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Differences between Nicotonic receptors in MEP and autonomic ganglia

- both activated by the agonist Ach, nicotine, and carbachol
- both antagonized by curare
- hexamethonium, an antagonist, blocks N2 receptors but not N1
- hexamethonium produces vasodilation can be used for the treatment of hypertension


- have affinity for muscarine (a mushroom poison when introduced into the body can mimic ACh on particular sites)
sites: effector cells activated by PS; effector cells activated by S cholinergic

Muscarinic Receptors


Types of Muscarinic Receptors

M1 - enhances gastric acid secretion
M2 - most abundant in the heart, smooth muscle in intestine, uterus, trachea, bladder
Mechanism of action: binding of agonist to M2--> inhibits adenylcyclase
M3 - smooth muscle of airways
Mech of action: formation of IP3 (inositol 1, 4, 5 triphosphate) and DAG(Diaglycerol) and increase in intracellular calcium
M4 - pancreatic acinar cells and islet tissue
M5 - sphincter muscle of iris, esophagus, parotid gland, cerebral blood vessel


are of the indirect ligand G protein linked type



Types of Adrenoceptors

Alpha 1 Receptors
Alpha 2 Receptors
Beta 1 Receptors
Beta 2 Receptors
Beta 3 Receptors


- location: radial muscle of iris; blood vessels of skin (vasoconstriction); sphincters of GIT and bladder
- antagonist: Prazosin
- mechanism of action: - involves a G protein (Gq) activate phospholipase C and increase the intracellular concentration of IP3

Alpha 1 Receptors


location: presynaptically (autoreceptors) inhibit release of NE ; GIT walls
selective antagonist: Yohimbine
Mechanism of Action: - involves Gi protein act through inhibition of adenylyl cyclase → decreased cAMP levels
activation of alpha 2 receptors in GIT wall → relaxation

Alpha 2 Receptors


location: prominent in the heart, salivary glands, adipose tissue, kidneys (promote renin secretion)
Mechanism of Action: involves Gs protein activation of adenylcyclase to increase cAMP concentration

Beta 1 Receptors


sites: predominate in smooth muscle of airways, blood vessels of skeletal muscles (vasodilation), GIT and bladder walls
Mechanism of Action: same as beta 1
- involves Gs protein activation of adenylyl cyclase to increase cAMP concentration

Beta 2 Receptors


- present on cells of brown adipose tissue
- activation causes thermogenesis (heat production)

Beta 3 Receptors


a drug that binds to the receptors for a neurotransmitter and that promotes the processes that are stimulated by that NT is said to be an agonist of that NT



a drug that blocks the action of a NT



- autonomic and somatic reactions work together to maintain essential body states and to effect necessary adaptation
- levels of autonomic integration within the CNS are arranged in a hierarchy
- CNS controls the activity of the ANS shows hierarchy in the control mechanism

Central Control of Autonomic Functions


- simple reflexes like contraction of a full bladder are integrated in the spinal cord

transection of the spinal cord >> spinal shock >> absence of reflexes, low ABP

Spinal Cord


- center for the regulation of the ANS
- called by Sherrington, “the HEAD GANGLION,” of the ANS because stimulation of this produces autonomic responses
sympathetic: posterior center
parasympathetic: anterior center
- integrates somatic, autonomic and endocrine functions
- mediates those reactions that maintain homeostasis



- unit that regulates emotional and instinctual behavior
- concerned with the following: regulation of feeding behavior; expression of rage and fear; control of sexual behavior

Limbic System


- refinement of control over the autonomic and somatic reactions
- examples: tells whether emotion is pleasant or unpleasant; responsible for voluntary control of respiration

Cerebral Cortex


- Where centers for regulation of cardiovascular and respiratory centers are located
- The medullary areas for the autonomic control of the CVS and respiratory system are called the vital areas because damage to them is fatal
- Deglutition, coughing, sneezing, gag reflex, vomiting reflexes are integrated in the medulla
- EXAMPLES: respiratory center, vasomotor center, swallowing center, vomiting

Medulla Oblongata


those that control pupillary responses to light are integrated in the ____



Muscarinic receptor in brain (presynaptic neuron) and enhances gastric acid secretion



-most abundant in the heart
- smooth muscle in intestine, uterus, trachea, bladder
- mechanism of action: binding of agonist>>inhibits adenylcyclase



-smooth muscle airways
- mechanism of action: formation of IP3 (inositol 1,4,5 triphosphate) and DAG (diaglycerol) and increase in intracellular calcium



-muscarinic receptors found in pancreatic acinar cells and islet tissue



Muscarimic receptor for sphincter muscle of iris, esophagus, parotid gland, cerebral blood vessel