N Flashcards
Na+/K+ ATPase
An ion transporter that expels 3 Na+ out of a cell and imports 2 K+, driven by the energy of ATP hydrolysis.
NaCaX
Sodium-calcium exchanger; a type of ion exchanger.
Nares
Nostrils.
Natriuretic
Leading to the appearance of sodium in the urine.
Natural Killer Cells
A type of lymphocyte that is part of the innate immune system of vertebrates that is capable of killing tumors or cells infected with viruses without prior stimulation by the immune system.
Near-Equilibrium Reaction
A reaction in which the products and substrates in vivo are near the concentrations that would arise if the enzymatic reaction were to reach equilibrium. The reaction is regulated by changes in the concentrations of substrates and products.
Negative Feedback Loop
A regulatory mechanism whereby a step late in a pathway causes a decrease in the activity of a step earlier in the pathway to reduce the flow through the pathway.
Negative Feedback Regulation
see negative feedback loop
A type of regulation in which the output of a pathway tends to decrease the activity of earlier steps in the pathway.
Negative Work
Work that arises when the muscle is lengthening.
Nematocyst
The stinging cell of cnidarians.
Nephridium
A primitive type of kidney tubule found in some invertebrates, such as annelids and mollusks; can also refer to the embryonic kidney of vertebrates.
Nephron
The multicellular unit of the kidney, consisting of the tubule and the vasculature that serves it, typically a glomerulus.
Nernst Equation
An expression that describes the ion concentration gradient across a permeable membrane in relation to the voltage when the system is at equilibrium.
Nerve
A cordlike structure composed of a collection of neuronal axons grouped together by connective tissues.
Nerve Net
Description of the structure of the nervous system of cnidarians.
Nervous System
Network of neurons and their supporting cells.
Net Energy
The proportion of metabolizable energy that is retained by the body, excluding that lost to specific dynamic action.
Neurogenic
A contraction that occurs in response to a nervous stimulus.
Neurogenic Muscle
A muscle that is activated by neuronal stimulation.
Neurohemal Organ
A region of multiple neurons that secrete hormones into the blood.
Neurohormone
A chemical messenger released from a neuron into the blood.
Neuromast
A structure consisting of a cup filled with a viscous gel and several hair cells; the functional unit of the lateral line system of fishes and amphibians.
Neuromodulators
Substances that alter neurotransmission, and thus regulate the action of neurotransmitters.
Neuromuscular Junction
The synapse between a motor neuron and a skeletal muscle cell.
Neurons (nerve cells)
Specialized cells in the nervous system that communicate using chemical and electrical signals. Many, but not all, neurons are excitable cells that generate action potentials.
Neuropeptides
Polypeptides that act as neurotransmitters.
Neurosecretory Cell
Neurons that produce and secrete neurohormones into the blood, typically in a region called a neurohemal organ.
Neurotransmitter
A chemical messenger released from a neuron into the synaptic cleft.
Neutral Evolution
Changes in gene frequency in a population over time that are solely the result of random mutation and that are not shaped by forces such as natural selection.
Neutral
The pH at which the concentration of H+ equals that of OH−.
Neutrophils
The most common type of white blood cell in the vertebrate immune system.
Nicotinic ACh Receptors
Ligand-gated ion channels that open in response to acetylcholine binding.
Nitric Oxide
A gaseous neurotransmitter and paracrine chemical signal that is involved in regulating many physiological processes; important vasodilator in vertebrates.
Nitrogen Narcosis
A state of altered consciousness similar to alcohol intoxication that can occur in humans when they dive to depths greater than 30 m while breathing air.
nociceptor
or nocioceptor
A sensory receptor that responds to noxious stimuli of various types (e.g., extreme heat or cold, extreme pressure, harmful chemicals, tissue damage); pain receptor.
Nocturnal
Active at night.
Nodes of Ranvier
A gap of exposed axonal membrane between two regions of myelin sheath.
Non-Competitive Inhibition
A mode of enzyme inhibition in which a molecule inhibits an enzyme by acting at a site distant from the active site; noncompetitive inhibitors can increase the K_m or reduce the V_max.
Noncovalent Bond
Includes four types of weak bonds that stabilize macromolecular structure.
Nondirectional Ventilation
Anatomical arrangement of the respiratory system in which the medium flows across the respiratory surface in a random or unpredictable direction.
Nonpolar
Having low solubility in water or other polar solvents.
Nonshivering Thermogenesis (NST)
Production of heat by chemical means without muscle contraction. Typically refers to heat production by brown adipose tissue; however, there are other means of NST.
Norepinephrine
or noradrenaline
A catecholamine neurotransmitter; in vertebrates, released by the sympathetic nervous system.
Nuclease
An enzyme that hydrolyzes nucleic acids; includes DNases and RNases.
Nucleator
or nucleating agent
A molecule or particle that triggers the formation of ice at subzero temperatures.
Nuclei (brain)
A cluster of cell bodies within the brain that act as an integrating center.
Nucleoside
A molecule composed of a nitrogenous base (purine or pyrimidine) linked to a ribose or deoxyribose sugar.
Nucleotide
A nucleoside with one or more phosphate groups, such as ATP.
Nymph
The larval form of a hemimetabolous insect that resembles in most respects the adult form of the insect, except lacking functional wings.
