Autonomic Nervous System: A Pharmacological Perspective Flashcards
Definition of autonomic nervous system
Neuronal groups and fibre connections they control heart, visceral organ, blood vessels ad gland activity and maintains homeostasis
Definition of adrenergic
Relating to nerve cells where adrenaline, noradrenaline or similar substances act as a neurotransmitter
Definition of cholinergic
Relating to nerve cells where acetylcholine acts as a neurotransmitter
Definition of contransmission
When other neurotransmitters are released along with acetylcholine or noradrenaline
Responses to a change in the environment and the varying demands on the body
Rapid
2 types
Voluntary, somatic nervous system => skeletal muscles
Involuntary, ANS => CV system, other organs
What is the autonomic nervous system
Neuronal groups and fibre connections that control activity of heart, viscera and vasculature, smooth muscle and glands
Maintains homeostasis directly/indirectly
Function of the parasympathetic branch
Digestion, excretion, visual accommodation
Rest and digest state
Localized innervation
Function of the sympathetic branch
Ongoing control of cardiovascular system and reflex response to stressful situations
Fight/flight state
More widespread innervation and effects
Type of efferent nerve pathways, parasympathetic salivary gland
Long preganglionic, Ach released onto N receptors
Ach released onto M receptors (salivary gland)
Type of efferent nerve pathways,
Sympathetic vasculature
Short preganglionic, Ach released onto N receptors
NA released onto adrenergic receptors (blood vessels)
Type of efferent nerve pathways,
Sympathetic sweat glands
Short preganglionic, Ach released onto N receptors
Ach released onto M receptors (sweat gland)
Type of efferent nerve pathway
Sympathetic adrenals
Long nerve, Ach released onto N receptors on adrenal medulla
NA/A released into blood, adrenergic receptors
Types of cholinergic receptors
Muscarinic
Nicotinic
Muscarinic receptors
Structure
M2?
M3?
5 subtypes M1-M5
G protein coupled
M2, cardiac => Gai/o => decrease in cAMP, slow HR and contractile force
M3, smooth muscle/glandular => Gaq => increase in IP3 and DAG => contract
Nicotinic receptors
Structure
N1
N2
5 subunits
N1, muscle receptor
N2, ganglionic receptor
Non selective cation channel, mainly admits Na+, K+, causes rapid cell depolarization
2 Ach binds to a1 subunits
a adrenergic receptors
Subtypes and functions
2 subtypes
a1, a2, each has 3 sub subtypes
a1 = Gq, stimulates IP3/DAG => increase [Ca2+]
In blood vessels
a2 = Gi, inhibits AC => decreases cAMP
Presynaptically, decrease release of NA
b adrenergic receptors
Subtypes and functions
3 subtypes, all activate Gs, increase cAMP via PKA
b1, main cardiac subtype
b2, main vascular, airways subtype (SMOOTH MUSCLE)
b3, mainly found in adipose and detrusor
Non adrenergic, non cholinergic neurotransmitters (NANC)
What are they
Why are they useful
Sometimes, Ach/NA released w other NT = cotransmitters
Stronger levels of stimulation => different NT release patterns
Allows for differential target cell function control
Occurs in ganglionic and post ganglionic synapses
V imp in CNS and ENS
Opposing sympathetic and parasympathetic effects
Heart rate
Nerves responsible
SAN stimulated => increased HR, BP, CO, force
VIA VAGUS
SAN inhibited => decreased HR, BP, CO
AVN innervated => decreased conduction speed to B of H
Opposing sympathetic and parasympathetic effects
GI tract, bladder and defaecation
Decreased GI motility, sphincter contraction, decreased digestion
Relaxed detrusor
VIA VAGUS
Relaxed sphincters, peristalsis
VIA PELVIC
Detrusor contracts, defaecation
Opposing sympathetic and parasympathetic effects
Airways
Increased bronchodilation
VIA VAGUS
Increased bronchoconstriction
Opposing sympathetic and parasympathetic effects
Pupils
Pupil dilation via iris dilator contraction
VIA OCULOMOTOR
Pupil constriction via iris sphincter
Visual accommodation via cililary muscle contraction
Opposing sympathetic and parasympathetic effects
Erection
Ejaculation
VIA PELVIC
Erection
Effects of the sympathetic and parasympathetic on vasculature
VC of splanchnic circulation
Heart artery dilation and skeletal muscle
VIA VAGUS
VD of splanchnic, renal (does not affect TPR)
VIA PELVIC
VD of penile (does not affect TPR)
Antagonistic effects of SNS and PNS on HR
SNS and PNS drive to organ is reciprocal
Opposing effects provide wide dynamic range over which organs can alter behavior
Under rest, HR is PNS dominated
One is excitatory, the other is inhibitory
The baroreceptor reflex
Increase in BP distends arterial wall, stimulates afferent nerve endings
Signal sent to brain stem (Nucleus tracts solitairius), compares BP to set point
Innervates parasympathetic, decrease HR and CO
Innervates sympathetic, decrease HR, CO, arterial constriction, TPR, venous constriction
BP falls to set point
Process of cholinergic neurotransmission
Acetyl CoA + Choline => Ach with choline acetyletransferase
Ach stored in vesicel to be released when [Ca2+] is high
Ach binds to receptor, depolarizes post synaptic membrane
Acetylcholinesterase breaks down Ach into choline and acetate and reabsorbed by presynaptic membrane
Inhibition of Ach breakdown
Medication?
Effects?
Ecothiopate/NEOGISTIME inhibits cholinesterase in the eye
Increases pupillary constriction
increases aqueous humous
decreases intraocular pressure
Increased salivation/sweating
ENS
What are the 2 types
What do they release
Myenteric and submucosal plexus of sensory, motor and interneurons, form 2 layers in GI tract walls
Uses variety of NANC NT, including Ach, vasoactive intestinal polypeptides and NO
Function of ENS
Coordinates and controls peristalsis, fluid transport, glandular secretion, blood flow
Effects on PNS, SNS on GI tract indirectly exerted by ENS
Effects of the sympathetic nervous system on the kidney and skin
Increased renin release from JGA
Piloerection
Inhibition of ACh
Medication?
Effects?
Botulinum toxin prevents Ach exocytosis
Prevents M receptor stimulation
-bladder relaxation
Importance of PKA in Gs
PKA phosphorylates
L type, Ryanodine receptors, PLB, SR in b1
Myosin light chain kinase in b2
