Wednesday, March 13, 2013

ANS Pharmacology

Autonomic Nervous System

Nerve receptor pharmacology 
Physiology: Ligand +receptor = action /effect
Pharmacology : Drugs that produce their  primary  therapeutic  effect by mimicking  altering the functions of  efferent portion  are called efferent drugs and  are discussed in the following  four chapters . 

Nerve system 

1-Inhibitor of CNS :
(e. g  sedative-hypnotics)
2-Excitement of CNS:coffein
3-Afferent nervous system :anesthetic D
4-Efferent nervous system:NE, Atropine   

According to the anatomy
ANS  lends itself to division into two major portions :

  • Autonomic  (The sympathetic  and the parasympathetic division ).
  • Somatic nervous system.

What are the difference according to  anatomy?

  • The somatic  nervous originate in the CNS travels directly to the skeletal muscle  without the mediation of ganglia,it  is under voluntary control ,whereas the autonomic  is an involuntary system .
  • The sympathetic preganglionic fibers leave  the CNS through the thoracic and lumbar spinal nerves ----it is short ;the ganglia of sympathetic  are close to the spinal cord 
  • By the contrast :The parasympathetic preganglionic fibers leave  the CNS  through the cranial nerves and the third and fourth sacral spinal roots----it is longer  
  • The post-ganglionic  fibers of  parasympathetic  are  usually shorter than the preganglionic fibers 
  • The  post-ganglionic  fibers are  branching to innervate more than one organ systems.

Differences between the actions:
In the periphery, provides the innervation to 

  • the heart+vessel;
  • glands ;
  • eye; 
  • smooth muscles; 
  • metabolism . 

It is therefore widely distributed throughout the body and regulates autonomic functions

The autonomic nervous system is also called the visceral, vegetative, or involuntary nervous system, which occur without direct conscious control. 
Such as: heart beat ;  blood pressure 

Somatic nervuous system contain no peripheral ganglia+ voluntary. Whereas smooth muscles and glands generally show some level of spontaneous activity independent of intact innervation
Such as: muscle contraction.

NOTE: When the spinal efferent nerves are interrupted, the skeletal muscles are paralyzed, and atrophy, such as --Myasthenia  gravis ( MG).

Summary of differences 

How to transmit signal ? Not structure, joint but Biological transducers=ganglia

The rapid  transmission of electrical  impulses over fibers that terminate  at effector cells ,which especially  responses to the release of neuromediator  substances .

The nerve endings have been called biologic transducers , that convert electrical energy into chemical energy. This conversion process involves the neurotransmitters.
One –by –one :
signal is amplified 
Preganlionic neuron emerge  from the brainstem or spinal cord and make  a synaptic  connection in ganglia
Its  function as relay stations between preganglionic  neuron and a second nerve cell. The post-ganglionic neuron. Terminate on effector organs 
Synapse: The place where a neuron communicates with another neuron or an effector cell (muscles or glands)
Synaptic cleft: The minute space (gap) separating axon and effectors, is a place that electrical signal is changed into a chemical signal
Presynaptic membrane: The membrane on the axon side of the synaptic cleft 
Nerve impulse causes release of neurotransmitter from presynaptic membrane into synaptic cleft and then reach the receptors in the post-synaptic membrane
Effect =  Strong affinity+  Strong intrinsic activity

Now that neurotransmitters are the chemical substances which bring the information from one neuron to another.
May be excitatory or inhibitory (reduce possibility of action potential), then  amplify signal. 

At least 20 different neurotransmitters

General Functions of ANS

Important organs that receive innervation from both the  sympathetic and parasympathetic nervous systems include;

  • The heart .
  • Eye.
  • Bronchial smooth muscle.
  • GI tract smooth muscle , and 
  • Genitourinary tract smooth muscle. 

When both innervated the same organs system ,they tend to have opposite actions .
For example : 
Both innervate the heart .The sympathetic system increase heart rate and contractility ( in order to run fast ) , while the parasympathetic system decrease heart rate ( in order to conserve energy ) .
 The one exception to opposite-effect rule is the salivary glands .Both sympathetic and parasympathetic systems increase secretion in the salivary glands ,but the secretions are of different types ( a few sympathetic post-ganglionic fibers are cholinergic fibers ===glands)
Remember that sympathetic system ( no matter which receptor type is involved ) is mediating the fight-or-flight response .

In the resting state ( not in fight-or-flight situation ) , most dually innervated organs are controlled by the parasympathetic system .

General function of Sympathetic System

  • pupils dilate
  • Heart rate is accelerated
  • blood pressure rises
  • blood glucose rises
  • the bronchioles dilate
  • Forget to empty the urinary bladder and rectum
  • blood flow is shifted from the skin and splanchnic region to the skeletal muscles
  • on the whole, the organism is better prepared for "fight or flight."

Para-sympathetic system
It  is concerned primarily with
1.  Conservation of energy ; It slows the heart rate, lowers the blood pressure, stimulates gastrointestinal movements and secretions;aids absorption of nutrients, protects the retina from excessive light, and empties the urinary bladder and rectum. 

2.  Maintenance of organ function during periods of minimal activity.

The effect is depend on which one  is predominant ?
Yoga & Health

  • Stimulate the endocrine system, balance the department of endocrine --Insulin release is increased (blood  sugar ↓)
  • good effect on some of endocrine  diseases(DM)
  • relieve yourself ---resting  body 
  • calm down--- resting brain 
  • make you more peaceful 

Some   diseases are caused by NMJ ‘s question

Myasthenia  gravis ( MG): Is the most common primary disorder of neuromuscular transmission. The usual cause is an acquired immunological abnormality, but some cases result from genetic abnormalities at the neuromuscular junction 

Hypokalemic periodic paralysis.
Parkinson’s Disease (PD):
is a disorder of the brain characterized by shaking (tremor) and difficulty with walking, movement, and coordination. It is associated with damage to a part of the brain that is involved with movement.

This is just basic knowledge about ANS. Stay here for further knowledge about receptors and drugs.

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