intro to autonomics and dermatomes

• Major ganglia in the sympathetic nervous system (fight or flight)


  • Paravertebral ganglia
  • Preaortic ganglia: celiac ganglion, superior mesenteric ganglion, inferior mesenteric ganglion, inferior hypogastric plexus
• Major ganglia in the parasympathetic nervous system (rest and digest)


  • Parasympathetic cranial ganglia (4): ciliary, otic, submandibular, pterygopalatine
  • Parasympathetic ganglia: small clusters close to/embedded in target organs
• Vagus nerve (CNX)


  Nerve that innervates the majority of parasympathetics
• Parasympathetic functions


  • GI motility (sphincters relaxes), mucus production (in nose, digestive, etc.), decrease heart rate, broncho-constriction, increased tear production, pupils constrict
• Structures that carry parasympathetic signals


  • Cranial nerves (head and neck)
  • Prearterial plexes
  • Pelvic splanchnic nerve (branch off ventral rami, not sympathetic chain)
• Major functions of the sympathetic nervous system


  • Contract smooth muscle sphincters (GI tract, eye)
  • Sweating
  • Increase heart rate
  • Bronchodilation
  • Dilate peripheral blood vessels
  • Constrict visceral vessels
  • Dry/clear/open oral and nasal passages
  • Fewer tears
• Lesions above Stellate ganglion


  No sympathetics to head and neck, Horner's syndrome: decreased sweating, droopy eyelid, constricted pupil
• White ramus and gray ramus communicans


  1. White ramus communicans: on-ramp to the freeway, location for a signal enters sympathetic chain

  2. Gray ramus communicans: off-ramp to freeway, location for a signal leaves sympathetic chain
• Main pathway for sympathetic signals travel and reach their targets


  1. Synapse in paravertebral (sympathetic chain) ganglion and continue to target OR exit sympathetic chain without synapsing, synapse at preaortic ganglion, then continue to target

  2. Sympathetics to periphera (head and neck, integument, blood vessels, etc.,): Synapse in paravertebral ganglia, Exit via gray ramus communicans, Distribute to targets on branches of dorsal and ventral rami, and arterial plexes

  3. Sympathetics to thorax: Synapse in paravertebral ganglia, Distributed to targets on periarterial plexes and cardiopulmonary n.

  4. Sympathetics to abdomen: Exit sympathetic chain via splanchnic nerve, Synapse at preaortic ganglia, Distribute to targets via prearterial plexes
• Dermatome


  Area of skin that receives cutaneous innervation from a particular spinal level
• Dermatomes "twist" during development, reflecting our evolutionary history and current locomotion, not all dermatome maps look the same
• Consistent dermatome/landmarks


  • C6: thumb
  • C7: middle finger
  • C8: pinky finger
  • T4: nipple line
  • T6: xiphoid process
  • T10: umbilicus
  • L5: big toe
  • S5: perianal region
• Cutaneous nerves


  Named, sensory nerves that supply the skin and other superficial structures
• Difference between dermatome and cutaneous nerve innervation patterns


  Dermatome borders are more vague and variable, Cutaneous nerve innervation patterns are more consistent and sharply defined borders
• Myotomes


  Area of muscle that receives cutaneous innervation from a particular spinal level
• Major myotomes


  • C1-2: cervical flexion
  • C3: lateral cervical flexion
  • C4: scapula elevation
  • C5: shoulder abduction
  • C6: elbow flexion, wrist extension
  • C7: elbow extension, wrist flexion
  • C8: thumb extension
  • T1: finger abduction
  • L1-2: hip flexion
  • L3: knee extension
  • L4: dorsiflexion
  • L5: big toe extension
  • S1: plantarflexion
  • S2: knee flexion
• Preganglionic neurons originate from the spinal cord and travel through white rami communicans to synapse with ganglia near target organs.