AUTONOMIC NERVOUS SYSTEM

AUTONOMIC

NERVOUS SYSTEM

assoc. prof. Edyta Mądry MD, PhD

Department of Physiology

Poznań University of Medical Sciences

Basic Functions of the Nervous System

1. Sensation

▪ Monitors changes/events occurring in and outside the body. Such changes are known as stimuli and the cells that monitor them are receptors.

2. Integration

▪ The parallel processing and interpretation of sensory information to determine the appropriate response

3. Reaction

▪ Motor output.

– The activation of muscles or glands (typically via the release of neurotransmitters (NTs))

Nervous System’s Organization

◼

2 big initial divisions:

1. Central Nervous System

▪ The brain + the spinal cord

– The center of integration and control

2. Peripheral Nervous System

▪ The nervous system outside of the brain and spinal cord

▪ Consists of:

– 31 Spinal nerves

▪ Carry info to and from the spinal cord

– 12 Cranial nerves

▪ Carry info to and from the brain

Peripheral Nervous System

◼ Responsible for communication btwn the CNS and the rest of the body.

◼ Can be divided into:

Sensory Division =Afferent division

– Conducts impulses from receptors to the CNS

– Informs the CNS of the state of the body interior and exterior – Sensory nerve fibers can be

somatic (from skin, skeletal muscles or joints) or visceral (from organs)

Motor Division=Efferent division

– Conducts impulses from CNS to effectors (muscles/glands) – Motor nerve fibers

Motor Efferent Division

◼

Can be divided further:

– Somatic nervous system

▪ Somatic nerve fibers that conduct impulses from the CNS to skeletal muscles

– Autonomic nervous system

▪ Conducts impulses from the CNS to smooth muscle, cardiac muscle, and glands.

Autonomic Nervous System

◼ Can be divided into:

– Sympathetic Nervous System – Parasympathetic Nervous

System

These 2 systems are antagonistic.

Typically, we balance these 2 to keep ourselves in a state of dynamic balance.

Autonomic Nervous System

– Sympathetic Nervous System

▪ “Fight or Flight”

– Parasympathetic Nervous System

▪ “Rest and Digest”

These 2 systems are antagonistic.

Typically, we balance these 2 to keep ourselves in a state of dynamic balance.

◼

Central components:

hypothalamus, certain brain stem regions and nuclei, spinal cord

◼

Peripheral

components:

ganglia and nerves (both sensory and efferent neurons)

Principal components of ANS

◼ Sympathetic division of ANS – central neurons

(preganglionic nerve cells) in the intermediolateral cell column of the spinal cord (Th1-12 i L1-3)

◼ Parasympathetic division of ANS - central neurons in the nuclei of cranial nerves: oculomotor (III), facial(VII), glossopharyngeal(IX), vagus(X) and in the

intermediolateral cell column of the spinal cord (S2-4)

◼ Enteric nervous system (ENS) – neurons lying within the walls of the gastrointestinal system (control of motility, secretion and blood flow)

◼ adrenal medulla !!!

Functional anatomy of ANS

(Th1-12 i L1-3) (III, VII, IX, X, S2-4)

Efferent pathways of ANS

Autonomic ganglion

Ganglionic transmision

Autonomic and somatic efferent

innervation

◼

smooth muscles

◼

heart

◼

glands

◼

nervous tissue

◼

adipose tissue

Effectors of ANS

◼ Central components:

hypothalamus, certain brain stem regions and nuclei, spinal cord

◼ Peripheral components:

ganglia and nerves (both sensory and efferent

neurons

)

Principal components of ANS

Autonomic Nervous System :

◼ controls visceral functions

◼ conscious control – minimal (UNVOLUNTARY)

Somatic Nervous Syste m:

◼ controls skeletal muscles

◼ under conscious control (VOLUNTARY)

AUTONOMIC NERVOUS SYSTEM

◼ Function of ANS is reflex (see the end of presentation) and simple autonomic reflexes in the peripheral parts of ANS may occur within

one organ

Autonomic Nervous System

Adrenal medulla

◼ Functionally related to the symathetic nervous system.

◼ It is regarded as a sympathetic ganglion in which the

postganglionic neurons have lost their axons and become secretory cells

◼ After hypothalamic stimulation it releases catecholamines, which may affect autonomic adrenic receptors

Adrenal medulla

Lie detection, truth verification

Polygraphy

AUTONOMICZNY UKŁAD

◼ Techniques based on meditation allow, to a certain degree,

consciously control AUN.

Autonomic Nervous System

The relaxation response -  in oxygen consumption,  HR,  RR,  respiration rate

Regulatory systems of ANS

◼ Limbic system - „cerebral cortex of the ANS”

(cortically stored past experiences can be evoked

by external stimuli (smells, sounds, sights).They can cause

emotional reactions leading to strong visceral responses coordinated by ANS)

◼ Hypothalamus

◼ Solitary nucleus of the medulla – coordinates heart and respiratory functions

◼ Circulating catecholamines – affect adrenergic receptors

Regulatory systems of ANS

General characteristics of ANS

◼ usually dual and antagonistic innervation of the visceral organs

◼ ganglia in the efferent pathways

◼ large quantity of synapses in the ganglia

◼ cotransmitters and neuromodulators (they may coexist at most

ganglionic synapses )

◼ postganglionic unmyelinated

nerve fibers in the efferent pathways

General characteristics of ANS

Anatomical

localization Pre-

ganglionic fibers

Post-

ganglionic fibers

Transmitter

(ganglia) Transmitter

(nerve fiber ends)

Sympathetic Thoraco- lumbar segments (Th1-12; L1- 3)

Short ^{Long ACh NE}

Para-

sympathetic Cranial and sacral

segments (III, VII, IX, X; S2-4)

Long Short ACh ACh

Comparison of efferent pathways

SNS and PNS

Different nerve endings in ANS

Diffuse synapses of SNS activate large surface area of one cell or

large number of cells Discrete („precise”) synapses of

PNS

◼ in the emergency situations; mobilization of energy sources

◼ increase in heart rate and force; RR

◼ redistribution of blood from viscera to active skeletal muscles and heart

◼ inhibition of gastrointestinal activity

◼ ACTH secretion and secretion of catecholamines

◼ dilation of respiratory airways

◼ widening of pupil and accomodation for far vision

◼ „cold” sweating

◼ total activation !!!

SNS ^– fight-or-flight respons

◼ energy accumulation from food (intestinal digestion and absorption);

waste products removal

◼ increases intestinal motility

◼ urination and defecation

◼ activated partially according to body demands !!!!

◼

dominates during the night

PNS –

“rest-and-digest”

A preganglionic fiber follows one of three pathways upon entering the paravertebral ganglia:

1

sympathetic chain to synapse in another chain ganglion

3. Passes through the chain ganglion and emerges without synapsing

Sympathetic Trunks and

Pathways

◼

Paradoxical fear

Paradoxical fear

when there is no escape route or no way to win

– causes massive activation of

parasympathetic division

– loss of control over urination and

defecation

PNS- normally dominates over

sympathetic impulses

Acetyl-CoA Choline+

Acetylcholine

Acetate Choline+

Choline acetyltransferase (ChAT) Acetylcholinesterase (AchE)

Acetylcholine metabolism

-

-NE they may be degraded by the

enzymes: monoamine oxidase (MAO) or catechol-O-methyltransferase

(COMT)

-NE may travel to the blood

Norepinephrine metabolism

◼ Cholinergic:

- sweat glands (except hands)

- vascular smooth muscles in skeletal muscle

- salivary glands

- vascular smooth muscles of penis (erection)

◼ Histaminic:

- vascular smooth muscles of skeletal muscle, skin, brain

NON-adrenergic sympathetic

fibers - ^examples

Viscero-visceral Viscero-somatic Somato-visceral From interoreceptors

– to internal organs (effectors)

e.g. micturition, defecation

From internal organs to SNS

e.g. reffered pain or muscular defense

(convergention of the afferent pathways onto

one spinal segment)

From exteroreceptors to internal organs

e.g. acupuncture, warm compresses

Reflexes of ANS

Pain stimuli arising from the viscera are perceived as

somatic in origin

- due to the fact that visceral pain afferents travel along the same pathways as somatic pain fibers

Referred Pain

Referred Pain

Referred Pain

Dr n. med. Edyta Mądry

Referred Pain

◼ Cholinergic:

-

nicotinic (N)

-

muscarinic (M)

◼ Adrenergic:

-

alpha 

-

beta 

Receptors for autonomic

transmitters

◼ ionotropic receptors are ion channels to which neurotransmitters bind directly in order to open them.

◼ localization:

- autonomic ganglia

- adrenal medulla

- motor end plate

◼ activation (via Ach) produces fEPSP of the ganglionic neurons

◼ The effect of ACh binding to nicotinic receptors is always stimulatory

◼ agonist - nicotine

◼ antagonist - atropine, hexamethonium (ANS), curare (motor end plate)

Cholinergic nicotinic receptors( N)

◼ Work via the second messenger system (IP3 and DAG)

◼ M1 – postsynaptic membranes;

M2 – presynaptic membranes

◼ Agonist - muscarine

◼ Antagonist –

- atropine,scopolamine M2), -pirenzepine (M1, M4)

◼ The effect of ACh binding:

– Can be either inhibitory or excitatory

– Depends on the receptor type of the target organ

Receptor type M2 – inhibition of adenylate cyclase – outflux of K ions – membrane

hyperpolarization

Amanita muscaria-source of muscarine

Cholinergic muscarinic receptors

(M1-M8)

◼

Alpha receptors – norepinephrine

◼

Beta receptors - epinephrine

Adrenergic receptors

◼ Rec 1 - salivary glands, mucus glands of bronchi,

muscles of: blood vessels, uterus, gastrointestinal tract

◼ They work via the second messenger system (IP3)

◼ Agonist – methoxamine, phenylephrine

◼ Antagonist –

prazosin (1) and phentolamine

(nonselective)

Adrenergic receptors 1

Adrenergic receptors 2

◼ Rec 2 – mainly in the presynaptic terminals - autoreceptors;

their activation controls the amount of neurotansmitter that is released (inhibition of reuptake-feedback inhibition)

◼ Inhibition of adenylate cyclase and inhibition of cAMP generation

Agonist – clonidine Antagonist - yohimbine

Adrenergic receptors 2

◼ 1 - heart, kidney, adipose tissue; 2 – smooth muscles of airways

◼ second messenger - cAMP

◼ Activation of presynaptic 2 receptors increases release of NE (feedback excitation)

◼ Agonist - phenoterol (2)

◼ Antagonist - propranolol (nonselective), metoprolol (1)

Adrenergic receptors 1 and 2

Which of the autonomic receptors is most important in ganglionic

transmission?

Ganglionic transmission

Phase 1: ACh binds to N receptor on ganglionic cell causes

depolarization (fEPSP);

ACh binds to M1 receptor (SIF cells) causes dopamine release;

Dopamine binds to D1 receptor causing K⁺ permeability and

hyperpolarization (IPSP)

Phase 2: ACh binds to M1 and M4 receptors causing K⁺ permeability and

slow depolarization (sEPSP)

Phase 3: (lsEPSP) Gn-RH as a neuromodulator causes slow

depolarization

The effects of AN S

1.

Which system is responsible for stress response?

2.

Describe the changes in fight-or-

flight reaction

Adrenergic and cholinergic stimulation

Organ SNS PNS

Heart  rate and force

(β1)  rate and force

(M1) Bronchi dilation (β2)

mucus–inhibition (α1)

constriction (M3) mucus-increase (M1)

Pupil dilation (α1) constriction (M1)

Adipose tissue  lipolysis (β3) no effect Kidney  urine production

(α1, β1)  urine production External male

reproductive organs ejaculation (α1) erection (M1)

Adrenergic and cholinergic stimulation

Organ SNS PNS

Bladder relaxation of

detrusor (β2, β3), contraction of

internal sphincter(α)

contraction of

detrusor (M2, M3), relaxation of

internal sphincter

Rectum contraction of

internal sphincter, relaxation of

smooth muscles

relaxation of

internal sphincter contraction of

smooth muscles Gastrointestinal

system  peristalsis (β2 ) and gastric juice production (α1, α2)

 peristalsis (M1) and gastric juice production (M1) Salivary glands production of high

viscosity saliva (α1)  production of watery saliva (M1)

Disorders of the Autonomic Nervous System: Raynaud’s Disease

◼

Raynaud’s disease – characterized by constriction of blood vessels

– Provoked by exposure to cold or by

emotional stress

Disorders of the Autonomic Nervous System: Hypertension

◼

Hypertension – high blood pressure

– Can result from overactive sympathetic

vasoconstriction

Disorders of the Autonomic Nervous System: Achalasia of the Cardia

◼

Achalasia of the cardia

– Defect in the autonomic

innervation of the

esophagus

cAMP receptors:

ATP cAMP

Protein kinase A

Cellular effects: e.g. increased influx of Ca⁺⁺ in heart; activation of lipase in the adipose tissue → lipolysis

Adenylate cyclase

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Phosphatidylinositol cycle receptors:

Phospholipase C

Phosphatidylinositol

biphosphate (PIP₂) Phosphatidylinositol (PIP)

IP₃

Inositol triphosphate

- release of Ca⁺⁺ from ER

diacylglycerolDG Protein kinase C - proton pump activation

- protein phosphorylation

T+R+G_s+GTP

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Convertion of an extracellular event - the binding of a signal molecule – into an intracellular response that

modifies the behavior of target cell

◼ Phase I – binding of first messenger (transmitter) to the receptor (T+R)

◼ Phase II – transduction of a signal into the intracellular compartment.

T+R complex interacts with a specific G-protein;

T+R+G complex binds GTP, which activates  subunit of G protein

◼ Phase III – activated  subunit of G protein activates (or inhibits) a specific enzyme (eg. adenylate cyclase or phospholipase C), which causes synthesis of second messenger

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When a first messenger binds to a G-protein coupled receptor, the receptor changes its conformation and activates several G-protein  subunits.

Each  subunit breaks away from the  complex, and activates a single effector protein, which in turn, generates many intracellular second -messenger molecules.

One second messenger activates many enzymes, and each

activated enzyme can regulate many target proteins (amplification)

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https://www.youtube.com/watch?v=ShBAvYDAV9I&index=6&list=PLXwnjgs_UWpIyKAZ 9yaEUbv8Sz1AMve45

Action of

Epinephrine

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Action of Epinephrine

Amplification

When a first messenger binds to a G-protein coupled receptor, the receptor changes its conformation and activates several G-protein  subunits.

Each  subunit breaks away from the  complex, and activates a single effector protein, which in turn, generates many intracellular second -messenger molecules.

One second messenger activates many enzymes, and each

activated enzyme can regulate many target proteins (amplification)

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Parasympathetic Responses

• Enhance “rest-and-digest” activities

• Mechanisms that help conserve and restore body energy during times of rest

• Normally dominate over sympathetic impulses

• SLUDD type responses = salivation, lacrimation, urination,

digestion & defecation and 3 “decreases”--- decreased HR, diameter of airways and diameter of pupil

• Paradoxical fear when there is no escape route or no way to win – causes massive activation of parasympathetic division

– loss of control over urination and defecation

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Reflexes

• Reflex is a fast, involuntary, unplanned sequence of actions that occurs in response to a particular stimulus.

• Some reflexes are inborn ( pulling your hand away from a hot)

• Other reflexes are learned or acquired.

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Reflex arc

• The pathway followed nerve impulses that produce a reflex is a reflex arc.

• A reflex arc includes the following five function components:

– sensory receptor – sensory neuron – integrating center – motor neuron

– effector

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