Autonomic Nervous System 1 Flashcards
What are the functions of the sympathetic nervous system?
Fight or flight
Stressful situations
Increase in blood flow to the skeletal muscle
Increase in heart rate
Increase in blood pressure
Increase in blood sugar level
Pupillary dilation (myadriasis)
What are the functions of the sympathetic nervous system?
Conservation and restoration / rest and digest
Decrease in heart rate
Increase in activity of gastrointestinal tract
Pupillary constriction (myosis)
What is vagitomy?
A surgical operation in which one or more branches of the vagus nerve are cut, typically to reduce the rate of gastric secretion (e.g. in treating peptic ulcers)
What’s the vagus nerve?
Parasympathetic fibers innervation of the thoracic and abdominal viscera
Describe the disynaptic pathway
Preganglionic neuron is myelinated (faster transmission)
Origin of preganglionic neuron is in the CNS
Origin of the postganglionic neuron is on the autonomic ganglia, in the peripheral NS
Preganglionic neuron releases Acetylcholine as neurotransmitter, which binds to cholinergic nicotinic receptors (nicotinic neuronal subtype Nn)
Describe sympathetic nervous structure
Origin: T1-L2 medullary segments
Sympathetic- short preganglionic neurons
Long postganglionic neurons
Sympathetic ganglia located near CNS
Ratio of preganglionic to postganglionic is 1:20
Describe the parasympathetic nervous system
Origin: brain stem & S2 -S4
Long preganglionic neurons
Short postganglionic neurons
Parasympathetic ganglia located far from CNS
Distinguish the origin between the sympathetic and parasympathetic nervous system
Sympathetic Origin: T1- L2 spinal cord segments (lateral horn)
Parasympathetic origin:brain stem (autonomic motor nuclei of III, IX, and X cranial nerves) and sacral spinal cord segments S2-S4
Contrast ganglia location of sympathetics and parasympathetic nervous system
Sympathetic: -paravertebral sympathetic ganglion chain
-Collateral ganglia (prevertebral)
Parasympathetic: ganglia located near or embedded within the target tissue
Contrast the dysynaptic cleft of sympathetic and parasympathetic nervous system
Sympathetic:
Short cholinergic preganglionic fiber
Long post ganglionic fiber
Parasympathetic:
- long preganglionic fiber
- short postganglionicfiber
Constraint the ratio of preganglionic fibers yo postganglionic fibers in the autonomic nervous system
Sympathetic- ratio of preganglionic fibers to postganglionic fibers is 1:20
Parasympathetic- ratio of preganglionic fibers to postganglionic fibers is 1:3
Contrast activity of sympathetic and parasympathetic division
Sympathetic: activity often involves massive discharge of the entire system
Parasympathetic: activity normally to discrete organs
Contrast sympathetic and parasympathetic postganglionic neurotransmitters
Sympathetic: primary neurotransmitter of postganglionic neuron is norepinephrine.
Parasympathetic: primary neurotransmitter of the postganglionic neurons is acetylcholine
What are the exceptions to the common rule in the nervous system?
Adrenal medulla: directly innervated by preganglionic sympathetic fibers
Sweat glands: innervated by cholinergic sympathetic postganglionic neurons
Receptors on the sweat. Glands are cholinergic muscuranic: M3
Renal vasculature smooth muscle:
-Innervated by dopaminergic sympathetic postganglionic neurons
Receptors on the renal vasculature are dopaminergic: D1
Describe the adrenal gland
Preganglionic sympathetic axons synapse on chromaffin cells may ACh binds to Nn receptors
Chromaffin cells releases Catecholamines into the circulation: 80% epinephrine (E), 20% norepinephrine (NE)
What causes phaeochromocytoma?
Most common tumor of the adrenal medulla in adults
Derived from chromaffin cells
Secrete epinephrine, norepinephrine, and dopamine
What are the symptoms of phaeochromocytoma?
Occurs in “spells” -relapse and remit
- Elevated blood pressure
- headache
- excessive sweating
- palpitations(tachycardia)
- pallor
Lab: elevated Catecholamines and their metabolites
How is phaeochromocytoma treated?
Surgery
Pre-op: phenoxybenzamine + beta-blocker
Explain cholinergic transmission within the presynaotic nerve (acetylcholine synthesis)
- Acetyl CoA synthesized in mitochondria
- Choline transported into the neuron via a sodium dependent carrier (CHT1)
- ACh synthesized in the cytoplasm from Acetyl CoA and choline, a reaction catalyzed by choline Acetyl transferase(ChAT)
- ACh transport into vesicles by the vesicular ACh transporter (VAChT)
- ACh released occurs when an action potential reaches the terminal and triggers calcium influx through voltage gated calcium channels
The uptake of choline is the rate limiting step in ACh synthesis
Explain cholinergic transmission across the synaptic cleft
Released ACh:
- ACh binds to cholinergic receptors: nicotinic or muscuranic in the postsynaptic membrane
- ACh binds to presynaptic M2 ACh receptors, which inhibit ACh release
- Acetylcholine (AChEj splits ACh into choline and acetate
What are orangophosphates?
These are usually used as insecticides by farmers: chlorothion, CoRal, Diazinion, Malathion, Paraoxon, Parathion, Phosdrin, TEPP, Thio-TEPP
Orangophosphates inhibit irreversibly the enzyme Anticholinesterase
What are the symptoms of orangophosphates?
Muscuranic : diarrhea, urination, miosis, bronchospasm, bradycardia, emesis, lacrimation, sweating, salivation
Nicotinic: neuromuscular junction
CNS effects: respiratory depression, lethargy, seizures, coma
How is orangophosphate poisoning. Treated?
Atropine+ pralidoxime
Explain adrenergic transmission in the presynaotic nerve
- Tyrosine is transported into the adrenergic neuron by system L
- Tyrosine is then converted to L-DOPA by the enzyme tyrosine hydroxylase
- DOPA is then converted to dopamine by DOPA decarboxylase
- Vesicular monoamine receptor (VMAT) translocate dopamine into synaptic vesicles
- Intravesicular dopamine-B-hydroxylase converts dopamine to NE
Tyrosine conversion to DOPA by tyrosine hydroxylase is the rate limiting step in the formation of NE
Explain adrenergic transmission in the synaptic cleft
Norepinephrine (NE):
-Released NE binds adrenergic receptors: alpha or beta on the postsynaptic membrane
- Released NE binds to presynaptic a2 autoreceptors which inhibits NE release
- Termination of the action of NE results from diffusion away from the receptor site and reuptake into the nerve terminal, mediated by the Na+ dependent NE transporter (NET)
What are the types of cholinergic receptors?
Nicotinic receptors (ionic channel linked)
Muscle type- Nm
Neuronal type-Nn
Both of these are ligand-gated sodium/potassium channels
Muscuranic receptirs(g-protein linked)
M1, M3, M5- are Gq linked(increases IP3, DAG & Ca2+)
M2,M4-Gi protein linked: decreased cAMP
What is the mechanism of function of M1?
Location: nerve endings
Mechanism: Gq linked protein
Major functions- increased IP3, DAG cascade
What is the mechanism of function of M2?
Heart, some nerve endings-location
Mechanism: Gi-coupled
Function: decreased cAMP, activates K+ channels
What is the mechanism of function of M3?
Location: effector cells: smooth muscle, glands, endothelium
Mechanism: Gq-linked
Major function: increased IP3, DAG cascade
What is the mechanism of function of Nn?
Location: ANS ganglia
Mechanism: Na+-K+ ion channel
Major functions: depolarizes, evokes action potential
What is the function of Nm?
Location: neuromuscular endplate
Mechanism: Na+-K+ ion channel
Major functions: depolarizes, evokes action potential, causing a muscular contraction
What are the main functions of Nn
Autonomic ganglia- postganglionic neuron activation
Adrenal medulla- chromaffin cells releases Catecholamines to bloodstream
Brain- neuronal development learning and memory
What are the functions of the M1 receptor?
Location:Brains(neurons)
Function: higher cognitive functions
Location: autonomic ganglia (neurons )
Function: stimulates enteric nervous system
Signal mechanism: Gq, increased IP3, DAG, Ca2+
What is the function of M2?
Location: presynaptic nerve terminal(neurons)
Function: inhibition of ACh release
Location: heart(mainly in the atria)
Function: decreased heart rate, decreased contractility of the atria
Mechanism of action: Gi protein, decreased cAMP
What are the functions of the M3 receptors?
Location: exocrine glands
Function: exocrine gland secretions(lacrimal, sweat, salivary, gastric acid)
Location: pancreatic B cells
Function: increased insulin
Location: smooth muscles
Gastrointestinal smooth muscle
Function: increased gut peristalsis
Location: detrusor muscle
Function: increase bladder contraction
Location: eye: pupillary sphincter muscle, ciliary muscle
Function: pupillary constriction and accommodation
Location: bronchial smooth muscle
Function: bronchial constriction
Location: endothelial cells
Function: endothelial NO-mediated vasodilation
Mechanism: Gq-protein
What are the adrenergic receptors?
B-receptors G protein linked
A-receptors-G protein linked
qis-a1,a2,b
What are the types of B receptors?
B1, B2, B3- Gs- protein linked increased cAMP
What are types of alpha receptors?
A1(a1A, a1B, a1D)-Gq-protein-linked
-Increased IP3, DAG, Ca2+
A2(a2a, a2B, a2C)
Gi- protein linked:
-decreased cAMP
What is the mechanism of function of a1 receptors?
Location: eff3ctor tissues: smooth muscle, glands
G protein: Gq
Second messenger: increased IP3, DAG
Major functions: increased Ca2+, causes contraction, secretion
What is the mechanism of action of Alpha 2 receptors?
Location: nerve endings, some smooth muscle
Second messengers: decreased cAMP
Major functions: decreased transmitter release (nerves), causes contraction(muscle)
What is the mechanism of action of beta 1 receptors?
Location: cardiac muscle, juxtaglomerular apparatus
G protein: Gs
Second messengers: increased cAMP
Increases heart rate, 8ncreased force, increased renin release
What is the mechanism of action of beta 2 receptors?
Smooth muscle of heart, liver, heart-location
G-protein- Gs
Increased cAMP
Major functions- relax smooth muscle; increased glycogenolysis; increased heart rate, force
What are the mechanism of action of the beta 3(B3) receptors?
Location: adipose cells
G protein: Gs
Second messengers: increased cAMP
Major function: lypolysis
What is the mechanism of action of dopamine (D1) receptors?
Location: smooth muscle
G-protein: Gs
Second messengers: increased cAMP
Major function: relax renal vasculature smooth muscle
What are the functions of a1 receptors?
Location: vascular smooth muscle
Function: vascular smooth muscle contraction
Location: eye dilator pupillae muscle
Function: pupillary dilation
Location: intestinal and bladder sphincter smooth muscle
Function: intestinal and bladder sphincter contraction
Signal mechanism: Gq protein
What are the functions of a2 receptors ?
Location:Presynaptic nerve terminal (neurons)
Function: decreased norepinephrine release
Location: pancreatic B cells
Function: decreased insulin release
Signal mechanism: Gi protein linked
What are the functions of B1 receptors?
Location: heart
Function: increase heart rate and contractility
Location: kidney(juxtaglomerular cells)
Function: increased renin release
Location: adipocytes
Function: increased lypolysis
G protein: Gs- protein
What is the function of B2 receptors?
Location: bronchial smooth muscle
Function: bronchial dilation
Location: blood vessels”s of skeletal muscle
Function: vasodilation
Location: uterine smooth muscle (myometrium)
Function: decreased uterine tone
What is the function of B3?
Location: brown adipose tissue
Function: thermogenesis
-increased lipolysis
Signal m3chanksm : Gs, increased cAMP
What is the dally innervated rule?
Most internal organs are innervated by both branches of the automonomic nervous system which exhibit antagonistic cells
Heart: sympathetic- norepinephrine B1 receptors, increased heart rate. Acetylcholine M2 receptors, decreased heart rate
Pupil: sympathetic- norepinephrine a1 receptors (increase in pupillary size)
Parasympathetic- acetylcholine M3 receptors (decreased pupillary size)
What is the main tone of arterioles?
Mainly sympathetic- a1
Loss of predominant tone leads to hypotension
What is the predominant tone of neuvs?
Sympathetic-a1
Loss of predominant tine results in venodilation
What is the predominant tone of Heart SA node?
Parasympathetic
Receptor type: M2
Loss of predominant tone leads to increased heart rate
What is the predominant tone of heart ventricle ?
Sympathetic- B1
Loss of predominant tone- loss of contractility
What is the predominant of the iris ?
Predominant tone- parasympathetic tone
Receptor type- M3
What is the predominant tone of ciliary muscle?
Parasympathetic
M3
What is the predominant tone of GI tract?
Parasympathetic-M3
What is the predominant tone of the urinary bladder ?
Parasympathetic-M3
What is the predominant tone of salivary bladder?
Parasympathetic -M3
What is the predominant tone of sweat glands?
Sympathetic
