44.Neurons, Glia, and Nervous Systems

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  • Created by: kpaul1234
  • Created on: 24-05-21 17:52
Define a neuron
A nervous system cell that can generate and conduct action potentials along an axon to a synapse with another cell.
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Define glia
One of the two classes of neural cells (along with neurons, with which glia interact); glia do not typically conduct action potentials. Types of glia include astrocytes, oligodendrocytes, and Schwann cells.
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Define Macroglia
Non-neuronal cells of the central and peripheral nervous system that provide homeostatic functions for neurons, modulate synaptic connections, provide myelin coverings for axons, and create the blood-brain or blood-spinal cord barrier.
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Define Microglia
Glial cells that act as macrophages and mediators of inflammatory responses in the central nervous system.
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Define the Central Nervous System (CNS)
That portion of the nervous system that is the site of most information processing, storage, and retrieval; in vertebrates, the brain and spinal cord. (Contrast with peripheral nervous system.)
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Define the Peripheral Nervous System (PNS)
The portion of the nervous system that transmits information to and from the central nervous system, consisting of neurons that extend or reside outside the brain or spinal cord and their supporting cells. (Contrast with central nervous system.)
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Define a cell body
The portion of the neuron that contains the nucleus and gives rise to dendrites and an axon.
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State the function of a dendrite
Branching fibers (processes) of a neuron. Dendrites are usually relatively short compared with the axon, and commonly carry information to the neuronal cell body.
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State the function of an axon
The process (branching structure) of a neuron that conducts action potentials away from the cell body.
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State the function of an axon terminal
The end portion of an axon, which passes action potentials to another cell. Axon terminals can form synapses and release neurotransmitter.
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Define an action potential (APs)
Generated by neurons, these are electrical signals that transmit information via waves of depolarization or hyperpolarization of the cell membrane.
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Define a Synapse
A specialized type of junction where a neuron meets its target cell (which can be another neuron or some other type of cell) and information in the form of neurotransmitter molecules is exchanged across a synaptic cleft.
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State the function of a neurotransmitter
A substance produced in and released by a neuron (the presynaptic cell) that diffuses across a synapse and excites or inhibits another cell (the postsynaptic cell).
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State the function of an oligodendrocyte
A type of glial cell that myelinates axons in the central nervous system.
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State the function of a Schwann cell
A type of glial cell that myelinates axons in the peripheral nervous system.
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State the function of Myelin
Concentric layers of plasma membrane that form a sheath around some axons; myelin provides the axon with electrical insulation and increases the rate of transmission of action potentials.
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State the function of an astrocytes
A type of glial cell that contributes to the blood–brain barrier by surrounding the smallest, most permeable blood vessels in the brain.
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State the function of a blood-brain barrier
The selective impermeability of blood vessels in the brain that prevents most chemicals from diffusing from the blood into the brain.
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Define a tripartite synapse
The idea that a synapse includes not only the pre-and postsynaptic neurons involved but also encompasses many connections with glial cells called astrocytes.
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Define membrane potential
The difference in electrical charge between the inside and the outside of a cell, caused by a difference in the distribution of ions.
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Define resting potential
The membrane potential of a living cell at rest. In cells at rest, the interior is negative to the exterior. (Contrast with action potential.)
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Define voltage
A measure of the difference in electrical charge between two points.
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Define a sodium-potassium pump
Antiporter responsible for primary active transport; it pumps sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients. Also called a sodium–potassium ATPase.
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Define an electrochemical gradient
The concentration gradient of an ion across a membrane plus the voltage difference across that membrane.
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Define a potassium equilibrium potential
The negative membrane potential that balances the tendency for K+ ions to diffuse out of the cell down its concentration gradient.
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State the Nernst equation
A mathematical statement that calculates the potential across a membrane permeable to a single type of ion that differs in concentration on the two sides of the membrane.
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Define patch clamping
Technique for isolating a tiny patch of membrane to allow the study of ion movement through a particular channel.
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State the function of a Voltage-gated channel
A type of gated channel that opens or closes when a certain voltage exists across the membrane in which it is inserted.
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State the function of a Chemically gated channel
A type of membrane channel that opens or closes depending on the presence or absence of a specific molecule that binds either to the channel protein itself or to a separate receptor that alters the three-dimensional shape of the channel protein.
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Define a mechanically gated channel
A molecular channel that opens or closes in response to mechanical force applied to the plasma membrane in which it is inserted.
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Define depo-larized
A change in the resting potential across a membrane so that the inside of the cell becomes less negative, or even positive, compared with the outside of the cell. (Contrast with hyperpolarization.)
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Define hyperpolarized
A change in the resting potential across a membrane so that the inside of a cell becomes more negative compared with the outside of the cell. (Contrast with depolarization.)
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Define a graded membrane potential
Small local change in membrane potential caused by opening or closing of ion channels.
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Define an axon hillock
The junction between an axon and the neuron’s cell body; where action potentials are generated.
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Define threshold
The level of depolarization that causes an electrically excitable membrane to fire an action potential.
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Define the refractory period
The time interval after an action potential during which another action potential cannot be elicited from an excitable membrane.
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Define an activation gate
The property of a voltage-gated Na+ ion channel that increases its permeability to Na+ ions when the membrane is depolarized.
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Define an inactivation gate
The property of a voltage-gated Na+ ion channel that decreases its permeability to Na+ when the membrane is depolarized.
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Define after-hyperpolarization or undershoot
A change in the resting potential across a membrane so that the inside of a cell becomes more negative compared with the outside of the cell. (Contrast with depolarization.)
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Define the nodes of Ranvier
A gap in the myelin sheath covering an axon; the point where the axonal membrane can fire action potentials.
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Define saltatory conduction
The rapid conduction of action potentials in myelinated axons; so called because action potentials appear to “jump” between nodes of Ranvier along the axon.
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Define an electrical synapse
A type of synapse at which action potentials spread directly from presynaptic cell to postsynaptic cell. (Contrast with chemical synapse.)
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Define a chemical synapse
Neural junction at which neurotransmitter molecules released from a presynaptic cell induce changes in a postsynaptic cell. (Contrast with electrical synapse.)
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Define a neuromuscular junction
Synapse (point of contact) where a motor neuron axon stimulates a muscle fiber cell.
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State the function of Acetylcholine (ACh)
A neurotransmitter that carries information across vertebrate neuromuscular junctions and some other synapses. It is then broken down by the enzyme acetylcholinesterase (AChE).
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Define a motor end plate
The depression in the postsynaptic membrane of the neuromuscular junction where the terminals of the motor neuron sit.
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Define a synaptic cleft
The space between the presynaptic cell and the postsynaptic cell in a chemical synapse.
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Define Spatial summation
In the production or inhibition of action potentials in a postsynaptic cell, the interaction of depolarizations and hyperpolarizations produced at different sites on the postsynaptic cell. (Contrast with temporal summation.)
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Define temporal summation
In the production or inhibition of action potentials in a postsynaptic cell, the interaction of depolarizations or hyperpolarizations produced by rapidly repeated stimulation of a single point on the postsynaptic cell. (Contrast with spatial summation.)
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Define an agonist
A chemical substance (e.g., a neurotransmitter) that elicits a specific response in a cell or tissue. (Contrast with antagonist.)
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Define an antagonist
A biochemical substance (e.g., a drug) that blocks the normal action of another biochemical substance. (Contrast with agonist.)
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Define a neural network
An organized group of neurons that contains three functional categories of neurons—afferent neurons, interneurons, and efferent neurons—and is capable of processing information.
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State the function of an Afferent neuron
Afferent neurons carry sensory information into the nervous system. That information comes from specialized sensory cells that transduce (convert) various kinds of sensory stimuli (e.g., light, heat, pressure) into APs.
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State the function of an Efferent neuron
Efferent neurons carry commands to physiological and behavioral effectors such as muscles and glands.
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State the function of an Interneuron
Interneurons integrate and store information and communicate between afferent and efferent neurons.
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Define a nerve net
Diffuse, loosely connected aggregations of nervous tissues in certain non-bilatarian animals such as cnidarians.
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State the function of the ganglia
A cluster of neurons that have similar characteristics or function.
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State the function of the brain
The centralized integrative center of a nervous system.
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Describe the spinal reflex
The conversion of afferent to efferent information in the spinal cord without participation of the brain.
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Define gray matter
In the nervous system, tissue that is rich in neuronal cell bodies. (Contrast with white matter.)
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Define white matter
In the central nervous system, tissue that is rich in axons. (Contrast with gray matter.)
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