Glossary Terms will appear here



Action potential: (nerve impulse) transient all or none reversal of a membrane potential produced by regenerative inward currents in excitable membranes



Active zone: Local region, within a presynaptic terminal, at which synaptic vesicles dock and are prepared for release by exocytosis


Adrenal medulla: central part of the adrenal gland which is an endocrine gland located next to the kidneys of mammals. It responds to nervous impulses related from stress.


Anions: negatively charged ion


Autonomic Nervous System: the efferent nerves that control involuntary visceral functions; classically subdivided into the sympathetic and parasympathetic sections


Axons: the elongated cylindrical process of a nerve cell along which action potentials are conducted; a nerve fiber


Axon hillock: the transitional region between an axon and the nerve cell body


cAMP: cyclic nucleotide produced by ATP, which functions a second messenger inside a cell for many hormones an neurotransmitters.


Central Nervous System (CNS): the collection of neurons and parts of neurons that are contained within the brain and spinal cord of vertebrates, or within the brain, ventral nerve cord, and major ganglia of invertebrates


Chemical synapse: a junction between a neuron and another cell in which the signal from the presynaptic neuron is carried across the synaptic cleft by neurotransmitter molecules


Dendrites: fine processes of a neuron, often providing the main receptive area of the cell onto which synaptic contacts are made


Depolarization: the reduction or reversal of the potential difference that exists across the cell membrane at rest


Effector cells: a cell that acts to change the condition of an organism in response to neuronal or hormonal signals


Electrochemical equilibrium: the state at which the concentration gradient of an ion across a membrane is precisely balanced by the electric potential across the membrane


Electrochemical gradient: The sum of the combined forces of concentration gradient and electrical gradient acting on an ion


Electrical synapse: a junction between two cells at which a signal is carried from one cell to the other by the passage of a charged particle through gap junctions


Excitatory post synaptic potential (EPSP): a change in the membrane potential of the postsynaptic cell that increases the probability of producing an action potential


Ganglion: a cluster of nerve cell bodies.


Gap junctions: Specializations for electrical coupling betwen cells, where cell membranes are only about 2 nm apart and tubular assemblies of proteins connect the apposed membranes


Glial cells (neuroglia): Inexcitable supportive cells associated with neurons in nervous tissue


hormone: One of many types of circulating chemical signals in all multicellular organisms that are formed in specialized cells, travel in body fluids and coordinate the various parts of the organism by integrating with target cells


hyperpolarization: an increase in potential difference across a membrane, making the cell interior more negative that it is at rest


Hypothalamus: The ventral part of the vertebrate forebrain; functions in maintaining homeostasis, especially in coordinating the endocrine and nervous systems secretes hormones of the posterior pituitary and releasing factors, which regulate the anterior pituitary.


inhibitory postsynaptic potential (IPSP): a change in the transmembrane potential of a postsynaptic cell that reduces the probability of producing an action potential


Medulla oblongata: in vertebrates, a cone-shaped neuronal mass that lies between the pons and spinal cord


Myelin sheath: a sheath formed by many layers of the membrane of schwann cells or oligodendrocyte wheel cells that are wrapped tightly around segments of axon in vertebrate nerve; serves as electrical insulation in saltatory conduction


neuron: a nerve cell


neurosecretory cells: neurons that receive signals from other nerve cells and respond by releasing hormones into body fluids or into a storage organ from which hormones are released at a later time


neurotransmitters: a chemical mediator released by a presynaptic nerve ending that interacts with receptor molecules in the post synaptic membrane


nodes of Ranvier: regularly spaced interruption (every mm) of the myelin sheath along an axon


Parasympathetic Nervous System: the cranosacral part of the ANS; in general, increased activity of these neurons supports vegetative function such as digestion


Peripheral Nervous System (PNS): the set of neurons and parts of neurons that lie outside of the CNS


Pheromone: A small volatile chemical signal that functions in communication between animals and acts much like a hormone in influencing physiology and behavior.


Pituitary gland: An endocrine gland at the base of the hypothalamus consists of a posterior gland, which stores and releases two hormones produced by the hypothalamus, and an anterior lobe, which produces and secretes many hormones that regulate body functions.


Post synaptic: located on the receiving side of a synaptic connection


Presynaptic: located on the sending side of a synaptic connection


Releasing hormone: A hormone produced by neurosecretory cells in the hypothalamus of the vertebrate brain that stimulates or inhibits the secretion of hormones by the anterior pituitary.


Repolarization: the return to resting polarity of the cell membrane that has been depolarized


Schwann cells: a neuroglial cell outside the CNS that wraps its membrane around axons during development to produce the insulating myelin sheath that envelopes peripheral axons in the regions between nodes of Ranvier



Sodium - Potassium pump: membrane protein responsible for maintaining asymmetrical concentrations of Na+ and K+ ions across the cell membrane


Soma: the nerve cell body


Somatic Nervous System: the part of the nervous system that receives input from the body


Spatial summation: integration by a postsynaptic neuron of simultaneous synaptic currents that arise from the terminals of different presynaptic neurons


Spike-initiating zone: Region of the nerve axon where an action potential is initiated. In many (but not all) neurons, the axon hillock


Sympathetic Nervous System: thoracolumbar part of the ANS; increased activity in sympathetic neurons typically provides metabolic support for vigorous physical activity, so this system has been called "the fight or flight system"


Synapse: a specialized area that connects to directly interacting nerve cells


Synaptic cleft: The space separating the cells at a synapse


Target cells: cells within the body that have the appropriate receptors to respond to specific hormones.


Temporal summation: summation of postsynaptic membrane potentials that occur close to one another in time, but not simultaneously


Threshold potential: the potential at which a response (action potential or muscle twitch) is produced