The Neuron

The Neuron: Part I

Biological Psychology Biopsychology/Psychobiology Branch of psychology that is concerned with the links between biology and behaviorBehavior GeneticsEvolutionary PsychologyNeuroscience: specifically focuses on the study of the brain and nervous systemBehavioral Neuroscientists Neuropsychologists

Nervous SystemElectrochemical communication system of the bodyNeuron: basic building block of the nervous systemNerve: bundles of neurons Brain contains 100 billion neuronsIf each neuron was a second, it would take over 3,170 years to tick off your neurons

Types of Neurons Sensory Neurons (afferent): carry messages from the tissues/sense organs inward to the brain and spinal cordMotor Neurons (efferent): carry messages from the spinal cord/brain to the muscles/glands Interneurons (association neurons): carry messages from neuron to neuronMirror neurons: involved in mimicking the behavior of others; Allows us to identify and empathize with others Neural CommunicationA two step process1. Takes place within a single neuron and involves the generation of an electrical signal2. Takes place between two neurons and involves the release of a chemical messenger Parts of the Neuron

Parts of the Neuron - Dendrites

Other cells do not have dendrites; unique to the neuron Parts of the Neuron - Soma

Nucleus: Contains chromosomesParts of the Neuron - Axon

Can vary in length (fractions of a millimeter to three feet)

Stub your toe: Cell body in lower back, axon down to toe!Parts of the Neuron Myelin Sheath

Degeneration of myelin = multiple sclerosis Parts of the Neuron - Terminals

Terminal Buttons Glial Cells (or glia; glue in Latin) Hold neurons in placeProvide nourishmentRemove waste productsPrevent harmful substances from passing from the bloodstream to the brain (blood-brain barrier)When damaged some glia form scar tissue, inhibiting repair(in brain and spinal cord); Glia in the other parts of the nervous system do not form scar tissue and help damaged axons regrow Form the myelin sheath Myelinated tissue = white matterUnmyelinated tissue = gray matterNot done growing until early adulthood (by 25) Neural CommunicationNeurons speak in a yes or no language electrochemical impulses Three Phases of Neural ActivityResting PotentialAction PotentialRefractory Period Resting Potential Neuron is not processing informationNeuron is polarizedMore negative ions (charged particles) inside the neuron than outsideLike a spring that has been compressed by not released

Na+ Na+Na+Na+Na+

K+ --K+-K+--K+-K+-- - +Action Potential When an incoming impulse exceeds the threshold of excitation, the membrane will open allowing an inflow of sodium ions Trigger of a gunHappens in steps down the axon of the neuron (channels open in a chain reaction; row of dominoes)Neuron is now depolarized (inside is positively charged compared to outside)This is an action potential (or neural impulse) ELECTRIC

Na+K+ Na+ K+ Na+ K+ Na+ Action Potential Cont.As a result of the depolarization, the potassium ions will flow out of the neuron (wants to repolarize)Neuron is now the opposite of how it needs to be to fire Can travel from 2 mph to 200 mph (3 million times slower than electricity) K+K+K+K+

Na+Na+K+ Na+Na+17Refractory PeriodPeriod where the neuron cannot create another action potentialIt is rechargingA sodium-potassium pump replaces the ions to their correct place (sodium outside, potassium inside) (1/1000 second) Unmyelinated v. Myelinated NeuronsAction potentials do not affect the entire axon at onceTakes place in small segments of the axon electrical charge is duplicated along the length of the axonUnmyelinated Axon: action potentials happen in a step-by-step process Myelinated Axon: action potentials are formed only at the sections of the axon between the myelinated sausages (called nodes of Ranvier) Can skip the sections that are myelinated (20 x faster)

Neural Signals Neurons communicate an excitatory effect, telling other neurons to fire ORAn inhibitory effect, telling other neurons to restA single neuron may have hundreds of dendrites and its axon may branch out to touch hundreds or thousands of other cells All-Or-None Principle Neurons either fire or they dont Cannot fire at 50%, 75%, 2%Strong signals CAN make a neuron more likely to fire Communication Between Neurons The Neuron Part IINeurons Do Not Touch Neurons do not touch each otherSynaptic Gap (cleft): fluid filled gap in between a sending and receiving neuronNeeds something to cross the gap.Neurotransmitters: chemical messengers that cross the gap and latch onto receptor sites on the dendrites of a receiving neuronKey and lock fit When They are DoneNeurotransmitters do not stay on receptor sites foreverThey are either:Reabsorbed by the sending neuronBroken down and recycled by the bodyReuptake: Process where unused/finished neurotransmitters are reabsorbed by the sending neuron

Neurotransmitters: Psychologists have discovered at least 50 kinds

Perfect Fit Neurotransmitters ACh - AcetylcholineThe messenger at every junction between a motor neuron and a skeletal muscle important in movement (ACh released, muscles moves)Also found in brain circuits related to learning and memoryThese circuits are the first to deteriorate in Alzheimers patients

Dopamine Associated with systems that govern movement, planning, reward Parkinsons Disease results when dopamine-releasing neurons in the brains movement circuits die Involved in reward centers that are active when we do things that promote survival sex, eating Addictive drugs (cocaine, methamphetamines) increase dopamine production Implicated in schizophrenia and ADHDSerotoninInvolved with systems regarding sleep, appetite, and mood (all closely related)Low levels are associated with depressionNorepinephrine Arousal, vigilance Also released by the parasympathetic nervous system (fight or flight system)Implicated in disturbances of arousal and vigilance like bipolar disorder and posttraumatic stress disorder Endorphins Endogenous MorphineModify our natural response to painRunners high (sense of well being and reduced pain, due to release of endorphins)

GABA (Gamma-Aminobutyric Acid)Inhibitory neurotransmitterInvolved in sleep, eating disorders, and extreme anxiety Undersupply has been linked to seizures, tremors, and insomnia Glutamate Excitatory neurotransmitter Oversupply can overstimulate brain, producing migraines are seizuresContained in MSG (monosodium glutamate) Neurotransmitters and MedicinesMany antidepressant medicines (Prozac) are SSRIs Selective Serotonin Reuptake Inhibitors Stops Serotonin from being sucked back up into sending neuron More serotonin available in synapse for binding on receptor sites ADHD (There are several types) Associated with: GABA, Dopamine, norepinephrine, or serotoninDrugs to treat ADHD either redistribute existing neurotransmitters, imitate certain neurotransmitters, or cause the production of neurotransmittersAdderall, Ritalin

Neurotransmitters and Medicine cont. Antipsychotic medication (chlorpromazine Thorazine) prevents dopamine from binding to receptor sites, which reduces hallucinations in schizophrenic patients Imposters! Agonists Agonist: compound that mimics neurotransmittersSort of fits in the lockBlack Widow VenomChemical structure is similar to AChLatches on to ACh receptor sites and mimics effect (movement)Venom +ACh = excessive, uncontrollable movements aka convulsions

Agonists (cont)Morphine, Oxycotinin, Heroin : Fake endorphins Body stops making own endorphinsEverything hurts when taken off quickly!Antagonists Block the receptor sites so that neurotransmitters cannot latch onCurare: Poison used by native tribes Blocks ACh sites paralysis! Botulin: Found in botox Paralyzes muscles by blocking ACh receptor sites

CaffeineBlocks the action of adenosine Adenosine inhibits the release of neurotransmitters related to arousal Forced wakefullness!