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To review the different types of neurons associated with the ANS. To clearly identify the position and role of the sympathetic trunk & collateral ganglia. To address the two different types of receptors for neurotransmitters of the sympathetic ANS: - Cholinergic Receptors - Adrenergic Receptors To relate how drugs interact (influence) the receptors seen in the sympathetic ANS. Types of Neurons of ANS Ganglion – Collection of nerve cell bodies outside of the CNS. Preganglionic Neurons – CB in CNS which projects its axon to a peripheral ganglion Postganglionic Neurons – CB in peripheral ganglion its axon projects to an effector. Spinal cord Dorsal root Sympathetic Trunk Ventral root Rib Paravertebral ganglia 3 cervical 11 thoracic 4 lumbar 4 sacral 1 coccygeal Sympathetic trunk ganglion Sympathetic trunk Ventral ramus of spinal nerve Gray ramus communicans White ramus communicans Thoracic splanchnic nerves (a) Location of the sympathetic trunk Figure 14.5a Pathways with Synapses in Collateral Ganglia Most fibers from T5 – L2 synapse in collateral ganglia They form thoracic, lumbar, and sacral splanchnic nerves Their ganglia include the celiac and the superior and inferior mesenteric Neurotransmitter Effects All somatic motor neurons release acetylcholine (ACh) Effects are always stimulatory ANS Preganglionic fibers release ACh Postganglionic fibers release norepinephrine or ACh at effectors Effect is either stimulatory or inhibitory, depending on type of receptors SYMPATHETIC NE ACh PARASYMPATHETIC AUTONOMIC NERVOUS SYSTEM Two-neuron chain from CNS to effector organs Somatic nervous system Acetylcholine (ACh) Ganglion Lightly myelinated preganglionic axons ACh Unmyelinated postganglionic axon Epinephrine and norepinephrine Adrenal medulla Blood vessel ACh ACh Lightly myelinated preganglionic axon Ganglion + Unmyelinated postganglionic axon Smooth muscle (e.g., in gut), glands, cardiac muscle Stimulatory or inhibitory, depending on neurotransmitter and receptors on effector organs Norepinephrine (NE) Figure 14.2 Neurotransmitters Cholinergic Receptors I. Cholinergic fibers release the neurotransmitter ACh Two types of receptors bind ACh II. Adrenergic fibers release the neurotransmitter NE Nicotinic (stimulatory) Found on: All ganglionic neurons both (sympath & para) Motor end plates of skeletal muscle cells Hormone-producing cells of the adrenal medulla 2. Muscarinic (inhibitory or excitatory)* Found on: All effector cells stimulated by postganglionic cholinergic fibers * depends on target organ 1. All ANS preganglionic axons All parasympathetic postganglionic axons Most sympathetic postganglionic axons Exceptions: sympathetic postganglionic fibers secrete ACh at sweat glands and some blood vessels in skeletal muscles Adrenergic Receptors Two types Alpha (α) (subtypes α1, α2) - Excitatory Beta (β) (subtypes β1, β2 , β3) Effects of NE depend on which subclass of receptor predominates on the target organ. β1 – increases heart activity β2 – relaxes smooth muscle of bronchioles Table 14.2 Effects of Drugs Over-the-counter drugs for colds, allergies, and nasal congestion Stimulate α-adrenergic receptors Beta-blockers Drugs that attach to β2 receptors to dilate lung bronchioles in asthmatics; other uses Table 14.2 Stimulus Visceral Reflexes Visceral reflex arcs have the same components as somatic reflexes Main difference: visceral reflex arc has two neurons in the motor pathway Visceral pain afferents travel along the same pathways as somatic pain fibers, contributing to the phenomenon of referred pain 1 Sensory receptor in viscera 2 Visceral sensory neuron 3 Integration center • May be preganglionic neuron (as shown) • May be a dorsal horn interneuron • May be within walls of gastrointestinal tract Dorsal root ganglion Spinal cord Autonomic ganglion 4 Efferent pathway (two-neuron chain) • Preganglionic neuron • Ganglionic neuron 5 Visceral effector Response Figure 14.7 HW for Week 4 Due in lab: Diseases & Disorders of the nervous system W.S. Labeling: pg 337 (spinal cord) pg. 378 (eye) Study Guide will be provided for in lab (Tuesday) Preview dissection of eye and eye related reflexes.