pineal gland and thalamus ppt from sensory chapter of anatomy

pineal gland and thalamus wonderful ppt from bd chaurasia

1. Submitted To: Submitted By: Studymafia.org Studymafia.org Pineal Gland and Thalamus

2. Table Contents Pineal gland • Structure • Functions • Melatonin & Functions Thalamus • Introduction • Physiology • Neurobiochemistry • Thalamus Infarctions and Syndromes ‹#›

3. Pineal Gland SITUATION AND STRUCTURE • Pineal gland or epiphysis is located in the diencephalic area of brain above the hypothalamus. • It is a small coneshaped structure with a length of about (5 mm × 7 mm). Pineal gland has two types of cells: 1. Large epithelial cells called parenchymal cells 2. Neuroglial cells. • In adults, the pineal gland is calcified. But, the epithelial cells exist and secrete the hormonal substance. ‹#›

4. Pineal Gland ‹#›

5. Structure of Pineal Gland The pineal stroma has two types of cells: neuroglial and parenchymal. Parenchymal cells are large epithelial cells with features suggesting that they have a secretory function. In infants, the pineal gland is large and the cells tend to be arranged in alveoli. In adults, the pineal gland gets calcified, i.e. small concretions of calcium phosphate and carbonate (pineal sand) appear in the tissue. ‹#›

6. Function Pineal gland has two functions: 1. It controls the sexual activities in animals by regulating the seasonal fertility. However, the pineal gland plays little role in regulating the sexual functions in human being 2. It secretes the hormone substance called melatonin. ‹#›

7. Melatonin Source of secretion • Melatonin is secreted by the parenchymal cells of pineal gland. Chemistry • Melatonin is an indole (N-acetyl -5-methoxy tryptamine). Actions of melatonin • Melatonin acts mainly on gonads. Its action differs from species to species. In some animals, it stimulates the gonads while in other animals, it inhibits the gonads. ‹#›

8. Melatonin • In humans, it inhibits the onset of puberty by inhibiting the gonads. The average plasma levels of melatonin at various age groups are: • 1–3 years of age: 250 pg/mL • 8–15 years of age: 120 pg/mL • 20–27 years of age: 70 pg/mL • 67–84 years of age: 30 pg/mL ‹#›

9. Functions of Melatonin 1. Role in circadian rhythm of the body. The dark-light cycle through suprachiasmatic nuclei of hypothalamus initiate neural and humoral signals that entrain a wide variety of well known circadian rhythms including diurnal variation in melatonin secretion. ‹#›

10. Functions of Melatonin 2. Effects on the gonads: Both inhibitory and facilitatory effects of melatonin on the gonads. 3. Effect on melanocyte-stimulating hormone (MSH) and adrenocorticotropic hormone (ACTH) secretion. • An inhibitory effect has been reported. 4. induction of sleep and inhibition of puberty. ‹#›

11. Regulation of melatonin secretion Melatonin secretion shows diurnal variation. • It is secreted more during dark period of the day than during the day light hours. • This correlates with various internal activities in different periods of the day, i.e. circadian rhythm. • Hypothalamus is responsible for circadian fluctuations of melatonin secretion. • Hypothalamus exerts its effect through the norepinephrine secreted by post-ganglionic sympathetic nerves (nervi conari) that innervate the pineal gland. ‹#›

12. Primary Divisions of the Brain ‹#›

13. Thalamus Largest component of the diencephalon. Paired symmetrical structure in the brain, perched on top of the brainstem Near the center of the brain, located obliquely (about 30°) and symmetrically on each side of the third ventricle Both parts of this structure are each about the size and shape of a walnut. ‹#›

14. Thalamus: Location and Relation Thalamus lies medially in the cerebrum. bounded medially by III venticle laterally by internal capsule and basal ganglia ventrally continuous with subthalamus. ‹#›

15. Thalamus Physiology Primarily - a relay station that modulates and coordinates the function of various systems Locus for integration, modulation, and intercommunication between various systems Has important motor, sensory, arousal, memory, behavioral, limbic, and cognitive functions The largest source of afferent fibers to thalamus is cerebral cortex and cortex is the primary destination for projection fibres from the Thalamus ‹#›

16. Neurobiochemistry of Thalamus Neurotransmitters identified in the thalamus: GABA is the inhibitory neurotransmitter in Afferent terminals from the GP and in local circuit neurons, and in efferent projections of the reticular nucleus and lateral geniculate nucleus; and Glutamate and aspartate are the excitatory neurotransmitters in corticothalamic and cerebellar terminals and in thalamocortical projection neurons. ‹#›

17. Thalamic Infarcts and Syndromes The conglomerate of signs and symptoms associated with thalamic lesions includes the following: sensory disturbances, thalamic pain, hemiparesis, dyskinesias, disturbances of consciousness, memory disturbances, affective disturbances, and disorders of language Most thalamic infarcts are reported in the posterolateral and the medial thalamic territories supplied by the geniculothalamic and paramedian arteries, respectively ‹#›

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