We would like to thank the for their premission to reproduce this
glossary. Some ammendations have been made.
A Acetylcholine:ÌýA 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.Ìý Action Potential:ÌýThis 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.Ìý Adrenal Cortex:ÌýAn 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.Ìý Adrenal Medulla:ÌýAn endocrine organ that
secretes epinephrine and norepinephrine for the activation of the
sympathetic nervous system.Ìý Affective Psychosis:ÌýA 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.Ìý Agonist:ÌýA neurotransmitter, a drug or
other molecule that stimulates receptors to produce a desired reaction.Ìý Amino Acid Transmitters:ÌýThe 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.Ìý Amygdala:ÌýA structure in the forebrain
that is an important component of the limbic system.Ìý Androgens:ÌýSex steroid hormones, including
testosterone, found in higher levels in males than females. They are
responsible for male sexual maturation.Ìý 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:ÌýA drug or other molecule that
blocks receptors. Antagonists inhibit the effects of agonists.Ìý Aphasia:ÌýDisturbance in language comprehension
or production, often as a result of a stroke.Ìý Auditory Nerve:ÌýA 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.Ìý Autonomic Nervous System:ÌýA part of the
peripheral nervous system responsible for regulating the activity
of internal organs. It includes the sympathetic and parasympathetic
nervous systems.Ìý Axon:ÌýThe fiberlike extension of a neuron
by which the cell sends information to target cells.Ìý
Basal Ganglia:ÌýClusters 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.Ìý 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:ÌýThe 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.Ìý Broca's Area:ÌýThe brain region located
in the frontal lobe of the left hemisphere that is important for the
production of speech.Ìý
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:ÌýThe 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.Ìý Cerebral Cortex:ÌýThe outermost layer of
the cerebral hemispheres of the brain. It is responsible for all forms
of conscious experience, including perception, emotion, thought and
planning.Ìý Cerebral Hemispheres:ÌýThe 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.Ìý Cerebrospinal Fluid:ÌýA liquid found within
the ventricles of the brain and the central canal of the spinal cord.Ìý Cholecystokinin:ÌýA 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.Ìý Circadian Rhythm:ÌýA cycle of behavior or
physiological change lasting approximately 24 hours.Ìý Classical Conditioning:ÌýLearning 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.Ìý Cochlea:ÌýA snail-shaped, fluid-filled organ
of the inner ear responsible for transducing motion into neurotransmission
to produce an auditory sensation.Ìý Cognition:ÌýThe 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.Ìý Cone:ÌýA primary receptor cell for vision
located in the retina. It is sensitive to color and used primarily
for daytime vision.Ìý Cornea:ÌýA thin, curved transparent membrane
on the surface of the front of the eye. It begins the focusing process
for vision.Ìý Corpus Callosum:ÌýThe large bundle of nerve
fibers linking the left and right cerebral hemispheres.Ìý Cortisol:ÌýA 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.Ìý 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.
Dendrite:ÌýA tree-like extension of the
neuron cell body. Along with the cell body, it receives information
from other neurons.Ìý Dopamine:ÌýA 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.Ìý Dorsal Horn:ÌýAn area of the spinal cord
where many nerve fibers from peripheral pain receptors meet other
ascending nerve fibers.Ìý
Endocrine Organ:ÌýAn organ that secretes
a hormone directly into the bloodstream to regulate cellular activity
of certain other organs.Ìý Endorphins:ÌýNeurotransmitters produced
in the brain that generate cellular and behavioral effects like those
of morphine.Ìý Epinephrine:ÌýA 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.Ìý Estrogens:ÌýA group of sex hormones found
more abundantly in females than males. They are responsible for female
sexual maturation and other functions.Ìý Evoked Potentials:ÌýA 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.Ìý Excitation:ÌýA change in the electrical
state of a neuron that is associated with an enhanced probability
of action potentials.Ìý
F Follicle-Stimulating Hormone:ÌýA 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.Ìý Forebrain:ÌýThe largest division of the
brain, which includes the cerebral cortex and basal ganglia. It is
credited with the highest intellectual functions.Ìý Frontal Lobe:ÌýOne 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.Ìý
Gamma-Amino Butyric Acid (GABA):ÌýAn amino
acid transmitter in the brain whose primary function is to inhibit
the firing of neurons.Ìý Glia :ÌýSpecialized cells that nourish and
support neurons.Ìý Glutamate:ÌýAn 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.Ìý Gonad:ÌýPrimary sex gland: testis in the
male and ovary in the female.Ìý Growth Cone:ÌýA distinctive structure at
the growing end of most axons. It is the site where new material is
added to the axon.Ìý
Hippocampus:ÌýA seahorse-shaped structure
located within the brain and considered an important part of the limbic
system. It functions in learning, memory and emotion.Ìý Hormones:ÌýChemical 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.Ìý Hypothalamus:ÌýA 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.Ìý
Immediate Memory:ÌýA 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.Ìý Inhibition:ÌýIn reference to neurons, it
is a synaptic message that prevents the recipient cell from firing.Ìý Ions:ÌýElectrically charged atoms or molecules.Ìý Iris:ÌýA 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.Ìý
Korsakoff's Syndrome:ÌýA 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.Ìý
Limbic System:ÌýA group of brain structures
- including the amygdala, hippocampus, septum and basal ganglia -
that work to help regulate emotion, memory and certain aspects of
movement.Ìý Long-Term Memory:ÌýThe final phase of memory
in which information storage may last from hours to a lifetime.Ìý
Mania:ÌýA mental disorder characterized by
excessive excitement. A form of psychosis with exalted feelings, delusions
of grandeur, elevated mood, psychomotor overactivity and overproduction
of ideas.Ìý Melatonin:ÌýProduced from serotonin, melatonin
is released by the pineal gland into the bloodstream. It affects physiological
changes related to time and lighting cycles.Ìý Memory Consolidation:ÌýThe physical and psychological
changes that take place as the brain organizes and restructures information
in order to make it a permanent part of memory.Ìý Metabolism:ÌýThe sum of all physical and
chemical changes that take place within an organism and all energy
transformations that occur within living cells.Ìý Mitochondria:ÌýSmall cylindrical particles
inside cells that provide energy for the cell by converting sugar
and oxygen into special energy molecules.Ìý Monoamine Oxidase (MAO):ÌýThe brain and liver
enzyme that normally breaks down the catecholamines norepinephrine,
serotonin and dopamine.Ìý Motor Neuron:ÌýA neuron that carries information
from the central nervous system to the muscle.Ìý Myasthenia Gravis:ÌýA 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.Ìý Myelin:ÌýCompact fatty material that surrounds
and insulates axons of some neurons.Ìý
Nerve Growth Factor:ÌýA substance whose role
is to guide neuronal growth during embryonic development, especially
in the peripheral nervous system.Ìý Neuron:ÌýNerve cell. It is specialized for
the transmission of information and characterized by long fibrous
projections called axons, and shorter, branch-like projections called
dendrites.Ìý Neurotransmitter:ÌýA chemical released by
neurons at a synapse for the purpose of relaying information via receptors.Ìý Nociceptors:ÌýIn animals, nerve endings that
signal the sensation of pain. In humans, they are called pain receptors.Ìý Norepinephrine:ÌýA 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.Ìý
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:ÌýA branch
of the autonomic nervous system concerned with the conservation of
the body's energy and resources during relaxed states.Ìý Parietal Lobe:ÌýOne of the four subdivisions
of the cerebral cortex. It plays a role in sensory processes, attention
and language.Ìý Peptides:ÌýChains of amino acids that can
function as neurotransmitters or hormones.Ìý Periaqueductal Gray Area:ÌýA 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.Ìý Peripheral Nervous System:ÌýA division of
the nervous system consisting of all nerves not part of the brain
or spinal cord.Ìý 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
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.
Phosphorylation:ÌýA 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.Ìý Pineal Gland:ÌýAn endocrine organ found in
the brain. In some animals, it seems to serve as a light-influenced
biological clock.Ìý Pituitary Gland:ÌýAn 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.Ìý Pons:ÌýA 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.Ìý
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 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?
Receptor Cell:ÌýSpecialized sensory cells
designed to pick up and transmit sensory information.Ìý Receptor Molecule:ÌýA 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.Ìý Reuptake:ÌýA process by which released neurotransmitters
are absorbed for subsequent re-use.Ìý Rod:ÌýA sensory neuron located in the periphery
of the retina. It is sensitive to light of low intensity and specialized
for nighttime vision.Ìý
Second Messengers:ÌýRecently 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.Ìý Sensitization:ÌýA change in behavior or biological
response by an organism that is produced by delivering a strong, generally
noxious, stimulus.Ìý Serotonin:ÌýA 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.Ìý Short-Term Memory:ÌýA phase of memory in
which a limited amount of information may be held for several seconds
to minutes.Ìý Stimulus:ÌýAn environmental event capable
of being detected by sensory receptors.Ìý Stroke:ÌýThe 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.Ìý Sympathetic Nervous System:ÌýA branch of
the autonomic nervous system responsible for mobilizing the body's
energy and resources during times of stress and arousal.Ìý 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:ÌýA gap between two neurons that
functions as the site of information transfer from one neuron to another.Ìý
Temporal Lobe:ÌýOne of the four major subdivisions
of each hemisphere of the cerebral cortex. It functions in auditory
perception, speech and complex visual perceptions.Ìý 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:ÌýA 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.Ìý
Ventricles:ÌýOf 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.Ìý
