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Nervous System

Nervous System. Nervous System. Functions Neurons Receptors: Interpret: Response:. Afferent. Efferent. Organization of Nervous System. Central Nervous System. Peripheral Nervous System. Motor (Efferent). Sensory(Afferent). ANS. Somatic. Sympathetic “Fight or Flight ”.

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Nervous System

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  1. Nervous System

  2. Nervous System • Functions • Neurons • Receptors: • Interpret: • Response: Afferent Efferent

  3. Organization of Nervous System Central Nervous System Peripheral Nervous System Motor (Efferent) Sensory(Afferent) ANS Somatic Sympathetic “Fight or Flight” Parasympathetic “Resting and Digesting”

  4. Cellular Organization: 2 types of Cells • Neurons • Responsible for conducting electrical impulses • Characterisitics • Long Life Span • Amitotic • High Metabolic Rate

  5. Dendrite, Cell Body and Axon

  6. Dendrites: Receive stimuli from receptorsCell Body: Contains nucleus and organelles; lacks centriolesAxon: Generate and transmit nerve impulses Secretingoutput Input conducting

  7. Sensory Neurons (Afferent) • Exteroceptors • Provide information of about external environment • I.e. • Proprioceptors • Monitor the position of skeletal muscles and joints • Interoceptors • Monitor the activities of internal systems and organs • I.e.

  8. Motor Neurons (Efferent) • Carry Instructions from CNS to muscles, tissues and organs • Called Effectors because they cause a response

  9. Interneurons • Located in brain and spinal cord • Analyze sensory input (afferent) and coordinate motor output (efferent)

  10. Neuroglia/Glial Cells • Supporting cells to neurons • Act as phagocytes • Outnumber Neurons • Mitotic

  11. Astrocytes • Secretes chemicals important for the maintenance of the Blood Brain Barrier • Feeds neurons • Repairs damaged neural tissues

  12. Ependymal Cells • Produce CSF (cerebrospinal fluid) • Line central cavities of brain and spinal cord These ciliated cells circulate CSF

  13. Microglia • Phagocytic cells • Produced by leukocytes (WBCs) • Fight infection

  14. Schwann Cells/Oligodendrocytes • Produce myelin sheath -increases the speed of impulses, insulator Myelin=lipid components Nodes of Ranvier-gaps in myelin sheath, axon contacts its external environment Schwann cells-glial cells in PNS that produce myelin sheath Mylenated vs. Unmyelinated axons Demylinated (multiple sclerosis)

  15. Unmyleninated vs. Myleninated Axon Ion transport occurs along the length of the axon in an unmyleninated axon. Ion transport occurs only where the Nodes of Ranvier are located in a myleninated axon.

  16. Na+-K+ PumpActive Transport – requires ATP

  17. Resting Membrane Potential • Measured as voltage difference across the membrane • Inside of membrane is -70 mV (.07 V) C battery = 1.5 V • Maintained by Na+K+ pump • 3 Na ions are pumped out for every • 2 K ions that are pumped in • Requires ATP; maintaining a concentration gradient

  18. More Na+ leave the cell than K+ enter. Resting Membrane Potential Polarized Charge difference of -70mv across membrane Inside of axon is negative compared to the outside. Outside Inside

  19. Na ions and K ions are actively pumped out and in the cell. Maintain a concentration gradient (difference) Ions do not reach equilibrium.

  20. Depolarization • Axon hillock is where impulse will begin • Na diffuses into axon • Reach -55mV = threshold • At threshold Na gates open; Na ions diffuse into axon • Reach +30 mV; Na gates close

  21. Graded Potential – depolarization occurs but you never reach threshold.Not enough Na+ moves into cell, impulse is not sent.

  22. Action Potential/Impulse • Enough neurons fire so red neuron reaches threshold • Impulse is sent to next neuron (green)

  23. Enough Na+ diffuses into the cell reaching thresholdNa+ continues to diffuse into cell until voltage rises to +30 mV. Action Potential

  24. Depolarization

  25. Depolarization

  26. Repolarization – Na gates close, K gates open. K+ diffuse out of cell

  27. Repolarization

  28. Repolarization • K+ ions diffuse out of the cell • Returning the inside of the cell to its negative charge.

  29. Movement of Ions across the membrane during an Impulse Depolarized Repolarized Polarized

  30. Hyperpolarization • Charge inside the axon goes below -70mV. • Caused by K+ leaving the cell and Na+ not able to enter the cell. • Increase in negative charge since + ions are leaving axon with no + ions being able to enter the neuron.

  31. Change in Ion permeability with Impulse. Why would Na+ enter the cell before K+? What is happening when Na+ enter the cell? What is happening when K+ leave the cell?

  32. Absolute Refractory Period • time needed to return the neuron’s membrane to Resting Membrane Potential • Limits the number of impulses that can be sent

  33. Intensity of Impulse • Number of times impulse is sent • More impulses; higher intensity

  34. Speed of Impulse • Presence of Myelin Sheath • Size of Neuron • Large neurons = less resistance; impulse travels faster through neurons larger in diameter

  35. Axon Bud • Responsible for sending chemical messengers (neurotransmitter) across the synapse. • Synaptic vesicles release NT by exocytosis • Receptor cells on the dendrites receive the NT.

  36. Axon Bud

  37. Exocytosis requires ATP

  38. Axon Bud Animation • Impulse travels to axon bud • Ca ions enter through gated channels of axon bud. • Ca attaches to vesicles; NT released by exocytosis. • NT attaches to receptor cells on dendrite • Na gates open in dendrite and Na ions begin to enter the dendrite. Reach Threshold = Action Potential

  39. How is the impulse stopped? • As long as the NT remains attached to a receptor, it will continue to send impulses. • NT is stopped by: • Reuptake of NT into vesicles; begin as soon as impulse begins in postsynaptic neuron • NT diffuses away from postsynaptic synapse • Enzymes break down NT. • I.e. neurotransmitter acetylcholine is broken down by acetylcholinerase • Acetylcholine → acetate + choline

  40. What happens at the Axon Bud!

  41. SSRI – Selective Serotonin Reuptake Inhibitor

  42. Antidepressants

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