Pain sensation Pain receptors are also called as nociceptors They are located at the ends of small 'C unmyelinated or myelinated A delta fibers a) Definition Pain sensation is unpleasant but protective sensation aroused by noxious stimuli that damage or can damage body tissues b) Physiology (properties & reaction) Purpose or importance: Protective Stimulus: noxious (chemicals like- Ach, bradykinin, serotonin, hydrogen ions, potassium ions, prostaglandins or mechanical or thermal) Receptors: free nerve endings (polymodal receptors) Adaptation : non or slow adapting receptors Nerve fibers: fast pain is carried by A-delta nerve fibers while slow pain by 'C' type. Neurotransmitters: glutamic acid (at spinal cord) for fast pain, substance P (at spinal cord) for slow pain and Lewis P factor for muscle pain, Pathway: lateral spinothalamic (specific neo spinothalamic for fast pain and diffuse and non specific paleo spinothalamic for slow pain) Reaction : pain is a
The pineal gland is a small, pea-shaped gland in the brain. It produces and regulates hormone melatnoni.
It is known from comparative anatomy that the pineal gland is a vestigial remnant of what was a third eye located high in the back of the head in some lower animals
Functions of Pineal gland
Pineal gland is believed to have role in the following functions.
(1) enhancing sex,
(2) staving off (preventing) infection,
(3) promoting sleep,
(4) enhancing mood, and
(5) increasing longevity (as much as 10 to 25 percent)
MELATONIN & CIRCADIAN RHYTHMS
Pineal pinealocytes contain melatonin and the enzymes responsible for its synthesis from serotonin, and they secrete the hormone into the blood and the cerebrospinal fluid
Secretion of melatonin
The cyclic activity of the suprachiasmatic nucleus (SCN) sets up a circadian rhythm for melatonin release. This rhythm is entrained to light/dark cycles by neurons in the retina. Light signals are relayed via the retinohypothalamic (RHT) fibers to the SCN. GABAergic neurons in the SCN inhibit neurons in the hypothalamic paraventricular nucleus (PVN) which then reduces the activities of intermediolateral nucleus (IML) and superior cervical ganglion (SCG) that regulate release of melatonin from the pineal gland
Role of Melatonin
Activation of melatonin receptors results in sleepiness and may function to synchronize the light-dark cycle. The diurnal change in melatonin secretion may function as a timing signal to coordinate events with the light-dark cycle in the environment. Melatonin synthesis and secretion are increased during the dark period of the day and maintained at a low level during daylight hours
Diurnal rhythms of compounds involved in melatonin synthesis in the pineal
Melatonin and the enzymes responsible for its synthesis from serotonin are found in pineal pinealocytes; melatonin is secreted into the bloodstream. Melatonin synthesis and secretion are increased during the dark period (shaded area) and maintained at a low level during the light period
Insomnia & Circadian Rhythm Disturbances of the Sleep-Wake State
Insomnia is defined as difficulty in initiating and/or maintaining sleep several times a week Individuals with persistent episodes of insomnia are more likely to experience accidents, a diminished work experience, and a poorer overall quality of life. Insomnia is often comorbid with depression
There are two major types of sleep disorders associated with disruption of the circadian rhythm. These are transient sleep disorders (jet lag, altered sleep cycle because of shift work, and illness) and chronic sleep disorders (delayed or advanced sleep phase syndrome),
Those with delayed sleep phase syndrome have the inability to fall asleep in the evenings and awaken in the mornings. However, they have a normal total sleep time. Those with advanced sleep phase syndrome consistently fall asleep in early evening and awaken in early morning. This is seen most often in the elderly and the depressed.
THERAPEUTIC HIGHLIGHTS
Light therapy is an effective treatment in individuals who experience disturbances in their circadian cycle. Melatonin can be used to treat jet lag and insomnia in elderly individuals Ramelteon is a MT1 and MT2 melatonin receptor agonist that is more effective than melatonin in treating insomnia.
Sexual drive and Reproduction
Many physiologists believe that this gland is a nonfunctional remnant, but others have claimed that it plays important roles in the control of sexual activities and reproduction Now, it appears that the pineal gland does indeed play a regulatory role in sexual and reproductive function in animals
It is not known if the pineal gland have a similar function for control of reproduction in humans Some of the tumors occuring in the region secrete excessive quantities of pineal hormones, whereas others are tumors of surrounding tissue and press on the pineal gland to destroy it. Both types of tumors are often associated with hypogonadal or hypergonadal function, so perhaps the pineal gland does play at least some role in controlling sexual drive and reproduction in humans.
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