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)

402

Hyperpolarization Phases

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

402

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.

402

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

402

Propagated

transmitted or spread

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