Sheet 3 ANS.pptx

Drugs affecting on The autonomic nervous system (ANS) Pharmacology, Lecture 3, Autonomic Nervous 1 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 2 sys...

Drugs affecting on The autonomic nervous system (ANS) Pharmacology, Lecture 3, Autonomic Nervous 1 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 2 system Dr Salem Abukres  1. Efferent neurons: carrying signals from the brain to the peripheral nervous system in order to initiate an action 2. Afferent neurons: sensing pressure in the carotid sinus and aortic arch bring in impulses from the auditory, visual and touch receptors. 5. Enteric neurons: the “brain of the gut.” This system functions independently of the CNS and controls the motility, exocrine and endocrine secretions Pharmacology, Lecture 3, Autonomic Nervous 3 system Dr Salem Abukres 1. Effects of stimulation of the sympathetic division: Increase heart rate and blood pressure, to mobilize energy stores of the body, and to increase blood flow to skeletal muscles and the heart while diverting flow from the skin and internal organs Dilation of the pupils and the bronchioles Affects GI motility and the function of the bladder and sexual organs 2. Fight or flight response: During emergencies: Triggered both by direct sympathetic activation of the effector organs and by stimulation of the adrenal medulla to release epinephrine A complete system Pharmacology, Lecture 3, Autonomic Nervous system Dr Salem 4 Abukres 2. Functions of the parasympathetic nervous system Maintaining homeostasis within the body Maintains essential bodily functions, such as digestive processes and elimination of wastes. It usually acts to oppose or balance the actions of the sympathetic division and is generally dominant over the sympathetic system in “rest and digest” situations. Is not a functional entity as such and it never discharges as a complete system. If it did, it would produce massive, undesirable, and unpleasant symptoms, such Pharmacology, as involuntary urination Lecture 3, Autonomic Nervous 5 system Dr Salem Abukres Reflex responses For example, a fall in blood pressure causes pressure- sensitive neurons (baroreceptors in the heart, vena cava, aortic arch, and carotid sinuses) to send fewer impulses to cardiovascular centres in the brain This prompts a reflex response of increased sympathetic output to the heart and vasculature and decreased parasympathetic output to the heart, which results in a compensatory rise in blood pressure and tachycardia Pharmacology, Lecture 3, Autonomic Nervous 6 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 7 system Dr Salem Abukres Emotions and the ANS: Stimuli that evoke strong feelings, such as rage, fear, and pleasure, can modify the activities of the ANS. Pharmacology, Lecture 3, Autonomic Nervous 8 system Dr Salem Abukres Dual innervation: Most organs in the body are innervated by both divisions of the ANS. Thus, vagal parasympathetic innervation slows the heart rate, and sympathetic innervation increases the heart rate. one system usually predominates in controlling the activity of a given organ This type of antagonism is considered to be dynamic and is fine-tuned at any given time to control homeostatic organ functions Pharmacology, Lecture 3, Autonomic Nervous 9 system Dr Salem Abukres 2. Organs receiving only sympathetic innervation: Adrenal medulla, kidney, pilomotor muscles, and sweat glands, Receive innervation only from the sympathetic system The control of blood pressure is also mainly a sympathetic activity, with essentially no participation by the parasympathetic system. Pharmacology, Lecture 3, Autonomic Nervous 10 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 11 system Dr Salem Abukres III. CHEMICAL SIGNALING BETWEEN CELLS A. Hormones: endocrine cells secrete hormones into the bloodstream B. Local mediators: chemicals that act locally, e.g Histamine , do not enter the blood C. Neurotransmitters: Communication between nerve cells and effector organs, Their release is triggered by the arrival of the action potential at the nerve ending, leading to depolarization An increase in intracellular Ca2+ initiates fusion of the synaptic vesicles with the presynaptic membrane and release of their contents (See the next slide) Types of neurotransmitters: norepinephrine (and epinephrine), acetylcholine, dopamine, serotonin, histamine, and ?-aminobutyric acid (GABA), are most commonly involved in the actions of therapeutically useful drugs Pharmacology, Lecture 3, Autonomic Nervous 12 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 13 system Dr Salem Abukres Neurotransmitters a. Acetylcholine: If transmission is mediated by acetylcholine, the neuron is termed cholinergic Mediates the transmission of nerve impulses across autonomic ganglia in both the sympathetic and parasympathetic nervous systems and at the adrenal medulla. Transmission from the autonomic postganglionic nerves to the effector organs in the parasympathetic system, and a few sympathetic system organs, also involves the release of acetylcholine Pharmacology, Lecture 3, Autonomic Nervous 14 system Dr Salem Abukres Neurotransmitters b. Norepinephrine and epinephrine: When norepinephrine or epinephrine is the transmitter, the fiber is termed adrenergic (adrenaline being another name for epinephrine). In the sympathetic system, norepinephrine mediates the transmission of nerve impulses from autonomic postganglionic nerves to effector organ Pharmacology, Lecture 3, Autonomic Nervous 15 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 16 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 17 system Dr Salem Abukres IV. SECOND–MESSENGER systems IN INTRACELLULAR RESPONSE Second-messenger molecules produced in response to a neurotransmitter binding to a receptor translate the extracellular signal into a response that may be further propagated or amplified within the cell The two most widely recognized second messengers are the adenylyl cyclase system and the calcium/phosphatidylinositol system [Note: Gs is one protein involved in the activation of adenylyl cyclase, and Gq is one subunit that activates phospholipase C to release diacylglycerol and inositol trisphosphate Pharmacology, Lecture 3, Autonomic Nervous 18 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 19 system Dr Salem Abukres Pharmacology, Lecture 3, Autonomic Nervous 20 system Dr Salem Abukres