Autonomic Nervous Autonomic Nervous SystemSystem

Organization Comparison of peripheral nervous system Components of the ANS Receptors/neurotransmitters Hypothalamic control Visceral function

Homeostasis & Homeostasis & OrganizationOrganization

Maintenance of the internal environment – what else?http://itc.gsw.edu/faculty/gfisk/anim/autonomicns.swf

Visceral efferent division of the human nervous system– respond via contraction/relaxation or secretion

– conduction of sensory impulses back to NTS

– feedback loop: visceral efferent & afferent system

Parasympathetic & sympathetic branches exit the spinal cord in different regions - craniosacral & thoracolumbar

Distribution of PNS: cranial Distribution of PNS: cranial nerve nuclei in brainstemnerve nuclei in brainstem

Oculomotor (III)

Facial (VII)

Glossopharyngeal (IX)

Vagus (X)

Sacral spinal nerves (S2-S4)

SNSSNS arises from thoracic & arises from thoracic & lumbar spinal cord levels – lumbar spinal cord levels – forming sympathetic trunkforming sympathetic trunk

intermediolateral(IML) cell column

(prevertebral)

Autonomic Autonomic sympathetic & sympathetic & parasympathetic parasympathetic pathwayspathways

Organization of Efferent Divisions of Organization of Efferent Divisions of the ANSthe ANS

1. How do the 2 autonomic branches differ anatomically?

2. The autonomic divisions are distinguished biochemically by their neurotransmitters & receptors explain?

Key questions for Key questions for understanding organization understanding organization & function of the ANS& function of the ANS

Cholinergic ReceptorsCholinergic Receptors

Nicotinic receptors:– preganglionic receptor for both PSN & SNS, at NMJ & in

the adrenal medulla

– responds to ACh; produce excitation binding opens ion channels influx of Na+ & efflux of K+

Muscarinic receptors (M1 & M2):

– postganglionic for PSN; located in heart, smooth muscle & glands; respond to ACh

– M1 receptor: IP3 is second messenger and ICCa2+]

– M2 receptor: inhibits adenylate cyclase result is [cAMP] & slows rate of depolarization

Adrenergic ReceptorsAdrenergic Receptorsreceptor activation mechanism

location produces of action

1 skin & splanchnic excitation formation of IP3

vascular SM, GI & ICCa2+]

& bladder sphincters

2 walls of GI tract inhibition inhibit adenylate

fat cells & platelets cyclase, [cAMP]

1 heart excitation produce cAMP,

activate adenylate

2 GI tract & bladder relaxation same as 1

vascular & bronchial SM

Varicosities NT released to ECF No cleft Effect:

– large area

– slow acting

– long duration

Synapses in Autonomic Synapses in Autonomic NervesNerves

Summary of two branches of the Summary of two branches of the ANSANS

Comparison of the Somatic & Comparison of the Somatic & Autonomic Nervous SystemsAutonomic Nervous Systems

ANS: is a two-neuron system:– preganglionic fibers & postganglionic fibers

– self-governed

– exclusively a reflex system

– innervates smooth muscle, viscera & glands

– ACh & norepinephrine (NE) -- neurotransmitters

Somatic nervous system: cell bodies in the CNS – axons extend to skeletal muscle:– lack ganglia (single-neuron system)

– voluntary/reflex system

– innervate skeletal muscle

– ACh is excitatory neurotransmitter

Adrenal Medulla: Adrenal Medulla: an extension of the an extension of the SN SSN S

acts like a combined autonomic ganglion & postsynaptic sympathetic nerve

releases epinephrine & norepinephrine (E = 80% & NE = 20%)

action of adrenals are under control of the hypothalamus

Integrates autonomic & neuro-endocrine functions; serves as a homeostatic center

Coordinates visceral activities in response to changes in environment

Final common pathway is located in brainstem

Hypothalamus Has Hypothalamus Has Central Control of Central Control of the ANSthe ANS

Structure SNS Stimulation PNS Stimulation

iris pupil dilation pupil constriction

salivary glands saliva production saliva production heart HR, conduction/force HR & conduction

blood vessels vasoconstrict/dilatate

lung relax SM SM contraction

GI tract motility peristalsis, motility digestion

liver glycogenolysis conserve glucose

kidney GFR urine secretion

sweat glands sweating

bladder wall relaxed, sphincter wall contracted closed sphincter relaxed

ANS & Visceral FunctionANS & Visceral Function