The Autonomic Nervous System

Nervous System Nervous System Central Peripheral Somatic Control out Autonomic Control inside

A.1. The autonomic nervous system: Figure 11-2 is regulated by the Hypothalamus It regulates activities of : (1) Visceral muscles : which are involuntary, and include (a)cardiac muscle, and (b)smooth muscle in arterioles and the gastro-intestinal tract (GIT). (2) Glands ( e.g., sweat glands and GIT glands ) It consists of 2 subdivisions:

Def: Involuntary control of the visceral organ activities eg (circulation, digestion, sweating, papillary size) Division: Sympathetic Parasympathetic

Functional Anatomy The autonomic nerves consist of two neutrons. 1. Preganglionic : Its cell body is located in the CNS. 2. Postganglionic : Its cell body in a ganglion outside the CNS. It innervates the effector organ.

Functional anatomy..cont Originate in the lateral horn cells in the spinal cord. Sympathetic: originate in the thoracic and lumbar regions of the spinal cord. (Thoracolumbar) Parasympathetic: originate from cranial nerves (3 rd, 7 th, 9 th, 10 th ), and sacral spinal nerves. (craniosacral) originate from cranial nerves (3 rd, 7 th, 9 th, 10 th ), and sacral spinal nerves. (craniosacral) C3,7,9,10 P P SYMP S2-4 T1-12 L2-3

Site of Ganglia Both systems are 2 neuron system. Sympathetic: Preganglionic fibers are very short, synapsing with cell bodies of postganglionic neurons within ganglia lie in sympathetic ganglion chain (sympathetic trunk). Postganglionic fibers originate in the ganglion chain terminate on the effector organs. Some preganglionic fibers pass through the ganglion chain without synapsing and terminate later in sympathetic collateral ganglia located halfway between the CNS and innervated organs. C °  T1 о T2 о T3 о effector organ Pre Post

Site of ganglia Parasympathetic: Ganglia are near or within the effector organs. Postganglionic fibers are shorter than Preganglionic

Parasympathetic (Craniosacral ) system : 1.The preganglionic neurons are located in the CNS. 1.The postganglionic neurons (located in parasympathetic ganglia) are either close to or embedded in their targets tissues.

Functions of the ANS The ANS controls involuntary visceral organ activities. Such as: circulation, digestion, sweating, and papillary size. The sympathetic and parasympathetic systems exert opposite effects. The sympathetic is activated during stress & emergencies. Prepare for “ fight or flight ”. The parasympathetic is concerned with vegetative functions (general housekeeping), eg: feeding, resting and sexual stimulation.

sympathetic and parasympathetic The ANS has 2 subdivisions :

ُُ Eye Iris Ciliary ms Lacrimal glands heart Peripheral bl vessels GIT Dilatation of pupil Relaxation (far vision) non Vasoconstriction Vasodilatation of sk ms Increase H.R Increase force of cont Dilatation of coronary bl vessl Relax of walls & Const of sphincters (filling promoted) bronchodilationlungs Costriction of pupil Contraction (nearvision) lacrimation non Decrease H.R Increase motility &secretion Relaxation of sphincters (emptying promoted) constriction SympatheticParasympathetic

Urinary bladder Sex organs Relax of walls & Cont of internal sphincter (filling promoted) ejaculation Cont of walls & Relax of internal sphincter (emptying promoted) Erection of penis Or clitoris Sympathetic Parasympathetic

Figure Figure 11- 3

Chemical or neural transmitter All preganglionic fibers release acetylcholin (Ach). All preganglionic fibers release acetylcholin (Ach). All parasympathetic postganglionic release Ach. All sympathetic postganglionic release noradrenalin, except sweat glands and blood vessels in skeletal muscle release Ach. Ach Para Noradrenaline except sweat gl bl vessl of skeletal ms) Symp Ach

Chemical Division of ANS Cholinergic ( Ach) 1. All preganglionic (para+symp) 2. All Para Post ganglionic. 3. Symp postganglionic at sweat glands and blood vessels in skletal ms. Adrenergic ( adrenalin&nor ) most symp post ganglionic  noradrenalin. most symp post ganglionic  noradrenalin. Adrenalin Adrenalin Adrenal medulla is a modified symp ganglion that does not give rise to postganglionic fibers. It secretes mainly adrenalin upon stimulation by preganglionic. Adrenalin Ach

Adrenal Medulla

Chemical transmitters..cont Chemical transmitters act locally either at the synapse or at the target cell receptors. Their effect lasts only for a few seconds because they are either destroyed or removed from the site of their release. Ach is removed by hydrolysis. Ach cholin+acetate Ach cholin+acetate cholinesterase

Noradrenalin is rapidly taken up by the nerve endings by active transport.

Biosynthesis and reuptake of noradrenalin

Receptors: Def : the site on the cell membrane with which the chemical transmitter combines to produce its effect on the cell.

Adrenergic receptors α is found in : –Iris –Blood vessels –GIT β is found in : –Heart –bl vessel of Skeletal muscle –GIT

Adrenergic receptors  Constriction on blood vessels Constriction on blood vessels  (  1,  2)  2 Dilatation coronary,bl vessel of skeletal ms  2 Dilatation coronary,bl vessel of skeletal ms Bronchial tree Bronchial tree

Adrenergic receptors 1.  -receptors Vasoconstrition Vasoconstrition Dilatation of pupil Dilatation of pupil Blocked by phentolamine Blocked by phentolamine

2.  receptors  1 Mainly in heart  H.R.&force Blocked by atenolol (hypertention)  2 In bronchial tree Cause bronchodilatation Stimulated by salbutamol (bronchial asthma)

Blocks both  1&  2 Not useful, C/I in asthmatic people Proprranlol

Cholinergic receptors Divided into : Nicotinic ( in all ganglia ) Muscarinic ( in effector tissues )

Cholinergic receptors Nicotinic In ganglia Stim by small dose of nicotine Inhibt by large dose of nicotine Not blocked by atropine Blocked by ganglion blocker hexamethoniumMuscarinic In target organs Blocked by atropine (for relief of colic&before surgery to reduce salivary&bronchial secretion to prevent inhaling these secretions).

Drugs that you should know Epinephrine. Salbutamol ( ventolin ). Propranolo ( inderal ). Atenolol ( tenormin ). Atropine. PrazosinPhentolamineHexamethonium

3.The neurotransmitter between the preganglionic and the postganglionic neuron is Ach. The receptors on the postganglionic neurons are of the cholinergic nicotinic type. 4.The neurotransmitter secreted by the postganglionic neuron is NorEpinephrine (NE). The receptors on the target are adrenergic receptors (alpha or beta). 5.There is a great divergence. The divergence implies diffuse adrenergic actions Sympathetic (Thoracolumbar):

3.The neurotransmitter between the preganglionic and the postganglionic neuron is Ach. The receptors on the postganglionic neurons are of the cholinergic nicotinic type. 4.The neurotransmitter secreted by the postganglionic neuron is Ach. The receptors on the target are of the muscarinic cholinergic type. 5.There is little divergence. The ratio (pre/post) = 1/3. 6.The limited divergence results in more specific cholinergic actions. Parasympathetic (Craniosacral)

Higher control Sympathetic sys is regulated by neurons in the Post part of the hypothalamus. Parasympathetic is regulated by neurons in the Anterior part of the hypothalamus.

Origin of preganglionic fiber Origin of postganglionic fiber (location of ganglion) Length and type of fiber Types of receptors for neurotransmitters Types of discharge Thoracic and lumbar Sympathetic ganglion chain or collateral ganglia ,  1,  2 Shorter cholinergic preganglionic fiber, long adrenergic post-ganglionic fiber (most) Mass discharge of whole system Emergency fight or flightDominance Cranial and scral Terminal ganglia (in or near effectors organ Nicotinic, muscarinic Long cholinergic preganglionic fiber, short cholinergic post- ganglionic fiber Involves discrete organ Relaxed situation SympatheticParasympathetic

Difference between Somatic & Autonomic Somatic innervates skeletal muscle. innervates skeletal muscle. Control is precise & voluntary. Neuronal connection located within CNS. Mylenated nerves transmit rapid impulses. Autonomic Innervate smooth &cardiac muscle, gland and viscera. Control is diffuse & involuntary. Nonmyelinated postganglionic nerves conduct slow impulses. Mylenated preganglionic nerves conduct rapid impulses. Stimulation increases or decreases activity.

Applied Neurophysioloy (1) Epinephrine : Stimulates both beta1 and beta2 receptors Useful in Tt of Asthma Contraindcated ( C/I ) in Hypertension or Heart disease. Why ? Salbutamol (ventolin ) : Stimlates mainly beta 2 receptors Used in Tt of Bronchial asthma Safer than epinephrine. Why ?

Applied Neurophysioloy (2) Propranolol ( Inderal ) : Blocks beta1 & beta2 Used in Tt of hypertension Should not be given to a patient with Bronchial Asthma. Why ? Atenolol ( Tenormin ) : Blocks only beta 1 Used in Tt of hypertension Safer than Inderal. Why ? Atropine : Blocks muscarinic receptors ( of Ach ) Used in Tt of colic