Autonomic nervous system

Autonomic Nervous System (ANS)   

Introduction :

Anatomically the nervous system is divided into: 

1. Central nervous system CNS. (brain & spinal cord ).

2. Peripheral nervous system PNS (cranial nerves ,spinal nerves &their branches).

* The peripheral nerves are 2 types:

1. Afferent (sensory) nerves: from sensory receptors to the CNS.

2. Efferent (motor) nerves: from CNS to the effector ( target ) organs.

* Functionally the nervous system is divided into: 

1\ Autonomic Nervous System (ANS). 

Which  regulates the involuntary body 

functions (digestion , absorption, 

circulation, respiration, sweating & others

2\ Somatic  Nervous System  (ANS) Which

  regulates the voluntary body functions  

(Activity of skeletal muscles) & Somatic 

sensation.

   * Autonomic Nervous System (ANS) 

The functional division of the nervous  that concerns with autonomic (involntary functions)

Anatomically it is made of :

* Central division CNS. (brain & spinal cord ).

* Peripheral division PNS (cranial nerves ,spinal nerves &their branches ).

* According to the origin of the efferent autonomic nerves from CNS, the ANS is divided into:

1\ Sympathetic NS (thoracolumbar ): The efferent nerves of which are 12 thoracic spinal nerves & first 2  or 3 lumbar spinal nerves.

2\ Parasympathetic NS.(craniosacral):  The efferent nerves of which are cranial nerves (oculomotor, facial, glossopharyngeal,& vagus) & sacral spinal nerves.

*Parasympathetic system

Each efferent is made of preganglionic nerve cell (neuron) & postganglionic neuron synapse by autonomic ganglion.

* Neurotransmitters in ANS:

Are chemical substances secreted by endings of preganglionic nerves to transmit the nerve impulse to the postganglionic nerves,  

NTs are also secreted by endings of postganglionic nerves to transmit the nerve impulse to the target  organs, They act by binding to receptors.

* They include:

1. Acetylcholine:

2. Norepinephrine (Noradrenaline).

* Acetylcholine 

Secreted by endings of: 

All preganglionic nerves of ANS to bind with Ach- nicotinic receptors on the autonomic ganglia.

All postganglionic parasympathetic nerves. Bind to muscarinic receptors.

Postganglionic sympathetic nerves to the sweat glands &blood vessels of skeletal muscles .

 Bind to muscarinic receptors.

Synthesis of acetylcholine

Noradrenaline ( Norepinephrine) 

Is secreted  by the endings of 

postganglionic sympathetic NS to bind with

adrenergic receptors (α1 , α2,  β1,  β2,  β3 ) on

the target organs. 

 Physiologic effects of ANS: 

Generally the parasympathetic effects are

dominant during rest, therefore are mostly  anabolic (store the energy). 

sympathetic effects are catabolic (use the 

stored energy) therefore are dominant 

during exercise & stresses & emergencies.

Parasympathetic :

Target organ

  effect

Heart:   Heart rate. ( blood pressure)

Blood vessels :Vasodilation 

Lung bronchi : Bronchoconstriction

Salivary glands:Secretion of waterysaliva.

Stomach:   gastric  motility &secretion Intestine : 
 intestinal motility & secretion Pancreas: Pancreatic secretions & Insulin.

Gall  bladder: Contraction & release of bile.

Liver:Glycogen storage .

Adipose tissue: Fats storage via Insulin.

Urinary bladder:  Contraction.

Penis:      Penile vasodilation & erection

Eye pupil :   Pupillary Constriction . 

    

sympathetic system :

Target organ

  effect

Heart : Heart rate & force of contraction via β1 receptors. 

Blood vessels : Vasoconstriction

( blood pressure)

Lung bronchi  Bronchodilation via β2 receptors.

Salivary glands : Secretion of little mucous    saliva.

Stomach : gastric  motility &secretion.

Intestine: intestinal motility &secretion.            

Pancreas:Pancreatic secretions & Insulin.      

Gall  bladder: Relaxation.

Liver: Glycogenolysis.

Adipose tissue:  Lipolysis.

Urinary bladder: Relaxation..

Penis: Penile vasoconstriction & ejaculation of semen

Eye pupil : Pupillary Dilation (mydriasis)

Sweat glands : stimulates sweat secretion .

*Blockers of receptors in ANS: 

Hexamethonium:  Nicotinic R blocker.

Atropine, Hyoscine: Muscarrinic R blocker.

Propanolol:  beta R blocker.

Atenolol: β1 R blocker.

Prozasine : alpha R blocker.