The Autonomic Nervous System
Visceral sensory
Visceral motor&
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Autonomic nervous system
The autonomic nervous system is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control
Visceral motor innervates non-skeletal (non-somatic) muscles
Visceral sensory will be covered later
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ANS is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control
Visceral motor innervates non-skeletal (non-somatic) muscles
Composed of a special group of neurons serving: Cardiac muscle (the heart) Smooth muscle (walls of viscera and blood vessels) Internal organs Skin
To repeat…
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Basic anatomical difference between the motor pathways of the voluntary somatic nervous system (to skeletal muscles) and those of the autonomic nervous system
Somatic division: Cell bodies of motor neurons reside in CNS (brain or
spinal cord) Their axons (sheathed in spinal nerves) extend all the
way to their skeletal muscles Autonomic system: chains of two motor neurons
1st = preganglionic neuron (in brain or cord) 2nd = gangionic neuron (cell body in ganglion outside
CNS) Slower because lightly or unmyelinated
(see next diagram)
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Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron
Axon of 2nd (ganglionic) neuron extends to the organ it serves
Diagram contrasts somatic (lower) and autonomic:
autonomic
somatic
Note: the autonomic ganglion is motor
this dorsal root ganglion is sensory
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Divisions of the autonomic nervous system (visceral motor part of it)
Parasympathetic division Sympathetic division
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Divisions of the autonomic nervous system
Parasympathetic division Sympathetic division
Serve most of the same organs but cause opposing or antagonistic effects
Parasympathetic: routine maintenance “rest &digest”
Sympathetic: mobilization & increased metabolism “fight, flight or fright” or “fight, flight or freeze”
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Where they come from
Parasympathetic:craniosacral
Sympathetic:thoracolumbar
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Parasympathetic nervous system“rest & digest”
Also called the craniosacral system because all its preganglionic neurons are in the brain stem or sacral levels of the spinal cord Cranial nerves III,VII, IX and X In lateral horn of gray matter from S2-S4
Only innervate internal organs (not skin) Acetylcholine is neurotransmitter at end
organ as well as at preganglionic synapse: “cholinergic”
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Parasympathetic continued
Cranial outflow III - pupils constrict VII - tears, nasal mucus, saliva IX – parotid salivary gland X (Vagus n) – visceral organs of thorax & abdomen:
Stimulates digestive glands Increases motility of smooth muscle of digestive tract Decreases heart rate Causes bronchial constriction
Sacral outflow (S2-4): form pelvic splanchnic nerves Supply 2nd half of large intestine Supply all the pelvic (genitourinary) organs
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Parasympathetic
(only look at this if it helps you)
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Sympathetic nervous system“fight, flight or fright”
Also called thoracolumbar system: all its neurons are in lateral horn of gray matter from T1-L2
Lead to every part of the body (unlike parasymp.) Easy to remember that when nervous, you sweat; when
afraid, hair stands on end; when excited blood pressure rises (vasoconstriction): these sympathetic only
Also causes: dry mouth, pupils to dilate, increased heart & respiratory rates to increase O2 to skeletal muscles, and liver to release glucose
Norepinephrine (aka noradrenaline) is neurotransmitter released by most postganglionic fibers (acetylcholine in preganglionic): “adrenergic”
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Sympathetic nervous system continued
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 are
Has three options…
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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 posganglionic 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
These synapse in prevertebral ganglion in front of aorta
Postganglionic axons follow arteries to organs
(see next slides for drawing examples)
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Synapse in chain ganglia at same level or different level
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Pass through ganglia and synapse in prevertebral ganglion
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Sympathetic
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Adrenal gland is exception
On top of kidneys
Adrenal medulla (inside part) is a major organ of the sympathetic nervous system
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Adrenal gland is exception
Synapse in gland Can cause body-wide
release of epinephrine aka adrenaline and norepinephrine in an extreme emergency(adrenaline “rush” or surge)
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Summary
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Visceral sensory system
Gives sensory input to autonomic nervous
system
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Visceral sensory neurons Monitor temperature, pain, irritation, chemical changes
and stretch in the visceral organs Brain interprets as hunger, fullness, pain, nausea, well-being
Receptors widely scattered – localization poor (e.g. which part is giving you the gas pain?)
Visceral sensory fibers run within autonomic nerves, especially vagus and sympathetic nerves Sympathetic nerves carry most pain fibers from visceral organs
of body trunk Simplified pathway: sensory neurons to spinothalamic
tract to thalamus to cerebral cortex Visceral pain is induced by stretching, infection and
cramping of internal organs but seldom by cutting (e.g. cutting off a colon polyp) or scraping them
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Referred pain: important to know
Pain in visceral organs is often perceived to be somatic in origin: referred to somatic regions of body that receive innervation from the same spinal cord segments
Plus left shoulder,from spleen
Anterior skin areas to which pain is referred from certain visceral organs
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Visceral sensory and autonomic neurons participate in visceral reflex arcs
Many are spinal reflexes such as defecation and micturitionreflexes
Some only involve peripheralneurons: spinal cord not involved(not shown)*
*e.g. “enteric” nervous system: 3 neuron reflex arcs entirely within the wall of the gut
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Central control of the Autonomic NS
Amygdala: main limbic region for emotions
-Stimulates sympathetic activity, especially previously learned fear-related behavior-Can be voluntary when decide to recall frightful experience - cerebral cortex acts through amygdala-Some people can regulate some autonomic activities by gaining extraordinary control over their emotions
Hypothalamus: main integration center
Reticular formation: most direct influence over autonomic function
HORNER’S SYNDROME
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Horner’s syndrome Horner's syndrome (also known as Bernard-Horner syndrome and oculosympathetic palsy)
is a combination of symptoms that arises when a group of nerves known as the sympathetic trunk is damaged. The symptoms occur on the ipsilateral side characterized by MIOSIS, PTOSIS, ANHIDROSIS.
Signs that are found in patients on the affected side of the face include partial ptosis : Weakness of the superior tarsal muscle upside-down ptosis (slight elevation of the lower lid) Anhidrosis Miosis : Inactivation of the dilator pupillae Enophthalmos : Weakness of the orbitalis muscle loss of ciliospinal reflex bloodshot conjunctiva, depending on the site of lesion.
In children, Horner's syndrome sometimes leads toheterochromia, a difference in eye color between the two eyes. This happens because a lack of sympathetic stimulation in childhood interferes with melanin pigmentation of the melanocytes in the superficial stroma of the iris.
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CAUSES Due to lesion or compression of one side of the cervical or thoracic sympathetic chain, which
generates symptoms on the ipsilateral (same side as lesion) side of the body. Lateral medullary syndrome Cluster headache - combination termed Horton's headache Trauma - base of neck, usually blunt trauma, sometimes surgery. Middle ear infection Tumors - often bronchogenic carcinoma of the superior fissure (Pancoast tumor) on apex of lung Aortic aneurysm, thoracic Neurofibromatosis type 1 Goiter Dissecting aortic aneurysm Thyroid carcinoma Multiple sclerosis Cervical rib traction on stellate ganglion Carotid artery dissection Klumpke paralysis Cavernous sinus thrombosis Sympathectomy Syringomyelia Nerve blocks, such as cervical plexus block, stellate ganglion or interscalene block As a complication of tube thoracostomy A Horner's syndrome may occur during a migraine attack and be relieved afterwards 29
Pathophysiology Horner syndrome is due to a deficiency ofsympathetic activity. The site of lesion to the
sympathetic outflow is on the ipsilateral side of the symptoms. The following are examples of conditions that cause the clinical appearance of Horner's syndrome:
First-order neuron disorder: Central lesions that involve the hypothalamospinal tract (e.g. transection of the cervical spinal cord).
Second-order neuron disorder: Preganglionic lesions (e.g. compression of the sympathetic chain by a lung tumor).
Third-order neuron disorder: Postganglionic lesions at the level of the internal carotid artery (e.g. a tumor in the cavernous sinus or a carotid artery dissection).
Partial Horner's syndrome In case of a third-neuron disorder, anhidrosis is limited to the middle part of the forehead or can be absent, resulting in a partial Horner's syndrome.
If someone has impaired sweating above the waist affecting only one side of the body, yet they do not have a clinically apparent Horner's syndrome, then the lesion is just below the stellate ganglion in the sympathetic chain.
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DIAGNOSIS Three tests are useful in confirming the presence and severity of Horner syndrome: Cocaine drop test: Cocaine eyedrops block the reuptake of norepinephrine resulting in the
dilation of a normal pupil. However, in Horner's syndrome the lack of norepinephrine in the synaptic cleft causes mydriatic failure. A more recently introduced approach that is more dependable and obviates the difficulties in obtaining cocaine is to apply the alpha-agonist apraclonidine to both eyes and observe the increased mydriatic effect (due to hypersensitivity) on the affected side of Horner syndrome (the opposite effect to what the cocaine test would produce in the presence of Horner's)
Paredrine test: This test helps to localize the cause of the miosis. If the third order neuron (the last of three neurons in the pathway which ultimately discharges norepinephrine into the synaptic cleft) is intact, then the amphetamine causes neurotransmitter vesicle release, thus releasing norepinephrine into the synaptic cleft and resulting in robust mydriasis of the affected pupil. If the lesion itself is of the third order neuron, then the amphetamine will have no effect and the pupil remains constricted. There is no pharmacological test to differentiate between a first and second order neuron lesion.
Dilation lag test.
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It is important to distinguish the ptosis caused by Horner's syndrome from the ptosis caused by a lesion to the oculomotor nerve. In the former, the ptosis occurs with a constricted pupil (due to a loss of sympathetics to the eye), whereas in the latter, the ptosis occurs with a dilated pupil (due to a loss of innervation to the sphincter pupillae). In a clinical setting, these two ptoses are fairly easy to distinguish. In addition to the blown pupil in a CNIII (oculomotor nerve) lesion, this ptosis is much more severe, occasionally occluding the whole eye. The ptosis of Horner syndrome can be quite mild or barely noticeable (partial ptosis).[citation needed]
When anisocoria occurs and the examiner is unsure whether the abnormal pupil is the constricted or dilated one, if a one-sided ptosis is present then the abnormally sized pupil can be presumed to be on the side of the ptosis.
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THANK YOU
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