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272 terms

Chapter 11; Fundamentals of the Nervous System and Nervous Tissue

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Nervous system
Master controllinng and communication system of the body
--Rapid, specific, usually cause immediate response
--electrical and chemical signals
--the body's speedy, electrochemical communication system, consisting of all the nerve cells of the peripheral and central nervous system

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Nervous system, functions
3 overlapping functions
1 sensory input
2 integration
3 motor output

EX; driving see red light (sensory input), nervous system interates information (red light means stop) and foot goes for brake (motor output)

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Sensory input
Nervous system receives information from environment (inside and outside of the body)

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Integration
nervous system processes and interprets sensory input / decides what should be done at each moment

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Motor output
conduction of signal from integration center to the effector cells (muscles or glands that carry out the signal)

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Nervous system, parts
Central Nervous system CNS
Peripheral Nervous system PNS

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Cental nervous system
the body system that is made up of the brain and spinal cord.
--dorsal body cavity
--acts as integrating and control center
--interprets incoming sensory info and dictates a response

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Peripheral Nervous system
the sensory and motor neurons that connect the central nervous system to the rest of the body
--outside CNS

--bundles of axons, extend from brain and spinal cord

--spinal nerves carry impulese to adn from the spinal cord

--cranial nerves carry impulses to and from the brain

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Perpheral Nervous system, functional subdivisions
--sensory / afferent division "carrying toward"
--input
--conveys impulses to CNS from sensory receptors in various parts of body

--motor / efferent division " carrying away" 2 parts
--output
--transmits impulses from CNS to effector organs, the muscles and glands
--brings about motor responses
-------motor subdivisions----------------------------------(based on part of body to respond----
1 somatic nervous system / voluntary nervous system
2 autonomic nervous system ANS / involuntary nervous system

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sensory division
of the PNS of made up of sensory, or afferent, neurons that convey information to the CNS from sensory receptors that monitor the external and internal environment.

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Afferent division
division of nervous system which transmits sensory information from somatic and visceral receptors and special sense organs to the CNS

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Somatic afferent fibers
sensory fibers conveying impulses from the skin, skeletal muscles, and joints

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Visceral afferent fibers
convey impulses from visceral organs (organs of ventral body cavity)

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Motor division
carries signals from the CNS to gland and muscle cells that carry out the body's response ( effector organs)

--2 main parts
1 somatic nervous system / voluntary
2 autonomic nervous system / involuntary

-- 2 function sub divisions
1 sympathetic division
2 parasympathetic division



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Efferent division
division of nervous system which carries motor commands to muscles and glands, which are effector organs

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Somatic Nervous system
--SNS; voluntary
--sensory neurons
--carry info from cutanious and special sense recetpors primarily to head
extremites to CNS & motor Neurons from CNS that conduct impulses to muscles
--division of the peripheral nervous system that controls the body's skeletal muscles' skeletal nervous system

--somatic motor nerve fibers conduct impulses from CNS to skeletal muscles

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Voluntary nervous system
controls conscious intent and contraction of skeletal muscles.

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Autonomic Nervous system
ANS
--Visceral motor nerve fibers
--sensory neurons
--info from receptors primarily in the viscera to CNS motor neurons
--CNS conduct impulses to smooth, heart muscle and glands
--the part of the nervous system of vertebrates that controls involuntary actions of the smooth muscles and heart and glands

-----------------------2 divisions---------------------------
Sympathetic - fight or flight
Parasympathetic - resting and digesting

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Involuntary Nervous system
consists of visceral motor nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands, also called AUTONOMIC NERVOUS SYSTEM

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Nervous System; levels of organization
Central nervouse CNS (brain & spinal cord) > Pheripheral nervous system PNS(cranial nerves and spinal nerves) > Motor / effferent division (motor nerve fibers/ skeletal) > Somatic( skin) nervous system & autonomic (stomach) nervous system > Sympathetic(heart) division & Parasympathetic(bladder) division

Sensory / afferent division > peripheral nervous > Central Nervous

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Nervous tissue, Histology
--nervous tissue / highly cellular
-- less than 20% of CNS is extracellular space
--cells are densely packed, tightly intertwined

--2 principle types of cells
1 supporting cells / neuroglia, smaller cells that surround and wrap more delicate neurons
2 neurons, excitable nerve cells, transmit electrical signals

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Neuroglia
Glial Cells
--smaller cells

6 types
4 in CNS - astrocytes, microglia, ependymal cells, oligodendrocytes
2 in PNS - satellilte cells, schwann cells

--each has unique function
--in general, supportive scaffolding for neurons
--some produce chemicals that guide young neurons to proper connections
--promote neuron health and growth
--wrap around and insulate neuronal processes to speed up action potential conduction

--nerve glue,
--sustentacular tissue that surrounds and supports neurons in the central nervous system

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Glial Cells
Neuroglia
--cells in the nervous system that support, nourish, and protect neurons

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Neurolglia, CNS
include
--astrocytes
--microglia
--ependymal cells
--oligodendrocytes

--branching processes (extensions)
--central cell body

--smaller size
--dark staining nuclie
--outnumber neurons in CNS by 10 to 1
--1/2 mass of brain

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Astrocytes
largest, most numerous glial cells; maintain blood-brain barrier to isolate CNS from general circulation; provide structural support for CNS; regulate ion and nutrient concentrations; perform repairs to stabilize tissue and prevent further injury

-- mop up leaked potassium ions & recapturing and recycling released neurotransmitters
--exchanges between capillaries and neurons
--connected by gap junctions

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Microglia
smallest neuroglial cells; phagocytic cells that enculf cellular debris, waste products and pathogens. increase in number as a result of infection or injury

--small ovoid cells / long thorny process
--monitor health in trouble micorglia migrate towards
--transform into type of macorphage that phagocytiszes mocroorganisms or neuronal debris
--proctective role / immune system denied access to CNS

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Epedymal Cells
--Squamous to columnar in form. Atypical epithelial cells that lie chambers and passageways filled with cerebro spinal fluid in brain and spinal cord.
Assist in producing circulating, monitor Cerebrospinal fluid

--cilitated
--form permeable barrier between cerebrospinal fluid that fills those cavities and tissue fluid bathin the cells of CNS

--beating of cilia helps to criculate cerebrospinnal fluid and cushions brain and spinal cord

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Oligodendrocytes
-- branch / fewer processes
--line up along thicker neroun fibers in CNS
--wrap tightly around fibers
--produce insulating coverings called myelin sheaths

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Myelin Sheath
a layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next

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Neuroglia, PNS
--2 kinds
--satellite cells
--Schwann cells

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Satellite Cells
surround neuron cell bodies in glanglia; protects and regulates nurtients for cell bodies in ganglia

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Schwann Cells
Neurolemmocytes,
--forms myelin sheath in PNS
--, Part of the neuron that produces the myelin sheath; functions in repair and regeneration of damaged nerves; wrap around the axon; aid the myelin in insulation

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Neurolemmocytes
schwann cells; form the myelin sheath around axons in the PNS and help with regeneration

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Neurons
nerve cells,
-- large, complex cells
--cell body & one or more slender processes
--plasma membrane is site of electrical signaling
--crucial in cell to cell interactins that occur during development

--Transmit and receive information throughout the nervous system through the conduction of electrical and chemical impulses

--Special characteristics
----extreme longevity
----amitotic
----high metabolic rate

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Nerve cells
neurons

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Extreme Longevity
Function for long time, possibly a person's lifetime
--over 100 years

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Amitotic
Lacks mitosis, can't be replace if destroyed.

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High metabolic rate
Requiring abundant supplies of oxygen and glucose.
--neurons cannot survive for more than a few minutes without oxygen

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Cell body
largest part of a typical neuron; contains the nucleus and much of the cytoplasm

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Neuron Cell body
--protein & membrane making machinery
--clustered free ribosomes
--rough endoplasmic reticulum ER (Nissl bodies/ chromatophilic substance)
--most active and best developed

conisists of spherical nucleus with a conspicous nucleolus surrounded by cyoplasm; Also called the perikaryon or soma, the cells body ranges in diameter from 5 to 140 um; biosynthetic center of neuron and contain usual organelles; focal point for outgrowth of neuron processes; mostlty located in CNS where they are protected by bones of skull and vertebral column

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Perikaryon
AKA; neuron cell body / soma / perikaryon
--cytoplasm surrounding the nucleus of a neuron

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Soma
AKA; neuron cell body
--the cell body of a neuron

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Biosynthetic Center
Cell body is major __________ of neuron; contains usual organelles

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Nissl bodies
AKA; Chromatophilic substance
--rough ER in neurons; site of proten synthesis

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Chromatophilic Substance
Nissl bodies;

--stains darkly with basic dyes
--Golgi apparatus well developed / forms arc or complete circle around nucleus

membranous sacs throughout cytoplasm that have ribosomes attached to their surface, produce proteins, glycogen, lipids or pigments

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Neurofibrils
--maintain cell shape and integrity
bundles of neurofilaments that provide support for dendrites and axon

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Neurofilaments
Gives the cell body shape and support
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Lipofuscin
--harmless by product of lysosmal activity "aging pigment"
--indigestible lipid of lipid peroxidation; brown pigment increased in atrophy and FR damage

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receptive region, part of
plasma membrane of cell body
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nuclei
clusters of cell bodies in the CNS

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Ganglia
groups of nerve cell bodies that coordinate incoming and outgoing nerve signals
PNS

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Processes
--armlike, extend rom cell body o all neurons
--brain & spinal cord CNS contain both neuron cell bodies and thier processes
--PNS consists chiely o neuron processes

--bundles o neuron processes are called
Tracts in CNS
Nerves in PNS

2 types of neuron processes
--dendrites
--axons

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Tracts
bundles of nerve fibers in the CNS
--neuron processes

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Nerves
-- bundles of neuron porcesses in PNS

bundled axons that form neural "cables" connecting the central nervous system with muscles, glands, and sense organs

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Dendrites
branching extensions of neuron that receives messages from neighboring neurons

--main receptive or input regions
--convey messages towards cell body
--not action potentials but short distance signals called graded potentials

--bristle with thorny appendages having bulbous or spiky ends called dendritic spines

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Receptive Regions
Dendrites are the main _________ or ______________

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Input Regions
Dendrties are main Input regions

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Dendritic spines
--points of close contact / synapses with other neurons

tiny projections from a dendrite that contain the chemical receivers that bind neurotransmitter molecules arriving from the synaptic cleft

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Graded potentials
small changes in membrane potential that by themselves are insufficient to trigger an action potential.

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Axon
long nerve fiber that conducts away from the cell body of the neuron

--functionally axon is conducting region of neuron
-- generates nerve impulses and transmits them away from cell body along plasma membrane or axolemma

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Axon Hillock
The conical region of a neuron's axon where it joins the cell body; typically the region where nerve signals is generated.

-- nerve impluse generated at junction of axon hillock and axon (trigger zone)
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Nerve Fiber
any long axon

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Axon Collaterals
an axon that has divided into several branches allowing a single nerve cell to influence a wide array of other cells
10,000 or more terminal branches or telodendria per neuron

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Terminal branches
AKA; Telodendria
called.............
--Axon terminals
--synaptic knobs
--boutons

--lie at the end of axons; form junctions with other cells
--can be 10,000 or more

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Telodendria
series of fine, terminal extensions branching from the axon tip,
--terminal branches of the axon

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Axon terminals
AKA; synaptic knobs & boutons

bulb like structers at end of axon contain neuro transmitters that carry neuron message into synapse

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Synaptic knobs
AKA; Axon terminals; boutons
distal tips of axon; stores and release neurotransmitters that passes info over to next neuron

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Boutons
AKA; Axon terminals & synaptic knobs
knoblike distal endings of the terminal branches, also called axonal terminals or synaptic knobs

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Conducting region
the axon is the conducting region of the neuron, generates nerve impulses and transmits them AWAY FROM CELL BODY, along axolemma (cell body)

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Axolemma
The plasma membrane of the axon

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Trigger Zone
nerve impulses arise most often at the junction of the axon hillock and initial segment

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Secretory Region
axon terminals release neurotransmitters

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Neurotransmitters
chemical messengers that traverse the synaptic gaps between neurons. When released by the sending neuron, neurotransmitters travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing whether that neuron will generate a neural impulse.

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Axon
--lacks Nissl bodies and Golgi apparatus involved in proteinn synthesis and packagig
--depends on cell body to reew necessary proteins and m;embrane components
--efficient transport mechanisms to distribute them
--quickly decay if cut or severly damaged

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Anterograde movement
from the cell body toward the axon terminals
--mitochondria, cytoskeletal elements, membrane components used to renew the axon plasma membrae & enzymes needed for sythesis of certain neurotrasmitters

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Retrograde movement
from axon terminal to cell body
--organelles beig returned to cell body for degradationn or recycling
--intracellular communication for advising cell body of conditions at azon terminals
--delivering to cell body vesicles containing signal molecules

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bidirectional trasport mechanism
--axonal trasport
--ATP dependent "motor" porteins, dinesin, dynein and myosin
--porpel cellular components along microtubules like trains along tracks at speeds up to 40 cm(15 in. per day)

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Retrograde Axonal transport
certain viruses and bacterial toxins that damage neural tissues use _______________ to reach cell body
-- polio, rabies, herpes simplex viruses, tetanus toxin
--micro RNA to suppress defective genes is under investigaion

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Myelin Sheath
--protects and electrically insulates fibers
--increases speed of trasmission of nerve impulses
--tight coil of wrapped membranes
--thickness depends on number of sprials

a layer of fatty tissue segmentally encasing the fibers of many neurons; enables vastly greater transmission speed of neural impulses as the impulse hops from one node to the next

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Myelinated Fibers
conduct nerve impulses rapidly
--axon bearing myelin sheath

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Unmyelinated fibers
gray matter, fibers lacking myelin sheaths
--dendrites are always __________
--conduct impulses quite slowley

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Neurilemma
additional sheath external to myelin that is formed by schwann cells and found only on axons in the peripheral nervous system
--portion of schwann cells
--includes part of its plasma membrane

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Nodes of Ranvier
AKA; myelin sheath gaps
--small gaps in the myelin sheath of medullated axons
-- 1mm apart at regualr intervals along myelinated axon

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Myelin Sheath Gaps
AKA; Nodes of Ranvier
--small gaps between the myelin sheath

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Myelination of nerve fiber (axon)
--Schwann cell envelopes axon
--Schwann cell rotates around axon, wrapping plasma membrane losely around it in successive layers
--Schwann cell cytoplasm is forced from between membranes. Tight membrane wrappings surrounding axon form myelin sheath

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Unmyelinated
axons that do not have a myelin sheath
-- typically thin fibers

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Oligodendrocytes
Cells that form CNS myelin sheaths
-- multiple flat processes that coil around as many as 60 axons at same time

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White matter
whitish nervous tissue of the CNS consisting of neurons and their myelin sheaths

--dense collections of myelinated fibers

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Gray Matter
Brain and spinal cord tissue that appears gray with the naked eye; consists mainly of neuronal cell bodies (nuclei) and lacks myelinated axons.
-- mostly nerve cell bodies and unmyelinated fibers

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Neurons, Structural Classification
Comparison table - 393-

grouped according to number of processes extending form thier cell body
3 major neuron groups
--mulitpolar
--bipolar
--unipolar

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Mulitpolar Neurons
3 or more processes
--one axon
--rest dendrites
--most common type in humans
-- 99%
--major neuron type in CNS

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Bipolar Neurons
neuron with 2 processes extending for it's cell body-- one axon, one dendrite; common in sensory systems
--retina of eye
--olfactory mucosa

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Unipolar Neurons
have single short processes that emerge from the cell body and divides T-like into proximal and distal branches
--distal process - peripheral process
--entering CNS is central proces
--chiefly in ganglia in the PNS where they function as sensory neurons

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Peripheral Process
dendrite of primary sensory (pseudounipolar) neuron
--3 factors that classify it as axon
1 generates and conducts an impulse (functional definition of axon
2 when large; heavily myelinated
3 uniform diameter and is undistinguishable microscopically from and axon

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Central Process
the part of the axon of a sensory neuron that conducts impulses from the perikaryon to the central nervous system

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Pseudounipolar Neurons
have one process; the dendritic portion of each of these extends away from the CNS and axon projects into CNS
--unipolar / orginate as bipolar

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Receptive Endings
sensory terminal of unipolar neurons at end of peripheral process

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Neurons, Functional Classification
--Groups neurons according to direction which nerve impulse travels relative to CNS
1 sensory neurons / afferent neurons
2 motor neurons / efferent neurons
3 interneurons / association neurons

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Sensory Neurons
AKA; Afferent Neurons

neurons that carry incoming information from the sense receptors to the central nervous system

--unipolar
--cell bodies loacated in sensory ganglia outside CNS

--fibers carrying sensory impulses form skin of great toe travel more that a meter before they reach their cell bodies in a ganglion close to spinal cord

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Motor Neurons
neurons that carry outgoing information from the central nervous system to the muscles and glands

--mulitpolar
--except for some of autonomic nervous system, cell bodies are located in CNS

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Interneurons
AKA; association neurons
neurons within the brain and spinal cord that communicate internally and intervene between the sensory inputs and motor outputs

--lie between motor and sensory neurons in neural pathways
--shuttle signals through CNS where integration occurs
--99% of neurons of body
--mulitpolar
--diversity in size and fiber branching patterns

--Purkinje & pyamidal cells

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Association Neurons
Also called interneurons, located only in the brain or spinal cord, these neurons contact sensory neurons to motor neurons; the switch board of the nervous system.

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Membrane Potentials
A difference in voltage across the plasma membrane of a neuron
--irritable or excitable
--responsive to stimuli

--when stimulated electrical impulse is generated and conducted along length of its axon ~ response called action potential or nerve impluse
--underlies virtuallly all functionl activities of nervous system

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Action Potential
AKA Nerve Impulse
a neural impulse; a brief electrical charge that travels down an axon. the action potential is generated by the movement of positively charged atoms in and out of channels in the axon's membrane

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Nerve Impluse
self propagating wave of electrical disturbance that travels along the surface of a neuron's plasma membrane

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Electricity, Basic principles
--human body is electrically neutral
-- same # of postive and negative charges-
-- areas where one type of charge predominates, making regions positively or negatively charged
--situations in which there are separated electrical charges of opposite sign have potential energy

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Voltage
the potential difference between two points; measured in volts or millivolts
--measure of potential energy generated by separated charge

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Potential Difference
the difference in electrical charge between two points in a circuit expressed in volts
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Current
flow of electrical charge from one poinnt to another

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Resistance
hindrance to charge flow provided by substances through which the current must pass

--high electrical resistance * insulators
--low resistance * conductors

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Insulators
materials that prevent electric charges from flowing through them easily

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Conductors
materials that allow electric charges to flow through them easily

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Ohm's law
relationshop between voltage, current and resistance
I=V/R
Current (I) is directly proportional ot voltage.
--greater the voltage (potential difference) greater current

--current in inversely related to resistance
--greater risistance .> smaller current
--resistance to current flow provided by plasma membranes

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Membrane Ion Channels
1. The cell has many gated ion channels.
EX: potassium ion channel allows only potassium ions to pass

-- large proteins, often several subunits
--amino acid chains snake back and forth across membrane

Leakage / nongated channels - always open
a. Chemically gated (ligand-gated) channels open when the appropriate chemical binds.
b. Voltage-gated channels open in response to a change in membrane potential.
c. Mechanically gated channels open when a membrane receptor is physically deformed.
2. When ion channels are open, ions diffuse across the membrane, creating electrical currents.

Ohm's Law Equation:
Voltage (V) = Current (I) X Resistance (R)

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leakage Channels
leakage or nongated channels are always open

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Nongated Channels
ion channels, also called leakage channels, that are always open
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Chemically gated Channels
AKA; ligand gated channels
open with binding of a specific neurotransmitter

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Ligand gated Channels
gated ion channels that respond to chemical stimulus

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Voltage gated channels
open and close in response to changes in the membrane potential
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Mechanically gated channels
open and close in response to physical deformation of receptors

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Ohm's Law
the relationship between voltage, current, and resistance

voltage = current X resistance

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Concentration gradients
molecules move from a place where concentration is high to where concentration is low (gradient refers to the level of concentration, so down a gradient means high=>low)

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Electrical Gradients
move toward area of opposite eletrical chage

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Electorchemical Gradient
Electrical and Concentration gradients constitute this

--it is ion flows along electrochemical gradients tha tunderlile all electrical phenomena in neurons

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Resting Membrane Potential
An electrical potential established across the plasma membrane of all cells by the Na+/K+ ATPase and the K+ leak channels. IN most cells, the resting membrane potential is approximately -70 mV with respect to the outside of the cell.

--resting membrane varies from -40mV to -90 mV in different types of neurons
--potential difference between two points is measured with voltmeter
--membrane is polarized / negativly charged on outside

--cell cytosol contains lower concentration of Na+ and higher K+ than extracellular fluid
-- negatively charged anionic proteins A- help balance positive charges of intracellular cations (primarly K+)
--extracellular fluid postivie charges of Na+ and other cations are balanced chiefly by chloride ions CI-
-- K+ most important in generating membrane potential

-- 75 times more permeable to potassium than to sodium, freely permeable to chloride ions

--K+ flowing out = negative inside
--Na+trickling in makes cell slightly more positive than it would be if only K+ flowed
--Na+ -K+ ATPases pumps maintain concentration gradients of Na+ and K= across membrane

--negative interior of cell is due to much greater diffusion of K+ out than Na+ into cell

--3 Na+ out 2 K+ in

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Sodium Potassium Pump
a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

--ATP driven
--3 Na+ out 2 K+ in

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Na+ -K+ ATPases Pumps
maintain concentration gradients of Na+ and K= across membrane

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Membrane Potential Signals
Graded potentials
action potentials

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Membrane Potential change
--produced by
1 anything that alters ion concentrations on the 2 sides of membrane
2 anything that changes membrane permeability to any ion

--permeability changes are important for information transfer

--depolarization
--hyperpolarization

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Graded Potentials
--incoming signals operating over short distances
--voltage changes produced by stimulation. The magnitude of change either hyperpolarization or depolarization depends on the strength of the stimulus.

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Action Potentials
AKA; Nerve Impulse
-- long distance signals of axons
--A rapid change in the membrane potential of an excitable cell, caused by stimulus-triggered, selective opening and closing of voltage-sensitive gates in sodium and potassium ion channels.

--100mV (from -70mV to +30mV)

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Depolarization
-- inside of membrane becomes less negative (moves closer to 0)
--change for -70mV to -65mV is depolarization

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Hyperolarization
--membrane potential increases, becomming more negative than resting potential
--change form -70mV to -75mV is hyperpolarization

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Receptor Potential
AKA; generator potential
--A slow, graded electrical potential produced by a receptor cell in response to a physical stimulus, heat, light, other

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Generator Potential
local change in resting potential of recptor cell that mediates between impact of stimuli and initiation of nerve impulses

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Postsynaptic Potential
the change in the membrane potential of a neuron that has received stimulation from another neuron

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Decremental
get weaker the farther they spread
-- current dies out within few milimeters of orgin

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Excitable Membranes
Only cells with ___________ -- neurons and muscle cells -- can generate action potential

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Nerve Impulse
AKA; action potential
--the electrical discharge that travels along a nerve fiber

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Action Potential, Generation
3 consecutive but overlapping changes in membrane permeability
1 resting state - no ions move through voltage gated channels -70mV
2 depolarization - caused by Na+ flowing into cell +30mV
3 Repolarization - caused by K+ flowing out of cell
-------------then action potential---------------
4 Hyperpolarization is caused by K+ continuing to leave cell

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Action Potential, Key players
Voltage gated Na+ channels
--closed at resting state; no Na+ enters cell through them
--Opened by depolarization allowing Na+ to enter cell
--Inactivated - channels automatically blocked by inactivation gates soon after they open

Voltage gated K+ channels - one gate & 2 states
--closed at resting state; no K+ exits cell
--opened by depolarization after a delay allowing K+ to exit cell

Events
1 resting state; all gated Na+ and K+ channels closed
2 depolarization; Na+ channels open & rushes in to between -55mVand -50mV (threshold) - (overshoots to about +30mV) - produces only a 0.012% change in intracellular Na+ concentration
3 Repolarization; Na+ channels are inactivating, and K+ channels open ( 1ms) -
4 Hyperploarization; some K+ channels remain open and Na+ channels reset

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Depolarization phase
chemical or mechanical stimulus caused a graded potential to reach at least (-55mV or threshold)

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Hyperpolarization Phases
K gates stay open lngr than Na gates, creat neg. overshot; ions go to orig. posit. and astrocytes remove extra K

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Activation gate
During resting conditions, the activation gate remains closed, but depolarization of the membrane to the threshold level causes both gates to change state and the activation gate responds faster.

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Inactivation Gate
the slow gate of the Na+ channel that closes to stop ion flow

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Threshold
certain critical level
-- -55mV to -50mV

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Positive Feedback
Feedback that tends to magnify a process or increase its output.

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Sodium Potassium Pump
a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

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Propagated
transmitted or spread

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Self Propagating
Most significant property of nerve action potentials that once the action potential is started, it moves along the nerve fibers automatically without change in its intensity

like domino effect

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Saltatory conduction
Rapid transmission of a nerve impulse along an axon, resulting from the action potential jumping from one node of Ranvier to another, skipping the myelin-sheathed regions of membrane.

--30 X's faster than continuous conduction


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Conduction of a nerve impulse
-stimulus to localized region
-depolarization
-stimulates depolarization in adjacent region of membrane
-action potential moves along surface of neuron membrane

Propagation of a nerve impulse is more accurate

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propagation of a nerve impulse
Conduction of nerve impulse
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All or None Phenomenon
It either happens completely or doesn't happen at all
--if number of Na+ ions entering cell is too low to achieve threshold, no AP will occur

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Threshold and the All or None Phenomenon
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Action Potential, Stimulus Intensity
--strong stimuli cause nerve impulses to be generated more often in a given time interval then do weak stimuli
--stimulus intensity is coded for by numer of impulses per second / frequency of action potentials rahter than by increases in strength / amplitude of individual Action Potential

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Action Potential, Refractory periods
absolute refractory period
relative refractory period

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Absolute refractory period
the minimum length of time after an action potential during which another action potential cannot begin

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Relative Refractory Period
a period after firing when a neuron is returning to its normal polarize state and will only fire again if the incoming message open parentheses impulse) is stronger than usual; returning to arresting state

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Action Potential, Conduction Velocity
how fast to AP's travel:
--most rapid 100 m/s or more found in neural pathways where speed is essential
--slower serve internal organs, gut, glands, blood vessels

Impulse Propagation 2 factors:
1 Axon diameter - larger axon's diameter; faster it conducts impulses
2 Degree of Myelination - AP's propagate because they are regenerated by voltae gated channels in membrane

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Continuous Conduction
Step-by-step depolarization of the entire length of an unmyelinated axon, relatively slow.

--type of AP propagation
Multiple Sclerosis
A chronic disease of the central nervous system marked by damage to the myelin sheath. Plaques occur in the brain and spinal cord causing tremor, weakness, incoordination, paresthesia, and disturbances in vision and speech
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Group A fibers
These nerve fibers are mostly somatic sensory and motor innervating the skin, skeletal muscles, joints. They are the largest in diameter of the nerve fibers, have thick myelin sheaths and conduct nerve impulses rapidly.

150 m/s....300mph

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Group B fibers
intermediate diameter, lightly myelinated ANS fibers.

15 m/s....30 mph

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Group C fibers
small, unmyelinated, sends signals slowest, sensory receptors in skin/viscera
-- incapable of saltatory conduction

1 m/s.....2 mph

406
Synapse
the junction between two neurons (axon-to-dendrite) or between a neuron and a muscle


406
Axodendritic Synapses
Synapses between the axon endings of one neuron and the dendrites of other neurons.

406
Axosomatic Synapses
Between axon endings of one neuron and cell bodies of other neurons

406
Axoaxonic
From axon to axon
406
Dendrodendritic
dendrite to dendrite
406
Dendrosomatic
between dendrites and cell bodies
406
Presynaptic Neuron
conducts impulses toward the synapse
406
Postsynaptic Neuron
transmits impulses away from the synapse
406
Neurons
Have anywhere from 1000 to 10,000 axon terminals making synapses, stimulated by - number of toher neurons
406
Electrical Synapses
i. Allows action potentials to spread from presynaptic cell to postsynaptic cell via gap junctions ii. Not as common as chemical synapses

406
Chemical Synapses
--specialized for release and reception of chemical neurotransmitters
i. Very common ii. Chemical synapses are called synaptic clefts; they separate presynaptic cell from postsynaptic cell 1. The cleft prevents an action potential from going directly from the pre to the postsynaptic cell

-- 2 parts
1 knob like axon terminal of presynaptic neuron, contain many tiny membrane bouded sacs called synaptic vesicles - contain thousands of neurotransmitter molecules
2 neurotransmitter receptor region on membrane of dendrite of cell body of postsynapitc neuron

407
Synaptic Vesicles
spherical sacs containing neurotransmitters
407
Synaptic Cleft
synaptic gap or synaptic space; tiny gap between the terminal of one neuron and the dendrites of another neuron (almost never touch); location of the transfer of an impulse from one neuron to the next
-- 30 - 50 nm one millionth of an inch wide

407
Chemical Event
transmission of signals across these synapses
407
Unidirectional Communication
transmission of signals across synapses is a chemical event that depends on the release diffusion and receptor binding of neurotransmitter molecules and results in _______ between neurons

407
Chemical synapses, Information transfer
1 action potential arrives at axon terminal
2 voltage gated ca2+ channels open and Ca2+ enters axon terminal
3 Ca2+ entry causes neurotransmitter containing vesicles to release their contents by exocytosis
4 Neruotransmitter diffuses across synaptic left and vivnds to specific receptors on postysynaptic membrane
5 binding of neurotransmitter open ion channels, resulting in graded potentials
6 Neurotransmitter effects are terminated in one of three ways
--reuptake
--degradation
--diffusion

408
Synaptotagmin
Calcium sensor protein on the synaptic vesicle membranes

408
Reuptake
by astrocytes or the presynaptic terminal, where neurotransmitter is stored or destoryed by enzymes as with norepinnephrine

408
Degradation
by enzymes associated with the ostsynaptic membrane or present in the synapse, as with acetylcholine

408
Diffusion
Away from the synapse

408
Synaptic Delay
the brief delay between the arrival of an action potential at the axon terminal and the creation of a postsynaptic potential
--lasts 0.3 - 5.0 ms making transmission rate limiting (slowest) step of neural transmission

408
Rate Limiting
408
Postsynaptic Potentials
excitatory or inhibitory. If the electrical response of the postsynaptic cell is an excitatory action, the cell well be depolarized; the membrane potential will become less negative. if inhibitory then it will be hyperpolarized.

408
Synaptic Integration
The summation of the inhibitory and excitatory signal received by a post-synaptic neuron which occurs because a neuron receives many signals

408
Excitatory Synapses
Depolarizes the postsynaptic membrane

411
Postsynaptic Membranes
generally do not generate AP's
--can reach 0 mV . > well above axons threshold -50mV

411
Excitatory postsynaptic Potentials
EPSP -- neurotransmitter binding causes depolarization of postsynaptic membrane; can help trigger AP distally at axon hillock

411
Action Potentials with Graded Potentials, Comparison
Table 410
Inhibitory Synapses
Hyperpolarize the postsynaptic neuron
--make membrane more permeable to K+ or C1-

412
Inhibitory Postsynaptic Potentials
(IPSPs) graded post-synaptic hyperpolarizations, which decrease the likelihood that an action potential will be generated

412
Summation by the postsynaptic Neuron
412
Summate
Like excitatory postsynaptic potentials, inhibitory postsynaptic potentials also ______.

412
Temporal summation
Occurs when a single synapse generates EPSPs so quickly that each is generated before the previous decays. This allows the EPSPs to add up to reach a threshold voltage that triggers an action potential.

412
Spatial summation
Integration by a postsynaptic neuron of inputs (EPSPs and IPSPs) from multiple sources.


412
Facilitated
Diffusion in which a carrier protein combines with a specific substance and moves it across the membrane from higher to lower concentrations
--partially depolarized neurons

412
Synaptic Potentiation
The process of training your synapses making something progressively easier
--continuous use of synapse enhances the presynaptic neurons ability to excite postsynaptic neuron producing larger that expected postsynaptic potentials

412
Presynaptic Inhibition
The action of a presynaptic terminal button in an axoaxonic synapse; reduces the amount of neurotransmitter released by the postsynaptic terminal button.

413
Long term potentiation
an increase in a synapse's firing potential after brief, rapid stimulation. believed to be a neural basis for learning and memory
--LTP

413
Actylcholine
ACh
--1st neurotransmitter identified
, Neurotransmitter sent from nerve to muscle cell

415
Acetylcholinesterase
AChE
enzyme that catalyzes breakdown of acetylcholine, preventing sustained muscle contraction from a single nerve impulse

415
Biogenic Amines
Neurotransmitter derived from amino acids, and include catecholamines (dopamine, epinephrine & norepinephrine) &
indolamines (histamine & serotonin)ä

415
Catecholamines
The neurotransmitters dopamine, epinephrine, and norepinephrine, which are active in both the brain and the peripheral sympathetic nervous system. These three molecules have certain structural similarities and are part of a larger class of neurotransmitters known as monoamines.

415
Indolamines
serotonin & histamine

415
Neurotrasnmitters and neuromodulators
Table 416
Dopamine
synthesized from amino acid tyrosine
--influences movement, learning, attention and emotion

418
Serotonin
a neurotransmitter involved in e.g. sleep and depression and memory
--synthesized from amino tryptophan

418
Histamine
a regulating body substance released in excess during allergic reactions causing swelling and inflammation of tissues
--synthesized from amino acid histidine

418
Amino Acids which a neurotransmitter role is certain
--gamma aminobutyric acid (GABA)
--glycine
--aspartate
--glutamate

418
Gamma aminobutyric acid
an amino acid that is found in the central nervous system

418
Glycine
the simplest amino acid found in proteins and the principal amino acid in sugar cane

418
Aspartate
an amino acid transmitter that is excitatory at many synapses

418
Glutamate
an excitatory neurotransmitter that helps strengthen synaptic connections between neurons
--amino acid

418
Peptides
chains of amino acids that can function as neurotransmitters of hormones

--neuropeptides
--substance P
--endorphins
--beta endorphin
--dynorphin
--enkephalins
--gut brain peptides

419
neuropeptides
relatively short chains of amino acids, serve as neurotransmitters.

418
Substance P
a neurotransmitter involved in pain perception

418
Endorphins
natural, opiatelike neurotransmitters linked to pain control and to pleasure
--include beta endorphin, dynorphin and enkephalins

418
Beta endorphin
an endorphin produced by the pituitary gland that suppresses pain

418
Dynorphin
the endorphin having the most potent analgesic effect

418
Enkephalins
An opioid neuromodulator. Widespread throughout the brain and dorsal horn of the spinal cord, are considered less potent then endorphins.

418
Gut brain peptides
Peptides produced in both the digestive tract and the central nervous system are called ______.
These include: substance P , vasoactive intestinal peptide(VIP), secretin, gastric inhibitory peptide(GIP) , cholecystokinin and neuropeptide Y (NPY)
419
Purines
nitrogeneous bases that have a double ring of carbon and nitrogen atoms such as adenine and guanine

--adenosine triphhosphate ATP
--Adenosine

419
Adenosine Triposphate
(ATP) is an organic molecule that acts as the main energy source for cell processes.

419
Adenosine
An inhibitory neurotransmitter that plays a role in promoting sleep and suppressing arousal. The levels in the brain increase every hour an organism is awake.

419
Nitric oxide
short lived toxic gas, defies all the official descriptions of neurotransmitters
--synthesized on demand and diffuses out of cells making it


419
Guanylyl Cyclase
enzyme that NO binds to stimulating the formation of cyclic GMP from GTP

419
Nitric Oxide Synthases
The enzyme responsible for the production of nitric oxide.

419
Carbon Monoxide
stimulates synthesis of cyclic GMP

419
Endocannabinoid
an endogenous ligand of cannabinoid receptors; thus, an analog of marijuana that is produced by the brain

419
Cannabinoid Receptors
most common G protein coupled receptors in the brain

419
Neurotransmitters, Classification by Function
Effects; Excitatory Versus Inhibitory
Actions; Direct Versus Indirect

419
Second messenger molecules
(1.5) Intracellular signalling molecules. Convey information from the cell membrane to the inside of the cell.
--via G protein pathways

420
Neuromodulator
a substance that influences the activity of synaptic transmitters

420
Channel linked receptors
AKA; ionotropic receptors
--are ligand-gated ion channels that mediate direct transmitter action, ionotropic receptors, allows small cations

420
Inotropic receptors
Direct Link to ion channel

420
G protein linked receptors
AKA; metabotropic receptors
--activate a class of membrane bound protein (g protein) which is released to migrate in the plane of the plasma membrane, starting a cascade of other effects.

421
Metabotropic Receptors
slow, does not contain an ion channel but may, when activated, use a G protein system to open a nearby ion channel

421
Cyclic AMP
Secondary chemical messenger that directs the synthesis of protein by ribosomes

421
Cyclic GMP
intracellular messenger molecule
--second messenger

421
Diacylglycerol
A second messenger produced by the cleavage of a certain kind of phospholipid in the plasma membrane.

421
Ca+
Calcium
--second messenger

421
Second Messengers
Cyclic AMP
--Cyclic GMP
--Diacylglycerol
--Ca+

421
Neural integration
the process by which inhibitory and excitatory postsynaptic potentials summate and control the rate of firing of a neuron

421
Neuronal pools
Functional groups of neurons that process and integrate information.


421
discharge zone
part of input neuron when acting alone can make the post synaptic cells fire

421
Facilitated Zone
broader zone where the neurons synapses with still other neurons in the pool with fewer synapses on each of them. it can stimulate those neurons to fire only with the assistance of other input neurons

421
Circuits
patterns of synaptic connections in neuronal pools

422
Diverging Circuits
One incoming fiber triggers responses in ever-increasing numbers of neurons farther along in a circuit.

422
Amplifying circuits
diverging circuits
422
Converging Circuits
pool receives input from several presynaptic neurons and the circuit has a funneling or concentrating effect- common in sensory and motor systems

422
Concentrating effect
circuit has a funnelling effect
422
Reverberating Circuits
the incoming signal travels through a chain of neurons, each of which makes collateral synapses with neurons in a previous part of the pathway

-AKA Oscillating Circuits

422
Oscillating Circuits
Neurons are arranged in a circular fashion that allows APs entering circuit produce more APs (after discharge) and this prolongs response to stimulus. This continues until fatigued or inhibited and this process is important in periodically active circuits. This is similar to positive feedback.
--involved in rhythmic activities
-----sleep wake cycle
-----breathing
-----swinging when walking

422
Parallel after discharge circuits
incoming fiber stimulates several neurons arranged in parallel arrays that eventually stimulate a common output cell

422
Serial Processing
is a pattern of stepwise information processing, from one neuron to another or from one neuronal pool to the next. This is the way sensory information is relayed between processing centers in the brain

--predictable all or nothing manner

423
Reflexes
automatic responses to stimuli
--rapid

423
Reflex arcs
the neural pathway in which reflexes occur that has five essential components- receptor, sensory neuron, CNS integration Center, motor neuron, and effector.

423
Parallel processing
the processing of several aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision. Contrasts with the step-by-step (serial) processing of most computers and of conscious problem solving.

423
Neural tube
a tube of ectodermal tissue in the embryo from which the brain and spinal cord develop

423
Neural Crest
formed from surface ectoderm

423
Neuroepithelial cells
beginning of neural tube

423
Neuroblasts
neural precursor cells

423
Growth cone
A distinctive structure at the growing end of most axons. It is the site where new material is added to the axon.
--prickly / fan like

424
Nerve cell adhesion molecule
N-CAM
--provide anchor points for growth cone


424
Neurotropins
chemicals that signal to growth cone.....come this way or go away or stop here

424
Nerve Growth Factor
substance whose role is to guide neuronal growth during embryonic development
--NGF

424
Filopodia
spikelike extensions that help pull growth cones in a direction

424
Apoptosis
a type of cell death in which the cell uses specialized cellular machinery to kill itself

424