Nervous System 1 2013

7/27/2019 Nervous System 1 2013

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GENERAL FUNCTIONS:

detects environmental changes (inside andoutside body)

interprets changes responds in order to maintain normal or sufficient

function (homeostasis)

SENSORY INPUT (sensory neurons)(gathers information from internal and external environment)

INTEGRATION (interneurons)

(interprets sensory input)

MOTOR OUTPUT (motor neurons)(responds via effector organs)


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ORGANIZATION:

2 Main Divisions:

1. Central Nervous Systemstructures located indorsal body cavityintegration and commandcentreinterprets sensory input

a) Brain

b) Spinal Cord


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2. Peripheral Nervous Systemstructures locatedoutside CNScontains nerves (bundles of axons) which

extend from brain and spinal cord; connects all parts ofbody (tissue beds) to CNS

i) sensory (afferent) divisionconveys impulses to CNSfrom sensory receptors located in different organs and

tissuesii) motor (efferent) divisionconveys impulses from CNSto effector organsmotor responses and secretion byglands in response to sensory information

a) Cranial Nervescarry impulses directly to and frombrain

b) Spinal Nervescarry impulses to and from spinalcord


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motor division is further sub-divided into:

a) somatic nervous systemvoluntary motor

controlb) autonomic nervous systeminvoluntary motorcontrol


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1. Somatic Nervous System

governs voluntary(conscious) actions

involves the brain and cranial or spinal nerves

effectors skeletal muscles2.Autonomic Nervous System

governsinvoluntary(unconscious)activity

involves the brain/brain stem, cranial and spinalnerves

effectors: glands, smooth muscle and cardiacmuscle


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Divisions of the Autonomic Nervous System

SYMPATHETIC PARASYMPATHETIC

Fight or Flight Responses Rest and Digest Responses

Mobilizes body during increased Conserves energy

activity

these systems work in oppositionto each other manyinvoluntarily controlled organs/effectors are

innervated by both sympathetic and parasympatheticnerve fibres(dual innervationbut not allwe will look at

the more significant exceptions to this and what thewisdom is in this arrangement) with dual innervation, end effect at level of organ is the

sum of opposing commands


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NEURAL TISSUE

98% of neural tissue is found in brain and spinal cord;

balance is found peripherally

1. Neuron - main cell type of nervous system

Characteristics of Neurons:

irritablerespond to stimuli

conductivesend impulses along axonviaproductionof action potential and its propagation

amitoticneurons located in CNS dont dividecant

be replaced if destruction/death of cell occurs longevitydesigned to last entire life of organism

(because of the above point)

high metabolic raterequire large oxygen and glucosesupplycells die/cease to function adequately rapidly

if supply is poor or absent


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Basic Neuronal Structure

a)soma(cell body)spherical nucleuscontainsall the same organelles as other cells, but lackscentrioles (no cellular division); soma is focal point

for extension of processes(see below); producesproteins and membranes required formaintenance of neuron

b)processesextend from soma; brain and spinal

cord (CNS) contain cell bodies and their processes;peripheral nervous system (PNS) consists mainlyofprocesses (dependent upon motor division inquestion)


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2 types of processes:

i) axon

each neuron has 1 axonarises from axonhillock, thennarrows to form the diameter of the

process; some neurons lack axons or are very short,while others have significant length (long axonsareknown as nerve fibres)

- at their distal ends, axons almost always branch

into several terminal branches(often thousands);at the ends of these branches aresynaptic knobs(AKA - axon terminalsor boutons)


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- axon is conducting region, with impulses usuallybeing transmitted away from cell body

- axon terminalsare thesecretory regionsof theneuron site of release of neurotransmitters forexcitation orinhibitionof target tissue (effectorcellsex. muscle tissue at neuromuscular junction;

may also allow communication with other neurons)


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ii) dendrite

each neuron has several dendrites(hundreds); they

are the main input regions(receive signals/impulsesfrom other neurons) responsible for conduction of

impulses toward cell body


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Other Neuronal Structures

c) myelin sheathlong or large-diametered nervefibres are covered by segmented sheath made ofprotein-lipid substance(layers of plasmamembrane)

- protects and insulates fibres and allows fasterimpulse transmission

- fibres lacking myelin sheaths (unmyelinated) areslower conductorsare usually thinner in diameter

(dendrites lack myelin)

- gaps left between segments of myelin are calledNodes of Ranvier


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- small axons in the CNS are also unmyelinated- myelinated fibresform white matterin the CNS;unmyelinated fibres andcell bodiesform the greymatterof the CNS


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Classification of Neurons by Function

a) Sensory (Afferent) Neurons

- impulses travel from receptors (dendrites) at level

of organs toward the CNS- processes are generally quite long; distal branchacts as receptorregion

- cell body is usually located outside the CNSin

sensory ganglia(cluster of cell bodies, oftenlocated close to spinal cord)


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c) Interneurons

- communication (links) between sensory andmotor neurons within the CNSintegration/interpretationoccurs here based onimpulse received from sensory neuron, thensynapse occurs between interneuron and motor

neuron

b) Motor(Efferent) Neurons

- impulses travel from CNS to effectors(ex. musclesand glands) in the peripheral regions; cell bodiesare located in CNS


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***Of greater interest for us regarding this basic pathway: monitoring of

the internal (physiological) environment, with subsequent involuntary

responses via smooth and cardiac muscle effectors (autonomic nervous

system).


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2. Neuroglial Cells (other supporting cells of thenervous system)

- characteristics:

a) no irritabilitydo not respond to stimuli

b) no conductivity

c) no release of neurotransmitters

d) mitoticare capable of division


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- sometypes of neuroglial cells of interest for us:

a) astrocyteslocated in CNS- star-shaped and cling to neurons and capillariesof CNS- allow transfer of nutrients, dissolved gases andions between neurons and blood- control blood flow through capillaries- absorb and recycle some neurotransmitters- extensions of astrocytes, in part, contribute tostructure of blood-brain barrier (assist in making

capillaries less permeable in CNS); well look at thismore closely later- provide structural framework for neurons in brain


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b) ependymal cells

- located in CNS

- cuboidal or columnar with processes whichcontact other glial cells

- may have cilia or microvilli; some producecerebrospinal fluid (CSF); line central cavity(ventricle) of brain and spinal cord well look at thismore closely later

- form barrier between CSF and fluid surroundingnerve cells


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NERVES

located in the PNS; contain nerve fibres(axons)and blood vesselswrapped in connective tissue

a) sensory nervessensory receptors of manyneurons, wrapped in connective tissue; cell bodies

are located in ganglion(cluster of cell bodies)outside of CNSb) motor nervesaxons of many neurons,wrapped in connective tissue; cell bodies are notcontained in the nerve, but in the spinal cord

(CNS)c) mixed nerveboth sensory receptors and axonsof many different neurons, wrapped in connectivetissue


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TRACTS

bundles of axons(nerve fibres) located inside theCNS; similar to nerves, but without the connectivetissue wrapping

a) Ascending Tractscarry sensory impulses from

spinal cord to brainb) Descending Tractstransmit motor impulsesfrom the brain to the spinal cord

FACTORS AFFECTING SPEED OF NERVE IMPULSES

1. myelin sheathincreased speed if myelinated2. size of fibreslarge diameter fibres conductimpulses faster


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SYNAPSE

synapse= area where 2 neurons meet (axon ofone neuroncommunicates with a dendrite of asecond)

pre-synaptic neuronis neuron conducting the

impulse toward the synapse; post-synaptic neuroncarries signal away from synapse post-synaptic cellsmay be neurons or effector

cells (ex. muscle cell or glandular cell) area where neuron meets effector(muscle or

gland) is neuroeffector junction(ex. neuromuscularjunction)


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SYNAPSES and IMPULSE CONDUCTION

- chemical synapsesuse release and reception of

neurotransmitters for communication

consist of 2 parts:

i) pre-synaptic axon terminalwhich contains

neurotransmitter substance (insynaptic vesicles)ii) post-synaptic receptorregion on dendriteofpost-synaptic neuron (or at effector cellmembrane)


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What Occurs at the Chemical Synapse?

pre and post-synaptic membranes are separatedby thesynaptic cleftfluid filled space acrosswhich chemical signal must travel

signal starts as electrical signal at pre-synapticmembrane (nerve impulse)impulse stimulatescalcium (Ca2+) channels on the synaptic bulb toopencalciumenters the pre-synapticmembranestimulatesneurotransmitter to bereleased into synaptic cleftneurotransmittercrosses the cleft neurotransmitter binds to

receptor on post-synaptic membrane andchemical signal is convertedback into electricalsignal at post-synaptic membrane post-synapticmembrane depolarizes, initiating an actionpotential (nerve impulse)


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napse h drive winter

2006

16


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TYPES OF SYNAPSES BY STIMULATED ACTIVITY

neurotransmitters can activateor inhibit cellactivities

1. Excitatory Synapses

neurotransmitter-receptor combination causessodium channels to open, allowing diffusion ofmassive amounts of sodium ions inside the cellDEPOLARIZATIONof membrane; cell polaritychanges from being negative to being positiveinside the cell membrane (does this sound familiar?I think you can expect to see some impulseactivation here!)


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2. Inhibitory Synapses

neurotransmitter-receptor combination causespotassium and chloride channelsto open, causingpotassium ions to leave the cell and chloride ions(which are negatively charged) to enter the cellHYPERPOLARIZATIONof membranecell polaritychanges, becoming more negative inside the cellmembrane(therefore, is it going to be more

difficult to cause an impulse if the inside of the cellis more negative? I bet it will be!)


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NERVE IMPULSE EXCITATION

purpose of impulse is to carry message from sense

organ to brain or from brain to effector; impulse isan electrical disturbance traveling down the lengthof a neuron; the movement of sodium andpotassium ions in and out of a neuron creates thedisturbance

1. Neurons at REST are POLARIZED

sodium ions are found on outside of neuron,potassium ions on inside; therefore, inside ofmembrane is negatively charged relative to theoutside because membrane is more permeable topotassium with constant leakage outof themembrane; the gradient for sodium to enter cell isgreater due to its concentrations on both sides ofthe membrane, but membrane is relativelyimpermeable to sodium; normal resting potential fornerve cells is approx. -70 mV


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2. DEPOLARIZATION of Neuron

when stimulus is applied (neurotransmitter), sodiumchannels open, and sodium enters themembraneelectrical potential is reversed; inside of

membrane becomes positive relative to outsidethreshold for potentialto cause impulse is approx.

-55 to -50 mV(potential often over shoots to +30mV, causing an initial spike in electrical activity)

in myelinated axons, the voltage-regulated sodium

channelsare concentrated at the Nodes ofRanvier


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3. Nerve IMPULSE is Carried

relatively negative charge outsideof membranestimulates next point on membrane to depolarizeand so on down the length of membrane

4. REPOLARIZATION of Neuron

reversal of charge lasts fractions of a second;sodium channels close, stopping the flow of

sodium ions and potassium channels open,allowing potassium ions to leave the insideof themembranereturns charge on outside to beingmore positive than inside again


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5. Neuron at Rest or POLARIZED

active transport mechanisms (Na+/K+-ATPasepumps) return membrane potential to restingpotential (remember, 2 potassium ions in, 3 sodium

ions out)

6. REFRACTORY Period

until resting potential is restored by active transport,stimulation with the creation of an impulse cannotoccur


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Neurotransmitters Messenger Molecules

chemical messenger molecules of nervous system

synthesized in cytoplasm of axon terminal; neuronsare limited in terms of types of transmitters theysynthesize by enzyme systems located in a specific

neuron once synthesized, neurotransmitters are stored in

synaptic vesicles(each terminal may containthousands of vesicles; each vesicle may contain upto 100,000 transmitter molecules)

nerve impulse causes vesicles to be moved into thecell membrane with release of transmitters into thesynaptic cleft


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action of transmitters is exerted on specific proteinsexisting on the post-synaptic membrane

RECEPTORSprecisely match size and shape ofspecific transmitter (lock and key theory)

the interaction of the transmitter with the receptorresults in a specific physiological response; theresponse may be excitatory or inhibitory in nature

if excitatory neurotransmitter is released at effectorcell (example: skeletal muscle cell), musclecontraction occurs

if inhibitory neurotransmitter is released at effectorcell (example: smooth muscle cell), muscle

contraction is inhibited receptors are named according to the type of

neurotransmitter with which they bind (ex.cholinergic receptors bind with acetylcholine)


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Basic Receptor Theory Direct vs. Indirect Receptorand Neurotransmitter Mechanisms

A. Direct Mechanismbinding of neurotransmitter tocell membrane receptors, causing opening ofmembrane ion channels (ex. seen with ACh onskeletal muscle cell membrane)

B. Indirect Mechanism- proteins on inner surface of plasma membrane ofeffector cells are activated by binding ofneurotransmitter to transmembrane receptors- the inner surface proteins (G-proteins) are then

activated to:a) open or close membrane ionchannelsor b)produce second messengermolecules which stimulate a series of enzymaticactivities inside effector cells; these series ofactivities then modify activities of other proteins(ex. channel proteins)


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examples of second messengers used via indirect

neurotransmitter and receptor mechanisms include:cyclic AMP, cyclic GMP, Ca2+and diacylglycerol

most amino acid based neurotransmitters, when they

bind with membrane receptors on effector cells, exert

their effects via second messenger systems these types of neurotransmitter/receptor interactions

tend to result in slower, longer-lasting and broader

physiological effects (ex.smooth and cardiac muscle

contraction stimulation or inhibition)

a well known and wide spread example of a secondmessenger system is the cyclic-AMP(c-AMP)

mechanism


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Cyclic-AMP Second Messenger Mechanism:

First Messenger Neurotransmitterbinds with

Target Cell Membrane Receptor

Receptor Configuration is modifiedand binds alternatively with

G Protein(plasma membrane protein) which moves freely through plasma

membrane until it binds with

Adenyl Cyclase(effector enzyme) which catalyzes

ATP (adenosine triphosphate) Cyclic-AMP(cyclic-adenosine monophosphate= ringshaped molecule)

C- AMP = second messenger

Activates further enzymatic cascades (by activating protein kinases), causingspecific cellular response, depending upon tissue target and enzymes

present at the effector site


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- stimulated enzymatic cascades from abovemechanism may result in:

a) altering cell membrane permeability(ex. opens orcloses cell membrane channels) to promote orprevent entry of substances into effector cells (ex.increased or decreased Ca2+entry into vascular orbronchiolar smooth and cardiac muscle cells)b) stimulation of smooth and cardiac muscle cellcontraction- ex. as more calcium ion enters vascularsmooth, bronchiolar smooth or cardiac muscle cells,muscle contraction occurs more readily or to a greater

degreec) inhibition of smooth and cardiac muscle cellcontraction- ex. as less calcium ion enters vascularsmooth, bronchiolar smooth or cardiac muscle cells,muscle contraction is inhibited
http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter17/animation__membrane-bound_receptors__g_proteins__and_ca2__channels.htmlhttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter17/animation__membrane-bound_receptors__g_proteins__and_ca2__channels.htmlhttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter17/animation__membrane-bound_receptors__g_proteins__and_ca2__channels.html


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neurotransmitters must be quickly removed afterexerting their effects on the post-synaptic

membrane or effector cell membrane in one of 3ways:

a) broken downby specific enzymes(ex.rememberacetylcholine is broken down by

acetylcholinesteraseat neuromuscular junction)

b) taken back up(reabsorbed) into the pre-synaptic neuron or axon terminal

c) diffuses/migrates away from synaptic cleft-concentration of neurotransmitter becomes toolow to exert further effects on post-synapticreceptor sites


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Major Classifications of Neurotransmitters and Their

Receptors

1. Acetylcholine(ACh) and Cholinergic Receptors

a) ACh released by all neurons that stimulateskeletal musclesvoluntary control (somatic)

- released at neuromuscular junction

- specific type of ACh receptor on skeletal muscle

cell membrane is called NICOTINICreceptor- neurotransmitter/receptor combination results inexcitatory response skeletal muscle contraction


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b) ACh released by motor neurons of theAUTONOMIC NERVOUS SYSTEM (ANS)- released specifically by all preganglionic axons(ganglion = cluster of cell bodies; so, released atregion where 2 or more neurons meet pre-ganglionic neuron and post-ganglionic neuron; orwhere pre-ganglionic neuron meets a gland)- receptors for ACh are located at all ANS ganglia

(sympathetic motor pathways andparasympathetic pathways) and on adrenalmedulla (gland on kidney)- these receptors are also specifically NICOTINICreceptors

- this neurotransmitter/receptor combination isalways excitatory results is impulse conductionto post-ganglionic neuron or release of hormonefrom a gland (adrenal gland)


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c) ACh released by all post-ganglionicparasympathetic

neurons

- receptors are located on all parasympathetic targetcells (involuntarily controlled tissues); ex. cardiac

muscle, pupillary muscle, bronchial smooth muscle,

gastrointestinal tract

- this specific type of receptor is called a MUSCARINIC

RECEPTOR

- may be inhibitory (inhibits smooth/cardiac muscle

contraction) or excitatory (stimulates smooth/cardiac

muscle contraction)

- whether inhibition or excitation occurs is dependentupon enzyme systems located in specific cell type (tend

to be indirect receptor mechanisms)

- ex. release of ACh at bronchial smooth muscle causes

excitation (bronchial smooth muscle contraction)


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Acetylcholine Site of Release Target Organ Effect

Cholinergic Receptor

Type

Nicotinic Neuromuscular junction Skeletal muscle Excitatory(voluntary)

By Pre-Ganglionic

Neuron at All ANS

ganglia (PNS)

Ganglia Excitatory(involuntary)

By Pre-GanglionicNeuron at Adrenal

Medulla

Hormone producing cells Excitatory (epinephrineand NErelease)

Muscarinic By Post-Ganglionic

Parasympathetic Motor

Neuron at target organ

Heart Inhibitory(decreased rate

of contraction)

By Post-GanglionicParasympathetic Motor

Neuron at target organ

Bronchioles Excitatory(bronchialsmooth muscle

contraction); increased

airways secretion

production


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2. Biogenic Amines and Adrenergic Receptors

a) Catecholamines and Adrenergic Receptors

in the PNS, norepinephrineis the mainneurotransmitter released by post-ganglionicneurons (so, released at involuntarily controlledtarget tissues) in thesympatheticnervous system- epinephrine(really a hormone) is released by theadrenal medulla (gland on kidneysite of largeganglion) in response tosympathetic nervoussystem stimulation

norepinephrine is also a hormone secreted here(in smaller amounts than epinephrine - very similarin chemical structure to epinephrine)


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- hormones exert their effects via circulation(releasedinto blood) at distal target organs

- both epinephrine or norepinephrine may be excitatory

or inhibitory, depending upon the target organ and the

receptor sub-types that they bind with at the target

organ; dopamine is also released by some sympatheticpost-ganglionic neurons (also very similar structurally to

NEmissing the hydroxyl group)

- the receptors on target organs for these transmitters

and/or hormones are known as adrenergic receptors


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ADRENERGIC RECEPTOR SUB-TYPES:

a) alpha adrenergic receptors ()- alpha-1(1)adrenergic receptorsfound onsmooth muscle cell membranes - binding withnorepinephrine or epinephrine is excitatory,causing smooth muscle contraction inperipheralarterioles (excitatory); RESULT= vasoconstriction- alpha-2(2)adrenergic receptorsfound onmembranes of sympathetic motor axon terminalsstimulation of these receptors inhibitsnorepinephrine release, causing less smoothmuscle contraction in peripheral arterioles(inhibitory) ; RESULT= relative vasodilation


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b) beta adrenergic receptors ()-beta-1 (

1

) receptorscardiac musclebinding withnorepinephrine or epinephrine is excitatory, increasingheart rate (chronotropy) and strength of contraction(inotropy)

- beta-2(2)receptorsbronchial smooth musclebinding with epinephrine (released by adrenal medulla)

causes bronchodilation (inhibitory action on bronchialsmooth muscleless contraction); binding withepinephrine at arterioles serving skeletal muscle andheart (coronary arterioles) causes less smooth musclecontraction and relative dilationof these blood vessels;(inhibitory)

- beta-3(3) receptors on tissue cells like fat tissueand liver; epinephrine stimulates increased glucoserelease by the liver and fatty acid mobilization fromadipose tissue cell into blood (metabolic fuels are mademore readily available)


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Receptor Site Sympathetic (adrenergic) Parasympathetic (muscar in ic)

Cardiovascular System

heart rate(chron otropic ef fect

rate of contraction)

1: increases

Via NE and E

Decreases

Via ACh

cardiac muscle contractility

(ino t rop icstrength of

contractility)

1: increases

Via NE and E

Decreases

Via ACh

vascular smooth muscle 1= contracts(decreases

peripheral blood supply skin,

GI tract, kidney, non-vital organs

via NE and E)

2= relaxes (increases

coronary and skeletal muscleblood supply via E)

no effect (no parasympathetic

innervation to blood vessels)

NE = norepinephrine; E = epinephrine; ACh = acetylcholine

Receptor Site Sympathetic (adrenergic ) Parasympathetic (muscar in ic)


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Receptor Site Sympathetic (adrenergic) Parasympathetic (muscar in ic)

Respiratory System

smooth muscle in bronchioles 2: relaxes (bronchodilation)

Via E

(no direct sympathetic

innervation to bronchial

smooth muscle)

Contracts(bronchoconstriction)

Via ACh

Other

pupil of eye 1: relaxes(dilates pupils)

Via NE and E

Contracts (constricts pupils)

Via ACh

Secretions (saliva) : decreased secretions (via

NE and E)

Stimulates watery secretions

Via ACh

adrenal medulla Nicotinic* - stimulatesincreased secretion of

epinephrine and

norepinephrinesee all

above effects



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Target Site Sympathetic(adrenergic) Parasympathetic(musc arin ic)

Liver 3: increased release of

stored glucose intocirculation

Via E

No effect (no parasympathetic

innervation)

Fat (Adipose) Tissue 3: increased lipolysis

(increased release of fatty

acids into circulation for

metabolism by cells more

ATP production)Via E

No effect (no parasympathetic

innervation)

Cellular Metabolism increased metabolic rate:

Via E (see above effects ie:

blood flow to vital regions and

fuel release into circulation,

etc.)



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CNS PNS EFFECTORS

Somatic Cell Body Skeletal Muscle (Ach - Nicotinic)

Sympathetic Cell Body Ganglion Smooth/Cardiac Muscle and Glands(ACh - Nicotinic) (Norepinephrine - Adrenergic)

Cell Body Adrenal Medulla Smooth/Cardiac Muscle and Glands(ACh - Nicotinic) (Epi/NorepiAdrenergic)

Para- Cell Body Ganglion Smooth/Cardiac Muscle and GlandsSympathetic (ACh/Nicotinic) (AChMuscarinic)

Pre-ganglionic Axon

Post-ganglionic Axon

Release of Hormones Directly into Circulation (Epinephrine and Norepinephrine)


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B/Indolamines

a) serotonin(feel good neurotransmitterreleased

in response to pain)b)histamineis released in the CNS (hypothalamus,but its affects are poorly understood) and by mastcells during inflammatory process (really amediator in this case, not a neurotransmitter) andacts as a powerful vasodilator(decreases smooth

muscle contractioninhibitory in the case of bloodvessels)- basophils and mast cells(found in tissuescontain mediators for inflammationa lot found inlung tissue) can release histamine during antigen-antibody (allergic) reactions and in response to

drugs and toxic products; histamine release causesbronchiolar smooth muscle contraction- H1and H2receptors for histamine are foundwidely throughout the body at target effectororgans


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Effects of Histamine

Receptor H1 H2

Heart Slowing of conduction - positive inotropic effect

(increased strength of

contractility)

- positive chronotropic effect(increased rate of contraction)

Blood Vessels (smooth

muscle)

Dilation Dilation

Bronchial (smooth muscle) Contraction


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3. Amino Acid Neurotransmitters

found only in CNS

GABA (gamma-aminobutyric acid)

- inhibitoryneurotransmitter that is very widelydistributed in the neurons of the brain (close to 40%of the synapses in the human brain work with GABAand therefore have GABA receptors)

- GABA receptors are channel receptors

- when GABA binds to them, they change shapeslightly to allow ions to pass through their centralchannel


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- allows mainly negatively charged chloride ions toenter the neuron, causing hyperpolarization of the

membrane, thus reducing its excitability- sedative drugs and agents used for the inductionof general anesthesia (hypnotics) enhance thenatural effect of GABA; in other words, they helpGABA to reduce neural activity even further

- classes of medications which enhance GABAbinding to receptors or mimic the effects of GABAinclude benzodiazepines (examples of commonagents include: midazolamAKA Versed and

lorazepamAKA Ativan) and hypnotic agents(examples of common agents include: propofol,ketamine, etomidate and barbituratesthiopentalis a common barbiturate)


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4. Peptides

A. endorphins and enkephalins(inhibitory)

- found in CNS (brain and spinal cord)- bind with opiate receptors: (mu), (delta), (kappa) and (sigma) and hyperpolarize neuronalcell membranes to inhibit pain reception- endorphins and enkephalins are known as naturalopiates (endogenous controllers of pain)- narcotic analgesics bind to opiate receptors inthe brain and spinal cord to mimicendorphin/enkephalin activity (specific drugs:codeine, morphine, Demerol, Dilaudid, fentanyl,oxycodone)


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B. Substance P

- found in PNS

- allows pain transmission (excitatory)

***See Tables in Marieb, Chapter 11 -Neurotransmitters

Nervous System 1 2013

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