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Physiology

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Central Nervous System

Question
8 out of 23
 

Exposure to darkness leads to increased melatonin secretion. It is brought about by:



A Decreasing the activity of suprachiasmatic nuclei

B Increasing the serotonin N-acetyl transferase

C Decreasing the hydroxy-indole-O-methyl transferase activity

D Blocking the release of norepinephrine from sympathetic nerve terminals

Ans. B Increasing the serotonin N-acetyl transferase

I. First Lets see the synthesis of melatonin from sertonin

a. Serotonin

b. N. Acetyl transferase + Acetyl CoA

c. N-Acetyl serotonin

d. J, Hydroxy indole – O- methyl transferase + S-Adenosylmethionine

e. Melatonin (N -acetyl- 5-methoxytryptamine)

II. ReguIation of Melatonin Secretion

a. In humans and all other species studied to date, melatonin synthesis and secretion are increased during the dark period of the day and maintained at a low level during the day-light hours. The remarkable diurnal variation in secretion is brought about by training of the hypothalamus to the light-dark cycle via retino-hypothalmic nerves

b. The hypothalamus in turn cause norepinephrine secretion by the postganglionic sympathetic nerves (nervi conari) that innervate the pineal gland.

c. The norepinephrine acts via adrenergic receptors in the pineal gland to increase interacellular cAMP, and the cAMP in turn produced a marked increase in N-acetyl transferase activity. This results in increased melatonin synthesis and secretion.

Exposure to darkness

Retinohypothalamic fibers

supra chiasmatic nuclei in hypothalamus

Preganglionic sympathetic neurons in spinal cord

Postganglionic sympathetic nerves (nervi conarii) arising in superior cervical ganglion

norepinephrine secretion in pineal gland

intracellular cAMP

N-Acetyltransferase activity

Hydroxyindole- O methyl transferase activity

Melatonin

Central Nervous System Flashcard List

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