Autonomics I

8/11/2019 Autonomics I

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Autonomics IDr. Gloria Roque


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The Autonomic Nervous System Organization of Nervous System

in Man

Central Nervous SystemBrainSpinal

Peripheral Nervous SystemSomatic nervous system Autonomic nervous system


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The Autonomic Nervous System Differences Between Somatic and Autonomic Nervous System Somatic Nervous System

Fibers do not synapse once they have left the centralnervous systemInnervates skeletal muscle Always leads to excitation of the muscle

Autonomic Nervous SystemFibers synapse once in ganglia after they have left thecentral nervous systemInnervates smooth or cardiac muscle or gland cellsCan lead to excitation or inhibition of the effector cells


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Summary of Differences Between

SNS and ANSParts of Differences SNS ANS

1. Efferent pathway 1 neuron pathway 2 neuron pathway

2. Effector/s Skeletal muscle Smooth MuscleCardiac Muscle

Glands/Organs3. Effect of effective stimulation Always excitation of skeletal

muscleExcitation or inhibition ofeffector

4. Sites of Inhibition of impulse - CNS- neuroeffector junction

- CNS- Ganglion- Neuroeffector junction

5. Function For locomotion Regulates visceral functions

CNS CNS

.


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The Autonomic Nervous System

Subdivisions of ANS: Sympathetic NS Parasympathetic NS

Differences between SYMP. &PARA. NS Anatomical Biochemical Physiological Pharmacological


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Anatomical Differences BetweenSympathetic and ParasympatheticDivisions of the ANS

SYMPATHETICDIVISION

PARASYMPATHETICDIVISION

(a) Origin of preganglionicfibers

Spinal nerves T1-L2(thoracolumbar division)

Cranial nerves III, VII, IX, X;spinal nerves S2-S4 (cranio-sacral division)

(b) Location of Ganglia In sympathetic chain(paravertebral ganglia orabdominal prevertebral or

collateral ganglion,preganglionic fibers usually;shorter than post-ganglionicfibers (except adrenal medulla)

In or near effector organs thuspreganglionic fibers usuallylonger than post-ganglionic

fibers

(c) Branching of Preganglionicfibers

Extensive branching ave. ratiopreganglionic to postganglionicfibers = 1:20

Limited branching; ave. ratio ofpreganglionic to post-ganglionic fibers 1.1 (except the

vagus)


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Biochemical Differences Between

Sympathetic & Parasympathetic Divisions The transmission of an impulse along a nerve fiber is an electricalphenomenon. In contrast, transmission, across synapses and neuroeffector junctions is mediated by chemical substances called neurohumors orneurotransmitter agents (NTA)

2 Main NTAs of the ANS Acetylcholine (Ach) Norepinephrine (NE)

Nerves secreting Ach are CHOLINERGIC NervesNerves secreting NE are ADRENERGIC Nerves

Biochemical subdivision of ANS - Cholinergic Division- Adrenergic Division

CNS

.

Preganglionic fiber

ganglion (synapse)

Postganglionic fiber

Neuroeffector junction


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Summary of Neurohumoral

Transmission AUTONOMICCHOLINERGICSympatheticCholinergic

Sympathetic Adrenergic

Parasympathetic

SOMATIC

CNS

ACH

CNS CNS CNS

ACH

ACH

effectorcell

effectorcell

effectorcell

effectorcell *

ACh ACh AChNE

Pregang. Pregang. Pregang.

SomaticFibers

Postgang. Postgang. Postgang.

Transmitter

Transmitter

Sweat Glands blood vessels of skeletal

musclespiloerector muscles

SkeletalMuscle


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4 Steps in Chemical Transmission

Process Synthesis and / storage of NTA inthe prejunctional fiber

Release of NTA from the storage vesicles (exocytosis) Interaction of NTA with receptors

and initiation of post junctionalactivity Destruction or dissipation

(deactivation) of NTA


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NTA: Acetylcholine (ACH) Synthesized and stored in vesicles at the terminal of

prejunctional fibers Released by the terminals ofnerve fiber upon arrival of nerve

impulse- Influx of Ca ++ precedes therelease


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NTA: Acetylcholine (ACH) Interaction with receptors to produce the response:

Ach on Cholinergic Receptors:NicotinicMuscarinic

Cholinergic transmission occurs at the following 4 locations:1. All parasympathetic

neuroeffector junctions2. Sympathetic cholinergic

neuroeffector junctions3. All peripheral ganglia

4. All somatic neuromuscular junctions

Response excitatory or inhibitory in ANS

Deactivation: by enzymatic hydrolysis byacetycholinesterase (Ach E)

muscarinicreceptors

nicotinicreceptors

cholinergicreceptors


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Summary of adrenergic

receptor subdivision Alpha ( ) receptorsstimulation excitatory responses

examples: vasoconstriction in skin and mucosa;contraction of gastrointestinal

sphincters; piloerectionexception: decreased gastrointestinal motility and tone

Beta ( ) stimulation inhibitory responsesexamples: vasodilation in skeletal muscles

relaxation of bronchial muscleexception: increased heart rate, contractility,conduction velocity

B1 Receptors - found in the heartB2 Receptors - elsewhere in the body


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Summary of Receptors AUTONOMIC

SympatheticCholinergic

Sympathetic Parasympathetic

SOMATIC

CNS CNS CNS CNS

effectorcell **

effectorcell *

effectorcell

effectorcell **

muscarinic nicotinicmuscarinic Adrenegic receptors

Nicotinic Nicotinic Nicotinic

** (skeletal muscle)

Adrenergic Cholinergic

*** (receptor type) B1 B2

depends on effector

organ

** sweat glands(most individuals);

blood vessels of

skeletal muscles


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Relationship of Adrenal Medulla

and SympatheticSympathetic preganglionic fiber innervatesthe adrenal medullary cells.

Stimulation of sympathetics also stimulateadrenal medullary cells secretion and

release of norepinephrine & epinephrine

into circulation B1 B2 receptors.+


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2 Sources of NE Sympathetic Adrenergic

Postganglionic Fibers

Adrenal Medulla


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Source of E: Adrenal MedullaNE strongly and B1 receptors

weakly B2 receptors

E strongly B1 B2 receptors.

- Adrenal medulla reinforcessympathetic effects

+

+

+

Autonomics I

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