Introduction to Nervous system..Pharma

The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body.

Important Functions:

4 important functions of the nervous system include control, coordination, communication and Integration.

Communication is by means of electric impulses  and neurotransmitters. Other systems for communication in the body are hormonal system and local hormones called autocoids.

Neuron is functional unit of the nervous system. Parts of the neuron include cell body, axons and dendrites. Axons are used for the conduction of impulses.

Neuron terminals form two junctions with neurons and effector cells known as synapse and neuroeffector junctions.

Whole nervous system is working in specific manner called reflex arc.

Components of Reflex Arc:

Reflex arc is a neural pathway that mediates a reflex action. The reflex arc typically consist of 5 components;

The receptor at the end of a sensory neuron reacts to a stimulus.

The sensory (afferent) neuron conducts nerve impulses along an afferent pathway towards the central nervous system (CNS).

The integration center consists of one or more synapses in the CNS.

A motor (efferent) neuron conducts a nerve impulse along an efferent pathway from the integration center to an effector.

An effector responds to the efferent impulses by contracting (if the effector is a muscle fiber) or secreting a product (if the effector is a gland).

Divisions of the Nervous system:

CNS consists of brain and spinal cord while PNS consists of nerve fibers originating from CNS.

PNS is divided into somatic and autonomic nervous systems. Autonomic is furthure divided into sympathetic and parasympathetic nervous systems.

Autonomic NS.. in this division, ganglions (aggregation of cell bodies) are present and neurotransmitters can be acetylecholine or epinephrine and nor-epinephrine.

Somatic NS.. In this division, no ganglions are present and neurotransmitter is only acetylcholine.

Sympathetic NS

Parasympathetic NS

Originates from thoracolumbar segments of the spinal cord. Thoracic=1-12…Lumbar=1-3.  Preganglionic fibers are short and postganglionic fibers are long.  Ganglions are located away from the effector organs. Ratio of pre and post ganglionic fibers may be 1:1(or more than 1 for post). So called fight or flight condition. In the time of stress, it is activated. It increases blood flow to muscles, brain and heart.

This division originates from the craniosacral region of the CNS. Cranial=3,7,9,10…Sacral=2,3,4. Preganglionic fibers are long and postganglionic fibers are short. Ganglions are located near the effector organs. Ratio of pre and post ganglionic fibers is 1:1. It decreases contration of the heart.

 

Cholinergic nerve fibers.. Which release acetylecholine as neurotransmitter. Adrenergic nerve fibers release acetylecholine and epinephrine or nor epinephrine as neurotransmitters.

Classes of drugs in Nervous system:

There are 6 classes of drugs in the nervous system;

• Cholinergic agonists
• Cholinergic antagonists
• Adrenergic agonists
• Adrenergic antagonists
• Ganglionic agonists
• Ganglionic antagonists

Stimulations in Nervous System:

There are 3 types of stimulations in nervous system;

• Physiological
• Electrical
• Pharmacological