Which neurotransmitter is active in both the peripheral and central nervous systems

Glossary: concepts and abbreviations

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A

Acalculia. See dyscaculia.

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. 

ADHA. Attention Deficit Hyperactivity Disorder.   A syndrome of learning and behavioural problems.  Characterised by difficulty in sustaining attention, impulsive behaviour (as in speaking out of turn), and often by hyperactivity - also referred to as minimal brain dysfunction.

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. 

Alzheimer's disease. A progressive degenerative disease of the brain associated with ageing, characterised by diffuse atrophy throughout the brain with distinctive lesions called senile plaques and clumps of fibrils called neurofibrillary tangles.  Cognitive processes of memory and attention are affected.

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. 

Amnesia. A memory deficit that occurs resulting in brain damage.

Amygdala. A part of the brain involved in emotions, emotional learning, and memory.  Each hemisphere contains an amygdala, shaped like an almond and located deep in the brain, near the inner surface of each temporal lobe.

Androgens: Sex steroid hormones, including testosterone, found in higher levels in males than females. They are responsible for male sexual maturation.

 
Angular gyrus. An area of the cortex in the parietal lobe associated with processing the sound structure of language and associated with reading.

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. 

Anterograde amnesia. The loss of ability to remember events post injury.

Aphasia: Disturbance in language comprehension or production, often as a result of a stroke. 

Apolipoprotein E. (Or "apoE").   Has been studied for many years for its involvement in cardiovascular diseases.   It has only recently been found that one allele (gene factor) of the aopE gene (E4) is a risk factor for Alzheimer's disease.

Artificial intelligence (AI).  A field of computer science which attempts to develop machines that behave intelligently.

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. 

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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. 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. 
 

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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. 

Cerebellum. A part of the brain located at the back and below the principal hemispheres, involved in the regulation of movement.

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 is also found in the brain. 

Choline. A chemical required for synthesising acetylcholine, a neurotransmitter needed for memory storage and muscle control.

Cholinergic systems. Also acetylcholine systems.  Systems in which the neurotransmitter acetylcholine is present, wihich occur at neuromuscular junctions between motor neurons and the brain.  The loss of acetylcholine (Ach) neurons is a contributing factor in Alzheimer's disease.

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. Operation of the mind which includes all aspects of perceiving, thinking, learning, and remembering.

Cognitive maps.  Mental representations of objects and places as located in the environment.

Cognitive neuroscience. Study and development of mind and brain research aimed at investigating the psychological, computational, and neuroscientific bases of cognition.

Cognitive science. Study of the mind.   An interdisciplinary science that draws upon many fields including neuroscience, psychology, philosophy, computer science, artificial intelligence, and linguistics.   The purpose of cognitive science is to develop models that help explain human cognition - perception, thinking, and learning.

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.

(cerebral) Cortex.  Outer layer of the brain.

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D

Decay theory.  The theory that forgetting is the result of spontaneous decay of memory traces over time.

Decoding.  An elementary process in learning to read alphabetic writing systems (for example, English, Spanish, German or Italian), in which unfamiliar words are deciphered by associating the letters within the word to corresponding speech sounds.

(senile) Dementia. A condition of deteriorated mentality that is characterised by marked decline from the individual's former intellectual level and often by emotional apathy.  Alzheimer's disease is one form of dementia.

Dendrite. A tree-like extension of the neuron cell body. Along with the cell body, it receives information from other neurons. 

Depression. A lowering of vitality of functional activity: the state of being below normal in physical or mental vitality.

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. 

Dyscalculia. Impairment of the ability to perform simple arithmetical computations, despite conventional instruction, adequate intelligence and socio-cultural opportunity.

Dyslexia. A disorder manifested by difficulty in learning to read despite conventional instruction, adequate intelligence, and socio-cultural opportunity.

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E

EEG. Electroencephalogram.  A measurement of the brain's electrical activity via electrodes.  EEG is derived from sensors placed in various spots on the scalp, which are sensitive to the summed activity of populations of neurons in a particular region of the brain.

Emotional intelligence. Sometimes referred to as emotional quotient ("EQ").  Individuals with emotional intelligence are able to relate to others with compassion and empathy, have well-developed social skills, and use this emotional awareness to direct their actions and behaviour.   The term was coined in 1990.

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. 

Epilepsy. A chronic nervous disorder in humans which produces convulsions of greater or lesser severity with clouding of consciousness; it involves changes in the state of consciousness and of motion due to either an inborn defect of a lesion of the brain produced by tumour, injury, toxic agents, or glandular disturbances.

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. 

ERP. Event-related potentials.   Electric signals are first recorded with an EEG.  Data from this technology is then time locked to the repeated presentation of a stimulus to the subject, in order to see the brain in action.  The resulting brain activation (or event-related potentials) can then be related to the stimulus event.

Estrogens. A group of sex hormones found more abundantly in females than males. They are responsible for female sexual maturation and other functions. 

Excitation. A change in the electrical state of a neuron that is associated with an enhanced probability of action potentials. 

Excitatory synapses.  Synapses where neurotransmitters decrease the potential difference across neuron membranes.

Experience-dependent. A property of a functional neural system in which variations in experience lead to variations in function, a property that might persist throughout the life-span.

Experience-expectant. A property of a functional neural system in which the development of the system has evolved to critically depend on stable environmental inputs that are roughly the same for all members of species (i.e. stimulation of both eyes in new-borns during development of ocular dominance columns).  This property is thought to operate early in life.

Explicit memory. Memories that can be retrieved by a conscious act, as in recall, and can be verbalised, in contrast to implicit or procedural memories, which are less verbally explicit.

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. 

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F

Fan effect.  The phenomenon that memory retrieval is slower when more additional material is associated with items composing the original memories.

fMRI. Functional Magnetic Resonance Imaging.  Use of an MRI scanner to view neural activity indirectly through changes in blood chemistry (such as the level of oxygen) and investigate increases in activity within brain areas that are associated with various forms of stimuli and mental tasks (see MRI).

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. 

Fragile X syndrome. One of the most common causes of inherited mental retardation and neuropsychiatric disease in human beings.

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, believed to be involved in planning and higher order thinking.

Functional imaging. Represents a range of measurement techniques in which the aim is to extract quantitative information about physiological function.

Fusiform gyrus. A cortical region running along the ventral (bottom) surface of the occipital-temporal lobes associated with visual processes.  Functional activity suggests that this area is specialised for visual face processing and visual word forms.

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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. 

Graphemes.  The smallest written unit of an alphabet, a single letter

Growth Cone. A distinctive structure at the growing end of most axons. It is the site where new material is added to the axon. 

Gyrus. The circular convolutions of the cortex of which each has been given an identifying name.

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H

(cerebral) Hemisphere. One of two sides of the brain classified as "left" and "right"

Hippocampus. A seahorse-shaped structure located within the brain and considered an important part of the limbic system. It functions in learning, memory and emotion. This part of the brain is also important in processing and storing long-term memories.

Hormones. Chemical messengers secreted by endocrine glands to regulate the activity of target cells. They play a role in sexual development, calcium and bone metabolism, growth and many other activities. 

Hypothalamus. A complex brain structure composed of many nuclei with various functions. These include regulating the activities of internal organs, monitoring information from the autonomic nervous system and controlling the pituitary gland. 

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I

Immediate Memory. A phase of memory that is extremely short-lived, with information stored only for a few seconds. It also is known as short-term and working memory.

 
Implicit memory. Memories that cannot be retrieved consciously but are activated as part of particular skills or action, and reflect learning a procedure of a pattern, which might be difficult to explicitly verbalize or consciously reflect upon (i.e. memory that allows you to engage in a procedure faster the second time, such as tying a shoe).

Information-processing approach.  An analysis of human cognition into a set of steps whereby abstract information is processed.

Inhibition. In reference to neurons, this is a synaptic message that prevents the recipient cell from firing. 

Interference theory.  The theory of forgetting when other memories interfere with the retention of the target memory.

Ions. Electrically charged atoms or molecules. 

IQ. A number held to express the relative intelligence of a person originally determined by dividing mental by chronological age and multiplying by 100.

Iris. A circular diaphragm that contains the muscles which alter the amount of light that enters the eye by dilating or constricting the pupil. It has an opening in its center. 

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K

Korsakoff's Syndrome. A disease associated with chronic alcoholism, resulting from a deficiency of vitamin B-1. Patients sustain damage to part of the thalamus and cerebellum. Symptoms include inflammation of nerves, muttering delirium, insomnia, illusions and hallucinations and a lasting amnesia. 

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L

Left-brained thinking. A lay term based on the misconception that higher level thought processes are strictly divided into roles that occur independently in different halves of the brain.  Thought to be based on exaggerations of specific findings of left hemisphere speclialisations, such as the neural systems that control speaking.

Limbic System. Also known as the "emotional brain".  It borders the thalamus and hyphothalamus and is made up of many of the deep brain structures - including the amygdala, hippocampus, septum and basal ganglia - that work to help regulate emotion, memory and certain aspects of movement. 

Lobe. Gross areas of the brain sectioned by function (occipital, temporal, parietal and frontal).

Long-Term Memory. The final phase of memory in which information storage may last from hours to a lifetime.

Long-term potentiation (LTP).  The increase in neuron responsiveness as a function of past stimulation.

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M

Mania. A mental disorder characterized by excessive excitement. A form of psychosis with exalted feelings, delusions of grandeur, elevated mood, psychomotor overactivity and overproduction of ideas. 

MEG. Magnetoencephalography.   A non-invasive functional brain imaging technique sensitive to rapid changes in brain activity.  Recording devices (SQUIDS) placed near the head are sensitive to small magnetic fluctuations associated with neural activity in the cortex.  Responses to events can be traced out on a millisecond time scale with good spatial resolution for those generators to which the technique is sensitive.

Melatonin. Produced from serotonin, melatonin is released by the pineal gland into the bloodstream. It affects physiological changes related to time and lighting cycles. 

Memory Consolidation. The physical and psychological changes that take place as the brain organizes and restructures information in order to make it a permanent part of memory. 

Memory span.  The amount of information that can be perfectly remembered in an immediate test of memory.

Mental imagery. Also known as visualisation.  Mental images are created by the brain from memories, imagination, or a combination of both.  It is hypothesised that brain areas responsible for perception are also implicated during mental imagery.

Mental images.  Internal representations consisting of visual and spatial information.

Metabolism. The sum of all physical and chemical changes that take place within an organism and all energy transformations that occur within living cells. 

Mitochondria. Small cylindrical particles inside cells that provide energy for the cell by converting sugar and oxygen into special energy molecules. 

Mnemonic technique.  A technique which enhances memory performance. Monoamine Oxidase (MAO). The brain and liver enzyme that normally breaks down the catecholamines norepinephrine, serotonin and dopamine. 

Motor Neuron. A neuron that carries information from the central nervous system to the muscle. MRI.  Magnetic Resonance Imaging.  A non-invasive technique used to create images of the structures within a living human brain, through the combination of a strong magnetic field and radio frequency impulses.

Multiple intelligences. Term originally coined to more fully explain the different and equally important ways of processing the environment.

Myasthenia Gravis. A disease in which acetylcholine receptors on the muscle cells are destroyed, so that muscles can no longer respond to the acetylcholine signal in order to contract. Symptoms include muscular weakness and progressively more common bouts of fatigue. Its cause is unknown but is more common in females than in males and usually strikes between the ages of 20 and 50. 

Myelin/Myellination.   Compact fatty material that surrounds and insulates axons of some neurons. Process by which nerves are covered by a protective fatty substance.  The sheath (myelin) aorund the nerve fibres acts electrically as a conduit in an electrical system, ensuring that messages sent by nerve fibres are not lost en route.

Myth of three. Also know as the "Myth of the Early Years".  This assumption states that only the first three years really matter in altering brain activity and after that the brain is insensitive to change.  This could be considered an extreme "critical period" viewpoint.

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Nerve Growth Factor. A substance whose role is to guide neuronal growth during embryonic development, especially in the peripheral nervous system. 

Neurodegenerative diseases. Disorders of the brain and nervous system leading to brain dysfunction and degeneration including Alzheimer's diseases, Parkinson's disease and other neurogenerative disorders that frequently occur with advancing age.

Neurogenesis. The birth of new cells in the brain, including neurons.

Neuromyth. Misconception generated by a misunderstanding, a misreading or misquoting of facts scientifically established (by brain research) to make a case for use of brain research, in education and other contexts.

Neuron. Nerve cell. It is specialized for the transmission of information and characterized by long fibrous projections called axons, and shorter, branch-like projections called dendrites. Basic building block of the nervous system; specialised cell for integration and transmission of information.

Neurotransmitter. A chemical released by neurons at a synapse for the purpose of relaying information via receptors. 

NIRS. Near Infrared Spectroscopy.   Non-invasive imaging method which allows measures of the concentrations of deoxygenated haemoglobin in the brain by near-infrared absorption. (near-infrared light at a wavelength between 700 nm and 900 nm can partially penetrate through human tissues).

Nociceptors. In animals, nerve endings that signal the sensation of pain. In humans, they are called pain receptors. 

Norepinephrine. A catecholamine neurotransmitter, produced both in the brain and in the peripheral nervous system. It seems to be involved in arousal, reward and regulation of sleep and mood, and the regulation of blood pressure. 

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Occipital lobe. Posterior region of the cerebral cortex receiving visual information.

Organelles. Small structures within a cell that maintain the cells and do the cells' work. 

OT. Optical Topography.   Non-invasive trans-cranial imaging method for higher-order brain functions.   This method, based on near-infrared spectroscopy, is robust to motion, so that a subject can be tested under natural conditions.

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P

Pain Asymbolia. People with this condition do not feel pain when, for example, stabbed in the finger with a sharp needle. Sometimes patients say they can feel the pain, but it doesn't hurt. They know they have been stabbed, but they do not experience the usual emotional reaction. The syndrome is often the result of damage to a part of the brain called the insular cortex. The stabbing sensation is received by one part of the brain. But the information is not passed on to another area, the one which normally classifies the experience as threatening and triggers - through the feeling of pain - an avoidance reaction.

Parasympathetic Nervous System. A branch of the autonomic nervous system concerned with the conservation of the body's energy and resources during relaxed states. 

Parietal Lobe. One of the four subdivisions of the cerebral cortex. It plays a role in sensory processes, attention and language. Involved in many functions such as processing spatial information, body image, orienting to locations, etc.

Peptides. Chains of amino acids that can function as neurotransmitters or hormones. 

Periaqueductal Gray Area. A cluster of neurons lying in the thalamus and pons. It contains endorphin-producing neurons and opiate receptor sites and thus can affect the sensation of pain. 

Peripheral Nervous System. A division of the nervous system consisting of all nerves which are not part of the brain or spinal cord. 

Perisylvian areas. Cortical regions that are adjacent to the sylvian fissure - majorfissure on the lateral surface of the brain running along the temporal lobe.  Periodicity relates to sensitive periods for certain types of learning.

PET. Positron Emission Tomography.   A variety of techniques that use positron emitting radionucleides to create an image of brain activity; often blood flow or metabolic activity.  PET produces three-dimensional, coloured images of chemicals or substances functioning within the brain.

Phantom Limbs. People who lose a limb through an accident or amputation sometimes continue to feel that it's still there. In his book, Phantoms In the Brain, Prof. Ramachandran suggests these sensations may be the result of the brain forming new connections. He describes how, when he used a cotton bud to stroke the face of a young amputee, the patient felt his missing hand was being touched as well. The area of the brain that receives sensations from the hand is right next to the one dealing with the face.

Phonemes.  Basic units of speech that make up words.

Phosphorylation. A process that modifies the properties of neurons by acting on an ion channel, neurotransmitter receptor or other regulatory molecule. During phosphorylation, a phosphate molecule is placed on another molecule resulting in the activation or inactivation of the receiving molecule. It may lead to a change in the functional activity of the receiving molecule. Phosphorylation is believed to be a necessary step in allowing some neurotransmitters to act and is often the result of second messenger activity. 

Pineal Gland. An endocrine organ found in the brain. In some animals, it seems to serve as a light-influenced biological clock. 

Pituitary Gland. An endocrine organ closely linked with the hypothalamus. In humans, it is composed of two lobes and secretes a number of hormones that regulate the activity of other endocrine organs in the body. 

Plasticity. Also "brain plasticity".  The phenomenon of how the brain changes and learns.

Pons. A part of the hindbrain that, with other brain structures, controls respiration and regulates heart rhythms. The pons is a major route by which the forebrain sends information to and receives information from the spinal cord and peripheral nervous system. 

Prefrontal cortex.  The region in front of the frontal cortex which is involved in planning and other higher-level cognition.

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Q

Qualia. A term for subjective sensations. In Phantoms In The Brain, Professor Ramachandran describes the riddle of qualia like this. How can the flux of ions and electrical currents in little specks of jelly, which are the neurons in my brain, generate the whole subjective world of sensations like red, warmth, cold or pain? By what magic is matter transmuted into the invisible fabric of feelings and sensations?

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Receptor Cell. Specialized sensory cells designed to pick up and transmit sensory information. 

Receptor Molecule. A specific molecule on the surface or inside of a cell with a characteristic chemical and physical structure. Many neurotransmitters and hormones exert their effects by binding to receptors on cells. 

Reuptake. A process by which released neurotransmitters are absorbed for subsequent re-use. Right-brained thinking. A lay term based on the misconception that higher level thought processes are strictly divided into roles that occur independently in different halves of the brain.  Thought to be based in exaggerations of specific findings of right hemisphere specialisation in some limited domains.

Rod. A sensory neuron located in the periphery of the retina. It is sensitive to light of low intensity and specialized for nighttime vision. 

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Science of Learning. Term that attempts to provide a label for the type of research possible when cognitive neuroscience research joins with educational research and practice.

Second Messengers. Recently recognized substances that trigger communications between different parts of a neuron. These chemicals are thought to play a role in the manufacture and release of neurotransmitters, intracellular movements, carbohydrate metabolism and, possibly, even processes of growth and development. Their direct effects on the genetic material of cells may lead to long-term alterations of behavior, such as memory. Senile plaques. A clear brain pathology associated with Alzheimer's disease.  These are clusters of abnormal cell processes surrounding masses of protein.

Sensitive period. Time frame in which a particular biological event is likely to occur best.  Scientists have documented sensitive periods for certain types of sensory stimuli (such as vision and speech sounds), and for certain emotional and cognitive experiences (attachment, language exposure). However, there are many mental skills, such as reading, vocabulary size, and the ability to see colour, which to do not appear to pass through tight sensitive periods in the development.

Sensitization. A change in behavior or biological response by an organism that is produced by delivering a strong, generally noxious, stimulus. 

Serotonin. A monoamine neurotransmitter believed to play many roles including, but not limited to, temperature regulation, sensory perception and the onset of sleep. Neurons using serotonin as a transmitter are found in the brain and in the gut. A number of antidepressant drugs are targeted to brain serotonin systems. 

Short-Term Memory. A phase of memory in which a limited amount of information may be held for several seconds to minutes. 

Split-brain patients.  Patients who have had the corpus callosum that connects left and right hemispheres surgically severed.

SPECT. Functional imaging using single photon emission computerized tomography

Stimulus. An environmental event capable of being detected by sensory receptors. 

Stroke. The third largest cause of death in America, stroke is an impeded blood supply to the brain. It can be caused by a blood clot forming in a blood vessel, a rupture of the blood vessel wall, an obstruction of flow caused by a clot or other material, or by pressure on a blood vessel (as by a tumor). Deprived of oxygen, which is carried by blood, nerve cells in the affected area cannot function and die. Thus, the part of the body controlled by those cells, cannot function either. Stroke can result in loss of consciousness and brain function, and death. 

Sympathetic Nervous System. A branch of the autonomic nervous system responsible for mobilizing the body's energy and resources during times of stress and arousal. 

Synesthaesia. A condition in which a person quite literally tastes a shape or sees a colour in a sound. This is not just a way of describing experiences as a poet might use metaphors. Synaesthetes actually experience the sensations.

Synapse. A gap between two neurons that functions as the site of information transfer from one neuron to another (called "target cell").

Synaptic density. Refers to the number of synapses associated with one neuron.  More synapses per neuron are thought to indicate a richer ability of representation and adaption.

Synaptic pruning: Process in brain development whereby unused synapses (connections among brain cells) are shed.  During pruning phase, experience and environment decide which synapses will be shed and which will be preserved.

Synaptogenesis.  Formation of a synapse.

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T

Temporal Lobe. One of the four major subdivisions of each hemisphere of the cerebral cortex. It functions in auditory perception, speech and complex visual perceptions. 

Temporal lobe epilepsy. A condition which may produce a heightened sense of self and has been linked to religious or spiritual experiences. Some people may undergo striking personality changes and may also become obsessed with abstract thoughts. One possible explanation is that repeated seizures may cause a strengthening of the connections between two areas of the brain - the temporal cortex and the amygdala. Patients have been observed to have a tendency to ascribe deep significance to everything around them (including themselves!).

Thalamus. A structure consisting of two egg-shaped masses of nerve tissue, each about the size of a walnut, deep within the brain. It is the key relay station for sensory information flowing into the brain, filtering out only information of particular importance from the mass of signals entering the brain. 

TMS. Transcranial magnetic stimulation.   A procedure in which electrical activity in the brain is influenced by a pulsed magnetic field.  Recently, TMS has been used to investigate aspects of cortical processing, including sensory and cognitive functions.

Trans-disciplinarity. Term used to explain the concept of bridging and fusing completely different disciplines resulting in a new discipline with its own conceptual structure, known to extend the borders of the original sciences and disciplines included in its formation.

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Ventricles. Of the four ventricles, comparatively large spaces filled with cerebrospinal fluid, three are located in the brain and one in the brainstem. The lateral ventricles, the two largest, are symmetrically placed above the brainstem, one in each hemisphere. Top

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Wernicke's Area. A brain region responsible for the comprehension of language and the production of meaningful speech. 

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Updated 9 July 2003

Which neurotransmitter is active in both peripheral and central nervous system?

What neurotransmitters are used in the peripheral nervous system?

Is serotonin a neurotransmitter in the central and peripheral nervous system?

Are neurotransmitters in the CNS or PNS?

What are the two most common neurotransmitters in the central nervous system?

Which neurotransmitter is inhibitory in both the CNS and PNS?