Action Potential Essay Example for Free

Action Potential Essay What opens first in response to a threshold stimulus? Voltage Gated (activation gates) Na+ channels open and Na+ diffuses in the cytoplasm What characterizes depolarization, 1st phase of action potential? Membrane changes from a negative value to a positive value What characterizes repolarization, 2nd phase of action potential? Once the membrane depolarizes to a peak value of 30+, it repolarizes to to its negative resting value of -70 What event triggers the generation of an action potential? The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV. ( This is the minimum value required to open enough voltage-gated Na+ channels so that depolarization is irreversible.) What is the first change to occur in response to a threshold stimulus? Voltage-gated Na+ channels change shape, and their activation gates open Resting State All gated Na+ and K+ channels are closed Step 2 Depolarization; Na+ Channels Open During the depolarization phase of the action potential, open Na+ channels allow Na+ ions to diffuse into the cell. This inward movement of positive charge makes the membrane potential more positive (less negative). The depolarization phase is a positive feedback cycle where open Na+ channels cause depolarization, which in turn causes more voltage-gated Na+ channels to open. Step 3 Repolarization; Na+ channels are inactivating and K+ Channels Open Step 4 Hyperpolarization; Some K+ channels remain open and Na+ channels reset How many gates/states do voltage gated Na+ channels have? two gates and three states Closed Na+ at the resting state, no Na+ enters the cell through them Opened Na+ opened by depolariztion, allowing Na+ to enter the cell Inactivated channels automatically blocked by inactivation gates soon after they open How many gates/states do voltage gated K+ channels have? one gate, two states Closed K+ at the resting state, no K+ leaves Opened K+ at depolarization, after delay, allowing K+ to leave Why is an action potential self-generating? depolarizing currents established by the influx of Na+ flow down the axon and trigger an action potential at the next segment The Na+ diffusing into the axon during the first phase of the action potential creates a depolarizing current that brings the next segment, or node, of the axon to threshold. Why does regeneration of the action potential occur in one direction, rather than in two directions? The inactivation gates of voltage-gated Na+ channels close in the node, or segment, that has just fired an action potential At the peak of the depolarization phase of the action potential, the inactivation gates close. Thus, the voltage-gated Na+ channels become absolutely refractory to another depolarizing stimulus. What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization? Inactivation gates of voltage-gated Na+ channels close, while activation gates of voltage-gated K+ channels open Closing of voltage-gated channels is time dependent. Typically, the inactivation gates of voltage-gated Na+ channels close about a millisecond after the activation gates open. At the same time, the activation gates of voltage-gated K+ channels open. What marks the end of the depolarization phase? As voltage-gated Na+ channels begin to inactivate, the membrane potential stops becoming more positive This marks the end of the depolarization phase of the action potential. Then, as voltage-gated K+ channels open, K+ ions rush out of the neuron, following their electrochemical gradient. This exit of positively-charged ions causes the interior of the cell to become more negative, repolarizing the membrane. The repolarization phase of the action potential, where voltage becomes more negative after the +30mV peak, is caused primarily by __________. The opening of voltage-gated K+ channels allows K+ ions to exit the cell, repolarizing the membrane. In other words, the exit of K+ ions makes the membrane potential more negative. K+ also exits through leakage channels during this phase because leakage channels are always active. However, most of the membrane permeability to K+ during this phase is due to voltage-gated channels. Voltage-gated K+ channels make the action potential more brief than it would otherwise be if only leakage channels were available to repolarize the membrane. During an action potential, hyperpolarization beyond (more negative to) the resting membrane potential is primarily due to __________. The large number of voltage-gated K+ channels opening during the repolarization phase quickly makes the membrane potential more negative as positively-charged K+ ions leave the cell. K+ ions continue to leave through open channels as the membrane potential passes (becomes more negative than) the resting potential. This hyperpolarization phase of the action potential is therefore due to K+ ions diffusing through voltage-gated K+ channels. The membrane potential remains more negative than the resting potential until voltage-gated K+ channels close. This period of hyperpolarization is important in relieving voltage-gated Na+ channels from inactivation, readying them for another action potential. During the hyperpolarization phase of the action potential, when the membrane potential is more negative than the resting membrane potential, what happens to voltage-gated ion channels? Voltage-gated K+ channels are opened by depolarization. This means that as the membrane potential repolarizes and then hyperpolarizes, these K+ channels close. With the closing of voltage-gated K+ channels, the membrane potential returns to the resting membrane potential via leakage channel activity. Resetting voltage-gated Na+ channels to the closed (but not inactivated) state prepares them for the next action potential. During the hyperpolarization phase of the action potential, voltage eventually returns to the resting membrane potential. What processes are primarily responsible for this return to the resting membrane potential? Voltage-gated K+ channels close. K+ and Na+ diffuse through leakage channels.

Sexual Predators :: Exploratory Essays Research Papers

Sexual Predators Childhood is supposed to be a time of discovery and play, not abuse. Was there ever such a world? Sexual predators have been lurking this planet for decades; now they're being marked for life because of there actions. Neighbors and the home towns of sexual predators are being alerted of their crimes and whereabouts by local police. Such towns have responded by putting up signs in their town, "CHILD MOLESTER TWO DOORS DOWN" (Popkin, pg 73). Others responded by burning or flooding their new neighbors out (Popkin). What did these convicted criminals do to deserve such punishment? They violated the most precious living creature on this planet, a child. Communities definitely have a right to know that a dangerous child molester is moving to their town. Child molesters have been convicted, charged and sentenced for their crimes for many years. Maybe people already have one as their next door neighbor. Do people really know the people they live by so well, that they would leave their own child with them? Also, if they had a legal right to, would they check out their neighbor's history at the police office, or trust them? In the summer of 1994, seven-year-old Megan Kanka was kidnapped, raped, then killed by convicted child molester Jesse Timmendequas. Her story started many parents to question the safety of their own children. The outraged community was never informed that Timmendequas and two other convicted child abusers had moved in across the street from Megan (Megan Kanka). Megan's death lit her parents' fires to do something about notifying communities of convicted child molesters. They began to lobby for "Megan's Law", a law that would require immediate community notification of convicted child abusers, who were living in their area (Popkin). Some critics contend that the law is unconstitutional because it adds additional punishment to offenders (Megan's Unfinished Legacy). Other critics say that it would drive predators into hiding and away from seeking counsel. Child molester Scott Murphy said, "Without counseling, you're the same person when you go to jail as when you get out"(Popkin, pg.73). Before the passing of the law, a group of offenders appealed the judges' ruling that the notification was unconstitutional because it's intended to protect children, not further punish criminals (Megan's Unfinished Legacy). The law was passed. The biggest problem that police officers face is determining which released sex offenders are the most dangerous.

Hamlet – Hero or Villain

Hamlet comes across as both a hero and a villain throughout ‘Hamlet’ at different intervals. His loyalty, morality, honesty and popularity are certainly heroic traits however one can’t deny his villainous ways in his dealings with Ophelia, his killing of Polonius and most importantly his delaying of killing Claudius. Hamlet is full of faults yet full of honourable intentions. His negative qualities are slim compared to his heroic qualities therefore I believe Hamlet to be a hero, a â€Å"prince among men†. When we first meet Hamlet, he is dressed all in black and conveys all the â€Å"moods, forms and shapes of grief†.This depression is caused by his father’s recent death. Gertrude, his mother and Claudius, his uncle have noticed however Hamlet’s melancholy is much more intense than he is letting on â€Å"too too sullied flesh would melt†. He’s unable to forget his father even when all those around him have resumed their m erry lives. â€Å"I shall not look upon his like again†. This demonstrates the loyal side of the prince. His grief is further intensified by the cold-hearted actions of his mother. Gertrude married her brother in law, Claudius â€Å"within a month† of her husband’s death.Hamlet is unable to understand her disloyalty â€Å"a beast that wants discourse of reason would have mourned longer†. He believes he is living in a society with no standards and so becomes disillusioned with life â€Å"how weary, stale flat and unprofitable seem to me all the uses of this world†. His loyalty is certainly a heroic trait. The anger he felt towards his mother had a very a negative effect on a Hamlet. He began to feel anger at women as a whole which leads me to his villainous dealings with Ophelia. Hamlet feels neglected when Ophelia as ordered by her father, Polonius repels his letters.He condemns all women with the criticism of moral fickleness â€Å"fraility thy n ame is woman†. He hates Ophelia one moment and longs to engage in sexual intimacy with her the next. â€Å"Lie between maids’ legs†. He mistreats her with heartless and demeaning behaviour. In the nunnery scene he denies he ever loved her and tells her â€Å"get thee to a nunnery†. His inconsistent treating of Ophelia eventually drives her to insanity. The actual recognition of his love for Ophelia can only come when Hamlet realizes that she is dead, and free from her tainted womanly trappings â€Å"I lov’d Ophelia†.This is without doubt one of the most villainous qualities of Hamlet. His cruel treating of Ophelia however can also be seen as a heroic trait. He is honest about his feelings towards her. He is honest throughout the whole play, which is rare in ‘Hamlet’ as most of the characters live their lives through deception. He doesn’t once hide his hatred of Claudius â€Å"a little more than kin and less than kind†, he is also honest of his disliking of Polonius when he says his words have no substance â€Å"words words word†.He eventually tells his mother how disgusted he is with her marriage â€Å"O shame, where is thy blush? † and admits he treated her with cruelty â€Å"I must be cruel only to be kind†. He is even honest about his own inaction as he â€Å"lets all sleep†. His honesty throughout the play is admirable and only further proves him to be a hero. He is without doubt a man of high morals which is an important feature of a hero. He agrees to avenge his father even though he almost crushed with the burden. â€Å"oh cursed spite that ever I was born to set it right†.It is clear that he does not want to murder but accepts the task nonetheless â€Å"I have sworn’t†. He also apologises to Laertes for killing Polonius and asks for forgiveness. â€Å"give me your pardon, sir I have done you wrong†. His moral character is what I m ost admire about Hamlet. However Hamlet’s bravery for accepting the burden of revenge only heightens our awareness of his most negative quality, inaction. Faced with evidence that his uncle murdered his father, Hamlet becomes obsessed with proving his uncle’s guilt.He delays the moment of revenge for as long as he possibly can. He even passes up the perfect chance to kill Claudius in the courtyard when he is praying claiming if he kills him now he is only sending him to heaven. â€Å"this is hire and salary, not revenge†. Hamlet is aware of his inaction and is very self-critical of it. He admires the player’s passion in the play and become annoyed at himself for being â€Å"unpregnant of my cause†. He is made further aware of his inaction when the young Fortinbras fights for land â€Å"that had nothing in but the name† while he â€Å"lets all sleep†.His procrastination is his biggest fault and is his ultimate downfall in the play. Ina ction is certainly not a heroic characteristic. After Hamlet returns from England he is a changed man. He tells how Horatio how â€Å"there’s a divinity that shapes our ends†. It is becoming clear that Hamlet now sees the role of avenger in a different light than he did earlier in the play. As a true hero he is conscious of the fact that he is acting as an agent of justice. This new attitude remains with Hamlet right through to the play’s conclusion.Claudius invites him to engage in a duel with Laertes and Hamlet freely embraces the challenge. Hamlet seems to be more self-confident about his own ability to take clear, effective action. We are given the picture of a noble and fine young man in the concluding scenes. He finally gets revenge on Claudius however is stabbed by Laertes by doing so. A true hero who sacrifices himself to bring justice and honesty back to the state of Denmark, even his enemy Fortinbras admits he would have â€Å"proved most royal† for the throne.Hamlet is a truly much loved prince who possesses a vast degree of human virtue and ability and whose death is not only tragic but extremely noble. His villainous qualities, however strong in the beginning, truly evaporate as the play concludes. An honest, loyal, brave and moral man, there is no doubt that Hamlet is a hero. I’d trust him to rule my country any time! A hero is defined in the oxford English dictionary as â€Å"a man, often of divine ancestry, who is endowed with great courage and strength, celebrated for his bold exploits. † You can’t deny it’s the perfect description of Hamlet!

Hume s Paradox And The Standard Of Taste - 1527 Words

Additionally, about Hume’s paradox, â€Å"if we wish to ascertain the standard of taste, we should observe those people who are expert in adjusting themselves to the aesthetic situation and in bracketing intrusive circumstances when they respond to artworks,† (Carroll). Not every individual is knowledgeable in this manner, in fact, there are quite a few that are. Therefore, Hume later states â€Å"thus, through the principles of taste be universal, and, nearly, if not entirely the same in all men; yet few are qualified to give judgment on any work of art, or establish their own sentiment as the standard of beauty,† (Hume 109). If the critic allows bias to enter his or her consciousness while providing judgment, that individual is not qualified for the task. When critics use their personal feelings to discern one work of art from another, a standard of taste is established as well. These specific critics have distinguishable characteristics as follows: a â€Å"st rong sense, united to delicate sentiment, improved by practice, perfected by comparison, and cleared of all prejudice, can alone entitle critics to this valuable character; and the joint verdict of such, wherever they are to be found, is the true standard of taste and beauty,† (Hume 109). This idea follows the idea that beauty is a feeling rather than a descriptive term as well. Of the Standard of Taste provides the notion that the feeling of pleasure is based on praise. Hume uses his paradox to explore the feeling beauty capturesShow MoreRelatedDecision Theory: a Brief Introduction28334 Words   |  114 Pagesdecision-making.........................................19 3.6 Numerical representation .............................................................20 3.7 Using utilities in decision-making ...............................................21 4. The standard representation of individual decisions ................................23 4.1 Alternatives ........................ ..........................................................23 4.2 Outcomes and states of nature ...................................Read MoreCleanth Brookss Essay Irony as a Principle of Structure9125 Words   |  37 Pagesquite haphazardly. Its concentration on the epic and dramatic forms also seems somewhat irrelevant to the contemporary Roman literary scene of his day. However, the lively autobiographical approach of the â€Å"Ars Poetica† and its expression of personal standards in literature make it unique as a work of criticism in the ancient world.A few quotes in particular from the work have passed into common literary parlance, including: â€Å"in medias res† (literally, â€Å"in the middle of things†, describing a popular narrativeRead MoreOrganisational Behavioure23151 Words   |  93 PagesROBBMC08.QXD.0132431521 12/15/05 12:25 PM Page 258 Reason is, and ought only to be the slave of the passions, and can never pretend to any other office than to serve and obey them. — David Hume Emotions and Moods After reading this chapter, you should be able to: 1 Differentiate emotions from moods. 5 2 Discuss the different aspects of emotions. Discuss the impact emotional labor has on employees. 6 Identify the sources of emotions and moods. DiscussRead MoreStephen P. Robbins Timothy A. Judge (2011) Organizational Behaviour 15th Edition New Jersey: Prentice Hall393164 Words   |  1573 Pagesand permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. To obtain permission(s) to use material from this work, please submit a written request to Pearson Education, Inc., Permissions Department, One Lake Street, Upper Saddle River, New Jersey 07458, or you may fax your request to 201-236-3290. Many of the designations by manufacturers