The Neuron: Part I

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 • 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. 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