ANATOMY & PHYSIOLOGY - CLUTCH CH THE AUTONOMIC NERVOUS SYSTEM.

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2 ANATOMY & PHYSIOLOGY - CLUTCH CONCEPT: THE AUTONOMIC NERVOUS SYSTEM: DIVISIONS AND STRUCTURE The Autonomic Nervous System and its Divisions: Autonomic Nervous System (ANS) controls all the involuntary, subconscious processes that keep you. Reflexes that maintain blood pressure, heart rate, respiratory rate, digestive function, O2 and CO2 levels, etc. The ANS has two divisions that usually have effects: Sympathetic Nervous System (SNS)= Fight-or-Flight. Make you ready for activity/stress. - Heart Rate, Digestion, etc. Parasympathetic Nervous System (PSNS)= Rest-and-Digest. Housekeeping functions in times of low activity. - Heart Rate, Digestion, etc. SNS and PSNS activity ( tone ) are like a see-saw SNS happens with PSNS, and vice-versa. It s up or down, never on or off. EXAMPLE: Some organs innervated by one or both autonomic divisions and the effects on those organs. Page 2

3 ANATOMY & PHYSIOLOGY - CLUTCH ANS Patterns from the CNS: The ANS exerts its effects via the nervous system autonomic nerves leave the CNS and project into the periphery. The SNS and PSNS have nerves that leave the CNS in separate, specific, predictable places. SNS nerves leave the CNS from the middle of the spinal cord, specifically segments T1 through L2. PSNS nerves leave the CNS from the brainstem and the sacral spinal cord. - Cranial Nerve X the Vagus nerve is the most important PSNS nerve. EXAMPLE: Note where the sympathetic and parasympathetic nerves leave in that same figure. Page 3

4 General ANS Patterns in the Periphery: Both divisions work via a two-neuron pathway. One neuron leaves the CNS, the second neuron synapses onto the target. Ganglion= The cluster of cell bodies in the periphery where the two neurons synapse with each other. Preganglionic Neuron= The first neuron (with its cell body in the CNS that synapses onto the second neuron). Postganglionic Neuron= The second neuron (with its cell body in a ganglion that synapses onto target organ). EXAMPLE: A schematic of general ANS patterns. CNS Pre-Ganglionic Neuron Ganglion Post-Ganglionic Neuron Target Organ Location of Synapses in the Periphery: The two divisions differ in where the preganglionic and postganglionic neurons synapse. SNS: Synapse in the Sympathetic Chain Ganglion, a chain of cell bodies running parallel to the spinal cord. -Preganglionic neuron has a short axon, postganglionic has a longer axon. PSNS: Synapse is in a small, discrete ganglion, on or near target organ. -Preganglionic neuron has a long axon, postganglionic has a very short axon. EXAMPLE: A comparison of synapse/ganglion location between the SNS and PSNS: SYMPATHETIC: Spinal Cord Sympathetic Chain (T1-L2) Ganglion Pre-Ganglionic Neuron Post-Ganglionic Neuron Target Organ PARASYMPATHETIC: CNS (Brainstem or Sacral Spinal Cord) Pre-Ganglionic Neuron Ganglion Near Target Organ Post-Ganglionic Neuron Target Organ Page 4

5 Neurotransmitter and Receptor Patterns: Note how there are two synapses in these pathways: preganglionic postganglionic and postganglionic receptor. The SNS and PSNS have different patterns for the NT and post-synaptic receptor used at each. SNS Neurotransmitter and Receptor Patterns: For neurons in the SNS: Preganglionic NT=Acetylcholine Postganglionic NT= Norepinephrine Postganglionic Receptor= nicotinic acetylcholine receptor. Target Organ Receptor= Adrenergic (possible subtypes: α1, β1, β2). EXAMPLE: A summary of the neurons, synapses, NTs, and receptors used by the sympathetic nervous system. Spinal Cord (T1-L2) Sympathetic Chain Ganglion Pre-Ganglionic Neuron Post-Ganglionic Neuron Target Organ NT= Acetylcholine Rec=Nicotinic AchR NT= Norepinephrine Rec=Adrenergic (α 1, β 1, β 2 ) PSNS Neurotransmitter and Receptor Patterns: For neurons in the PSNS: Preganglionic NT=Acetylcholine Postganglionic NT= Acetylcholine Postganglionic Receptor= nicotinic acetylcholine receptor Target Organ Receptor= muscarinic acetylcholine receptor EXAMPLE: A summary of the neurons, synapses, NTs, and receptors used by the parasympathetic nervous system. CNS (Brainstem or Sacral Spinal Cord) Pre-Ganglionic Neuron Ganglion Near Target Organ Post-Ganglionic Neuron Target Organ NT= Acetylcholine Rec=Nicotinic AchR NT=Acetylcholine Rec=Muscarininc AchR Page 5

6 PRACTICE 1: Oxybutynin is a drug used to relieve urinary incontinence. One of its major side effects is constipation. Based on that side effect, which branch of the autonomic nervous system is likely blocked by oxybutynin? a) Sympathetic NS. b) Parasympathetic NS. PRACTICE 2: Albuterol is a drug used to treat asthma. One of its major side effects is tachycardia (an increase in heart rate). Based on that side effect, which branch of the autonomic nervous is likely activated by albuterol? a) Sympathetic NS. b) Parasympathetic NS. PRACTICE 3: A cardiothoracic surgeon is implanting a pacemaker in a patient s heart. In the process she damages an autonomic ganglion located within the wall of the patient s heart. Which branch of the autonomic nervous system will be directly affected by damage to this ganglion? a) Sympathetic NS. b) Parasympathetic NS. PRACTICE 4: Rocuronium is a drug that blocks nicotinic acetylcholine receptors. On which of the following type(s) of cell(s) can rocuronium act? (Choose all that apply.) a) Pre-ganglionic sympathetic neurons. b) Pre-ganglionic parasympathetic neurons. c) Post-ganglionic sympathetic neurons. d) Post-ganglionic parasympathetic neurons. e) Targets of sympathetic innervation. f) Targets of parasympathetic innervation. Page 6

7 PRACTICE 5: Propranolol is a drug that blocks β adrenergic receptors. On which of the following type(s) of cell(s) can propranolol act? (Choose all that apply.) a) Pre-ganglionic sympathetic neurons. b) Pre-ganglionic parasympathetic neurons. c) Post-ganglionic sympathetic neurons. d) Post-ganglionic parasympathetic neurons. e) Targets of sympathetic innervation. f) Targets of parasympathetic innervation. PRACTICE 6: Physostigmine is a drug that blocks acetylcholinesterase, thereby raising the amount of acetylcholine present in the synaptic cleft at all synapses that use Ach as an NT. Which of the following type(s) of cell(s) will be affected by the actions of physostigmine? (Choose all that apply.) a) Pre-ganglionic sympathetic neurons. b) Pre-ganglionic parasympathetic neurons. c) Post-ganglionic sympathetic neurons. d) Post-ganglionic parasympathetic neurons. e) Targets of sympathetic innervation. f) Targets of parasympathetic innervation. PRACTICE 7: Atropine is a drug that blocks muscarinic acetylcholine receptors. On which of the following type(s) of cell(s) can atropine act? (Choose all that apply.) a) Pre-ganglionic sympathetic neurons. b) Pre-ganglionic parasympathetic neurons. c) Post-ganglionic sympathetic neurons. d) Post-ganglionic parasympathetic neurons. e) Targets of sympathetic innervation. f) Targets of parasympathetic innervation. Page 7

8 CONCEPT: PARASYMPATHETIC DIVISION The parasympathetic division maintains homeostasis at rest There are two main components: the cranial and sacral The cranial components of the parasympathetic division include several cranial nerves - Oculomotor nerve (CN III): extends to ciliary ganglion to cause pupil and lens contraction - Facial (CN VII): extends to pterygopalatine ganglion and submandibular ganglion - Causes gland secretion (lacrimal, salivary) - Glossopharyngeal (CN IX): extends to otic ganglion to cause parotid gland secretion - Vagus (CN X): travels to various viscera The sacral components include the pelvic splanchnic nerves in S2-S4 spinal cord segments - Organs innervated here include the intestine, rectum, bladder, ureter, and reproductive organs Page 8

9 EXAMPLE: Page 9

10 CONCEPT: SYMPATHETIC DIVISION ORGANIZATION The sympathetic division is more complex than the parasympathetic division The lateral horn of T1-L2 spinal cord regions hold the pre-ganglionic cell bodies - They then exit the spinal cord through the ventral horn and the anterior roots of T1-L2 spinal nerves Sympathetic trunk ganglia sit lateral to the vertebral column and anterior to the spinal nerves - Looks like a pearl necklace, where the trunks are the strings and the pearls are the ganglions - One sympathetic trunk ganglion is associated with each spinal nerve Exception: there are 3 cervical ganglia; superior, middle, inferior (not 8 for C1-C8) EXAMPLE: Page 10

11 Rami communicantes connect the spinal nerves to the sympathetic trunk - White rami communicantes is the area where preganglionic axons enter the sympathetic trunk - Gray rami communicantes is the area where postganglionic axons leave the trunk to the spinal nerve EXAMPLE: Page 11

12 Sympathetic splanchnic nerves are preganglionic axons that don t synapse with the sympathetic trunk ganglion - Terminate in prevertebral ganglia located in the cavity - Celiac ganglia synapse with the greater thoracic splanchnic nerves (T5-T9) - Innervate: stomach, spleen, gallbladder, liver, small intestine, pancreas - Superior mesenteric ganglia synapse with preganglionic neurons from T10-T12 - Innervate: small intestine, large intestine, pancreas, kidneys, ureters - Inferior mesenteric ganglia synapse with preganglionic axons from L1-L2 - Innervate: large intestine, rectum, urinary bladder, ureters, reproductive organs Page 12

13 EXAMPLE: Page 13

14 ANATOMY & PHYSIOLOGY - CLUTCH CONCEPT: SYMPATHETIC PATHWAYS There are 4 pathways sympathetic preganglionic neurons synapse with the 1. Spinal nerve pathway - Spinal cord à white rami communicansà sympathetic trunk ganglion à gray rami communicans à spinal nerve à skin gland, vessels, and muscles 2. Postganglionic sympathetic nerve pathway - Spinal cord à white rami communicans à sympathetic trunk ganglion à internal organs, skin and eye Page 14

15 ANATOMY & PHYSIOLOGY - CLUTCH 3. Splanchnic nerve pathway - Spinal cord à white rami communicans à through the sympathetic trunk ganglion (does not synapse here) à prevertebral ganglia à abdominal and pelvic organs 4. Adrenal medulla pathway - Spinal cord à white rami communicans à sympathetic trunk (does not synapse here) à preverebral ganglion (does not synapse here) à synapse on adrenal medulla (part of adrenal gland) EXAMPLE: Page 15

16 CONCEPT: AUTONOMIC PLEXUSES Autonomic plexuses are groups collections of various types of axons These axons include: - Sympathetic postganglionic axons - Parasympathetic preganglionic axons - Visceral sensory axons The collections of axons do not synapse with each other, just similar organs EXAMPLE: Page 16

17 There are 5 main autonomic plexuses The cardiac plexus is found in the mediastinum, controls heart rate and blood pressure - Sympathetic: Postganglionic axons from the cervical and thoracic sympathetic trunk ganglia - Works to increase heart rate and blood pressure - Parasympathetic Preganglionic axons from the nerve - Works to decrease heart rate Page 17

18 The pulmonary plexus controls bronchodilation and - Sympathetic: Postganglionic axons from the cervical and thoracic sympathetic trunk ganglia - Works to cause bronchodilation (increase bronchi diameter) - Parasympathetic Preganglionic axons from the vagus nerve - Works to cause bronchoconstrction (decrease bronchi diameter) EXAMPLE Page 18

19 The esophogeal plexus controls of the esophagus - Sympathetic: Postganglionic axons from the cervical sympathetic trunk ganglia - Works to inhibits muscle movement - Parasympathetic Preganglionic axons from the vagus nerve - Works to control swallowing reflex EXAMPLE: Page 19

20 The abdominal aortic plexus controls abdominal and pelvic organs - Sympathetic: Postganglionic axons from the prevertebral ganglia - Parasympathetic Preganglionic axons from the vagus nerve and pelvic splanchnic nerves - Composed of sub-plexuses: - Celiac plexus, superior mesenteric plexus, and inferior mesenteric plexus EXAMPLE: Page 20

21 The hypogastric plexus controls pelvic - Sympathetic: Postganglionic axons from the aortic plexus and lumbar region of sympathetic trunk - Parasympathetic Preganglionic axons from pelvic splanchnic nerves EXAMPLE: Page 21