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A2 nervesystemscolstons

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  • 1. Nervous Systems Colston’s School
  • 2. Structure of a Vertebrate Neuron
  • 3. Diversity of Nervous Systems Simple, slow moving animals like hydra have neurons arranged in a network of bipolar neurons called a nerve net.
  • 4. Basic Tasks of the Nervous System Sensory Input: Monitor both external and internal environments. Integration: Process the information and often integrate it with stored information. Motor output: If necessary, signal effector organs to make an appropriate response.
  • 5. Anatomy of a nerve • Cell body: functional portion • Dendrites: short extensions that receive signals • Axon: long extension that transmits impulses away
  • 6. Nerve Impulse – The Action Potential Threshold potential will trigger an action potential or nerve impulse The action potential is an all-or-none response
  • 7. Nerve Impulse – The Action Potential A nerve is stimulated, (A.P.) usually at one point, and then is propagated along the axon. The role of sodium and potassium ions in propagating an Action Potential is crucial. Na+ and K+ both move in apposing directions to generate a potential difference all along the axon. Positive and negatives attract.
  • 8. Myelinated Neurons • Many vertebrate peripheral neurons have an insulating sheath around the axon called myelin which is formed by Schwann cells. • Myelin sheathing allows these neurons to conduct nerve impulses faster than in non-myelinated neurons.
  • 9. Saltatory Conduction in Myelinated Axons Myelin sheathing has bare patches of axon called nodes of Ranvier Action potentials jump from node to node Fig. 48.11
  • 10. How does a signal move from one neuron to another? • A synapse divides 2 neurons • The action potential will not move across the synapse • Neuro transmitters – Released by the signal cell to the receiver cell – Move by diffusion
  • 11. Types of chemical synapse • Acetylcholine: neuromuscular junctions, glands, brain and spinal cord • Norepinepherine: affects brain regions concerned with emotions, dreaming
  • 12. Spinal Reflex • Knee-patellar is the classic example, but there are many reflexes • Blinking your eye • Salivating when expecting food • Going to the toilet as an infant
  • 13. The Autonomic Nervous System • The outer nervous system controls the body’s activities that you don’t think about • The outer nervous system controls activities in your small intestine, your breathing, and your heartbeat.
  • 14. The sense organs - eye • Sense organs carry messages about the environment to the central nervous system
  • 15. Parts of the Eye Detectors on the Fovea – Rods • light intensity and motion sensitive – Cones • color sensitive The blind spot for the eye is cause by the optic nerve.
  • 16. Myopia (Near-Sightedness) People with near-sightedness cannot see clearly at distance.
  • 17. Hyperopia (Farsightedness) People with far-sightedness cannot see clearly up close
  • 18. Addictive Drug Use: Tobacco, Alcohol, & Illicit Drugs
  • 19. Pharmacology of Addictive Drugs • All addictive drugs produce: • Short-term pleasure to some degree • Long-term negative consequences • Tolerance & physical dependence • A withdrawal syndrome • Activation of dopamine neurons in the Nucleus Accumbens
  • 20. Transmission Across the Synapse Source: Gray
  • 21. How Drugs Become Addictive
  • 22. Detail of Axon Terminal
  • 23. Detail of the Synapse Itself Neurotransmitter molecules (e.g., Acetylcholine or Dopamine) Postsynaptic membrane
  • 24. How binding sites work Binding site
  • 25. Neurotransmitter re-uptake helps keep binding sites clear
  • 26. Cocaine inhibits the re-uptake of dopamine producing effects such as increased heart rate and blood pressure
  • 27. Nicotine fills & activates acetylcholine binding sites producing effects such as increased heart rate and blood pressure
  • 28. What is Addiction? • All definitions describe behaviour which produces positive sensations in the short term, but negative consequences in the long term • A straightforward definition: – Compulsive use – Loss of control – Use despite harm * Portnoy
  • 29. How People Start Using Drugs • Genetics • Predisposing risk factors: – Age 11-22 for onset – Primitive character structures • Especially Conduct Disorder – Peer influence – Parental influence – Smoking and alcohol use • Constricted temporal focus?
  • 30. 80 Nicotine Use is Associated With Other Drug Use 5+drugs % of Students " 70 60 50 2-4 drugs 40 30 20 1 drug 10 0 NO NE ( ON E 61. 2) (14 .7 OC C (8. 7) 1- 5 /d ( 7. 6 ) ) Cigarettes smoked per day 6- 1 0/d (3. 4) 11 +/d (4. 4) Kozlowski, Coambs, et al., 1989 Nicotine Use is Associated With Other Drug Use
  • 31. Some People Never Start • Factors which reduce risk: – Age 35+ – Nuanced character structures – No Peer influence – No Parental drug use history – No other smoking or alcohol abuse • E.G., the SISAP
  • 32. Basic Treatment For Addiction • Treat the urges directly, if possible • Establish why the person uses the drug • What needs are being fulfilled by that drug? • Find methods to fulfil those needs without the drug
  • 33. How People Quit Drug Abuse • Most quit on their own (cold turkey) • Most use no medication • Probably those people who can quit easily do so • Clinicians tend to see the difficult cases • Ambivalence is normal • Most quit by age 40
  • 34. Relapse Prevention • Plan for relapse: Abstinence Violation Effect • Relapse is common: it is not failure! • Repeated relapse is associated with success in quitting • Learn from it in next attempt • Find a way to control urges