LEC 5 AUTONOMIC NERVOUS SYSTEM

LEC 5 AUTONOMIC NERVOUS SYSTEM
General consideration
NERVOUS SYSTEM
The nervous system is the most important organization, which controls and integrates the different bodily functions. Nervous system is divided into:
Central nervous system: It includes brain and spinal cord. Peripheral nervous system it consists of:
Somatic nervous system
It is concerned with consciously controlled functions .e.g. Sensory and motor system .Nerves originating from CNS directly supply the skeletal muscles without the mediation of ganglia.The somatic nervous system is under voluntary control ,whereas the autonomic nervous system is an involuntary system.
Autonomic nervous system (ANS)
The Autonomic nervous system (ANS) is also called as visceral or involuntary nervous system .It controls the vegetative functions of the body such as the circulation ,respiration ,digestion and maintenance of body temperature.
ANS is divided on physiological and anatomical ground into two parts :
• Sympathetic system
• Parasympathetic system
Sympathetic system
The function of sympathetic system is catabolic in nature. Sympathetic system has property of adjusting the body in response to stressful situations, such as trauma, fear, hypoglycemia, cold and exercise. Its stimulation cause increased heart rate and blood pressure., increased blood flow to skeletal muscles and heart while diverting blood from the skin by constriction of its vessels. Sympathetic stimulation also results in dilation of pupil and the bronchioles.
Parasympathetic system
Parasympathetic system maintains the essential bodily functions .This system is concerned primarily with the conservation and restoration of energy. It slows the heart, lowers arteries pressure, increase GIT motility and secretions and empties the bladder and rectum. It usually acts to oppose or balance the actions of sympathetic system and is dominant over sympathetic system during rest.
Mostly organs in the body are innervated by both sympathetic and parasympathetic
system, and they oppose the action of each other, in this way balance is maintained e.g sympathetic system innervating the heart and increase heart rate, while the parasympathetic system innervating the heart through vagus nerve decreases the heart rate .
Adrenal medulla , kidney , pilomotor muscles and sweat glands only receive sympathetic system. control of blood pressure is also mainly a sympathetic activity.
TRANSMISSION OF IMPULSE
Transmission of nerve impulse from one nerve fiber to another or from a nerve fiber to an effector organ is mediated through the release of transmitters from stimulated nerve ending .two chemical transmitters have been identified in automatic nerves.
• Acetylcholine
• Noradrenaline
The nerves which release acetylcholine are called cholinergic nerves while the other which release noradrenaline are termed as adrenergic nerves.
Stimulation of parasympathetic system results in the release of acetylcholine. Therefore this system is called cholinergic system, while stimulation of post ganglionic sympathetic nerves release noradrenalin and this system is called adrenergic system.
Mechanism of Neurotransmission :
• arrival of the nerve action potential at the nerve ending leads to release of transmitter into the synaptic cleft .
• Combination of the transmitter with receptors in the effectors organ.
• Changes in the permeability and then initiation of response in the effectors organ.
• Destruction of transmitter. This is achieved by one or both of the following processes.
• Enzymatic destruction :
cholinesterase destroys acetylcholine while the monoamine oxidase (MAO) and catechol-o-transferase destroy noradrenaline in synaptic cleft .
• Re-uptake
Re-uptake of transmitter by axonal terminals occurs for noradrenaline at adrenergic nerve endings.
Cholinergic Transmission :
Acetylcholine functions as a chemical transmitter at all cholinergic sites in the body . It is released from :
• Somatic motor nerve ending where it is responsible for neuromuscular transmission.
• preganglionic sympathetic and parasympathetic nerve ending where it is
responsible for ganglionic transmission.
• preganglionic nerves to the adrenal medulla.
• All postganglionic parasympathetic nerve endings and the postganglionic sympathetic nerve endings to sweat glands and blood vessels.

• Between some neurons within CNS.
Adrenergic Transmission:
Noradrenaline is a chemical transmitter which is released from postganglionic sympathetic nerve endings with exception of those supplying the sweat gland and blood vessels.