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Nervous system

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Nervous system

  1. 1. Nervous System Function Neurons Base unit that has very simple function – “decide” whether totransmit signal or not Organization Billions of Neurons (estimates of 100 billion) Very complex interconnections Create systems/circuits that can function independently (parallelprocessing) “Simple decisions” passed to “higher” levels for that addadditional information to create generate more complexdecisions (hierarchical processing) Very expensive - less than 2% of weight but uses 20% ofenergy
  2. 2. Neuron Structure Cell Body Nucleus – genetic information Dendrites Receive information Axon Carry information “long” distances Myelin (Multiple Sclerosis) Axon Terminals Transmit information
  3. 3. Neuron - Structure
  4. 4. Neuron Function Electrical Activity Used to transmit signal within neuron Chemical Activity Used to transmit signal between neurons Synapse – small gap that physically separatesneurons Neurotransmitters – special “chemicals” thatneurons use to transmit message across thesynapse
  5. 5. Neuron Function Electrical Activity Resting Potential Inside negative (-70 mV) compared to outside Inside has high K+ (negativity comes from proteins& other negative ions) Outside has high Na+ Forces at work Electrical Diffusion
  6. 6. Neuron Function Electrical Activity Graded Potential Depolarization – Inside less negative (e.g., Na+ enters) Hyperpolarization – Inside more negative (e.g., Cl- enters) Action Potential When graded reaches approximately -55mV Electrical impulse that travels down cell – axon to axonterminals Axon terminals release neurotransmitter
  7. 7. Neuron Function Electrical Activity Restoring Resting Potential Sodium-Potassium Pump – moves Na+ out of celland K+ into cell This requires cell to use energy
  8. 8. Neuron Function Chemical (Neurotransmitter) Activity Leads to graded potentials in neuron Excitatory NTs – causes depolarization in neuron Initiatory NTs – causes hyperpolarization inneuron
  9. 9. Neuron – Excitation & Inhibition
  10. 10. Neuron - Synapse
  11. 11. Synapse Types Multiple ways of connecting Examples Axon to Dendrite – excite or inhibit neuron Axon to Axon Terminal – moderate NT release Axon to Extracellular Space or blood – potentialfor diffuse effects
  12. 12. Synapse Types
  13. 13. Synapse Function Neurotransmitter cycle in Axon Terminals Synthesis Storage Release Inactivation Reuptake Degradation Neural transmission problems if cycle disrupted(e.g., drugs) at any step
  14. 14. Synapse Function
  15. 15. Synapse Function
  16. 16. Neurotransmitter Types Small Molecules Nine – Acetylcholine (ACh), dopamine (DA),norepinephrine (NE), epinephrine (adrenaline), serotonin(5-HT), histamine, GABA, glycine, glutamate Simple (or no) alterations to basic food components Glutamate & glycine are amino acids DA and NE from tyrosine & 5-HT made from tryptophan Manufactured in axon terminals Large quantity and have short duration
  17. 17. Note: There are four criteria by whichneurotransmitters are defined. 1. It must be synthesized in thepresynaptic cell.2. It must be released by the presynapticterminal in sufficient quantities to producea measurable effect on the postsynapticcell.3. When administered artificially, it mimicsnatural release.4. A specific, known mechanism exists forit to be removed from the synaptic cleft.
  18. 18. Acetylcholine (ACh)• -Arousal and orgasm- voluntary muscular control and propertone- enhance energy and stamina- memory- long-term planning- mental focus
  19. 19. dopamine (DA) - Alertness- Motivation- motor control- immune function- Ego hardening,confidence, optimism- Sexual Desire- Fat gain and loss- lean muscle gain- Bone density- ability to sleep soundly- Inhibits prolactin- thinking, planning, andproblem solving- Aggression- Increase psychic andcreative ability- Reduction ofcompulsivety- Salience and paranoia- Processing of pain- Increase sociability
  20. 20. norepinephrine (NE) - Increase physicalenergy- Reducecompulsivety- Increase heart rate- Increase BP- Aggression- Alertness- Wakefulness/sleepcycle- Memory and learning- Orgasm- Decrease blood flow toextremities- Increase heart rate- Maintenance ofattention- Cerebral plasticity
  21. 21. epinephrine (adrenaline) - increases supply of oxygen and glucoseto brain and muscles- Surpresses digestion- Increase heart rate and stroke volume- Pupil dilation- constricts arterioles in skin and GI tract- Dilates arterioles in skeletal muscles- Elevates blood sugar levels
  22. 22. serotonin (5-HT) - Decrease thought- Anaesthesize emotions- Decrease Agression and anger- Decrease Anxiety- Promote satiety and decreaseappetite- Elevates Pain threshold- Reducescompulsivety/impulsivety- Decrease Sexual Desire- Thermoregulation (5-HT1A)- Stimulate Emesis (5-HT3)- Cerebrospinal fluid secretion (5-HT2C)- Platelate aggregation (5-HT2A)- Smooth muscle contraction,vasoconstriction, and vasodilation (5-HT2A)- Release oxytocin (5-HT1A)- Learning (5-HT2A & 5-HT4)- Memory (5-HT4)- Neuronal excitation (5-HT2A, 5-HT3,& 5-HT4)- GI motility (5-HT4)- Neuronal inhibition (5-HT1A)- Cerebral vasoconstriction (5-HT1D)- Pulmonary vasoconstriction (5-HT1B)- Presynaptic inhbition (5-HT1B)
  23. 23. histamine H1- Vasodilation- Bronchoconstriction- Smooth muscle activation- separation of endothelial cells (responsible for hives)- Pain and itching due to insect stings- Allergic rhinitis- Motion sicknessH2- stimulates gastric acid secretion- Potent stimulant of cAMP production- increases the intracellular Ca2+ concentrations and release Ca2+ from intracellularstores.H3- presynaptically inhibits the release of a number of other neurotransmittersincluding, but probably notlimited to dopamine, histamine, GABA, acetylcholine, noradrenaline, and 5-HT. Itleads to inhibition of the formation of cAMPH4- H4 Receptors mediate Chemotaxis and Calcium Mobilization of Mast Cells
  24. 24. GABA - synthesized from glutamate - Reduce physical tension- Reduce Anxiety- Reduce Insomnia- Elevates pain threshold- Reduces blood pressure- Decrease heart rate- Reduce compulsivety
  25. 25. GlycineGlutamate and Aspartate excitatory neurotransmitters
  26. 26. Neurotransmitter Types Peptides 50+ and grouped into families depending on function Opoids (enkephalins, dynorphin) – pain Gastrins (gastrin, cholocystokinin) – food digestion 2 or more amino acids and made in cell body (ribosomes)from DNA instruction Slower to manufacture & transport Small concentrations and longer durations Gases At least 2 – nitric oxide (NO) & carbon monoxide (CO) Can work on releasing cell
  27. 27. Neurotransmitter Function No one to one relation between type andfunction Same NT can be used in different places withvery different effects Acetylcholine – contracts muscles, used inautonomic nervous system, and brain
  28. 28. Neurotransmitter Receptor Proteins Channel Proteins NT binding site and channel trough membrane NT opens a channel to allow chemical flow (Na+) acrossmembrane Second Messengers NT binding site – NT activates a “second messenger” (1stis the NT) inside the cell Change function of cell (e.g., change protein production topermanently alter cell function for learning)
  29. 29. Neurotransmitter Receptor Proteins
  30. 30. Neurotransmitter Receptor Proteins Usually multiple receptors for a given NT Acetylcholine Nicotinic receptor – found a junction betweenneuron and muscle Muscarinic receptor – more prevalent in brain Acetylcholine affects both Drugs can have more specific effects (or notdepending on the drug) Nicotine & curare –affect nicotinic but not muscarinic
  31. 31. Neurotransmitter Receptor Proteins Usually multiple receptors for a given NT Serotonin (5-HT) 13 known receptors grouped into 6 families People with schizophrenia have an excess of onetype Demonstrates how genetic differences can influencemotivational temperaments Dopamine 5 known receptors grouped into 2 families
  32. 32. Psychoactive Drug Overview Two Broad effects on NT function Facilitate or increase function of a specific NT Inhibit or Decrease function of a specific NT 2 Broad effects accomplished by alteringany of the 7 synapse functions (previousslide) Acetylcholine
  33. 33. Psychoactive Drug Overview Acetylcohine Example Axon Release Black widow spider venom – released from axon terminals Botulinum toxin (Botox) – blocks release from axonterminals Synapse Stimulation Nicotine – mimics ACh Curare – blocks ACh from getting to terminals Inactivation Physostigmine – blocks effect of enzyme that destroys ACh
  34. 34. Psychoactive Drug Overview
  35. 35. Psychoactive Drug Overview Nervous System adapts drug presence Inhibitory drug – may create more proteinreceptors to detect smaller amounts of NTs thatare getting to postsynaptic cell Excitatory drug – may remove protein receptors NS now requires drug for functioning Inhibitory drug – “normal” signals are too strong Excitatory drug – “normal” signals not strongenough
  36. 36. Nervous System Organization
  37. 37. Nervous System Organization Central Nervous System (CNS) Spinal Cord – simple decisions & information transmission Brain – “complex” decisions Peripheral Nervous System (PNS) Somatic – sensory information & voluntary movement Autonomic Sympathetic – increases support increased physical activity Parasympathetic – increases support decreased physicalactivity Enteric – gastrointestinal system
  38. 38. Autonomic Nervous System
  39. 39. Nervous System Organization Neuron Groups Peripheral NS Nerve – collection of axons in PNS Ganglia – collection of cell bodies & dendrites Central NS Tract – collection of axons in CNS (White Matter) Nuclei – collection of cell bodies (Grey Matter) Glial Cells Support and assist neurons (many types) Produce myelin, nourishment, repair, waist disposal, etc.
  40. 40. Spinal Cord 31 segments with pairs (left & right) nervescarrying sensory and efferent information Functions Ascending and descending neural tracts Interneurons responsible for spinal reflexes(relatively simple decisions) Link sensory information (e.g., pain) with motorresponse (e.g., muscle contraction)
  41. 41. Brain Structure Very Complex Many different ways of describing brainstructures (location, function, etc.) General Principles Layered Lateralized
  42. 42. Brain Neural Systems Brain circuits responsible for brain function E.g., - vision, hearing, movement, reward System could be Localized (vision) or diffuse (arousal) General (vision) or specific (color vision) Broad Divisions Sensory Motor Association
  43. 43. Brain Complex behaviors (fear/defensive learning)depend on many systems Sensory Learning Memory Output Differences in a function (e.g., motivation) mightbe due to different reasons (e.g., sensory,learning, etc.)
  44. 44. Studying Brain Function Gross lesions Structural assessments Selective lesions specific neurotoxins transient lesions Local functioning Single-cell recording Neurotransmitter measurement & manipulation Gene expressions Non-invasive measures Functional MRI EEG & ERP

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