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Lecture 15

Lecture 15. PNS Bio-5 Anatomy JPHubbard Hartnell College. What is a nerve? Bundle of axons outside CNS, includes connective tissue coverings + blood vessels Coverings Endoneurium – covers single axon Perineurium – covers a bundle (fascicle) of axons Epineurium – covers many fascicles

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Lecture 15

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  1. Lecture 15 PNS Bio-5 Anatomy JPHubbard Hartnell College

  2. What is a nerve? • Bundle of axons outside CNS, includes connective tissue coverings + blood vessels • Coverings • Endoneurium – covers single axon • Perineurium – covers a bundle (fascicle) of axons • Epineurium – covers many fascicles • Axon = fiber • Nerve may include both afferent and efferent fibers

  3. Fig. 9.16

  4. Neuron wrapped in myelin sheath Epineurium Perineurium Axon of neuron

  5. As previous slide – magnified view Endoneurium Axon Myelin Sheath (Schwaan Cell

  6. Node of Ranvier ?

  7. Nerve Repair: Limited ability for regeneration (repair) PNS can repair damaged dendrites or axons CNS little repair are possible Axons & dendrites of PNS may be repaired if: neuron cell body remains intact schwann cells remain active and form a tube scar tissue does not form too rapidly

  8. Organization of the Nervous System CNS is brain and spinal cord PNS is everything else

  9. Autonomic vs. Somatic Nervous Systems • Somatic – • input from exteroceptors, propioceptors • Excitatory • Output to skeletal muscle • Single, heavy myelinated fiber • acetylcholine • Autonomic • Input from interoceptors • Excitatory or inhibitory • Output to visceral effectors • 2, lighter fibers, preganglionicmyelinated • Acetylcholine/epinephrine

  10. How many neurons in somatic pathway? • In autonomic pathway? • What happens to the preganglionic neuron in an autonomic pathway? • Where does the preganglionic neuron in an autonomic pathway arise?

  11. Plexuses Plexuses (singular: plexus): closely interwoven network of nerves outside CNS • Above and Below thoracic regions: • No rami communicantes • Ventral roots interwoven  plexuses • Cervical  phrenic nerve • Brachial  5 nerves – median, ulnar, radial • Lumbosacral plexus  femoral, sciatic (tibial + common fibular) + others

  12. Branches off Brachial Plexus

  13. Dermatomes and Myotomes • Regions monitored/controlled by pairs of spinal nerves • Some overlap exists • Significance: • Damage  specific regions impacted • Overlap: anesthesia needs to impact more than one nerve

  14. Motor Output by ANS dual innervation to most effectors --sympatheticdivision: ‘fight or flight’ increases heart rate, respiration, etc. --parasympatheticdivision: ’rest and digest’ “SLUDD” responses: - salivation - lacrimation - urination - digestion - defecation

  15. Parasympathetic Division • Craniosacral outflow • Output via cranial nerves or from sacral plexus • Long myelinated preganglionic fiber • Synapse in ganglion w/i or near effector • Short non-myelinated post ganglionic fibers • Localized effects • Neurotransmitter acetylcholine (cholinergic) – may be stimulatory or inhibitory • Effect depends on receptor

  16. Sympathetic Division • Thoracolumbar outflow • Output T1-L2 • Short myelinatedpreganglionic fiber • Enters in ganglion lateral to spinal cord • Remote from effector • Long non-myelinated post ganglionic fibers • Broad effects • Neurotransmitters acetylcholine (cholinergic) and/or adrenaline • generally excitatory

  17. Sympathetic Preganglionic fibers • Enter white rami – then do one of these: • Synapse in same trunk ganglion • Ascend/descend in sympathetic trunk – then form synapse • Pass through trunk w/o synapsing • Enter splanchnic nerve  collateral (preverterbral) ganglia • Enter adrenal medulla via greater splanchnic nerve

  18. Dorsal root Ventral root Dorsal ramus: Mixed from/to dorsal regions Dorsal root ganglion + ventral root Ventral ramus – from/to ant. body wall and limbs Rami communicantes Gray rami White rami Sympathetic ganglion

  19. Continues in splanchnic nerve

  20. Sympathetic chain ganglia Splanchnic nerve

  21. Prevertebral (Collateral ganglia) – preganglionic sympathetic fibers may synapse in these Celiac ganglion Superior mesenteric ganglion Inferior mesenteric ganglion

  22. Where does a preganglionic fiber in the sympathetic division synapse? • Where do preganglionic fibers in the sympathetic division arise? • What is the impact of sympathetic output? • Why do we refer to output from the parasympathetic division as craniosacral? • Which division has output involving cranial nerves? • What is a spanchnic nerve? • Which aspect of the ANS innervates the adrenal medulla? • What neurotransmitters are associated with the sympathetic division? • With the parasympathetic division? • In the ANS myelinated fibers are associated with ____________ fibers.

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