Autonomic nervous system D.Nimer D.Rania Gabr D.Safaa D.Elsherbiny

Objectives Review the subdivisions of the nervous system. Review the general arrangement and compare the sympathetic and parasympathetic parts. Describe the following plans Para vertebral ganglia. Prevertebral ganglia. Parasympathetic ganglia. Splanchnic nerves. Autonomic plexuses Map out the various plexuses in head and neck, thorax, abdomen and pelvis. Make a list of the components of the system. Review the basic structure of sympathetic trunk. Describe the source of sympathetic system in the neck and make a list of target organs.

Describe the Para vertebral sympathetic ganglia in the abdomen, their locations and target organs. Discuss the relation of this system to the adrenal medulla. Discuss the sympathetic innervation of blood vessels. Make a list of the components of the system. Make a list of cranial nerves having parasympathetic activity. Describe the parasympathetic ganglia in the head and neck, their locations and target organs. Describe the sacral parasympathetic out flow. Make a list of its target organs.

The Autonomic Nervous System and Visceral Sensory Neurons

Autonomic Nervous System Concerned with the innervation and control of visceral organs, smooth muscles and glands Along with the endocrine system, its primary function is homeostasis of the internal environment The visceral receptors include chemoreceptors, baroreceptors, and osmoreceptors. Ischemia or stretch can cause extreme pain Distributed both in the central and peripheral nervous system Like the somatic nervous system, it has sensory (afferent) & motor (efferent) neurons and interneurons

The AFFERENT impulses originate in the visceral receptors, travel via afferent pathways to the CNS and terminate on the sensory neurons at different levels Like the somatic system, the cell bodies of the sensory neurons are located in the sensory ganglia sensory ganglia Somatic Autonomic

The EFFERENT pathway is made up of preganglionic and postganglionic neurons The cell bodies of the preganglionic neurons are located in the brain and spinal cord. Their axons synapse with the postganglionic neurons whose cell bodies are located in the autonomic ganglia

Comparison of Autonomic and Somatic Motor Systems Autonomic nervous system Chain of two motor neurons Preganglionic neuron Postganglionic neuron Conduction is slower due to thinly or unmyelinated axons Pre-ganglionic Post-ganglionic Ganglion

nicotinic receptors always cholinergic cholinergic or adrenergic muscarinic or adrenergic receptors

Neurotransmitter of the Autonomic Nervous System preganglionic axons Acetylcholine for both divisions (cholinergic) postganglionic axons Sympathetic: mostly norepinephrine Parasympathetic: acetylcholine

Somatic motor system Autonomic motor system Effector Skeletal muscle Cardiac muscle, smooth muscle, glands Type of control Voluntary Involuntary Neural pathway One motor neuron extends from the CNS to skeletal muscle Chain of two motor neurons: Preganglionic & Postganglionic neuron Action on effectors Always excitatory May be excitatory or inhibitory Neurotransmitter Acetylcholine Acetylcholine or norepinephrine Rate of conduction Rapid due to myelinated axons Slower due to thinly myelinated or unmyelinated axons Visceral motor system is different from somatic motor system in many respects

Based on the anatomical, physiological and pharmacological characteristics, the autonomic nervous system is divided into: Sympathetic: Activated during exercise, excitement, and emergencies. “fight, flight, or fright” Parasympathetic: Concerned with conserving energy. “rest and digest” The heart rate is slowed, pupils are constricted, peristalsis and glandular activity is increased, sphincters are opened, and the bladder wall is contracted. Both divisions operate in conjunction with one another (have antagonistic control over the viscera) to maintain a stable internal environment

Parasympathetic Division Forms thoracolumbar outflow: Issues from (T1-L2 )segments of spinal cord Ganglia are close to the CNS (longer postganglionic fiber) Each preganglionic fiber synapses with many postganglionic neurons that pass to many visceral effectors Forms craniosacral outflow: Issues from (brain & S2-S4 ) segments of spinal cord Ganglia are near or within the viscera (longer preganglionic fiber) Each preganglionic fiber usually synapses with four or five postganglionic neurons that pass to a single visceral effector

Parasympathetic Division Cranial Outflow Emerges from brain Preganglionic neurons located in nuclei of the 3rd,7th, 9th & 10th cranial nerves, in the brain stem Postganglionic fibers are carried by 3rd,7th, 9th & 10th cranial nerves and innervate organs of the head, neck, thorax, and abdomen Sacral Outflow Emerges from S2-S4 Preganglionic neurons located in lateral horn of spinal gray matter carried by pelvic splanchnic nerves Postganglionic fibers to innervate organs of the pelvis and lower abdomen

Parasympathetic Ganglia Multiple, small, located nearer the viscera Ganglia related to innervation of: head & neck: (ciliary, otic, pterygopalatine & submandibular). thoracic, abdominal & pelvic viscera.

Sympathetic Division Thoracolumbar outflow: Emerges from T1-L2 segments of spinal cord Preganglionic neurons located in the lateral gray horn.

Regardless of target, all begin same: Preganglionic axons exit spinal cord through ventral root and enter spinal nerve Exit spinal nerve via communicating ramus Enter sympathetic trunk/chain where postganglionic neurons :- Has three options…

Options of preganglionic axons in sympathetic trunk 1- Synapse on postganglionic neuron in chain ganglion then return to spinal nerve and follow its branch to the skin 2- Ascend or descend within sympathetic trunk, synapse with a postganglionic neuron within a chain ganglion, and return to spinal nerve at that level and follow branches to skin 3- Enter sympathetic chain, pass through without synapsing, form a splanchnic nerve that passes toward thoracic or abdominal organs Postganglionic axons follow arteries to organs

Fibers that pass through the ganglia of the sympathetic trunk without synapsing, These myelinated fibers leave the sympathetic trunk as -Greater splanchnic which synapse in celiac plexus, renal plexus, and suprarenal medulla. -Lesser splanchnic which synapse in lower part of the celiac plexus. -Lowest or least splanchnic nerves which synapse in renal plexus..

The splanchnic nerves, therefore, are formed of preganglionic fibers. The postganglionic fibers are distributed to the smooth muscle and glands of the viscera. The ratio of preganglionic to postganglionic sympathetic fibers is about 1:10, permitting a wide control of involuntary structures

Sympathetic Pathways to Periphery:Synapse in chain ganglia at same level or different level Preganglionic fibers run in the ventral roots of the spinal nerve Travel through the spinal nerve, and then join the sympathetic chain via the white rami communicans. (myelinated axons) (WRC) The postganglionic fibers enter back into the spinal nerve through grey rami communicans (GRC) (nonmyelinated axons) Figure 15.9 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings

Pass through ganglia and synapse in prevertebral ganglion

Sympathetic Ganglia Multiple, large in size Located nearer the central nervous system: Based on their relation to the vertebral column, they are grouped into: Prevertebral Paravertebral

Prevertebral Ganglia Unpaired, not segmentally arranged Located in abdomen, anterior to the vertebral column Main ganglia Celiac Superior mesenteric Inferior mesenteric Aorticorenal

Paravertebral Ganglia Consist of the right and left sympathetic chains or trunks. The chains lie next to the vertebral column throughout its length There is approximately one ganglion associated with each spinal cord segment, except in the cervical and the sacral regions. The chains end into a common ‘ganglion impar’ in front of coccyx

T1 to L2 ventral rami are connected to the sympathetic chain via white rami communicantes, which carry preganglionic sympathetic fibers to the sympathetic chain All the ventral rami receive postganglionic sympathetic fibers from sympathetic chain by a gray ramus Delete this slide

The Role of the Adrenal Medulla in the Sympathetic Division Major organ of the sympathetic nervous system Secretes great quantities epinephrine (a little norepinephrine) Stimulated to secrete by preganglionic sympathetic fibers

Distribution of Autonomic Fibers Both divisions innervate mostly the same structures & operate in conjunction with one another (have antagonistic control over the viscus) to maintain a stable internal environment Some viscera do not possess dual control e.g. sweat glands, adrenal medulla, erector pili muscles and many blood vessels have only sympathetic innervation

Higher Control of the Autonomic Nervous System The hypothalamus has a controlling influence on the autonomic system and regulates balance between sympathetic and parasympathetic activity levels The hypothalamus integrates the autonomic and neuroendocrine systems to preserve body homeostasis