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Autonomic Nervous system
Dr. Sumera Gul
Associate Professor
Department of Physiology
Wah Medical College
Learning Objectives
• At the end of the lecture the students should be able to:
• Explain the general organization and physiological anatomy of ANS
• Elucidate the different, neurotransmitters, receptors and effector organs of ANS
• Discuss various functions of ANS
• Describe autonomic reflexes
• Explain the various drugs effecting ANS
What do you know about Autonomic Nervous system?
Autonomic Nervous System
• “Auto” = self
• “Nomos” = law
• By definition it is entirely a motor(efferent) system & autonomous in the sense that most of its functions are carried out below conscious level, hence it is independent of volitional control, thus enjoys some degree of autonomy
Autonomic Nervous System
• Controls visceral functions
• Very rapid and prompt
• Intense
• Subconscious
• Since it is not under conscious control, how much would be cortical representation?
General Organization
Afferent Visceral Neurons
Activation centers
Spinal cord, brain stem, hypothalamus
Limbic system.
Efferent autonomic signals
Sympathetic , Parasympathetic and ???
Somatic Autonomic
cutaneous receptors chemoreceptorsproprioceptors baroreceptorsspecial senses mechanoreceptors
may become conscious unconscious
excitatory for skeletal excitatory or inhibitory formuscles cardiac muscle, smooth
muscles, and glands
single motor neuron two motor neurons
Overview of Autonomic Pathways
Preganglionic neuron
• 1. First autonomic motor neurons
• 2. Cell body located in gray matter of spinal cord or brain
• 3. Passes from the CNS in a spinal or cranial nerve
• 4. Axon terminates in a ganglion
Overview of Autonomic Pathways
Ganglion
• 1. Collection of nerve cell bodies located in a specific
site outside the CNS
• 2. Cell bodies give rise to postganglionic neurons
Overview of Autonomic Pathways
Postganglionic neuron
• 1. Second of the two autonomic motor neurons
• 2. Cell body located in ganglion
• 3. Postganglionic axon passes from the ganglion to the effector
• 4. Peripheral effector is either stimulated or inhibited
Division of Autonomic Nervous System
Sympathetic Nervous System
• 1. Lateral gray horns
• 2. Thoracolumbar outflow (T1-L2)
• 3. Ganglia
a. Sympathetic trunk (paravertebral)
b. Prevertebral (collateral)
c. Adrenal Medulla
• 4. Preganglionic axons short
• 5. Postganglionic axons long
Parasympathetic Nervous System
• 1. Lateral gray horns (S2-4)
• 2. Cranial gray matter
(CN III, VII, IX, X)
• 3. Craniosacral outflow
• 4. Terminal ganglia
• 5. Preganglionic axons long
• 6. Postganglionic axons short
Physiological Effects of ANS
Receptors and Neurotransmitters in ANS
ANS Neurotransmitters
Cholinergic Adrenergic
acetylcholine norepinephrine
all preganglionic neurons most postganglionic
all postganglionic parasympathetic neurons sympathetic neurons
few postganglionic sympathetic neurons
acetylcholinesterase catechol-O-methyl transferase
monoamine oxidase
Nicotinic and Muscarinic receptors Alpha and Beta receptors
•
Neurotransmitters and Receptors
Receptors
-At ganglia: sympathetic and parasympathetic have nicotinic receptors at the post synaptic membrane
-on effector cells: Muscarinic receptors
• Muscarinic receptors : GPCR
• Nicotinic receptors: Ligand gated ion channels
• Alpha and Beta receptors: GPCR
Drugs Affecting Autonomic Nervous System
• adrenergic or sympathomimetic drugs• isoproterenol stimulates both beta1 and beta2 receptors
• albuterol stimulates only beta2 receptors
Some drugs act indirectly by increasing the release of norepinephrine from its storage terminals
• amphetamine
Drugs Affecting Autonomic Nervous System
Some drugs block the effect of norepinephrine and epinephrine
Beta blockers
• beta1 - metoprolol
Alpha blockers/ Antagonists
Drugs Affecting Autonomic Nervous System
Parasympathomimetic drugs• nicotine
• activates nicotinic receptors
Cholinesterase inhibitors• neostigmine
• potentiates the effect of acetylcholine
Antimuscarinic drugs• atropine
• blocks the effect of acetylcholine on effector cells