Autonomic Nervous System: Sympathetic and Parasympathetic Divisions, Study notes of Communication

Download Autonomic Nervous System: Sympathetic and Parasympathetic Divisions and more Study notes Communication in PDF only on Docsity!

Autonomic Nervous

System

Dr Brijendra Singh

MBBS,MS,DNB,MNAMS Prof & Head Anatomy AIIMS Rishikesh 25/01/

Functions

• Sympathetic & parasympathetic divisions typically

function in opposition to each other.

• But this opposition is better termed

complementary in nature rather than antagonistic.

• Sympathetic as accelerator and parasympathetic as

brake.

• Sympathetic  quick responses.
• Parasympathetic functions with actions that do not

require immediate reaction.

• Sympathetic  "fight or flight"
• Parasympathetic  "rest and digest".

Autonomic Nervous System

• 2 divisions:
  • Sympathetic
    • “Fight or flight”
    • “E” division
    • Exercise, Excitement, Emergency & Embarrassment
  • Parasympathetic
    • “Rest and digest”
    • “D” division
    • Digestion, Defecation, & Diuresis

Functions

• Sympathetic & parasympathetic divisions typically

function in opposition to each other.

• But this opposition is better termed

complementary in nature rather than antagonistic.

• Sympathetic as accelerator and parasympathetic as

brake.

• Sympathetic  quick responses.
• Parasympathetic functions with actions that do not

require immediate reaction.

• Sympathetic  "fight or flight"
• Parasympathetic  "rest and digest".

Receptors

• Parasympathetic nervous system uses only acetylcholine (ACh) as its neurotransmitter.
• ACh acts on two types of receptors, muscarinic and nicotinic cholinergic receptors.
• Most transmissions occur in two stages:
• When stimulated, preganglionic nerve releases ACh at ganglion, which acts on nicotinic receptors of postganglionic nerve.
• Postganglionic nerve then releases ACh to stimulate muscarinic receptors of target organ.

Sympathetic (adrenergic, with exceptions)

• cardiac output increases
• SA node: heart rate (chronotropic) β1, β2: increases
• cardiac muscle: contractility (inotropic )β1, β2: increases
• conduction at AV node β1: increases
• vascular smooth muscle M3: contracts; α = contracts & β2 = relaxes
• smooth muscles of bronchioles β2: relaxes (major contribution); α1: contracts (minor contribution)
• pupil of eye α1: relaxes
• ciliary muscle β2: relaxes
• salivary glands: secretionsβ: stimulates viscous, amylase secretions; α1 = stimulates potassium cation
• smooth muscles of GI tract - α, β2: relaxes
• sphincters of GI tract - α1: contracts
• glands of GI tract - inhibits

Parasympathetic (muscarinic)

• cardiac output M2: decreases
• SA node: heart rate (chronotropic) M2: decreases
• cardiac muscle: contractility (inotropic) M2: decreases (atria only)
• conduction at AV node M2: decreases
• smooth muscles of bronchioles M3: contracts
• pupil of eye M3: contracts
• ciliary muscle M3: contracts
• salivary glands: secretions stimulates watery secretions
• GI tract motility M1, M3: increases
• smooth muscles of GI tract M3: contracts
• sphincters of GI tract M3: relaxes
• glands of GI tract M3: secretes

Specific task

• Emergency branch causes arteries to muscles to relax in order to deliver more blood, allowing greater capacity to act and At same time,reduces blood flow to skin, kidneys, and digestive tract.
• In contrast, calming branch helps to regulate bodily functions and soothe body once stressor has passed, preventing body from remaining too long in a state of mobilization.
• Left mobilized and unchecked, these body functions could lead to disease. Some actions of calming branch appear to reduce harmful effects of emergency branch’s response to stress.
• Various “stress hormones” travel through blood and stimulate release of other hormones, which affect bodily processes such as metabolic rate and sexual functions.

Stress reaction

• When stress occurs, sympathetic nervous system is triggered.
• Norepinephrine is released by nerves, and epinephrine is secreted by adrenal glands. By activating receptors in blood vessels and other structures, these substances ready heart and working muscles for action.
• Acetylcholine is released in parasympathetic nervous system, producing calming effects.
• Digestive tract is stimulated to digest a meal, heart rate slows, and pupils of eyes become smaller.
• Neuroendocrine system also maintains the body’s normal internal functioning.

Response to stress

Thank you