Physio Exam 1

Relative refractory period AND frequency of action potentials

All action potentials have a fixed magnitude however neurons can nonetheless distinguish differences in signal strength. What enables this?

Schwann cells are comprised of multiple wrappings of cell membrane excluding most of cytoplasm and the nucleus. Most of the cytoplasm and the nucleus is exclude into the outer wrapping layer called the neurilemma. Signal transduction rates are controlled by salatory conduction. Schwann cells literally wrap around specific aspects along the axon creating areas of insulation. The nodes of Ravier are the areas along the axon not covered by Schwann cells. Charge polarity changes progressing along the plasma membrane surface of the axon only occur at nodes of Ravier, skipping areas covered by Schwann cells. We can assume for this process that the movement of charges in the ICF between nodes is essentially instantaneous. Therefore, the effective length for transduction is ONLY the combined length of the nodes.

Explain the interrelationship between the myelin sheath and the neurilemma. These cell components are associated with what cell? What is the physiological role provided by this cell in regard to communication?

a - Too large so no diffusion b - Rate of diffusion will decrease due to increase in X or distance through which diffusion will take place c - Increase in diffusion from side 1 to 2 d - Double diffusion rate, everything else being equal e - Everything else being equal will quadruple diffusion rate.

Presume you have a porous membrane with a pore size of 10 KDaltons. For the following situations how is the rate of diffusion affected? a- A concentration difference across the membrane for a molecule with a MW of 15 KDaltons. b- Instead of a single membrane layer, a stack of 5 layers is used. c- Increase the concentration of a 5 KDalton solute on side 1 while reducing it on the other side 2 d- Exchange membrane for a membrane with twice as many pores per unit surface area. e- Double concentration differential for a diffusible solute across the membrane while substituting a membrane with comparable porosity but only half as thick.

A neuron has a resting potential of -70 mV. Upon a depolarizing stimulation that reaches threshold stimulus, the Na voltage gates open, greatly increasing the permeability of Na which flows into the cell down its concentration gradient. This results in an increase in membrane potential to +30 mV at which point the Na voltage gates close and the K voltage gates open. K permeability is greatly increased and K flows out of the cell down its concentration gradient. This drives the membrane potential away from zero until at -80 mV the K voltage gates close. There is a rapid adjustment via leaky gates for Na and K of the membrane potential back to -70 mV Under no circumstances does the action potential magnitude change.

"Walk" me through an action potential in a neuron. Beginning at a resting membrane potential, state the order of events and make sure to discuss ions involved and any changes in membrane permeability and potential. Under what physiological situations does the magnitude of the action potential change?

cells, extracellular matrix, hormones, blood supply

4 critical components to tissue repair/regeneration

The molecule is not plasma membrane soluble. The molecule is passively entering the ICF but being actively pumped into the ECF

A molecule in solution is in a greater concentration in the ECF compared to the ICF but overtime there is no equilibration of concentration across compartments. What are plausible explanation(s)?

Via second messenger cascade pathways. These pathways consist of multiple levels of regulatory interactions which are important for the following: 1. They physically transfer the signal from the place at which it is received to some other part of the cell where the response is expected 2. They amplify the signal received, making it stronger 3. The signal can be modulated, regulated, by other possibly interfering factors prevailing inside or outside the cell

A protein based hormone binds to a cell surface receptor. How does this external event result in cell behavior changes, or rather how does apparent communication get to the nucleus? And what is the nature of this communication and why is it so complex? (There are 4 reasons but you can discuss 2)

Effectively, unmyelinated axons have many ion channels (because no Schwann cells) so more ions cross during an action potential and must be returned to their original compartments which will require Na + K+ pump which requires ATP.

An unmyelinated axon has a much greater requirement for ATP than a myelinated axon of the same diameter and length. Please speculate why?

Because EPSP is a graded potential it spreads detrimentally from its source. Therefore assumingpresynaptic neuron A and B both initiate EPSPs of the same magnitude and frequency, the EPSPS from Aswill be of greater strength when they reach the axon hillock then the EPSPs from B. Temporal summationof the larger EPSPs from A may bring the axon hillock to threshold and initiate an action potential in thepostsynaptic neuron whereas temporal summation of weaker EPSPs from B may not be sufficient to bringto threshold.

Assume presynaptic excitatory neuron A terminates on a postsynaptic cell near the axon hillockand presynaptic excitatory neuron B terminates on the same postsynaptic cell on a dendrite located on theside of the cell boy opposite the axon hillock. Explain why rapid firing of presynaptic neuron A could bringthe postsynaptic neuron to threshold through temporal summation, thus initiating an action potential,whereas firing of presynaptic neuron B at the same frequency and the same magnitude of EPSPs may notbring the postsynaptic neuron to threshold

c. Na moves from side 1 to 2 because of its concentration gradient. Cl remains on side 1. This creates unbalanced charges thus a membrane potential with negative on side 1 because Cl does not move across membrane. Na does not continue to move till concentration equilibrium is reached because of opposing electrical gradient.

Assume that a membrane permeable to Na+ but not to Cl- separates two solutions. The concentration of sodium chloride on side 1 is much higher than on side 2. Which of the following ionic movements would occur? Why? a.Na + would move until its concentration gradient is dissipated (i.e. until the concentration of Na+ on side 2 is the same as the concentration of Na+ on side 1). b.Cl- would move down its concentration gradient from side 1 to side 2. c.A membrane potential, negative on side 1, would develop. d.A membrane potential, positive on side 1, would develop. e.None of the above is correct.

The hand could be pulled away from the hot stove by flexing of the elbow accomplished by summation of EPSPs at the cell bodies of the neurons controlling the biceps, thus bringing these neurons to threshold. The subsequent action potentials generated in these neurons would stimulate contraction of the biceps. Simultaneous contraction of the triceps, would straighten the arm, could be prevented by generation of IPSPs at the cell bodies of the neurons controlling this muscle. These IPSPs would keep the triceps' neurons from reaching threshold and firing so that the triceps would not be stimulated to contract

Assume you a touched a hot stove with your finger. Contraction of the biceps causes bending of the elbow, whereas contractions of the triceps causes extension of the arm. What pattern of EPSPS and IPSPs would you expect to be initiated as a reflex in the cell bodies of the neurons controlling these muscles to pull your hand away from the painful stimulus?

Tight junctions-protein molecules in adjacent plasma membranes fuse together, forming an impermeable junction between those cells Desmosomes-are anchoring junctions, mechanical couplings scattered like rivets along sides of abutting cells. On cytoplasmic face are plaques, buttonlike thickenings. Adjacent cells are held together by linker proteins, cadherins. Cap Junctions- An interconnecting channel, connexons, allowing chemical substances to pass between adjacent cells

Cell junctions occur via specific cell to cell interactions. List and differentiate between the three types of specialized cell junctions

Subthreshold stimulus would transiently depolarize the membrane but not sufficiently to bring the membrane to threshold, so no action potential would occur. For a threshold stimulus, the stimulus will bring the membrane to threshold thus an action potential would occur. For suprathreshold stimulus an action potential of the same magnitude and duration would occur as to a threshold stimulus. Because of the all-or-none law, a stimulus would not produce a larger action potential BUT the magnitude as the stimulus is coded in the frequency of action potentials

Compare the expected changes in membrane potential of a neuron stimulated with a subthreshold stimulus, a threshold stimulus, and a suprathreshold stimulus.

More positive. Because the electrochemical gradient for Na+ is inward the membrane potential would become more positive as a result of an increased influx of Na+ into the cell if the membrane were more permeable to Na+ than to K+. This is what happens during the rising phase of an action potential once threshold potential is reached.

Compared to the resting potential, would the membrane potential become more negative or more positive if the membrane were more permeable to Na+ than to K+? Why? Describe a possible situation where this would occur if it occurs.

A multipolar neuron has more than two cellular processes extending from its soma; the axonal anddendritic ends. Because its communication involves multiple neurons, it may or may not haveoligiodendrocytes and astrocytes associated with it. The oligodendrocytes acing like Schwann cells with thesensory neuron and astrocytes helping to form the blood brain barrier. The afferent sensory neuron is aunipolar neuron with a single cellular process extending from its soma with the bulk of its length, up to ~1meter/yd, is as an axon. AND, this is also important there are Schwann cells all along its length separatedby Nodes of Ranvier. These glial cells strung like pearls along a pearl necklace enable saltatoryconduction, the jumping of action potentials from node to node creating a faster communication pathway.Also the diameter of the afferent neuron is likely greater which further increases signal transduction speed

Consider two neurons, a processing multipolar neuron in the brain and an afferent sensoryneuron being in fingertip proceeding to an interneuron. Discuss the differences between these two neuronsboth structurally and functionally. In other words, how does their respective function dictate structure andfunction? Make sure you discuss any involvement of glial cells

Ability to adjust strength of lens so that both near and far sources can be focused on retina. In Myopia or nearsightedness, the eyeball is too long or lens too strong. Uncorrected far source is focused in front of retina while near source is focused on retina without accommodation. In Hyperopia or farsightedness, the eyeball is too short or lens too weak. Uncorrected far source is focused on retina with accommodation while near sours remains unfocused even with accommodation.

Define accommodation. How does the function of accommodation change during uncorrected Myopia and Hyperopia?

Intrinsic controls are specific to an organ. They can maintain homeostasis within themselves e.g. the heart can control its own heart rate Extrinsic controls are initiated outside of the organ and involves nervous and/or endocrine systems. They are made of several organs that work towards a common goal Sight, smell of food examples of extrinsic control of stomach whereas physically filling the stomach with food would be an intrinsic control.

Define and Give me examples of intrinsic and extrinsic control?

Dynamic state of equilibrium, balance or status quo in which internal conditions vary, but always within narrow limits. A change in the controlled variable is sensed by receptors in the control center, which increasing release of positive effecting control aspect to increase controlled variable concentration. The increased concentration is sensed by control center and will decrease subsequent release of positive control aspect. Intrinsic control is local control mechanisms inherent to an organ or a tissue.Extrinsic control is regulatory mechanisms initiated outside of an organ or a tissue. Positive feedback- As the controlled variable increases this results in more release of controlled variable Negative feedback- As the controlled variable increases this results in less release of controlled variable

Define homeostatic control? How is this accomplished (include in your answer the interacting components of a control system)? Explain the difference between intrinsic and extrinsic control. Explain the difference in positive feedback and negative feedback control.

Hierarchy of structural organization-the is a defined order progressing from molecular level through cell, tissue, organ, organ system, to organism level Complementarity of structure and function- anatomy and physiology are inseparable because function alwas follows structure, o what a structure can do is dependent on its specific form. Homeostasis- dynamic state of equilibrium or status quo in which internal conditions vary, but always within relatively narrow limits.

Define the 3 underlying concepts or ideas for physiology.

There is limited Na+ diffusional transport. Transport is primarily via membrane protein channels. Cortisol is a steroid/lipid based molecule so it freely diffuses across the membrane, down its concentration gradient.Insulin as a protein molecule does not diffuse through the membrane but must bind to cell surface receptors.O2 readily diffuses across the membrane, down its concentration gradient.

Describe diffusional transport of Na+, cortisol, insulin (a protein-based hormone) and O2 in respect to the plasma membrane.

The path begins when CO2 first crosses the tissue cell membrane to the tissue interstitial fluid to theendothelial cell membrane (both sides) to the blood and RBC cell membrane to the lungs and theendothelial cell membrane to interstitial fluid to epithelial cell in the lungs (just saying cell membrane isgood enough here) to exit into the atmospheric air

Describe the path of CO2from the tissue cells to the atmosphere. Specifically trace the barriersand compartments CO2must transverse. Keep it general (ie. At the level of detail we are currently at). Don'tforget cell barriers along the way

Air —> lungs across epithelial cell layer —> (cell membrane) —> interstital space —> endothelial cell (cell membrane) —> blood —> RBC (cell membrane) —> endothelial cell (cell membrane) —> tissue interstitial fluid —> cell membrane —> into cell.

Describe the path of O 2 from the atmosphere to tissue cells. Specifically trace the barriers and compartments O 2 must transverse. Keep it general (ie. At the level of detail we are currently at). Don't forget cell barriers along the way.

Neurons are composed of a cell body (soma) where a majority of their cellular organelles are located, and several projections from the cell body that are classified as dendrites and axons. Projecting from the cell body are dendrites that receive synaptic input from axon terminals from other neurons. The dendrites receive information (afferent) while the axons transmit information (efferent). At axodendritic synapses (or terminal axon buds within the synaptic cleft), neurotransmitters are released from axon terminals onto the dendrites to generate a change in membrane potential. This allows the integration of numerous synaptic inputs onto the cell body. The action potential travels along the length of the axon in one direction until it reaches the axon terminal, where a synapse is formed for the transfer of signal to the next neuron or effector organ.

Describe the structure of a "generalized" neuron and the important consequences of that arrangement.

Passive (no direct energy) Na and K gates occur generally throughout the neuron. There are many more Kgates than Na gates resulting in a increased permeability of K compared to Na, and this interaction isessential in establishing membrane potential. There are also Na/K pumps (direct energy require) occurringgenerally throughout the neuron which are involved in maintaining membrane potential and reestablishingmembrane potential requiring energy to pump against respective concentration gradients. There are Naand K voltage gates primarily along the axon which are involved in conducting action potentials. These donot require direct energy. On the soma or dendritic surfaces there can be various gated channels such aschemical, electrical or mechanical controlled that induce a graded potential. These do not require directenergy.

Describe the types of carrier mediated transport that occur within a neuron. Focus your answerupon sodium and potassium and how transport differences determine function. Also mention if energy isdirectly involved

EPSP is excitatory postsynaptic potentials that occur at excitatory synapses and move a postsynaptic neuron toward its threshold. IPSP is inhibitory postsynaptic potentials that occur at inhibitory synapses and move a postsynaptic neuron away from its threshold

Differentiate between EPSP and IPSP

There is no direct involvement as EPSP and IPSP only occur with graded potentials.

Differentiate between EPSP and IPSP within an action potential

During absolute refractory period another action potential is not possible because sufficient membrane potential has not been reestablished. During relative refractory period, enough membrane potential has been reestablished for another action potential to occur. Absolute refractory period-because during this phase another action potential is not possible because the membrane potential is not yet begun to be reestablished. Relative refractory period-Strong stimuli cause nerve impulses to be generated more often in a given time interval than do weak stimuli. Thus, stimulus intensity is coded for by the number of impulses generated per second, by frequency of impulse transmission, rather than by increases in the strength of the individual action potentials. This can only occur during relative prior to return to complete membrane potential.

Differentiate between absolute and relative refractory period. Which process affects directionality of signal transmission along the axon; why? Which process affects the ability of a cell to respond to varying afferent signal strength despite an "all or none" response of the action potential; why?

Equilibrium Potential K+ --> concentration gradient is outward, Electrical gradient is inward Na+ --> Concentration gradient is inward, Electrical gradient is outward Resting Membrane Potential K+ --> concentration gradient is outward, Electrical gradient is inward Na+ --> Concentration gradient is inward Electrical gradient is inward

Differentiate between equilibrium potential and membrane potential. I am especially interestedin the following: 1) define the two; 2) how is the concentration gradient affected in each case for Na+andK+; and 3) how is the electrical gradient affected in each case for Na+ and K+.

Membrane potential refers to the separation of charges across the membrane. The equilibrium potential refers to the potential that exists when the net outward diffusion of an ion no longer occurs but is in equilibrium due to the balance between its electrical gradient and its concentration gradient. The separation of opposite charges across the plasma membrane. The Na+-K+ pump actively transports Na+ out and K+ into the cell (contribution 20% membrane potential). This maintains a higher ECF Na concentration and a higher ICF K+ concentration. K+ is the primary determinant of membrane potential because of its increased passive permeability across membrane. Membrane impermeable negatively charged large anionic proteins help to establish the charge differential across the membrane. The relatively large net diffusion of K+ to ECF establishes the membrane potential a -70 mV (contribution 80 % membrane potential). The lower membrane permeability of Na+ neutralizes the potential from the EK+ of -90 mV.

Differentiate between membrane potential and equilibrium potential. Now, differentiate between membrane permeability and the Na+-K+ pump in their respective roles for establishing resting membrane potential. What is the role of large anionic proteins inside the cell to establishing membrane potential?

Temporal summation occurs when one or more presynaptic neurons transmit impulses in rapid-fire order and waves of neurotransmitter release occur in quick succession. The first impulse produces a slight EPSP followed by addition EPSP impulses by subsequent impulses summing to threshold. Spatial summation occurs when the postsyanaptic neuron is stimulated by a large number of terminals form the same or different neurons at the same time which sum to threshold.

Differentiate between temporal and spatial summation.

Clotting of blood is a positive feedback response. For blood clotting the variable is patency of the vessel to transport blood the receptor/control center is simply the area of injury, and the effector is the cascade of events resulting in clotting. This is an extrinsic control. The body temperature regulation is a negative feedback response. Temperature is the variable and the control center is the brain and effectors as noted in the figure. This is an extrinsic control system.

Differentiate between the regulation of clotting blood after injury and maintaining core body temperature. First, identify for each "system" the type of feedback involved. And, in a generalized manner, or specific is you wish, discuss, diagram, and/or illustrate one of the two "systems." Make sure you identify the variable, the receptor/control center, and the effecter within your example system. Show the appropriate feedback. Oh, one final question, for the "system" you choose, is the regulation intrinsic or extrinsic?

Unidirectional propagation is a result of the absolute refractory period, the duration time following the initiation of an action potential in which a second action potential can not be generated. Thus, since an action potential initiates at the axon hillock signal propagation proceeds unidirectionally away from the hillock down the axon. The speed that an action potential can move along the axon is dependent upon the electrical resistance of the axon. The electrical resistance of the axon is determined by the diameter of the axon, with the larger diameter axon having a lower resistance (conduction velocity will be greater) than a smaller diameter axon. In axons that are myelinated, action potentials will occur at discrete points along the axon, known as the nodes of Ranvier, Thus, the action potential jumps from node to node (saltatory conduction). The resistance of the membrane under the insulative myelin sheath is great enough that there is only a small amount of current lost as it moves between nodes. Because the action potential is jumping from node to node, the speed of the action potential along the axon is greatly increased. Relative refractory period-Strong stimuli cause nerve impulses to be generated more often in a given time interval than do weak stimuli. Thus, stimulus intensity is coded for by the number of impulses generated per second, by frequency of impulse transmission, rather than by increases in the strength of the individual action potentials. This can only occur during relative prior to return to complete membrane potential.

Discuss why under normal physiological circumstances an action potential is unidirectional. Next, what determines the rate of action potential transmission along the axon. And, last, what enables discrimination between signal strength during action potential transmission.

However, regardless of the example you selected to discuss you needed to place in perspective the variable, receptor/control center, and effector....plus where feedback and what kind of feedback comes in.

Discuss, diagram, and/or illustrate one example of a physiological control system. Make sure you identify the variable, the receptor/control center, and the effecter within your example system. Also identify within the system the type of feedback involved.

No. Solutes according to Ficks Law will passively transport down their concentration gradient. Energy is required to concentrate a solute across a membrane against its concentration gradient. Fick's Law is passive and obeys the restrictions as detailed in..... Carrier mediated transport is dependent upon a carrier molecule in the plasma membrane which transports the substance across the plasma membrane. Characteristics of carrier mediated transport are specificity, saturation, and competition.

Do the transport processes regulated by Fick's Law require energy input from the cell? Why? When does a cell have to expend energy to transport a substance across its plasma membrane? Compare Fick's Law to carrier mediated transport.

At resting state all gated Na and K channels closed. During depolarization phase (a), Na gates are open but K channels remain closed. During repolarization, Na inactivation gates close (b) the Na channels and K channels open (c). During hyperpolarization (d) both gates of Na channels have closed, but K channels remain open. Return to resting state (e).

Draw an action potential diagram and explain the sequence of events of an action potential

An action potential proceeds down the afferent axon. Upon reaching the axonal terminal buds the action potential stimulates the influx of Ca into the axon. This results in the exocytosis of neurotransmitters into the synaptic cleft. Neurotransmitters diffuse to the efferent neuron where they bind to receptor gated ion channels resulting in an influx of Na into the efferent neuron which propagates the afferent signal to the efferent neuron.

Explain the process of how signaling between neurons occurs.

A. Scenario 1: No, because of the lack of temporal overlap the two potentials remain subthreshold, no temporal summation A. Scenario 2: No, because even though they can be summed (both potentials overlap temporally) the do not add to threshold potential One potential is excitatory and the other inhibitory, cancelling each other out One or both potentials are spaced beyond spatial overlap Both potentials are inhibitory Both potentials are excitatory but do not add up to threshold

Graded potentials control the initiation of an action potential. Remembering all you now know regarding graded potentials answer the following questions: For these questions assume a graded potential has to achieve a threshold potential (-55 mV) to initiate an action potential that the potential occurs in a 10 msec timeframe. A. Tell me if an action potential occurs AND explain your answer in no more than a single sentence Scenario 1- A single afferent neuron terminal bud fires resulting two postsynaptic potentials of 10 mV 30 msec apart. Scenario 2 -A single afferent neuron terminal bud fires resulting in two postsynaptic potentials, of 5 mV and the other of 9 mV both within 5 msec apart.

Because the action potential is an all or none response frequency of action potentials must be used todenote changes in signal strength. A greater frequency denotes greater signal strength a lesser frequencydenotes less signal strength. Therefore when the signal strength decreases this mean the number of actionpotentials proceeding down the PRESYNAPTIC axon per unit time decreases. For the POSTSYNAPTICneuron this means less graded potential because its magnitude can change. Every time an action potentialreaches the synapse it induces the release of neurotransmitters to signal the postsynaptic neuron.Because neruotransmitters are rapidly degraded as frequency of action potentials increase the rate ofneurotransmitter release is increased increasing the amount maintained in the synaptic cleft. As the signalstrength decreases this means reduced frequency of action potentials with less overall release ofneruotransmitters and thus lessor graded potentials.

How do action potentials in the presynaptic neuron communicate to a postsynaptic neuron achange in signal strength from a higher to lower signal strength? Be careful here your answer MUSTconsider both the presynaptic neuron and the postsynaptic neuron

Increase net signal strength through temporal summation. The first impulse produces a slight EPSP followed by addition EPSP impulses by subsequent impulses summing to threshold.

If an afferent axon is firing with increased frequency how will this likely impact an efferent neuron response?

Spatial summation occurs when the postsynaptic neuron is stimulated by a large number of terminals form the same or different neurons at the same time which sum to threshold.

If multiple afferent axons is firing in the same time frame with convergence on the efferent neuron

a. There would be no signal transmission across synaptic cleft and no neuron to neuron communication b. The Na/K pump would stop working. K and Na via their passive channels go toward their respective concentration equilibriums with a loss of membrane potential. AlSO ATP IS NECESSARY FOR NEUROTRANSMITTER RELEASE!!!! c. Na continues to flow into neuron, it becomes completely depolarized and unable to transmit sigal

In the neuron communication process, think about the effects of certain poisons/toxins. What would be the effect of the following: a. a poison that blocked neurotransmitter release b. a poison that blocked ATP generation c. a poison that inhibited the closure of sodium voltage gated channels/a poison that inhibited the degradation of neurotransmitter in the synaptic cleft

Your jerk your hand back away from fire.Reflex arc-The neural pathway involved in accomplishing a response that occurs automatically without conscious effort. Components and order of response- pain receptor, afferent pathway, integrating center (ineroneuron), efferent pathway, effector (muscles to jerk back)Your scream is delayed because the reflex arc is a separate branch occurring at the integrating center or interoneuron.

It is a crisp February night (actually its bloody cold) in Cook's Forest. You and some friends are lounging around a campfire enjoying the sounds of the night, the COLD fresh air, friendship, and of course beer. Earlier in the evening, you kicked off your shoes and socks to get more comfortable. Now, your tootsies are turning blue. Without thinking, you start to place one your feet over the burning embers. What happens next? What is this physiological response referred to? Describe the process. Beyond likely inebriation, why is your scream of intense pain delayed?

First, a reflex arc consists of an afferent neuron, intermediate (or interneuron) neuron and efferent neuron.The afferent and efferent neurons are in the peripheral nervous system while the intermediate is in thecentral nervous system. Second, disrupting the disruption in the myelin sheath results in greatly compromised rate of signaltransmission. Third, disrupting the Ca voltage gated channels stops the communication sequence within the afferentneuron by blocking the release of neurotransmitters to the intermediate neuron,Fourth, disrupting the Na voltage gated channels disrupts the sequence by inhibiting a conductive actionpotential sequence at the afferent neuron axon. Fifth, transmission would stop with the interneuron because signal conduction to the efferent neuron did notoccur.

Lets consider a reflex arc. First, what neurons comprise this relatively simple network andwhere is their distribution between the central and peripheral nervous system? Second, what wouldhappens to a communication sequence if there is a disruption in the myelin sheath? Third, what wouldhappen if Ca voltage gated channels were blocked an alternative poison? Fourth, What would happen if Navoltage gated channels were blocked by yet another poison? Fifth, what would if the threshold stimulus atthe axon hillock on the interneuron was not achieved?

Intitiation and propagation of action potentials would not occur in nerve fibers that have been treated with the anesthetic because blockage of Na+ channels would prevent the massive opening of voltage gated Na+ channels at the threshold potential. As a result, pain impulses would not be initiated and propagated to the brain and reach the level of conscious awareness.

Local anesthetics blocks Na+ channels. Explain how this prevents the transmission of pain impulses to the brain.

Lateral inhibition. Within a receptor field, the point stimulated most will have the greatest frequency ofaction potentials above baseline activity. This ensures transmission from these immediate area (say on theskin) whereas the area surrounding where the frequency is below some value will be inhibited in a lateralaspect to the higher frequency thus transmission will be stopped, in essence focusing the transmissionarea. This process allows for finer sensory area discrimination

Look at the palm of your hand. Take your pen/pencil, close your eyes; now touch the center ofyour palm, then touch the outer periphery in a couple of places. Now assuming that your entire palm is asingle receptor field, how does you nervous system discern or differentiate specific locations within thesingle receptor field and not just be restricted to only distinguishing palm or not?

Schwann cells. Signal transduction rates are controlled by saltatory conduction. Schwann cells literally wrap around specific aspects along the axon creating areas of insulation. The nodes of Ravier are the areas along the axon not covered by Schwann cells. Charge polarity changes progressing along the plasma membrane surface of the axon only occur at nodes of Ravier, skipping areas covered by Schwann cells. We can assume for this process that the movement of charges in the ICF between nodes is essentially instantaneous. Therefore, the effective length for transduction is ONLY the combined length of the nodes. By example, if nodes comprise 10 % of axon length then transduction speed is reduced by 90%.

Multiple sclerosis is an autoimmune disease where the body destroys the myelin sheath surrounding myelinated nerve fibers. With what cell is the myelin sheath associated? What is the physiological role provided by this cell and the myelin sheath in regard to nerve communication? What happens to nerve communication during multiple sclerosis?

Because only the postsynaptic neuron has cell surface neurotransmitter receptors

Neurons communicate to each other via presynaptic to post-synaptic transmission of chemical messengers. In consideration of this, answer the following questions.Why is the communication flow unidirectional from presynaptic to post-synaptic neuron?

Accommodation. Accommodation is the process where the eye controls the relative strength of the lens. When the circular shaped ciliary muscles are relaxed the overall diameter of the muscle group increases. This process results in a pulling force on the ligaments attached to the muscle group and to the lens which is suspended in the middle of the muscular circle. The applied force stretches the lens flattening it make it a weak convex shape. This is the default enabling long distance vision. The eye adjusts to short distance vision by inducing contraction of the muscle group relaxing the tension applied to the lens and it returns to its default more thick convex shape increasing its strength. This allows for convergence of divergent light rays entering the lens from the objects a relative short distance away.

Normally speaking, unlike those of us of slightly more advanced age and eyes that are beginning to wear out, the eye has the ability to focus light rights representing objects both near and far in the field of view. How is this accomplished? What is the process called and explain it. Your eye has the ability to focus light images representing light rays both parallel and diverging. How is this accomplished?

The terminal axon bud of the afferent neuron comes in close, but not physical, contact with the efferent neuron. An action potential is propagated down the axon to the bud where the electrical signal stimulates the release of neurotransmitters via exocytosis. These neurotransmitters diffuse across the synaptic cleft and bind to their receptors, thus eliciting a graded potential that will then have a regulatory effect on the efferent neuron. The nature of the effect will depend upon the nature of the postsynaptic potential, whether it is an EPSP or IPSP and its relative signal strength. In any case, this postsynaptic graded potential will control the transmission of any efferent action potential firing.

Outline, sketch or discuss how neurons communicate with each other.

You are suffering from Hyperopia or Farsightedness which happens when your eyeball is too short or the lens too weak. Uncorrected far source focused on retina with accommodation while near source focused behind retina even with accommodation. Accommodation is the autonomic function when the eye can alter its lens strength by contracting the ciliary muscle thus reducing the tensile stretching of the lens. When the tensile load is reduced the elastomeric nature of the lens results to is "fatter" stronger shape. To correct, a convex lens is needed to converges light rays prior to them reaching the eye. This now means that far distant light rays focus on the retina without accommodation and near source rays can focus with accomodation.

Over years and years, not a really long time looking back, your eye changes shape such that the lens strength is less than what it currently is. Some things are now blurry and out-of-focus while others remain in focus. Explain your clinical problem, and how to correct it. Make sure accommodation is included in your answer.

Na permeability is permeable during the absolutewhile K is permeable during both the absolute and inthe relative refractory periods. Na permeabilityprecedes K permeability such that it the Na voltagegates open at threshold then close at maximum +30mV representing peak of permeability. At +30 mV Kvoltage gates open then say open longer through thehyperpolarization phase of the action potential. Youmay discuss absolute and relative refractory periodsbut they are not necessary for full points. A figure likethis works too.

Please discuss the relative permeabilities of Na and K during an action potential. Please feel free to sketch me a graph of an action potential and indicate permeability changes during an action potential

A depolarization of the resting membrane potential is the result. Because the intracellular concentration ofK+ is reduced, the concentration gradient for K+ from the inside to the outside of the plasma membrane isalso reduced. Thus, the rate at which K+ diff use out of the cell is reduced, and a smaller charge differenceacross the plasma membrane is required to oppose the diffusion of the K+ out of the cell. Therefore, thepotential difference across the plasma membrane is reduced, and the cell is depolarized

Predict the consequence of a reduced intracellular K+ concentration on the resting membranepotential. Why?

a. Would depend if the membrane contains transport channels. If no, no transport, if yes as concentration difference goes up transport will increase along the differential gradient b. Rate of diffusion will increase down its concentration gradient. This is because O2 readily diffuses c. Increase in diffusion from side 1 to 2 d. Double diffusion rate assuming a concentration difference e. This will reduce CO2 diffusion rate.

Presume you have an artificial plasma membrane. For the following situations how is transport impacted? a-A concentration difference across the membrane for Na. b-Increase O2 concentration difference across membrane c-Increase the concentration of a fatty acid on side 1 while reducing it on the other side 2. d-Transport of Na assuming that increase the number of passive Na channels by 2 times per unit surface area. e-Tripling the thickness of the membrane on CO2transport.

1. They physically transfer the signal from the place at which it is received to some other part of the cell where the response is expected. 2. They amplify the signal received, making it stronger. 3.They distribute the signal so that it influences several processes in parallel; at any step in the pathway, the signal can diverge and be relayed to several different intracellular targets, creating branches in the flow and causing a complex response. 4. The signal can be modulated, regulated, by other possibly interfering factors prevailing inside or outside the cell.

Secondary messengers or intracellular signaling cascades provide for four critical functions? Please briefly, very briefly discuss two such functions.

SLOW DOWN During an action potential, Na+ enters and K+ leaves the cell. Repeated action potentials would eventually "run down" the Na+ and K+ concentration gradients were it not for the Na+-K+ pump returning the Na+ that entered back to the outside and the K+ that left back to the inside. Indeed, the rate of the pump activity is accelerated by the increase in both ICF Na+ and ECF K+ concentrations that occurs as a result of action potential activity, thus hastening the restoration of the concentration gradients. Therefore, as the concentration differences are decreased there is less work to be performed to restore concentration gradients therefore the pump slows down.

The rate at which the Na+-K+ pump operates is not constant but is controlled by a combined effect of changes in ICF Na+ concentration and ECF K+ concentration. Do you think a decrease in both ICF Na+ and ECF K+ concentrations would accelerate or slow down the Na+-K+ pump? What would be the benefit of this response?

Both forms of vesicular transport entail exocytosis. One type is the exocytosis of neurotransmitters to thesynaptic cleft to provide chemical signal transmission between the presynaptic (afferent) neuron and thepostsynaptic (efferent) cell. Communication distance is in the order of 50 nm so very short distance.Another type is the release of extracellular vesicles. They are released by essentially every cell in the bodyand can communicate not only locally but also systemically. Extracellular vesicles contain multiple signalingmolecules.

There are 2 types of vesicular transport that are involved in cell signaling discussed class. Pleasediscuss them paying special interest as to the communication distances within the body as well as definingwhat type of vesicular transport they entail.

No differences

There are only two cell types in the body capable of generating action potentials, neurons and muscle cells. Both receive presynaptic communication from a presynaptic neuron. What I want here is a discussion, in its simplest form, of the differences between neuron to neuron and neuron to muscle cell communication we have discussed to date.

They can communicate directly via the following-- desmasomes which provide mechanical coupling communication signaling between them such that cadherin protein linkers physically connect the two cells vial plaques allowing mechanical signals gap junctions which are interconnecting channels allowing chemical substances of small molecular weightto be exchanged between these cells without the signaling molecules entering the interstitial fluid paracrine secretion of signaling molecules from one of the cells that enter the interstitial environment tosignal the adjacent cell

Two adjacent cells have the ability to directly communicate with one another. Please describethree examples of direct communication between these two cells. Please limit your discussion to theimmediate surrounding environment of these cells

1. One potential is excitatory and the other inhibitory, cancelling each other out One or both potentials are spaced beyond spatial overlap Both potentials are inhibitory Both potentials are excitatory but do not add up to threshold 2. Both potentials are excitatory and sum to threshold. One is excitatory, the other inhibitory but sum is still to threshold

Two afferent neuron terminal buds fire resulting in two postsynaptic potentials essentially simultaneously. Tell me, in each of the following scenarios (multiple answers can be correct), the explanation for the indicated result. Result 1- No action potential results (give me two possible reasons, NOT just one) Result 2 - An action potential results

For the purposes of either potential the variables of surface area, molecular weight of ions and thethickness of the membrane are "fixed" therefore they do not change. Only permeability and concentrationdifference across the membrane effectively change. During membrane potential K is more passivelypermeable than Na by 50-75 times. Negative charged components inside and out are for this discussionnot transported. The K moves out down its concentration gradient and Na moves in down its concentrationgradient. Because their concentration gradients are similar it is permeability that affects transport acrossthe membrane. Therefore the membrane potential is primarily driven by greater loss of + ions from insidethe cell resulting in a potential of -70 mV.During an action potential, Na permeability precedes K permeability such that it the Na voltage gates openat threshold then close at maximum +30 mV representing peak of permeability. At +30 mV K voltage gatesopen then say open longer through the hyperpolarization phase of the action potential. The concentrationgradients are defined as for membrane potential.

Using Fick's Law, please differentiate between membrane potential and an action potential.Make sure in your answer you mention all the variables of Fick's law and their importance here. Make sureyou discuss how the tendency for passive Fick's driven transport to flatten the concentration gradient isovercome.

All are carrier mediated forms. Passive sodium and potassium gates involved in establishing membrane potential. Sodium and potassium pump involved in maintaining and reestablishing membrane potential requiring energy to pump against respective concentration gradients. This is the only transport that requires energy within this question. Sodium voltage gated channels and potassium gates involved in action potential. Chemical, electrical and mechanical gated channels for sodium involved in creation of graded potential. And one extra, Na chemical gated channels at post synaptic membrane.

What are the methods of cellular membrane transport related to signal transduction involving a neuron? Furthermore differentiate between them indicating what types of substances are transported by each method, and state whether each is a passive or active means of transport.

Memory is based not on individual cells but on a pathway of cells referred to as memory trace resulting from new synapses or existing synapses being modified to make transmission easier. The three different forms of memory are immediate, short-term and long-term.

What is the physical basis of memory and what are the different forms of memory

Action potentials are restricted to the axon hillock and axon, and serve to conduct an electrical signal down the length of a neuron. This is anatomically enabled due to voltage gated channels being restricted to these locations. Graded potentials occur on dendrites and soma of the neuron and are responsible for receiving communication from outside the neuron. In the case above, this means the afferent neuron.

What is the role of graded potentials and action potentials in neuron communication? Make sure to relate cell anatomy to function.

Graded potential. Both toward and away from threshold. EPSP is excitatory postsynaptic potentials that occur at excitatory synapses and move a postsynaptic neuron toward its threshold. IPSP is inhibitory postsynaptic potentials that occur at inhibitory synapses and move a postsynaptic neuron away from its threshold

What is the type of potential created at the immediate postsynaptic neuron? In relation to the postsynaptic neuron's resting membrane potential threshold in what direction to does the potential go, and if more that one direction is possible distinguish between them.

Action potentials are self-regenerating and because the axon plasma membrane surface is lined with Na+voltage gates the action potential proceeds from its initiation down to the terminal button. Direction ismaintained because of absolute refractory period insures direction is maintained away from axon hillock.

When a graded potential initiates threshold firing at the axon hillock, why does the resulting action potential proceed to the axon terminal buttons? Why does it not go back upon itself?

The dialysis fluid should not contain urea. Bc urea is small, it will diffuse thru the dialysis membrane from area of high concentration (blood) to area of low concentration (dialysis fluid). To prevent osmosis, the dialysis fluid should have an osmotic concentration similar to blood plasma's, but w/ higher concentrations of solutes such as bicarbonate ions or glucose. As urea diffuses into the dialysis fluid, glucose and bicarbonate diffuse into the blood; as a result the solute concentrations remain in balance and no osmosis occurs.

When kidneys are failing, dialysis is used to filter blood to remove wastes. What should the composition of dialysis fluid be for it remove urea (a small molecule) without changing the blood volume (removing water from the blood?

Active transport. Leveling off of the curve designates saturation of a carrier molecule, so carrier-mediated transport is involved. The graph indicates that active transport is being utilized instead of facilitated diffusion because the concentration of the substance in the intracellular fluid is greater than the concentration in the extracellular fluid is greater than the concentration in the extracellular fluid at all points until transport maximum is reached. Thus, the substance is being moved against a concentration gradient, so active transport must be the method of transport used.

Which of the following transport methods is being utilized to transfer the substance INTO the cell- diffusion down a concentration gradient; facilitated diffusion; active transport; it is impossible to tell with the information provided. WHY?

Q = (C*P*A)/(MW*X) the magnitude or steepness of the concentration gradient; as it increases, it increases diffusion rate the permeability of the membrane to the substance; as it increases, it increases diffusion rate the surface area of the membrane across which diffusion is taking place; increase --> increases diffusion rate the molecular weight of the substance; increase --> decreases diffusion rate the distance through which diffusion must take place; increase -->decreases diffusion rate

Write out Fick's Law. Define how the various components of Ficks Law regulate diffusion rate across a porous membrane.

With cyanide poisoning, the cellular activities that depend on ATP expenditure could not continue, such as synthesis of new chemical compounds, membrane transport, and mechanical work. The resultant inability of the heart to pump blood and failure of the respiratory muscles to accomplish breathing would lead to imminent death.

You're a rookie detective investigating your first murder case. From the medical examiner's report you know that death was caused by cyanide poisoning. What was the mechanism of action of cyanide?