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Section 5 Regulation of the Visceral Function by the Nervous System
ANS • We subdivide the ANS into the parasympathetic, sympathetic, and enteric divisions. • The enteric system is essentially an independent nervous system responsible for regulation of digestive functions. • The ANS coordinates cardiovascular, respiratory, digestive, excretory and reproductive systems.
Somatic Skeletal muscle Conscious and unconscious movement Skeletal muscle contracts One synapse Acetylcholine Autonomic Smooth and cardiac muscle and glands Unconscious regulation Target tissues stimulated or inhibited Two synapses Acetycholine by preganglionic neurons and ACh or norepinephrine by postganglionic neurons Somatic and Autonomic Nervous System
Preganglionic cell bodies in lateral horns of spinal cord T1-L2 Sympathetic Division
Parasympathetic Division • Preganglionic cell bodies in nuclei of brainstem or lateral parts of spinal cord gray matter from S2-S4 • Preganglionic axons from brain pass to ganglia through cranial nerves • Preganglionic axons from sacral region pass through pelvic nerves to ganglia • Preganglionic axons pass to terminal ganglia within wall of or near organ innervated
2. Neurotransmitters and Neuroreceptors • Acetylcholine and Norepinephrine • All preganglionic neurons are cholinergic • Parasympathetic post ganglionic neurons are cholinergic • Sympathetic post ganglionic neurons are adrenergic except • Sympathetics innervating sweat glands, blood vessels in skeletal muscle, and piloerection muscles are cholinergic
SOMATIC NERVOUS SYSTEM Striated muscle ACh AUTONOMIC NERVOUS SYSTEM Heart Sm. mus. Glands Sympathetic ACh NE Sweat glands ACh ACh E, NE ACh Ad. M. Heart Sm. mus. Glands Parasympathetic ACh ACh Neurotransmitters
Acetylcholine • Nicotinic receptors • Nm (muscular-type or N2): skeletal muscle • Nn (neuron-type, or N1): autonomic ganglia, CNS • Muscarinic receptors • Postganglionic parasympathetic and a few sympathetic sites, CNS (also autonomic gang.) • Receptor subtypes: M1-5
Catecholamines • Norepinephrine • Postganglionic sympathetic, CNS, adrenal medulla • Receptors: a1, a2, b1 • Epinephrine • Adrenal medulla, CNS • Receptors: a1, a2, b1 , b2 • Dopamine • Autonomic ganglia, CNS • Receptors: D(1-5), a1, b1
SNS • Sympathetic nervous system prototypically “fight” or “flight”. • Associated with increased • energy expenditure, • cardiopulmonary adjustments for intense activity, • blood flow adjustments for maximum energy expenditure.
SNS - Fight & Flight Reaction You’re walking alone at night and all the sudden you hear an unfamiliar noise near by… In a matter of seconds, • your heart rate increases dramatically, • blood vessels in your skeletal muscles dilate, • blood vessels in the visceral muscles constrict, • digestion is ceased, • your liver ramps up glucose release, • your pupils dilate, • salivary production decreases, • sweat increases.
Parasympathetic Nervous System • If that noise turns out to be the result of wind, then the body is returned to “pre-noise” state. • This is the job of the parasympathetic nervous system.
Autonomic Nervous System • Parasympathicus • Wind down, relaxation, digestion • Dominated by Acetylcholine • Sympathicus • Fight & Flight Reaction • Dominated by Noradrenaline (Adrenaline) • Fear, exercise, rage
Interactions of the ANS • Most visceral organs are innervated by both types of nerves. • Most blood vessels are innervated only by sympathetic nerves. • PS activity dominates the heart and GI tract. • Activation of the sympathetic division causes wide spread, long-lasting mobilization of the fight-or-flight response. • PS effects are highly localized and short lived.
II. Central Regulation of Visceral Function 1.Spinal cord bladder and rectum reflex (micturition and defecation) the baroreceptor reflex, sweating of the skin
2. Medulla oblongata Vital (respiratory and cardiovascular) center: Other autonomic reflexes: Swallow, cough, sneeze, gag, and vomit.
3. Hypothalamus Tu :19.17
Hypothalamic Functions 1). Body temperature: • heat loss center in anterior HT (preoptic area) • stimulates sweating and peripheral vasodilation, • lesions cause hyperthermia; • heat gain center in posterior HT • stimulates cutaneous vasoconstriction, piloerection, shivering; • lesions cause poikilothermy • (the difference between poikilothermal or cold-blooded animal and homoiothermal or warm-blooded animal)
Hypothalamic Functions • 2). Food intake: • ventromedial and paraventricular nuclei are satiety centers, • lesion causes obesity; • lateral HT (feeding center) stimulates food and water intake
Hypothalamus Functions • 3) Water balance • ADH (vasopressin) • Osmotic pressure in hypothalamus – Thirst - Drink
4) Sleep/wake cycle: • suprachiasmatic nuc is biological clock; • preoptic nuc can initiate sleep; • lat HT can change cortical arousal; • post HT lesion can cause coma or impaired arousal
Hypothalamus Functions 5). Emotions and behavior: • ventromedial lesions can cause viciousness/rage • Posterior HT stimulates sympathetic functions • Anterior HT stimulates parasympathetic functions • Mamillary nuclei: recent memory
Hypothalamus Functions • 6). Circadian: • Almost all land animals coordinate their behavior according to circadian rhythms, the daily cycles of lightness and darkness that result from the spin of the earth. • Most if not all living organisms have rhythmic fluctuation in bodily function that are about 24 hs in length. (sleep-wake, and body temperature cycles). • Suprachiasmatic muclei (SCN)
Hypothalamus Functions 7) Regulation of the Endocrine Function
Cornea Physiology (Table 5-1) Iris Lens Eye Ciliary muscle
Atria Heart SA node AV node Ventricles