Ans 2008

THE AUTONOMIC NERVOUS SYSTEM

Date: June 16, 2008 Lecturer: Dr. Mang C. Yu

AUTONOMIC NERVOUS SYSTEM Innervates cardiac muscle, smooth muscle, glandular tissues TWO DIVISIONS: 1. Sympathetic Nervous System (Thoraco-lumbar Outflow) 2. Parasympathetic Nervous System (Cranial-sacral Outflow)

ANS: TWO-NEURON CHAIN SYSTEM

SYMPATHETIC NERVOUS SYSTEM: 1. First neuron (preganglionic) located at intermediolateral gray column (lateral horn) of spinal cord from T1 to L2 2. Second neuron (postganglionic) located at paravertebral ganglia (sympathetic trunk) and prevertebral ganglia (coeliac, mesenteric, aortico-renal ganglia)

SYMPATHETIC NERVOUS SYSTEM

SYMPATHETIC INNERVATION OF VISCERAL ORGANS

PARASYMPATHETIC NERVOUS SYSTEM TWO PARTS: CRANIAL AND SACRAL

A. Cranial portion: associated with 3, 7, 9, 10 cranial nerves Nerve

First Neuron (Preganglionic)

Second Neuron (Postganglionic)

Oculomotor Facial

Edinger-Westphal Nucl Superior Salivatory Nucl

Ciliary ganglion Pterygopalatine gang Submandibular gang Otic gang Cardiac plexus, Terminal gang

Glossopharyngeal Inferior Salivatory Nucl Vagus Dorsal Vagal Motor Nucl

B. Sacral Portion: associated with S2, 3 and 4 segments spinal cord 1st neuron - intermediolateral gray matter 2nd neuron- Terminal ganglia, pelvic plexus

PARASYMPATHETIC NERVOUS SYSTEM

MODE OF INNERVATION OF ANS (TO REACH TARGETS) 1. VIA SPINAL NERVES 2. VIA CRANIAL NERVES 3. VIA OWN NERVES, e.g, VAGUS NERVES, SPLANCHNIC NERVE (greater, lesser and least splanchnic nerves) 4. VIA BLOOD VESSELS, ESPECIALLY VIA CAROTID ARTERIES TO TARGETS IN HEAD REGIONS

NEUROTRANSMITTERS OF ANS SYMPATHETIC NERVOUS SYSTEM Preganglionic neurons: Acetylcholine Postganglionic neurons: Norepinephrine (Adrenergic) PARASYMPATHETIC NERVOUS SYSTEM Preganglionic neurons: Acetylcholine Postganglionic neurons: Acetylcholine (Cholinergic)

FUNCTIONS OF ANS (1) Sympathetic Division Fright, fight, flight e.g. dilates pupils, increases heart rate and output, increases respiration Neuro-endocrine Axis Adrenal Medulla: Acts as a component of sympathetic postganglionic neurons Under stressful situations (exams, worries), a steady output of epinephrine mobilizes blood sugar and fatty acids

FUNCTIONS OF ANS (2) Parasympathetic Division Generally maintains bodily functions, restorative processes Constricts pupils, slows heart rate and reduces cardiac output Increases glandular secretion and peristalsis in digestive process, absorption of nutrients; eliminates waste products via micturition, defecation

AUTONOMIC CONTROL OF THE HEART

AUTONOMIC CONTROL OF BLADDER

Hypothalamus: Highest Center of ANS Feeding behavior; Drinking (Water and Salt intake); Thermo-regulation; Control of blood flow by adjusting cardiac output; Regulation of energy metabolism by monitoring blood glucose level; Digestive functions; Regulation of reproductive activities such as sexual orientation; mating behavior

Amygdala: Plays Important Roles in ANS Functions

CLINICAL CORRELATIONS A. Diseases of the sympathetic division: 1. Horner’s syndrome (anhydrosis, miosis, ptosis) 2. Angina pectoris: severe pain in cardiac ischemia due to constriction of coronary blood vessels as a result of sympathetic stimulation. The pain felt radiates from left chest and shoulder and inner arm following the track of spinal nerve T1, a classic example of “referred pain” 3. Raynaud’s disease: over-stimulation of sympathetic nervous system on terminal vessels in lower limbs, leading to “dry gangrene”

CLINICAL CORRELATIONS B. Diseases of the parasympathetic division: 1. Hirschsprung’s disease (congenital megacolon): lack of bowel movements due to absence of parasympathetic neurons in terminal ganglia (myenteric and submucosal plexuses), resulting in greatly extended bowls, and constipation 2. Peptic ulcer: over-stimulation of the vagus nerve, leading to excessive secretion of highly acidic gastric juice - ulcer