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The Neuron: Part I.

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1 The Neuron: Part I

2 Biological Psychology Biopsychology/Psychobiology
Branch of psychology that is concerned with the links between biology and behavior Behavior Genetics Evolutionary Psychology Neuroscience: specifically focuses on the study of the brain and nervous system Behavioral Neuroscientists Neuropsychologists

3 Nervous System Electrochemical communication system of the body
Neuron: basic building block of the nervous system Nerve: bundles of neurons Brain contains 100 billion neurons If each neuron was a second, it would take over 3,170 years to tick off your neurons

4 Types of Neurons Sensory Neurons (afferent): carry messages from the tissues/sense organs inward to the brain and spinal cord Motor Neurons (efferent): carry messages from the spinal cord/brain to the muscles/glands Interneurons (association neurons): carry messages from neuron to neuron Mirror neurons: involved in mimicking the behavior of others; Allows us to identify and empathize with others

5 Neural Communication A two step process
1. Takes place within a single neuron and involves the generation of an electrical signal 2. Takes place between two neurons and involves the release of a chemical messenger

6 Parts of the Neuron

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

8 Parts of the Neuron - Soma
Nucleus: Contains chromosomes

9 Parts 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!

10 Parts of the Neuron – Myelin Sheath
Degeneration of myelin = multiple sclerosis

11 Parts of the Neuron - Terminals
Terminal Buttons

12 Glial Cells (or glia; glue in Latin)
Hold neurons in place Provide nourishment Remove waste products Prevent 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 matter Unmyelinated tissue = gray matter Not done growing until early adulthood (by 25)

13 Neural Communication Neurons speak in a “yes” or “no” language – electrochemical impulses

14 Three Phases of Neural Activity
Resting Potential Action Potential Refractory Period

15 Resting Potential - + Neuron is not processing information
Neuron is polarized More negative ions (charged particles) inside the neuron than outside Like a spring that has been compressed by not released Na+ Na+ Na+ Na+ Na+ K K+ - K+ - - K+ - K+ - - + -

16 Action Potential Trigger of a gun
When an incoming impulse exceeds the threshold of excitation, the membrane will open allowing an inflow of sodium ions Trigger of a gun Happens 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+

17 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+

18 Refractory Period Period where the neuron cannot create another action potential It is recharging A sodium-potassium pump replaces the ions to their correct place (sodium outside, potassium inside) (1/1000 second)

19 Unmyelinated v. Myelinated Neurons
Action potentials do not affect the entire axon at once Takes place in small segments of the axon  electrical charge is duplicated along the length of the axon Unmyelinated 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)


21 Neural Signals Neurons communicate an excitatory effect, telling other neurons to fire OR An inhibitory effect, telling other neurons to rest A single neuron may have hundreds of dendrites and its axon may branch out to touch hundreds or thousands of other cells

22 All-Or-None Principle
Neurons either fire or they don’t Cannot fire at 50%, 75%, 2% Strong signals CAN make a neuron more likely to fire

23 Communication Between Neurons
The Neuron Part II Communication Between Neurons

24 Neurons Do Not Touch Neurons do not touch each other
Synaptic Gap (cleft): fluid filled gap in between a sending and receiving neuron Needs something to cross the gap…. Neurotransmitters: chemical messengers who cross the gap and latch onto receptor sites on the dendrites of a receiving neuron Key and lock fit

25 When They are Done… Neurotransmitters do not stay on receptor sites forever They are either: Reabsorbed by the sending neuron Broken down and recycled by the body Reuptake: Process where unused/finished neurotransmitters are reabsorbed by the sending neuron









34 Neurotransmitters: Psychologists have discovered at least 50 kinds

35 Perfect Fit Neurotransmitters

36 ACh - Acetylcholine The 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 memory These circuits are the first to deteriorate in Alzheimer’s patients

37 Dopamine Associated with systems that govern movement, planning, reward Parkinson’s Disease results when dopamine-releasing neurons in the brain’s movement circuits die Involved in reward centers that are active when we do things that promote survival – sex, eating Addiction drugs (cocaine, methamphetamines) increase dopamine production Implicated in schizophrenia and ADHD

38 Serotonin Involved with systems regarding sleep, appetite, and mood (all closely related) Low levels are associated with depression

39 Norepinephrine 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

40 Endorphins Endogenous Morphine Modify our natural response to pain
“Runners high” (sense of well being and reduced pain, due to release of endorphins)

41 GABA Inhibitory neurotransmitter
Involved in sleep, eating disorders, and extreme anxiety Undersupply has been linked to seizures, tremors, and insomnia

42 Glutamate Excitatory neurotransmitter
Oversupply can overstimulate brain, producing migraines are seizures Contained in MSG (monosodium glutamate)

43 Neurotransmitters and Medicines
Many 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 serotonin Drugs to treat ADHD either redistribute existing neurotransmitters, imitate certain neurotransmitters, or cause the production of neurotransmitters Adderall, Ritalin

44 Neurotransmitters and Medicine
Antipsychotic medication (chlorpromazine – Thorazine) prevents dopamine from binding to receptor sites, which reduces hallucinations in schizophrenic patients


46 Imposters! Agonists Agonist: compound that mimics neurotransmitters
Sort of fits Black Widow Venom Chemical structure is similar to ACh Latches on to ACh receptor sites and mimics effect (movement) Venom +ACh = excessive, uncontrollable movements aka convulsions


48 Agonists (cont) Morphine, Oxycotinin, Heroin : Fake endorphins
Body stops making own endorphins Everything hurts when taken off quickly!

49 Antagonists Block the receptor sites so that neurotransmitters cannot latch on Curare: Poison used by native tribes Blocks ACh sites  paralysis! Botulin: Found in botox Paralyzes muscles by blocking ACh receptor sites


51 Caffeine Blocks the action of adenosine
Adenosine inhibits the release of neurotransmitters related to arousal Forced wakefullness!

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