REGULATION OF SALIVARY SECRETION

REGULATION OF SALIVARY SECRETION

Salivary secretion is regulated only by nervous mechanism. Autonomic nervous system is involved in the regulation of salivary secretion.

NERVE SUPPLY TO SALIVARY GLANDS

Salivary glands are supplied by both parasympathetic and sympathetic divisions of autonomic nervous system.

PARASYMPATHETIC FIBERS

Parasympathetic Fibers to Submandibular and Sublingual Glands

Parasympathetic preganglionic fibers to submandibular and sublingual glands arise from the superior salivatory nucleus, situated in pons. After taking origin from this nucleus, the preganglionic fibers run through nervus intermedius of Wrisberg, geniculate ganglion, the motor fibers of facial nerve, chorda tympani branch of facial nerve and lingual branch of trigeminal nerve and finally reach the submaxillary ganglion . Postganglionic fibers arising from this ganglion supply the submaxillary and sublingual glands.

Parasympathetic Fibers to Parotid Gland

Parasympathetic preganglionic fibers to parotid gland arise from inferior salivatory nucleus situated in the

upper part of medulla oblongata. From here, the fibers pass through the tympanic branch of glossopharyngeal nerve, tympanic plexus and lesser petrosal nerve and end in otic ganglion.

Postganglionic fibers arise from this ganglion and supply the parotid gland by passing through auriculotemporal branch in mandibular division of trigeminal nerve.

Function of Parasympathetic Fibers

Stimulation of parasympathetic fibers of salivary gland causes secretion of saliva with large quantity of water. It is because the parasympathetic fibers activate the acinar cells and dilate the blood vessels of salivary glands. However, the amount of organic constituents in saliva is less. The neurotransmitter is acetylcholine.

SYMPATHETIC FIBERS

Sympathetic preganglionic fibers to salivary glands arise from the lateral horns of first and second thoracic segments of spinal cord. The fibers leave the cord through the anterior nerve roots and end in superior cervical ganglion of the sympathetic chain.Postganglionic fibers arise from this ganglion and

are distributed to the salivary glands along the nerve plexus, around the arteries supplying the glands.

Function of Sympathetic Fibers

Stimulation of sympathetic fibers causes secretion of saliva, which is thick and rich in organic constituents such as mucus. It is because, these fibers activate the acinar cells and cause vasoconstriction. The neurotransmitter is noradrenaline.

REFLEX REGULATION OF SALIVARY SECRETION

Salivary secretion is regulated by nervous mechanism through reflex action.

Salivary reflexes are of two types:

1. Unconditioned reflex.

2. Conditioned reflex.

1. Unconditioned Reflex

Unconditioned reflex is the inborn reflex that is present since birth. It does not need any previous experience. This reflex induces salivary secretion when any substance is placed in the mouth. It is due to

the stimulation of nerve endings in the mucus membrane of the oral cavity.

2. Conditioned Reflex

Conditioned reflex is the one that is acquired by experience and it needs previous experience. Presence of food in the mouth is not necessary to elicit this reflex. The stimuli for this reflex are the sight, smell, hearing or thought of food.

 

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