Objectives z Know ANS divisionsand organization z Functional units z Principal neurotransmitters z Receptor types z Identify sensory input to ANS z Explain how it integrates function (BP) z List main physiological responses under ANS control z Distinguish SNS from PSNS mediatedresponses z Understand the consequences of ANS dysregulation
Autonomic vs. Somatic Nervous System • AUTONOMIC Effectors: cardiac & smooth muscle, viscera & glands Efferent: 2‐neuron chain Neurotransmitter (NT) effects Stimulatory or inhibitory dependent on NT & receptor type SOMATIC Effectors: skeletal muscles Efferent: Heavily myelinated axons from CNS to muscle Neurotransmitter Effects: Acetylcholine excitatory effect in nicotinic (N1) receptors
1 z Autonomic Nervous System z Efferent motor neurons: innervate viscera & involuntary muscle z Afferent sensory neurons respond to: z Stretch (heart, arteries)
z Glucose, PCO2, PO2 (blood) z Osmolarity & pH (blood & intestinal content) z Temperature (skin & internal organs)
SNS & PSNS Functional unit
2 neuron pathway
2 Sympathetic
z Preganglionic: z Preganglionic Cholinergic neuron; neurons Nicoti n ic recept(Ntor (N2) z Thoracolumbar spinal z Postganglionic: cord: T1-L3 Adrenergic neuron; z Postganglionic Adrenergic receptor neurons z α 1: vasculature z Paravertebral or z α 2: presynaptic prevertebral ganglia z β 1: heart, adipose z Distant to target organ z β 2 : bronchioles, vasculature z β 3: adipose- thermogenic
Parasympathetic z Preganglionic z Preganglionic: Cholinergic neurons neuron; Nicotinic (N2) receptor z Brainstem: cranial nerve z Nicotinic: ion-gated nuclei z Postganglionic: Cholinergic z III oculomotor neuron; Muscarinic receptor z VII facial z G-protein coupled z IX glossopharyngeal z Effect on cell z X Vagus z Excitatory or inhibitory: z Sacral spinal cord receptor & oogargan specifi c z Postganglionic neurons z Parasympathetic ganglia z Near or in wall of target organ
3 Neurotransmitters z Principal: Acetylcholine & norepinephrine z NtditilNon traditional z ATP z Colocalized with NE in SNS z Purinoceptors (i.e., smooth muscle cells) z Nitric oxide z Pre & postganglionic neurons SNS & PSNS
Enteric nervous system
z 2 networks of neurons z Myenteric z Motility z Submucous z Secretions z 3 types of neurons z Motor z Sensory z mechanical, thermal, osmotic & chemical z Interneurons
z Part of the PNS z Operates largely independently of the CNS z Coordinates gastrointestinal function z Monitors the state of lumen and gut wall z Responds appropriately z Activating intrinsic reflexes z Mixing and propulsive & peristaltic movements z Change blood flow & secretions of water & electrolytes
Enteric nervous system z Neurons & glia organized into ganglia z Neurotransmitters: z Acetylcholine z ↑ motility z ↑ intestinal secretions z ↑ enteric hormone release z NihiNorepinephrine z ↓ acetylcholine effects z Others: VIP, opioids, 5-HT, Substance P, NO, etc.
5 SNS: “fight or flight”
z Dilation of pupils z ↑ HR, contractility &BP& BP z Blood flow z ↓ non-essential organs z ↑ Bronchial dilation z ↑ Respiratory rate z ↑ Fuel mobilization z Glucose & FFA Exercise Excitement Embarrassment
PSNS: “rest-digest”
z Conserve & restore energy z Normally PSNS tone > SNS z SLUDD responses: z salivation, lacrimation, urination, digestion & defecation z 3 “decreases” z ↓ HR, airway & pupil diameter z PdilfParadoxical fear z No escape/“No win situation” Digestion z Massive PSNS activation z Loss of urination & defecation Defecation control Diuresis z ↓HR & BP
6 SNS/PSNS
z Dual/antagonistic: GI, CV z Exclusive SNS z Adrenal medulla z Sweat glands z Erector pili muscles z Kidneys: RAS →↑ MABP z Most blood vessels z Exclusive PSNS z Erectile tissues
SNS/PSNS: Dual/antagonistic modulation of CV function. z Carotid sinus & aortic arch pressure z Afferent signals integrated in brainstem z ↑ Pressure z ↓ SNS activity & ↓ BP z ↑ PSNS activity & ↓ HR z ↓ Pressure z ↑ SNS activity & ↑ HR & BP
7 SNS & PSNS: Dual/antagonistic modulation of GI function
z PSNS favors digestive processes z Increased gut motility, acid & enzyme secretions z Relaxation of sphincters z SNS inhibits digestive processes z Contraction of sphincters z Pyy,loric, ileo-cecal & internal anal z Inhibition of motor neurons throughout the gut
SNS: Exclusive modulation of thermoregulation z ↑ Environmental temperature z ↓ Environmental temperature z Sweat gland activation z Skin vasoconstriction z Skin vasodilation z Blood retained in vital organs z Warm blood to surface z Shivering z Piloerection
8 ANS during fever z Increased body temperature 1-4°C z Upregulation of thermostatic set point z Body “feels cold” z Autonomics kick in z Skin vasoconstriction z Blood retained in vital organs z Shivering z Piloerection z No sweating
SNS/PSNS: Cooperative control of sexual function z Erection z PSNS: Vasodilation of penile blood vessels z ACh & NO z SNS: ↓ tone during erection z Emission (ejaculation) z SNS: smooth muscle contraction distal epididymis z Emission
9 Autonomic nervous system z ANS divisions and organization z Functional units z Principal neurotransmitters z Receptor types z Sensory input to ANS & role in control of BP z Main physiological responses under SNS & PSNS contro l z Coordinated/antagonistic/exclusive z ANS dysfunction? z Examples? Manifestations?
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