Autonomic Nervous System (ANS): ANS is the major involuntary, unconscious, automatic portion of the nervous system. involuntary voluntary The motor (efferent)portion of the ANS is the major pathway for information transmission from CNS to the involuntary effector tissues (smooth m, cardiac m, and exocrine gland). There is 2 major subdivision:- Parasympathetic ANS (PANS) Sympathetic ANS (SANS) *Note: Enteric Nervous System (ENS) is the semiautonomous part of ANS located in the GIT will be discussed -in between lectures- later. Now let us looking to the sympathetic, parsympathetic (and also somatic ) communications at more close view: figure (refresh the mind for information you got in physiology )
The adrenal medulla is considered to be a modified sympathetic ganglion; the medulla is embryonically and anatomically homologous to the sympathetic ganglia * NOTES: -All parasympathetic post ganglionic fibers contain acetylcholine (Ach) -All sympathetic postganglionic fibers contain Norepinephrine (NE) {also named Noradrenaline (NA)}.The exception is postganglionic fibers innervating the skin, which use Ach -All preganglionic fibers (both sympathetic and parasympathetic) contain Ach -In the somatic nervous system, only a single fiber goes straight to the skeletal muscle and releases Ach.
*NOTE: In ANS Transmissions of regulatory signal occur via synaps as in the following figure: Synthesis, storage, release, receptor binding and degradation of Ach:
*Synthesis, storage, release, receptor binding and degredation of NE:
*Receptors in ANS: 1-Nicotinic Receptors : 2 Subtypes of nicotinic receptors: N1 receptors are in sympathetic and parasympathetic ganglia (effects blocked with ganglionic blockers ). N2 receptors are at the neuromuscular junction (effects blocked with neuromuscular blockers). 2-Muscarinic Receptors : M1, M2, M3 and M4 3-Adrenoceptors: a-alpha receptors : α1 α2 b-beta receptors: β1 β2 β3. C-Dopamine receptors -They are especially important in renal and splanchnic vessels(mostly visera of the GITsuch as pancreas, spleen, stomach, small intestine, colon) as well as brain. - Five subtypes, D1 is the most important dopamine receptor on periphral effector cells. D2 receptors are found in presynaptic nerve terminal. Balance between PSNS and SNS: **** Most tissues are innervated by both parasympathetics and sympathetics nerves in a balanced relation, however there are some exceptions to this: Tissues predominantly sympathetic nerves (Keep in mind): Blood vessels Adipose tissue Skin Kidney. liver ( BASKL) Tissues predominantly parasympathetic nerves: Bronchi
*THE FOLLOWING FIGURE SHOULD BE MEMORIZED: Increase aqueous hummer drainge aqueous hummer
Effect on eye:??????? -Aqueous humour is a gelatinous fluid produced by the eye ciliary body ( within ciliary muscle) and secreted to anterior chamber. this fluid is responsible for intraocular pressure. Sympathetic innervations will relax the the cilliary body and consequently increase production and secretion of Aqueous humour and thus increase intraocular pressure. Parasympathetic innervations will contract the the cilliary body and consequently decrease production and secretion of Aqueous humour and thus decrease intraocular pressure. Also Parasympathetic innervations will open channel of schlemm and consequently increase drainage and of Aqueous humour from the anterior chamber and thus decrease intraocular pressure. Intraocular pressure= sympathetic Aqueous humour production- Parasympathetic Aqueous humour drainage through channel of schlemm.
Effects on urinary bladder: In essence parasympathetic innervations will contract the detrusor thus promote urination. Whereas sympathetic innervations will relax the detrusor thus delay urination. *THE FOLLOWING TABLE SHOULD BE MEMORIZED ( keep it in the mind very important)
*Remember at similar condition the PSNS predominate Digest and Rest *Remember at similar condition the SNS predominate
Fight and Flight Generally, it can be said that: Parasympathetics are involved with anabolic processes, rest and digest response whereas Sympathetics are involved with catabolic processes, flight and fright. Parasympathetics: 1. Decrease heart rate 2. (bronchial constriction) 3. Small pupils (contraction of the circular muscle) 4. Increased salivation 5. Increased gut motility Sympathetics: 1. Increased heart rate and force of contraction (β1 ) 5. Bronchioles dilate ( β2) 4. Pupils dilate (contraction of radial muscles) (α1) 6. Blood sugar rises (α1) ( β2) 7. Hair becomes erected on skin (α1)
Drugs affecting the ANS @Cholinergic Agonists 1-DIRECT ACTING: Muscarinic agonists 2-INDIRECT ACTING (reversible): 3-INDIRECT ACTING (irreversible): 4-REACTIVATION OF ACETYLCHOLINESTERASE : @Cholinergic Antagonists 1-ANTIMUSCARINIC AGENTS: 2-GANGLIONIC BLOCKERS: 3-NEUROMUSCULAR BLOCKERS: @Adrenergic Agonists 1-DIRECT-ACTING AGENTS: 2-INDIRECT-ACTING AGENTS: 3-DIRECT AND INDIRECT ACTING (mixed action) AGENTS: @Adrenergic Antagonists 1-α-BLOCKERS : 2-β- BLOCKERS: 3-Drugs affecting neurotransmitter uptake or release :