Autonomic Nervous System (ANS)

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Autonomic Nervous System (ANS)

Objective

At the end of this lecture, student will be able to

Describe the autonomic nervous system

Differentiate between sympathetic and parasympathetic nervous system

Explain neurohumoral transmission

Explain location, function and characterisation of cholinergic receptors

Content

ANS

Introduction to autonomic nervous system

Sympathetic and parasympathetic nervous system

Neurohumoral transmission

Location, function and characterisation of cholinergic receptors

Some degree of autonomy (Langley -1898)

Innervates heart, smooth muscle, glands, viscera

Possess inherent physiological activity

Nervous influence augment/ reduces initial function level

Interference does not completely abolish

Built in protective mechanism

Skeletal muscle: interferences – Completely paralysis

Divisions of Nervous System

Divisions of ANS

• Sympathetic – Stress / fight or flight
• Parasympathetic – Tissue building reactions

Control of ANS

• Represented at all levels of CNS

• Autonomic functions are regulated by RF along with cranial nerve nuclei

• Hypothalamus: Posterior, lateral & midline nuclei

• Thalamus: center and relay station for sensory perception

• Limbic system: Relate emotions to CNS

Autonomic Innervation

ANS Neurotransmitters

Differences between Sympathetic and Parasympathetic NS

	Sympathetic	Parasympathetic
Origin	Dorsolumbar (T1 to L2/L3)	Craniosacral (III, VII, IX, X, S2-S4
Post GF	Long	Short
Transmitter	NA, Ach	Ach
Transmitter stability	Stable, diffuses, wider action	Degrades rapidly
Function	Taking stress/ emergency	Assimilation of food, conservation of energy

Neurohumoral Transmission

• Elliot (1905) – PS function by release of Adr like substances

• Dixon (1907) – Vagus nerve release muscarine like chemical

• Otto Loewi (1921) – Direct proof by perfusing two frog heart

• 1926 – Ach

• Von Euler (1946) – Sympathetic transmitter NA

Criteria to be a Neurotransmitter

• Should be present in presynaptic neuron

• Should be released in the medium following nerve stimulation

• Identicla response to nerve stimulation

• Antagonised

Steps involved in Neurohumoral transmission

• Impulse conduction

• Transmitter release

• Transmitter action on post junctional membrane

• Post junctional activity

• Termination of transmitter action

Neurohumoral Transmission

Co –Transmission

• Classical one neuron – one transmitter over simplification

• Release more than one neurotransmitter

• Purines: ATP, adenosine

• Peptides: NPY, VIP

• Sub P, Enkephalins, Somatostatins

• NANC

Cholinergic System and Drugs

• Major NT – Ach

• Locally synthesized in cholinergic nerve endings

• Degraded by AChE

Synthesis of Acetylcholine

Receptors

• Located on autonomic effector cells

• Heart, blood vessels, eye, smooth muscle, GIT glands, repiratory, urinary tracts, sweat glands, CNS

• Post synaptic receptors & Presynaptic auto receptors

• M1 – M5

• NN, NM

Sites of Cholinergic Action and Types of Receptor

S. No	Site	Receptor	Agonist	Antagonist
1	All post ganglionic PS & few post ganglionic S	M	Muscarine	Atropine
2	Ganglia & Adrenal medulla	NN	DMPP	Hexamethonium
3	Skeletal muscle	NM	PTMA	Curare
4	CNS (Cortex, BG, Spinal cord)	M	Muscarine	Atropine
		N	Carbachol	Curare

Location and Function of Cholinergic Receptors

M1 – Neuronal	M2 – Cardiac	M3 – Smooth muscle and gland
Ganglia: EPSP Gastric glands: + Secretion CNS: Learning and memory function	SA Node: Hyperpolarisation AV: Conduction velocity Atrium: FOC Ventricle: FOC Nerve endings: Ach release CNS: Tremor, analgesic Smooth muscle: Contraction	Smooth muscle: Contraction Iris: Pupil constriction Ciliary muscle: Contraction Exocrine glands: Secretion Vascular endothelium: Release of NO, Vasodilation

Characteristic of Cholinergic Receptors

M1 – Neuronal	M2 – Cardiac	M3 – Smooth muscle and gland
GPCR	GPCR	GPCR
IP3 / DAG PLA2	K+ opening cAMP	IP3 / DAG PLA2

M4: + or – of NT release in brain

M5: Facilitate DA release and mediate reward behavior

FAQs

Can stress permanently damage the Autonomic Nervous System? Chronic stress can lead to dysregulation of the ANS, but with proper stress management, the system can often recover.
Are there natural ways to support Autonomic Nervous System health? Yes, adopting a balanced diet, regular exercise, and stress management techniques can support ANS health naturally.
How does aging affect the Autonomic Nervous System? Aging brings natural changes to ANS function, emphasizing the need for tailored healthcare strategies in the elderly.
Can dysautonomia be cured? While there may not be a cure for dysautonomia, various treatments and lifestyle modifications can help manage symptoms effectively.
Are there any new breakthroughs in autonomic neuroscience? Ongoing research in autonomic neuroscience continues to uncover new insights and potential breakthroughs in understanding and treating ANS-related conditions.