ANS Introductio

n

Dr.U.P.RathnakarMD.DIH.PGDHM

ANS-PharmacologyNervous systemSympathetic and ParasympatheticFunctions and ConnectionsReceptors –Symp[Adrenergic] &

P.Symp[Cholinergic]NeurotransmittersNeurotransmissionCholinergic agonists and antagonistsAdrenergic agonists and antagonists

Motor

Sensory

Enteric

Neuronal connections-Somatic & ANS

Autonomic Somatic

Supplies all innervated Sk.Muscles structures

Synapses outside CNS Inside C.S.axis Ganglia No ganglia

Peripheral plexus + Absent Post ganglionic fibres Post ganglionic fibres

non-myelinated myelinated

Spontaneous activity Nil

in effectors

Interruption of nerve supply Disuse Atrophy

-no atrophy

NA and Adrenaline Acetylcholine

Flight, Fight and Fright Sit & Digest

Sympathtic P.Sympathtic

Organ Sympathtic P.Sympathetic [Flight & Fright] [Sit & Digest]

Survival Possible Not possible Eye MydriasisMiosis Heart Stim. Dep. Bronchi Dilation Spasm GIT ↓Motility ↑Motility ↓Secretion ↑SecretionContracts spincter Relaxes spincters UB Relaxes detrusor Contracts detrusor, Contracts trigone Relaxes trigone &

& spincter spincter

Sexual organs Ejaculation Erection

Sk.MusclesContractility increased

Adrenergic receptors[Symp]Receptors: α1a, α1b, α1d,

α 2a α2b α2c

β1, β2, β3

Neurotransmitter- Nor adrenaline, Adrenaline

Receptors- ParasympetheticCHOLINERGIC

Muscarinic= M1, M2, M3, M4, M5

Nicotinic= NN, NM

Neurotransmitter = Acetylcholine

Neurohumoral transmission“ Nerve impulses elicit responses in effector organs and post synaptic neurones through liberation of specific chemical transmitters”

Junctional transmission Vs Nerve conduction

 

History: Neurotransmission

Initially thought tobe electrical.

Otto Lewi → Frog hearts perfused in series →

Stim.vagosymp.trunk of I organ

→Perfusate produced inhibitory effect on II heart. →

Vagus stoffe. ( Acceleran stoffe.)

Tachycardia or Bradycardia

TachycardiaOr Bradycardia

Otto Lewi’s experiment

Flow of Chemic

alsubstan

ce

Otto Lewi’s Expt

Criteria: NeurotransmitterShould be present in

Presynaptic neurones

Should be Released on nerve impulse

Application of sub. Produces Similar response to nerve stimulation

Effects are antagonised or

potentiated by other sub. Which also similarly alter nerve stimulation.

Steps in neurotransmission: Impulse conductionArrival of impulseSynthesis Storage & release

of transmitter

Combination of transmitter

with P.J. receptors

Postjunctional activity: Excitatory[EPSP] or Inhibitory[IPSP]

Termination of neurotransmitter action

[Diffusion, destruction, reuptak

Impulse conduction:

Arrival of impulse→ ↑ Na conductance→ Depolarization→Inside (+)ve→(K flows out→Repolarization) →Action potential→Impulse propogation.

Storage & release of transmitter:

Neurotransmitter synthesized and stored in pre junctional nerve endings in “Synaptic Vesicles”

Arrival of nerve impulse→Fuses vesicular and axonal membrane(small amounts constantly released without impulse)

Ca entry fluidizes membrane→Contents of vesicle released→Exocytosis

Other protiens also participate in docking and fusion.

Presynaptic receptors modulate transmitter release

Combination of transmitter with P.J. receptors and P.J.potential:

Excitatory post synaptic potential(EPSP): ↑ permeability to cations-Na or Ca→ Depolarization→ EPSP

IPSP: ↑ permeability to K or Cl→ Hyperpolarization→ IPSP

Postjunctional activity: EPSP more than threshold level

→AP→ActivityIPSP(neurones, smooth muscles not in

Sk.muscles) → Opposes excitatory impulses

Final response depends on summation of all responses

Termination of neurotransmitter action:

Dissipation or destructionACHE(acetylcholinesterase) →Hydrolyzes Ach. →if ACHE is inhibited action prolonged

Adrenergic- Diffusion, Reuptake

NON-Electrogenic functions of neurotransmitter:

Continuos low grade release→No P.J. activity→ But imp. For turn over of enzymes of synthesis, inactivation, maintainance of pre and post synaptic transmission. These are trophic actions of neurotransmitter.

Co-Transmitter: Other transmitters released along with principal transmitter

Ach-VIP, NA-ATPOther cotransmitters- Adenosine,

neuropeptide-Y, NO, Somatostatin etc. NANC: Nonadrenergic-noncholinergic

transmission-exists in ANS. Principal transmitter is not Ach or NA. Eg. In GIT, GUT, (adenosine, ATP)

NN

NM

M1 M2 M3

α1α2

β1β2β

3

NN

NN

α1α2

β1β2β

3