The chorda tympani branch of the facial nerve (cranial nerve VII), which is carried by the lingual branch (of the trigeminal nerve), allow for special sensory taste fibers for the anterior two-thirds of the tongue. The general sensory innervation for the anterior two=thirds of the tongue is provided by the lingual branch of the mandibular nerve from the trigeminal nerve (cranial nerve V).

The glossopharyngeal nerve (cranial nerve IX) provides sensory and taste to the posterior one-third of the tongue. Hypoglossal nerve (cranial nerve XII) provides motor innervation for all the muscles of the tongue (except for palatoglossus which is innervated by the pharyngeal branch of the vagus nerve (cranial nerve X). 

The dermatome responsible for sensation at the level of the nipple is T4.

C2 is responsible for sensation at the posterior half of the skull "cap" and C4 at the level of a low collar shirt. T10 is responsible for sensation at the level of the navel (to remember this think bellybutton...belly buTEN). L4 includes the kneecaps.

Astrocytes provide support and nutrition to neurons within the brain and spinal cord. Myelin sheath insulates the axons of some neurons which allows them to conduct impulses faster. Nerve fibers are single nerve axons that are surrounded by a sheath of connective tissue.  Nerves themselves are cordlike structures that transmit nerve impulses. 

Both A delta and C fibers are associated with the perception of pain. This can be broken down more specifically to A delta fibers that are slightly mylinated and carry "Fast" sharp pain that is immediately felt. While C fibers carry "slow" pain due to being unmyelinated and is associated with chronic pain.

C fibers are associated with chronic pain perception because they transmit "slow pain". This is due to the fibers being unmyelinated. In addition, these fibers send projections to the limbic system and the thalamus which causes the brain to develop chronic pain associations.

Neurotransmitters will never enter the postsynaptic neuron. They will attach to receptors on the membrane of the postsynaptic neuron, release, and then be dealt with while in the synaptic cleft. In some instances, the neurotransmitter simply diffuses away from the synapse, but in most cases synaptic proteins help to recycle the molecules. Some enzymes will break the neurotransmitter into parts, which then reenter the presynaptic neuron and are reassembled. Acetylcholinesterase is a common example of this type of enzyme. Other neurons use membrane pumps to retrieve neurotransmitter from the synaptic cleft.

Once an action potential has reached the end of the presynaptic neuron, voltage-gated calcium channels are stimulated, allowing calcium to enter the neuron. This influx of calcium stimulates the release of neurotransmitters into the synaptic cleft.

The neurotransmitters then bind to receptors on the surface of the postsynaptic neuron to generate small electrical stimuli. The sum of these stimuli must reach threshold in order for an action potential to be generated.

GABA and acetylcholine are two common neurotransmitters. GABA generally inhibits the postsynaptic neuron, while acetylcholine generally excites/stimulates the postsynaptic neuron.

Acetylcholine activates muscarinic receptors in postganglioinic parasympathetic nervous tissue and nicotinic receptors in skeletal muscle fibers, and preganglionic sympathetic and parasympathetic nervous tissue.

Muscarinic acetylcholine receptors (mAChRs) are found in the G protein-receptor complexes in the cell membrane of certain neurons. The suffix -ergic means exhibiting or stimulating the activity of. For example, dopaminergic receptors bind to dopamine. 

Neurotransmitters are packaged in vesicles, traveling through the synaptic cleft (space between neurons) from the pre-synaptic membrane to the post-synaptic membrane, where they bind to their receptors and influence the post-synaptic membrane potential.