Autonomic Nervous System

Question 1

Enteric Nervous System

Answer 1

o ~100 million neurons (intrinsic neuronal network of GI tract – from esophagus to anus)
o Functions: reflexive functions of GI tract (gut secretions, absorption , & mixing/moving of food)
o Control:
 SNS inhibits its function
 PSNS excites/stimulates its function – vagus nerve
o Diverse neurotransmitters (ACh, NE, 5-HT)
o Arterial Supply: celiac trunk, SMA, IMA
o Venous Return: portal system to liver
o Meissner’s (submucus) Plexus - in the submucosa
o Auerbach’s (myenteric) Plexus – between the inner circular and outer longitudinal muscles

Question 2

Sympathetic nervous System

Answer 2

– a.k.a. thoraco-lumbar outflow
o Two neuron hook-up system (SHORT preganglionic; LONG postganglionic neurons)
 Myelinated preganglionic axons
 Unmyelinated postganglionic axons
o Receives input via general visceral afferents that synapse in dorsal root ganglion
 Dorsal root ganglion – pseudo-unipolar – where sensory neurons from viscera SYNAPSE; one axon has branches to both the peripheral and central nervous system

Question 3

Preganglionic Sympathetic Neurons

Answer 3

– located in lateral horn (column) of spinal cord (T1-L2/3)
o Axons exit the spinal cord via ventral root and travel on spinal nerves to reach ganglion (sympathetic or parasympathetic)
 Spinal nerve – forms after the dorsal and ventral root come together
• Dorsal primary rami – innervates deep muscles of back and medial/lateral cutaneous branches
o Main Function: send postganglionic fibers to skin to innervate smooth muscle of blood vessels, arrector pili muscles of hair cells in skin, sweat glands
• Vental primary rami – innervates superficial muscles of back and medial/lateral/anterior/posterior cutaneous branches
o White ramus communicantes – myelinated
o Gray ramus communicantes – unmyelinated

Question 4

Postganglionic Sympathetic Neurons: synapse at different level

Answer 4

o Lateral horn  ventral root  spinal nerve  white ramus communicantes  up/down sympathetic trunk  SYNAPSE at different level of vertebrae (cervical /lumbar/sacral ganglia) gray ramus communicantes 
 Above level of T1 there are inferior/middle/superior cervical ganglion that send out postganglionic fibers that form cardiac plexus to supply heart

Question 5

Postganglionic Sympathetic Neurons: synapse at same level

Answer 5

o Lateral horn  ventral root  spinal nerve  white ramus communicantes  SYNAPSE sympathetic trunk  gray ramus communicantes  peripheral nerve
 T1-T2 Intermedio-lateral Cell Column  superior cervical ganglion  pupillary dilator muscles, sweat glands, and vascular smooth muscle in head/neck
 Ex: eye, mouth glands, parotid glands, heart, bronchi

Question 6

Postganglionic Sympathetic Neurons: splanchnic nerves

Answer 6

o Lateral horn  ventral root  spinal nerve  white ramus communicantes  preganglionic splanchnic (greater, lesser, least) nerves  SYNAPSE prevertebral (collateral) ganglion (celiac/superior mesenteric/inferior mesenteric)  to viscera
 Greater splanchnic – T5-T9  celiac ganglion (stomach, small intestine)
 Lesser splanchnic – T10-T11  superior mesenteric ganglion (small intestine, beginning of large intestine via ENS)
 Least splanchnic – T11  inferior mesenteric ganglion (end of large intestine via ENS, ductus deferens)

Question 7

Postganglionic Sympathetic Neurons: adrenal

Answer 7

o Lateral horn  ventral root  spinal nerve  white ramus communicantes  sympathetic trunk  gray ramus communicantes  SYNAPSE adrenal medulla
 NO postganglionic neurons; the preganglionic neuron themselves secrete catecholamines and are derived from neurocrest

Question 8

Parasympathetic

Answer 8

– a.k.a. cranio-sacral outflow from brainstem nuclei travel on oculomotor (III), facial (VII), glossopharyngeal (IX), vagus (X) – hitchhike a ride on the cranial nerves

Question 9

Parasympathetic involving oculomotor nerve

Answer 9

o Nucleus of Edinger-Westphal nucleus  oculomotor (III) nerve  ciliary ganglion  pupillary constrictor and ciliary muscles

Question 10

Parasympathetic involving facial nerve

Answer 10

o Lacrimal Nucleus  facial (VII) nerve  greater postnasal nerve  pterygopalatine ganglion  lacrimal and nasal glands
o Superior Salivatory Nucleus  facial (VII) nerve  chorda tympani nerve  submandibular ganglion  submandibular, salivary, sublingual glands and oral mucosa

Question 11

Parasympathetic involving glossopharyngeal nerve

Answer 11

o Inferior Salivatory Nucleus  glossopharyngeal (IX) nerve  lesser petrosal nerve  otic ganglion  parotid gland

Question 12

Parasympathetic involving vagus nerve

Answer 12

o Nucleus ambiguous  vagus (X) nerve  heart
o Dorsal Vagal Nucleus  Vagus (X) nerve  remaining thoracic and abdominal viscera UP TO left colic flexure
o Dorsal Vagal Nucleus  pharyngeal (X) nerve  superior laryngeal nerve  enteric ganglion  pharyngeal mucosal glands
o Dorsal Vagal Nucleus  internal laryngeal (X) nerve  recurrent laryngeal nerve  enteric ganglion  laryngeal mucosal glands

Question 13

Parasympathetic Sacral Outflow

Answer 13

• from sacral spinal cord levels and travel on sacral nerves S2, S3, S4
  o Supplies AFTER left colic flexure of large intestine, urinary bladder, & genital erectile tissue
  o Travel as pelvic splanchnic nerve to parasympathetic ganglion

Question 14

Autonomic Distribution of the Eye

Answer 14

o SNS: preganglionic fibers ascend from T1/T2  SYNAPSE superior cervical ganglion  postganglion axons travel on internal carotid artery and form plexus  pass through ciliary ganglion  travel to eye via short ciliary nerve
o PSNS: preganglionic Edinger-Westphal nerves travel along oculomotor nerve  SYNAPSE ciliary ganglion  travel to eye via short ciliary nerve
o Afferent sensory fibers: send signal to brainstem (trigeminal ganglion)

Question 15

Autonomic Distribution of Lacrimal Gland

Answer 15

o SNS: preganglionic fibers ascend from T1/T2  SYNAPSE superior cervical ganglion  travel via internal carotid artery  deep petrosal nerve  joins with great petrosal nerve  continues as nerve of pterygoid canal  pterygopalatine ganglion
 Deep petrosal nerve – ONLY purely sympathetic nerve in the body
o PSNS: superior salivatory nucleus  along facial nerve  to great petrosal nerve  joins SNS fibers to join pterygoid canal  pterygopalatine ganglion
 Great petrosal nerve  PURELY parasympathetic nerve
o Deep and great petrosal nerves come together to form nerve of pterygoid canal (mix of postganglionic SNS and preganglionic PSNS); fibers continue to pterygopalataine ganglion
 SNS fibers go through nose via blood vessels for nasal mucosal & lacrimal gland supply
 PSNS fibers synapse & go down to maxillary nerve then lacrimal nerve & lacrimal gland

Question 16

Autonomic Distribution of Submandibular and Sublingual Glands

Answer 16

o SNS: fibers from T1/T2 ascend  SYNAPSE superior cervical ganglion  travel along maxillary artery branch of external carotid artery  mucosa of nose, hard/soft palate, and into larynx/pharynx
o PSNS: superior salivatory nucleus along facial nerve to chorda tympani nerve  joins with lingual nerve to reach and SYNAPSE submandibular ganglion  sends fibers to submandibular and sublingual salivary glands and also to larynx/pharynx
 Chorda tympani preganglionic parasympathetic nerve has two-way traffic  carries taste fibers from anterior 2/3 of tongue back to brainstem
 Chorda tympani and great petrosal nerves innervate ALL of the salivary glands

Question 17

Autonomic Distribution of Parotid Gland

Answer 17

o SNS: fibers from T1/T2 ascend  SYNAPSE superior cervical ganglion  postganglionic fibers travel on branches of external carotid artery to parotid gland
o PSNS: inferior salivatory nucleus  fibers along glossopharyngeal nerve  tympanic nerve  tympanic plexus  lesser petrosal nerve  SYNAPSE otic ganglion  postganglion axons travel with auriculotemporal nerve to the parotid gland
 Auriculotemporal nerve has a hole in the middle of it to allow the middle meningeal artery to pass through and supply the dura mater

Question 18

Types of Synapses and Receptors used in Autonomic Nervous System

Answer 18

SNS
 Preganglionic neurons – cholinergic synapses an d nicotinic receptors
 Postganglionic neurons – adrenergic synapses and alpha/beta adrenergic receptors

PSNS
 Preganglionic – cholinergic synapses and nicotinic receptors
 Postganglionic – cholinergic synapses and muscarinic receptors