4,5 - Autonomic Nervous System

Question 1

Divisions of the nervous system (diagram)

Answer 1

Question 2

Background and purpose of the autonomic nervous system (ANS)

Answer 2

• The purpose of the ANS is to regulate the body’s internal environment
  -Prepare the body for perceived stress
  -Promote recovery and routine maintenance
• Visceral motor neurons innervates non-skeletal
  (non-somatic) muscles
  -Cardiac muscle
  -Smooth muscle (blood vessels, walls of viscera)
  -Glands
  -Skin
• Generally not under conscious control
• Modulatory:
  -End organ effectors do not depend entirely on the ANS for proper function, but serve to adjust their activity in accordance with needs of the body
  →ex: heart can function if nerves are severed
• Homeostasis
  -Provides the optimal internal environment during normal and stressful periods

Question 3

Sympathetic Division of the ANS

Answer 3

• Extreme responses referred to as “fight or flight”
  -Responses involved in stress, anger, fear
  -Increase in heart rate, breathing rate, increased blood pressure
• Ordinary responses may be subtle and hardly noticed

Question 4

Motor neuron vs. Sympathetic neuron:

Answer 4

• Somatic Nervous System
  -One neuron pathway
  -Originates in ventral horn
  -Heavily myelinated
  →Fast conduction
• Sympathetic division of ANS
  -Two neuron pathway
  →First preganglionic neuron originates in lateral horn
  →T1-T12; L1-L2 (also called thoracolumbar division)
  →Second ganglionic neuron synapses outside of CNS
  -Lightly myelinated or unmyelinated → slow

Question 5

Sympathetic neurons

Answer 5

Pre- and post-ganglionic fibers both demonstrate
convergence and divergence
* No 1-1 relationship between pre and post ganglionic neurons
* Neuronal convergence: each postganglionic cell may receive synapses from multiple preganglionic cells
* Divergence: each preganglionic fiber branches and synapses with multiple postganglionic fibers
* Sympathetic division → widespread effect!

Question 6

Sympathetic preganglionic fibers

Answer 6

Question 7

Ganglion in sympathetic division

Answer 7

• Sympathetic chain
  -Located on each anterolateral
  side of vertebral column
  -Extend from base of skull to
  coccyx
  -~22 ganglia

Question 8

Sympathetic chain/sympathethic trunk

Answer 8

• Sympathetic chain
  -Located on each anterolateral
  side of vertebral column
  -Extend from base of skull to
  coccyx
  -~22 ganglia
• Neuron enters through white
  ramus communicans

1. Synapse in chain ganglion and follow to skin
2. Ascend/descend to superior/inferior ganglion and synapse
3. Pass through the chain without synapsing

Question 9

Ganglion in sympathetic division

Answer 9

• Sympathetic ganglion outside of chain
• Input from the splanchnic nerves
• Collateral ganglia (prevertebral ganglia)
  -Celiac ganglion
  →stomach, liver, gallbladder, spleen
  -Superior mesenteric ganglion
  →small intestine, ascending and transverse colon
  -Inferior mesenteric ganglion
  →descending colon, kidney, bladder

Question 10

Sympathetic Division: pre and post-ganglionic

Answer 10

• Preganglionic
  -Short in length
  -Synapse with postganglionic neuron near cord
  -Cholinergic: Release acetylcholine (ACh) to activate nicotinic receptors on postganglionic neuron
• Postganglionic
  -Long
  -Synapse on target viscera, etc.
  -Adrenergic: Release norepinephrine (NE) on adrenergic receptors on neuroeffector junction
  -Exception: Postganglionic neurons innervating sweat glands (thermoregulation) release ACh

Question 11

cholinergic receptors

Answer 11

Question 12

Noradrenergic Junction

Answer 12

NE synthesis/release
* Adrenergic neurons transport precursor amino acid tyrosine into nerve ending
* Tyrosine is converted to dopamine and
transported into vesicle by vesicular monoamine transporter (VMAT)
* Dopamine converted to NE
* Opening of voltage-sensitive Ca2+ channels causes physiologic release of transmitter

Fate of NE after release
* Reabsorbed by nerve terminal by NE transporter and either reused or broken down by the enzyme monoamine oxidase (MAO)
* Diffuse into surrounding tissue
* Some picked up by the bloodstream, circulates through body

Question 13

Adrenergic receptors

Answer 13

Alpha (⍺) receptors (⍺1, ⍺2) are generally excitatory (i.e. constriction/contraction) except in gut

Beta (β) receptors (β1, β2, β3) are inhibitory (e.g. relaxation in lung) or excitatory (e.g. heart, liver and fat cells)

Question 14

⍺-Adrenergic receptors

Answer 14

Question 15

β-Adrenergic receptors

Answer 15

Question 16

Autonomic Neuroeffector Junctions

Answer 16

Question 17

overview of the sympathetic division of the autonomic nervous system (diagram)

Answer 17

Question 18

Adrenal medulla

Answer 18

• Middle (medulla) of gland
• Postganglionic cells have lost their axons
• Nicotinic receptors
• Contains phenylethanolamine-N-methyltransferase
• Systemic release of epinephrine and norepinephrine in extreme cases
• 80% epinephrine/20% norepi

Question 19

Overview of the Autonomic Nervous System (sympathetic and parasympathetic divisions and innervations diagram)

Answer 19

Question 20

Parasympathetic division background and key features

Answer 20

• Key features
  -Recovery, routine maintenance, digestion and waste elimination
  -“Rest and Digest”
  -Originates in cranium and sacral cord (S2-4) (para = “around”)
  →Also called Craniosacral division
  -Cholinergic
• Similarities w/ sympathetic division
  -Two neuron pathway, preganglionic and postganglionic
  -Use nicotinic receptors in ganglionic synapse
  -Varicosity at effector organ
• Differences
  -Craniosacral origin
  -No parasympathetic innervation of skin/extremities
  -Muscarinic receptors at target organ
  -Long preganglionic fibers, short postganglionic fibers
  -Minimal convergence and divergence → more direct effects
• Neural divergence
  -There is some neural divergence, but much less than in sympathetic division
  -Relatively selective in its stimulation of target organs

Question 21

Cranial nerves (background)

Answer 21

• Nerves that emerge directly from the brain
• 12 pairs of cranial nerves, numbered I to XII, from rostral to caudal
• The names of the cranial nerves reflect their general distribution and function
• Bundles of sensory and motor neurons that transmit information from sensory receptors and innervate muscles or glands

Question 22

cranial nerves (list)

Answer 22

Question 23

Cranial nerves in the parasympathetic division

Answer 23

Cranial Nerves
* III – pupils constrict (near vision); ciliary muscles contract (spherical lens)
* VII – glands of face (tears, nasal mucus, submandibular and sublingual salivary glands) increase secretion
* IX – increased secretion of parotid salivary gland
* X – visceral organs of thorax and abdomen
-Decreases heart rate
-Causes bronchial constriction
-Stimulates digestive glands (e.g. in liver, pancreas)
-Increases smooth muscle motility of digestive tract

Question 24

CN III: Oculomotor

Answer 24

• Eye muscles including ciliary and sphincter pupillae
• ANS nucleus: Edinger-Westphal in the midbrain (mesencephalon)

Question 25

CN VII: Facial

Answer 25

* Muscles/glands of face, taste * ANS nucleus: Superior salivatory nucleus (pons) * Two branches: -sphenopalatine ganglion -submandibular (submaxillary) ganglion

Question 26

CN IX: Glossopharyngeal

Answer 26

* Sensory fibers, parasympathetic fibers to the parotid gland via the otic ganglion * ANS nucleus: Inferior salivatory nucleus (medulla)

Question 27

CN X: Vagus

Answer 27

* Muscles of the larynx, pharynx, palate * Motor/sensory from the gut tube, heart and lungs * ANS nucleus: Dorsal motor nucleus (medulla) * Ganglia near viscera

Question 28

Parasympathethic division (diagram)

Answer 28

Question 29

Parasympathetic division * Sacral Cord (S2-S4)

Answer 29

**Sacral Cord (S2-S4)** * Pelvic splanchnic nerves * Smooth muscle and glands of the pelvis -Promotes digestion and waste elimination via the descending colon -Contracts bladder wall -Preparation for sexual activity (e.g. erection of penis)

Question 30

Sympathetic vs. Parasympathetic: Neurotransmitters

Answer 30

**Sympathetic Division** * Preganglionic – Cholinergic (nicotinic) * Postganglionic – Adrenergic (a and b) **Parasympathetic Division** * Preganglionic – Cholinergic (nicotinic) * Postganglionic – Cholinergic (muscarinic)

Question 31

Cholinergic Synapse

Answer 31

Question 32

Muscarinic receptor subtypes

Answer 32

* G-protein (Gi, Gq) * Inhibitory in the heart -K+ channels, Inhibition of adenylate cyclase * Excitatory in smooth muscle and glands -Increased intracellular calcium * 5 different subtypes (M1-M5)

Question 33

Muscarinic receptors

Answer 33

Question 34

Muscarinic M2

Answer 34

Question 35

Muscarinic M3

Answer 35

Question 36

End Organ Innervation

Answer 36

Question 37

Dual Innervation

Answer 37

**Antagonistic** * Effects oppose each other * e.g. sympathetic activation speeds up heart while parasympathetic activation slows down the heart **Cooperative** * Divisions produce a unified overall effect * e.g. male sexual response → parasympathetic: mediates erection while sympathetic mediates ejaculation **Dominant tone** * Even though both divisions innervate a single organ, one may have greater tonic activity ***Dual Innervation** is not always necessary to produce opposite effects* * e.g. in some instances this occurs with the control of blood pressure (extremities and body wall) * The sympathetic fibers of blood vessels have a baseline sympathetic tone which keeps the blood vessel in a state of partial constriction – vasomotor tone * increase in firing rate causes vasoconstriction * decrease in firing rate causes vasodilation (allowing smooth muscle to relax)

Question 38

Diagramatic overview of the ANS (sympathetic, parasympathetic)

Answer 38

Question 39

Horner’s Syndrome

Answer 39

* Primarily an acquired pathologic condition, but may also be congenital: →Interruption of central pathway, preganglionic neurons, and postganglionic neurons can result in Horner’s Syndrome * Ipsilateral loss of sympathetic innervation to: -smooth muscle of upper eyelid – drooping (ptosis) -dilator pupillae muscle – pupillary constriction (miosis) -sweat glands of face – causing anhidrosis -smooth muscle of blood vessels – vasodialation (skin becomes flush and warm to the touch) * Preganglionic neuron axons are anatomically related to: (symptoms can include) * spine * apex of lung * cervical pleura * subclavian artery * common carotid * internal jugular * thyroid gland * upper ribs

Question 40

Denervation Hypersensitivity

Answer 40

* Autonomic lesion eliminates the release of neurotransmitter at ganglion or on effector * Denervated structures show an increase in sensitivity to their neurotransmitters, which at times may be found in circulation * e.g. pupillary response (dilation) in Horner’s Syndrome following adrenal medulla activation

Question 41

Raynaud’s Disease

Answer 41

* Disease of peripheral vascular innervation, possibly from enhanced NE sensitivity * Initially affects the fingers and toes, but may also spread to involve larger areas * Treatment: sympathetic pharmacologic blockers or sympathectomy