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Understanding the Nervous System: Functions, Structures, and Neuron Types

This chapter delves into the complex functions of the nervous system, which regulates our actions and defines our identity. It discusses how the system senses changes in homeostasis, analyzes responses, and triggers appropriate reactions. The composition of nervous tissue is highlighted, including neurons and neuroglia, with a focus on their structures such as dendrites, axons, and synapses. The central and peripheral nervous systems are explored along with their roles in sensory, motor, and integrative functions. Essential neuronal classifications and glial cell types are also covered.

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Understanding the Nervous System: Functions, Structures, and Neuron Types

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  1. CHAPTER 10NERVOUS SYSTEM 1

  2. FUNCTION • CONTROLS WHAT WE DO AND DETERMINES WHO WE ARE • SENSE CHANGES IN HOMEOSTASIS , ANALYZE THE CHANGE AND INITIATE THE CORRECT RESPONSE

  3. COMPOSISTION • NERVOUS TISSUE MOSTLY • BLOOD VESSELS • CONNECTIVE TISSUE

  4. NERVOUS TISSUE TYPES • NEURONS: NERVE CELLS • NEUROGLIA

  5. NEURONS • FUNCTIONS: • STIMULATED BY CHEMICAL OR PHYSICAL CHANGES IN THE ENVIRONMENT • PARTS: • DENDRITES • CELL BODY/ SOMA • AXON • NERVE IMPULSE **A NERVE IS A COLLECTION OF NEURONS

  6. NEURON http://vv.carleton.ca/~neil/neural/neuron-a.html http://vv.carleton.ca/~neil/neural/neuron-a.html

  7. PARTS • SYNAPSE • NEUROTRANSMITTERS • CARRY IMPULSE ACROSS SYNAPSE

  8. ORGANS • CENTRAL NERVOUS SYSTEM: CNS • BRAIN • SPINAL CORD • PERIPHERAL NERVOUS SYSTEM: PNS • CRANIAL AND SPINAL NERVES • CONNNECTS CNS TO REST OF BODY • TWO PARTS: • SENSORY • MOTOR: TWO PARTS • SOMATIC NERVOUS SYSTEM • TO SKELETAL MUSCLES • AUTONOMIC NERVOUS SYSTEM • TO SMOOTH AND CARDIAC MUSCLE AND GLANDS

  9. GENERAL FUNCTIONS • RECEIVING INFORMATION: SENSORY • RECEPTORS ON ENDS OF THE PERIPHERAL NEURONS • STIMULATED BY (?) AND FORM IMPULSE OFTEN TO CNS • INTERPRETING INFORMATION: INTEGRATIVE • IMPULSES ARE ANALYZED AND CREATE SENSATIONS, FORM MEMORIES, PRODUCE THOUGHTS; • SUBCONCIOUS OR CONCIOUS DECISIONS MADE • REACTING TO INFORMATION: MOTOR • SUBCONCIOUS OR CONCIOUS DECISIONS ARE CARRIED OUT • EFFECTORS: MUSCLES AND GLANDS • SOMATIC NERVOUS SYSTEM: CONCIOUS; SKELETAL MUSCLES • AUTONOMIC NERVOUS SYSTEM: UNCONCIOUS; SMOOTH, CARDIAC MUSCLE AND GLANDS

  10. PARTS • VARY IN SIZE AND SHAPE; SIZE AND LENGTH OF DENDRITES AND AXONS AND NUMBER OF PROCESSES • CELL BODY: CONTAINS • GRANULAR CYTOPLASM • MITOCHONDRIA • LYSOSOMES • GOLGI APPARATUS • MICROTUBULES • NEUROFIBRILS: EXTEND INTO AXON • NISSL BODIES: CHROMATOPHILIC SUBSTANCE: ROUGH ER (?) • INCLUSIONS • NUCLEUS WITH NUCLEOLUS

  11. NEUROFIBRILS NEUROFIBRILS IN KITTEN NEURONS http://www5.bartleby.com/107/illus629.html

  12. NISSL BODIES SMALL ARROWS http://www.biomedcentral.com/content/figures/1471-2202-6-19-5-l.jpg

  13. DENDRITES • USUALLY BRANCHED • DENDRITIC SPINES: CONTACT POINTS • AXON • AXONAL HILLOCK • CYTOPLASM: • MITOCHONDRIA; MICROTUBULES, NEUROFIBRILS • COLLATERALS • AXON TERMINALS WITH SYNAPTIC KNOB

  14. DENDRITIC SPINES http://www.udel.edu/biology/Wags/histopage/colorpage/cne/cne.htm

  15. AXONAL TRANSPORT • CARRIES MATERIAL MADE IN CELL BODY TO END OF AXON • VESICLES, MITOCHONDRIA, IONS, NUTRIENTS, NEUROTRANSMITTERS

  16. http://www.lookfordiagnosis.com/mesh_info.php?term=axonal+transport&lang=1http://www.lookfordiagnosis.com/mesh_info.php?term=axonal+transport&lang=1

  17. SCHWANN CELLS www.mc.vanderbilt.edu/histology/slide.php?image_name=myelin&slide_file=images/histology/nervous_tissue/display/schwann3.jpg&image_id=1058

  18. MYELINATED NEURONS • HAVE SCHWANN CELLS (PNS) OR OLIGODENDROCYTES (CNS) • WHITE MATTER • INCREASE SPEED OF TRANSMISSION • UNMYELINATED • NO MYELIN • GRAY MATTER

  19. CLASSIFICATION OF NEURONS • STRUCTURAL • MULTIPOLAR • MOST NEURONS • WITH CELL BODIES • IN CNS • BIPOLAR • SPECIALIZED • STRUCTURES (EYES) • UNIPOLAR • SOME HAVE • GANGLIA http://library.thinkquest.org/C0126536/main.php?currentchap=1&currentsect=neuron.htm

  20. FUNCTIONAL CLASSIFICATION • SENSORY NEURONS/ AFFERENT • TO CNS • SENSES/ RECEPTORS • MOST UNIPOLAR (SOME BIPOLAR) • INTERNEURONS/ASSOCIATION/ • INTERNUNCIAL • IN CNS • MULTIPOLAR • TRANSFER IMPULSES TO BE INTERPRETED • MOTOR NEURONS/ EFFERENT • MULTIPOLAR • FROM CNS TO EFFECTORS • SOME VOLUNTARY/ SOME INVOLUNTARY

  21. NEUROGLIA • FUNCTION: • SCAFFOLDING; CONTROL SITES OF NEURONAL CONTACT; EMBRYONIC: GUIDE DEVELOPMENT, PLACEMENT AND SPECIALIZATION OF NEURONS; • PRODUCE GROWTH FACTORS THAT NOURISH NEURONS; REMOVE ACCUMULATING IONS AND NEUROTRANSMITTERS BETWEEN NEURONS; HELP FORMATION AND MAINTAINENCE OF SYNAPSES

  22. CLASSIFICATION OF NEUROGLIACNS • ASTROCYTES • STAR SHAPED • LOCATED BETWEEN BLOOD VESSELS AND NEURONS • SUPPOSRT NEURONS, AID METABOLISM OF SUBSTANCES (GLUCOSE); REGULATE ION CONCENTRATIONS; FORM SCAR TISSUE; MOVEMENT OF SUBSTANCES FROM BLOOD; RELEASE GROWTH FACTORS; PART OF BLOOD BRAIN BARRIER; • GAP JUNCTIONS http://medcell.med.yale.edu/ systems_cell_biology/nervous/ neuroglia.php

  23. OLIGODENDROCYTES • SIMILAR SHAPE BUT SMALLER • FORM MYELIN BUT ONLY PROCESS WRAP AROUND NEURONS SO COVER MANY CELLS BUT NO NEURILEMMA

  24. MICROGLIA • SMALL WITH FEWER PROCESSES • THROUGH OUT CNS • PHAGOCYTIZE BACTERIA • PROLIFERATE WHEN INJURY OCCURS • EPENDYMA • CUBOIDAL, COLUMNAR MAY BE CILIATED • FORM INNER LINING OF CENTRAL CANAL OF SPINAL CORD AND VENTRICLES AND CHOROID PLEXUSES • GAP JUNCTIONS: ALLOWING MOVEMENT BETWEEN CEREBROSPINAL FLIUD AND INTERSTITIAL FLUID OF BRAIN

  25. http://www.google.com/imgres?q=satellite+cells+pns+function&hlhttp://www.google.com/imgres?q=satellite+cells+pns+function&hl

  26. ABNORMAL NEUROGLIA • BRAIN TUMORS • ALS • HUNTINGTON’S DISEASES

  27. PNS • SCWHANN CELLS • SATELLITE CELLS • SUPPORT GANGLIA NOT SURE OF S[PECIFIC FUNCTION • FORM AN ENVELOPE AROUND EACH CELL BODY IN GANGLIA

  28. A: Satellite cells B: Schwann cells http://www.google.com/imgres?q=satellite+cells+pns+function&hl=en&sa

  29. NEURON REPAIR • INJURY TO CELL BODY = DEATH; NOT REPLACED UNLESS A STEM CELL IS STIMULATED • PNS: AXON MAY REGENERATE: • INJURY: • DISTAL PORTION DIES • MACROPHAGES REMOVE DEBRIES • PROXIMAL END DEVELOPS SPROUTS • NEUROGLIA RELEASE GROWTH FACTORS WHICH STIMULATE ONE SPROUT TO GROW INTO A TUBE FORMED BY BASEMENT MEMBRANE AND CONNECTIVE TISSUE • SCHWANN CELLS PROLIFERATE FORMING NEW MYELIN • GROWS 3-4MM/DAY; MAY NOT GROW TO PROPER POSITION

  30. NEURON REPAIR • CNS: • INJURY: • DISTAL PORTION DIES SLOWLY • OLIGODENDROCYTES DON’T FORM A NEURILEMMAE AND DON’T PROLIFERATE SO SPROUT USUALLY ISN’T DIRECTED TO GROW PROPERLY physproject-2011.wikispaces.com

  31. SYNAPTIC TRANSMISSION • PRESYNAPTIC NEURON STIMULATES OR INHIBITS THE POST SYNAPTIC NEURON • IMPULSE REACHES THE AXON TERMINAL AND THE CHANGE IN THE MEMBRANE OPENS THE CALCIUM CHANNELS AND CALCIUM DIFFUSES IN • CAUSING THE SYNAPTIC VESSICLES TO FUSE WITH THE CELL MEMBRANE AND RELEASE THE NEUROTRANSMITTERS BY EXOCYTOSIS • THE NEUROTRANSMITTER ATTACHES TO A RECEPTOR ON THE POST SYNAPTIC NEURON AND STIMULATES OR INHIBITS THE NEURON • THE EFFECT DEPENDS ON THE INPUT FROM 1 TO 100,000+ PRESYNAPTIC NEURONS AND THEIR INPUT

  32. http://www.ucl.ac.uk/~sjjgsca/NerveSynapse.html

  33. http://scienceaid.co.uk/biology/humans/nerves.html

  34. RESTING CELL MEMBRANE POTENTIAL • USUALLY POLARIZED: THE INSIDE IS MORE NEGATIVE THAN THE OUTSIDE BECAUSE OF THE SODIUM/POTASSIUM PUMP AND THE GATED CHANNELS ARE NOT OPEN • THE MEMBRANE IS MORE PERMEABLE TO POTASSIUM THAN SODIUM, SO POTASSIUM DIFFUSES OUT MORE READILY THAN SODIUM DIFFUSES IN • THERE ARE CELL FORMED ANIONS (PHOSPHATE, SULFATE AND PROTEINS) THAT CAN NOT DIFFUSE OUT OF THE CELL • SO THE OUTSIDE IS MORE POSITIVE AND THE INSIDE IS MORE NEGATIVE • THIS DIFFERENCE IS MEASURED IN MILLIVOLTS; THIS RESTING POTENTIAL IS -70 MILLIVOLTS • THIS NEGATIVE POTENTIAL ALLOWS SODIUM TO DIFFUSE INTO THE CELL BUT INHIBITS THE DIFFUSION OF POTASSIUM OUT OF THE CELL (ABOUT 3Na TO 2 K) WHICH THE PUMP REPLACES (3Na OUT TO 2 K IN)

  35. http://tle.westone.wa.gov.au/content/items/969144ed-0d3b-fa04-2e88-8b23de2a630c/1/human_bio_science_3b.zip/content/002_nervous_control/media/cc2_g015a.gifhttp://tle.westone.wa.gov.au/content/items/969144ed-0d3b-fa04-2e88-8b23de2a630c/1/human_bio_science_3b.zip/content/002_nervous_control/media/cc2_g015a.gif

  36. LOCAL MEMBRANE POTENTIAL CHANGES • NEURONS ARE HIGHLY EXCITABLE: RESPOND TO CHANGES • USUALLY OPENS A GATED ION CHANNEL • IF INSIDE BECOMES MORE NEGATIVE= HYPERPOLARIZED • IF INSIDE IS LESS NEGATIVE= DEPOLARIZED • CHANGES ARE GRADED= GREATER THE STIMULATION/ GREATER THE HYPERPOLARIZATION OR DEPOLARIZATION • IF DEPOLARIZATION REACHES -55MILLIVOLTS = THRESHOLD STIMULATION AND STARTS AN ACTION POTENTIAL= IMPULSE

  37. HYPERPOLARIZATION http://www.jci.org/articles/view/29063/figure/2

  38. DEPOLARIZATION

  39. ACTION POTENTIAL/IMPULSE • AT AXONAL HILLOCK MEMBRANE IS MOST LIKELY TO BE STIMULATED TO THRESHOLD = TRIGGER ZONE, CONTAINS LOTS OF VOLTAGE-GATED SODIUM CHANNELS • WHEN THRESHOLD IS REACHED THE CHANNELS OPEN AND Na DIFFUSES IN CHANGING POTENTIAL TO +30mV • Na CHANNELS CLOSE AND K CHANNELS OPEN AND K DIFFUSES OUT MAKING INSIDE NEGATIVE AGAIN= REPOLARIZATION • K CHANNELS CLOSE AND RESTING POTENTIAL IS REFORMED • ACTION POTENTIAL AT TRIGGER ZONE CUSES AN ELECTRICAL STIMULTION A SHORT DISTANCE ON THE MEMBRANE CAUSING ANOTHER ACTION POTENTIAL AND SO FORTH ALONG THE WHOLE AXON = IMPULSE • SODIUM IS PUMPED OUT, POTASSIUM IS PUMPED IN RESTORING THE RESTING POTENTIAL

  40. http://web.lemoyne.edu/~hevern/psy340_10S/graphics/action_potential.jpghttp://web.lemoyne.edu/~hevern/psy340_10S/graphics/action_potential.jpg

  41. http://www.google.com/imgres?imgurl=http://www.millerandlevine.com/chapter/35/figure35-7.jpg&imgrefurl=http://http://www.google.com/imgres?imgurl=http://www.millerandlevine.com/chapter/35/figure35-7.jpg&imgrefurl=http://

  42. HOW THE IMPUPLSE FORMS AND TRAVELS • http://www.youtube.com/watch?v=9euDb4TN3b0 • http://www.youtube.com/watch?feature=endscreen&v=7EyhsOewnH4&NR=1 • http://www.youtube.com/watch?NR=1&v=rWrnz-CiM7A&feature=fvwp http://www.youtube.com/watch?feature=endscreen&v=7EyhsOewnH4&NR=1

  43. ALL OR NONE • IF THRESHOLD IS REACHED THE AXON RESPONDS COMPLETELY • A GREATER STIMULUS RESULTS IN MORE IMPULSES PER SECOND NOT A STRONGER IMPULSE

  44. REFRACTORY PERIOD • ABSOLUTE • 1/2500 OF A SECOND • SODIUM PERMEABILITY • IS CHANGING/ CAN’T • RESPOND • RELATIVE • CLOSE TO RESTING POTENTIAL • RESPONDS TO A STRONGER STIMULUS TAKES 10-30 MILLISECONDS COULD HAVE UP TO 700 IMPULSES PER SECOND BUT USUALLY ONLY ABOUT 100 http://scienceaid.co.uk/biology/humans/nerves.html

  45. IMPULSE CONDUCTION • MYELINATED NEURON: • SALTATORY CONDUCTION • FASTER • UNMYELINATED • WHOLE AXON: SLOWER • LARGE AXON DIAMETER • FASTER • SMALL DIAMETER • SLOWER • THICK MYELINATED: • 120 M/S • THIN UNMYELINATED: • .5 M/S

  46. SYNAPTIC POTENTIALS • NEUROTRANSMITTERS OPEN OR CLOSE CHEMICALLY-GATED CHANNELS WHEN ATTACH TO RECEPTORS • LOCAL POTENTIALS = SYNAPTIC POTENTIALS • EXCITATORY POSTSYNAPTIC POTENTIAL • OPENS SODIUM CHANNELS = DEPOLARIZES • 15 MILLISECONDS • INHIBITORY POSTSYNAPTIC POTENTIAL • OPENS POTASSIUM OR CHLORIDE CHANNELS = HYPERPOLARIZED • INTEGRATED SUM OF EPSPS AND IPSPS DETERMINES RESPONSE • THE TRIGGER ZONE OR IN SOME THE DISTAL PERIPHERAL PROCESS IS MOST SENSITIVE SO THE DECISION-MAKING PART

  47. NEUROTRANSMITTERS • 30 – 50; FINDING NEW ONES • SOME NEURONS RELEASE ONLY 1; SOME 2 OR MORE • TYPES: • Ach • SKELETAL MUSCLES • MONOAMINES/BIOGENIC AMINES/MODIFIED AMINO ACIDS • NOREPINEPHRINE; DOPAMINE; SROTONIN; HISTAMINE • UNMODIFIED AMINO ACIDS • GLYCINE; ASPARTIC ACID; GABA; GLUTAMATE • NEUROPEPTIDES • ENKEPHALIN; ENDORPHIN; SUBSTANCE P • GASES • NITRIC OXIDE

  48. NEUROTRANSMITTER PRODUCTION • PEPTIDES: • ROUGH ER OF CELL BODY AND TRANSPORTED TO AXON TERMINAL • OTHERS • FORMED IN CYTOPLASM OF TERMINALS AND PACKAGED THE MORE CALCIUM THAT ENTERS THE MORE NEUROTRANSMITTERS RELEASED

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