A&P 11: Fundamentals of the Nervous System & Nervous Tissue Flashcards
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Nervous system
A
master controlling and communicating system of the body
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Sensory input
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information gathered by the nervous system
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Integration
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process of the nervous system processing and interpreting sensory input and deciding what should be done at each moment
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Motor output
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the nervous system activates effector organs (muscles and glands) to cause a response, called this
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Central nervous system
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brain and spinal cord; integrating and control center of the nervous system; interprets sensory input and dictates motor output based on reflexes, current conditions, and past experience
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Peripheral nervous system
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part of the nervous system outside the CNS; consists mainly of nerves that extend from the brain and spinal cord
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Sensory (afferent) division
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part of the PNS; consists of nerve fibers (axons) that convey impulses TO the CNS from sensory receptors located throughout the body
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Motor (efferent) division
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part of the PNS; transmits impulses FROM the CNS to effector organs (muscle and glands)
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Somatic nervous system
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composed of somatic motor nerve fibers that conduct impulses from the CNS to skeletal muscles; often referred to as the voluntary nervous system because it allows us to consciously control our skeletal muscles
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Autonomic nervous system (ANS)
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consists of visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands; AKA the involuntary nervous system
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Sympathetic division
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division of the ANS that prepares the body for activity or to cope with some stressor (danger, excitement, etc.); the fight, fright, and flight subdivision
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Parasympathetic division
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division of the ANS that oversees digestion, elimination, and glandular function; the resting and digesting subdivision
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Neuroglia
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nonexcitable cells of neural tissue that support, protect, and insulate the neurons; glial cells
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Astrocytes
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shaped like delicate branching sea anemones, these are the most versatile glial cells; numerous radiating processes cling to neurons and their synaptic endings, and cover nearby capillaries; support/brace neurons and anchor them to their nutrient supply line
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Microglial cells
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small and ovoid with relatively long thorny processes, which touch nearby neurons, monitoring their health; phagocytizes microorganisms or neuronal debris
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Ependymal cells
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range in shape from squamous to columnar, and many are ciliated; line the central cavities of the brain and spinal cord, where they form a fairly permeable barrier between the cerebrospinal fluid that fills those cavities and the tissue fluid bathing the cells of the CNS
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Oligodendrocytes
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branch, but with fewer processes than astrocytes; line up along the thicker nerve fibers in the CNS and wrap their processes tightly around the fibers, producing an insulating covering (myelin sheath)
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Satellite cells
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surround neuron cell bodies in the PNS; thought to have the same function as astrocytes
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Schwann cells
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AKA neurolemmocytes; surround all nerve fibers in the PNS and form myelin sheaths around the thicker nerve fibers; functionally similar to oligodendrocytes; vital to regeneration of damaged peripheral nerve fibers
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Neurons
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nerve cells; structural units of the nervous system; typically large, specialized cells that conduct messages in the form of nerve impulses from one part of the body to another
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Neuron cell body
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consists of a spherical nucleus with a conspicuous nucleolus surrounded by cytoplasm
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Perikaryon (soma)
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another name for the neuron cell body; major biosynthetic center of a neuron; contains the usual organelles
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Chromatophilic substance
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rough ER of a neuron; AKA Nissl bodies; stains darkly with basic dyes; most active and best developed rough ER in the body
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Neurofibrils
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bundles of intermediate filaments; important in maintaining cell shape and integrity; form a network throughout the cell body
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Nuclei
clusters of cell bodies in the CNS
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Ganglia
cell bodies that lie along the nerves in the PNS
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Processes
armlike ___ extend from the cell body of all neurons
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Tracts
bundles of neuron processes in the CNS
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Nerves
bundles of neuron processes in the PNS
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Dendrites
short, tapering, diffusely branching extensions; convey incoming messages TOWARD the cell body
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Receptive (input) regions
dendrites; provide an enormous surface area for receiving signals from other neurons
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Axon
each neuron has a single one of these
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Axon hillock
the initial region of the axon arises from a cone-shaped area of the cell body called this; then narrows to form a slender process that is uniform in diameter for the rest of its length
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Nerve fiber
any long axon
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Axon collaterals
branches of an axon; extend from the axon at right angles
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Terminal branches
terminal arborizations; profuse branching at the end of an axon (10,000+)
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Axon terminals (terminal boutons)
the knoblike distal endings of the terminal branches of an axon
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Conducting region
axon is the ___ ___ of the neuron - it generates nerve impulses and transmits them, typically away from the cell body, along the plasma membrane
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Axolemma
plasma membrane of the neuron
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Secretory region
axon terminals are the ___ ___ of the neuron
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Myelin sheath
many nerve fibers, particularly those that are long or large in diameter, are covered with this whitish, fatty (protein-lipoid), segmented ___ ___
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Myelinated fibers
axons bearing a myelin sheath; conduct nerve impulses rapidly
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Nonmyelinated fibers
axons without a myelin sheath; conduct impulses slowly; dendrites are always _____
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Nodes of Ranvier
myelin sheath gaps; occur at regular intervals (1 mm apart) along a myelinated axon
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White matter
regions of the brain and spinal cord containing dense collections of myelinated fibers; primarily fiber tracts
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Gray matter
contains mostly nerve cell bodies and nonmyelinated fibers
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Multipolar neurons
have 3+ processes - one axon and the rest dendrites; most common neuron type in humans (>99%); major type of neuron in the CNS
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Bipolar neurons
neurons with 2 processes (axon and dendrite); extend from opposite sides of the cell body; rare; found in some of the special sense organs (retina, olfactory mucosa)
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Unipolar neurons
neurons with a single short process that emerges from the cell body and divides T-like into proximal and distal branches; found chiefly in ganglia in the PNS, where they function as sensory neurons
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Peripheral process
the more distal process of a unipolar neuron; often associated with a sensory receptor
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Central process
proximal process of a unipolar neuron; enters the CNS
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Pseudounipolar neurons
unipolar neurons are more accurately called this, because they originate as bipolar neurons
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Sensory (afferent) neurons
transmit impulses from sensory receptors in the skin or internal organs toward or into the CNS
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Motor (efferent) neurons
carry impulses away from the CNS to the effector organs (muscles and glands) of the body periphery; multipolar; except for some neurons of the ANS, their cell bodies are located in the CNS
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Interneurons (association neurons)
neurons that lie between motor and sensory neurons in neural pathways and shuttle signals through CNS pathways where integration occurs; most are confined within the CNS; make up over 99% of the neurons of the body, including most of those in the CNS
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Voltage
measure of potential energy generated by separated charge; measured in volts (V) or millivolts (1 mV)
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Potential difference (potential)
voltage is always measured between 2 points and is called the ___ or the __ ___ between the points
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Current
flow of electrical charge from one point to another; can be used to do work
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Resistance
hindrance to charge flow provided by substances through which the current must pass; if high = insulator; if low = conductor
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Ohm's Law
current (I) = voltage (V)/resistance (R); current is directly proportional to voltage; there is no net current between points that have the same potential; current is inversely related to resistance
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Leakage (nongated) channels
channels that are always open
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Chemically gated (ligand-gated) channels
channels that open when the appropriate chemical (in this case a neurotransmitter) binds
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Voltage-gated channels
channels that open and close in response to changes in the membrane potential
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Mechanically-gated channels
channels that open in response to physical deformation of the receptor (as in sensory receptors for touch and pressure)
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Electrochemical gradient
together, electrical and concentration gradients constitute this; ions flowing along these underlie all electrical events in neurons
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Resting membrane potential
potential difference in a resting neuron
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Polarized
state of a plasma membrane of an unstimulated neuron or muscle cell in which the inside of the cell is relatively negative in comparison to the outside; the resting state
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Sodium-potassium pump (Na+ - K+ ATPase)
stabilizes the resting membrane potential by maintaining the concentration gradients for sodium and potassium
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Depolarization
a decrease in membrane potential; the inside of the membrane becomes less negative (moves closer to zero) than the resting potential; also includes events in which the membrane potential reverses and moves above zero to become positive
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Hyperpolarization
an increase in membrane potential; the inside of the membrane becomes more negative (moves further from zero) than the resting potential
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Graded potentials
short-lived, localized changes in membrane potential that can be either depolarizations or hyperpolarizations; cause current flows that decrease in magnitude with distance
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Action potential (AP)
a brief reversal of membrane potential with a total amplitude (change in voltage) of about 100 mV
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Nerve impulse
in a neuron, an action potential; typically generated only in axons
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Threshold
when depolarization at the stimulation site reaches this certain critical level (often between -55 & -50 mV), depolarization becomes self-generating
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Repolarization
restoration of the internal negativity of the resting neuron; both the abrupt decline in Na+ permeability and the increased permeability to K+ contribute to repolarization
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All-or-none phenomenon
an action potential either happens completely or doesn't happen at all
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Propagated
if it is to serve as the neuron's signaling device, an AP must do this along the entire axon's length
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Absolute refractory period
the period, from the opening of the Na+ channels until the Na+ channels begin to reset to their original resting state; ensure that each AP is a separate, all-or-none event and enforces one-way transmission of the AP
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Relative refractory period
interval following the absolute refractory period
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Continuous conduction
AP propagation involving nonmyelinated axons
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Saltatory conduction
AP's are triggered only at the myelin sheath gaps; the electrical signal appears to jump from gap to gap along the axon; 30x faster than continuous conduction
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Multiple sclerosis
demyelinating disease; autoimmune; gradually destroys myelin sheaths in the CNS, reducing them to nonfunctional hardened lesions called scleroses
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Group A fibers
mostly somatic sensory and motor fibers serving the skin, skeletal muscles, and joints; have the largest diameter and thick myelin sheaths; conduct impulses at speeds ranging up to 150 m/s (>300mph)
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Group B fibers
lightly myelinated fibers of intermediate diameter; transmit impulses at an average rate of 15m/s (30mph)
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Group C fibers
smallest diameter; nonmyelinated; incapable of saltatory conduction and conduct impulses at a leisurely pace (1m/s or 2mph or less)
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Synapse
junction that mediates information transfer from 1 neuron to the next or from a neuron to an effector cell
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Axodendritic synapses
synapses between the axon endings of 1 neuron and the dendrites of other neurons
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Axosomatic synapses
synapses between axon endings of 1 neuron and cell bodies (soma) of other neurons
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Presynaptic neuron
the neuron conducting impulses toward the synapse
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Postsynaptic neuron
the neuron transmitting the electrical signal away from the synapse
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Electrical synapses
less common type of synapse; consist of gap junctions like those found between certain other body cells; contain protein channels (connexons) that intimately connect they cytoplasm of adjacent neurons and allow ions and small molecules to flow directly from 1 neuron to the next
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Chemical synapses
synapses specialized to allow the release and reception of chemical neurotransmitters
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Synaptic vesicles
tiny, membrane-bounded sacs, each containing thousands of neurotransmitter molecules
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Synaptic cleft
presynaptic and postsynaptic membranes are always separated by this fluid-filled space approximately 30-50 nm wide
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Synaptic delay
time required for a signal to cross a synapse between 2 neurons; rate-determining step of neural transmission
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Excitatory postsynaptic potentials (EPSPs)
local graded depolarization events that occur at excitatory postsynaptic membranes
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Inhibitory postsynaptic potentials (IPSPs)
hyperpolarizing changes in potential
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Summate
add together
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Temporal summation
occurs when 1 or more presynaptic neurons transmit impulses in rapid-fire order and bursts of neurotransmitter are released in quick succession
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Spatial summation
occurs when the postsynaptic neuron is stimulated simultaneously by a large number of terminals from one (or more commonly) many presynaptic neurons
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Facilitated
partially depolarized neurons are more easily excited by successive depolarization events because they are already near threshold
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Synaptic potentiation
repeated or continuous use of a synapse (even for short periods) enhances the presynaptic neuron's ability to excite the postsynaptic neuron, producing larger-than-expected EPSPs
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Presynaptic inhibition
occurs when the release of excitatory neurotransmitter by one neuron is inhibited by the activity of another neuron via an axo-axonal synapse
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Acetylcholine (ACh)
1st neurotransmitter identified; best understood neurotransmitter because it is released at neuromuscular junctions (easier to study than synapses buried in the CNS)
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Acetylcholinesterase (AChE)
enzyme that releases ACh and degrades it to acetic acid and choline; located in the synaptic cleft and on postsynaptic membranes
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Biogenic amines
include the catecholamines (dopamine, norepinephrine, and epinephrine) and indolamines (serotonin, histamine)
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Catecholamines
dopamine, norepinephrine (NE), and epinephrine
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Indolamines
serotonin and histamine
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Amino acids (as neurotransmitters)
glutamate, aspartate, glycine, gamma-aminobutyric acid
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Neuropeptides
strings of amino acids; include a broad spectrum of molecules with diverse effects
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Substance P
neuropeptide; important mediator of pain signals
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Endorphins
include beta ____, dynorphin, and enkephalins; act as natural opiates, reducing our perception of pain under stressful conditions
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Gut-brain peptides
neuropeptides produced by nonneural body tissues; widespread in the gastrointestinal tract; examples: somatostatin and cholecystokinin
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Adenosine triphosphate (ATP)
cell's universal form of energy; major neurotransmitter (perhaps the most primitive one) in both the CNS and the PNS
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Adenosine
part of ATP; acts outside of cells on adenosine receptors; potent inhibitor in the brain; caffeine's well-known stimulatory effects result from blocking these receptors
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Nitric acid (NO)
activates guanylyl cyclase (enzyme that makes the 2nd messenger cyclic GMP; participates in a variety of processes in the brain, including the formation of new memories by increasing the strength of certain synapses; neurotransmitter binding to the postsynaptic receptors indirectly activates ___ ___ synthase, the enzyme that makes ___ ___; acts as a retrograde messenger that sends a signal to increase synaptic strength
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Carbon monoxide (CO)
activates guanylyl cyclase (enzyme that makes the 2nd messenger cyclic GMP; mode of action similar to NO
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Hydrogen sulfide (H2S)
most recently discovered gasotransmitter; appears to act directly on ion channels and other proteins to alter their function
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Endocannabinoids
natural neurotransmitters made by the brain; act at the same receptors as THC (active ingredient in marijuana); their receptors (cannabinoid receptors) are the most common G protein-linked receptors in the brain
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Neuromodulator
term used to describe a chemical messenger released by a neuron that does not directly cause EPSPs or IPSPs but instead affects the strength of synaptic transmission
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Channel-linked receptors
ionotropic receptors; ligand-gated ion channels that mediate direct neurotransmitter action; composed of several protein subunits in a rosette around a central pore; as the ligand binds to 1+ receptor subunits, the proteins change shape; this event opens the central channel and allows ions to pass; as a result the membrane potential of the target cell changes; always located precisely opposite sides of neurotransmitter release
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G protein-linked receptors
activity mediated by these is indirect, complex, slow, and often prolonged; receptors in this class are transmembrane protein complexes - include muscarinic ACh receptors and those that bind the biogenic amines and neuropeptides
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Second messengers
cyclic AMP, cyclic GMP, diaclglycerol, or Ca2; act as go-betweens to regulate (open/close) ion channels or activate kinase enzymes that initiate a cascade of enzymatic reactions in the target cells
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Neural integration
neuronal pools and their patterns of communicating with other parts of the nervous system
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Neuronal pools
functional groups of neurons that integrate incoming information received from receptors or different __ ___ and then forward the proceeded info to other destinations
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Circuits
patterns of synaptic connections in neuronal pools; determine the pool's functional capabilities
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Serial processing
the whole system works in a predictable all-or-nothing manner
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Reflexes
rapid, automatic responses to stimuli, in which a particular stimulus always causes the same response
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Reflex arcs
reflexes occur over neural pathways called this that have 5 essential components - receptor, sensory neuron, CNS integration center, motor neuron, and effector
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Parallel processing
inputs are segregated into many pathways and different parts of the neural circuitry deal simultaneously with the information delivered by each pathway
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Neuroblasts
potential neurons
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Growth cone
the growing tip of an axon; a prickly fanlike structure that gives the axon the ability to interact with its environment
