Autonomic Nervous System Overview

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Questions and Answers

Which statement correctly describes the origin of the sympathetic nervous system?

  • It arises solely from the cervical spinal segments.
  • It originates primarily from the sacral spinal cord segments.
  • It is derived from the lateral horn of all thoracic segments and upper lumbar segments. (correct)
  • It arises from the cranial nerve nuclei in the brainstem.

What characterizes the parasympathetic division of the autonomic nervous system?

  • It only arises from cranial nerves.
  • It arises from cranial nerves III, VII, IX, and X, and sacral spinal cord segments. (correct)
  • It primarily uses co-lateral ganglia for synapses.
  • It is also known as thoraco-lumbar outflow.

What is one of the main functions of autonomic ganglia?

  • They serve as the site for neurotransmitter production.
  • They exclusively distribute signals from the CNS to the limbs.
  • They function as relay stations for preganglionic and postganglionic neurons. (correct)
  • They act solely as sensory processing centers.

Which ganglia location is not associated with the sympathetic nervous system?

<p>Cranial ganglia (D)</p> Signup and view all the answers

What is the primary effect of parasympathomimetic drugs like acetylcholine?

<p>They stimulate peripheral cholinergic receptors. (B)</p> Signup and view all the answers

Which of the following statements about adrenergic receptors is correct?

<p>They can be classified into alpha and beta types. (B)</p> Signup and view all the answers

What role do ganglion blockers like nicotine in large doses play?

<p>Block ganglionic transmission. (C)</p> Signup and view all the answers

What is a common use for atropine, a parasympatholytic drug?

<p>To dilate the pupil before operations. (C)</p> Signup and view all the answers

Which option correctly describes the formation of noradrenaline?

<p>Synthesized from the amino acid phenylalanine. (D)</p> Signup and view all the answers

What effect do beta-1 receptors have when stimulated?

<p>They increase heart rate and contractility. (D)</p> Signup and view all the answers

How do sympatholytic drugs like phentolamine function?

<p>They block the action of alpha-1 receptors. (D)</p> Signup and view all the answers

Which statement correctly describes the release of acetylcholine (Ach)?

<p>Ach is released by both preganglionic and postganglionic parasympathetic fibers. (B)</p> Signup and view all the answers

Which anatomical locations are typically associated with parasympathetic ganglia?

<p>Inside the organ or very near to the organ (B)</p> Signup and view all the answers

What is the primary effect of the sympathetic nervous system?

<p>Generalized and catabolic effects (A)</p> Signup and view all the answers

Which one of the following organs does NOT have a parasympathetic supply?

<p>Spleen (A)</p> Signup and view all the answers

Which chemical transmitter is secreted by cholinergic neurons at the end of their fibers?

<p>Acetylcholine (Ach) (B)</p> Signup and view all the answers

In terms of autonomic control, which statement is true regarding the organization of the nervous system?

<p>Most organs receive dual nerve supply from both systems (B)</p> Signup and view all the answers

Which of the following organs is primarily affected by the sympathetic nervous system's response to stress?

<p>Adrenal medulla (A)</p> Signup and view all the answers

Which neurotransmitter is secreted during the fight-or-flight response?

<p>Epinephrine (A)</p> Signup and view all the answers

Flashcards

Autonomic Nervous System

The part of the nervous system responsible for regulating involuntary bodily functions like heart rate, digestion, and breathing.

Sympathetic Nervous System

A division of the autonomic nervous system that prepares the body for 'fight-or-flight' responses, increasing heart rate, blood pressure, and alertness.

Parasympathetic Nervous System

A division of the autonomic nervous system that helps the body conserve energy and maintain a state of rest and relaxation.

Autonomic Ganglia

Clusters of nerve cell bodies outside the central nervous system (CNS) where preganglionic and postganglionic neurons of the autonomic nervous system connect.

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Lateral (Sympathetic) Chain

Groups of sympathetic ganglia located along the spinal cord, forming a chain-like structure on either side of the vertebral column.

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Where are parasympathetic ganglia located?

Parasympathetic ganglia are usually located within or very close to the target organ they innervate.

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What is the primary function of the sympathetic nervous system?

The sympathetic nervous system prepares the body for 'fight-or-flight' responses, increasing heart rate, blood pressure, and alertness.

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What is the primary function of the parasympathetic nervous system?

The parasympathetic nervous system helps the body conserve energy and maintain a state of rest and relaxation.

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What is the effect of the sympathetic system on the body?

The sympathetic nervous system has a widespread and generalized effect, affecting multiple organs simultaneously.

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What is the effect of the parasympathetic system on the body?

The parasympathetic nervous system has a more localized effect, affecting specific organs individually.

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How does the sympathetic system affect energy metabolism?

The sympathetic nervous system promotes catabolic processes, breaking down energy stores to fuel the body for action.

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How does the parasympathetic system affect energy metabolism?

The parasympathetic nervous system promotes anabolic processes, building up and restoring energy reserves.

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What is the role of adrenaline in the autonomic nervous system?

Adrenaline is not a neurotransmitter in the autonomic nervous system. It is secreted as a hormone into the bloodstream by the adrenal medulla, and also acts as a neurotransmitter in the brain.

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What is Acetylcholine and its function?

Acetylcholine (Ach) is a neurotransmitter that serves as a chemical messenger for both the parasympathetic and sympathetic nervous systems with some exceptions. It is essential for regulating various functions, including heart rate, digestion, and muscle contraction.

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What is the neurotransmitter released by postganglionic sympathetic fibers?

Postganglionic sympathetic fibers, with the exception of those that innervate sweat glands and blood vessels of skeletal muscles, release norepinephrine (NE) as their neurotransmitter. This process allows for the transmission of impulses from the sympathetic nervous system to target organs.

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How does Nicotine act as both a stimulant and a blocker?

Nicotine, in small doses, acts as a ganglion stimulant, mimicking the effects of acetylcholine and increasing nerve activity. However, at high doses, it becomes a ganglion blocker, inhibiting nerve transmission by blocking acetylcholine receptors.

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What is the action of parasympathomimetic drugs?

Parasympathomimetic drugs mimic the effects of acetylcholine by stimulating muscarinic receptors on target organs. These drugs induce effects typically associated with the parasympathetic nervous system.

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What are the effects of parasympatholytic drugs?

Parasympatholytic drugs, also known as acetylcholine antagonists, block the action of acetylcholine at muscarinic receptors, preventing the transmission of parasympathetic nerve impulses. These drugs are commonly used to manage certain medical conditions.

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Where does norepinephrine get formed and released?

Norepinephrine, derived from the amino acid phenylalanine, is a neurotransmitter primarily released by postganglionic sympathetic fibers. It is also produced by the adrenal medulla and plays a crucial role in the 'fight-or-flight' response.

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What are adrenergic receptors and their subtypes?

Adrenergic receptors are specialized protein molecules on the surface of target cells. They are classified into alpha (α1, α2, α3) and beta (β1, β2) subtypes, with the alpha type mainly involved in vasoconstriction and the beta type influencing functions like heart rate and bronchodilation.

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What are the effects of sympathomimetic drugs?

Sympathomimetic drugs stimulate adrenergic receptors, mimicking the effects of norepinephrine and epinephrine, primarily acting on the beta-1 and beta-2 receptors. They are often used to treat heart conditions and in emergency situations.

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Study Notes

Autonomic Nervous System

  • The autonomic nervous system (ANS) is responsible for regulating involuntary bodily functions
  • The ANS is divided into two main branches: the sympathetic and parasympathetic nervous systems

Sympathetic Nervous System

  • Originates from the lateral horn of all thoracic segments and the upper two lumbar segments (thoraco-lumbar outflow)
  • Contains a chain ganglia and collateral ganglia that innervate various organs (heart, lungs, digestive system, etc.)
  • Postganglionic fibers project to spinal nerves innervating structures like skin, blood vessels, sweat glands, muscle tissue
  • The sympathetic system often elicits widespread effects, creating "fight or flight" responses

Parasympathetic Nervous System

  • Has two origins: cranial nerves (III, VII, IX, and X) and sacral segments (S2-S4; craniosacral outflow).
  • Parasympathetic ganglia are usually located near or within the organs they innervate (terminal ganglia).
  • Postganglionic fibers are usually short, which means effects are localized, and tend to have an overall calming effect on the body. This allows for "rest and digest" functions like digestion and rest.

Autonomic Ganglia

  • Ganglia act as relay stations and distribution centers for the ANS.
  • They house synapses between preganglionic and postganglionic neurons
  • Different types of ganglia exist, categorized as lateral (sympathetic chain) ganglia and co-lateral/terminal ganglia.
  • Different ganglia are located in various places in the body to control the function of certain organs

Functions of Autonomic Ganglia

  • Relay stations where ANS functions can be controlled
  • Distribution centers, each preganglionic nerve fiber relays with 8–9 postganglionic neurons
  • Sympathetic ganglia are mostly located in the sympathetic chain (lateral ganglia) or in collateral ganglia

Types of Chemical Transmitters

  • Acetylcholine (ACh) is a chemical transmitter secreted by cholinergic neurons.
  • Nor-adrenaline (NA) is secreted by adrenergic neurons.

Sites of Release of Acetylcholine

  • Acetylcholine (ACh) is released at all autonomic ganglia (both sympathetic and parasympathetic).
  • Acetylcholine (ACh) is released at the end of parasympathetic postganglionic fibers.
  • Acetylcholine (ACh) is released at the end of sympathetic postganglionic fibers that innervate blood vessels of skeletal muscle, sweat glands, and the adrenal medulla

Drugs Affecting the Nervous System

  • Ganglion stimulants use small doses of nicotine, while ganglion blockers use high doses.
  • Parasympathomimetic drugs mimic parasympathetic responses and include ACh and methacholine

Muscarinic Drugs

  • These drugs stimulate peripheral cholinergic receptors
  • An example is muscarine, a substance that stimulates muscarinic receptors

Parasympatholytic Drugs

  • These drugs block muscarinic-like actions of ACh
  • Atropine is an example of a parasympatholytic drug

Noradrenaline

  • Noradrenaline is formed from the amino acid phenylalanine.
  • Released by postganglionic sympathetic fibers (with exceptions)
  • Adrenergic receptors, which are found in effector organs, either cause vasoconstriction or vasodilation
  • Can cause either heart contraction or lung/bronchial relaxation, depending on the specific receptors involved

Sympathomimetic Drugs

  • These drugs stimulate beta 1 & 2 receptors, including isoprenaline.
  • Isoprenaline is not specific because it works on both beta 1 and 2 receptors.

Sympatholytic Drugs

  • Alpha blockers block alpha 1 receptors (e.g., phentolamine)
  • Beta 1 receptor blockers (e.g., atenolol) are antihypertensive drugs
  • Beta 1 and 2 blockers, including propranolol (Inderal), are also commonly used to manage hypertension or other conditions

Special Features of Autonomic Nerves

  • They control the activity of visceral organs
  • They show a baseline level of discharge
  • Sympathetic stimulation generally affects many areas, while parasympathetic effects are more localized

Non-adrenergic Non-cholinergic Autonomic Neurons

  • Found in the intrinsic nerves of the gut (enteric nervous system)
  • Release peptide transmitters (e.g., encephalin, GABA, NO)
  • Function in regulating gut motility and the release of gut hormones

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