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Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
Pinel basics ch03
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Pinel basics ch03

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  • 1. Chapter 3 Neural Activity and How to Study It How Neurons Work <ul><li>This multimedia product and its contents are protected under copyright law. The following are prohibited by law: </li></ul><ul><li>any public performance or display, including transmission of any image over a network; </li></ul><ul><li>preparation of any derivative work, including the extraction, in whole or in part, of any images; </li></ul><ul><li>any rental, lease, or lending of the program. </li></ul>
  • 2. Parkinson’s Disease <ul><li>The case of Mr. d’Orta demonstrates the importance of understanding how neurons work </li></ul><ul><li>A lack of dopamine underlies this movement disorder, but it can’t be treated with dopamine </li></ul><ul><li>Why not? </li></ul>
  • 3. The Neuron’s Resting Membrane Potential <ul><li>Inside of the neuron is negative with respect to the outside </li></ul><ul><li>Resting membrane potential is about -70mV </li></ul><ul><li>Membrane is polarized, it carries a charge </li></ul><ul><li>Why? </li></ul>
  • 4. Ionic Basis of the Resting Potential <ul><li>Ions, charged particles, are unevenly distributed </li></ul><ul><li>Sodium, potassium, and chloride ions are the main ones to be concerned with </li></ul><ul><li>There are more negative charges inside the neuron than there are outside </li></ul>
  • 5. Why is there greater negative charge inside? <ul><li>Two properties of the neural membrane contribute to the difference </li></ul><ul><ul><li>Differential permeability – some substances pass through the membrane more easily than others, moving through ion channels that can open and close </li></ul></ul><ul><ul><li>Sodium potassium pumps – move positively charged sodium ions out, while moving fewer positively charged potassium ions in </li></ul></ul>
  • 6. Sodium <ul><li>There is great pressure on sodium to move into the resting neuron </li></ul><ul><li>Positively charged sodium is attracted to the internal negative charge </li></ul><ul><li>Random motion – as there is more sodium out than in, sodium tends to leak in </li></ul>
  • 7. <ul><li>Figure 3.1 (NEW) </li></ul>
  • 8. Postsynaptic Potentials and Action Potentials <ul><li>Neurotransmitters bind at postsynaptic receptors </li></ul><ul><li>These chemical messengers bind and cause electrical changes </li></ul><ul><ul><li>Depolarizations (making the membrane potential less negative) </li></ul></ul><ul><ul><li>Hyperpolarizations (making the membrane potential more negative) </li></ul></ul>
  • 9. Postsynaptic Potentials (PSPs) <ul><li>Postsynaptic depolarizations = Excitatory PSPs (EPSPs) </li></ul><ul><li>Postsynaptic hyperpolarizations = Inhibitory PSPs (IPSPs) </li></ul><ul><li>EPSPs make it more likely a neuron will fire, IPSPs make it less likely </li></ul><ul><li>PSPs are graded potentials – their size varies </li></ul>
  • 10. EPSPs and IPSPs <ul><li>Travel passively from their site of origination </li></ul><ul><li>Decremental – they get smaller as they travel </li></ul><ul><li>1 EPSP typically will not suffice to cause a neuron to “fire” and release neurotransmitter – summation is needed </li></ul>
  • 11. Integration of PSPs and Generation of Action Potentials (APs) <ul><li>In order to generate an AP (or “fire”), the threshold of activation must be reached </li></ul><ul><li>Integration of IPSPs and EPSPs must result in a potential of about -65mV in order to generate an AP </li></ul>
  • 12. Integration <ul><li>Adding or combining a number of individual signals into one overall signal </li></ul><ul><li>Temporal summation – integration of events happening at different times </li></ul><ul><li>Spatial - integration of events happening at different places </li></ul>
  • 13. What type of summation occurs when: <ul><li>One neuron fires rapidly? </li></ul><ul><li>Multiple neurons fire at the same time? </li></ul><ul><li>Several neurons fire repeatedly? </li></ul><ul><li>Both temporal and spatial summation occur simultaneously </li></ul>
  • 14.  
  • 15.  
  • 16. The Action Potential <ul><li>All-or-none, when threshold is reached the neuron “fires” and the action potential either occurs or it does not </li></ul><ul><li>Like a gun, it either fires or it does not </li></ul>
  • 17. Sodium Ions and Action Potentials <ul><li>When summation results in the threshold of excitation (-65mV) being reached, voltage-activated sodium channels open and sodium rushes in </li></ul><ul><li>Remember, at rest, all forces act to move sodium into the cell </li></ul><ul><li>Membrane potential moves from -70 to about +50mV, a considerable depolarization </li></ul>
  • 18. <ul><li>Figure 3.5 (4.6) </li></ul>
  • 19. Refractory Periods <ul><li>Absolute – impossible to initiate another action potential </li></ul><ul><li>Relative – harder to initiate another action potential </li></ul><ul><li>Prevent the backwards movement of APs and limit the rate of firing </li></ul>
  • 20. Axonal Conduction of Action Potentials (APs) <ul><li>The AP travels passively along the axonal membrane until it reaches an area with voltage-gated sodium channels </li></ul><ul><li>Opening sodium channels is an active process that then leads to a new action potential </li></ul><ul><li>This new action potential then travels passively to the next area of voltage-gated sodium channels </li></ul><ul><li>This process is repeated again and again </li></ul>
  • 21. PSPs Vs Action Potentials (APs) <ul><li>EPSPs/IPSPs </li></ul><ul><li>Decremental </li></ul><ul><li>Fast </li></ul><ul><li>Passive (energy is not used) </li></ul><ul><li>Action Potentials </li></ul><ul><li>Nondecremental </li></ul><ul><li>Conducted more slowly than PSPs </li></ul><ul><li>Passive and active </li></ul>
  • 22. Conduction in Myelinated Axons <ul><li>Passive movement of AP within myelinated portions occurs instantly </li></ul><ul><li>Nodes of Ranvier (unmyelinated) </li></ul><ul><ul><li>Where ion channels are found </li></ul></ul><ul><ul><li>Where full AP is seen </li></ul></ul><ul><ul><li>AP appears to jump from node to node </li></ul></ul><ul><ul><ul><li>Saltatory conduction </li></ul></ul></ul>
  • 23. Conduction in Neurons without Axons <ul><li>Many neurons in mammalian brains do not have axons </li></ul><ul><li>Neural conduction is typically by graded, decrementally conducted potentials </li></ul>
  • 24. Structure of Synapses <ul><li>Most common </li></ul><ul><ul><li>Axodendritic – axons on dendrites </li></ul></ul><ul><ul><li>Axosomatic – axons on cell bodies </li></ul></ul><ul><li>Directed – release and binding sites are close </li></ul><ul><li>Nondirected – release and binding sites are at some distance </li></ul>
  • 25. Synthesis and Transport of Neurotransmitter (NT) Molecules <ul><li>Small - synthesized in the terminal button and packaged in synaptic vesicles </li></ul><ul><li>Large - assembled in the cell body, packaged in vesicles, and then transported to the axon terminal </li></ul><ul><ul><li>Peptides – chains of amino acids </li></ul></ul><ul><li>Coexistence – many neurons contain both small-molecule and large-molecule NT </li></ul>
  • 26. Release of NT Molecules <ul><li>Exocytosis – the process of NT release </li></ul><ul><li>The arrival of an AP at the terminal opens voltage-activated calcium channels </li></ul><ul><li>The entry of calcium causes vesicles to fuse with the terminal membrane and release their contents </li></ul>
  • 27. Activation of Receptors by NT <ul><li>Released NT produces signals in postsynaptic neurons by binding to receptors </li></ul><ul><li>Receptors are specific for a given NT </li></ul><ul><li>Ligand – a molecule that binds to another. </li></ul><ul><li>A NT is a ligand of its receptor </li></ul>
  • 28. Receptors <ul><li>There are multiple receptor types for a given NT </li></ul><ul><li>Ionotropic receptors – associated with ligand-activated ion channels </li></ul><ul><li>Metabotropic receptors – associated with signal proteins and G proteins </li></ul>
  • 29. Ionotropic Receptors <ul><li>NT binds and an associated ion channel opens or closes, causing a PSP </li></ul><ul><li>If sodium channels are opened, for example, an EPSP occurs due to the entry of sodium </li></ul>
  • 30. Metabotropic Receptors <ul><li>Effects are slower, longer-lasting, more diffuse, and more varied </li></ul><ul><li>NT (1 st messenger) binds > G protein subunit breaks away > ion channel opened/closed OR a 2 nd messenger is synthesized > 2 nd messengers may have a wide variety of effects </li></ul>
  • 31.  
  • 32. Autoreceptors <ul><li>Metabotropic receptors </li></ul><ul><ul><li>Bind to their neuron’s own NT molecules </li></ul></ul><ul><ul><li>Located on the presynaptic membrane </li></ul></ul><ul><li>Usually monitor the number of neurotransmitter molecules on the synapse </li></ul>
  • 33. Termination of NT Effects <ul><li>As long as NT is in the synapse, it is active – activity must somehow be turned off </li></ul><ul><li>Reuptake – scoop up and recycle NT </li></ul><ul><li>Enzymatic degradation – a NT is broken down by enzymes </li></ul><ul><ul><li>Example - acetylcholinesterase </li></ul></ul>
  • 34. The Neurotransmitters <ul><li>Four classes of small-molecule NT </li></ul><ul><li>One large-molecule variety – peptides or neuropeptides </li></ul><ul><li>Most NT produce either excitation or inhibition, but some may do both by having different effects at different receptor subtypes </li></ul>
  • 35. Small-molecule Neurotransmitters <ul><li>Amino acids – the building blocks of proteins </li></ul><ul><li>Monoamines – all synthesized from a single amino acid </li></ul><ul><li>Soluble gases </li></ul><ul><li>Acetylcholine (ACh) – activity terminated by enzymatic degradation </li></ul>
  • 36. Amino Acid Neurotransmitters <ul><li>Usually found at fast-acting directed synapses in the CNS </li></ul><ul><li>Glutamate – Most prevalent excitatory neurotransmitter in the CNS </li></ul><ul><li>GABA – </li></ul><ul><ul><li>synthesized from glutamate </li></ul></ul><ul><ul><li>Most prevalent inhibitory NT in the CNS </li></ul></ul><ul><li>Aspartate and glycine </li></ul>
  • 37. Monoamines <ul><li>Effects tend to be diffuse </li></ul><ul><li>Catecholamines – synthesized from tyrosine </li></ul><ul><ul><li>Dopamine </li></ul></ul><ul><ul><li>Norepinephrine </li></ul></ul><ul><ul><li>Epinephrine </li></ul></ul><ul><li>Indolamines – synthesized from tryptophan </li></ul><ul><ul><li>Serotonin </li></ul></ul>
  • 38. Soluble-Gases and ACh <ul><li>Soluble gases – exist only briefly </li></ul><ul><ul><li>Nitric oxide and carbon monoxide </li></ul></ul><ul><ul><li>Retrograde transmission – backwards communication </li></ul></ul><ul><li>Acetylcholine (Ach) </li></ul><ul><ul><li>Acetyl group + choline </li></ul></ul><ul><ul><li>Neuromuscular junction </li></ul></ul>
  • 39. Neuropeptides <ul><li>Large molecules, close to 100 identified </li></ul><ul><li>Example – endorphins </li></ul><ul><ul><li>“ Endogenous opiates” </li></ul></ul><ul><ul><li>Produce analgesia (pain suppression) </li></ul></ul><ul><ul><li>Receptors were identified before the natural ligand was </li></ul></ul>
  • 40. How Biopsychologists Study the Brain <ul><li>Stereotaxic surgery </li></ul><ul><li>Conventional, lesion, stimulation, and recording methods </li></ul><ul><li>Pharmacological methods </li></ul><ul><li>Brain imaging </li></ul><ul><li>Genetic engineering </li></ul>
  • 41. Stereotaxic Surgery <ul><li>Used to position experimental devices within the brain </li></ul><ul><li>Stereotaxic atlas – provides coordinates for locating structures within the brain </li></ul><ul><li>Bregma – a point on the top of the skull often used as a reference point </li></ul><ul><li>Sterotaxic instrument – used to hold head steady and guide the device to be inserted </li></ul>
  • 42.  
  • 43. Lesion Methods <ul><li>Lesion (or destroy) a structure to observe the effect on behavior </li></ul><ul><li>Electrolytic lesion – electrical current used to destroy the target structure </li></ul><ul><li>Aspiration lesions – suction - cortex </li></ul><ul><li>Knife cuts – may damage surrounding area </li></ul>
  • 44.  
  • 45. Stimulation Methods <ul><li>Conventional methods involve using brain stimulation to determine the effects of a given brain structure </li></ul><ul><li>Current is delivered used a permanently implanted electrode </li></ul><ul><li>Rarely used in humans </li></ul>
  • 46. Recording Methods <ul><li>Unit recording – recording the activity of individual neurons </li></ul><ul><li>Multiple-unit recording – recording the overall firing rate of many neurons in an area </li></ul><ul><li>EEG – electrodes on the scalp record the difference between 2 large electrodes </li></ul>
  • 47.  
  • 48. Pharmacological Methods <ul><li>Many drugs act to alter NT activity </li></ul><ul><li>Agonists – increase or facilitate </li></ul><ul><li>Antagonists – decrease or inhibit </li></ul><ul><li>Drugs may act to alter NT activity at any point, from synthesis to termination </li></ul>
  • 49.  
  • 50.  
  • 51. Agonist - Example <ul><li>Cocaine - catecholamine agonist </li></ul><ul><li>Blocks reuptake – preventing the activity of the neurotransmitter from being “turned off” </li></ul><ul><li>Cocaine causes dopamine and norepinephrine to remain active in the synapse for a longer period of time </li></ul>
  • 52. Acetylcholine Antagonists <ul><li>Curare – Binds and blocks nicotinic receptors, the ionotropic receptors at the neuromuscular junction </li></ul><ul><ul><li>Causes paralysis </li></ul></ul><ul><li>Botox – Blocks release of acetylcholine at the neuromuscular junction </li></ul><ul><ul><li>A deadly poison </li></ul></ul><ul><ul><li>Minute doses at specific places, however, has medical and cosmetic uses </li></ul></ul>
  • 53. Selective Chemical Lesions <ul><li>Neural poisons (neurotoxins) selectively target specific nervous system components </li></ul><ul><li>Kainic acid – destroys cell bodies </li></ul><ul><li>6-hydroxydopamine (6-OHDA) – destroys noradrenergic and dopaminergic neurons </li></ul>
  • 54. Brain Imaging <ul><li>Contrast X-Rays – inject something that absorbs X-rays less or more than surrounding tissue </li></ul><ul><ul><li>Cerebral angiography </li></ul></ul><ul><li>X-Ray Computed Tomography (CT) </li></ul><ul><ul><li>2-D images combined to create a 3-D one </li></ul></ul><ul><li>Magnetic Resonance Imaging (MRI) </li></ul><ul><ul><li>Produces 3-D images with high spatial resolution </li></ul></ul>
  • 55. Brain Imaging <ul><li>Positron Emission Tomography (PET) </li></ul><ul><ul><li>Inject radioactive 2-DG </li></ul></ul><ul><li>Functional MRI (fMRI) </li></ul><ul><ul><li>Visualizing oxygen flow in the brain </li></ul></ul><ul><ul><li>Currently the predominant brain recording technique of cognitive neuroscience </li></ul></ul>
  • 56. fMRI Vs PET <ul><li>Nothing injected. </li></ul><ul><li>Provides both structural and functional information in one image </li></ul><ul><li>Spatial resolution is better than with PET </li></ul><ul><li>Can create 3-D images of activity over the entire brain </li></ul>
  • 57. Weaknesses of fMRI <ul><li>To create an fMRI image, brain activity from many subjects is needed and there are differences among people </li></ul><ul><li>Not able to detect small areas of brain activity </li></ul><ul><li>Only infers neural activity from changes in blood flow </li></ul>
  • 58. Genetic Engineering <ul><li>Gene knockout techniques </li></ul><ul><ul><li>Subjects missing a given gene can provide insight into what the gene controls </li></ul></ul><ul><ul><li>Difficult to interpret results – most behavior is controlled by many genes and removing one gene may alter the expression of others </li></ul></ul><ul><li>Gene replacement techniques </li></ul><ul><li>Both are currently being intensely studied </li></ul>

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