Pineal gland

The pineal gland is attached to the roof of the third ventricle, and lies outside the blood-brain barrier. It weighs 100-150 mg and has a length of about 9 mm. It is a homologue of the third or parietal eye of the lower vertebrates. The pineal starts to involute just prior to puberty. The gland consists of neurons, neuroglial cells and pinealocytes, which secrete melatonin into the CSF.

The environmental light-dark cycle and autonomic circadial stimulation by the suprachiasmatic nuclei of the hypothalamus (the endogenous circadian oscillator) modulate the secretion of melatonin by the pineal (which takes place in the dark phase of the cycle). This contributes to the maintenance of biological rhythms.

Melatonin is derived from circulating L-tryptophan. It is not stored in the pineal. There is a gradual increase in levels of melatonin at night and a reduction in the morning of serum melatonin levels. Melatonin can induce a phase shift in the circadian oscillation of activity of the suprachiasmatic nuclei. This may help in the amelioration of the symptoms of jet lag.

The thalamus is a paired grey matter mass situated deeply in the forebrain. ?

The functions of the thalamus include: a i

Integration modification and relay of motor and sensory (apart from olfactory) |'

inputs to the cerebral cortex; Awareness of nociceptive stimuli in non-discriminative form; Control of subjective responses to sensation;

Activation and arousal: processes information that influences electro-cortical activity in the sleep-wake cycle through the ascending reticular activating system;

Modification of the affective component of behaviour upon limbic system communications. The thalamus comprises several groups of relay nuclei: Ventral Medial Lateral Intralaminar Midline

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