The vast majority of neurons are myelinated (by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system) in order to allow for saltatory conduction, which greatly increases conduction speed. This occurs as the action potential "leaps" from one node of Ranvier to the next node of Ranvier rather than having to pass down the entire length of the axon. 

The soma is the cell body of the neuron (D). The soma is the site of neuron metabolism and protein synthesis.

The dendrites of the neuron (A) receive incoming action potential signals. The axon (B) sends the action potential outward from the soma to the axon terminal (C). Vesicles of neurotransmitter are released from the axon terminal to the dendrites of other nearby neurons. Neurons can have numerous dendrites, but will only have one soma and one axon.

The sympathetic nervous system is responsible for stress responses, while the parasympathetic nervous system is responsible for resting responses. The sympathetic nervous system causes increased heart rate, pupil dilation, suppressed digestion, inhibited salivation, and dilated bronchi.

The most basic anatomy for a neuron involves three structures: a soma, a dendrite, and an axon. The dendrite receives an electrical impulse and sends it to the cell body, or soma. The axon will then send the action potential towards its synapse with another neuron. The axon hillock is a wider region of the axon where the soma and axon join together.

While every neuron will have only one soma and one axon, some neurons have several dendrites. This means that a neuron can receive information from several different locations through different dendrites, but can only send it in one direction along the single axon.

The parasympathetic nervous system is responsible for the "rest and digest" functions of the body. The sympathetic nervous system is associated with "fight or flight" responses in the body. Increased blood flow to skeletal muscles is a common result of the sympathetic nervous system being stimulated, not the parasympathetic nervous system.

The nervous system has two major divisions: the central nervous system and the peripheral nervous system. The peripheral nervous system is further divided into the somatic nervous system and the autonomic nervous system. The autonomic nervous system can then be divided into the sympathetic and parasympathetic branches.

General: Central and Peripheral

Peripheral: Somatic and Autonomic

Autonomic: Sympathetic and Parasympathetic

The vagus nerve is responsible for slowing down the heart rate. It also increases digestive activity. Knowing this, we can conclude that the vagus nerve has a "rest and digest" function in the body. This means that it is part of the parasympathetic nervous system.

The sympathetic nervous system is responsible for stress responses, or "fight or flight." The somatic nervous system is under voluntary control, while the autonomic nervous system is involuntary. Both the sympathetic and parasympathetic divisions fall under the autonomic umbrella. The central nervous system includes only the brain and spinal cord.

Reflex arcs are unique neural pathways due to the fact they are constructed to cause voluntary muscles to move without a stimulus being integrated in the brain. Instead, the integration of the stimulus occurs in the spinal cord, where an efferent signal is immediately created towards the voluntary muscle. 

The sympathetic nervous system is responsible for the "fight or flight" response. The parasympathetic nervous system does the opposite (rest and digest). The enteric nervous system helps with digestion. The remaining two answer choices are too broad and do not answer the question as well as the sympathetic nervous system. Note that the sympathetic and parasympathetic nervous systems are branches of the autonomic nervous system, which itself is a branch of the parasympathetic nervous system.

The sodium potassium-pump is used in order to establish the negative resting potential in neurons. Since both sodium and potassium ions are positively charged, there needs to be more ions leaving the cell compared to ions entering. The pump accomplishes this by pumping three sodium ions out of the cell, while pumping two potassium ions into the cell. This loss of positive charge inside the cell results in the negative resting potential of neurons.

Thank about the net transfer of ions. Three positive sodium ions out of the cell for every two positive potassium ions into the cell is the same as one positive ion leaving the cell. When positive ions leave, the inside of the cell becomes more negative, helping the cell reach its resting potential of around –70mV.