Autonomic Nervous System-I PDF

‫بسم الله الرحمن الرحيم‬ Autonomic Nervous System-I Dr.Mohammed Sharique Ahmed Quadri Dr. Abdelrahman Mustafa Department of Basic Medical Sciences Division of Physiology Faculty of Medicine Almaarefa University  PNS: E...

‫بسم الله الرحمن الرحيم‬ Autonomic Nervous System-I Dr.Mohammed Sharique Ahmed Quadri Dr. Abdelrahman Mustafa Department of Basic Medical Sciences Division of Physiology Faculty of Medicine Almaarefa University  PNS: Efferent Division PNS is Communication link by which CNS controls activities of muscles and glands Two divisions of PNS – Autonomic nervous system (ANS) Involuntary branch of PNS Innervates cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, and adipose tissue – Somatic nervous system Subject to voluntary control Innervates skeletal muscle  Autonomic Nervous System The portion of the nervous system which controls most visceral functions (involuntary ones )of the body is called as autonomic nervous system. eg : – Arterial pressure – heart rate – GI motility – GI secretion – Urinary bladder emptying – Sweating – Body temperature  Autonomic Nervous System The efferent autonomic signals are transmitted to the various organs of the body through 2 major subdivision. 1)Sympathetic nervous system 2)Parasympathetic nervous system  Functional anatomy of the ANS Sympathetic nerve fibers originate in the spinal cord along with the spinal nerve between T1-L2/L3 ( thoraco lumbar ). Parasympathetic nerve fibers originate from brain stem (midbrain, pons, and medulla) or the sacral spinal cord ( craniosacral). The preganglionic fibers originates from nuclei of cranial nerves (CN) III, VII, IX and X or from sacral spinal segments S2-S4.  Functional anatomy of the ANS Autonomic nerve pathway – Extends from CNS to an innervated organ – Two-neuron chains Preganglionic fiber (synapses with cell body of second neuron) Postganglionic fiber (innervates effector organ)  Sympathetic nervous system Sympathetic nerve fibers originate in the spinal cord along with the spinal nerve between T1 – L2. ( thoraco lumbar ) Length of the pre & postganglionic fibers Preganglionic fibers – are shorter Post ganglionic fibers – are longer  Sympathetic nervous system Pre ganglionic sympathetic fibers ALWAYS cholinergic, i.e. secretes Ach. This activates nicotinic receptors in the post ganglionic fibers. Post ganglionic fibers are adrenergic. , i.e. secretes adrenaline and noradrenaline They act on adrenoreceptors One of the exception is post ganglionic fibers supplying thermoregulatory sweat glands that is cholinergic that acts on muscarinic receptors.  Sympathetic nervous system Sympathetic system dominates in emergency or stressful (“fight-or-flight”) situations – Promotes responses that prepare body for strenuous physical activity  Functions of the sympathetic NS sympathetic NS is characterized by: – It discharges during emergency and stress ( fight and flight reaction). – It acts as one unit (generalized action). – It has catabolic action. – Delays evacuation of visceral content.  Parasympathetic nervous system Parasympathetic system originates from brain stem (midbrain, pons, and medulla) or the sacral spinal cord ( craniosacral). The preganglionic fibers originates from nuclei of cranial nerves (CN) III, VII, IX and X or from sacral spinal segments S2- S4.  Parasympathetic nervous system Length of the pre & postganglionic fibers Preganglionic fibers –are longer Post ganglionic fibers – are shorter Pre ganglionic para sympathetic fibers ALWAYS cholinergic, ie secretes Ach. This activates nicotinic receptors in the post ganglionic fibers. Post ganglionic para sympathetic fibers ALWAYS cholinergic, ie secretes Ach. This activates nicotinic or muscarinic receptors in the post ganglionic fibers.  Parasympathetic nervous system Parasympathetic system dominates in quiet, relaxed (“rest-and-digest”) situations – Promotes body-maintenance activities such as digestion – It allows the body to recover from stress  Functions of the parasympathetic NS Parasympathetic NS is characterized by: – It discharges during rest and sleep. – Its action is localized. – It has anabolic action (conserve body stores ). – It increases gastrointestinal secretion & motility i.e. secretomotor.  ANS Sympathetic Nervous System Parasympathetic Nervous System Fibers originate in thoracic and lumbar Fibers originate from cranial and sacral areas of regions of spinal cord CNS Most preganglionic fibers are short Preganglionic fibers are longer Long postganglionic fibers Very short postganglionic fibers Preganglionic fibers release acetylcholine Preganglionic fibers release acetylcholine (Ach) (Ach) Most postganglionic fibers release Postganglionic fibers release acetylcholine noradrenaline (norepinephrine), EXCEPT in sweat gland (Ach) Autonomic ganglion is prevertebral & Autonomic ganglia is near effector organ paravertebral Autonomic Ganglia 16  ANS INNERVATIONS Most visceral organs innervated by both sympathetic and parasympathetic fibers In general produce opposite effects in a particular organ Dual innervation of organs by both branches of ANS allows precise control over organ’s activity Effect of ANS ON VARIOUS ORGANS Effect of ANS ON VARIOUS ORGANS  Effect of ANS ON VARIOUS ORGANS ORGAN S P HEART + - CONSTRICT(MOST DILATE (PENIS BLOOD ORGANS) AND CLITORIS) VESSELS DILATE ( VESSELS IN SKELETAL MUSCLES) BRONCHIOLES DILATE CONSTRICT PUPIL DILATE CONSTRICT DIGESTION INHIBIT ENHANCE  Exceptions to general rule of dual reciprocal innervation Exceptions to general rule of dual reciprocal innervation by the two branches of autonomic nervous system – Most arterioles and veins receive only sympathetic nerve fibers( except blood vessels of penis & clitoris) – Most sweat glands are innervated only by sympathetic nerves – Salivary glands are innervated by both ANS divisions but activity is not antagonistic – both stimulate salivary secretion Distinguishing Characteristics of Sympathetic and Parasympathetic Nervous Systems  References Human physiology by Lauralee Sherwood, seventh edition Text book physiology by Guyton &Hall,11th edition Text book of physiology by Linda.s contanzo,third edition