We would like to thank the Society for Neuroscience for their premission to reproduce this glossary. Some ammendations have been made.
A
Acetylcholine: A neurotransmitter in both the brain, where it may help regulate memory, and in the peripheral nervous system, where it controls the actions of skeletal and smooth muscle.
Action Potential: This occurs when a neuron is activated and temporarily reverses the electrical state of its interior membrane from negative to positive. This electrical charge travels along the axon to the neuron's terminal where it triggers or inhibits the release of a neurotransmitter and then disappears.
Adrenal Cortex: An endocrine organ that secretes corticosteroids for metabolic functions: aldosterone for sodium retention in the kidneys, androgens for male sexual development, and estrogens for female sexual development.
Adrenal Medulla: An endocrine organ that secretes epinephrine and norepinephrine for the activation of the sympathetic nervous system.
Affective Psychosis: A psychiatric disease relating to mood states. It is generally characterized by depression unrelated to events in the life of the patient, which alternates with periods of normal mood or with periods of excessive, inappropriate euphoria and mania.
Agonist: A neurotransmitter, a drug or other molecule that stimulates receptors to produce a desired reaction.
Amino Acid Transmitters: The most prevalent neurotransmitters in the brain, these include glutamate and aspartate, which have excitatory actions, and glycine and gamma-amino butyric acid (GABA) which have inhibitory actions.
Amygdala: A structure in the forebrain that is an important component of the limbic system.
Androgens: Sex steroid hormones, including testosterone, found in higher levels in males than females. They are responsible for male sexual maturation.
Anosognosia: A syndrome in which a person with a paralysed limb claims it is still functioning. One of Professor Ramachandran's patients, who had suffered a stroke which had paralysed the left side of her body, refused to accept that her arm couldn't move. Even though lucid in every other aspect (including awareness of the fact that she had suffered a stroke) she claimed her left arm was carrying out tasks even though clearly it wasn't. Anosognosia means denial of illness. An explanation may involve close analysis of the different roles of the left and right hemispheres of the brain.
Antagonist: A drug or other molecule that blocks receptors. Antagonists inhibit the effects of agonists.
Aphasia: Disturbance in language comprehension or production, often as a result of a stroke.
Auditory Nerve: A bundle of nerve fibers extending from the cochlea of the ear to the brain, which contains two branches: the cochlear nerve that transmits sound information and the vestibular nerve that relays information related to balance.
Autonomic Nervous System: A part of the peripheral nervous system responsible for regulating the activity of internal organs. It includes the sympathetic and parasympathetic nervous systems.
Axon: The fiberlike extension of a neuron by which the cell sends information to target cells.
B
Basal Ganglia: Clusters of neurons, which include the caudate nucleus, putamen, globus pallidus and substantia nigra, that are located deep in the brain and play an important role in movement. Cell death in the substantia nigra contributes to Parkinsonian signs.
Blindsight: Some patients who are effectively blind because of brain damage can carry out tasks which appear to be impossible unless they can see the objects. For instance they can reach out and grasp an object, accurately describe whether a stick is vertical or horizontal, or post a letter through a narrow slot . The explanation appears to be that visual information travels along two pathways in the brain. If only one is damaged, a patient may lose the ability to see an object but still be aware of its location and orientation.
Blindspots: Blindspots can be produced by a variety of factors. In fact everyone has a small blindspot in each eye caused by the area of the retina which connects to the optic nerve. To test this, visit our Mindgames section. These blindspots are often filled in by the brain using information based on the surrounding visual image. In some cases, patients report seeing unrelated images in their blindspots. One reported seeing cartoon characters. This phenomenon may involve other pathways in the brain.
Brainstem: The major route by which the forebrain sends information to and receives information from the spinal cord and peripheral nerves. It controls, among other things, respiration and regulation of heart rhythms.
Broca's Area: The brain region located in the frontal lobe of the left hemisphere that is important for the production of speech.
C
Capgras' delusion: A rare syndrome in which the patient is convinced that close relatives usually parents, spouse, children or siblings are impostors. It may be caused by damage to the connections between the areas of the brain dealing with face recognition and emotional response. A sufferer might recognise the faces of his loved ones but not feel the emotional reaction normally associated with the experience.
Catecholamines: The neurotransmitters dopamine, epinephrine and norepinephrine that are active both in the brain and the peripheral sympathetic nervous system. These three molecules have certain structural similarities and are part of a larger class of neurotransmitters known as monoamines.
Cerebral Cortex: The outermost layer of the cerebral hemispheres of the brain. It is responsible for all forms of conscious experience, including perception, emotion, thought and planning.
Cerebral Hemispheres: The two specialized halves of the brain. The left hemisphere is specialized for speech, writing, language and calculation; the right hemisphere is specialized for spatial abilities, face recognition in vision and some aspects of music perception and production.
Cerebrospinal Fluid: A liquid found within the ventricles of the brain and the central canal of the spinal cord.
Cholecystokinin: A hormone released from the lining of the stomach during the early stages of digestion which acts as a powerful suppressant of normal eating. It also is found in the brain.
Circadian Rhythm: A cycle of behavior or physiological change lasting approximately 24 hours.
Classical Conditioning: Learning in which a stimulus that naturally produces a specific response (unconditioned stimulus) is repeatedly paired with a neutral stimulus (conditioned stimulus). As a result, the conditioned stimulus can become able to evoke a response similar to that of the unconditioned stimulus.
Cochlea: A snail-shaped, fluid-filled organ of the inner ear responsible for transducing motion into neurotransmission to produce an auditory sensation.
Cognition: The process or processes by which an organism gains knowledge of or becomes aware of events or objects in its environment and uses that knowledge for comprehension and problem-solving.
Cone: A primary receptor cell for vision located in the retina. It is sensitive to color and used primarily for daytime vision.
Cornea: A thin, curved transparent membrane on the surface of the front of the eye. It begins the focusing process for vision.
Corpus Callosum: The large bundle of nerve fibers linking the left and right cerebral hemispheres.
Cortisol: A hormone manufactured by the adrenal cortex. In humans, it is secreted in greatest quantities before dawn, readying the body for the activities of the coming day.
Cotard's syndrome: A disorder in which a patient asserts that he is dead, claiming to smell rotting flesh or worms crawling over his skin. It may be an exaggerated form of Capgras' delusion, in which not just one sensory area (ie face recognition) but all of them are cut off from the limbic system. This would lead to a complete lack of emotional contact with the world.
D
Dendrite: A tree-like extension of the neuron cell body. Along with the cell body, it receives information from other neurons.
Dopamine: A catecholamine neurotransmitter known to have multiple functions depending on where it acts. Dopamine-containing neurons in the substantia nigra of the brainstem project to the caudate nucleus and are destroyed in Parkinson's victims. Dopamine is thought to regulate emotional responses, and play a role in schizophrenia and cocaine abuse.
Dorsal Horn: An area of the spinal cord where many nerve fibers from peripheral pain receptors meet other ascending nerve fibers.
E
Endocrine Organ: An organ that secretes a hormone directly into the bloodstream to regulate cellular activity of certain other organs.
Endorphins: Neurotransmitters produced in the brain that generate cellular and behavioral effects like those of morphine.
Epinephrine: A hormone, released by the adrenal medulla and the brain, that acts with norepinephrine to activate the sympathetic division of the autonomic nervous system. Sometimes called adrenaline.
Estrogens: A group of sex hormones found more abundantly in females than males. They are responsible for female sexual maturation and other functions.
Evoked Potentials: A measure of the brain's electrical activity in response to sensory stimuli. This is obtained by placing electrodes on the surface of the scalp (or more rarely, inside the head), repeatedly administering a stimulus, and then using a computer to average the results.
Excitation: A change in the electrical state of a neuron that is associated with an enhanced probability of action potentials.
F
Follicle-Stimulating Hormone: A hormone released by the pituitary gland. It stimulates the production of sperm in the male and growth of the follicle (which produces the egg) in the female.
Forebrain: The largest division of the brain, which includes the cerebral cortex and basal ganglia. It is credited with the highest intellectual functions.
Frontal Lobe: One of the four divisions (parietal, temporal, occipital) of each hemisphere of the cerebral cortex. It has a role in controlling movement and associating the functions of other cortical areas.
G
Gamma-Amino Butyric Acid (GABA): An amino acid transmitter in the brain whose primary function is to inhibit the firing of neurons.
Glia : Specialized cells that nourish and support neurons.
Glutamate: An amino acid neurotransmitter that acts to excite neurons. Glutamate probably stimulates N-methyl-D-aspartate (NMDA) receptors that have been implicated in activities ranging from learning and memory to development and specification of nerve contacts in a developing animal. Stimulation of NMDA receptors may promote beneficial changes, while overstimulation may be the cause of nerve cell damage or death in neurological trauma and stroke.
Gonad: Primary sex gland: testis in the male and ovary in the female.
