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Neural Tissue

Neural Tissue. Parts list. Overview: Nervous system functions. Sensory input (info travels “in” along afferent pathways) Sensory neurons Integration (information is processed) Spinal cord and brain Motor output (info results in a response, travels along efferent pathways)

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Neural Tissue

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  1. Neural Tissue Parts list

  2. Overview: Nervous system functions • Sensory input (info travels “in” along afferentpathways) • Sensory neurons • Integration (information is processed) • Spinal cord and brain • Motor output (info results in a response, travels along efferentpathways) • Stimulation of skeletal muscle, smooth muscle, cardiac muscle, & glands

  3. Sensory-Motor Pathways

  4. Overview

  5. Neural tissue: specialized cells • Neurons • Supporting cells (non-excitable cells) or neuroglia; outnumber neurons 10 to 1 • Blood vessels • Connective tissue

  6. Neurons • Specialized cells that communicate with other cells via changes in the membrane potential and synaptic connections • Characteristics: • Extremely long-lived (> 100yrs) • Amitotic • Extremely high metabolic rate

  7. Typical Neuron

  8. Neurons have special names for cell structures • Cell body: contains the nucleus • Perikaryon: cytoplasm around the nucleus • Nisslbodies are localized RER and ribosomes

  9. Typical motor neuron

  10. Synapse of a motor neuron

  11. Classified by structure

  12. Classified by function(sensory or motor)

  13. Neuroglia are supporting cells

  14. Neuroglia are supporting cells Wandering police force CNS Regulating/recycling/maintaining myelinate axons Circulate CSF PNS

  15. Ependymal cells make and help circulate CSF

  16. Schwann cells in PNS

  17. Nerve regeneration is assisted by Schwann cells

  18. Neurophysiology

  19. Overview

  20. Neurons are excitable cells • Have we talked about a model in another cell for propagation of an impulse? • How does the chemical composition of the cell membrane promote a separation of ions? • Which ions are in greater concentration inside the cell? Outside the cell?

  21. Electrochemical gradient • A charge difference exists, like between poles of a battery. • Intracellular: high concentration of K+ ions & negatively charged proteins • Extracellular: high concentration of Na+ & Cl- ions

  22. Two gradients = • The sum of the chemical and electrical forces acting across the membrane = Electrochemical gradient (AKA membrane potential) • Size of the potential difference is measured in milliVolts (mV) • Neurons have a resting transmembrane potential of approx. -70mV

  23. Resting Membrane Potential

  24. Electrochemical gradient

  25. Ion diffusion in neurons • Ions are always diffusing, BUT can cross membrane quickly ONLY through channels • Types of channels • Passive or leak channels (ungated; always open) • Active or gated channels (always closed, unless…)

  26. Gated Channels • Chemically regulated: Respond to presence of particular chemicals • Voltage regulated: respond to changes in membrane potential • Mechanically regulated: respond to physical deformation Have we seen examples of these channels in other tissue?

  27. Gated Channels chemical electrical mechanical

  28. If gated channels open… • What happens to the transmembrane potential?

  29. Graded Potential • A change in the transmembrane potential that does not travel far from the area of stimulation • Definitions • Depolarization: shift towards 0mV • Repolarization: shift towards the resting membrane potential (~-60mV) • Hyperpolarization: membrane becomes more negative

  30. Graded Potential

  31. Graded Potential

  32. Graded Potential

  33. Action Potential • Propagated changes in the transmembrane potential that affect an entire excitable membrane and results in release of a neurotransmitter • ALL OR NOTHING response.

  34. Action Potential

  35. Action Potential

  36. AP Propagation

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