CREATEDATE 11/4/09 11:28 PM Lecture 9 ? The Autonomic Nervous System Autonomic Nervous System: Controls the body?s internal environment in a coordinated manner; basically controls the involuntary/not thought about movement of organs Helps control heart rate, BP, digestion, respiration, blood pH, etc ( all of this is done at a subconscious level ( activity of organs thus must be coordinated Targets smooth muscle, cardiac muscle. Exocrine glands, some endocrine glands, lymphoid tissue and adipose Somatic Nervous System: voluntary movement 2 Divisions of Autonomic Nervous system Sympathetic Nervous System: active during stressful situations, high levels of physical activity( fight or flight *remember sympathetic sympathizes and gives you courage to fight or run away Parasympathetic Nervous System: active during rest and digest SNS and PNS work together in a reciprocal fashion to regulate body function The exception to the dual reciprocal enervation by the two branches of the ANS( most arterioles and veins receive only sympathetic nerve fibers & sweat glands only receive sympathetic nerve fibers & both stimulate salivary gland (not antagonistic) The Autonomic nerve pathway consists of a 2 neuron chain ( from spinal cord or brainstem to effector organs Cell body of first neuron series is located in CNS and its axon (the preganglionic fiber) synapses with the cell body of the second neuron (postganglionic fiber) that innervates the effector organ Sympathetic Neurons: Emerge from mid back or thoracic and lumbar regions of spine (T1-L2) Preganglionic neurons are short Preganglionic neurons synapse in paired ganglia adjacent to spinal cord Preganglionic neuron also synapses on adrenal medulla (endocrine gland) ( functionally a part of sympathetic nervous system and releases epinephrine into blood (no postganglionic fiber) 20% norepinephrine released, 80% epinephrine released Parasympathetic Neurons Emerge from cranial nerves 3, 7, 9, 10 and from S2-S4 sacral (lower) region of spine Long preganglionic nerves Preganglionic nerves synapse at ganglia near organ innervated -In the sympathetic nervous system and the parasympathetic nervous system, preganglionic fibers use neurotransmitter acetylcholine in ganglia. -The postganglionic fibers, however, use different neurotransmitters the SNS uses norepinephrine (NE) and epinephrine (in the case of adrenal medulla) receptor for preganglionic NT is nicotinic receptor for postganglionic NT is alpha 1,2 and beta 1,2 the PSNS uses acetylcholine receptor for preganglionic NT is nicotinic receptor for postganglionic NT is muscarinic Tissues enervated by the ANS have several receptor types Cholinergic Receptors(ACh) Nicotinic receptors- on all postganglionic cell bodies Nicotine = agonist Binds to ACh released from both SNS and PSNS (preganglionic) Directly opens N+ and K+ channel ( leads to depolarization Curare = antagonist Muscarinic receptors- found on effector cell membranes (PSNS) Bind to ACh released from parasympathetic postganglionic fibers Muscarine = agonist Atropine = antagonist G-protien coupled mechanism In sweat glands: ACh binds to receptor ( G protein subunit dissociates ( G-protien binds to K+ channel causing it to open Adrenergic Receptors (bind to norepinephrine and epinephrine) Found in sympathetic branch G-protien linked with various 2nd messengers Alpha Receptors Greater sensitivity to norepinephrine Most common (alpha 1) ( excites effector (Ca+ in increased) ( muscle contraction or excretion by exocytosis ( Ex: increased contraction of smooth muscle ( arteriolar constriction Alpha 2 receptors: inhibit effector response ( GI tract/ pancreas/ digestive system Beta Receptors: Clinically more important B1 (epinephrine and norepinephrine)- excitation of heart B2 (epinephrine)- inhibitory Smooth muscle relaxation of some blood vessels and bronchioles B3- (norepinephrine) ? adipose Beta blockers- antagonists( propranolol HINT: activation by subscript 1 receptors and inhibition by subscript 2 receptors Effects of Parasympathetic and Sympathetic NS on different organs Heart: SNS- increased rate, increased force of contraction (b1) PSNS- decreased rate decreased force of contraction Blood Vessels: receive only sympathetic nerve fibers SNS- constriction of vessels (a1)( regulation by increasing tonic/ decreasing firing rate above/below tonic level PSNS- dilation of vessels supplying penis and clitoris Lungs SNS- dilation of bronchioles PSNS- constriction of bronchioles Digestive Tract SNS- decreased movement(a2,b2), constriction of sphincter(a1), inhibits secretion (a2) PSNS- increased movement, relaxation of sphincter Bladder SNS- Relaxation PSNS- contraction (emptying) Eye SNS- Dilation, adjustment of eye for far vision PSNS- constriction Liver SNS- Glucose released PSNS- none Adipose SNS- adds fatty acids ***NEED TO FINISH*** Neuroeffector Junction: synapse between postganglionic cell and target ANS synapse has varicosities containing neurotransmitters May supply many cells, resulting in less specific communication Synthesis of NT is in varicosity Postganglionic nerve cells form multiple variscosities where pulses of NT are released onto effector organs Varicosities are spread out ( wider release of NT throughout organ ( thus neurotransmitter spreads out over multiple cells (not just local effect) Termination of NT activity ACh: actylcholinesterase- inactivates ACh ( on endplate and binds with some ACh released ( even the receptor bound ACh detaches and binds with AChE and eventually all ACh is inactivated Catecholamine reuptake Repacking Or Degradation (MAO) Blocked by cocaine Agonists and Antagonists Antagonists Bind to receptor and block NTs response Agonist Bind to receptor and mimic NTs response a direct agonist/antagonist( mimics or blocks NT at receptor an indirect agonist/antagonist ( mimics/blocks secretion, reuptake, or degradation of NT at synapse cholinergic receptor NT is ACh indirect ag/antag is AChE inhibitors muscarinic agonist is muscarine and antagonist is atropine nicotinic agonist is nicotine and antagonist is curare adrenergic receptor NT is NE or epinephrine indirect ag/antag: amphetamines stimulate NE release, and cocaine prevents NE uptake alpha agonist is phenelephrine and antagonist is ?alpha blockers? beta agonist is isoprotenerol and antagonist is ?beta blockers? CNS Control of Autonomic Function Can be influenced by prefrontal association complex through its involvement with emotional expression characteristic of individuals personality Hypothalamus- plays important role in integrating autonomic, somatic, and endocrine responses that automatically accompany various emotional and behavioral states Medulla- within brainstem, is region directly responsible for autonomic output Some autonomic reflexes such as peeing, pooping, and erection are integrated at level of spinal cord Hypothalamus is involved in coordination of ANS responses Temperature regulation Regulation of food intake Regulation of water intake Emotional behavior Papez Circuit Limbic system helps control emotional behavior in part by influence of hypothalamus Circuit connects limbic lobe with hypothalmus Control of Urinary Bladder - 3 sets of muscles used detrusor muscle- used to empty bladder B2 and muscarinic receptors Internal sphincter- used to retain fluid in bladder A1 and muscarinic receptors External Sphincter- retains fluid Voluntary control During Filling, sympathetic nervous system is active Internal sphincter contracts and detrusor relaxes During Peeing parasympathetic system is active Internal sphincter and external sphincter relax Detrusor muscle contracts forcing urine out Fight or Flight (sympathetic respose) Hypothalamus ( activates sympathetic nervous system and adrenal cortical system ( SNS activates adrenal medulla and activates glands and smooth muscles ( adrenal medulla releases epinephrine and norepinephrine into blood ( adrenal cortical system activates pituitary to release ACH with releases other hormones into blood ( neural activity combined with hormones in blood constitute fight or flight response
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