Autonomic nervous system
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An introductory lecture to the autonomic nervous system.
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Autonomic nervous system
- 1. Autonomic Nervous System Csilla Egri, KIN 306 Spring 2012 ain, fright, and being a mom; all ways of activating e sympathetic nervous system
- 2. Outline Function of the autonomic nervous system (ANS) Organization of the ANS Major neurotransmitters Classical Nonclassical Central control of ANS function 2
- 3. Function of the ANS 3 Autonomic Nervous System Parasympathetic: Rest and digest Sympathetic: Flight or fight • vasodilates vessels to the GI tracts • constricts the pupil • constrict bronchioles • stimulates salivary gland secretions and peristalsis • sexual arousal • vasocontricts vessels to GI tract and skin • vasodilates vessels to skeletal muscle and lungs • dilates bronchioles • increases heart rate and contractility • dilates pupils • inhibits peristalsis • constricts intestinal sphincters and urinary sphincter**so why can you pee your pants if you’re really scared?
- 4. Organization of the ANS 4 ANS efferents all originate in the CNS and innervate tissues via a two-synapse pathway Preganglionic neurons columns of cells in the brain stem and spinal cord that synapse on: Postganglionic neurons In peripheral ganglia interposed between CNS and target cells Check: What are ganglia?
- 5. Organization of the ANS5 SNS preganglionic neurons Spinal cord between T1-L3 in the _________ horn Exit thru ventral roots Synapse on many paravertebral or prevertebral ganglia located far from target organs B&B Figure 15-4
- 6. Organization of the ANS6 PNS preganglionic neurons Nuclei of medulla, pons, midbrain and segments S2-S4 of spinal cord Synapse on many distant terminal ganglia close to target organ B&B Figure 15-4
- 7. ANS afferent division 7 All visceral organs densely innervated by afferent neurons Monitor nociceptive input and mechanical and physiological stimuli such as diameter of vessels, blood gas concentrations, pH, glucose, and temperature Stimuli often don’t reach consciousness, instead initiate ANS reflex arcs
- 8. Classical neurotransmitters of the ANS8 Both branches of the ANS release Ach from preganglionic neurons that act on N2 nicotinic receptors B&B Figure 15-8 Check: To what family of receptors do N2 receptors belong?
- 9. Classical neurotransmitters of the ANS9 NTs released by postganglionic neurons of each branch differ B&B Figure 15-8 Check: To what family of receptors do muscarinic ACh receptors and adrenergic receptors belong?
- 10. Classical neurotransmitters of the ANS10 Postganglionic neurons PNS • release ACh onto muscarinic receptors • results in stimulation or inhibition of target cell, depending on downstream signalling cascade • response is slow and prolonged SNS • most release norepinephrine (NE) that act on α or β adrenergic receptors* • neuroendocrine branch innervating the adrenal medulla has postganglionic chromaffin cells releasing epinephrine (Epi) into the bloodstream * Except for innervation of sweat glands, where SNS postganglionic neurons release ACh that acts on muscarinic receptors
- 11. Adrenergic receptors Agonists Typical target cell response α1 NE ≥ Epi Ciliary muscles of iris: pupil dilation Blood vessels: vasoconstriction α2 NE ≥ Epi Can be located presynaptically as well, modulate NT release β1 Epi > NE Heart: increased heart rate and contraction β2 Epi > NE Bronchioles: bronchodilation Skeletal muscle vasculature: vasodilation β3 Epi > NE Fat cells: lipolysis Classical neurotransmitters of the ANS11 Acetylcholine receptors Agonists Typical target cell response N2 ACh, nicotine Trigger EPSP on postganglionic neuron M1-M5 ACh, muscarine Varied, can be excitatory or inhibitory, heterogeneous distribution *N1 receptors are not part of the ANS, they are part of the somatic nervous system and initiate action potentials at the neuromuscular junction
- 12. Nonclassical neurotransmitters of the ANS12 Some postganglionic SNS/PNS neurons contain muscarinic receptors for Ach Results in varied response in target cell to ACh ANS can release numerous “nonclassical” neurotransmitters Colocalized in ANS axon terminals and can participate in cotransmission with cholinergic or adrenergic neurotransmitters Examples: glutamate, glycine, substance P, serotonin, neuropeptide Y, ATP, NO
- 13. Central control of ANS function 13 ANS activity controlled by reflex pathways in spinal cord and brainstem as well as descending controls originating from higher autonomic brain regions Reflex examples: Pupillary light reflex Light excites retinal cells which send connections to PNS ganglia in the brainstem constriction of pupil size Micturition reflex (overcome by potty training… hopefully) Distension of bladder sensed by mechanoreceptors which send connections to pontine micturation centre (PMC) in the pons SNS input to bladder decreases, PNS input increases voiding of
- 14. Central control of ANS function 14 Autonomic brain regions: Hypothalamus Temperature regulation Hypothalamic thermoreceptors have connections to SNS Cold temp. increased SNS activity shivering, increased metabolism, cutaneous vasoconstriction Regulation of food intake Hypothalamic glucoreceptors Blood glucose falls release of opioid peptides and pancreatic peptides (enteric nervous system connections) stimulate food intake Emotional behaviour Limbic system sends connections to hypothalamus and other brain regions (ex. PMC) Influence dietary behaviour Can pee your pants when your scared!
- 15. Objectives After this lecture you should be able to: List the general functions of the ANS Describe ANS neuronal connections Compare and contrast SNS and PNS neurotransmitters and receptors Describe the role of central control of ANS function 15
- 16. 16 1. What would happen if you administered a systemic nicotinic receptor antagonist? What about a systemic adrenergic antagonist? 2. Atropine, when applied as eye drops, mimics the effect of the sympathetic nervous system by blocking receptors of the parasympathetic branch. What is the effect on the eye and what specific receptors is atropine an antagonist? Test your knowledge
Editor's Notes
- ANS can be regarded part of the motor system because it controls effectors such as smooth and cardiac muscle and glands.
- The sns and pns work antagonistically to regulate body functions. Flight or fight is uncommon event and does not represent day to day activity of SNS. These systems work together to maintain homeostasis. Not entirely antagonistic control, because not all structures are innervated by both systems.
- Ganglia: mass of nerve cell bodies and dendrites Provide relay points and intermediary connections between nerves of the body. They integrate afferent input from the viscera and have independent control mechanisms. Also contain interneurons.
- Also called the thoracolumbar division. Lateral Horn (lecture 1 anatomy of nervous sytem) Prevertebral plexus located in the abdominal cavity. Paravertebral ganglia form two sets of ganglia, one lateral to each side of the spinal cord.
- Sometimes called the craniosacral divsion
- Stimuli often don’t reach conscious perception, instead initiate ANS reflex arcs.
- From lecture 3: nicotinic receptors are ionotropic receptors that are ligand gated ion channels. Permeable to Na and K with entry of Na dominating. Receptor activation leads to rapid depolarization of post ganglionic cell. N2 receptors are stimulated by agonist tetramethylammonium, but resistant to D-tubocurarine, whereas N1 (skeletal muscle) are stimulated by decamethonium and blocked by D-tubocurarine. Major neurotrans-mitters of the autonomic nervous system. In the case of the somatic neuron, the pathway between the central nervous system and effector cell is monosynaptic. The neuron releases acetylcholine (ACh), which binds to N1-type nicotinic receptors on the postsynaptic membrane (i.e., skeletal muscle cell). In the case of both the parasympathetic and sympathetic divisions, the preganglionic neuron releases ACh, which acts at N2-type nicotinic receptors on the postsynaptic membrane of the postganglionic neuron. In the case of the postganglionic parasympathetic neuron, the neuro-transmitter is ACh, but the postsynaptic receptor is a muscarinic receptor, which is a metabotropic (i.e., G-protein-linked) receptor of one of five subtypes (M1 -M5). In the case of most postganglionic sympathetic neurons, the neurotransmitter is norepinephrine. The postsynaptic receptor is a metabo-tropic (i.e., G-protein-linked) adrenergic receptor of one of two major subtypes (α and β).
- From lecture 3: nicotinic receptors are ionotropic receptors that are ligand gated ion channels. Permeable to Na and K with entry of Na dominating. Receptor activation leads to rapid depolarization of post ganglionic cell. N2 receptors are stimulated by agonist tetramethylammonium, but resistant to D-tubocurarine, whereas N1 (skeletal muscle) are stimulated by decamethonium and blocked by D-tubocurarine. Major neurotrans-mitters of the autonomic nervous system. In the case of the somatic neuron, the pathway between the central nervous system and effector cell is monosynaptic. The neuron releases acetylcholine (ACh), which binds to N1-type nicotinic receptors on the postsynaptic membrane (i.e., skeletal muscle cell). In the case of both the parasympathetic and sympathetic divisions, the preganglionic neuron releases ACh, which acts at N2-type nicotinic receptors on the postsynaptic membrane of the postganglionic neuron. In the case of the postganglionic parasympathetic neuron, the neuro-transmitter is ACh, but the postsynaptic receptor is a muscarinic receptor, which is a metabotropic (i.e., G-protein-linked) receptor of one of five subtypes (M1 -M5). In the case of most postganglionic sympathetic neurons, the neurotransmitter is norepinephrine. The postsynaptic receptor is a metabo-tropic (i.e., G-protein-linked) adrenergic receptor of one of two major subtypes (α and β).
- Nicotine and muscarine are plant alkaloids
- These are neuromodulators; modify firing rates, alter membrane potentials or have unknown functions. Not clear what controls the release of each NT, sometimes it depends on firing frequency in presynaptic neuron
- SNS postganglionic output normally inhibits smooth muscles of the bladder and excites internal sphincter to prevent voiding
- You already know of its importance in controlling endocrine function, now we will overview its control of ANS fxn. Blood pressure regulation in medulla, respiration control in medulla and pons Regions in the hypothalamus respond to heat loss and heat gain (loss preoptic region and anterior hypothalamus) Lateral hypothalamus contains a feeding center