Drugs Acting On The Autonomic Nervous System Flashcards
(13 cards)
What is the autonomic nervous system (ANS)?
The autonomic nervous system (ANS) is a component of the peripheral nervous system that regulates involuntary physiologic processes including heart rate, blood pressure, respiration, digestion, and sexual arousal.
Control of the ANS often involves negative feedback, and there are many different afferent (sensory) fibres that carry information to centres in the hypothalamus and medulla, these centres control the outflow of the autonomic nervous system, which is divided into two major component parts: The Sympathetic & Parasympathetic Systems
Many organs are innervated by both systems, which generally have opposing actions.
What effects does the sympathetic nervous system have on energy metabolism, the heart, the arteries, the pupils, the bronchi and the GI tract?
Energy Metabolism - Increases conversion of stored energy to free energy
Heart - Increased heart rate and contractile force, increased cardiac output
Arteries - Vasoconstriction within the arteries that supply the skin and viscera, vasodilation within the skeletal muscle
Pupils - Dilation of the pupils
Bronchi - Dilation of the bronchioles
GI Tract - Decreased GI tract motility and production of secretions
What effects does the parasympathetic nervous system have on energy metabolism, the heart, the arteries, the pupils, the bronchi and the GI tract?
Energy Metabolism - Decreases conversion of stored energy to free energy
Heart - Decreased cardiac output and heart rate
Arteries - Generally causes vasodilation
Pupils - Constriction of the pupils
Bronchi - Constriction of the bronchioles and increased bronchosecretion
GI Tract - Increased GI tract motility and secretion
Which neurotransmitter substances act on the sympathetic nervous system and where are they released?
Noradrenaline - Is released from the nerve endings of postganglionic sympathetic nerves
Adrenaline - Released from the adrenal medulla. Some preganglionic sympathetic nerve fibres pass directly to the adrenal medulla, which stimulates the release of adrenaline into the bloodstream.
What receptors do adrenaline and noradrenaline act on to produce their effects on effector organs?
Adrenoceptors
Alpha 1 (a1) - Located primarily in smooth muscle cells
Alpha 2 (a2) - Spread throughout the central and peripheral nervous system
Beta 1 (b1) - Located throughout the body but primarily within the heart, the kidneys and adipose tissue
Beta 2 (b2) - Located throughout the body but primarily within the bronchial smooth muscle, vascular smooth muscle and the alveoli
What neurotransmitter substance is released by all pre-ganglionic autonomic nerves (sympathetic and parasympathetic) and all post-ganglionic parasympathetic nerves?
Acetylcholine
What receptors does acetylcholine act on?
Cholinoreceptors (of which there are two subtypes)
Muscarinic receptors
M1- Located in brain and gastric parietal cells
M2 - Located in heart
M3 - Located in smooth muscle and glands
Nicotinic receptors - Located in autonomic ganglia, skeletal muscle neuromuscular junction and adrenal medulla
What effect does stimulation of b1 adrenoceptors have on the heart?
Stimulation of b1 adrenoceptors causes an increased concentration of calcium within the myocardium, causing muscle contraction, which results in…
Increased heart rate (chronotropic effect)
Increased force of contraction (inotroptic effect)
What effect does stimulation of b1 adrenoceptors have on the kidneys?
Stimulation of b1 adrenoceptors promotes the release of renin (converter of angiotensinogen into angiotensin I) activating the renin-angiotensin-aldosterone system, which results in the production of angiotensin II which causes…
Vasoconstriction - Increasing total peripheral resistance
The release of aldosterone from the adrenal medulla, which increases reabsorption of sodium and salt - Increasing total blood volume
What effect does the stimulation of b2 adrenoceptors have on the bronchial, uterine and vascular smooth muscle?
Within smooth muscle cells, the stimulation of b2 adrenoceptors causes increased levels of intracellular cyclic adenosine mono phosphate (cAMP), which activates protein kinase A (PKA), an enzyme that inhibits the activity of myosin light chain kinase (MLCK), an enzyme which is required for smooth muscle contraction. This causes…
Vasodilation (primarily within the lungs, skeletal muscle and coronary arteries)
Bronchodilation
Relaxation of the uterine smooth muscle
What effects does the stimulation of alpha adrenoceptors have on vascular smooth muscle?
Stimulation of alpha adrenoceptors increases intracellular calcium levels, in smooth muscle cells calmodulin binds to calcium in order to activate MLCK, which induces muscle contraction by allowing myosin to interact with actin. This causes…
Vasoconstriction
What effect does stimulation of muscarinic cholinoceptors have on the heart, lungs, eyes and GI tract
Heart - Reduce heart rate and force of contraction
Lungs - Induces bronchoconstriction and bronchosecretion
Eyes - Increases lacrimal gland secretion and pupillary constriction
Gi Tract - Increases GI tract motility secretions
