AUTONOMIC NERVOUS SYSTEM

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AUTONOMIC NERVOUS SYSTEM

CLASSIFICATION OF NERVOUS SYSTEM:

NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM
A. Brain
B. Spinal cord
PERIPHERAL NERVOUS SYSTEM
 A. SOMATIC NERVOUS SYSTEM
  B. AUTONOMIC NERVOUS SYSTEM
 1. Parasympathetic Nervous System
 2. Sympathetic Nervous System
  3. Enteric Nervous System
ANS
The autonomic nervous system (ANS) is largely autonomous (independent) in that its activities are not under direct conscious control. 
PARASYMPATHETIC NS
SYMPATHETIC NS

COMPONENTS OF ANS

Pre-ganglionic fibers 
Ganglia
Post-ganglionic fibres
Effector organ (gland,muscle)

JUNCTIONAL GAPS:

SYNAPSE

Communication between
 two neurons
NEUROEFFECTOR 

    JUNCTIONS

b/w neuron & effector 
 organ
Neurotransmitter is release 
Which excite the post
 synaptic receptor
Receptors 
Particular three dimensional structure having affinity for different types of neurotransmitters and also recognize and identifies the stimulus.
                                         or 
Specialized reactive chemical groups present on macromolecules  and have affinity to combine with neurotransmitter or drug and form chemical bonds that may be covalent, hydrogen, ionic or Vander wall forces and also have ability to stimulate the activity.

Neurotransmitters 

Substances which are synthesized in the fibers and release upon stimulus in junctional gaps and have ability to stimulate their specific receptors.
        Examples
         Acetylcholine
        Norepinephrine

CRITERIA FOR NEUROTRANSMITTERS:

PRESENCE IN NERVES
SYNTHESIS IN NERVES

 RELEASE FROM NERVES

STIMULATION OF RECEPTORS

 EXOGENOUS EFFECTS

Properties of neurotransmitters

Should be identified in nerve fibers
Should be synthesized in nerve fibers
Raw material should be available in nerve fiber
Should release on stimulus in synaptic cleft
Should be able to stimulate its receptors
When given externally should also stimulate its receptors

Sympathetic and Parasympathetic Divisions 

Issue from different regions of the CNS
Sympathetic – also called the thoracolumbar division
Parasympathetic – also called the craniosacral division

Comparison of Somatic and Autonomic Nervous Systems

PARASYMPATHETIC  OUT FLOW

Craniosacral division: Preganglionic neurons originate from the cranial nerves III, VII, IX and X and sacral spinal nerves S2-S4
Preganglionic fibers run via:
Oculomotor nerve (III)
Facial nerve (VII)
Glossopharyngeal nerve (IX)
Vagus nerve (X)
Cell bodies located in cranial nerve nuclei in the brain stem

Parasympathetic Divisions

The preganglionic fibers are long and the post are short.
Have a localized action 
Pre fibers are mylienated so the impulse transmission is fast
Both pre & post fibers are cholinergic
Neurotransmitter acetylcholine 

Cholinergic Neurons

Cholinergic neurons → acetylcholine (ACh).
Cholinergic neurons include-
All sympathetic and parasympathetic preganglionic neurons.
Sympathetic postganglionic neurons that innervate most sweat glands.
All parasympathetic postganglionic neurons.

Cholinergic Receptors

Cholinergic receptors are innervated  by acetylcholine.

Two types: 
Nicotinic receptors(ionotropic receptor)
NN  - neuronal (ganglia, CNS)
NM  - skeletal muscle
Muscarinic receptors(G- PROTEIN COUPLED RECERTOR)
M1,M2,M3,M4,M5
Mechanisms  of  Drug –receptor  Interaction
M1,M4,M5 CNS,NERVES
M2 Heart
                M3 Glands,smooth muscle,endothelium
M1,M3,M5 are Gq-coupled receptor  with IP3&DAG as 2nd messenger
M2,M4 are Gi receptor  with inhibition of cAMP
SYMPATHETIC(FIGHT OR FLIGHT)
Thoracolumbar division- Preganglionic neurons originate from the thoracic and lumbar levels of the spinal cord (T1-L2).
Preganglionic fibers are long & myleinated
Pre fibers are cholinergic
Post fibers are adrenergic and are non-myleinated
Post fibers are long give  very diffuse actions
Adrenergic Neurons and Receptors
Release  norepinephrine (noradrenaline)OR epinephrine.
sympathetic postganglionic neurons are adrenergic.
Two types of receptors: 
Alpha receptors-
Beta receptors-
ADRENERGIC  RECEPTORS
Alpha—1        (Excitatory)
Alpha—2        (Inhibitory)
  Beta--1           (Excitatory)
  Beta—2          (Inhibitory)
  Beta—3          (Lipolysis) 

MECHANISM  OF  ADRENORECEPTOR  STIMULATION

Alpha-1  G-Protein  Stimulation of phospholipase C (PLC), Conversion of PIP2 into IP3 and DAG
    Increase in free Ca ions, phosphorylation of proteins
Alpha—2  Inhibition of Adenylyl cyclase
Beta—receptors Stimulation of Adenylyl cyclase, Conversion of ATP to cAMP


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