AUTONOMIC NERVOUS SYSTEM ANATOMY AND TESTS

Arvind kulkarni

Introduction

• Autonomous – self driven .• Usually self driven up to the point that they

may not involve conscious control .• Highly integrated with other neural circuits.• It is the system that controls non striated

muscles and glands . • The boundary between autonomic and non-

autonomic systems is blurry .

• Central autonomic centers- hypothalamus, amygdala, basal forebrain , ventral striatum , brainstem and spinal cord .

• Peripheral autonomic system- sympathetic and parasympathetic divisions .

Divisions

• Sympathetic ( thoracolumbar ) system• Parasympathetic ( craniosacral ) system • Enteric system .

Sympathetic Parasympathetic

Preganglionic fibers arise from IML column of T1-L3

Cranial outflow – GVE of 3rd ,7th , 9th ,10th , bulbar portion of 11th Sacral outflow- fibers from S2-S4 of SC.

Preganglionic fibers are short terminate on ganglia some distance away from viscera

Preganglionic fibers are long – end in peripheral ganglia near or on the viscera

One Preganglionic fibers synapse with many post ganglionic -

One Preganglionic fiber synapse with only one post ganglionic

Prevertebral ganglia-viscera of abdomen and pelvis. Para vertebral sympathetic chainCollateral gangliaTerminal ganglia.

e.g.- E-W nucleus-ciliary , sup salivatory nucleus- submandibular and inf salivatory nucleus-otic ,lacrimal- pterygopalatine, n ambiguus.Pelvic splanchnic nerves

Adrenergic Synaptic Transmission

• Transmission at these synapses is called adrenergic: Norepinephrine released by most postganglionic sympathetic

nerve fibers.Epinephrine, released by the adrenal medulla

• Collectively called Catecholamines

Responses to Adrenergic Stimulation

• Beta adrenergic receptors:Produce their effects by stimulating production of

cAMPNE binds to receptorG-protein dissociates into

a subunit or bg- complex

Responses to Adrenergic Stimulation

• Depending upon tissue, either a subunit or bg-complex produces the effects• Alpha subunit- Activates adenylate cyclase Producing cAMP

cAMP activates protein kinase Opening ion channels

Responses to Adrenergic Stimulation (continued)

• Has both excitatory and inhibitory effects.• Responses due to different membrane

receptor proteins.a1 : constricts visceral smooth muscles.a2 : contraction of smooth muscle. b1 : increases HR and force of contraction.b2 : relaxes bronchial smooth muscles.b3: adipose tissue, function unknown

Anatomy of the chain

• Rami communicantes from the spinal nerves connect to the chain

A closer look at spinal nerves

Routes of Preganglionic Axons

• Cell bodies of neurons #1 lie in the lateral gray horns of the spinal cord

• The axons of neurons #1 leave the spinal cord via the ventral root

• These axons pass to the spinal nerve• Axons leave the spinal nerve via the white

branches (rami communicantes)• Connect with the sympathetic chain ganglia

Routes of Preganglionic Axons

• There are 3 possible routes that sympathetic neurons may follow

• Possibility #1: synapses within the ganglion at that level and– Second neuron leaves at that level via the gray

ramus communicans, exits to the visceral effector

Routes of Preganglionic Axons

• Possibility #2: neuron #1 goes up or down the chain and synapses at some other level.– Second neuron: leaves at that other level via the

gray ramus communicantes, and exits to the visceral effector.

Routes of Preganglionic Axons

• Possibility #3: neuron #1 does not synapse in the chain (exception!!) but exits and synapses in a collateral ganglion near a major blood vessel.– Neuron #2 travels from that ganglion to the

visceral effector.

Where are the Collateral Ganglia ?

• Location –Near a major blood vessel– Celiac ganglion• Innervates upper abdominal viscera

– Superior mesenteric• Innervates middle abdominal viscera

– Inferior mesenteric• Innervates lower abdominal & pelvic organs

The Adrenal Medulla

• Yet another type of innervation:– Going to the adrenal medulla– No synapse in ganglia– No synapse in collateral ganglia– YES synapse in the adrenal medulla

Adrenal Medulla

• Only Preganglionic neurons are in this pathway

• Neuron #1 stimulates the medulla, • The medulla releases norepinephrine and

epinephrine (adrenaline) to blood

Human Anatomy 5th ed. 2005Benjamin Cummings

Adrenal Medulla

Human Anatomy, 3rd editionPrentice Hall, © 2001

Figure 17-06

Parasympathetic system

• Rest and digest system .

Parasympathetic division

• Cell bodies are in the brain or in the gray matter of the spinal cord (sacral region)

• Neurons #1 exit the cranial region through cranial nerves 3, 7, 9, & 10 or

• Neurons #1 exit the spinal cord through the sacral spinal nerves

Parasympathetic

• Neurons #1 are long and synapse with neurons #2 (short) in ganglia

• Ganglia are found on, or –near the visceral effector

Central autonomic network

• Peripheral ANS is under the control of higher centers in cerebral cortex.

• hypothalamus, amygdala, basal forebrain , ventral striatum , brainstem and spinal cord .

• Most important of these is hypothalamus

hypothalamus

• Ventral diencephalon – lies just below the thalamus and above pituitary

• Wt- 4 gm • Autonomic pathways I/l brainstem

tegmentum ant fasciculus in SC widely distributed mainly in Reticulospinal tract terminate at appropriate level at IML level of SC.

Tests of assessment

• Bedside tests –• General physical and neurological examination-

acromegaly , dwarfism , s/o endocrine imbalance, sexual immaturity – hypothalamic .

• Dryness of skin- spoon test , sweat droplets at papillary ridges +20 ophthalmic lens , changes in skin temperature ,color, alopecia , hypertrichosis, thickening or fragility of nails ,absent piloerection , decreased hand wrinkling in water and skin atrophy.

• Tests for OH- BP changes in supine and standing . 1,3,5 min .

• HR Changes - > 30 bpm on standing. Or > 120 bpm

• Absent reflex tachycardia .• POTS- >30 bpm or >120 bpm without fall in BP.• Sustained hand grip, mental stress , cold pressor

test- DBP at least 15 mm hg/ HR >10 bpm

• Resting tachycardia – parasymp dysfunction .• Bladder- palpation for distention, anal wink

and bulbocavernous reflex . internal anal sphincter reflex.

• Lacrimal gland tear production- schirmer test-place a strip of sterile filter paper in lower conjuctival sac – measurement of degree of wetting over 5 min.

• vagal tone- beat to beat variability of HR– deep breathing, standing , valsalva.

• HR- DB sinus arrhythmia , pulse variability , R-R interval on ECG

• HR – standing- ( 30:15 ratio) ratio of R-R Interval at beat 30 /R-R at beat 15.

• Normal > 1.04•

• Valsalva-• Phase 1- increased IT pressure rise in BP• Phase 2- gradual fall in BP due to impaired

venous return • Phase 3- brief fall due to release of pressure • Phase 4 – normal overshoots BP for 1 min

absence indicates early autonomic dysfunction .

• Tilt table test – neurocardiogenic syncope• Thermoregulatory and sudomotor function-• SSR- peripheral sympathetic function• QSART- quantitative sudomotor axon reflex test.-

postganglionic sudomotor fibers- sweat output iontophoresis into the skin of acetylcholine

• Thermoregulatory sweat test ( TST )- both central and peripheral sympathetic function- sweat response in response to changes in body temperature.

• Thank you.