Neurotransmitters and hormones are both chemical signals, but hormones are used in the endocrine system, released from glands into the blood, while neurotransmitters are released from the axon terminals of neurons to signal other neurons. Signals travel across neurons as electrical signals caused by the movement of large numbers of atomic ions across the membrane via protein channels. Charged proteins would be too large to quickly move through the channels in such large numbers.

Schwann cells are responsible for the myelination of axons in the peripheral nervous system.

Oligodendrocytes also myelinate axons, but they are found in the central nervous system. Astrocytes and satellite cells help support neurons, but do not contribute myelin to axons.

The central nervous system houses the brain and spinal cord only. The peripheral nervous system refers to all other nervous structures in the body.

Free nerve endings are usually located just under the skin, and respond to pain and large changes in temperature, making them part of the peripheral nervous system.

Oligodendrocytes, white matter, and gray matter are only found in the central nervous system. Interneurons are most commonly found in the spinal cord, but can be found in either the peripheral or central nervous system.

The components of the central nervous system are the brain and the spinal cord only. The remaining structures of the nervous system belong to the peripheral nervous system. The hemispheres of the brain and the spinal cord are part of the central nervous system. The hippocampus, cerebellum, hypothalamus, thalamus, and cerebral cortex are structures within the brain. The hippocampus is responsible for memory storage and the cerebellum is associated with balance and coordination. The cerebrum is responsible for processing information and higher thought. These structures are also part of the central nervous system.

The cranial nerves attach directly to the spinal cord, but branch out into the periphery. They are not considered part of the central nervous system. The adrenal glands and parathyroid glands are part of the endocrine system. Though they can respond to stimulation from the nervous system, they cannot be classified as part of the peripheral or central nervous system.

The thymus is an endrocrine gland located above the heart and is not part of the nervous system.

Though the pineal gland is found within the skull, it is not composed of nervous tissue and is not considered part of the central nervous system. Instead, it is an endocrine organ that interacts with the nervous tissue of the brain that surrounds it.

The thalamus and cerebellum are both structures of the brain, and are thus part of the central nervous system. Microglia function as macrophages in the central nervous system to prevent infection within the blood-brain barrier.

There are two major criteria that can be used to define nervous system categorizations. The first is location in the body. The central nervous system consists only of the brain and spinal cord, while the peripheral nervous system extends throughout the rest of the body. The central nervous system is enclosed by the blood-brain barrier, separating it from the rest of the body. The second classifier is mechanism of control. Some nervous pathways can be controlled voluntarily (somatic), while others are involuntary (autonomic).

The sympathetic and parasympathetic divisions are both peripheral autonomic pathways.

The nervous system has two principle divisions for function and two principle divisions for structure. Structurally, there are the central and peripheral nervous system divisions. Functionally, there are the somatic and autonomic divisions.

The spinal cord is found in the central nervous system, and is structurally divided into afferent sensory neurons and efferent motor neurons. Sensory neuron cell bodies are found in the dorsal root ganglion, while somatic motor neurons are found in the ventral horn of the spinal cord.

The nervous system has two principle divisions for function and two principle divisions for structure. Structurally, there are the central and peripheral nervous system divisions. Functionally, there are the somatic and autonomic divisions.

The somatic nervous system is responsible for voluntary actions, namely the innervation of skeletal muscle. The autonomic nervous system is responsible for all involuntary actions, including smooth muscle contraction, glandular stimulation, and other functions.

The peripheral nervous system carries both somatic and autonomic signals, innervating the entire periphery (not just skeletal muscle). The sympathetic and parasympathetic divisions of the nervous system are both autonomic. Though they innervate some skeletal muscles, they also play keys roles in other bodily functions, such as heart rate and blood pressure regulation.

The somatic nervous system is the only division to only innervate skeletal muscle.

The somatic nervous system is responsible for chiefly voluntary, conscious behavior, such as choosing a reaction to external stimuli sensed by one of the traditional five senses. The autonomic nervous system is responsible for involuntary bodily function, and can respond to sensations such as gas concentrations in the blood, changes in blood pressure, and slight deviations in body temperature, among many others.