Neuroscience: A Journey Through the Brain

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Neuroscience Glossary

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Acetylcholine (ACh): A neurotransmitter liberated by vertebrate motor neurons, preganglionic autonomic neurons, and in various central nervous system pathways.

Action Potential (AP): A brief, regenerative, all-or-nothing electrical potential that propagates along an axon.

Adrenaline: A hormone secreted by the adrenal medulla. Also called Epinephrine.

Afferent: An axon conducting action potentials towards the central nervous system. See Efferent.

Agonist: A molecule that activates a receptor. See Antagonist.

Amygdala: Structure of the limbic system in the anterior temporal lobe. Also a structure in the basal ganglia.

Antagonist: A molecule that prevents the activation of a receptor. See Agonist.

Anterior: Towards the nose end; also called rostral. See Posterior.

Anterograde: The direction from the neuron's cell body toward the axon terminal. See Retrograde.

Arachnoid Membrane: The middle menynx.

Autonomic Nervous System (ANS): The division of the PNS innvervating viscera, skin, smooth muscle, glands and the heart. See Parasympathetic and Sympathetic.

Axon: The process(es) of a neuron that conduct action potentials.

Axon Hillock: The region of the axon closest to the cell body where the action potential often originates.



Basal Ganglia: Groups of cerebral nuclei that play a role in the control and production of movement.

Bilateral: On both sides of the body. See Unilateral.

Biogenic Amine: A general term referring to any of several bioactive amines. See epinephrine, norepinephrine, dopamine and serotonin.

Bipolar Cell: A neuron that has two major processes extending from the cell body.

Blood-Brain Barrier: Functional barrier produced by glial cells wrapped around blood vessels preventing access of many blood-borne molecules to the brain.



Capacitance: Property of the cell membrane that enables it to store and separate electrical charge.

Catecholamine: A general class of neurotransmitters including dopamine, epinephrine and norepinephrine.

Caudate: A nucleus of the basal ganglia extending from the amygdala; along with the putamen forms the striatum.

Cell Body: The portion of the neuron containing genetic material and cellular organelles.

Central Fissure: Long deep fissure on the lateral surface of the cerebral cortex.

Central Nervous System (CNS): The part of the nervous system consisting of the brian and spinal cord. See PNS.

Cerebellar Peduncles: Three large pairs of tracts connecting the cerebellum to the rest of the brain stem.

Cerebellum: Structure in the metencephalon situated just dorsal to the pons. It is involved in the coordination of movement.

Cerebral Cortex: The outer layer of the cerebral hemispheres largely composed of gray matter.

CSF (Cerebrospinal fluid):  The liquid that fills the ventricles of the brain and the spaces between the meninges.

Channel: A pathway through a membrane for ions or molecules to pass through.

Cingulate Cortex: Large area of limbic cortex on the medial surface of each cerebral hemisphere dorsal to the corpus callosum.

Choroid Plexus: Folded processes that project into the ventricles and secrete CSF.

Cochlea: The spiral-shaped bony canal in the inner ear containing the hair cells that transduce sound.

Commissure: Large tracts that span the longitudinal fissure.

Conductance: A measure of the ability to conduct electricity. Inverse of Resistance.

Connexon: A channel that connects the cytoplasm of two cells in a gap junction.

Contralateral: On the opposite side of the body. See Ipsilateral.

Coronal: Plane that is parallel to the surface of the face.

Corpus Callosum: The largest cerebral commissure.

Cranial Nerves: The 12 sets of efferent fibers that exit the CNS directly from the brain rather than from the spinal cord. In order they are: Olfactory, Optic, Oculomotor, Trochlear, Trigeminal, Aducens, Facial, Vestibulocochlear, Glossopharyngeal, Vagus, Accessory and Hypoglossal nerves.

Cross Section: Section cut at a right angle to any long, narrow structure.



Dendrite: Process of a neuron that acts as the post-synaptic receptor region.

Depolarization: Change in membrane potential to a more positive potential. See Hyperpolarization.

Diencephalon: Composed of the thalamus and hypothalamus.

Dopamine: A neurotransmitter released in the nervous system.

Dorsal: Towards the surface of the back or top of the head. Also see Superior.

Dorsal Stream: In the visual system, the pathway from visual cortex to the parietal lobe; also called the 'Where' or 'How' pathway. See Ventral Stream.

Dura Mater: The toughest, outermost menynx.



Efferent: An axon conducting action potentials outward from the central nervous system. See Afferent.

EEG (Electroencephalogram): A recording of electrical brain activity by electrodes placed on the scalp.

EMG (Electromyogram): A recording of muscular activity by external electrodes.

Epinephrine: See Adrenaline.

Equilibrium Potential: Membrane potential at which there is no net passive movement of a permeant ion species into or out of a cell.

EPSP (Excitatory Post-Synaptic Potential): Depolarization of the post-synaptic cell upon excitation by an excitatory transmitter released by the pre-synaptic cell. See IPSP.

Extrafusal: Muscle fibers that generate force; not within the sensory muscle spindles. Innervated by alpha motor neurons. See Intrafusal.



Fissure:  Deep grooves in the cerebral hemispheres. See sulcus.

Forebrain: The most anterior swelling of the neural tube; also called the prosencephalon. Gives rise to the Telencephalon and Diencephalon.

Fornix: The major tract of the limbic system projecting from the hippocampus, circling the thalamus, and terminating in the septum and mammillary bodies.

Fovea: Central part of the retina composed of densely packed cones; the area of highest visual acuity.

Frontal Lobe: Region of the cerebral hemispheres anterior to the central fissure.



G Proteins: Receptor-coupled proteins that bind guanine nucleotides and activate intracellular messenger systems.

Ganglion: In the PNS, a collection of neuron cell bodies. See Nuclei.

Gap Junction: A connection between two cells bridged by connexons.

Glial Cells: In the nervous system, cells that support and protect neurons.

Globus Pallidus:  A nucleus of the basal ganglia located between the thalamus and the putamen.

Glutamate: A neurotransmitter often released at excitatory synapses in the CNS.

Glycine: A neurotransmitter often released at inhibitory synapses in the spinal cord and brainstem.

Gray Matter: The part of the CNS composed mainly of cell bodies. See White Matter.

Growth Cone: The expanded tip of a growing axon.

Gyrus: Large convolution between adjacent fissures.



Hair Cells: Sensory cells in which bending of stereocilia (the "hairs") causes a change in membrane potential.

Hindbrain: The post posterior swelling on the neural tube; also called the rhombencephalon. Gives rise to the Mesencephalon and the Myelencephalon.

Hippocampus: Structure of the limbic system extending from the amygdala anteriorally to the cingulate cortex and fornix posteriorally.

Horizontal: Plane parallel to the horizon when a person stands upright.

Hyperpolarization: The change in membrane potential to a more negative value. See Depolarization.

Hypothalamus: The diencephalic structure located beneath the anterior end of the thalamus and composed of many pairs of nuclei.



Inactivation: Reduction in conductance of a voltage-gated channel even though the activating voltage is maintained.

Inferior: Toward the ventral surface of the primate head.

Inferior Colliculi: The posterior pair of nuclei in the tectum that play a role in audition.

IPSP (Inhibitory Post-Synaptic Potential): The (usually) hyperpolarizing change in post-synaptic membrane potential produced by an inhibitory neurotransmitter released from the pre-synaptic cell. See EPSP.

Interneuron: A neuron that is neither purely sensory nor motor, but that connects other neurons.

Ionotropic: Type of receptor associated with ion channels.

Ipsilateral: On the same side of the body. See Contralateral.







Lateral: Away from the midsaggital plane. See Medial.

Lateral Geniculate Nucleus (LGN): Nucleus in the thalamus that acts as a relay in the visual pathway.

Length Constant: The distance over which the potential falls to 37% of its original maximum value in an axon or in a muscle fibre.

Limbic System: A circuit of midline structures circling the thalamus that plays a role in the control and production of emotional behavior.

Longitudinal Fissure: The deep midline chiasm between the two cerebral hemispheres.


Long-Term Potentiation (LTP): An increase in size of a synaptic potential lasting one hour or more.



Magnetic Resonance Imaging (MRI): A brain imaging technique that provides high resolution pictures of brain structures, is relatively non-invasive, and shows changes in real time.

Magnocellular: Pathways from large retinal ganglion and LGN cells to cortical visual areas; sensitive to movement. See Dorsal Stream.

Mammillary Bodies:  Hypothalmic nuclei just posterior to the pituitary and part of the limbic system.

Massa Intermedia: Commissure in the third ventricle that connects the left and right diencephalon.

Medial: Toward the midsaggital plane. See Lateral.

Meninges: Membranes covering the brain and the spinal cord. (Singular : menynx). See Dura Mater, Arachnoid Membrane, and Pia Mater.

Mesencephalon: The midbrain; part of the brainstem. Composed of the tectum, which comprises the superior and inferior colliculi, and the tegmentum, which comprises the peri-aqueductal grey, the substantia nigra, and the red nucleus.

Metabotropic: Type of receptors that are associated with G-proteins.

Metencephalon: Middle part of the brainstem composed of the pons and the cerebellum.

Midbrain: The middle swelling on the neural tube, also called the mesencephalon.

Midsaggital: A saggital section in the midline of the brain.

Motor Neuron: A neuron that innervated muscle fibers.

Motor Unit: A single motor neuron and the muscle fibers it innervates.

Muscarinic: A type of ACh receptor activated by muscarine that is coupled by a G-protein to intracellular messenging systems.

Muscle Spindle: Structure in skeletal muscles containing small muscle fibers and sensory receptors activated by stretch.

Myelencephalon: The most posterior part of the brainstem. Also called the medulla.

Myelin: Schwann cells (PNS) or oligodendroglia (CNS) that form a high-resistance sheath around the axon of a neuron. See Glial Cells.




Nerve: In the PNS, a collection of axons.

Neural Crest: Formed from neural plate cells that break away as the neural tube is being formed in the vertebrate embryo.

Neural Groove: The groove that develops down the center of the neural plate in a vertebrate embryo.

Neural Plate: The tissue on the dorsal surface of the vertebrate embryo that develops in the nervous system.

Neural Tube: Tube filled with CSF formed when the lips of the neural groove fuse. Develops into the CNS.

Neurotransmitter: A chemical substance released in quanta by the pre-synaptic cell that causes an effect (usually a change in ion permeability to one or more ions) on the post-synaptic cell.

Nicotinic: A type of ACh receptor activated by nicotine that is a cation channel when activated.

Nociceptive:  Responds to painful or noxious stimuli.

Node of Ranvier: Local area of unmyelinated axon that occurs at intervals along a myelinated axon.

Noradrenaline: Transmitter released by most sympathetic nerve terminals. Also called Norepinephrine.

Norepinephrine: See Noradrenaline.

Nucleus: In the CNS, a group of cell bodies (plural: nuclei). See Ganglia. Also a component of the cell body containing genetic material.



Occipital Lobe: Region at the posterior pole of the cerebral hemisphere.

Oligodendroglia: Glial cells in the CNS that form the myelin sheath..

Optic Chiasm: The point of decussation (crossing) of optic nerves.



Parasympathetic: The cranial and sacral divisions of the ANS.

Parietal Lobe: Region of the cerebral hemisphere posterior to the central fissure and superior to the lateral fissure.

Parvocellular: Pathways from small retinal ganglion and LGN cells to cortical visual areas; sensitive to color and form. See Ventral Stream.

Patch Clamp: A technique for measuring currents passing through single membrane channels. A small patch of membrane is sealed to the tip of a micropipette and a patch is created. See Whole Cell Recording.

Periaqueductal Grey (PAG): Area of the tegmentum located around the cerebral aqueduct involved in the suppression of pain.

Peripheral Nervous System (PNS): The part of the vertebrate nervous system located outside the skull and spine.

Pia Mater: The innermost and most delicate menynx.

Pituitary Gland: The anterior portion releases tropic hormones in response to hypothalamic releasing hormones. The posterior portion releases vasopressin (antidiuretic hormone) and oxytocin from neuronal terminals that have their cell bodies in the hypothalamus.

PET (Position Emission Tomography): A brain imaging technique that maps active brain areas via an injection of 2-deoxyglucose, which emits positrons when taken up by actively metabolizing cells.

Pons: The ventral part of the metencephalon. It includes the fourth ventricle and the nuclei of cranial nerves 5, 6, 7, and 8.

Posterior: Toward the tail end; also called caudal. See Anterior.

Post-Synaptic: On the receiving end of the nervous signal; where the receptors for neurotransmitters released from the pre-synaptic cell are located. See Pre-Synaptic.

Putamen: Nucleus of the basal ganglia located just lateral to the globus pallidus; with the caudate it forms the striatum.

Pre-synaptic: The site from which the neurotransmitter is released or from which the nervous signal is sent. See Post-Synaptic.



Quantal Release: Secretion of discrete amounts of neurotransmitter (quanta) into the synpatic cleft.



Receptive Field: The area of the periphery whose stimulation increases the firing of a neuron.

Receptor: A molecule in the cell membrane that binds a chemical substance, such as a neurotransmitter.

Red Nuclei:  Tegmental nuclei important in the sensorimotor system.

Reflex: Involuntary movement elicited by activation of sensory receptors.

Refractory Period: The time following an action potential during which normal stimulation will not cause another action potential. During the absolute refractory period, no stimulation will evoke neuronal firing. The relative refractory period requires supra-threshold stimuli to evoke an action potential.

Resistance: Property of the cell membrane reflecting the difficulty ions encounter when trying to pass through it. The inverse of Conductance.

Resting Potential: The steady electrical potential across a membrane. In humans, the value is around -70mV, meaning the inside is negative relative to the outside of the cell.

Retrograde: The direction from the axon terminal toward the cell body. See Anterograde.

Roots: Bundles of fibers that emerge from the spinal cord. Sensory roots are on the dorsal surface; motor roots are on the ventral surface.



Saggital: Plane parallel to the vertical plane that divides the brain in half. See Midsaggital.

Saltatory: The type of conduction along a myelinated axon where the leading edge of the action potential 'jumps' from node to node, increasing the speed of axonal conduction.

Schwann Cell: Satellite cell in the PNS that is responsible for making the myelin sheath.

Second Messenger System: A series of molecular reactions inside a cell initiated by binding of molecules to extracellular receptor sites. It leads to a functional cellular response, such as the opening of ion channels.

Septum: Nucleus in the limbic system located on the midline at the anterior tip of the cingulate cortex.

Serotonin: A neurotransmitter. Also called 5HT (5-hydroxytryptamine).

Soma: The cell body of an axon.

Somatic Nervous System: Division of the PNS that conducts signals from sensory receptors to the CNS and signals from the CNS to skeletal muscles.

Striatum:  Structure in the basal ganglia composed of the caudate and putamen.

Subarachnoid Space: Space filled by CSF between the arachnoid membrane and pia mater.

Substantia Nigra: Tegmental nuclei involved in the sensorimotor system.

Sulcus: Small grooves in the cerebral hemispheres. See fissures.

Superior: Toward the dorsal surface of the primate head.

Superior Colliculi: The anterior pair of nuclei in the tectum that play a role in vision.

Sympathetic: The thoracic and lumbar divisions of the ANS.

Synapse: The site at which neurons make functional contact. The space between cells is termed the 'synaptic cleft'.

Synaptic Vesicles: Membrane sacs that store neurotransmitter molecules ready for release near the presynaptic membrane.



Tectum:  The dorsal surface of the midbrain, composed of the superior and inferior colliculi.

Tegmentum: The ventral portion of the midbrain, composed of the red nuclei, the PAG, and the Substantia Nigra.

Telencephalon: The cerebral hemispheres.

Temporal Lobe: Region of the cerebral hemisphere inferior to the lateral fissure.

Tetanus: A train of action potentials; the requirement for development of LTP.

Tetraethylammonium (TEA): Selective blocker of voltage-gated potassium channels.

Tetrodotoxin (TTX): Toxin from puffer fish that selectively blocks voltage-gated sodium channels.

Thalamus: A structure in the diencephalon composed of two lobes, one on each side of the third ventricle.

Threshold: The critical value for membrane potential or depolarization at which an action potential is initiated.

Time Constant: A measure of the rate of buildup and decay of a localized potential; equal to the product of the resistance and capacitance of the membrane.

Tract: In the CNS, a group of axons.



Unilateral: On one side of the body. See Bilateral.



Ventral: Toward the surface of the chest and stomach or bottom of the head. See also Inferior.

Ventral Stream: In the visual system, the pathway from the occipital lobe to the temporal lobe; also called the 'What' pathway. See Dorsal Stream.

Ventricles: Cavities within the brain containing CSF.

Voltage Clamp: Technique for holding the membrane potential constant while measuring currents across the cell membrane.



White Matter: The part of the nervous system consisting of myelinated fiber tracts.

Whole Cell Recording: Recording of membrane currents in an intact cell by applying gentle suction to a micropipette patched on to the cell membrane to create an opening.








Created and Maintained by: Melissa Davies
Last Updated: April 10, 2002 08:54 AM