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Glossary
a posteriori
Latin for “from what comes after,” referring to things that we learn through our senses in our experience of the world. [E]
a priori
Latin for “from what comes before,” referring to things that the mind must know before having any experiences and that are required before the mind can even have an experience. [E]
acetylcholine (ACh)
The neurotransmitter released by parasympathetic fibers as well as vertebrate motor neurons. [4, 6]
acetylcholine receptors (AChRs)
The integral membrane proteins, consisting of several subunits, that respond to the neurotransmitter acetylcholine. [6]
acetylcholinesterase
An enzyme that breaks down acetylcholine to halt neurotransmission. [6]
achaete-scute complex (AS-C)
The complex of proneural gene products that bind together and serve as transcription factors to direct early differentiation into neurons. [1]
actin
A protein that mediates contraction of cell parts, such as filopodia of growth cones. [5]
active zone
The portion of the presynaptic terminal that actively releases neurotransmitter. [6]
agenesis of the corpus callosum (AgCC)
The condition of being born with the corpus callosum either absent or severely reduced. [5]
agrin
A large proteoglycan that serves as a signal and inductive factor at neuromuscular junctions. [6]
allele
A particular version of a given gene. Different alleles may differ in the functionality of the protein produced. [A]
amblyopia
Reduced visual acuity of one eye, that is not caused by optical or retinal impairments. [9]
AMPA
amyotrophic lateral sclerosis (ALS)
A neurodegenerative disease characterized by muscle wasting and death of motor neurons. [7]
androgen receptor (AR)
A member of the steroid receptor superfamily with a high affinity for androgens such as testosterone. [7]
androgens
A class of steroid hormones, including testosterone, found in high concentrations in male vertebrates. [7]
anosmia
The condition of being unable to detect odors. [3, 9]
Antennapedia
A Hox gene in which mutations result in the formation of a leg where an antenna normally forms. [2]
anterior commissure
A relatively small collection of axons, found in the ventral portion of the brain, that communicate between the two cerebral hemispheres. [5]
anterograde transport
The transport of materials within axons in the direction of the axonal terminals. [5]
anteroventral periventricular nucleus (AVPV)
A hypothalamic region that has a greater volume in females than in males in rats and mice. [7]
antibodies
Also called immunoglobulins. Large, Y-shaped proteins produced by the immune system that recognize and bind to particular shapes in molecules. [3, A]
apoptosis
Cell death that occurs as a natural process during normal development. [7]
aromatization
Here, the single-step reaction, catalyzed by the enzyme aromatase, that converts androgens such as testosterone into estrogens such as estradiol. [7]
astrotactin
A gene that is expressed by cerebellar granule cells to help them to grip glial fibers for migration. [3]
ataxia
Lack of motor coordination. [6]
attachment
Here, the strong emotional bond between an infant and one or more caregivers. [10]
attractive
Here, referring to materials to which growth cones readily attach. [5]
autism spectrum disorder (ASD)
A disorder of social interaction that may be accompanied by problems in communication and severely limited behavior and/or interests. [5]
autonomic ganglia
Collections of neurons outside the central nervous system that provide autonomic innervation of body organs. [3]
autonomic nervous system
The neural system that regulates activity of many organ systems and consists of the sympathetic nervous system and the parasympathetic nervous system. It is largely outside of our conscious control. [8]
autoradiogram
A preparation where tissue “takes its own picture” by exposing chemical film to radioactively labeled markers. [8]
autoradiography
A process in which a tissue “takes its own picture” when photographic film is exposed to radioactively labeled markers. [3]
axonal transport
The process by which materials are moved within axons, in both directions, along microtubules. [5]
basal lamina
A particularly thick layer of extracellular matrix that surrounds mature muscle fibers and many organs. [3, 5, 6]
Bcl-2
An anti-apoptotic protein in mammals. Its homologue in worms is CED-9. [7]
Bergmann glia
Long, slender glial cells in cerebellar cortex that guide neurons migrating from the external granule cell layer to the internal granule cell layer. [3]
β-catenin
A transcription factor that also regulates cell adhesion and plays a role in several stages of neural development. [1, 6]
beta-galactosidase (β-Gal)
A bacterial enzyme, encoded by the lacZ gene, that often serves as a reporter gene or marker in studies of neural development. [3]
bicoid
A transcription factor that is concentrated in the presumptive anterior end of the embryo and directs formation of the head. [2]
binocular deprivation
A procedure of depriving both eyes of light. [9]
binocular
Referring to two eyes. [8]
birthdate
Here, the time during development when a given cell underwent its final mitosis before differentiating into a neuron or glial cell. [3]
bithorax
A Hox gene in which mutations can result in the doubling of the thorax in Drosophila. [2]
blastocoel
The hollow, fluid-filled cavity inside a blastula. [1]
blastomeres
The individual cells that make up a blastula. [1]
blastopore
A small dimple on the surface of a blastula that will invaginate to start forming the primitive gut. [1]
blastula
The earliest stage of an embryo, typically a spherical clump of cells. [1]
blotting
Transferring DNA, RNA, or protein fragments to nitrocellulose following separation via gel electrophoresis. The blotted substance can then be labeled. [A]
bone morphogenetic protein (BMP)
A class of growth factors that act to encourage ectodermal cells to take on an epidermal, rather than a neural, fate. It is part of the transforming growth factor beta (TGF
brain-derived neurotrophic factor (BDNF)
A factor, originally isolated from pig brains, that supports the developmental survival of DRG cells, but not sympathetic cells. [7]
bride of sevenless (boss)
A gene in Drosophila that encodes the membrane-bound protein boss, which is expressed in photoreceptor 8 and binds sevenless in a nearby cell, inducing it to become photoreceptor 7. [4]
bungarotoxin
A toxin found in the venom of certain snakes that irreversibly binds to and blocks nicotinic acetylcholine receptors. [8]
Caenorhabditis elegans
A microscopic roundworm that offers a valuable model of cell differentiation. [1]
calcium-dependent cell adhesion molecules (cadherins)
A class of transmembrane proteins, the adhesive properties of which are sensitive to local levels of calcium. [5, 6]
calmodulin
A protein that binds Ca2+, regulating intracellular concentrations of the ion. [6]
Cas9
CRISPR associated enzyme 9. A bacterial enzyme that induces a break in double-stranded DNA as part of the CRISPR system. [A]
caspase-3
One of the last in a cascade of caspases activated during apoptosis. It seems to act as the “executioner” that dooms the cell. [7]
caspase-9
One of the earliest in a cascade of caspases leading to apoptosis. [7]
caspases
Cysteine-dependent aspartate-directed proteases, including CED-3, which cleave many different proteins. [7]
castration
Surgical removal of the gonads, typically testes. [7]
caudal
Referring to the tail end. [2]
ced (cell death abnormal)
A collection of genes, originally isolated in C. elegans, that regulates apoptosis. [7]
ced-3
A gene that encodes a protease, CED-3, to dismantle cell machinery as part of the process of apoptosis. [7]
cell adhesion molecules (CAMs)
A class of molecules, found in extracellular regions, that adhere to some cells and not others. [3, 5]
cell-autonomous response
The condition when a particular influence acts directly upon a cell to affect it, as opposed to acting first on another cell, which then affects the cell of interest. [7]
cell-cell interactions
Here, the process by which developing cells communicate with one another and direct each other’s fate. [1]
cells
The basic building blocks of life. [1]
cellular differentiation
The process by which individual cells in an organism become progressively more specialized and different from one another. [1]
cellularization
The process in which cell walls are formed between the nuclei in a syncytium. [2]
central nervous system (CNS)
The brain and spinal cord in vertebrate species, derived from the neural tube. [1]
cerebellum
A brain region attached to the pons that plays an important role in coordination of movement. [2]
chemoaffinity hypothesis
Roger Sperry’s proposal that axonal growth cones seek out a particular target cell based on chemical signals that mark both. It explains how regenerating retinal cells manage to reestablish their original synaptic contacts with tectal cells. [5, 9]
chemotaxis
The process of displaying chemotropism. [5]
chemotropism
The tendency to follow along a particular chemical trail. [5]
chimera
Here, an individual made up of cells displaying more than one genotype, formed from the combination of cells from two separate zygotes. Typically, such an individual has received genes from more than two parents. [1, 4]
chordin
A gene that encodes the protein chordin, which exerts an organizer-like effect on ectoderm, shifting it from an epidermal to a neural fate. [1]
chromosome
A complex of condensed strands of DNA and associated protein molecules; found in the nucleus of cells. [A]
ciliary neurotrophic factor (CNTF)
A trophic factor that prevents developmental death of neurons in the ciliary ganglia. [7]
clone
Here, the reproduction of a gene so that it can be sequenced and/or manipulated. [A]
codon
A set of three nucleotides that uniquely encodes one particular amino acid. [A]
colinearity
The property of Hox genes in which their order on the chromosome matches the order in which they are expressed along the anterior-posterior axis of the body. [2]
collagen
A long-chained filamentous protein that contributes to the formation of extracellular matrix and is especially prominent in connective tissue. [3, 5, 6]
commissural neuron
A neuron that extends its axon across the body midline. [5]
commitment
Here, the tendency of a cell to take on a particular fate even in the face of particular challenges. Its meaning is restricted to only those challenges that have been tested. [1]
concentration gradient
The condition in which a particular substance, such as a CAM, is more concentrated at one end of a structure than at another. [5]
conditional specification of cell fate
The developmental strategy in which each cell’s fate depends on environmental conditions, primarily the fate of neighboring cells. [1]
conspecific
An individual of the same species. [10]
construct
Here, a stretch of DNA that has been manipulated before being inserted into an organism’s genome to create a transgenic animal. [4]
contact guidance
The process by which growth cones are guided upon direct contact with the membranes of other cells. [5]
contralateral
Referring to the opposite side of the body or brain. [8]
corpus callosum (CC)
The large bundle of axons that communicate between the two cerebral hemispheres in placental mammals. [5]
cortical plate
In developing cortex, the expanding layer of postmitotic cells that settle beneath the marginal zone and above the intermediate zone. It will form layers II–VI. [3]
cortical preplate
The region between the ventricular zone and marginal zone in developing vertebral cerebral cortex, which develops into the gray matter of the neocortex. [3]
Cre-recombinase
A bacterial enzyme that recognizes loxP, which is a specific sequence of nucleotides, and recombines the DNA at loxP sites. [A]
CRISPR
clustered regularly interspaced short palindromic repeats. A system of gene manipulation that evolved in single-celled organisms and is exploited by scientists for gene editing. [1, A]
crystallization
Here, the process by which a young male bird makes the transition from highly variable plastic song to an adult song, which tends to be rather stereotyped. [10]
curare
A toxin found in various South American plants that blocks nicotinic acetylcholine receptors. [8]
dam
Here, a mother of a domesticated animal. [3]
death genes
A term for those genes that are activated in cells during apoptosis, including proteases to dismantle proteins and nucleases to fragment DNA. [7]
decapentaplegic (dpp)
The gene that encodes dpp, a bone morphogenetic protein homologue in insects that halts mitosis in the optic disk and promotes differentiation of photoreceptors. It also induces ectodermal cells to an epidermal, rather than a neural, fate. [4]
delamination
Here, the process by which one cell in a cluster of proneural gene–expressing cells detaches from the sheet of neighboring cells to enter the insect body interior. The cell then differentiates into a neuroblast. [1]
Delta
A membrane-bound protein that binds to Notch found on the surface of adjoining cells. Delta directs that target cell away from a neural fate and toward an epidermal fate. [1]
dentate gyrus
A portion of the hippocampal formation. It is known for continued neurogenesis in adulthood. [8]
deoxyribonucleic acid (DNA)
A nucleic acid that is present in the chromosomes of cells and encodes hereditary information. [A]
Diablo
Also known as Smac. A protein that promotes apoptosis, in part by blocking the action of IAPs. [7]
diencephalon
The portion of the vertebrate brain that consists of the thalamus and hypothalamus. [2]
dimer
A complex of two proteins that bind together to form a functional unit. [1]
divergence
Here, the gradual change in the structure and function of the different versions of a gene that had been duplicated. [6]
dizygotic twins
A pair of twins derived from two fertilized eggs, who are therefore no more genetically related than any other pair of siblings. [10]
DNA sequencing
The process by which the order of nucleotides in a gene, or amino acids in a protein, is determined. [A]
dorsal lip of the blastopore
An embryonic region of the blastopore that can induce the development of a second nervous system, and therefore a second individual from an embryo. [1]
dorsal root ganglion (DRG)
A collection of neuron cell bodies embedded in vertebrate dorsal roots of the spinal cord that provides neurites to gather sensory information from the periphery and transmit it to the dorsal horn of the spinal cord. The bifurcated axons of the DRG extend one process to the periphery while the other conducts that information to the dorsal horn. [3, 7]
Drosophila melanogaster
The common fruit fly, a valuable model organism for studies of genetics and cellular differentiation. [1]
duplication
Here, replication of a gene in the course of evolution. [6]
ectoderm
The outermost of the three germ layers. [1]
embryo
The earliest stage of development of a new individual, typically a spherical collection of cells. [1]
embryonic stem cells
Cells found in embryos that display totipotency. [1]
empiricists
Philosophers who believed that the only way to gain knowledge of the world is through information provided by the senses. [I]
Emx2
A homeobox gene highly expressed in the posterior portion of the developing vertebrate cortex. [2]
endoderm
The innermost of the three germ layers. [1]
Enhancer of split, or E(spl)
A protein that dimerizes to a Notch fragment. Together they suppress proneural gene expression. [1]
enhancer region
The regulatory region that may be upstream or downstream of the structural gene, which plays a role in controlling transcription of that gene. [1]
Enlightenment
The period, roughly 1650–1750, when European thinkers began rebelling against the traditional hierarchies of monarchs and religion in favor of reason and science. [I]
environmental enrichment
The stimulation provided to domesticated animals intended to boost brain development, including social stimulation and access to physical objects. [10]
ephrin receptors
A family of receptor tyrosine kinase (RTK) molecules that bind to ephrins. [5]
ephrins
A family of membrane-bound signaling molecules that bind to ephrin receptors, which are part of the receptor tyrosine kinase (RTK) superfamily. [2, 3, 5, 6]
epidermis
Skin tissue, derived from ectodermal cells that do not become neural tissue. [1]
epigenesis
Here, the process in which successively more, and successively more complex, body structures appear in development. [1]
epigenetic
A variably defined term that often refers to a change in the genome, other than the sequence of nucleotides, that has a lasting effect on expression of a gene (see Box 10.1). [10]
epistemology
The study of knowledge and how we gain it. [P]
epitope
The particular shape of a molecule that a given antibody recognizes and binds. [3]
ErbB
A family of membrane-bound receptors that respond to neuregulins. [6]
estrogen
A class of steroid hormones, including estradiol, secreted by the ovaries. [7]
estrogen receptors
Two members of the steroid receptor superfamily that have a high affinity for estrogens such as estradiol. [7]
eukaryote
Any organism whose cells have the genetic material contained within a nuclear envelope. [A]
external granule cell layer
A layer of granule neurons that migrate to the top of the developing cerebellum before migrating ventrally to form the internal granule cell layer. [3]
extracellular matrix (ECM)
The collection of various long-chain molecules that loosely bind one another to form a layer outside many cell membranes. [5, 6]
fasciculation
Here, the tendency of axonal growth cones to adhere to and follow along a preexisting bundle of axons. [5]
fate
Here, the particular structure and function that a given cell takes on in the course of cellular differentiation. [1]
fate map
A representation of which parts of an embryo will give rise to various parts of the adult body. [2]
fetus
A stage of development reached once major organs and body parts are in place. [1]
fibroblast growth factors (FGFs)
A family of proteins that act upon a family of receptor tyrosine kinase (RTK) receptors. They are concentrated in the posterior portions of the developing vertebrate nervous system and demarcate the midbrain/hindbrain junction. [2, 4]
fibronectin
A long-chained glycoprotein that contributes to the formation of the extracellular matrix. [3, 5]
filopodia
The slender, rodlike extensions of membrane produced by growth cones. [5]
5-bromo-2′-deoxyuridine (BrdU)
A synthetic nucleotide that can serve as a substitute for thymidine in the synthesis of DNA but can be readily distinguished from thymidine by the use of antibodies. [3]
floor plate
The ventral portion of the vertebrate neural tube, the developing spinal cord. [2, 5]
Flynn effect
The increase in average human performance on IQ tests that has been observed worldwide over the past century. [10]
follistatin
A gene that encodes the protein follistatin, which exerts an organizer-like effect on ectoderm, shifting it from an epidermal to a neural fate. [1]
forkhead box P2 (FOXP2)
A gene encoding the transcription factor FOXP2, which is implicated in language in humans, song in birds, and ultrasonic vocalizations in mice. [10]
Form
Also called Platonic Form. An eternal, perfect “blueprint” of an object or concept that we recognize in its imperfect, highly variable real-life examples. [P]
fragile X syndrome (FXS)
A disorder caused by extended repeats of CGG trinucleotides in the gene named fragile X mental retardation 1 (FMR1). [6]
fraternal birth order effect
The well-established finding that the more brothers a boy’s mother carried before him, the more likely he is to grow up to be gay. [7]
Frazzled
A family of membrane-bound receptors that respond to netrins. [5]
Frizzled
A cell surface receptor protein that responds to Wnt. [2]
fruitless (fru)
A gene in Drosophila that produces functional transcripts only in males and induces the development of male-specific neural circuits that control male courtship and mating. [7]
G proteins
A family of proteins, named for their binding to GDP and GTP, that transmit intracellular signals. [6]
ganglionic eminences (GEs)
Transient bumps along the lateral ventricles of the developing telencephalon, from which neurons migrate tangentially across radial glia. [3]
gap genes
Genes that encode a class of transcription factors, the expression of which is regulated by maternal polarity genes. [2]
gastrula
An embryo that has formed a primitive gut, a tube that passes through the embryo. [1]
gastrulation
The process by which a blastula becomes a gastrula; the formation of a primitive gut. [1]
gel electrophoresis
A method of separating molecules of differing size or electrical charge by forcing them to flow through a gel. [A]
gene
A stretch of DNA that represents a functional unit of inheritance, specifying the structure of one or more proteins. [1]
gene duplication and divergence
The evolutionary process by which a gene duplication is followed by successive divergence in the sequence and function of the two copies. [2]
genotype
The total genetic makeup of an individual, typically determined at conception. [1,A]
germ layers
Here, the three layers of cells formed in the course of gastrulation. [1]
glial fibrillary acidic protein (GFAP)
A structural protein normally expressed in radial glia and astrocytes but not neurons. [3]
gliogenesis
The mitosis of cells that will give rise to glia. [3]
glucocorticoid
A class of steroid hormones, primarily released from the adrenal cortex, named for their role in regulating glucose metabolism. [10]
glucocorticoid receptor
A member of the steroid receptor superfamily that normally binds and responds to glucocorticoids. [10]
gonadotropin-releasing hormone (GnRH)
A protein released by neurons in the hypothalamus into the median eminence, which directs anterior pituitary cells to secrete the gonadotropins: follicle-stimulating hormone (FSH) and luteinizing hormone (LH). [3]
gray matter
The outer portion of the vertebrate cortex predominated by neuronal and glial cell bodies rather than myelin, hence dark in color in postmortem preparations. It is organized in six layers in mammals. [3]
growth cones
The extensions of dendrites and axons that grow away from the cell body to make synaptic contacts. [5]
guide RNA (gRNA)
A strand of RNA designed to hybridize with a targeted nucleotide sequence in DNA in order to guide the Cas9 enzyme to break the DNA at that site. [A]
guidepost cells
Certain cells that seem to serve as targets for axonal growth cones establishing a particular pathway. [5]
Guillain-Barré syndrome
An autoimmune disorder attacking Schwann cells, demyelinating axons and causing varying degrees of weakness and tingling. [6]
gynandromorph
A rare individual that displays both male and female features in a species in which most individuals are either uniformly male or female. [7]
halteres
Paired structures that serve as counterweights to maintain balance in the flight of some flies. [2]
Hansen’s disease
Formerly called leprosy. A chronic bacterial disease that causes nerve damage and disfiguring sores on the limbs and face. [4]
Hebbian synapse
A synapse that grows stronger when it repeatedly succeeds in driving the postsynaptic cell to fire and grows weaker when it repeatedly fails to drive the postsynaptic cell. [8]
hedgehog (hh)
A gene in Drosophila that is a homologue of Sonic hedgehog (Shh). It encodes the secreted protein hedgehog, which influences cell differentiation. [4]
hermaphrodite
An individual capable of reproducing as either a male (producing sperm) or female (producing ova). [1]
heterophilic binding
The property of two different materials that readily bind to one another. [5]
hippocampus
A portion of the limbic system that is known to be important for learning and memory. [8]
homeobox
A nucleotide sequence that produces a DNA-binding domain in many transcription factor proteins. It is found in Hox genes and many other transcription factors. [2]
homeotic selector genes or Hox genes
Also called simply homeotic genes. A class of genes in which mutations tend to result in swapping out one body part for another, as when mutation of Antennapedia results in the formation of legs where antennae normally form. [2]
homophilic binding
The property of a material that readily binds to itself. [5]
hormones
Chemical signals released into circulation by one group of cells that affect cells elsewhere in the body. [7]
hunchback
A transcription factor that is one of the class of gap genes that is inhibited by the nanos protein. [2]
hybridization
The process by which a string of nucleotides becomes linked to a complementary series of nucleotides. [A]
immunocytochemistry (ICC)
A method for detecting a particular protein in tissues in which an antibody recognizes and binds to the protein and then chemical methods are used to leave a visible reaction product around each antibody. Sometimes called immunohistochemistry (IHC) to emphasize study of tissues. [A,3]
imprinting
Here, the tendency of young animals, primarily birds, to visually note the characteristics of a parent and then follow that parent. [10]
in situ hybridization
A method for detecting particular RNA transcripts in tissue sections by providing a nucleotide probe that is complementary to, and will therefore hybridize with, the transcript of interest. [A]
induction
Here, the process by which one group of cells directs the differentiation of other, nearby cells. [1]
inhibitors of apoptosis proteins (IAPs)
A family of proteins that block caspases and in other ways avert apoptosis. [7]
innate
A vaguely defined term, roughly equivalent to instinct, said to typify some behaviors of some nonhuman animals. [10]
inner cell mass
In mammals, the clump of cells found inside the blastula, which will give rise to the individual’s body. The remainder of the blastula will contribute to the placenta and related tissues. [1]
instinct
A vaguely defined term said to typify some behaviors of some nonhuman animals. [10]
integrins
A family of adhesive molecules that are both membrane bound and secreted into the extracellular matrix. [5]
intellectual disability
A lifelong impairment in intellectual function and adaptive behavior, formerly known as mental retardation. [6]
intelligence quotient (IQ)
A measure of intelligence based on performance on certain tests of abstract reasoning. [10]
intermediate zone
The layer between the ventricular zone and marginal zone of the developing vertebrate brain. [3]
internal granule layer
A layer of small neurons ventral to the Purkinje cell layer in the vertebrate cerebellar cortex. [3]
ion channels
Membrane-bound proteins that, when activated, open up to allow select ions to cross the membrane. [6]
ionotropic
Referring to a class of neurotransmitter receptor that includes an ion channel to affect the electrical potential across the postsynaptic cell’s membrane. [8]
ipsilateral
Referring to the same side of the body or brain. [8]
Isl-1, Isl-2
Homeotic genes that encode the transcription factors Isl-1 and Isl-2, which are expressed in developing motor neurons. [4]
jimpy
Mice with an X-linked recessive mutation of the myelin proteolipid protein that results in severe lack of CNS myelin, tremors, and convulsions. [6]
kainate
A synthetic compound that binds a class of ionotropic glutamate receptors with high affinity. [8]
Kallmann syndrome
A condition in which individuals fail to reach puberty and are unable to detect odors. [3]
kinases
Enzymes that promote the addition of phosphates to particular sites on proteins, a process called phosphorylation. [6]
knockin
Referring to an animal in which an endogenous gene has been deliberately replaced with another allele, often an allele associated with a human disorder. [4]
knockout
Here, an animal in which a particular gene has been deliberately removed or disabled. [1, 4]
L1 cell adhesion molecule (L1)
Also called L1CAM. An important cell adhesion molecule. [5]
lacZ
A bacterial gene that encodes the enzyme beta-galactosidase. [3]
lamellipodia
The sheetlike extensions of membrane produced by growth cones. [5]
laminin
A long-chained glycoprotein that readily binds other molecules and is a major component of the extracellular matrix and connective tissue. [3, 5, 6]
lateral geniculate nucleus (LGN)
A nucleus of the thalamus that receives projections from the eyes. [8]
lateral inhibition
The process by which neighboring cells in a tissue layer inhibit one another, as in the competition between ectodermal cells for a neural fate that is mediated by the Delta-Notch system. [1]
layer IV
The fourth layer down from the pial surface in vertebrate neocortex. It is predominated by input from the thalamus and other cortical regions. [8]
ligand-gated ion channels
Membrane-bound proteins that open up an ion channel in response to a ligand such as a neurotransmitter. [6]
Lim domains
Domains found in various transcription factors that form zinc fingers to bind DNA in the process of gene regulation. [4]
long-term potentiation (LTP)
Long-lasting strengthening of synaptic strength seen after the induction of a tetanus in presynaptic afferents. It is observable in several neuronal pathways of the hippocampal formation. [8]
lordosis
Literally, the arching of the back that elevates the shoulders and hips; here, a posture displayed by receptive female rodents to permit copulation. [7]
loxP
A specific sequence of nucleotides recognized by the enzyme Cre-recombinase. If the enzyme encounters a pair of loxP sites in a gene, it will remove the DNA between the two sites and recombine the gene, usually rendering the gene product dysfunctional. [A]
LRP4
A receptor for agrin that forms a complex with MuSK. [6]
marginal zone
The outermost layer of the developing vertebrate brain. By adulthood it will form the molecular layer of the cerebral cortex. [3]
maternal effect
Influences the mother has on ontogeny of offspring apart from the particular genes she contributed. [1]
maternal polarity genes
A class of genes provided by the mother such that their products are unevenly distributed in the zygote and thereby specify the anterior-posterior axis. [2]
Mauthner cells
Large identifiable neurons found in the brainstem in many fishes and amphibians. [5]
mec-3
A gene in C. elegans that encodes the protein mec-3, which binds to the protein unc-86. The two proteins together regulate expression of genes important for differentiation into a touch receptor neuron. [1]
melanocytes
Neural crest-derived pigment cells that provide color to the skin. [3]
meninges
The three layers of tissue protecting the vertebrate central nervous system. [3]
mesencephalon
Also called midbrain. The middle segment of the embryonic vertebrate brain. It will develop into the adult midbrain. [2]
mesoderm
The germ layer that forms between the ectoderm and endoderm. [1]
messenger RNA (mRNA)
A strand of RNA that carries the code of a section of a DNA strand to the cytoplasm. [A]
metabotropic
Referring to a class of neurotransmitter receptor that uses a second messenger system to biochemically alter the postsynaptic target. [8]
metalloproteases
Enzymes that break down proteins and require atoms of a metal such as zinc to function. [3]
metazoan
A multicellular animal. [1]
metencephalon
A subdivision of the hindbrain that includes the cerebellum and the pons. [2]
microglia
The class of glial cells that clean up debris and residue in the nervous system. [7]
microtubules
The long filamentous materials formed from tubulin that provide internal structure for cells. [5]
mitogen
A substance that promotes mitosis. [2]
mitosis
The process of cell division in which both resulting cells receive the full complement of genetic material. [3]
mitotic figures
The tangled threads of duplicated chromosomes being pulled apart that are seen in cells undergoing mitosis. [3]
mitotic lineage
The sequence of mitosis during ontogeny that gives rise to a particular cell in an individual. In C. elegans there is an invariant relationship between mitotic lineage and cell fate. [1]
modern synthesis
The fusion of Darwin’s theory of evolution by natural selection with Mendel’s notion that genes represent discrete units of inheritance that are passed on either whole or not at all. [1]
molecular layer
The outermost layer of the vertebrate cerebral cortex, consisting primarily of dendrites and axons with relatively few cell bodies. [3]
Molyneux’s problem
A famous thought experiment that asks whether an adult enabled to see for the first time would be able to make sense of his or her vision. [I, 9]
monocular
Referring to one eye. [8]
monocular deprivation
A procedure of depriving one eye of light. [9]
monozygotic twins
A pair of twins derived from a single fertilized egg, who therefore share all the same genes. [10]
morphogenetic furrow
The prominent indentation of the insect optic disc that moves anteriorly, marking the differentiation of photoreceptors. [4]
mosaic specification of fate
A strategy for cellular differentiation in which each cell follows a particular fate no matter what neighboring cells might be doing, as in C. elegans. [1]
motor neurons
Neurons that send axons out to the periphery to innervate and control muscles. [2]
motor unit
A motor neuron and all the muscle fibers that it innervates. [8]
multiple sclerosis (MS)
An autoimmune disease attacking CNS myelin, causing highly variable degrees of impairment of motor and sensory processes. [6]
muscle-specific kinase (MuSK)
A membrane-bound kinase found exclusively in muscle fibers that serves as a receptor for agrin. [6]
myelencephalon
Also called medulla. The caudal-most portion of the vertebrate brainstem, which blends into the rostral spinal cord. [2]
myelin
The fatty, whitish sheet of membrane wrapped around some axons, provided by a glial cell. [6]
myelin basic protein (MBP)
An important component of myelin for both oligodendrocytes and Schwann cells. [6]
myelin oligodendrocyte glycoprotein (MOG)
An important membrane-bound glycoprotein component of myelin in the CNS. [6]
myoblasts
An embryonic muscle cell of mesodermal origin. [6]
myofibers
Also called muscle fibers. Multinucleate cells formed from the fusion of several myoblasts that have assembled the molecular machinery for contraction. [6]
myotubes
Multinucleate cells formed from the fusion of several myoblasts. [6]
nanos
A transcription factor that is concentrated in the presumptive posterior end of the embryo. [2]
nasal
Referring to the nose. For example, the nasal retina is the medial portion of the retina in vertebrates. [8]
neocortex
The six-layered outer region of the mammalian cerebral cortex. [3]
neoteny
An instance when a descendant species halts development at what was a juvenile stage of its ancestral species and becomes sexually mature at that stage. [4]
nerve growth factor (NGF)
The first isolated and identified neurotrophic factor, critical for the developmental survival of DRG and sympathetic cells. [7]
nerve net
A system of interconnected neurons found in jellyfish and related animals. [1]
netrins
A family of secreted, diffusible proteins that attract some growth cones while repelling others. [5]
neural cadherin (N-cadherin)
Also called NCad. A cadherin that is important in neural development. [3, 5]
neuronal cell adhesion molecule (NCAM)
Also called neural-CAM. An adhesive molecule expressed by many neurons. [3, 5, 6]
neural crest
A collection of ectodermal cells that break away from the developing neural tube to lie sandwiched between the tube and overlying ectoderm. [1]
neural plate
The earliest stage in the development of the vertebrate nervous system from the ectoderm. [1]
neural tube
The early, tube-shaped stage of vertebrate nervous system development. [1]
neuregulins
A family of signaling proteins, part of a much larger family of epidermal growth factors, that are membrane bound but can be cleaved to produce a diffusible signal. [6]
neurexins
A family of membrane-bound proteins found in presynaptic terminals that bind to neuroligins. [6]
neuroblast
A cell that will divide to produce neural cells. [1, 3]
neurogenesis
The mitosis of cells that will give rise to neurons. [3]
neuroligins
A family of membrane-bound proteins found in postsynaptic sites that bind neurexins. [6]
neuromuscular junction (NMJ)
The large chemical synapse found between the terminal of a motor neuron and its muscle target. [6]
neuron doctrine
The early twentieth-century proposal that neurons are structurally distinct from one another and communicate across gaps called synapses. [5]
neuropilins
A family of membrane receptor proteins that govern growth cone guidance. They bind and respond to semaphorins. [5, 9]
neurotransmitter receptors
Proteins embedded in the postsynaptic membrane that bind to neurotransmitter in the cleft and trigger a response in the target cell. [6]
neurotrophic
Referring specifically to the capacity of a factor to prevent the death of neural cells. [7]
neurotrophin-3 (NT-3)
A member of the neurotrophin family, discovered after NGF and BDNF. [7]
neurotrophin-4 (NT-4)
The fourth-discovered member of the neurotrophin family. [7]
neurotrophins
The family of neurotrophic factors that includes NGF, BDNF, and the other neurotrophins, which are designated by number. [7]
neurotropic
Referring to materials that attract neuronal growth cones. [5]
neurula
An embryo that has begun forming a nervous system, typically after the completion of gastrulation. [1]
neurulation
The process in which an embryo transitions from gastrula to neurula. [1]
NMdA
N-methyl-d-aspartate, a synthetic compound that binds with high affinity a class of ionotropic glutamate receptors that are known for imparting a Hebbian-like plasticity. [8]
node of Ranvier
The gap between successive segments of myelin in myelinated axons. [6]
node
Here, the anterior-most portion of the primitive streak, which will give rise to the brain. [1]
noggin
A gene that encodes the protein noggin, which exerts an organizer-like effect on ectoderm, shifting it from an epidermal to a neural fate. [1]
Nogo
A membrane-bound protein expressed by oligodendrocytes that inhibits neurite outgrowth. It is the product of a member of the reticulon gene family. [6]
norepinephrine (NE)
A catecholaminergic neurotransmitter released by most sympathetic fibers to activate the “fight or flight” response in various organs. [4]
Northern blot
A method of detecting a particular RNA transcript in a tissue or organ, by separating RNA from that source with gel electrophoresis, blotting the separated RNAs onto nitrocellulose, and then using a nucleotide probe to hybridize with, and highlight, the transcript of interest. [A]
Notch
A membrane-bound protein that binds to Delta found on the surface of adjoining cells. [1]
notochord
An embryonic rod-shaped structure that is derived from mesodermal tissue in all vertebrates and that induces formation of the ventral neural tube above. [1, 2]
nucleotide
A portion of a DNA or RNA molecule that is composed of a single base and the adjoining sugar-phosphate unit of the strand. [A]
nucleus
Here, the spherical central structure of a cell that contains the chromosomes. [A]
observational learning
The process by which an individual first learns how to accomplish some task by watching another individual do it. [10]
ocular dominance band
A region of neural tissue that is predominated by input from one eye or the other, such as in layer IV of primary visual cortex. [8]
ocular dominance histograms
Plots depicting the distribution of visual cortical neurons in terms of the extent to which they respond to stimuli in both eyes. [9]
olfactory bulb
An anterior projection of the brain that terminates in the upper nasal passages and, through small openings in the skull, receives axons from olfactory receptor neurons. [3, 9]
olfactory ensheathing glia (OEGs)
Glia found in the olfactory epithelium that guide newly generated olfactory receptor neurons into place. [3]
olfactory glomeruli
Spherical clusters of cells in the vertebrate olfactory bulb that process information from a particular class of olfactory sensory neurons and therefore a particular odor. [9]
olfactory placode
A plate-shaped collection of cells outside the developing brain, from which cells migrate through the olfactory bulb and to the rest of the brain. [3]
olfactory receptor protein
A protein embedded in the membrane of olfactory sensory neurons that binds odorants on the extracellular surface and triggers second messenger systems within the neurons. [9]
olfactory sensory neurons (OSNs)
The primary sensory neurons of the olfactory system, which contact and recognize particular odorants. [3, 9]
oligodendrocyte
A glial cell that provides myelination for axons in the central nervous system. [6]
ommatidium
A cluster of photoreceptors and supporting cells that form a single visual unit in the compound eye of an insect. Many ommatidia make up the eye. [4]
ontogeny
The process of individual development; growing up and growing old. [1]
optic nerve
The bundle of axons of retinal ganglion cells that exit the eye and project to the brain. [8]
organizational hypothesis
The proposal that the same testicular steroids that act early in life to permanently masculinize the vertebrate body also permanently masculinize the brain and therefore behavior. [7]
organizer
Here, a hypothesized signal from the dorsal lip of the blastopore that induces formation of a nervous system. [1]
Otx2
A homeobox gene required for development of the vertebrate midbrain and forebrain. [2]
p75
A low-affinity receptor for the neurotrophins. [7]
pair-rule genes
Genes that encode a class of transcription factors, the expression of which is regulated by gap genes. [2]
parable of the cave
Plato’s thought experiment about the concept of reality that people would have if they grew up seeing only the shadows of objects in the world. [P]
parallel fibers
The long axons from granule neurons of the cerebellum that innervate Purkinje neuron dendrites. [3]
parasympathetic ganglia
The ganglia scattered throughout the body that receive input from either the brainstem or sacral spinal cord. The neurons within the parasympathetic ganglia send their cholinergic axons to innervate various organs. [8]
parasympathetic nervous system
The portion of the autonomic nervous system that generally facilitates relaxation and recuperation of the body. [8]
parentese
The lilting, singsong style of speaking often directed at infants across cultures. [10]
Pax6
A homeobox gene highly expressed in the anterior portion of the developing vertebrate cortex. [2]
peptide
A short string of amino acids. Longer strings of amino acids are called proteins. [A]
peripheral myelin protein-22 (PMP22)
An important structural component of myelin in the peripheral nervous system. [6]
peripheral nervous system (PNS)
The entire nervous system other than the central nervous system; it includes the enteric and autonomic nervous system. It is derived from neural crest cells. [1,3]
phagocytes
Immune-related cells that attack and dismantle debris and invading microbes. [7]
pharynx
The tube lining the mouth that connects to the rest of the digestive system. [1]
phenotype
The sum total of physical characteristics that an individual displays at a particular time. [1]
philosophy
The study of the fundamental nature of knowledge, existence, and reality itself. [P]
phoneme
A particular speech sound used in language. Different human languages may use different subsets of phonemes. [10]
pia mater
Also called simply pia. The innermost layer of the vertebrate meninges, found along the outer surface of the brain. [3]
pioneer neurons
Neurons that are the first in a region to send out axonal growth cones to establish a path that many later-arising axons will follow. [5]
plastic song
An early stage in birdsong learning in which the song is highly variable. [10]
pleiotropy
The phenomenon in which a single gene plays a role in several, seemingly unrelated, traits. [3]
plexins
A family of receptors that bind and respond to semaphorins. [5]
polylysines
Long-chain molecules consisting of many lysines strung together. [5]
polymerase chain reaction (PCR)
Also called gene amplification. A method for reproducing a particular RNA or DNA sequence manyfold, allowing amplification for sequencing or manipulating the sequence. [A]
polyneuronal innervation
The condition of having more than one neuron innervate a target, such as a muscle fiber in newborn rats. [8]
pons
The portion of the brainstem caudal to the midbrain, to which the cerebellum is attached. [2]
postsynaptic densities (PSDs)
Dense regions of a postsynaptic site that are specialized to detect and respond to neurotransmitter from the presynaptic terminal. [6]
postsynaptic density (PSD) proteins
Also called scaffolding proteins. A large family of proteins that bind many other proteins to anchor the components for postsynaptic responses. [6]
postsynaptic region
The portion of a neuronal target specialized to respond to a presynaptic terminal. [6]
potassium-chloride cotransporter
A specialized membrane-bound protein that pushes both potassium and chloride ions out of cells. [6]
preformationism
The notion that all the structures of an individual are present in microscopic form at conception, so development consists of simple growth of structures already present. [1]
prefrontal cortex
The portion of the vertebrate cortex found at the extreme anterior pole. [8]
presynaptic terminal
The region of the axon terminal at a synapse. [6]
primary visual cortex (V1)
Also called striate cortex. The region of the occipital lobe where most visual information first arrives in the cortex. [8]
primitive streak
The beginnings of the nervous system in the vertebrate embryo, marking the midline of the developing individual. [1]
probe
A manufactured sequence of DNA or RNA that is made to include a label (a colorful or radio-active molecule) that lets us track its location. [A]
Probst bundles
Malformations caused by growing axons that fail to produce a corpus callosum. [5]
promoter region
The regulatory region that tends to be upstream from the structural gene. [1]
proneural genes
A collection of genes that tend to be expressed in cells that will go on to differentiate into neurons and glia. [1]
prosencephalon
Also called forebrain. The most anterior aspect of the embryonic vertebrate brain. It will develop into the telencephalon and diencephalon. [2]
prototype
A model or concept that best typifies members of a category; a “best example.” [I]
protozoan
A single-celled microscopic animal. [1]
Purkinje cells
The large, multipolar neurons that form a single layer in the vertebrate cerebellar cortex. [3]
pyknotic
A characteristic appearance of cells undergoing apoptosis. A pyknotic cell looks as if the nucleus is collapsing upon itself. [7]
radial glial cells
Also called simply radial glia. Long, slender glial cells that stretch from the ventricular surface to the pial surface in the vertebrate cerebral cortex. [3]
rapsyn
A cytoplasmic protein that binds the intracellular components of several acetylcholine receptors, effectively anchoring them together. [6]
rationalist philosophers
Philosophers who believed that the only way to understand the true nature of the world is by use of the intellect and reason, rather than the senses. [P]
realizator genes
A class of genes, the expression of which is controlled by Hox genes, that direct the actual construction of particular body parts. [2]
receptivity
Here, the willingness of a female to allow a male to mate with her. [7]
receptor tyrosine kinase (RTK)
A family of membrane-bound signaling proteins that, when activated by a ligand, phosphorylate tyrosine sites on particular intracellular proteins. [4]
redundancy
Here, the phenomenon in which several genes play a role in a process such that loss of one may have a relatively minor effect. [3]
reelin
A gene that encodes the protein reelin and when dysfunctional results in very a disorganized cerebellum and cerebrum in mice. [3]
regulatory portion of the gene
The stretches of DNA adjacent to the structural gene, which play a role in regulating transcription of that gene. [1]
repulsive
Here, referring to materials to which growth cones will not attach. Repulsive signals often cause the collapse of filopodia that contact them. [5]
retinal ganglion cells (RGCs)
The class of retinal neurons that send their axons out the optic nerve to transmit visual information to the brain. [8]
retinoic acid (RA)
A steroid-like molecule, concentrated in the posterior end of vertebrate embryos, that promotes development of posterior structures. It is a powerful teratogen. [2]
retinoic acid receptor (RAR)
A member of the steroid receptor superfamily that serves as a receptor for retinoic acid. [2]
retinoic acid response element (RARE)
A specific sequence of DNA nucleotides that is bound by the retinoic acid–retinoic acid receptor complex, thereby regulating expression of the associated gene. [2]
retrograde messenger
Here, a chemical signal emanating from the postsynaptic cell that affects the presynaptic cell. [8]
retrograde transport
The transport of materials within axons in the direction of the cell body. [5]
rhombencephalon
Also called hindbrain. The caudal-most segment of the embryonic vertebrate brain. It will develop into the metencephalon (pons and cerebellum) and myelencephalon (medulla). [2]
rhombomeres
A group of prominently segmented portions of the embryonic rhombencephalon. [2]
ribonucleic acid (RNA)
A nucleic acid that implements information found in DNA. [A]
ribosomes
Structures in the cell body where genetic information is translated to produce proteins. [A]
roof plate
The dorsal portion of the vertebrate neural tube. [2]
rostral
Referring to the head end. [2]
rostral migratory stream (RMS)
A collection of cells that migrate from the anterior horn of the lateral ventricles to the olfactory bulbs in adult mammals. [3]
roundabout (Robo)
A family of membrane-bound receptors that respond to diffusible Slit proteins. [5]
savant
A person with extraordinary talent in a specific endeavor, such as calculations, music, or memory. [5]
scaffolding proteins
A family of proteins that anchor intracellular portions of transmembrane proteins, such as neurotransmitter receptors in postsynaptic sites. [6]
Schwann cells
Glial cells that provide myelin sheaths for axons in the peripheral nervous system and cap neuromuscular junctions. [4, 6]
segment polarity genes
Genes that encode a class of signaling factors, the expression of which is regulated by pair-rule genes. [2]
self-regulation
Also known simply as regulation. Here, the process by which embryos manage to compensate for missing or damaged cells and nevertheless produce an entire individual. [1]
semaphorins
A family of secreted and membrane-bound molecules that often serve to repulse growth cones, including those that express neuropilin or plexins, and so direct them away from a boundary. [5, 9]
sensitive period
Here, the period during ontogeny when a particular manipulation must be made to affect neural development. [9]
sevenless
A gene that encodes a receptor tyrosine kinase (RTK) and that when stimulated triggers differentiation of photoreceptor 7 in Drosophila. [4]
sex-determining region of the Y (Sry)
The gene on the Y chromosome of mammals that promotes the indifferent gonad to develop as a testis. [7]
sexual differentiation
The process by which females and males diverge from each other in structure during ontogeny. [7]
sexual dimorphism
A structural difference between males and females of a species. [7]
sexual imprinting
The tendency of many birds and mammals to prefer mating with individuals that resemble their parents. [10]
sexually dimorphic nucleus of the preoptic area (SDN-POA)
A nucleus in the hypothalamus of many mammals that has a greater volume in males than females. [7]
signal peptide
A particular sequence of N-terminal amino acids that directs the full protein to the cell’s secretory pathway. [2]
SKN-1
A transcription factor in C. elegans that is more concentrated at one end of an egg or zygote, which will give rise to the posterior half of the individual. [1]
Slit
A family of diffusible proteins that mark the midline in the developing nervous system. [5]
SNARE complex
A combination of SNAREs that anchor a vesicle into position for fusion to the presynaptic membrane and release of neurotransmitter. [6]
SNAREs
Soluble-N-ethylmaleimide-sensitive attachment receptors, a family of long-chain proteins that regulate membrane fusion. [6]
sog
A gene that encodes the protein sog, an insect homologue of chordin, which blocks BMP signaling to direct ectodermal cells to differentiate into a neural, rather than epidermal, fate. [1]
somites
Paired blocks of mesoderm found on either side of the neural tube. [3]
Sonic hedgehog (Shh)
A gene that encodes the signaling protein that is secreted by the notochord and induces formation of the floor plate and the differentiation of motor neurons in the vertebrate neural tube. [2]
Southern blot
A method of detecting a particular DNA sequence in the genome of an organism, by separating DNA with gel electrophoresis, blotting the separated DNAs onto nitrocellulose, and then using a nucleotide probe to hybridize with, and highlight, the gene of interest. [A]
spinal nucleus of the bulbocavernosus (SNB)
A sexually dimorphic collection of motor neurons in the spinal cord that innervate muscles attached to the penis in rats and mice. [7]
spontaneous abortion
The accidental loss of an embryo, sometimes called a miscarriage. [2]
stereotype threat
The emotional state experienced when exposed to a derogatory stereotype about a group to which you belong. [10]
stop codon
A trio of nucleotides in DNA to mark the end of transcription. [A]
strabismus
A deviation of one or both eyes, such that they do not converge on the same region of visual space. [9]
structural portion of the gene
The portion of DNA in a gene that encodes for a particular sequence of amino acids and therefore a particular protein. [1]
subgranular zone
The portion of the dentate gyrus where cells divide in adulthood to contribute new neurons to the overlying granular layer. [3]
subsynaptic nuclei
The group of nuclei within a muscle fiber that lie closest to the neuromuscular junction. [6]
subventricular zone (SVZ)
The region just next to the ventricular zone, where many cells divide to provide neurons and glia to the developing vertebrate brain and, in at least some brain regions, new neurons in adulthood. [3]
sudden infant death syndrome (SIDS)
Also called crib death. The unexplained failure to breathe that sometimes kills infants in the first year of life. [10]
superoxide dismutase (SOD)
A protein that normally neutralizes free radicals. Mutations of this gene can cause ALS in humans. [7]
sweat glands
Specialized structures that release sweat onto the skin surface to reduce body temperature. They are activated by the release of acetylcholine from sympathetic fibers. [4]
sympathetic ganglia
The two chains of interconnected ganglia alongside the vertebral column that receive input from the sympathetic preganglionic neurons in the spinal cord. The neurons within the sympathetic ganglia send their axons out to innervate various organs, where they usually release norepinephrine. [7, 8]
sympathetic nervous system
The portion of the autonomic nervous system that generally prepares the body for action. [8]
synapse rearrangement
The process in which some synapses are withdrawn while new synapses form. [8]
synaptic cleft
The gap between the presynaptic terminal and postsynaptic region of a synapse. [6]
synaptic vesicles
Roughly spherical containers of neurotransmitter found in presynaptic terminals. [6]
synaptotagmin
An enzyme that binds to vesicle membranes and serves as a calcium sensor to trigger fusion of the membrane and release of neurotransmitter. [6]
syncytium
A single cell containing several nuclei. [2]
tabula rasa
Latin for “blank slate,” the idea that we enter the world with minds that are empty of innate ideas, and so we must gain information through experience. [I]
telencephalon
The anterior-most portion of the vertebrate brain, consisting of the cerebral cortex and related subcortical structures such as the basal ganglia and hippocampus. [2]
temporal
Here, referring to the side of the head. For example, the temporal retina is the lateral portion of the retina in vertebrates. [8]
temporal summation
The property of neurons that fire only when sufficient synaptic stimulation occurs within a particular period of time to reach threshold. [E]
teratogen
A substance that causes malformations in development. [2]
terminal Schwann cell
Specialized Schwann cells that surround and cap neuromuscular junctions, effectively isolating them from other influences. [6]
testosterone
The principle androgen secreted from the vertebrate testes, found in higher concentrations in males than females. [7]
tetanus
A sustained burst of rapid neuronal firing. [8]
tetrodotoxin (TTX)
A toxin found in the ovaries of pufferfish that blocks voltage-dependent sodium channels and thus prevents conduction of action potentials. [8]
TGF
A class of receptors that bind transforming growth factors, including BMP. [1]
thymidine
A nucleotide used in the synthesis of DNA. Because thymidine is not used in RNA, it can serve as a DNA-specific marker. [3]
topographic projections
The property of axonal projections in which the pattern of input represents a spatial array, as in the projection of retinal axons onto the brain. [E]
totipotency
Total potency; the ability of early embryonic cells to differentiate into any type of cell in the individual. [1]
transcript
The mRNA strand that is produced when a stretch of DNA is “read.” [A]
transcription
The process during which mRNA forms bases complementary to a strand of DNA. The resulting message (called a transcript) is then used to translate the DNA code into protein molecules. [A]
transcription factors
Proteins that bind to DNA and regulate the extent to which genes are expressed. [1]
transgene
A gene that has been artificially introduced into a model organism. [1]
transgenic
Referring to an organism in which foreign DNA has been deliberately inserted. [1, 4, A]
translation
The process by which amino acids are linked together (directed by an mRNA molecule) to form protein molecules. [A]
transmembrane proteins
Proteins that, due to having several hydrophobic domains, are embedded in a cell membrane. They include ion channels and neurotransmitter receptors. [6]
transsynaptic transport
The transfer of a chemical marker across a synapse. [8]
trembler
Mice with an autosomal dominant mutation of peripheral myelin protein-22 that results in demyelination and impaired locomotion. [6]
TrkA
The first-identified neurotrophin receptor, which has a high affinity for NGF. [7]
TrkB
The second-identified neurotrophin receptor, which has a high affinity for BDNF and the other neurotrophins except NGF. [7]
TrkC
The third-identified neurotrophin receptor, which has a high affinity for neurotrophin-3. [7]
trophic
Here, referring to the capacity of a factor to prevent the death of a cell, as if “feeding” it. [7]
tropic
Here, referring to the capacity of a factor to attract a growing neuronal process. [7]
tropomyosin receptor kinase (Trk)
A subfamily of the receptor tyrosine kinase (RTK) family that serve as receptors for neurotrophins. [7]
tubulin
The specialized protein that assembles to form microtubules providing structure to the cytoplasm. [5]
TUNEL
TdT-dUTP nick end labeling, a method to enzymatically label the various “nicks” in DNA that has been fragmented in preparation for apoptosis. [7]
tyrosine kinases
Enzymes that phosphorylate particular tyrosine molecules found in particular proteins. [6]
Ultrabithorax
A Hox gene complex that affects the fate of cells in the thorax of Drosophila. [2]
unc-5
A family of membrane-bound receptors that respond to netrins. [5]
unc-86
A gene in C. elegans that encodes the protein unc-86, which directs certain late-dividing cells to become touch receptor neurons. [1]
ventricular zone
The regions adjacent to the ventricles of the brain and central canal of the spinal cord, where cell division continues throughout life. [3]
vital dyes
Relatively nontoxic synthetic dyes that can be used to label living cells. [2]
voltage-gated ion channels
Membrane-bound proteins that open up an ion channel in response to particular membrane potentials. [6]
Western blot
A method of detecting a particular protein molecule in a tissue or organ, by separating proteins from that source with gel electrophoresis, blotting the separated proteins onto nitrocellulose, and then using an antibody that binds, and highlights, the protein of interest. [A]
whisker barrel
A column of somatosensory cortex that receives sensory information from a single whisker. [9]
white matter
The inner portion of the vertebrate brain, consisting primarily of myelinated axons coursing to or from the cerebral cortex, hence light in color in postmortem preparations. [3, 8]
Williams syndrome
A disorder characterized by fluent linguistic function but poor performance on standard IQ tests and great difficulty with spatial processing. [10]
Wnt
A gene that encodes the secreted protein Wnt, which is concentrated in the posterior end of vertebrate embryos. [2]
Xenopus laevis
The African clawed frog, a valuable vertebrate model species. [1]
zinc fingers
Relatively small stretches of amino acids found in various transcription factors that bind to DNA in the process of gene regulation. [4]
zygote
A fertilized egg; the single cell that will divide and grow to form a new individual. [1]"