action potential: pulse of electrical activity that occurs when a neuron sends information down its axon.

amygdala: almond-shaped structure deep within the brain, at the front of the temporal lobe; the amygdala is where emotions are processed.

arborization: growth and branching out of dendrites

astrocytes: star-shaped cells in the brain and spinal cord. They are the most abundant cells in the brain and are responsible for a wide variety of functions, such as providing nutrients to neural tissue and helping repair cells in the brain and spinal cord damaged by traumatic injury.

axon: part of the neuron that carries an impulse toward the synapse, which then transmits a chemical message to other neurons.

brain plasticity: the capacity of the brain to change structure and function, especially in response to the stimulation of repeated experiences. Plasticity is at its highest during childhood, when the brain is developing, but it is also present during adulthood, and it is the mechanism for learning and memory.

cannabinoids: both a class of chemical compounds that are found within the cannabis plant (marijuana) and also forms that occur naturally in the brain (called endocannabinoids). These substances interact with specific endogenous receptors in the brain that help reduce pain and anxiety.

cortisol: a hormone produced in the human body by the adrenal gland and released in response to stress, diverting energy toward any immediate threat, small or large. Many things in the environment can affect cortisol levels, from caffeine to sleep deprivation. Too much cortisol can suppress the immune system, raise blood pressure, and damage neurons, especially in the hippocampus.

dendrite: the branch-like part of a neuron that receives information from other neurons. Dendrites make contacts with the axons of nearby neurons, and usually the synapses are found on dendritic spines.

dopamine: a neurotransmitter that helps control the brain’s reward and pleasure centers.

endocannabinoids: the brain’s own naturally occurring cannabinoids, composed of molecules known as lipids.

endorphins: produced by the body during exercise, they interact with opiate receptors in the brain to reduce our perception of pain, much like morphine.

epinephrine: also known as adrenaline, a hormone that is released in response to strong emotions, such as fear and anger, and that, by sending energy to the muscles and increasing the heart rate, prepares the body for “fight or flight.”

frontal lobe: one of the four main regions of the brain, positioned at the frontmost portion of the brain and responsible for many executive functions, such as reasoning, planning, and other complex cognitive processes.

GABA: acronym for gamma-aminobutyric acid, a neurotransmitter that inhibits activity at the synapse. It’s important if your brain is overreacting to a stimulus.

glia: helper cells that aid myelin production, for instance, or that, in the case of astrocytes, a type of glial cell, digest parts of dead neurons. Unlike neurons, glial cells do not carry nerve impulses.

glutamate: synaptic receptors that are the brain’s main excitatory neurotransmitters. They are particularly important in memory formation and learning.

gray matter: the cortex, or part of the brain that contains neurons, as opposed to the white matter, which underlies the cortical gray matter.

gyri: the ridges in the brain’s wrinkled gray matter.

hippocampus: the part of the brain, located in the temporal lobes, involved chiefly in the processing of memories.

hypothalamus: the part of the brain, located just above the brainstem, that is responsible for major metabolic processes such as body temperature, hunger, thirst, and sleep.

limbic system: the part of the brain, located on both sides of the thalamus and just under the cerebrum, that includes structures involved in emotion, motivation, and memory.

long-term potentiation: abbreviated LTP, the long-lasting form of plasticity, or enhancement of synaptic transmissions between neurons, that is the main mechanism for learning and memory.

melatonin: hormone produced by the brain’s pineal gland that helps regulate circadian sleep rhythms.

myelin: the white matter that lines the axons, helping transmit the brain’s signals faster and more efficiently. Myelin covers many kinds of axons in the brain, spinal cord, and peripheral nerves.

neuron: the unique cells found in the nervous system that signal one another using neurotransmitters.

neurotransmitters: the chemical messengers released from one neuron, across the synaptic cleft, to a receptor site on the adjacent neuron.

occipital lobes: the part of the brain, located in the back, that houses the visual cortex.

parietal lobes: the brain region, located behind the frontal lobes and in front of the occipital, that is responsible for various senses, such as touch, as well as for visuospatial processing.

prefrontal lobes: the most anterior part of the frontal lobes, located behind the forehead, that is responsible for, among many other tasks, modulating social behavior, decision-making, and personality expression.

sulci: the grooves on the surface of the cerebral cortex that make up part of the “wrinkles” of the brain’s gray matter.

synapse: structure at the end of a neuron through which an electrical or chemical message is passed to another neuron. All thinking, feeling, movement, etc., depends on the transmission of messages through synapses.

synaptogenesis: the process of forming new synapses, occurring throughout a person’s life span but mostly during critical periods such as infancy, childhood, and adolescence.

temporal lobes: the areas, located at the sides of the brain, that process smell and sound and complex visual-recognition processes.

THC: acronym for tetrahydrocannabinol, the main active, mind-altering ingredient in cannabis.

ventral tegmental area (VTA): a group of neurons that is close to the midline on the floor of the midbrain, whose neurons connect to many areas of the brain, and that is the origin of the brain’s dopamine system. For that reason it plays a large role in the brain’s natural reward circuitry and is implicated in drug addiction.

white matter: the part of the brain that contains myelinated axon tracts responsible for transmitting electrical and chemical messages between neurons.