Autonomic Nervous SystemNerve 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 .
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 ;
- 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 .
- 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."
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 ?
- 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.