Autonomic Nervous System

Prof. K. Sivapalan

Autonomic Nervous System 2

Comparison Somatic NS

• Voluntary

• External sensory and motor

• Motor- 1 neuron

• Sensory in dorsal horn, motor in ventral horn

Autonomic NS

• Involuntary

• Internal sensory and motor

• Motor- 2 neurons

• Sensory in dorsal part of lateral horn, Motor in ventral part of lateral horn.

May 2013

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Divisions of ANSSympathetic

• Thoraco-lumbar outflow - T1 to L2

• Short preganglionic

• Preganglionic ending- acetyl choline

• Post ganglionic- noradrenalin, others in some areas

• Fight or flight - catabolic

Parasympathetic

• Cranio-sacral outflow – 3,7,9,10 and S-2,3,4

• Long preganglionic

• Preganglionic ending- acetyl choline

• Post ganglionic- acetyl choline, others in some areas

• Anabolic

May 2013

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General Facts

• Most organs- dual innervation with opposing effects

• Exceptions- blood vessels, reproductive function

• Preganglionic- myelinated [white rami]

• Postganglionic- nonmyelinated [gray rami]

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Receptors

• Any cell responds to chemical substances only if they bind with a receptor.

• The chemical may be a neuro-transmitter or a hormone

• The receptor may be located on the cell membrane, in the cytoplasm or in the nucleus

• Substances that bind to receptors in side the cell will have to go through the cell membrane

• Most of the receptors are located on the outer surface of the cell membrane and also to effector molecules in the membrane or in the interior of the cell.

• They sometimes act directly and some times through second messangers

May 2013

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Receptors for Neurotransmitters

• Chemicals released from the nerve endings are called neuritransmitters

• They generally increase or decrease permeability of specific ions by acting on the ligand gated channels

• Alteration of sodium or potassium permiability will depolarize or hyperpolarize the membrane.

• Alteration of calcium permiability may, in addition, bring about change in the action directly

• Another mechanism is being linked to an enzyme such as adenylyl cyclase leading to formation of cAMP.

• The action of autonomic nerves on the effector organs depends on the transmitter and more importantly on the type of receptor and its associated mechanisms

May 2013

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Acetyl Choline Receptors

• Structure-

• Nicotinic and muscarinic receptors

• Muscarine is a poison from toadstool [a fungus]

• Muscarinic receptors are found in effectors innervated by post ganglionic cholinergic endings

• Nicotinic receptors are found in autonomic ganglia and in motor end plates

May 2013

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Adrenergic Receptors

• Noradrenaline [norepinephrine] and adrenaline [epinephrine] are known as catecholamines.

• The receptors are categorised into alpha [α] and beta [β]. Each one is further subdivided into 1 and 2. The classification is based on the specific substances that stimulate and inhibit the functions.

• Noradrenaline excites mainly α receptors and to a lessor extent on β receptors.

• Adrenaline acts on both receptors equally.

May 2013