Research has shown that different parts of the brain handle different tasks. Typically, the right hemisphere of the brain handles most visual-spatial functions while the left hemisphere handles language. Exceptions to this rule are when a person is born or develops some sort of brain abnormality or damage. In this case, the brain often adapts so that one hemisphere takes over the job of the other one. 

The corpus callosum is a large band of fibers that relays signals between the two hemispheres of the brain.

Endorphins—released during exercise, sex, and excitement—work in relieving pain symptoms. Analgesics, painkillers, are developed to have similar neurological reactions with longer-lasting effects.

The occipital lobe is important for the sense of sight, and contains areas such as the primary visual cortex (i.e. V1). The temporal lobe is important for the sense of hearing. The parietal lobe is important for integrating sensory information of all types. Last, the frontal lobe is important for planning and decision-making.

The sympathetic nervous system is responsible for the "fight or flight" response, which is generally due to a rush of adrenaline that allows the body to respond maximally to a potential threat. 

While interesting, the other answers are incorrect. The parasympathetic nervous system is incorrect because this is the system that counters the body's stress response produced by the sympathetic nervous system. The central nervous system is responsible for the nerves within the skeletal structure as well as motor movements. It consists of the brainstem and spinal cord. Last, the somatic nervous system controls voluntary muscle movements. 

Melanin is a pigment found in the skin and eyes, but also in the brain. It is not to be confused with melatonin, a hormone and neurotransmitter. Acetylcholine is a neurotransmitter associated with, among other things, the stimulation of muscle contractions. Norepinephrine is both a hormone and a neurotransmitter and helps return the body to homeostasis after the release of epinephrine (adrenaline). Last, glutamate is a neurotransmitter associated with nearly all (about 90%) synapse connections.

The hippocampus is a brain structure located in the limbic system, which is associated with memory and emotion. Arguably, its most important role is associated with the transfer of information from short-term to long-term memory. Patients with non-functional hippocampi have little to no trouble consulting their long-term memories made before damaging this region; however, they are unable to form new long-term memories.

The frontal lobe contains the motor strip and is responsible for speech production. The motor strip is composed of all sending, or efferent neurons. When activated, these neurons contract muscles throughout the body. Speech production occurs in Broca's area, located in the left frontal lobe. Speech is produced through muscle actions; therefore, it is also dependent on efferent neurons in the frontal lobe.

The parietal lobe contains the input strip and has association areas involved with the following: math, body image, and spatial orientation. The input strip is the opposite of the motor strip located in the frontal lobe. The input strip receives information from sensory neurons from all over the body. The association area for math is located in the left angular gyrus. Association areas for body image and spatial orientation give us awareness of our body in 3D space and enable us to envision 3D space.

Broca’s aphasia results from damage to Broca’s area. It is a language disorder in which the individual has difficulty expressing language through speech and writing. These individuals must exert great effort to generate even ungrammatical or poorly structured speech. For this reason Broca’s aphasia is also called non-fluent aphasia; however, it is thought that their ability to understand language is significantly less affected. Contrastingly, Wernicke’s aphasia is a language disorder in which the individual is able to generate syntactically correct language that is semantically nonsensical (e.g. “the football offered to wash its hand). These individuals also do not seem to understand or correctly interpret language either. This aphasia is also called fluent aphasia and is related to damage to Wernicke’s area. Broca’s aphasia is located in the left frontal lobe in the brain, while Wernicke’s area is located in the left temporal lobe.