Download Physiological overview of the

Physiological overview of the
Autonomic Nervous System
The Autonomic Nervous System
The Autonomic Nervous System
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Efferent system that controls viscera
Coordinates cardiovascular, respiratory, digestive, urinary, and reproductive functions to
maintain homeostasis.
Comparison of SNS and ANS
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Effectors (Targets)
– Somatic NS controls skeletal muscle
– Autonomic NS controls smooth/cardiac muscle & glands
Comparison of SNS and ANS
• Efferent pathways
– Somatic
• no ganglia
• myelinated axon from ventral horn of cord all the way to effector
– Autonomic
• 2 neuron pathway
– 1st is preganglionic and body resides in brain/spinal cord
» myelinated axons
nd
– 2 is postganglionic and body resides in autonomic ganglion
» unmyelinated axon
Comparison of SNS and ANS
Comparison of Somatic and Autonomic Systems
sympathetic
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short preganglionic axon
long postganglionic axon
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long preganglionic axon
short postganglionic axon
parasympathetic
Comparison of SNS and ANS
• Neurotransmitters
– Somatic
• all motor neurons release
acetylcholine (ACH) which is always
stimulatory
– Autonomic
• ACH & norepinephrine (NE)
– All preganglionic fibers release
ACH
– All postganglionic
Parasympathetic fibers release
ACH
– Most postganglionic Sympathetic
fibers release NE
– NT’s can be stimulatory or inhibitory based on receptor types
Divisions of the ANS: Sympathetic
Sympathetic pathways to the head
• Preganglionic fibers from T1-T4
ascend sympathetic chain to synapse
superior cervical ganglion
Some Major effects:
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dilates iris of eyes
inhibits salivary glands
Sympathetic pathways to the thorax
w/
• Fibers from T1-T6
• Synapse in middle & inferior cervical ganglia
• Some fibers synapse at their respective level & the postganglionic fibers pass directly to the
organ served
– Heart, aorta, lungs, esophagus, thyroid, & skin
Pathways with Synapses in Collateral Ganglia
• Fibers T5-L2 pass through the sympathetic chain without synapsing
• They form thoracic, lumbar, and sacral splanchnic nerves
• Their ganglia include the celiac, the superior and inferior mesenterics, and the hypogastric
Sympathetic pathway to the abdomen
• Fibers from T5-L2 traveling in the thoracic splanchnic nerves
• Synapse in mainly the celiac & superior mesenteric ganglia
• Serve stomach, intestines, liver, spleen, & kidneys
Sympathetic pathways to the pelvis
• Fibers from T10 – L2 descend to the lumbar & sacral sympathetic chain ganglia
• Some synapse there & most go out lumbar & sacral splanchnic nerves to the inferior
mesenteric & hypogastric ganglia
• Serves intestine, urinary bladder, & pelvic reproductive organs
Activation of the Sympathetic NS
• Sympathetic Activation is controlled by the hypothalamus
– Postganglionic axon terminals release NE onto targets
– Adrenals release NE and E into blood
Activation of the Sympathetic NS
• Sympathetic Activation is controlled by the hypothalamus
– Postganglionic axon terminals release NE onto targets
– Adrenals release NE and E into blood
Activation of the Sympathetic NS
• Sympathetic Activation is controlled by the hypothalamus
– Postganglionic axon terminals release NE onto targets
– Adrenals release NE and E into blood
• Outcomes
– increased alertness via reticular activating system
– dilation of pupils
– feeling of energy and euphoria
– insensitivity to pain
– elevation of blood pressure, heart rate, respiratory rate
– increase in muscle tone (person looks tense, may shiver)
– breakdown of glycogen reserves, release of lipids
– inhibition of organs not needed for short-term survival
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Stimulation of the Sympathetic NS
stimulation of preganglionic neuron
preganglionic axon releases ACh onto post ganglionic neuron
ACh activates postganglionic neuron
action potential in a postganglionic neuron lead to the release of NE onto target tissue/organ
axon terminals branch into varicosities (swollen segments) which are each packed with NE
NE acts until it is reabsorbed or broken down by monoamine oxidase (MAO)
Effects of E and NE
Adrenergic Receptors (g-coupled)
– Alpha 1
• NE and E, excitatory
• contraction of smooth muscle
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Alpha 2
• NE and E, inhibitory
• found more in parasympathetic
Effects of E and NE
Adrenergic Receptors (g-coupled)
– Beta 1
• mostly E, excitatory
• accelerates cellular metabolism
• increase heart rate
– Beta 2
• mostly E, inhibitory
• relaxes smooth muscle in respiratory tract
• asthma treatment
– Beta 3
• mostly E, excitatory
• found in fat, leads to lipolysis
Drugs that target the system
• Tricyclic antidepressants – thought to inhibit
reuptake of NE (as well as E and serotonin)
• Pseudoephedrine– stimulate -adrenergic receptors gives relief to nasal decongestion
• Beta-blockers –antagonists of 1 receptors (if selective), reduce heart rate and prevent
arrhythmias
Acetylcholine and Nitric Oxide (NO)
• A few sympathetic postganglionic neurons release ACh or NO onto their targets.
• Include innervation of:
– sweat glands of skin
• increased secretion
– blood vessels to skeletal muscles and brain
• dilation, increased blood flow
• In general ACh & NO vasodilates, NE vasocontricts
Divisions of the ANS: Parasympathetic
• Pregangiolonic fibers:
– cranial nerves III,VII,IX, & X
– S2-S4
• Long preganglionic fibers synapse in terminal or intramural ganglia
Parasympathetic Division Outflow
Cranial
Outflow
Sacral
Outflow
Cranial Nerve
Ganglion
Effector Organ(s)
Occulomotor (III) Ciliary
Eye (constriction of
pupils & bulging of
lens for close
vision)
Facial (VII)
Submadibular &
sublingual salivary
glands, nasal, and
lacrimal glands
Pterygopalatine
Submandibular
Glossopharyngeal Otic
(IX)
Parotid salivary
glands
Vagus (X)
Located within the
walls of target
organs
(Intramural)
Heart, lungs,
bronchi, aorta,
liver, gall bladder,
stomach, small
intestine., proximal
½ of large intestine
S2-S4 lateral
horns
Located within the Large intestine,
walls of the target urinary bladder,
organs (Intramural) ureters, and
reproductive organs
Parasympathetic Division Outflow
Parasympathetic NS ganglia
• Terminal ganglia
– pterygopalatine
– ciliary
– submandibular
– otic
• Intramural ganglia
– embedded in the tissue of the target organ
Parasympathetic Activation
• SLUDD – Salivation, Lacrimation, Urination, Digestion, Defecation
• Active at rest (until we enter fight/flight situation)
– constriction of pupils
– secretion of digestive fluids
– secretion of hormones to promote nutrient absorption
– sexual arousal
– peristalsis
– urination
– constriction of respiratory pathways
– reduction heart rate
Parasympathetic Division Activation
• All postganglionic neurons release ACh
• neuromuscular/ neuroglandular junctions are small, effects are short-lived
Effect of ACh
• Two receptors bind with ACh
– Nicotinic receptor (binds with nicotine too)
• found in targets of sympathetic & parasympathetic
division as well as neuromuscular junction of SNS
• ACh always excitatory here, opening chemically
gated NA+ channel (ionotropic effect)
Effect of ACh
• Two receptors bind with ACh
– Muscarinic receptors (binds with muscarine too)
• mostly in parasympathetic division targets
• Receptor is g-coupled (metabotropic, not ionotropic)
• Can be excitatory or inhibitory depending on cell
Drugs that target the system
• Atropine
– blocks muscarinic ACh receptors
– used in resuscitation to increase heart rate
– belladonna
• Neostigmine
– inhibits AChE
– used to treat myasthenia gravis (rag doll disease)
• ACh receptor activity blocked by autoimmune factors, muscle weakness
Dual Innervation
• Most vital organs have dual innervation, receiving signals from both the sympathetic and
parasympathetic ANS divisions.
Autonomic Tone
• Autonomic motor neurons have a resting level of activity,
giving an autonomic tone.
• Allows you to increase or decrease activity
Sympathetic Tone
• The sympathetic division controls blood pressure and keeps the blood vessels in a continual
state of partial constriction
• This sympathetic tone (vasomotor tone):
– Constricts blood vessels and causes blood pressure to rise as needed
– Prompts vessels to dilate if blood pressure is to be decreased
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Unique Roles of the Sympathetic Division
Functions not subject to parasympathetic regulation:
– activity of:
• the adrenal glands
• the sweat glands
• the errector pili muscles
• the kidneys
• most blood vessels
Unique Roles of the Sympathetic Division
The sympathetic division totally controls:
– thermoregulatory responses to heat
– release of renin from the kidneys
– metabolic effects
• Increases the metabolic rate of body cells
• Raises blood glucose levels
• Mobilizes fat as a food source
• Stimulates the reticular activating system (RAS) of the brain, increasing mental
alertness
Parasympathetic Tone
• Slows the heart
• Dictates normal activity levels of the digestive and urinary systems
– The sympathetic division can override these effects during times of stress
– Drugs that block parasympathetic responses increase heart rate and block fecal and urinary
retention
Sometimes the systems have cooperative effects
• ANS cooperation is best seen in control of the external genitalia
– Parasympathetic fibers cause vasodilation and are responsible for erection of the penis and
clitoris
– Sympathetic fibers cause ejaculation of semen in males and reflex peristalsis in females
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Visceral reflex Arcs
Components:
– Receptor
– sensory neuron
– integration center
• long: in CNS
• short: in ganglia
– enteric NS
– 2 motor neurons
– Effector
Parasympathetic Reflexes
– peristalsis of digestive tract
– defecation and urination
– pupil constriction
– swallowing
– baroreceptor reflex (reduction in heart rate)
– coughing reflex
– sexual arousal
Sympathetic Reflexes
– Cardioacceleratory reflex (increase HR)
– Vasomotor reflex
– Pupillary reflex (dilation)
– Ejaculation
Levels of ANS Control
• The hypothalamus is the main integration center of ANS
activity
• Subconscious cerebral input via limbic system influences
hypothalamic function
• Other controls come from the cerebral cortex, the reticular
formation, and the spinal cord