GABA is the only neurotransmitter to actively suppress the formation of an action potential when binding to the dendrites on the postsynaptic neuron.

Norepinephrine, dopamine, serotonin, and glutamate have various physiological effects in different regions of the body, but all acts to stimulate the formation of an action potential.

The basal ganglia is a structure of the cerebrum that contains grey matter called the putamen, caudate nucleus, and globus pallidus. There are also two midbrain structures called the subthalamic nucleus and substantia nigra.

The voltage-gated channels along the axonal plasma membrane open and close in response to changes in voltage, and may exist in three distinct states: deactivated, activated, and inactivated. While the axon is at rest, these channels are said to be deactivated; they are impermeable to sodium ions since their activation gates are closed. Once the neuron gets depolarized to the threshold of the voltage-gated sodium channels, the activation gates open, allowing the influx of sodium down its concentration gradient into the cell. During this time the channels are in their activated state. At the peak of the action potential the activation gates are still open, but the inactivation gates close, stopping the flow of sodium through the channels. The channels are in the inactivated state due to the cell becoming depolarized. Once the membrane potential drops back down towards resting, the inactivation gates open, and the activation gates close, thereby deactivating the channels again, until another action potential depolarizes the membrane.

Neurons are the cells that make up the nervous system. Neurons are large, permanent cells that do not divide during adulthood and spend most of their lives in the G0 phase of the cell cycle. If part of a neuron is damaged, it undergoes Wallerian degeneration, meaning that the neuron degenerates distal to the injury, and does not undergo reactive gliosis in response to injury. Astrocytes, a type of glial cell, do this.

There are two types of support cells that myelinate axons in the nervous system: oligodendrocytes and Schwann cells. The difference between these two cell types is their location in the nervous system. Oligodendrocytes myelinate axons in the central nervous system, and Schwann cells myelinate axons in the peripheral nervous system.

Ependymal cells secrete cerebrospinal fluid and astrocytes help form and regulate the blood-brain barrier.

The pupillary sphincter muscles contain muscarinic cholinergic receptors that help the eyes to respond to parasympathetic tone. When this parasympathetic signal is blocked (antagonized) via atropine, you will observe a "sympathetic response" at the level of the pupil. In this scenario, you would observe the sympathetic response of pupil dilation. Hint: "aTROP'ine" and "seeing a TROPical setting" both cause your pupils to dilate nice and wide!

Cell bodies of preganglionic neurons are located in the central nervous system (CNS); they synapse onto autonomic ganglia. Parasympathetic ganglia are located in or near the effector organs giving them long preganglionic fibers and short postganglionic fiber. Sympathetic ganglia are located in the paravertebral chain, thus they have short preganglionic fibers and long postganglionic fibers.

Preganglionic neurons of the parasympathetic nervous system originate in the nuclei of the craniosacral region (cranial nerves and in the spinal cord segments of S2-S4). Those of the sympathetic nervous system originate in the thoracolumbar region (spinal cord segments of T1-L3).

The basal ganglia is a structure of the cerebrum that contains grey matter called the putamen, caudate nucleus, and globus pallidus. There are also two midbrain structures called the subthalamic nucleus and substantia nigra.

The autonomic nervous system (ANS) consists of a set of pathways to and from the central nervous system (CNS) that innervate and regulate smooth muscle, cardiac muscle, and glands. The ANS is distinct from the somatic nervous system, which innervates skeletal muscle. The ANS has three divisions the sympathetic, parasympathetic, and enteric nervous systems.