NEET BIOLOGY BY SHASHI SIR

  Neurotransmitters are chemical messengers that transmit a message from a nerve cell across the synapse to a target cell. The target can be another nerve cell, or a muscle cell, or a gland cell. They are chemicals made by the nerve cell specifically to transmit the message. Discovery Until the early 20th century, scientists assumed that the majority of synaptic communication in the brain was electrical. However, through histological examinations by Ramón y Cajal, a 20 to 40 nm gap between neurons, known today as the synaptic cleft, was discovered. The presence of such a gap suggested communication via chemical messengers traversing the synaptic cleft, and in 1921 German pharmacologist Otto Loewi confirmed that neurons can communicate by releasing chemicals. Through a series of experiments involving the vagus nerves of frogs, Loewi was able to manually slow the heart rate of frogs by controlling the amount of saline solution present around the vagus nerve. Upon completion of this expe

  Nephrons  Each kidney has nearly one million complex tubular structures called nephrons (Figure 19.3), which are the functional units. Each nephron has two parts – the glomerulus and the renal tubule. Glomerulus is a tuft of capillaries formed bythe afferent arteriole – a fine branch of renal artery. Blood from the glomerulus is carried away by an efferent arteriole   The nephridium (plural nephridia) is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidney. Nephridia remove metabolic wastes from an animal's body. In addition to two basic categories ( metanephridia and protonephridia ), other types may exist. Metanephridia A metanephridium (meta = "after") is a type of excretory gland found in many types of invertebrates such as annelids, arthropods and mollusca. (In mollusca, it is known as the Bojanus organ.) A metanephridium typically consists of a ciliated funnel opening into the body cavity, or coelom connected to a duct

  * Biosphere reserves in bold are part of World Network of Biosphere Reserves Sl. No Year Name State Type Key Fauna 1 2008 Great Rann of Kutch Gujarat Desert Indian Wild Ass 2 1989 Gulf of Mannar Tamil Nadu Coasts Dugong or Sea Cow 3 1989 Sundarbans West Bengal Gangetic Delta Royal Bengal Tiger 4 2009 Cold Desert Himachal Pradesh Western Himalayas Snow Leopard 5 1988 Nanda Devi Uttarakhand Western Himalayas NA 6 1986 Nilgiri Biosphere Reserve Tamil Nadu, Kerala and Karnataka Western Ghats Nilgiri Tahr, Lion-tailed macaque 7 1998 Dihang-Dibang Arunachal Pradesh Eastern Himalaya NA 8 1999 Pachmarhi Biosphere Reserve Madhya Pradesh Semi-Arid Giant Squirrel, Flying Squirre l 9 2010 Seshachalam Hills Andhra Pradesh Eastern Ghats NA 10 1994 Simlipal Odisha Deccan Peninsula Gaur, Royal Bengal Tiger, Wild elephant 11 2005 Achanakamar -Amarkantak Madhya Pradesh, Chhattisgarh Maikala Hills NA 12 1989 Manas Assam East Himalayas Golden Langur, Red Panda 13 2000 Khangchendzonga Sikkim East Himalay