TIS

Chapter 1

Neuroscience Vocabulary

 

accommodation

Decrease in spike firing rate with time.

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acetylcholine

A neurotransmitter that connects nerves to muscles. Also active at other synapses in CNS/ANS. Chemical structure.

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action potential

A spike in membrane voltage caused by opening and closing of Na and K channels. This is the signal that is conducted down the axon to transmit information to other neurons.

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active (excitable) Membrane

Membranes that have voltage-sensitive channels

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afferent

An axon, neuron or tract that brings information in towards the central nervous system

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after-hyperpolarization

Hyperpolarization after an action potential

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agonist

A drug that will activate a particular receptor, opposite of antagonist

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amino acid

The building blocks of peptides and proteins. Some amino acids also serve as neurotransmitters

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ampa receptor

A kind of glutamate receptor that mediates excitatory (depolarizing) signals. The channel conducts both Na+ and K+.

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amygdala

A nucleus involved in emotional and sexual behavior. Part of the limbic system

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anatomy

The study of structures in biology. Contrasted with physiology.

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antagonist

A drug that will block a particular receptor, opposite of agonist

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aphasia

Loss of language skills following brain damage.

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area mt

One of many areas for higher cortical processing of vision. This one mediates the visual perception of motion.

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artificial neural network (ANN)

Networks of simple units that do complex things due to their connectivity. The computer science/engineering approach to computational neuroscience.

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association cortex

An area of cortex that does not receive primary sensory (or give off primary motor) information; some of these areas are thought to be involved in integrating or associating different types of information

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associative long term potentiation

Increased strength in a weakly stimulated synapse with strong activation in a nearby synapse. This has been shown to occur in some areas of hippocampus

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astrocytes

Glial cells that are involved in nutritive support for neurons and in maintaining concentrations in the extracellular space.

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attention

A neural mechanism that permits brain function to be focused on a particular sensory stream.

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autonomic nervous system (ANS)

A section of the nervous system innervating organs.

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axon

The axon is classically regarded as the output side of the neuron. In vertebrates, axons may be myelinated. Conduction of signals down the axons is due to action potentials which are self-regenerative signals that propagate by saltatory conduction. A myelinated axon is shown at the bottom of this picture.

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axon collateral

A branch of an axon.

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axon hillock

The initial part of the axon. This may be where action potentials start in some neurons.

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axon terminal

The end of an axon. There is usually a synapse here.

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basal ganglia

A large nuclear complex rostral (anterior) to the thalamus. Involved in motor activity, planning, initiative.

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binding problem

The brain somehow has to bind together information about a single object that is processed in different places. For example a visual image is taken apart so that motion, color, shape and other aspects can be separately analyzed, yet somehow one has a unitary percept of what's being seen.

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blind spot

The area in which one cannot see because light rays fall on the optic disk. The optic disk has no photoreceptors. Somehow this blindness is ignored by the brain, an act of completion

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blood-brain barrier

A barrier that keeps bad stuff floating around in the blood from getting into the brain.

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bouton en passant

(= synaptic bouton) A synapse that is not at an axon terminal but is just a swelling as the axon passes by a dendrite.

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brain

The part of the CNS within the skull

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brainstem

The part of the CNS between the thalamus and the spinal cord

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cable equation

An equation that describes how voltage attenuates along an electrical cable. Originally proposed by Lord Kelvin to describe the reduction of telegraph signals from Europe to North America, it is also used to describe attenuation of membrane voltage down a passive neural membrane such as a passive dendrite.

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cascade

A chemical amplification process where the product of one enzyme (or a second messenger) augments the rate of another enzyme which creates a large amount of another messenger controlling yet another enzyme. A few such steps can turn a relatively small chemical signal into a large number of signaling molecules.

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CAT scan

Computerized axial imaging. An imaging method that recreates 2 dimensional cross sections using transforms of x-ray conductance through tissue. Also called CT scan.

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cauda equina

The big "horses tail" of nerves at the base of the spinal cord.

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caudal

The tail side of the body. In the brain this is toward the back (posterior) and in the spinal cord it's towards the bottom (inferior).

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cell assembly

Hebb hypothesized that cell assemblies (groups of simultaneously active neurons) could represent perceived or remembered objects.

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cell body

Synonym for soma

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central nervous system (CNS)

The brain (including retina and brainstem) and spinal cord

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cerebellum

A complex movement control center at the caudal end of the brain overlying the brainstem.

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cerebral cortex

Grey matter at the surface of the brain

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cerebrospinal fluid (CSF)

The fluid that bathes the CNS and lies inside the ventricles

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chemical synapse

A synapse where information is conveyed by the diffusion of a neurotransmitter across the synaptic cleft to bind to and activate receptors on the other side

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chunking

The ability of the brain to organize complex multi-part information into a single remembered object. An example is seen in remembering a telephone number -- it is hard to remember as a collection of digits but chunking into a set of 3 followed by a set of 4 makes it easier

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co-transmitters

Different neurotransmitters released at a single synapse.

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completion

The ability of the nervous system to ignore inconsistencies or gaps in incoming information to construct a complete story. Neglect syndromes may be in part caused by excessive completion.

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conduction velocity

The speed of spike (action potential) conduction along an axon

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consolidation

Putative process whereby memories are moved from temporary storage in hippocampus to more permanent storage in cerebral cortex

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contralateral

The other side. Most of the brain innervates contralateral structures. Opposite of ipsilateral.

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contralateral neglect syndrome

A very odd syndrome often seen after strokes affecting the non-dominant hemisphere. The patient may deny that the contralateral side of his body belongs to him or her.

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convergence

Multiple inputs coming into one neuron

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coronal plane

The vertical plane that runs from left to right (or lateral to medial) and up to down (ventral to dorsal). An example would be the coronal plane running from ear to ear

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corpus callosum

The large white matter that connects the two hemispheres

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corticospinal tract

(aka pyramidal tract) A tract of that starts in motor cortex and goes down to the spinal cord. Responsible for some aspects of fine motor control.

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critical period

A limited period of time when a particular aspect of brain development is sensitive to a change in the external environment

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current

Movement of charge. In a wire this represents a wave of electrons moving but in living tissue current is carried by ions. current I is measured in Amperes (amps).

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current clamp

Holding a steady current in a neuron and watching how the voltage responds.

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cytoarchitectonic map

A map of the cerebral cortex that distinguishes areas according to anatomical differences such as the prominence of a particular cortical layer.

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cytoplasm

The contiguous fluid inside a cell that lies outside the organelles.

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Dale's principle

the hypothesis that a single neuron has only one transmitter that is given off at all its synapses. Although this has turned out to be wrong in part (see co-transmitters), it seems to still hold true that major neurotransmitters such as glutamate and GABA are not coexpressed by a single neuron.

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delta waves

slow waves (< 4 Hz) of the EEG seen in deep sleep

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dendrite

Cellular extensions from the soma. They are generally fatter and shorter than axons and are never myelinated. Dendrites were classically thought to be electrically passive but it now appears that many are active. Dendrites are classically regarded as the input side of the cell. Again this is not always the case. Note the apical dendrites at the top of the picture and the basal dendrites to the side.

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dendritic spine

A spiny excrescence off the side of a dendrite. Often the site of an excitatory synapse. Has specialized internal structures presumed related to its signal carrying function.

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dendritic tree

The full set of dendrites that belong to a neuron.

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depolarization

Change in membrane potential positive from the resting membrane potential. This is usually associated with excitation of the cell.

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diffusion

The tendency of particles at a high concentration to move to places where they are not so concentrated.

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disinhibition

Removal or reduction of inhibitory action in a neural circuit.

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divergence

Multiple outputs coming from one neuron

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dominant hemisphere

The cerebral hemisphere that controls language. This is the left hemisphere in most people.

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dorsal

The back side of the body. For the CNS this would be posterior in the spinal cord and superior (up) in the brain.

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driving force

The potential felt by ions of a particular type. This depends on the difference between the current membrane potential and the Nernst potential corresponding to the concentration difference across the membrane.

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efferent

An axon, neuron or tract that takes information out away from the CNS.

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electrical self-stimulation

A mechanism for allowing an animal to deliver small electric currents to activate a particular spot in its own brain.

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electrical synapse

A gap junction connection between cells that allows direct current flow that can thereby pass electrical signals from one cell to another.

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electrochemical equilibrium

A balance between diffusive force in one direction and a membrane potential gradient in the other direction. The membrane potential where this occurs is the Nernst potential.

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electroencephalogram (EEG)

A recording of electrical signals from the brain made on the skin of the head.

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endorphin

A peptide neurotransmitter that is active at the same location where opium or morphine acts.

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enteric nervous system

The nervous system that runs the gut. It can function on its own even after being completely disconnected from other parts of the nervous system.

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epilepsy

A brain disorder where repeated seizures occur.

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equilibrium potential

The Nernst potential that produces electrochemical equilibrium for a particular ion.

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excitatory postsynaptic potential (EPSP)

Depolarization of the postsynaptic membrane potential due to synaptic action. Nominally excitatory.

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exocytosis

Release of material from a cell due to fusion of a vesicle with the cell membrane. This is how neurotransmitters are released into the synaptic cleft.

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extracellular

The outside of cells.

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facilitation

The ability of incoming excitatory signals to produce a transient increased excitability. Generally shorter in duration as compared to potentiation.

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fovea

The central part of the retina that has the most acute vision

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frequency coding

The notion that increases in spike frequency are an important part of the code of the nervous system. Also called rate coding.

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frontal lobe

The most anterior lobe of the brain. Thought to play a role in initiative and planning.

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functional magnetic resonance imaging (fMRI)

A technique for imaging physiological activity using magnets and radio waves

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gaba

The major inhibitory neurotransmitter in the CNS

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ganglion (plural, ganglia)

A collections of neurons lying outside the CNS

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gap junction

An ion channel that connects two cells together.

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gating

The ability of channels to be opened or closed either by membrane potential (voltage-gated) or by the arrival of a neurotransmitter or other chemical (ligand-gated)

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glial cell

The most common type of neuron in the nervous system. These cells play roles in support, hormone release, and balancing extracellular concentrations. Two important types are astrocytes and oligodendroglia.

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glutamate

An amino acid that is the major excitatory neurotransmitter in the central nervous system.

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grandmother cell theory

The theory that the brain codes involves specific neurons that stand for specific things in the world -- ie a neuron that lights up when grandma is seen, heard, smelled or touched

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grey matter

Brain volumes made up of cell bodies such as cerebral cortex, basal ganglia and thalamus. Looks grey when you cut open a brain.

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gyrus (Plural: gyri)

The cerebral hemispheres are folded; gyri are the ridges.

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habituation

A nonassociative learning form leading to decreased behavioral responses to repeated stimulation

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Hebb synapse

A synapse that that increases in strength when both the presynaptic and postsynaptic neurons are active at the same time.

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hippocampus

A cortical area in the temporal lobe. This area is involved in declarative memory (memory for events).

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Hodgkin-Huxley equation

A set of equations that describe the evolution of the action potential by taking account of changes in conductance of voltage-sensitive sodium and potassium channels.

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horizontal plane

The horizontal plane is horizontal with the person in the anatomical position. it runs rostral (front) to caudal (back); medial to lateral (also left to right).

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Huntington's disease

An inherited movement disorder characterized by dance-like movements.

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hyperpolarize

Change in membrane potential negative from the resting membrane potential. This is usually associated with inhibition of the cell.

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in vitro

Study of biological tissue that has been taken out of the organism. (means "in glass")

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in vivo

Studyof biological tissue in the intact organism. (means "in life")

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inactivation

Closing of an ion channel with time.

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inhibitory postsynaptic potential (IPSP)

Neurotransmitter-induced postsynaptic potential making the postsynaptic neuron less likely to fire action potentials

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innervate

For a neuron to connect up synaptically with something

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integration

Combination of incoming signals in a neuron or neuronal unit.

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interneuron

A neuron with axons that only project locally. In the cortex many of these appear to be inhibitory.

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intracellular

The inside of a cell.

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invertebrate

An animal without a spine. Can be divided into squishies (clam, octopus, leech) and crunchies (insect, limulus, lobster).

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ion

A charged atom. The most important ions in the nervous system are Na+,K+,Cl-,Ca++. The superscript tells you what type of charge it is and whether it is monovalent (one +) or divalent (two +s).

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ion channel

An protein that lies in the cell membrane (integral membrane protein) that has a hole that allows ions to pass from one side of the membrane to the other. Most of these ion channels are selective, only allowing passive of certain ions and not letting others through. Picture: Diagrams

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ipsilateral

On the same side of the midline or body, opposite of contralateral.

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lateral

Towards the side. For example, the ears are lateral to the brain.

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lateral geniculate nucleus (LGN)

An area of the thalamus that relays information from the retina.

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learning

Storage of new information in a biological or artificial system.

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length constant

Space constant

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ligand-gated channels

An ion channel which opens and closes depending on the arrival of some chemical -- usually either a neurotransmitter or second messenger

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limbic system

A set of interconnected brain structures that may be involved in emotion (see Papez circuit).

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limulus

The horseshoe crab, an animal whose visual mechanisms have been heavily studied. Picture

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lipid bilayer

The architecture of membranes in living things. Can be understood by thinking of a soap bubble. Soaps are amphoteric: one end is fatty and the other end is ionic. This allows them to clean: one end sticks to grease (hydrophobic = hates water) and the other end sticks to water (hydrophilic = loves water). In a soap bubble all the hydrophilic ends stick out and the hydrophobic ends point inward and interact to form a membrane. A lipid bilayer is like 2 soap bubbles one inside the other with the inner one's hydrophilic heads sticking in to the cytoplasm.

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long term potentiation (LTP)

A persistent strengthening of synaptic strength that may be the neural analogue of the Hebb synapse. NMDA receptors are involved in this process.

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long-term depression (LTD)

A persistent weakening of synaptic strength.

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magnetic resonance imaging (MRI)

A technique for imaging the anatomy of the brain using magnets and radio waves.

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map

An area in the nervous system where some aspect of the sensory world is represented. This may be topographic as in vision or touch or may represent some other aspect of the stimulus as in a tonotopic (frequency-oriented) map for hearing. Maps are not always continuous, they may be patchy or scattered.

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medial

Towards the middle. For example, the nose is medial to the cheeks.

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membrane capacitance

The ability of the membrane to store charge by keeping positive and negative charge separated on opposite sides of the membrane. Diagram

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membrane conductance

The inverse of membrane resistance. The ease with which a particular ion can move across the membrane. Conductance, g is measured in Siemens S. (See Ohm's law)

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membrane potential

The voltage drop across a membrane. Specifically, the difference in force that a charge would feel at opposite sides of the membrane. This term is synonomous with membrane voltage or membrane polarization. One speaks of membrane voltage or potential being changed in a depolarizing (more positive) or hyperpolarizing (more negative) direction. (see resting membrane potential)

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membrane resistance

Measurement of the difficulty that a charge has moving from one side of the membrane to the other. Resistance R is measured in Ohms. Resistance is related to current and voltage by R=V/I, Ohm's law. Resistance = 1 / conductance

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memory

Storage of information.

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microelectrode

A small glass tube tapered toward the tip that can be inserted into neurons to allow intracellular recording. Slightly bigger microelectrodes may be made of different materials and used in extracellular recording. Picture

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micron

10-6 meters. A neuron soma may be 5-30 microns in diameter.

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milliseconds

10-3 seconds. A typical action potential duration is 1-2 ms.

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millivolt

10-3 volts. A typical neuron resting membrane potential is about -75 mV.

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motor cortex

Cortical areas that control movement

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myelin

The insulation that is wrapped around axons by oligodendroglia which permits faster conduction velocity by saltatory conduction.

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neglect syndrome

Contralateral neglect syndrome

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Nernst equation

An equation for calculating the equilibrium potential of a particular ion

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Nernst potential

The equilibrium potential for a particular ion. This is the potential that balances out the chemical diffusive gradient to produce electrochemical equilibrium.

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nerve

A bundle of axons in the peripheral nervous system. Nerves run to muscles and from sensory organs in the periphery.

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neuron

The principal information carrying element of the nervous system. These can differ widely in shape and connectivity. Most neurons have a soma, dendrites and an axon. Two important neuron types are pyramidal cells and inhibitory interneurons. Generic neuron picture

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neuron doctrine

The concept put forth by Cajal that suggested that neurons are separate cells. This was contested by Golgi's reticular hypothesis that suggested that the nervous system was just one big continuous network.

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neuronal membrane

The lipid bilayer that separates the outside from the inside of a neuron.

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neuropeptides

Peptides (short sequences of amino acids) that serve as neurotransmitters

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neuropharmacology

Study of how drugs alter neural function

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neuropil

Areas where numerous dendrites and axons come together making connections.

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neurotransmitter

A chemical released across a chemical synapse to communicate from one neuron to another.

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NMDA receptor

A type of glutamate receptor that provides a more prolonged time course of excitation than does AMPA and appears to be responsible for triggering long term potentiation.

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node of Ranvier

A gap in the myelin sheath where action potentials can be generated. The jumping of the action potential from one node to the next is saltatory conduction

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non-dominant hemisphere

The cerebral hemisphere that doesn't control language. This is the right hemisphere in most people. It is thought to play a role in spatial tasks.

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nucleus

A collection of cell bodies in the central nervous system. Also, an organelle that is responsible for reproduction in a cell.

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occipital lobe

The rearmost cortex where the primary visual area lies.

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Ohm's law

V=IR (voltage equals current times resistance); since g=1/R can also write I=gV

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olfaction

the sense of smell

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oligodendrocytes

These cells directly provide the myelin sheath wrapping that provides insulation for axons.

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optic chiasm

The crossing point for the optic nerves (which are not really nerves) coming from the retina.

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organelle

The cell has an anatomy too. Organelles are the organs of the cell and include stuff for making energy, for reproducing and for making proteins.

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orientation column

An area of visual cortex with neurons that respond primarily to line segments seen on the retina that have a particular angle with the horizontal

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Papez circuit

A set of interconnections within the limbic system that were proposed (by Papez) to form the emotion system.

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parallel processing

The idea that calculation in the brain involves many paths working in parallel simultaneously (opposite of serial processing)

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parietal lobe

The large middle region between occipital and frontal lobes. Houses language in the dominant hemisphere and spatial functions in the non-dominant hemisphere. Has many areas of association cortex.

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Parkinson's disease

A movement disorder featuring tremor, rigidity, reduced movement (except for the tremor) and tendency to fall. Associated with loss of dopaminergic neurons in the substantia nigra.

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passive membrane

Membranes that lack voltage-sensitive channels. Voltage in such membranes is governed by the cable equation

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perikaryon

Synonym for soma

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peripheral nervous system (PNS)

The nervous system that lies outside of the brain and spine.

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phasic

A transient response to a continuing stimulus, opposite of tonic.

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physiology

The study of functional interactions in biology. Contrasted with anatomy.

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plasticity

Changes in neural connectivity

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positron emission tomography (PET)

A technique for imaging physiological activity using radioactive substances. Picture.

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posterior

Backwards, depending on the position in the CNS corresponds to either caudal or dorsal.

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postsynaptic

The part of a synapse on the receiving side

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postsynaptic potential (PSP)

Change in voltage in the postsynaptic membrane caused by activation at that synapse.

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potential

Voltage

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presynaptic

The part of a synapse on the transmitting side

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primary sensory cortex

An area of cortex that receives sensory information directly from the thalamus or other non-cortical area

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primary visual cortex

The primary sensory area for vision

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proprioception

sensation of movement in muscles and joints

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prosopagnosia

a neurological condition where specific faces can't be recognized

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proximal

Closer to the center of the body, opposite of distal

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pyramidal cell

A characteristic neuron of the cortex that has a cell body shaped like a pyramid which gives off a large apical dendrite.

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pyramidal tract

Corticospinal tract

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rate coding

Frequency coding

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realistic" neural network

Networks of neurons simulated to be relatively close to the real thing. The quotes around realistic are necessary because the complexity of neurons makes it impossible to accurately simulate them at this time. A neurophysiological approach to neural networks.

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receptive field

The receptive field of a neuron are the union of all those locations where stimulation will activate that neuron. For touch this could be an area of skin while for vision this would be the area (visual field) that this neuron "sees"

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receptor

A site on a cell membrane where a chemical can bind. Most receptors are highly selective, they will only bind a particular type of chemical and not others. Receptors are the site where the neurotransmitter binds on the postsynaptic membrane.

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recurrent collaterals

Axon collaterals that come back and synapse either on the same neuron or on the same type of neuron that they come from

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reflex

A stereotyped closed stimulus-response loop

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relative refractory period

A period during which a repeated neuron stimulation must be increased in order to generate another action potential

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resting membrane potential

The membrane potential that a neuron will remain at in the absence of stimulation of activity. It is determined by a complex function that takes into account relative permeabilities of different ions and their respective Nernst potentials. Usually somewhere near -75 mV.

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reticular activating system

An area of brainstem that causes arousal or wakening when stimulated. Damage to this area can cause coma.

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rostral

The head side of the body. In the brain this is toward the front (anterior) and in the spinal cord it's towards the top (superior). Opposite of caudal.

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sagittal plane

The vertical plane that runs from front to back and up to down. Mid-sagittal would be the plane that runs through the middle of the nose.

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saltatory conduction

The jumping of an action potential from one node of Ranvier to the next in a myelinated axon.

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second messenger

An intracellular chemical that transmits a message between one place and another. In many cases a neurotransmitter activates a receptor that then secondarily relays the information to open an ion channel or activate another series of chemicals.

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sensory channel

A psychophysics term for a neural pathway for a particular sense or aspect of a sense.

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soma

The cell body of a neuron. This is where most of the metabolic activity of the neuron is centered. It has the organelles for producing energy and creating proteins. In the classical view, signals generally pass through the soma on the way from the dendrite (input) to the axon (output). The soma is in the middle of this picture

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space constant (lambda)

The distance along a passive dendrite for a fixed voltage to decline by 1/e (~37%)

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spatial summation

Adding up of synaptic potentials arriving at different places on one cell

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spike

An action potential

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spike frequency

The frequency at which spikes occur. Usually between 5-100 Hz in most cell types.

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spike-initiation zone

A specialized area with particularly high concentrations of voltage-gated ion channels that is the first to generate an action potential.

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spinal cord

The part of the central nervous system that lies in the spine

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spontaneous activity

The "resting" firing of a neuron when not being stimulated.

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stimulus

A maneuver that can activate a sensory receptor.

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sulcus (pl. sulci)

The cortex is a folded 2-dimensional sheet. The infoldings are sulci.

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summation

The nonlinear adding together of multiple synaptic inputs.

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synapse

Synapses are the connections between neurons. Some are electric but in vertebrates most are chemical, involving the diffusion of a chemical messenger from one side (presynaptic) to the other (postsynaptic) across the synaptic cleft. Two important neurotransmitters are glutamate and GABA. Chemical synapses.

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synaptic cleft

The region separating the presynaptic and postsynaptic membranes at chemical synapse

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synaptic transmission

The sending of information across the synapse, usually by means of release and reception of a neurotransmitter

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synaptic vesicle

Organelles found in the presynaptic cell that store and release neurotransmitter

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temporal lobe

A lobe of the brain lying mostly inferior (ventral) and pointing forward (rostral-ward) from below the major fissure. The auditory area and hippocampus (memory area) are in the temporal lobe.

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temporal summation

Adding together of postsynaptic potentials arriving one after another at a synapse

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terminal

The end of an axon

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terminal arbor

A bunch of axon branches at the end of an axon

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tetrodotoxin (TTX)

A poison that comes from the puffer fish and blocks voltage-sensitive sodium channels. Allegedly used in the voodoo religion for creating zombies.

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thalamus

A large collection of nuclei that forms the major entry point for most sensory systems to the brain. It is also involved in sleep.

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threshold

An activation level that causes a neuron or neural analog to pass from a quiescent to an excited state. In the case of a neuron this would be the voltage where an action potential would be generated.

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time constant (tau)

The amount of time it takes a fixed voltage to die off by 1/e (~37%)

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tonic

A sustained response to a continuing stimulus, opposite of phasic

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tract

A bundle of axons that run together in the CNS

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ventral

The belly side of the body. For the CNS this would be anterior in the spinal cord and inferior (down) in the brain.

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ventricles

Large cavities in the brain containing fluid

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vesicle

An organelle that can store a chemical, keeping it from floating loose around the cytoplasm. See synaptic vesicle

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voltage

A measure of the force that a charge experiences due to an electric field. Symbol: V, units: volts, (also called potential)

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voltage clamp

Holding a steady voltage in a neuron and watching how the current responds.

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voltage-gated channel

Synonym for Voltage-sensitive channel

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voltage-sensitive channel

An ion channel that opens or closes in response to changes in membrane potential.

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white matter

Brain volumes made up of axons going from one place to another. Looks white when you cut open a brain.

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