Neurobiology Glossary S - Z, Blackwell Science

NEUROBIOLOGY Molecules, Cells and Systems
Gary G. Matthews

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Glossary
[ A-E ] [ F-L ] [ M-R ] [ S-Z ]

Glossary

saccade: A rapid eye movement used to alter eye position within the orbit, causing a rapid adjustment of the fixation point to different positions in the visual world.
saccule: The horizontally oriented otolith organ of the labyrinth.
saltatory conduction: A form of action potential propagation found in myelinated axons, in which action potentials jump from one node of Ranvier to the next.
sarcomere: The basic repeating unit of striation along the length of myofibrils of striated muscle cells. The sarcomere is defined as extending from one Z line to the next Z line.
sarcoplasmic reticulum: An intracellular store of calcium ions wrapped around the contractile apparatus of myofibrils in striated muscle cells. Calcium released from the sarcoplasmic reticulum triggers contraction.
saxitoxin: A naturally occurring biological toxin that blocks voltage-dependent sodium channels and prevents neurons from firing action potentials.
Schwann cell: A type of glial cell that forms the myelin sheath around axons in the peripheral nervous system.
semicircular canals: The acceleration-sensing, fluid-filled loops that form part of the labyrinth.
sensitization: Enhancement of the strength of a reflexive response produced by the presentation of a noxious stimulus.
sensory adaptation: The reduction in activity of a sensory neuron during sustained application of a sensory stimulus.
sensory neuron: A neuron whose activity is affected by the presence of a particular type of sensory stimulus.
sensory transduction: The conversion of stimulus energy into an electrical signal in a primary sensory receptor neuron.
sinoatrial (SA) node: A specialized group of cardiac muscle cells in the right atrium that normally control the rate of the heart beat.
skeletal muscle: A type of striated muscle responsible for movement of body parts.
SNAP-25: A membrane protein involved in docking and/or fusion of synaptic vesicles at active zones of synaptic terminals.
sodium pump (Na+-K+ ATPase): A membrane protein that uses energy released by hydrolysis of ATP to actively transport sodium out of the cell and potassium into the cell.
soma: The cell body of a cell, where the nucleus is located.
somatic nervous system: The division of the nervous system that controls the skeletal muscles, as distinguished from the autonomic nervous system.
somatopic map: A form of neural organization in which neighboring regions of a body structure project to or are controlled by neighboring neurons in the brain region that receive sensory inputs from or send motor output to the body structure.
somatosensory system: The sensory system that receives and processes sensory information from the body, including the skin, muscles, and joints.
spatial summation: Summation of postsynaptic responses in a postsynaptic cell from two or more synaptic inputs that are active at about the same time.
spinal canal: The fluid filled space at the center of the spinal cord. The spinal canal is continuous with the ventricles of the brain.
spinal nerve: The mixed motor and sensory nerve connected to the spinal cord at a particular vertebral segment.
spinocerebellar tract: The sensory pathway in the spinal cord carrying ascending axons to the cerebellum.
spiral ganglion: The ganglion in the cochlea containing the cell bodies of sensory neurons that receive inputs from the cochlear hair cells and send axons via the auditory nerve (cranial nerve VIII) to the cochlear nucleus of the brainstem.
stellate cell: A neuron whose dendrites radiate approximately equally in all directions from the soma, producing a starlike pattern.
stem cell: An undifferentiated precursor cell that retains the ability to give rise to a variety of cell types. In the nervous system, stem cells can give rise to various neuron subtypes and to glial cells.
striated muscle cell: A type of muscle cell in which the contractile machinery forms a regular, repeating array, which gives the cell a striped (striated) appearance when viewed through the light microscope.
striatum: A collective term for the caudate nucleus and putamen, which are two of the basal ganglia of the forebrain.
substantia nigra: A midbrain region involved in the control of motor behavior. Loss of dopamine-releasing neurons of the substantia nigra underlies the movement disorder called Parkinson's disease.
sulcus (plural: sulci): An infolding, or groove, in the cortical surface. A sulcus separates neighboring gyri.
superior colliculus: A brain region on the dorsal surface of the midbrain that is involved in the control of eye movements.
superior olivary nucleus (superior olive): A nucleus in the brainstem that is involved in the processing of auditory information. The superior olivary nucleus receives inputs from the cochlear nuclei and sends outputs to the inferior colliculus.
supplemental motor area: A higher order cortical motor area located in the medial part of the frontal lobe, just anterior to the primary motor cortex.
suprachiasmatic nucleus: A nucleus of the hypothalamus responsible for synchronizing circadian rhythms in other organs and tissues.
Sylvian fissure: The large sulcus that separates the temporal lobe from the rest of the cerebral cortex. It is also called the lateral sulcus.
sympathetic chains: A series of interconnected sympathetic nuclei (the paravertebral ganglia) that parallel both sides of the vertebral column.
sympathetic division: A division of the autonomic nervous system, containing autonomic motor neurons that release the neurotransmitter norepinephrine. Actions of the sympathetic nervous system typically oppose the actions of the other division of the autonomic nervous system, the parasympathetic division.
synapse: The contact point where a neuron transfers information to a target cell.
synaptic cleft: The extracellular space separating the presynaptic cell and the postsynaptic cell at a synapse.
synaptic vesicle: A small, membrane-bound structure in which neurotransmitter molecules are stored within synaptic terminals.
synaptobrevin: A membrane protein associated with the membrane of synaptic vesicles. Synaptobrevin forms a complex (the SNARE complex) with the plasma membrane proteins syntaxin and SNAP-25 and is thought to play a role in vesicle targeting at the active zone.
synaptotagmin: A membrane protein associated with the membrane of synaptic vesicles that is thought to be responsible for the control of vesicle exocytosis by calcium ions.
syntaxin: A membrane protein involved in docking and/or fusion of synaptic vesicles at active zones of synaptic terminals.

taste bud: A cluster of cells on the surface of the tongue, containing taste receptor cells.
tectorial membrane: A sheet of tissue overlying the organ of Corti in the cochlea. Cilia of outer hair cells are embedded into the surface of the tectorial membrane.
telencephalon: A subdivision of the forebrain, comprising the cerebrum and the basal ganglia.
temporal summation: Summation of successive postsynaptic responses in a postsynaptic cell from two or more action potentials arriving within a brief period in the same synaptic terminal.
tetraethylammonium (TEA): A drug that blocks potassium channels.
tetrodotoxin: A biological toxin that blocks voltage-dependent sodium channels.
thalamus: One of the two subdivisions of the diencephalon. The thalamus receives and processes sensory information and sends the sensory information to the appropriate regions of the cerebral cortex. The thalamus also plays important roles in motor control.
thermoreceptors: Primary sensory neurons that respond to changes in skin or body temperature. thick filament. A longitudinal filament found in striated muscle cells, made up of the protein myosin.
thin filament: A longitudinal filament found in striated muscle cells, made up of the protein actin and the associated proteins tropomyosin and troponin.
third ventricle: The part of the brain ventricles that extends from the midbrain through the diencephalon.
threshold (threshold potential): The value of membrane potential that must be reached in an excitable cell to trigger an action potential.
tonotopic map: The orderly projection of inputs originating from the cochlea to sensory areas in the brain, such that neighboring neurons in the target regions respond to progressively higher frequencies.
transducin: A G protein that is activated by photoactivated rhodopsin during transduction in photoreceptors.
transgenic animal: An animal in which the natural genetic material has been altered by the insertion of exogenous DNA or the deletion of endogenous DNA.
transverse tubules: Invaginations of the plasma membrane in skeletal muscle cells that provide a path for depolarization during the muscle action potential to spread to the cell interior.
trkA, trkB, trkC: Tyrosin receptor kinase molecules that act as receptors for neurotrophin molecules in cells.
tropomyosin: A protein associated with the thin filaments of striated muscle cells. Tropomyosin controls the access of myosin to the myosin binding site of actin.
troponin: A calcium binding molecule associated with the thin filaments of striated muscle cells. Binding of calcium to troponin initiates contraction.
tubulin: A protein molecule that polymerizes to form the backbone of microtubules. tympanic membrane. The eardrum, which transfers sound pressure waves to the bones of the middle ear.

undershoot: The transient period of increased negativity at the termination of an action potential.
utricle: The vertically oriented otolith organ of the labyrinth.

vasopressin (antidiuretic hormone; ADH): A hormone released by magnocellular neurosecretory cells of the hypothalamus in the posterior pituitary gland.
ventral column: The white matter on the ventral surface of the spinal cord, containing descending motor axons of the corticospinal tract, the vestibulospinal tract, and the reticulospinal tract.
ventral corticospinal tract: The portion of the ventral column containing descending axons of neurons whose cell bodies are located in the primary motor cortex.
ventral root: The fiber bundle containing outgoing (efferent) motor axons exiting the spinal cord at each vertebral segment.
ventricles: The fluid-filled core of the brain, filled with cerebrospinal fluid.
ventricular zone: The inner layer of the neural tube, next to the fluid-filled ventricle. Dividing precursor cells that give rise to the nervous system are found in the ventricular zone.
vestibular ganglion: A ganglion located just outside the labyrinth of the inner ear, containing the cell bodies of sensory neurons that receive inputs from the hair cells of the semicircular canals.
vestibular nuclei: Nuclei in the brainstem that receive synaptic inputs from sensory neurons of the vestibular ganglion.
vestibulo-ocular reflex: The reflex that induces eye movements in response to head rotation to keep the eyes fixated at a constant point in space.
vestibulospinal tract: A fiber pathway originating in the vestibular nucleus of the brainstem and projecting to the spinal cord. Activation of the vestibulospinal tract promotes limb extension.
voltage-sensitive sodium channel: A sodium channel whose conducting state depends on voltage. Opening of voltage-sensitive sodium channels underlies the depolarizing phase of the action potential.

Wernicke's area: Part of the temporal lobe surrounding the primary auditory cortex. Damage in Wernicke's area produces deficits in understanding spoken language (receptive aphasia).
white matter: Regions of the central nervous system containing few neuronal cell bodies and many myelinated axons. The myelin sheaths are opaque compared to surrounding regions containing mostly neuronal cell bodies (gray matter).

Z line: A crosswise line connecting thin filaments within a myofibril. The sarcomere is defined as extending from one Z line to the next Z line.

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