Autonomic Nervous System Ch 9 The Autonomic Nervous System

SLOs Review the organization of the ANS Describe how neural regulation of smooth and cardiac muscles differs from that of skeletal muscles Describe the structure and innervation pathways of the two branches of the ANS Explain the relationship between the sympathetic NS and the adrenal medulla. Identify the NTs of the sympathetic and parasympathetic divisions, and the hormones released by the adrenal medulla Describe the effects of adrenergic stimulation on different organs, and identify the types of adrenergic receptors involved Describe the effects of cholinergic stimulation on different organs, and identify the types of cholinergic receptors involved Give examples and explain the prinicple of agonists and antagonists of the ANS Explain how  blockers and atropine affect the ANS Explain and give examples for dual innervation

9.1 Neural Control of Involuntary Effectors Visceral Effector Organs ANS regulates organs not under voluntary control ES (Ch 11) Smooth muscles (Ch 12) Heart and circulatory system (Chs 13 & 14) Target organs not completely dependent on ANS innervation. Will not atrophy if nerve cut (unlike skeletal muscle) Cardiac muscle contracts independent of nerve stimulation. ANS speeds up or slows down intrinsic contractions. ANS stimulates or inhibits depending on ___________ present in organ receptors

Somatic vs. Autonomic System

Neurotransmitters Somatic motor neurons release only _____________which is always excitatory. Autonomic neurons release _____________ and _____________. Response may be excitatory or inhibitory depending on __________

Anatomical Differences between somatic NS and ANS Somatic motor neurons have cell bodies in _____________ of the spinal cord. One neuron travels from spinal cord to effector. ANS has two sets of neurons in the PNS.

Autonomic pathway: 2 Efferent Neurons in Series Preganglionic neuron cell body in CNS Synapsis in autonomic ganglion outside CNS  divergence Postganglionic neurons target cells? Compare to Fig 9-1

_______________ Division of the ANS 9.2 _______________ Division of the ANS = Thoracolumbar division (T1 to L2) Preganglionic neurons from thoracolumbar region of spinal cord Paravertebral ganglia (Sympathetic chain of ganglia) Prevertebral (or collateral) ganglia Long postganglionic axons secrete NE onto adrenergic receptors Compare to Fig 9-5

_______________ Division of the ANS = Craniosacral Division Long preganglionic axons from brain & S2- S4 Terminal or intramural ganglia Postganglio nic neurons secrete Ach onto cholinergic muscarinic receptors Compare to Fig 9-5

9.3 Functions of the ANS Responsible for homeostasis of BP, HR, Resp., H2O balance, Temp. . . Mostly dual innervation; antagonistic Tonic activity (unlike somatic NS) Sympathetic: fight-or-flight through release of _______ Parasympathetic: rest and digest Sympathetic Functions The sympathetic division activates the body for “fight or flight” through the release of norepinephrine from postganglionic neurons and the secretion of epinephrine from the adrenal medulla. Prepares the body for intense physical activity in emergencies by increasing heart rate and blood glucose levels and by diverting blood to skeletal muscles Tonically regulates heart, blood vessels, and other organs

Adernergic and Cholinergic Synaptic Transmission Acetylcholine (ACh) → cholinergic (nicotinic or muscarinic) neurons and receptors Secreted from preganglionic neurons of both divisions Postganglionic neurons of para-symp. division Norepinephrine (NE) → adrenergic ( and ) neurons and receptors Postganglionic neurons of sympathetic division

NTs of Autonomic NS Fig 9-7

Catecholamine Family of Molecules Tyrosin derivatives Adrenergic synapses Fig 9-8

Adrenal Medulla More similar to a) anterior b) posterior pituitary ??? Modified ___________ Adrenal gland subdivided into medulla and __________

Neuroeffector Junction of ANS = Synapse between postganglionic cell and target organ Most are different from model synapse  Axon has varicosities containing NT NT synthesized in axon Compare to Fig 9.9

Varicosities of Sympathetic and Parasympathetic Division Release different NTs Fig 9.9 Form “synapses en passant” - in passing. Dual Innervation: Sympathetic and parasympathetic neurons innervate same tissue, releasng different NTs Dual innervation

Responses to Adrenergic Stimulation E in the blood or NE from sympathetic nerves Response depends on receptors α1 and α2 β1 and β2 All use G-proteins & 2nd messenger systems Stimulation: heart, dilatory muscles of iris, vasoconstriction of many blood vessels Inhibition: bronchodilation

Clinical Application:  Blockers  - Receptors Clinically more important even though not as abundant as  receptors 1 E = NE  Excitation heart 2 not innervated! E > NE!  usually inhibitory: smooth muscle relaxation of some blood vessels and bronchioles Antagonist “ -blockers” = ______________(e.g.: Propranolol and atenolol) Atenolol used for high BP medicine Toprol-XL, metoprolol succinate, is a beta1-selective (cardioselective) adrenoceptor blocking agent, for oral administration, available as extended release tablets. Clinical Application:  Blockers

Drugs that mimic adrenergic responses Agonists: Promote the process stimulated by the NT Antagonists: Block the NT action Agonists and antagonists are used for many medical applications Sympathomimetic drugs (also known as adrenergic drugs and adrenergic amines) are stimulant compounds which mimic the effects of agonists of the sympathetic nervous system such as the catecholamines (epinephrine (adrenaline), norepinephrine (noradrenaline), dopamine, etc.) These drugs can act through several mechanisms, such as directly activating postsynaptic receptors, blocking breakdown and reuptake of certain neurotransmitters, or stimulating production and release of catecholamines. A parasympathomimetic drug, sometimes called a cholinomimetic drug, is a substance that stimulates the parasympathetic nervous system (PSNS).[1] These chemicals are also called cholinergic drugs because acetylcholine (ACh) is the neurotransmitter used by the PSNS. Chemicals in this family can act either directly by stimulating the nicotinic or muscarinic receptors (thus mimicking acetylcholine), or indirectly by inhibiting cholinesterase, promoting acetylcholine release, or other mechanisms.[2] Some chemical weapons such as sarin or VX, non-lethal riot control agents such as tear gas, and insecticides such as diazinon fall into this category. A parasympatholytic agent is a substance or activity that reduces the activity of the parasympathetic nervous system.[1] (The parasympathetic nervous system is often colloquially described as the "Feed and Breed" or "Rest and Digest" portion of the autonomic nervous system. The parasympathetic nervous system becomes strongly engaged during or after a meal and during times when the body is at rest.) The term parasympatholytic typically refers to the effect of a drug, although some poisons act to block the parasympathetic nervous system as well. Most drugs with parasympatholytic properties are anticholinergics. "Parasympatholytic" and sympathomimetic agents have similar but not identical effects. For example, both cause mydriasis, but parasympatholytics reduce accommodation (cycloplegia), whereas sympathomimetics do not. A sympatholytic (or sympathoplegic) drug is a medication which inhibits the postganglionic functioning of the sympathetic nervous system (SNS).[1] They are indicated for various functions, for example they may be used as antihypertensives. They are also used to treat anxiety, such as Generalized Anxiety Disorder, Panic Disorder and PTSD.

One more time: Review of Location of NTs of ANS Compare to Fig 9-7

Responses to Cholinergic Stimulation ACh released from preganglionic neurons of the sympathetic and parasympathetic division is stimulatory. ACh from postganglionic neurons of the parasympathetic division can be stimulatory or inhibitory, depending on _________. 2 major subtypes of receptors: In general, sympathetic and parasympathetic effects are opposite  hence: Dual innerervation

Nicotinic cholinergic receptors Review from Ch 7 Outcome of opening monovalent Na+ / K+ channels? Curare inactivates this receptor  = ____________ (see Table 11-3) Nicotine = agonist When acetylcholine opens nonspecific cation channels on the neuromusclar junction, more Na+ enters the cell than K+ leaves. The ECF and ICF concentrations of Na+ and K+ are shown in the table below. Explain what causes net entry of Na+.   ECF ICF Na+ 150 mM 50 mM K+ The concentration gradients of the two ions are equal and opposite. However, the interior of the cell is negative relative to the outside, therefore favoring Na+ entry over K+ efflux.

Muscarinic cholinergic receptors Review Ch 7 Muscarine = _________ G-protein coupled mechanisms Amanita muscaria Clinical Aplication: Atropine Muscarin is agonist Atropin is antagoist Atropin is __________ for these receptors

Comparison of Nicotinic & Muscarinic ACh Receptors Fig 9.11 Be able to explain what happens in each of the above situations

Cholinergic Receptors & Responses to ACh

Summary of Autonomic Functions

Organs with Dual Innervation Most visceral organs Mostly dual innervation is antagonistic. E.g.: Heart rate – sym increases, para decreases Digestive functions – sym decreases, para increases Pupil diameter – sym dilates, para constricts

Clinical Investigation: Sophia was nervous about her upcoming exam.... The End Clinical Investigation: Sophia was nervous about her upcoming exam....