Autonomic nervous system Flashcards
what does somatic nervous system comprise of
Motor and sensory pathways regulating voluntary motor control of skeletal muscles
ANS comprise of
Motor & sensory pathways regulating the body’s internal environment through involuntary control of organ systems (smooth muscle, cardiac muscle, and glands)
Sympathetic
Parasympathetic
located in CNS and PNS
Coordinates and maintains a steady state among the visceral internal organs
Neurons
Preganglionic:
cell body in CNS (myelinated B fibers)
Postganglionic:
cell body in autonomic ganglia (unmyelinated C fibers)
Divisions of ANS
Sympathetic
Parasympathetic
+/- Enteric
what are the locations of autonomic centers
Hypothalamus (influenced by connections to limbic system) Brain stem Medulla Pons Spinal Cord spmbsh
Function of ANS
Controls Visceral Functions(Involuntary smooth muscles,cardiac muscles and Glands funcrtions) Partial control Systemic blood pressure GI motility and secretion Urinary bladder emptying Sweating and body temperature
Sympathetic innervation
Thoracolumbar: Preganglionic neurons cell bodies located in (T1-L2/3) of spinal cord
Intermediolateral horn of grey matter
Post ganglionic neuron cell bodies are located in ganglia
Paravertebral chains (either side spinal column)
Prevertebral ganglia (i.e. celiac, superior, inferior mesenteric ganglia in abdomen)
Short preganglionic neurons, long post
Mode of action and innervation of Sympathetic Nervous system
Mobilizes energy stores in times of need
“Fight or flight response”.
Nerve fibers leave the spinal cord ventrally via white rami and travel to 22 paravertebral ganglia (the sympathetic chain ganglia)
From there they can:
Synapse with post-ganglionic neuron at
- same level OR
- Move caudad or cephalad
- synapse at another level ganglia without synapsing to collateral ganglia surrounding the abdominal aorta (celiac, superior mesenteric, inferior mesenteric)
Some ganglia have inhibitory interneurons as well
Where does the SNS outflow to
Piloerector muscle sweat gland Blood vessel Eye Heart bronchi pylorus adrenal Medulla Kidney ureter intestine illeocecal valve anal sphincter detrusor bladder Hypogastric plexus
celiac ganglion
what do the (Thoracolumbar division) comprise of
Post-ganglionic nerve cell bodies found in ganglia of paravertebral chain exit to travel to various peripheral organs
Return to spinal nerves via gray rami travel with these nerves to blood vessels, piloerector muscles and sweat glands
What does the distribution of SNS fibre depend on
Distribution of SNS fibers is based on embryonic development and NOT spinal segments
T1 SNS fibers usually ascend into the paravertebral sympathetic chain to head
T2 neck
T3-6 chest
T7-11 abdomen
T12-L2 legs
Patterns of Innervation: PSNS“Rest and Energy Restoration”
Parasympathetic innervation Pre-ganglionic neurons arise in “Cranial” (medullary CN 3,7, 9, 10) “Sacral” (spinal cord S2-4) regions Post-ganglionic neurons cell bodies located in: Target organs Discrete ganglia in the head and neck (i.e. ciliary ganglia) Long preganglionic neurons, short post
Parasympathetic Nervous System “Craniosacral division”
Functions
Functions to conserve and restore energy
“Rest or repose response”
Receives innervation from cell bodies located in:
cranial nerve nuclei (travel via III, V, VII, IX, X)
75% of PSNS fibers are in vagus (X) passing to abdominal and thoracic areas
sacral region of the spinal cord
Preganglionic neurons travel to ganglia close to the organs they innervate
Where does the Parasympathetic Nervous System Craniosacral division innervate
Vagus X = PSNS to heart, lungs, esophagus, stomach, small intestine, liver, gallbladder, pancreas, upper uterus
Cranial Nerve III – Edinger-Westphal nucleus: eye
Cranial Nerve V – Submandibular gland
Cranial Nerve VII –Superior salivatory nucleus: lacrimal, nasal, submaxillary glands
Cranial Nerve IX – Inferior salivatory nucleus: parotid gland
S2-3 (sometimes S1-4) – distal colon, rectum, bladder, lower uterus, external genitalia,anal sphincter
Parasympathetic Nervous System Craniosacral division……
Postganglionic neurons include
located in cranial ganglia, including:
Ciliary ganglion (preganglionic input is from the Edinger-Westphal nucleus)
Pterygopalatine and submandibular ganglia (input from the superior salivatory nucleus)
Otic ganglion (input from the inferior salivatory nucleus).
Other parasympathetic postganglionic neurons are located near or in the walls of visceral organs in the thoracic, abdominal, and pelvic cavities.
COmpare PSNS vs SNS
Often SNS & PSNS actions often (but not always) antagonistic
SNS = self preservation: most important function is maintenance of vasomotor tone
PSNS = rest for the organism but “excitatory” visceral functions such as digestion(Peristalsis and bladder contaction.
slide 13
For SNS
saliva drys up
heart pumps
depolarization in the sa node to increase
contractility fast and maximal force
Speed Av node conduction
Bronchioles to dilate
Epinephrine high
Liver to release glucose…Gluconeogenis and Glycogenolysis
no peristalsis
no bladder contraction for urine
anal sphincter nice tone
blood vessel to dialate so skeletal muscle get blood..
veins in leg constricted to get more preload
Slide 13
PSNS Lacrimal gland constrict saliver gland salivate more heart slow down pSNS lung constriction ....b Bronchoconstriction can happen bladder constriction sphincter relaxation
How does SNS respond to stress
SNS = amplification response with diffuse innervation
Postural changes
Exercise
Emergency massive response- fight or flight
How does PSNs respond to stress
PSNS = discrete and narrowly targeted responses
what does both system exhibit at rest
Both systems exhibit“baseline tone” at rest
Heart rate – vagal (at the Sa node)….Ach continuous ly released at the Sa nodes
predominance
Blood vessels- SNS tone
Sympathetic Preganglionic fibres release what?
Neurotransmitter = Secrete Acetylcholine Receptor = Cholinergic (nicotinic – n type)
Sympathetic postganglionic fibers
screte what?
Neurotransmitter = Secrete Norepinephrine
Receptor Type = Adrenergic
Parasympathetic pre- and postganglionic fibers
releasae what
Neurotransmitter = Secrete Acetylcholine
Receptor Type = Cholinergic (nicotinic- n-type at ganglia; muscarinic at organ)
3 major anomalies (exceptions to the rule)
for release of Neurotransmitter
Adrenal medulla (acts like a ganglia but releases NE and Epi as HORMONES)
Norepi 20%
Epi 80%
Sweat glands
Innervated anatomically by SNS
Post ganglionic nerve releases Ach onto a muscarinic Ach receptor
Thus … “sympathetic cholinergic fibers”
Blood vessel smooth muscle
Almost all have no innervation by PSNS
However, there are muscarinic Ach receptors present on the blood vessels (activate NO with eventual vasodilation if you had a situation with circulating Ach)
PNS Receptors subclass Cholinergic Receptors
Cholinergic Receptors(responde to acetycholine)Parasympathetic side Nicotinic Ach receptors Nm and Nn Muscarinic Ach receptors M1-5
Adrenergic receptors(responds to NE..sympathetic)
Alpha (1,2)
Beta (1, 2, 3)
PNS Receptors subclass Adrenergic receptors(responds to NE..sympathetic)
(1,2)
(1, 2, 3)
Mechanism of Action of Neurotransmitters (i.e. norepi, epi, dopamine, acetylcholine)
Activation of G-protein coupled receptor (D,Beta and alpha))
NT binds receptor & activates a G-protein
G-protein will activate or inhibit an intracellular enzyme (adenylate cyclase→cAMP, phospholipase C) or will open or close an ion channel
Usually the G-protein “cascade” has an eventual positive or negative effect on the amount of intracellular Ca2+ = physiological effect
Receptor type will dictate the activity of the G protein
Example Beta-1 receptors increase cAMP via G proteins. cAMP stimulates the Na-K pump and protein phosphorylation reactions leading to metabolic and pharmacologic effects we see clinically (increased heart rate and contractility, etc.)
Mecahanism of neurotransmitter effect
Different parts of the body have different types & densities of receptors (skeletal muscle VS venous smooth muscle VS myocardium VS bronchial smooth muscle etc.)
The specific effect depends on the type of receptor stimulated, receptor density in a given tissue, and what the second messengers activate at a molecular level in the cell.
Receptors will up or down regulate based upon plasma concentrations of catecholamines (endogenous or exogenous)
Effects of second messenger on receptors
Adenylate cyclase activates cAMP = smooth muscle dilation (Bronchioles blood vessels)
Increased cAMP = vasodilation (also increased strength of cardiac contraction, and increased heart rate)
Decreased cAMP= vasoconstriction
PLC(Phospholipase C) activated activates IP3 & DAG results in increased PKC and increased free Ca2+ = vasoconstriction
* Again… do not forget that The specific effect depends on the type of receptor stimulated, receptor density in a given tissue, and what the second messengers activate at a molecular level in the cell.
Know slide 22
The Big table
Cholinergic Receptor Subtypes
Muscarinic and Nicotinic receptors
Muscarinic receptors (G-Protein Coupled)
Muscarinic receptors (G-Protein Coupled)
M1, M3, M5 inositol phosphate pathway (primarily)
M2, M4 inhibit adenylyl cyclase reduce cAMP (primarily)
M1: CNS, stomach
M2: Widely expressed
cardiac (inotropy/chronotropy), ganglia
smooth muscle bladder, GI, uterus
M3: smooth muscle, glandular tissues, work with M2
M4: CNS (ganglia)
M5: cerebral bld vessels, pupil, esophagus, parotid gland
Nicotinic receptors (Pentameric (5 subunit) structures /ligand-gated ion channels
Nm: skeletal muscle at NMJ
Nn: autonomic ganglia, adrenal medulla, CNS
All Nn receptors are not parasympathetic.
Characteristics of Acetylcholine
Does not have effcet outside the synapse
Synthesis
Choline (active transport brings it into the cytoplasm) and acetyl coenzyme A (formed by mitochondria) form acetylcholine under the influence of the enzyme choline acetyltransferase
Storage
Stored in synaptic vesicles released in response to an action potential
Metabolism
Brief effect <1 ms rapid hydrolysis by acetylcholinesterase to choline and acetate
Choline is transported back into nerve endings used for synthesis of new acetylcholine
Neurotransmitter effects and selectivity on receptors
Norepinephrine* alpha 1,alpha 2,beta 1…….no effect or need alot to activate beta 2
Epinephrine alpha1,alpha 2,beta 1 and beta 2 .release from Medulla
Dopamine D1=D2
need more to affect beta and a lot more for alpha
Norepi characteristics
Formation
In cytoplasm dopamine formed
Dopamine enters synaptic vesicle
In synaptic vesicle converted to norepinephrine
Storage and Release
Norepi stored in vesicle until action potential
With action potential the norepi is released from postganglionic SNS nerve endings into ECF via exocytosis
Effect of Norepi is affected by reuptake…
Termination of Action
Reuptake back into postganglionic sympathetic nerve endings (#1- 80% of released norepi can be reused)
Dilution by diffusion from receptors
Metabolism by the enzymes monoamine oxidase (MAO- cytoplasm) and catechol-o-methyltransferase (COMT - liver)
Epinephrine charateristics
Formation - synthesized in the medulla of the adrenal gland (chromaffin cells) in the same enzymatic pathway that coverts the amino acid tyrosine into NE and dopamine (epinephrine is the final step)
Storage and Release – Released after simulation of the adrenal medulla by pre-ganglionic sympathetic neurons by Ach
Termination of Action – COMT and MAO
KNow slides 27,30,31
pls go through it
Adrenal medulla function i
Innervated by preganglionic fibers that bypass the paravertebral ganglia
Fibers directly from spinal cord to adrenal medulla
Cells of adrenal medulla are analagous to post-ganglionic neurons
SNS stimulation results in release of catecholamine hormones (released into systemic circulation instead of the synapse)
80% epinephrine
20% norepinephrine
Mechanism of action of adrenal medulla
Release of epi & norepi by adrenal medulla occurs after acetylcholine is released by preganglionic cholinergic fibers
Acetylcholine increases the permeability of calcium by acting on plasma membrane receptors of adrenal medulla cells
Calcium ions result in the exocytosis of the hormones into systemic circulation
Results = similar to direct stimulation by the SNS however prolonged response 10-30 seconds (COMT)
Review slides 33_35
…review
