BIOMEDICAL INSTRUMENTATION

BIOMEDICAL INSTRUMENTATIONMODULE-1PROF. DR. JOYANTA KUMAR ROYDEPARTMENT OF APPLIED ELECTRONICS & INSTRUMENTATION ENGINEERINGNARULA INSTITUTE OF TECHNOLOGY

WWW.dr-joyanta-kumarroy.com1Subjects of discussionIntroduction to Biomedical InstrumentationHuman BodyPhysiology of Heart and Circulatory systemPhysiology of Respiratory systemPhysiology of Brain and Nervous systemNeurons and Bio-signals

The Module -1 course duration : 3 lectures

The lecture content will be available at http//www.dr-joyanta-kumar-roy.com

2Dr. J. K. RoyBOOKS AND REFERENCES FOR STUDY1. Hand Book of Biomedical Instrumentation, R S Khandpur, McGraw Hill2.BioInstrumentation, John G. Webster, Wiley India3.Biomedical Instrumentation & Measurement, Cronwell L, Pearson4.Medical Instrumentation, Application and Design, Webster JS5. Introduction to Biomedical Instrumentation and measurement, Astor B R, McMillan6. Introduction to Biomedical Equipment Technology, Carr, Pearson7. Biomedical Instrumentation, Chatterjee & Millar, Cengage Learning8. Internet search engines like : Google, Bing etc.3Dr. J. K. Roy

Human MachineBest creature of the Planet

Greatest creation of God

Finest TechnologyOf the world4Dr. J. K. RoyHuman BodyThe human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs. By the time the human reaches adulthood, the body consists of close to 100 trillion cells, the basic unit of life. These cells are organized biologically to eventually form the whole body.

Organ System:

The organ systems of the body include the musculoskeletal system, cardiovascular system, digestive system, endocrine system, integumentary system, urinary system, lymphatic system, immune system, respiratory system, nervous system and reproductive system.

Constituents of the human bodyIn a normal man weighing 60kgConstituentWeight [2]Percent of atoms[2]Oxygen38.8kg25.5%Carbon10.9kg9.5%Hydrogen6.0kg6.3%Nitrogen1.9kg1.4%Calcium1.2kg0.2%Phosphorus0.6kg0.2%Potassium0.2kg0.07%5Dr. J. K. RoyCardiovascular systemThe cardiovascular system comprises the heart, veins, arteries and capillaries. The primary function of the heart is to circulate the blood, and through the blood, oxygen and vital minerals are transferred to the tissues and organs that comprise the body. The left side of the main organ (left ventricle and left atrium) is responsible for pumping blood to all parts of the body, while the right side (right ventricle and right atrium) pumps only to the lungs for re-oxygenation of the blood. The heart itself is divided into three layers called the endocardium, myocardium and epicardium,(liquidation) which vary in thickness and function.

Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow.6Dr. J. K. Roy

The cardiovascular system is a complex hydraulic system, which performs the essential service of transportation of oxygen, carbon-di-oxide, numerous chemical compounds and blood cells.

Structurally, the Heart is divided into right and left parts. Each parts has two chambers called atrium and ventricle.

The Heart has four valves:The Tricuspid valve or Right atria-ventricular valveBicuspid mitral valve or Left atria-ventricular valvePulmonary valveAortic Valve

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Heart valvelocationFunctionThe Tricuspid valve Between right atrium & ventriclePrevent backward flow of blood from right ventricle to right atriumBicuspid mitral valve Between left atrium & left ventriclePrevents backward flow of blood from left ventricle to left atriumPulmonary valveAt the right ventricleDoes not allow blood to come back at right ventricleAortic ValveBetween left ventricle and aortaPrevents the return of blood to the left ventricle from Aorta8Dr. J. K. RoyThe Heart wall

Consist of 3 layersThe pericardium: Outer layer of Heart. It keeps the outer surface moist and prevent friction due to Heart beats

The myocardium:Middle layer of the Heart, which made of short cylindrical muscle fibers. The muscle is automatic in action, contracting & relaxing rhythmically through out the life.

The endocardium:The inner layer of the Heart provides smooth lining for blood flow9Dr. J. K. RoyEngineering Point of View

Fig: Circulatory system10Dr. J. K. RoyBlood transport mechanismThe blood is carried to the various parts of the body(organs) through Blood vessels. The blood vessels are classified into:

Arteries : The arteries are thick walled and they carry the oxygenated blood away from the HeartVeins: They are thin walled and they carry deoxygenated blood with carbon di oxide towards heartCapillaries :Smallest and the last level of blood vessels which supply food and oxygen to the organs.From the engineering point of view Heart act as pump and drives blood through blood vessels of the circulatory system consist of four chamber muscular pump that beats 72 per minutes on an average for normal adult, sending blood to every part of the body. The pump act as two synchronized but functionally isolated two stage pump. The first stage of each pump (Atrium) collects blood from hydraulic system and pumps to the second stage (the ventricle). In this process the heart pumps the blood through pulmonary circulation to the lungs and through the systematic circulation to the other parts of the body.Pulmonary circulation: The venous deoxygenated blood flows from right ventricle to the pulmonary artery to the lungs, where it is oxygenated and gives of carbon di oxide. The oxygenated blood then flows through pulmonary veins to the left atrium.Systematic Circulation: The blood is forced through blood vessels which are elastic. The blood flows through left atrium to left ventricle and is pumped through aorta and its branches the arteries to the out of the bodies. Through arterioles (Small and fine arteries) the blood is distributed through capillaries to the human body organs. Where it gives up oxygen and other relevant chemical compounds and taken up carbon di oxide and product of combustion.

11Dr. J. K. RoyThe blood returns to the heart from different routes. It usually passes from the Venus side of the capillaries. The heart itself is supplied by two small but highly important arteries, called Coronary arteries. If they blocked by Coronary Thrombosis, Myocardial infraction follows, often leading to fatal situation.

The Heart rate is partially controlled by autonomic nervous system and partially by Hormone action. These control the heart pumps speed, efficiency and blood flow pattern through the system.

The circulatory system is the Transport mechanism by which body takes food, oxygen, water and other essentials are transported to the tissue cells and their waste product are transported away. This happens through the diffusion process, in which nourishment from blood cells diffuses through capillary wall into the interstitial fluid. Similarly carbon di oxide and waste product from interstitial fluid diffuses through wall to the blood cell.

The condition of the Cardio vascular system is examined by the hemodynamic measurement and recording the electrical activity of Heart muscles (Electro cardiography)

For assessing the performance of Heart as a pump, the measurement of cardiac output (amount of blood flow per unit time)i.e by measuring blood pressure and flow at various location of the Circulatory system12Dr. J. K. RoyTHE END OF INTRODUCTION TO THE CARDIOVASCULAR SYSTEM13Dr. J. K. RoyThe Physiology of RespirationThis presentation takes you through the basic anatomy and physiology of the respiratory systemYou can complete the questions in your GM402M workbook as you work through this presentationKeep clicking your mouse to take you through the presentation14Dr. J. K. RoyWhy do we need to breathe?Breathing gets oxygen into the body so that cells can make energyCells use this energy to contract muscles and power the thousands of biochemical reactions that take place in the cell every secondWithout oxygen, cells cant make energy and without energy, cells would die15Dr. J. K. RoyIMPORTANT CONCEPTThe supply of blood and oxygen to cells and tissues is called PERFUSIONIf perfusion stops then cells die

16Dr. J. K. RoyEnergy productionInside the cells most energy is made by the mitochondria. This energy is in the form of ATP*

*adenosine triphosphate a small packet of energyIn the process of energy production Oxygen is consumed by the cells Carbon dioxide is produced as a waste gas Glucose fuels the process17Dr. J. K. Roy

18Dr. J. K. RoyHow do cells get their oxygen?Oxygen (O2) from the air in the lungs diffuses into the bloodIt is transported in the blood to the cellsOxygen diffuses from the blood into the cells

19Dr. J. K. RoyHow do cells dispose of their carbon dioxide?Carbon dioxide (CO2) from the cells diffuses into the bloodIt is transported in the blood to the lungsIn the lungs carbon dioxide diffuses into the air and is breathed out20Dr. J. K. RoyMovement of O2 and CO2 between lungs and cells

21Dr. J. K. RoyThe anatomy of the Respiratory SystemThe respiratory system consists of a series of tubes that transfer air from outside the body to the small air sacs in the lungs where gas exchange take place the alveoliThe diagram on the next page shows the basic layout of the system label the diagram in your workbook22Dr. J. K. Roy

Look at the structure of the respiratory system and label the diagram in your workbook

23Dr. J. K. RoyAlveoliAt the end of the smallest bronchioles are the alveoliThere are millions of alveoli in each lungAlveoli are surrounded by a network of small blood vessels called capillaries

24Dr. J. K. RoyAlveoli and adjacent capillariesterminal bronchiolealveolicapillaries25Dr. J. K. RoyGas exchange in the alveoliOxygen diffuses from the alveoli to the blood in the capillariesCarbon dioxide diffuses from the blood in the capillaries to the alveoli26Dr. J. K. Roy

27Dr. J. K. RoyWhat is diffusion?Diffusion is a process that occurs when there is a difference in the concentration of a substance between two areas The substance, for example oxygen, will diffuse from an area of high concentration to an area of low concentrationNo energy is required from the body for this process28Dr. J. K. Roy

29Dr. J. K. RoyVentilation (breathing)It is the changes in pressure that cause air to enter and leave the lungsBreathing air in and out of the lungs As the ribs rise and fall and the diaphragm domes and flattens, the volume and pressure in the lungs changes

30Dr. J. K. RoyVentilation (breathing)

31Dr. J. K. RoyVentilation (breathing)Inspiration (breathing in)Ribs rise and diaphragm flattensVolume increases and pressure decreasesAir enters the lungsExpiration (breathing out)Ribs fall and diaphragm domesVolume decreases and pressure increasesAir leaves the lungs

32Dr. J. K. RoyControl of VentilationAs we exercise, the body needs to obtain more oxygen and remove more carbon dioxide (CO2)This is done by increasing the rate and depth of breathingAn increase in carbon dioxide in the blood is the main trigger that increases the rate and depth of breathing33Dr. J. K. RoyControl of VentilationChemoreceptors in the respiratory centre in the brain stems medulla detect an increase in blood CO2 levelsThe intercostal and phrenic nerves increase the rate and depth of breathingAdditional chemoreceptors on arteries near the heart monitor oxygen and blood acidity34Dr. J. K. Royrespiratorycentres in medullachemoreceptorson aorta and carotid arteryheartbrainintercostal nerve to externalintercostal musclesphrenic nerve to diaphragmdiaphragmribsControl of Respiration35Dr. J. K. RoyDiseases such as emphysema, bronchitis and asthma can impede the movement of gas between the alveoli and the bloodCO2 levels can build up in the blood known as hypercapniaThis stimulates the chemoreceptors in the respiratory centre of the brainThe rate and depth of breathing increases to expire more CO2 and reduce levels in the bloodResponse to hypercapnia36Dr. J. K. RoyThe Physiology of NERVOUS SYSTEM37Dr. J. K. RoyCentral Nervous System:CNS

Spinal CordBrainThe Spinal CordForamen magnum to L1 or L2 Runs through the vertebral canal of the vertebral column

FunctionsSensory and motor innervation of entire body inferior to the head through the spinal nervesTwo-way conduction pathway between the body and the brainMajor center for reflexes39Dr. J. K. Roy

Spinal cord

http://www.apparelyzed.com/spinalcord.html40Dr. J. K. RoyProtectiOn:

41Dr. J. K. RoyAnatomical classificationCerebral hemispheresDiencephalonThalamusHypothalamusBrain stemMidbrainPonsMedullaCerebellum

Spinal cord

42Dr. J. K. RoyParts of BrainCerebrumDiencephalonBrainstemCerebellum

43Dr. J. K. RoysimplifiedBack of brain: perceptionTop of brain: movementFront of brain: thinking

44Dr. J. K. RoyCerebral hemispheresLobes: under bones of same name

Frontal

Parietal

Temporal

Occipital

Plus: Insula (buried deep in lateral sulcus)

45Dr. J. K. RoyHomunculus little manBody map: human body spatially representedWhere on cortex; upside down

46Dr. J. K. RoyPrefrontal cortex: cognitionExecutive functioninge.g. multiple step problem solving requiring temporary storage of info (working memory)

This area is remodeled during adolescence until the age of 25 and is very important for well-being; it coordinates the brain/body and inter-personal world as a wholeSocial skillsAppreciating humorConscienceMoodMental flexibilityEmpathy

IntellectAbstract ideasJudgmentPersonalityImpulse controlPersistenceComplex ReasoningLong-term planning

47Dr. J. K. RoyReticular formationRuns through central core of medulla, pons and midbrain

Reticular activatingsystem (RAS): keeps the cerebral cortex alert and consciousSome motor control

48Dr. J. K. Roy48THE END OF PHYSIOLOGY OF HUMAN BRAIN & NERVOUS SYSTEM49Dr. J. K. RoyBiomedical signals: Origins and dynamic characteristics50Dr. J. K. RoyBIOMEDICAL SIGNALS:

ORIGIN AND DYNAMIC CHARACTERISTICS51Neurons and SynapsesTypes of NeuronsSensoryMotorInterneurons5252Key words: Types of neurons; sensory neurons; motor neurons; interneurons; afferent nerves; efferent nerves

SpinalCordBrainSensoryNeuronSensory NeuronsINPUT From sensory organs to the brain and spinal cord.Drawing shows a somatosensory neuron

Vision, hearing, taste and smell nerves are cranial, not spinal

5353Key words: sensory neurons; afferent nerves; types of neurons

SpinalCordBrainSensoryNeuronMotorNeuronMotor NeuronsOUTPUT From the brain and spinal cord To the muscles and glands.

5454Key words: Motor neurons; efferent nerves; types of neurons

SpinalCordBrainSensoryNeuronMotorNeuronInterneuronsInterneurons carry information between other neurons only found in the brain and spinal cord.

5555Key words: interneurons; types of neuronsStructures of a neuron

5656Key words: Neuron; sructures of neurons

The cell bodyRound, centrally located structure Contains DNAControls protein manufacturing Directs metabolismNo role in neural signalingContains the cells Nucleus5757Key words: Cell body; soma; cell nucleus

Interesting facts:

The DNA in the nucleus of the cell has lost its ability to divide. therefore, when a neuron dies,for the most part, the adult brain cannot simply grow new neurons. (Note there are a few exceptions to this rule.)

The relative inability to grow new neurons leads to two interesting questions:

Q1: How do brain tumors (cancer) occur?A: Unlike neurons, glial cells can divide and grow new cells throughout one's lifetime. Most brain tumors are limited to glial cells, not neurons.

Q2: If a person cannot grow new neurons, how does the brain change in order to accomodate new learning?A: One mechanism by which the brain adapts to help you learn new information involves the structure on the next slide: the dendrites.

DendritesInformation collectorsReceive inputs from neighboring neuronsInputs may number in thousandsIf enough inputs the cells AXON may generate an output5858Key words: dendrite

Interesting facts:

- The word DENDRITE comes from the Greek word for tree. This may serve as a useful analogy in discussing the dendrites for several reasons:1. The dendrites branch repeatedly from the cell body (to increase the surface area of the cell to better allow the cell to receive incoming information). These radiations from the cell body are often referred to as a dendritic tree.2. In terms of function, the dendrites function similiarly to the roots of a tree. Just as the roots take water and other nutrients from the soil and carry them to other parts of the tree, the dendrites collect information and and spread it to other parts of the neuron.

Dendritic GrowthMature neurons generally cant divide But new dendrites can growProvides room for more connections to other neuronsNew connections are basis for learning

5959Key words: dendrite

Interesting facts:

- The word DENDRITE comes from the Greek word for tree. This may serve as a useful analogy in discussing the dendrites for several reasons:1. The dendrites branch repeatedly from the cell body (to increase the surface area of the cell to better allow the cell to receive incoming information). These radiations from the cell body are often referred to as a dendritic tree.2. In terms of function, the dendrites function similiarly to the roots of a tree. Just as the roots take water and other nutrients from the soil and carry them to other parts of the tree, the dendrites collect information and and spread it to other parts of the neuron.

AxonThe cells output structureOne axon per cell, 2 distinct partstubelike structure branches at end that connect to dendrites of other cells

6060Key words: axon; action potentials

Interesting facts:

- The diameter of an axon may vary from approximately 1mm-20mm.

- An axon may travel long distances to reach it's destination (longest axon is approximately 3 feet in humans and 10 feet in giraffes).Myelin sheathWhite fatty casing on axon Acts as an electrical insulator Not present on all cellsWhen present increases the speed of neural signals down the axon.

Myelin Sheath6161Key words: myelin sheath; action potentials; axon

Interesting facts:

- The myelin sheath is NOT a part of the axon. The myelin sheath is actually formed of glial cells (oligodendricytes and Schwann cells) that wrap around the axon.

- You may have often heard the brain referred to as either white matter or gray matter. The myelin sheath appears white in nature. Hence, the term white matter refers to areas of the brain that are myelinated. Gray matter refers to areas of the brain that are unmyelinated.

- When you accidentally cut yourself, you often visually notice that you've cut yourself before you actually feel any pain from the cut. The reason for this is that visual information uses myelinated axons; whereas, pain information uses unmyelinated axons.

- The loss of myelin is a significant factor in the disease multiple sclerosis (MS). When myelin is lost, the high-speed transmission of information is slowed down or blocked completely, which could lead the person with the inability to walk, write or speak. How neurons communicateNeurons communicate by means of an electrical signal called the Action Potential

Action Potentials are based on movements of ions between the outside and inside of the cell

When an Action Potential occurs a molecular message is sent to neighboring neurons62Dr. J. K. RoyPlasma Membrane

FUNCTION OF PLASMA MEMBRANE

Oxygen, carbon di oxide and water can easily cross plasma membrane large molecule and ions only can move through protein channel

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WATERK+ ,Cl-WATERK+ ,Cl-108 mM Cata ions12mM Na+125mM K+5mM Cl-120mM Na+5mM K+125mM Cl-Intra-cellular FluidExtra-cellular FluidNa+ 1------= ----K+ 30Na+ 10------= ----K+ 1Cell membraneCell membraneInsideInsideoutsideoutside64Ion concentrationsCell Membrane in resting stateK+Na+Cl-K+A-Outside of CellInside of CellNa+Cl-65Dr. J. K. Roy65Key words: ion concentrations; cell membrane; intracellular fluid; extracellular fluid; Na+; Cl-; K+

Slide ten represents a schematic of the typical concentrations of the intracellular and extracellular fluids. There are large concentrations of sodium and chloride ions concentrations of on the outside of the cell (relative to inside the cell). There are large concentrations of potassium ions and protein molecules on the insde of the cell (relative to concentrations on the outside of the cell).

The Cell Membrane is Semi-PermeableCell Membrane at restNa+Cl-K+Na+Cl-K+A-Outside of CellInside of CellPotassium (K+) can pass through to equalize its concentrationSodium and Chlorine cannot pass throughResult - inside is negative relative to outside- 70 mv66Dr. J. K. Roy66Key words: Cell membrane; semi-permeable; K+; Na+; Cl-

The cell membrane is semi-permeable. That is, when the neuron is at rest, the cell membrane allows some ions (K+) to pass freely through the cell membrane, whereas other ions (such as Na+ and Cl-) cannot.

Hit enter once and K+ ions will slowly pass through the cell membrane.

After K+ animation is finished, hit enter again and animation showing that Na+ and l- ions cannot pass through the membrane will occur.

Resting Potential

At rest the inside of the cell is at -70 milli voltsWith inputs to dendrites inside becomes more positive if resting potential rises above threshold an action potential starts to travel from cell body down the axonFigure shows resting axon being approached by an AP

-90mV(a) Polarized Cell67Depolarization ahead of AP

AP opens cell membrane to allow sodium (NA+) ininside of cell rapidly becomes more positive than outsidethis depolarization travels down the axon as leading edge of the AP-90mV(a) De-polarized Cell68Repolarization follows

After depolarization potassium (K+) moves out restoring the inside to a negative voltageThis is called repolarizationThe rapid depolarization and repolarization produce a pattern called a spike discharge6969Finally, Hyperpolarization

Repolarization leads to a voltage below the resting potential, called hyperpolarizationNow neuron cannot produce a new action potentialThis is the refractory period

70Resting PotentialRecall the definition of VM from the muscle lectures.Neurons are also highly polarized (w/ a VM of about 70mV) due to:Differential membrane permeability to K+ and Na+ The electrogenic nature of the Na+/K+ pumpThe presence of intracellular impermeable anionsChanges in VM allow for the generation of action potentials and thus informative intercellular communication.71Dr. J. K. RoyGraded PotentialsLets consider a stimulus at the dendrite of a neuron.The stimulus could cause Na+ channels to open and this would lead to depolarization. Why?However, dendrites and somata typically lack voltage-gated channels, which are found in abundance on the axon hillock and axolemma.So what cannot occur on dendrites and somata?Thus, the question we must answer is, what does this depolarization do?72Dr. J. K. RoyGraded PotentialsThe positive charge carried by the Na+ spreads as a wave of depolarization through the cytoplasm (much like the ripples created by a stone tossed into a pond).As the Na+ drifts, some of it will leak back out of the membrane.What this means is that the degree of depolarization caused by the graded potential decreases with distance from the origin.

73Dr. J. K. RoyGraded PotentialsTheir initial amplitude may be of almost any size it simply depends on how much Na+ originally entered the cell.

If the initial amplitude of the GP is sufficient, it will spread all the way to the axon hillock where V-gated channels reside.

If the arriving potential change is suprathreshold, an AP will be initiated in the axon hillock and it will travel down the axon to the synaptic knob where it will cause NT exocytosis. If the potential change is subthreshold, then no AP will ensue and nothing will happen.74Dr. J. K. RoyNERNST POTENTIALThe chemical potential gradient due to different concentrationsbetween inside and outside of the cell is given by NERNST RELATION

u - vENS = NERNST POTENTIAL = 61.6u + v

Where u = Mobility of cataions ( Negative ions)v = Mobility of Anaions (Positive ions)75Dr. J. K. RoyELECTRICAL EQUIVALENT CIRCUIT OF CELL MEMBRANE1 50KC1 KRKR NaR NadEKE Na38 KInside of the cellOut side of the cell91mV62mVC = Capacitance of the CellRK = Relative permeability of the membrane to the flow of K+ ionR Na = Relative permeability of the membrane to the flow of Na+ ion at polarized conditionR Nad =Relative permeability of the membrane to the flow of Na+ ion at De-polarized condition

EK = 61.6 log (30/1) = 91 mV Nernst Potential when Polarized

E na = 61.6 log (10/1) = 62 mV Nernst Potential when De-polarized

Net K Current + Net Na Current = 0

Net K Gradien Net na Gradient EK + EC -Ena + EC+ = + = 0 RK Rna RK Rna

76Dr. J. K. RoyAction PotentialsIf VM reaches threshold, Na+ channels open and Na+ influx ensues, depolarizing the cell and causing the VM to increase. This is the rising phase of an AP. Eventually, the Na+ channel will have inactivated and the K+ channels will be open. Now, K+ effluxes and repolarization occurs. This is the falling phase. K+ channels are slow to open and slow to close. This causes the VM to take a brief dip below resting VM. This dip is the undershoot and is an example of hyperpolarization.

77Dr. J. K. Roy

78Dr. J. K. RoyNa+ ChannelsThey have 2 gates.At rest, one is closed (the activation gate) and the other is open (the inactivation gate).Suprathreshold depolarization affects both of them.

1279Dr. J. K. Roy

34

580Dr. J. K. RoyAbsolute Refractory PeriodDuring the time interval between the opening of the Na+ channel activation gate and the opening of the inactivation gate, a Na+ channel CANNOT be stimulated.This is the ABSOLUTE REFRACTORY PERIOD.A Na+ channel cannot be involved in another AP until the inactivation gate has been reset.This being said, can you determine why an AP is said to be unidirectional.What are the advantages of such a scenario?81Dr. J. K. RoyRelative Refractory PeriodCould an AP be generated during the undershoot?Yes! But it would take an initial stimulus that is much, much stronger than usual.WHY?This situation is known as the relative refractory period.Imagine, if you will, a toilet.

When you pull the handle, water floods the bowl. This event takes a couple of seconds and you cannot stop it in the middle. Once the bowl empties, the flush is complete. Now the upper tank is empty. If you try pulling the handle at this point, nothing happens (absolute refractory). Wait for the upper tank to begin refilling. You can now flush again, but the intensity of the flushes increases as the upper tank refills (relative refractory)82Dr. J. K. RoyTIMEVMIn this figure, what do the red and blue box represent?83Dr. J. K. RoySome Action Potential QuestionsWhat does it mean when we say an AP is all or none?Can you ever have an AP?How does the concept of threshold relate to the all or none notion?Will one AP ever be bigger than another?Why or why not?84Dr. J. K. RoyAction Potential ConductionIf an AP is generated at the axon hillock, it will travel all the way down to the synaptic knob.The manner in which it travels depends on whether the neuron is myelinated or unmyelinated.Unmyelinated neurons undergo the continuous conduction of an AP whereas myelinated neurons undergo saltatory conduction of an AP.85Dr. J. K. RoyContinuous ConductionOccurs in unmyelinated axons.In this situation, the wave of de- and repolarization simply travels from one patch of membrane to the next adjacent patch.APs moved in this fashion along the sarcolemma of a muscle fiber as well.Analogous to dominoes falling.

86Dr. J. K. RoySaltatory ConductionOccurs in myelinated axons.Saltare is a Latin word meaning to leap.Recall that the myelin sheath is not completed. There exist myelin free regions along the axon, the nodes of Ranvier.

87Dr. J. K. Roy

88Dr. J. K. RoyRates of AP ConductionWhich do you think has a faster rate of AP conduction myelinated or unmyelinated axons?Which do you think would conduct an AP faster an axon with a large diameter or an axon with a small diameter?The answer to #1 is a myelinated axon. If you cant see why, then answer this question: could you move 100ft faster if you walked heel to toe or if you bounded in a way that there were 3ft in between your feet with each step? The answer to #2 is an axon with a large diameter. If you cant see why, then answer this question: could you move faster if you walked through a hallway that was 6ft wide or if you walked through a hallway that was 1ft wide? 89Dr. J. K. RoyNeuron to NeuronAxons branch out and end near dendrites of neighboring cellsAxon terminals are the tips of the axons branchesA gap separates the axon terminals from dendritesGap is the Synapse

CellBodyDendriteAxon9090Key words: axon terminal

.Synapseaxon terminals contain small storage sacs called synaptic vesicles

vesicles contain neurotransmitter molecules

SendingNeuronSynapseAxonTerminal919191key words: axon terminal; synaptic vesicles; neurotransmittersNeurotransmitter ReleaseAction Potential causes vesicle to openNeurotransmitter released into synapse

Locks onto receptor molecule in postsynaptic membrane

92Locks and KeysNeurotransmitter molecules have specific shapes

positive ions (NA+ ) depolarize the neuron negative ions (CL-) hyperpolarizeWhen NT binds to receptor, ions enter

Receptor molecules have binding sites93Some Drugs work on receptorsSome drugs are shaped like neurotransmittersAntagonists : fit the receptor but poorly and block the NTe.g. beta blockers

Agonists : fit receptor well and act like the NTe.g. nicotine.

94THE END OF MODULE -195Dr. J. K. Roy95