ME02 - Autonomic Physiology Flashcards
What composes the reflex arc?
afferent limb
integrating center
efferent limb
What are autonomic pathways?
Used by afferent fibers from visceral structures to reach CNS
Where are visceral afferents found?
CNS 7,8,9,10
Thoracic and Lumbar Dorsal Roots
Sacral Roots
Most organs are parasympathetically innervated, except for
Sweat glands
Blood Vessels
Somatic Autonomic Pathway Neurons Innervation of effector NTs Effect of NTs Location Location of NT synthesis and storage Postsynaptic receptors
Somatic Autonomic
Pathway Single-neuron Two-neuron
Neurons Alpha motor Preganglionic, Postganglionic
Effector Skeletal muscle Visceral Structures
Innervation Skeletal muscle Visceral effector cells
of effector innervated by a single maybe innervated by many
motor neuron postganglionic neurons
NTs ACh only ACh and NE
Effect of NTs Leads to contraction Inhibitory/Exhibitory
Location NMJ Motor end plate NEJ Target Organ
Location of NT Synthesized and Synthesized and stored in
synthesis and stored in axon beads/varicosities that line
storage terminals branching networks of
postganglionic neurons
Postsynaptic Nicotinic receptor Widely distributed on target
receptors at motor end plate issues; no specialized region
On Autonomic
SNS PNS
Origin/Roots of fiber
Location of ganglia
Length of fiber
Preganglionic
PostganglionicSNS PNS
Origin/Roots of fiber Thoracolumbar Craniosacral
Location of ganglia Paravertebral Near the target organ
Length of fiber
Preganglionic Short Long
Postganglionic Long Short
On Neurotransmitter
SNS PNS
Preganglionic
Postganglionic
On Neurotransmitter
SNS PNS
Preganglionic ACh ACh
Postganglionic NE,Epi, Dopamine ACh
On Receptors
SNS PNS
Ganglionic
Target Organ
SNS PNS
Ganglionic Nn (Nicotinic neural) Nn
Target Organ alpha, beta Dopamine M, N
On Response
SNS PNS
General response
Specific
SNS PNS
General response Fight, Flight, Fright Rest and Digest
Specific
Part of the nervous system responsible for HOMEOSTASIS
Regulatory in function especially in visceral organs
Essentially motor
Autonomic Nervous System
Without ANS, survival is possible?
True, nut the ability to adapt to stressors from the environment will be severely compromised
What are the striking characteristics of ANS?
Rapidity and Intensity with which it can change visceral functions
Example: Increase HR 2x within 3-5 sec
Cause seating within secs
ANS is classified based on
Anatomical Differences
Functional Differences
Biochemical Differences
Pharmacologic Differences
[ANATOMIC DIFFERENCES]
Sympathetic NS
Parasympathetic NS
Enteric NS/Intramural Nerve Plexus or GIT
[NEUROCHEMICAL DIFFERENCES]
Adrenergic
Cholinergic
Non-Adrenergic, Non Cholinergic
Adrenergic alpha, beta Dopamine | Sympathetic NS
Cholinergic ACh | Parasympathetic NS
Non-Adrenergic, Non Cholinergic Substance P
– Uses NO as NT rather than ACh, regulation of smooth muscle contraction and potent vasodilator
Considered as the “mini-brain” because it contains all elements of Nervous System
Can function autonomously
Enteric Nervous System
Enteric Nervous System can function autonomously but normal GI funciton often requires communication between the CNS and the ENS
True
ENS is just confined within GIT walls
True
What are the two divisions of ENS
Myenteric/Auerbach’s Plexus
Meissner’s/Submucosal Plexus
Larger Division of the ANS where it prepares the individual to cope with “emergency”
Ensures that the body can respond appropriately to a stressful or emergency situation
“FIGHT OR FLIGHT”
Sympathetic Nervous System
Explain response of SNS in
Mydriasis
Increased ABP
Vasoconstriction
There is increase skeletal muscle strength and Increased ventilation
Explain Response of SNS in
lowering threshold in the reticular formation
Reticular formation pertains to the “wakefulness”
so it decrease the threshold to PREPARE for stressful situation
Explain the response of SNS in
Decreased GIT Activity
Elevation of plasma glucose and fatty acid lvels
Increase in Mental Activity
There is metabolic effect on the liver:
Gluconeogenesis, Glycogenolysis
Get glucose from new sourcesm fats for stressful situation
There is Tendency to be hyperglycemic
There is redistribution of blood from skin and splanchnic regions towards skeletal muscle
Prepare self for emergency situation
A neuroendocrine organ
Adrenal Medulla
Reasons why Adrenal Medulla is considered to be a PART OF THE ANS
Nerve supply to AM is anatomically and biochemically IDENTICAL to the autonomic preganglionic nerve fibers
Adrenomedullary cells are embryologically, anatomically and functionally identical to postganglionic autonomic nerve fibers
2 reasons why Adrenal Medulla is considered as COMPONENT OF SNS AND NOT PNS
Origin of nerve supply is THORACOLUMBAR
Adrenomedullary cells secrete catecholamines -EPI and NorEPI
Outflows of SNS and PNS
SNS - Thoracolumbar outflow
PNS - Craniosacral Outflow
Dominates in Quite, Relaxed situation
Tends to conserve energy and restore body’s resources (anabolic)
Parasympathetic Nervous System
Cranial Nerves involved in the PNS
CN 3,7 and 9 - visceral structures in the head
CN 10 - structures in the thorax and upper abdomen
Pelvic branch of 2nd-4th spinal nerves - pelvic structures
[Anatomical/Structural Differences of the ANS]
SNS PNS
Origin of preganglion neuron
Location of peripheral ganglia
Length of preganglionic fiber
Length of postganglionic fiber
Degree of branching of pregang.
SNS PNS
Origin of preganglion neuron thoracolumbar craniosacral
Location of peripheral ganglia paravertebral target organ
Length of preganglionic fiber short long
Length of postganglionic fiber long short
Degree of branching of pregang. more branching less branching
[FUNCTIONAL DIFFERENCES OF SNS AND PNS]
SNS PNS
Nature of activity
Energy utilization
Response
Range of Effect
Fiber connections
Branching of pregang
NTs involved
Duration of responseSNS PNS
Nature of activity fight or flight rest or digest
Energy utilization catabolic anabolic
Response emergency & stress digestion & absorption
Range of Effect widespread region localized to single organ
Fiber connections divergent 1:20 1:1 or 1:2
Branching of pregang extensive limited
NTs involved ACh all over No ACh in circulation
Duration of response sustained short duration
ANS principle of Dual Innervation
Exert opposite effects but operate reciprocally to produce coordinated responses
2 divisions can also act in a synergistic manner
Examples of dual innervations in the ANS
SNS PNS
(EYES) radial muscle of iris circular muscle of iris
(PENIS) ejaculation erection
Single innervation in ANS
Sympathetic - Sweat glands, Adrenal glands, Most blood vessels, Pilomotor muscle
Parasympathetic - Lacrimal muscle (tear glands)
- Ciliary muscle (accomodation for near vision)
Sweat gland component
Receptor: Eccrine glands
NTs: ACh
Receptor: Muscarinic
Neurohormonal Transmission
Steps involved in Transmission of Impulses across Synapse
- Synthesis and storage of transmitter substance at axon terminal
- release of transmitter substance into synaptic cleft
- Binding of transmitter and receptors
- Dissipation of transmitter substance
Synthesis and Storage of ACh
- Cytoplasm of axon terminal by acetylation
- Stored as clear round vesicles
Choline (from ECF) enters axon terminal by active transport
acetyl CoA and ATP
In Synthesis of ACh, enzyme that is synthesized in the soma and brought to the axon by axoplasmic transport
Choline acetyltransferase
Synthesis and Storage for NorEpi
From AA Phenylalanine and Tyrosine
Requires cortisol from adrenal cortex
In adrenal medulla,
PNMT - catalyzes the conversion of NorEPI to EPI
[Binding of Neurotransmitter to Receptor]
T-R complex increase in conductance
- > to all ions (Na, K, Cl) - Depolarization occurs | EPSP
- > to small ions (K and Cl) - Hyperpolarization | IPSP no AP
Dissipation/Destruction/Deactivation of Neurotransmitter
ACh - enzymatic destruciton via acetylcholinesterase
NorEPI - active reuptake by prejunctional fiber diffusion into EC
COMT - if NE is still in synaptic cleft
MAO - if NE is in axoplasm of Preganglionic fiber
[Divisions of ANS based on BIOCHEMICAL DIFFERENCES]
Cholinergic nerves
Adrenergic nerves
NANC
Peptides released by PNS of GIT which are co-released with ACh innervation to sweat glands
Substance P
VIP - Vasoactive intersyinal peptide
CGRP - Calcitonin-gene related peptide
Autonomic Receptors
Location:
MOA:
Location: Cell bodies of Postganglionic Neurons
MOA: When NT binds with receptor _> conformational change»_space; cell either activated or inhibited
How do NTs work?
Altering 2nd messenger enzymes
Autonomic receptors are coupled with GTP-binding proteins
Gproteins activate cAMP, IP3 and DAG
2nd messenger amplifies and executes action
Affinity for nicotine (small amounts)
Excess acts as “blocking agent” by persistent depolarization
NICOTINIC RECEPTOR
Sites: MEP, all autonomic ganglia, chromaffin cells of AM
Types: N1 and N2
MOA: Direct-ligand gated ion channel
Differences between Nicotinic receptors in MEP and autonomic ganglia
Both activated by ACh, nicotine and carbachol
Antagonized by curare
Blocks N2 receptors but not N1
Produces vasodilation
Can be used as treatment for hypertension
Hexamethonium
Nicotinic Receptors’ Blocking Agents
(Autonomic Ganglia) TEA-tetraethylammonium and Hexamethonium
(MEP) Curare and Succinylcholine
Affinity for muscarine
MUSCARINIC RECEPTORS Sites: Effector cells activated by PS MOA: GPCR Indirect ligand-gated type GPCR acts directly on ion channel without mediation of 2nd messenger Blocking agent: Atropine
Types of Muscarinic Receptor
Location Mechanism Major Function
M1
M2
M3
M4
M5Gq-coupled - INC IP3, DAG
M1 - Gastric acid secretion | Nerve ending|
M3 - Smooth muscle airway, INC Ca | Effector cells, smooth glands
Gi-coupled - DEC IP3, DAG
M2 - Bind agonist to M2 inhibit adenylcyclase | HEART, Smooth muscle in intestine, trachea, gallbladder
Na-K ion channel - Depolarize, evokes ACTION POTENTIAL
Nn - ANS Ganglia
Nm - NM end plate
M4 - Pancreatic acinar cells and islet tissue
M5 - Sphincter muscle of iris, esophagus, parotid gland, cerebral blood vessel
Indirect ligand G protein linked type
Adrenocreceptors
TYPES OF ADRENORECEPTORS
Gq - INC IP3, DAG»_space; INC Ca, contraction, secretion,
alpha 1(smooth muscle and glands, ribs, BV, sphincter, bladder)
MOA: Activate phospholipase C
Gi - DEC cAMP»_space; DEC transmitter release of NE, relaxation
alpha 2 (nerve ending, GIT walls)
MOA: inhibit adenylyl cyclase > decrease CAMP
Gs - INC cAMP
beta 1 (heart, salivary glands, adipose tissue, kidney)
MOA: Activation of adenylyl cyclase» Inc HR, Rennin Release
beta 2 (Smooth ms of Airways, Liver, Lungs, BV skeletal muscles) MOA: Relax bronchial smooth ms. Inc glycogenolysis, HR
beta 3 (Lipocytes, brown adipose tissue) MOA: Thermogenesis, Lipolysis
delta 1 (smooth muscle) MOA: Relax renal BV
Antagonists present
Alpha 1 - Pazosin | Blood vessels | Vasoconstriction
Alpha 2 - Yohimbine | Presynaptic neuron | Vasodilation
GPCR with adrenoreceptor and cholinoceptor
Gq - Alpha 1, M1, M3
Gi - Alpha 2, M2
Gs - Beta 1, Beta 2,
NANC
Neuropeptide Y - co released with NE
VIP - vasoactive intestinal peptide
GRP - calcitonin gene related peptide
NO - vasodilation
Sensitivities to E and NE
Alpha 1 - E= or >NE | isoproterenol ineffective
Alpha 2 - NE>E | isoproterenol ineffective
Beta 1 - Isoproterenol > E and NE I E=NE
Isoproterenol exerts more effect on cardiac muscles
Beta 2 E> isopreterenol > NE
AUTONOMIC DRUGS
ParasympaTHOMIMETIC - potentiate cholinergic effects
ParasympaTHOLYTIC - block cholinergic effects
Sympa THOMIMETIC - potentiate adrenergic effects
SympaTHOLYTIC - block adrenergic effects
Drug that binds receptors for NT and promotes process stimulated by that NT
Agonist
Drug that blocks NT
Antagonist
Examples of ParasympaTHOMIMETIC
Pilocarpine - interact w muscarinic imitating Ach
Nicotine - interact w nicotinic that interact with ACh
Neostigmine - inhibit acetylcholinesterase
Examples of ParasympaTHOLYTIC
Hemicholine - inhibit uptake of choline from blood to axon
Botulinum Toxin - inhibit ACh release
Atropine, Homatropine, Scopolamine - competes with ACh sites (muscarinic)
Hexamethonium - ganglionic blocking agents
Curare, Succinylcholine - Neuromuscular blockers
Examples of SympaTHOMIMETIC
Methoxamine - Interact w alpha receptors
Salbutamol - interact w beta receptors
Ephedrine, Amphetamine - release of NE from storage vesicles
Cocaine - prevent uptake of NE
Examples of SympaTHOLYTIC
Reserpine - inhibit diffusion of NE
Guanethedine - Block NE release
Ergot Alkaloids - Block effects of NE
Propanolol - Competes w NE at beta receptors
Center for regulation of ANS
Head Ganglion
Hypothalamus
Sympathetic: Posterior center
Parasympathetic: Anterior center
Regulates emotional and instinctual behavior
Feeding behavior
Expression of rage and anger
Control of sexual behavior
Limbic System
Refinement of control over autonomic and somatic
Cerebral Cortex
Centers for regulation of cardiovascular and respiratory center
Vasomotor center, swallowing , vommiting
Medulla Oblongata
Pupillary responses to light
Midbrain
Pathways involved in the Nervous System
Somatic NS - alpha motor neuron links CNS to skeletal muscles
Autonomic NS - autonomic neurons links CNS to visceral muscle
