The medulla oblongata is responsible for autonomic functions, such as breathing rate and heart rate regulation. Dysfunction of the medulla oblongata could result in problems with breathing rhythm.

The cerebellum is responsible for coordination and balance. The hypothalamus regulates the fight-or-flight response, sex drive, thirst, and hunger. The midbrain is the center for auditory and visual signal relay to the cortex. The hippocampus functions in the retention of memories.

The neuron has three major portions: the dendrites, the cell body, and the axon. The dendrites receive electrical stimulation from other neurons, and the axon sends electrical signals to other neurons.

Signals travel down the axon until they reach the axon terminal. Vesicles of neurotransmitter are released from the axon terminal, where they travel across the synapse to the dendrite of the post-synaptic neuron. This initiates a signal in the dendrite, which is carried to the cell body. Signals from different dendrites sum together in the axon hillock, which can stimulate depolarization of the axon and allow for signal propagation.

Accommodation of the lens for near vision is a parasympathetic controlled response. Each of the other answer choices is a sympathetic controlled response. The parasympathetic nervous system pertains to "rest and digest" activities. The sympathetic nervous system pertains to "fight or flight" activities. In the case of the eye lens, the ciliary muscle is innervated by parasympathetic fibers, which, when activated, cause the muscle to contract and change the shape of the lens. This alters the refractive capability in a way to accommodate near vision.

Spinal nerves coming off of the spinal cord can be thought of as the combination of both posterior and anterior roots. This means that they contain both sensory and motor neuron axons. These nerves can also carry autonomic functions to organs of the body as well.

Relaxation of bronchial smooth muscle is an involuntary process, which is accomplished by the autonomic system rather than the somatic. It is also a part of the "fight or flight" response, which relates to the sympathetic system. Postganglionic neurons directly stimulate target tissues, while preganglionic neurons stimulate postganglionic neurons.

The nervous system has a variety of support cells in addition to neurons. These support cells are collectively called the neuroglia.

Microglia are used to remove debris from the nervous system, astrocytes provide support to neurons, and Schwann cells are used to myelinate the axons in the peripheral nervous system. It is the role of ependymal cells to synthesize and circulate cerebrospinal fluid using their cilia.

The cerebellum is found in the posterior portion of the brain and controls balance and coordination. The cerebrum controls upper level cognition, such as conscious thought, and memory. The hypothalamus is a crucial endocrine structure and helps regulate hormone secretion from the pituitary and body homeostasis. The brain stem controls the most basic duties of the body, which include breathing rate, heart rate, and blood pressure.

Digestion and excretion are not consciously controlled, which means that they fall under the control of the autonomic nervous system. The autonomic nervous system has two branches: the sympathetic and parasympathetic nervous systems. The sympathetic nervous system is involved in "fight or flight" activities, while the parasympathetic nervous system controls "rest and digest" activities. As a result, digestive and excretory activity is increased by the parasympathetic nervous system.

The central nervous system contain components of both the sympathetic and parasympathetic nervous system and controls a variety of nervous functions. Only the brain and spinal cord are considered part of the central nervous system. The somatic nervous system is under voluntary control, and is primarily linked to skeletal muscle.

The main stages of an action potential are depolarization, hyperpolarization, and repolarization. The resting membrane potential of the cell is roughly –65mV. During depolarization the neuron initiates the action potential by opening voltage-gated sodium channels. This allows an influx of sodium ions, which raises to membrane potential to roughly 50mV. Sodium channels are quick to react to the action potential stimulus, but voltage-gated potassium channels are slower. After the depolarization, the potassium channels open, allowing for a rapid efflux of potassium ions. This causes the membrane potential to rapidly drop, so much so that it becomes more negative than the resting potential. This drop below resting potential is known as hyperpolarization. Repolarization then occurs by action of the sodium-potassium pump, which uses ATP to reestablish the resting potential by removing sodium and importing potassium.

The absolute refractory period occurs when the initial gating mechanism of the sodium channels is activated, making them impervious to stimuli. In contract, the relative refractory period is closely linked to hyperpolarization and describes the period during which the cell can be stimulated, but only if the stimulus is large enough to overcome the hyperpolarized environment and reach threshold.

The action potential is composed of key changes in voltage for the neuronal cell body. The resting voltage in the cell is negative, due to the action of the sodium-potassium pump. When an action potential reaches the cell, voltage-gated sodium channels open, and sodium ions rush into the cell. This raises the voltage inside the cell in a process called depolarization.

As the voltage in the cell rises, the sodium channels begin to close, and voltage-gated potassium channels begin to open. As potassium ions exit the cell, the voltage drops back down to negative once again. This process is called repolarization. It takes a bit longer for the potassium channels to close, which causes a temporary hyperpolarization of the cell; however, once they close and the cell will eventually return to the initial negative resting potential by action of the sodium-potassium pump.