic neurons of the gastrointestinal tract, which release substance P and nitric oxide. Adrenergic neurons release norepinephrine. 

Norepinephrine is released by adrenergic neurons.

Cholinergic neurons release acetylcholine as their neurotransmitter (in the sympathetic or parasympathetic nervous system).

Nonadrenergic, noncholinergic neurons (which include postganglionic parasympathetic neurons of the gastrointestinal tract) release substance P and nitric oxide.

The depolarization of the presynaptic membrane causes voltage-gated calcium channels to enter from the extracellular space. This causes the synaptic vessels which are docked on the presynaptic terminal to fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft. 

Acetylcholine is the neurotransmitter found at the neuromuscular junction and many other synapses found in the nervous system. It binds to receptors on the postsynaptic membrane to induce muscular contraction.

GABA is the most common inhibitory neurotransmitter in the brain. Glutamate is the most common excitatory neurotransmitter in the brain. Dopamine is a monoamine which can sometimes be inhibitory, but is not the most common. 

Nociceptors are pain receptors that. Mechanoreceptors respond when tissue is deformed by mechanical forces. Photoreceptors respond to light. Chemoreceptors respond to chemicals. Thermoreceptors respond to changes in temperature. 

Pacinian corpuscles are found in deeper in the dermis rather than in the dermal papillae. Merkel cells are found in the epidermal-dermal border and are responsible for perception of light and touch. Carcinoma is a type of tumor. Meissner's corpuscles are the mechanoreceptors that are found in the dermal papillae, and are very sensitive to light touches.

When there is tissue damage, substance P plays a very important role in the sensation of pain through stimulating primary afferent neurons in pain perception pathways. Enkephalin is a neurotransmitter that inhibits the neurons that transmit pain impulses to the brain. Serotonin is a monoamine neurotransmitter and dopamine is a catecholamine/phenethylamine neurotransmitter.