Autonomic Nervous System - Module 1 - QUIZ 1
G protein-coupled adenylyl-cAMP system Steps 1 - 5
(1) Signal molecule binds to G protein-linked receptor, which activates the G protein (2) G protein turns on adenylyl cyclase, an amplifier enzyme (3) adenylyl cyclase converts ATP to cyclic AMP (4) cAMP activates protein kinase A (5) protein kinase A phosphorylates other proteins, leading ultimately to a cellular response Example: SNS NE + Beta-1 -> increase secretion of saliva
Mechanism of action of autonomic receptors: Muscarinic receptor: (1) target tissue, (2) sensitivity, (3)mechanism of action
(1) all organs of PNS, sweat glands, sympathetic postganglionic neurons that end on blood vessels in some skeletal muscles (2) Ach (3) IP3, increase intracellular [Ca+] (the main mech), some M recep. act by inhibiting adenylyl cyclase, the cardiac SA node M recep. act directly via the G protein (no second messenger is involved)
Mechanism of action of autonomic receptors: Alpha 2 receptor: (1) target tissue, (2) sensitivity, (3)mechanism of action
(1) gastrointestinal tract and pancreas (2) NE > E (3) Inhibition of adenylyl cyclase, decrease cAMP
Mechanism of action of autonomic receptors: Beta 1 receptor: (1) target tissue, (2) sensitivity, (3)mechanism of action
(1) heart, salivary glands, kidney (2) NE = E (3) stimulation of adenylyl cyclase, increase cAMP
G protein-coupled phospholipase C system Steps 1 - 5
(1) signal molecule activates receptor and associated G protein (2) G protein phospholipase C (PL-C), and amplifier enzyme (3) PL-C converts membrane phospholipids into diacylglycerol (DAG) which remains in the membrane and IP3 which diffuses into the cytoplasm (4) DAG activates protein kinase C (PK-C) which phosphorylates proteins (5) IP3 causes release of Ca2+ from organelles, creating a Ca2+ signal
Mechanism of action of autonomic receptors: Nivotinic receptor: (1) target tissue, (2) sensitivity, (3)mechanism of action
(1) skeletal muscle, motor end plate, postganglionic neurons of SNS, PNS, and Adrenal medulla (2) Ach (3) opening Na+ and K+ channels -> depolarization
Mechanism of action of autonomic receptors: Beta 2 receptor: (1) target tissue, (2) sensitivity, (3)mechanism of action
(1) vascular smooth muscle of skeletal muscle, gastrointestinal tract, a wall of the bladder, wall bronchioles (2) E > NE (3) stimulation of adenylyl cyclase, increase cAMP Ep (beta-2) -> dilates arterioles in heart, liver and skeletal muscle
Mechanism of action of autonomic receptors: Alpha 1 receptor: (1) target tissue, (2) sensitivity, (3)mechanism of action
(1) vascular smooth muscle, skin, renal, and splanchnic most symp, target tissues (2) NE > E (NE [alpha-1] -> constricts arterioles in most tissues) (3) IP3, increase intracellular [Ca2+]
Classic neurotransmitters of the PNS:
Ach
2 types of neurons:
Afferent and Efferent
Cholinoreceptors: Nicotinic - agonists and antagonists
Agonists: Ach and Nicotine Antagonists: Curare (blocks neuromuscular N1 receptors) Hexamethonium (blocks ganglionic N2 receptors)
Cholinoreceptors; Muscarinic: Agonists and Antagonists
Agonists: Ach, Muscarine Antagonists: Atropine
Adrenoreceptors; Alpha 1; Agonists and Antagonists
Agonists: Norepinephrine, Phenylephrine Antagonists: Phenoxybenzamine, Prazosin
Adrenoreceptors; b2, agonists and antagonists
Agonists: epinephrine, norepinephrine Antagonists: Propranolol, Butoxamine
Adrenoreceptors; b1, agonists and antagonists
Agonists: norepinephrine, epinephrine, dobutamine Antagonists: Propranolol, Metoprolol
Adrenoreceptors; Alpha 2; Agonists and Antagonists
Agonists; Clonidine Antagonists; Tohimbine
This controls most viscera functions of the body, regulates activity of smooth muscle, cardiac muscle, and certain glands
Autonomic nervous system
PNS effect on Bronchioles Cholinergic Receptors
Constricts M3
Detrusor Muscle State; Control Mechanism - When Emptying of Bladder
Contracted, Parasympathetic M3 (IP3, increase intracellular [Ca2+])
Internal Sphincter: Muscle State; Control Mechanism - When Filling of Bladder
Contracted, Sympathetic alpha 1 (IP3, increase intracellular [Ca2+])
External Sphincter: Muscle State; Control Mechanism - When Filling of Bladder
Contracted, voluntary
PNS effect on Bladder Cholinergic receptors
Contracts bladder wall to empty relaxes sphincter M3
PNS effects on the Heart: Cholinergic Receptors
Decreased heart rate decreased contractility (atria) decreased AP conduction velocity in AV node M2
SNS effects on the GI tract Adrenergic Receptors
Decreased motility and secretion - alpha 2 and Beta 2 constricts sphincters - alpha 1 increased saliva secretion - Beta - 1
SNS effects on Bronchioles Adrenergic Receptors
Dilates Beta - 2
SNS effect on Pupil Adrenergic receptors
Dilates pupil (radial muscle) -> (mydriasis) alhpa - 1
PNS effects on GI tract Cholinergic Receptors
Increased motility and secretion - M3 relaxes sphincters - M1 Increased saliva secretion
Detrusor: Muscle State; Control Mechanism - When Filling of Bladder
It is relaxed, Sympathetic beta-2 (stimul, adenylyl cyclases, increase in cAMP)
Internal Sphincter: Muscle State; Control Mechanism - When Emptying of Bladder
Relaced, Parasympathetic M3
PNS effect on Vascular Smooth Muscle Cholinergic receptors
Relaxation -> endothelium releases EDRF (NO) M
External Sphincter: Muscle State; Control Mechanism - When Emptying of Bladder
Relaxed, Voluntary
SNS in effect on bladder Adrenergic receptors
Relaxes bladder wall to fill - Beta 2 constricts sphincter - Alpha 1
Non-classic neurotransmitters:
VIP (vasoactive intestinal peptide), NO (nitric oxide)
All somatic motor pathways consist of
a single motor neuron
SNS - Postganglionic neurons are adrenergic in
all of the effector organs (NA+ adrenergic receptors) exceptions: sweat glands (they are cholinergic: Ach+ muscarinic cholinoreceptor)
PNS - postganglionic neurons are always cholinergic in
all of the effector organs, (Ach+ muscarinic cholinoceptor)
Structurally, the ANS includes:
autonomic sensory neurons (2), integrating centers in the CNS (3), autonomic motor neurons (4)
Dual innervation is the innervation by
both the SNS and PNS
SNS - Preganglionic neurons are always
cholinergic (release Ach+ nicotinic receptors)
PNS - preganglionic neurons are always
cholinergic: (release Ach+ nicotinic receptors)
FUnctionally, the ANS usually operates without
conscious control
SNS effect on vascular smooth muscle adrenergic receptors
constricts in skin and splanchnic - alpha 1 dilates in skeletal muscle and liver - beta 2
PNS effect on Pupil Cholinergic receptors
constricts pupil (circular sphincter muscle) (miosis) M3
ANS is most important in two situations:
in emergencies that cause stress and require us to fight or flight - Sympathetic Nervous System In no emergencies that allow us to rest and digest - parasympathetic nervous system
SNS effects on the Heart: Adrenergic Receptors:
increased heart rate increased contractility increased AP conduction velocity in AV node Beta-1
PNS - neurotransmitters are
metabotropic
Exception to reciprocal innervation:
most arterioles and veins are innervated by only sympathetic nerve fibers -> Alpha-1 receptors bind mainly NE -> contraction of the smooth muscle and constriction of the arterioles
ANS provides dual / reciprocal innervation to
most target tissues Exceptions: smooth muscle of blood vessels, chromaffin cells of adrenal medulla, and sweat glands receive only sympathetic innervation
Efferent Neurons:
motor; receive impulses from the brain and spinal cord and transmit to the effector organ
Resting and Digesting division of the autonomic nervous system Fibers arise from cranial nerves (3, 7, 9, and 10) and sacral nerves (craniosacral division) Ganglia lie near the organ that is innervated (long preganglionic fibers, short postganglionic fibers) Postganglionic axons release acetylcholine dominates at times when energy sources are restored and calmer conditions permit eating, voiding the bladder, emptying the color, etc
parasympathetic nervous system
Norepinephrine (NE) is released by
postganglionic sympathetic nerve fibers
Afferent Neurons:
sensory; send impulses to the CNS
the autonomic nervous system is activated by centers located in the
spinal cord, brain stem, and hypothalamus (also limbic cortex can transmit signals to the lower centers)
Dual Innervation Effects; Antagonistic:
sympathetic and parasympathetic fibers innervate the same cells actions counteract each other ex: heart rate is increased by SNS and slowed by PNS but: motility of the digestive tract is stimulated by the PNS and inhibited by the SNS
Dual Innervation; Effects; Complementary:
sympathetic and parasympathetic stimulation produces similar effects (salivary gland secretion)
originate in thoracolumbar regions of the CNS ganglia lie very near the spinal cord (short preganglionic fibers, long postganglionic fibers) postganglionic axons release NE dominates in situations that require mobilizing the body's resources (especially metabolic energies) for dealing with challenges to survival
sympathetic nervous system
Autonomic motor pathways consist of
two motor neurons in series
