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UNIT 5

Sensory and Immune systems

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Nervous system

The task of nervous system is tocoordinate the mental processesby which we perceive, act, learnand remember.

The human brain is a networkof billions of individual nervecells interconnected in systemsthat construct our perceptionsof the external world, fix ourattention, and control themachinery of our actions.

The nervous system has twoclasses of cells: nerve cells(neurons) and glial cells (glia).

Neurotransmitters

Neuropeptides

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Supporting Cells (Neuroglial

Cells) in the CNSNeuroglia usually only refers tosupporting cells in the CNS, but can be used

for PNSGlial cells have branching processes and a

central cell body

Outnumber neurons 10 to 1 (the guy on the right

had an inordinate amount of them).Make up half the mass of the brain

Can divide throughout life

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Glial cells Glial cells are support cells.

They are more in number than neurons.

There are between 10 and 50 times more glia than neurons in the brain of humans.

The name for these cells derives from the Greek word for glue. In actual terms, the

glia do not commonly hold nerve cells together but surround the neurons.

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Types of Glial Cells in the CNS: Astrocytes,

Oligodendrocytes, and Microglia

Astrocytes: Mostabundant glial cell type,irregular star-shaped cellbodies .

Take up and release ions to

control the environmentaround neurons

Recapture and recycleneurotransmitters

Involved with synapseformation in developingneural tissue

Produce moleculesnecessary for neuralgrowth

Propagate calcium signalsthat may be involved inmemory

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Oligodendrocytes: Have

few branches.

Wrap their cell processes

around axons in CNS Produce myelin sheaths

for rapid conduction of

nerve impulses

Schwann cells surround

axons in the PNS and form

myelin sheath around

axons of the PNS

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Microglia: Smallest

and least abundant.

Phagocytes themacrophages of the CNS

Engulf invading

microorganisms and

dead neurons

Derived from blood cellscalled monocytes

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Nerve cells- Neurons Nerve cells are the main signaling units of the nervous system.

A typical neuron has four morphologically defined regions:

thecell body, dendrites, the axon, and presynaptic terminal

The cell body (soma) is the metabolic center of the cell. It

contains the nucleus which stores the genes of the cell, as well

as the endoplasmic reticulum, an extension of the nucleus

where the cells proteins are synthesized.

The cell body gives rise to two kinds of processes: several short

dendrites and one, long, tubular axon.

These processes vary in number & relative length but always

serve to conduct impulses (with dendrites conducting impulses

toward the cell body and axons conducting impulses away

from the cell body as shown in the figure).

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Action Potential

A neuron receives inputfrom other neurons(typically many thousands).All the input signals areintegrated. Once inputexceeds a critical level, the

neuron discharges a spike -an electrical pulse thattravels from the body, downthe axon, to the nextneuron(s) (or otherreceptors). This spikingevent is also calleddepolarization, and isfollowed by a refractoryperiod, during which theneuron is unable to fire.

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Synapse

The axon endings (OutputZone) almost touch the

dendrites or cell body of thenext neuron.

Transmission of an electricalsignal from one neuron to thenext is effected by

neurotransmitters, chemicalswhich are released from thefirst neuron and which bind toreceptors in the second. Thislink is called a synapse.

The extent to which the signal

from one neuron is passed on tothe next depends on manyfactors, e.g. the amount ofneurotransmitter available, thenumber and arrangement ofreceptors, amount ofneurotransmitter reabsorbed,

etc.

neurotransmitter

neurotransmitter

neurotransmitter

neurotransmitter

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Sensory Input and Motor Output

Sensory signals picked up by sensory receptors

Carried by afferent nerve fibers of PNS to the CNS

Motor signals are carried away from the CNS

Carried by efferent nerve fibers of PNS to effectors

Innervate muscles and glands

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The dendrites branch out in

a tree-like fashion and are

the main apparatus for

receiving incoming signals

from other nerve cells.

In contrast, the axon extends

away from the cell body and

is the main conducting unit

for carrying signals for other

neurons.

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An axon can convey electrical signals alongdistances ranging from 0.1 mm to 3 m. Theseelectrical signals called action potentials arerapid, transient with an amplitude of 100 mVand a duration of about 1ms.

Neurons can respond to stimuli and conductimpulses because a membrane potential isestablished across the cell membrane. In otherwords, there is an unequal distribution of ions(charged atoms) on the two sides of a nerve cellmembrane.

This can be illustrated with a voltmeter: Withone electrode placed inside a neuron and theother outside, the voltmeter is 'measuring' thedifference in the distribution of ions on theinside versus the outside (see the adjoiningfigure). And, in this example, the voltmeterreads -70 mV (mV = millivolts). In other words,

the inside of the neuron is slightly negativerelative to the outside. This difference isreferred to as the Resting Membrane Potential.It is called a RESTING potential because itoccurs when a membrane is not beingstimulated or conducting impulses (in otherwords, it's resting).

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Yes or NoYes or No

YesYes

Nerve

Conduction

Axon hillock orAxon hillock or

Initial segmentInitial segment

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Neural Networks in the Brain

Thebrain is not a homogeneousorgan.At the largest anatomicalscale, we distinguish cortex,midbrain, brainstem, andcerebellum. Each of these can behierarchically subdivided intomany regions, and areas withineach region, either according tothe anatomical structure of theneural networks within it, oraccording to the functionperformed by them.

In addition to these long-rangeconnections, neurons also link upwith many thousands of theirneighbors. In this way they formvery dense, complex localnetworks:

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Computer-based Neural Networks

The brain's network of neurons forms a massively parallel informationprocessing system. This contrasts with conventional computers, inwhich a single processor executes a single series of instructions.

Despite of being built with very slow hardware, the brain has quiteremarkable capabilities: its performance tends to degrade gracefully under partial damage. In contrast,

most programs and engineered systems are brittle: if you remove some arbitraryparts, very likely the whole will cease to function.

it can learn (reorganize itself) from experience.

this means that partial recovery from damage is possible if healthy units canlearn to take over the functions previously carried out by the damaged areas.

it performs massively parallel computations extremely efficiently. For example,

complex visual perception occurs within less than 100 ms, that is, 10 processingsteps!

it supports our intelligence and self-awareness. (Nobody knows yet how thisoccurs.)

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Applications of Neural Networks Aerospace: High performance aircraft autopilots, flight path simulations, aircraft

control systems, autopilot enhancements, aircraft component simulations, aircraftcomponent fault detectors

Automotive: Automobile automatic guidance systems, warranty activity analyzers Banking: Check and other document readers, credit application evaluators

Cognitive science: Modeling higher level reasoning, language, problem solving,Modeling lower level reasoning, vision, audition speech recognition, speechgeneration

Defense: Weapon steering, target tracking, object discrimination, facialrecognition, new kinds of sensors, sonar, radar and image signal processing

including data compression, feature extraction and noise suppression, signal/imageidentification

Electronics: Code sequence prediction, integrated circuit chip layout, processcontrol, chip failure analysis, machine vision, voice synthesis, nonlinear modeling

Entertainment: Animation, special effects, market forecasting

Financial: Real estate appraisal, loan advisor, mortgage screening, corporate bondrating, credit line use analysis, portfolio trading program, corporate financialanalysis, currency price prediction

Insurance: Policy application evaluation, product optimization

Manufacturing: Manufacturing process control, product design and analysis,process and machine diagnosis, real-time particle identification, visual qualityinspection systems, beer testing, welding quality analysis, paper quality prediction,computer chip quality analysis, analysis of grinding operations, chemical productdesign analysis, machine maintenance analysis, project bidding, planning and

management, dynamic modeling of chemical process systems

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Mathematics: Nonparametric statistical analysis and regression.

Medical: Breast cancer cell analysis, EEG and ECG analysis, prosthesis design,optimization of transplant times, hospital expense reduction, hospital qualityimprovement, emergency room test advisement

Neurobiology: Modeling models of how the brain works, neuron-level, higherlevels: vision, hearing, etc. Overlaps with cognitive folks.

Oil andGas: Exploration

Philosophy: Can human souls/behavior be explained in terms of symbols, or does itrequire something lower level, like a neurally based model?

Robotics: Trajectory control, forklift robot, manipulator controllers, visionsystems

Speech: Speech recognition, speech compression, vowel classification, text tospeech synthesis

Securities: Market analysis, automatic bond rating, stock trading advisory systems

Telecommunications: Image and data compression, automated informationservices, real-time translation of spoken language, customer payment processing

systems Transportation: Truck brake diagnosis systems, vehicle scheduling, routing

systems

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Disorders of the Nervous System

Multiple sclerosis common cause of neural disability

Varies widely in intensity among those affected

Cause is incompletely understood

An autoimmune disease

Immune system attacks the myelin around axons in the CNS

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Alzheimers Disease:

Age-associated disorder

Loss of memory, cognition,

and executive performances

Deposits of amyloid

plaques and neurofibrillary

tangles that interfere with

neuronal functions

Loss of cholinergicneuronal functions

Parkinsons Disease:

Age-associated disorder

Rigidity and incoordination

interfering with mobility Loss of dopaminergic

neuronal functions

Alzheimers Disease

Parkinsons Disease

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List of neurodegenerative diseases Alexander's disease

Alper's disease

Alzheimer's disease Amyotrophic lateral sclerosis

Ataxia telangiectasia

Batten disease (also known asSpielmeyer-Vogt-Sjogren-Battendisease)

Bovine spongiform encephalopathy(BSE)

Canavan disease

Cockayne syndrome

Corticobasal degeneration

Creutzfeldt-Jakob disease

Huntington's disease

HIV-associated dementia Kennedy's disease

Krabbe's disease

Lewy body dementia

Machado-Joseph disease(Spinocerebellar ataxia type 3)

Multiple sclerosis Multiple System Atrophy

NarcolepsyNeuroborreliosis

Parkinson's diseasePelizaeus-Merzbacher DiseasePick's diseasePrimary lateral sclerosisPrion diseasesRefsum's disease

Schilder's diseaseSubacute combined degeneration of spinalcord secondary to Pernicious Anaemia

SchizophreniaSpielmeyer-Vogt-Sjogren-Batten disease(also known as Batten disease)

Spinocerebellar ataxia (multiple types withvarying characteristics)

Spinal muscular atrophySteele-Richardson-Olszewski diseaseTabes dorsalis

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Immune SystemIntroduction

Fluid Systems of the Body

Innate Immunity

Adaptive or Acquired ImmunityCell-mediated immunity

Humoral immunity

Immune Engineering

Cell Signaling

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Eukaryotic Cells, Bacteria, and Viruses

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Body Defenses: Overview Physical barriers: skin & epithelial linings & cilia

Chemical: acids, mucous & lysozymes

Immune defenses internal

Innate, non-specific, immediate response (min/hrs)

Acquired attack a specific pathogen (antigen)

Steps in Immune defense

Detect invader/foreign cells

Communicate alarm & recruit immune cells

Suppress or destroy invader

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Markers of Self

Muscle cell

Nervecell

Epithelialcell

Leukocyte

At the heart of the immune response is the ability to distinguish

between self and non-self.

Every cell in your body carries the same set of distinctive

surface proteins that distinguish you as self.

Normally your immune cells do not attack your own bodytissues, which all carry the same pattern of self-markers; rather,

your immune system coexists peaceably with your other body

cells in a state known as self-tolerance.

This set of unique markers on human cells is called the major

histocompatibility complex (MHC) proteins.

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Markers of Non-self

Non-self leukocyte

Bacteria

Non-self nerve cell

SARS virus

Antigen = any non-self substance

VirusBacteria

Non-self cell (foreign cell)

Epitope = The distinctive markers on antigens that trigger an

immune response

Antigen

Epitope

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Blood

Blood is 55% liquid (plasma) and 45% cellular

Cellular component of blood:

Red blood cells = carry oxygen

White blood cells = immune system Platelets = clot blood

All blood cells arise from apluri-potent stem cell found

in bone marrow

Stem Cell

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Blood cells

Red Blood cells

White blood cells (immune cells)

Platelets

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Leukocytes in the Blood

Red Blood Cells 5.0 X 106/mm3

Platelets 2.5 X 105/mm3

Leukocytes 7.3 X 103/mm3

1 Neutrophil 50-70%

2 Lymphocyte 20-40%

3 Monocyte 1-6%

4 Eosinophil 1-3%

5 Basophil

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Organs of the Immune System

Tonsils and adenoids

Lymph nodes

Bone marrow

Appendix

Lymphatic vessels

Lymph nodes

Thymus

Peyers patches

Spleen

Lymphatic vessels

Lymph nodes

Bone marrow, the soft tissue in the hollow centerof bones, is the ultimate source of all blood cells,including the immune cells.

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Lymphatic System

The organs of your immune system are connected

with one another and with other organs of the body bya network of lymphatic vessels.

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Lymphatic System

Lymph nodeLymphatic vessel

The organs of your immune system are connected

with one another and with other organs of the body bya network of lymphatic vessels.

1. Lymphatic vessels closely

parallels the bodys veins and

arteries

- Lymphatic vessels carry lymph,a clear fluid that bathes the

bodys tissues

- Cells/fluids are exchanged

between blood and lymphatic

vessels, enabling thelymphatic system to monitor

the body for invading

microbes.

2. Lymph nodes contain high levels

of immune cells

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Remove cellular debris and

respond to invasion by foreignpathogens

Monocyte-macrophage system -Fixed and free

Microphages Neutrophils and

eosinophils

Move by diapedesis

Exhibit chemotaxis

Nonspecific Defenses, Phagocytes

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Constant monitoring of normal tissue by NK cells

NK cells Recognize cell surface markers on foreign cells

Destroy cells with foreign antigens

Nonspecific Defenses, Immunological surveillance

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Inflammation

Diabetic foot ulcer

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Adaptive or Acquired

Immunity

Acquired afterbirth

Seen only in

vertebrates

Characteristicfeatures are:

Diversity Specificity

Self vs non-self

Memory

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Immune Response System

Made up of two cellular systems (lymphocytes)

1. Humoral immunity - B cells

2. Cell-mediaed immunity - T cells

B cells make

antibodies

T cells mountdirect attack on

foreign/infected

cell

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Humoral (Antibody-mediated) immunity

Mediated by B cells

Antigen can activate B cell intwo ways:

direct binding

provokes less vigorous response

B cells process antigen (act as APC)

and display processed antigen withMHC proteins

TH cells recognise processed antigen

TH cells provide co-stimulation for

B cell

Activated B cell proliferates and differentiates

plasma cells

secrete antibodies with same

antigen binding properties as

receptors

memory B cells

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Summary ofAcquired Immunity

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Immunity: Active and Passive

Artificially acquired

Passive immunityActive immunity

Naturally acquired Naturally acquired

Artificially acquired

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HIV/AIDS Patient Aging

Smoking causes cancer

Diabetes Rheumatoid arthritis

Malaria-parasitic disease

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Immune Engineering

The complexity of the

immune system can becompared to that of thebrain.

There is a vast number ofcells, molecules, andorgans that compose the

immune system, and thesehave to act in concert, andtogether with other vitalsystems, so as to promoteand maintain life.

Neither can the immune

system act in isolation tomaintain life, nor can ahigher organism livewithout an immunesystem.

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Artificial immune systems (AIS) compose a new

computational intelligence approach inspired bytheoretical and experimental immunology withapplications to problem solving.

Like all new approach, the field still lacks a more

formal description and better theoretical foundations.

The application of mathematical analysis and modelingto immunology may result in outcomes such as a deeperand more quantitative description of how the immunesystem works, a more critical analysis of hypothesis, itcan assist in the prediction of behaviors and the designof experiments.

G l P i i l f C ll Si li

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General Principles of Cell Signaling

Unicellular organisms resemblingpresent-day bacteria were present on

Earth for about 2.5 billion years beforethe first multicellular organismappeared.

One reason why multicellularity wasso slow the evolve may have beenrelated to the difficulty of developingthe elaborate cell communication

mechanisms that a multicellularorganism needs.

These communication mechanismsdepend heavily on extracellularsignalmolecules, which are produced by thecells to signal to their neighbors or tocells further away.

The signal molecules are mainlyproteins.

These proteins include cell-surfacereceptor proteins, which bind thesignal molecule, plus a variety ofintracellular signaling proteins thatdistribute the signal to appropriateparts of the cell.

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Th A Th K Cl f C ll S f R t P t i

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There Are Three Known Classes of Cell-Surface Receptor Proteins:

Ion-Channel-linked,G-Protein-linked, and Enzyme-linked