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  1. Biting mechanism of Snakes Dr. Nidhi Tripathi
  2. • Most of the Indian snakes are non-poisonous and harmless creatures. • Of 330 Indian species only 69 are poisonous comprising 29 species of sea snakes and 40 species of land snakes. • In which only 4 are deadliest- cobra, kraits, viper & sea snake. • Poisonous snake have a poison apparatus in head and a pair of larger teeth or fangs in upper jaw. • When they bite, there may be two large circular punctures made by the fangs on the skin of the victim. • But non-poisonous snakes have neither poison apparatus nor fangs. When they bite, they leave many small pricks only.
  3. key to identify poisonous & non- poisonous snakes of India
  4. • Poison apparatus of snakes consist toxic substance which is considered as poison or venom. • The poison and venom both substances are toxic in nature but the difference are;  Poison- its origin may be plant or animal. If the plants and animals produce toxic reaction after eating them than the plants and animals supposed to be poisonous.  Venom- it has animal origin. there should be presence of some poison apparatus and hypodermal needle. When substance injected into the body of enemy or victim by those animals having poisonous apparatus it is called venomous.
  5. Poison Apparatus • All the poisonous snakes have poison apparatus in their heads, which is not found in non-poisonous snakes. This apparatus includes: (i) a pair of poison glands (ii) poison ducts (iii) fangs (iv) muscles
  6. Poison glands • Two sac-like poison glands are situated one on either inner side of the upper jaw, below the eyes and somewhat behind them. • Poison glands are modified superior labial or parotid gland (modified salivary gland). • Size and shape of poison glands is varied depending upon species, these are small and oval in sea snakes and large and tubular in vipers.
  7. • Poison gland is held in position with the help of ligaments. Anterior ligament attaches anterior end of the gland with maxilla and the posterior ligament attaches the gland to the quadrate. • Each gland is thickly encapsulated with fibrous connective tissue and mostly covered by a fan- shaped constrictor muscle also called as temporal or masseter muscle. • Stretching of muscles during biting squeezes poison from gland into its duct.
  8. Poison ducts • A narrow poison duct leads anteriorly from each poison gland to the base of a poison fang to enter its groove or canal.
  9. Fangs • Fangs are certain specialized teeth attached to maxillary bones. • They are long, curved, sharp and pointed. • They serve as hypodermic needles for injecting poison into the body of victim. • When a functional fang is lost or damaged, it is replaced by one of the reserved fang. • On the basis of structure and position 3 types of fangs occur in poisonous snakes: (a) Solenoglyphous (b) Proteroglyphous (c) Opisthoglyphous
  10. Different types of fangs
  11. Solenglyphous fang: • A hollow poison canal, lined with enamel runs through the fang opening at the tip (solen, pipe + glyph, hollowed) • In vipers and rattle snakes, this single large functional fang occurs on the front of each maxilla. • Its base is covered on all sides by a sheath containing a few reserve and developing fangs. • The fangs are movable and turned inside to lie close to the roof of mouth when it is closed.
  12. • Proteroglyphous fang: in cobras, kraits coral snakes and sea snake, fangs are small, at the front of maxillae and permanently erect. • Each fang is grooved all along its anterior face (protero, first). • Opisthoglyphous fang: in some poisonous snakes, in family colubridae, fangs are small, lie at the back of maxillae and each grooved along its posterior border (opistho, behind)
  13. Muscles • There are 4 muscles involved in the biting mechanism. 1. Digestric muscles- its contraction, open the mouth. 2. Sphenopterygoid muscles- contraction result in forward movement of pterygoid and up-pushing of the ectopterygoid 3. Constrictor muscles- its stretching cause squeezing the poison gland. 4. Temporal muscles- its contraction, mouth closed
  14. Skull of a viper showing biting mechanism
  15. Biting mechanism • The skull and jaw bones of poisonous snakes are very flexible. • They are loosely or movably articulated thus allowing a considerable degree of adjustment during the act of swallowing or striking. • In cobras, the fangs are permanently erect. • But in vipers, the large fangs lie against the roof of mouth when closed. Therefore, mechanism for biting serves two main purposes- (1) erection of fangs and (2) injection of poison into the victim’s body.
  16. • The mechanism of biting is a complicated process and the sequences of biting may be discussed in these successive steps. 1. When a viper wants to strike, a series of movements occur in a chain. Contraction of digastric muscles lower the mandible so that mouth open. 2. As mouth opens and lower end of quadrate thrusts forward. This in turn, pushes forward the pterygoid. Now the sphenopterygoid muscles contract. This contraction results in the forward movement of pterygoid and up- pushing of the ectopterygoid.
  17. 3. The upward movement of the ectopterygoid brings about a rotation of the maxilla on its own axis round the lacrimal and as the end result the fang is raised and comes to its striking position . 4. A simultaneous stretching of constrictor muscles around the poison gland, forces its poison through poison duct into the canal or groove of fang to be injected into the victim. 5. When mouth is closed by the contraction of temporal muscles, the above movements are reversed. The fangs embed in the prey which is drawn into the mouth. At the same time the vertical fangs rotate to become horizontal.
  18. Venom and Antivenom • Venom is a clear sticky liquid of faint yellow or greenish colour. • It is tasteless and odourless and acidic in reaction. • It is a complex mixture of enzymes and specific toxins and is a good digestive juice. • It is fatal only when mixed with blood. • It can be swallowed and if there is no scratch in mouth or alimentary tract, it will pass out with faeces without doing any harm. • In laboratory it can be precipitated in reagent such as silver nitrate and potassium permagnate.
  19. • It can also be dried and kept indefinitely, retaining its poisonous properties. • Dried poison or crystals of poison can be dissolved in water, salt solution or glycerine, it will be equally poisonous. • Snake venom is secreted by poison gland, found in the head of snake. And injected in victim or bitten prey body by fangs, serving as hypodermic needle. • Venom has evolved in snakes as an aid to capturing and subduing prey. • Snake biting is certainly in most of the cases, is just an accident.
  20. • Snake venom is of 2 type- neurotoxin and haemotoxin. • Most snake venom consist both, but one of them may be predominant. • The venom of different snakes has its own characteristic effect. • Degree of virulence differs not only in different snakes but in the same snake under different circumstances. • The bitten person may die or recover depending upon the amount injected and its virulence.
  21. Haemotoxin • The venom of viper is Haemotoxic, it contains an endotheliotoxin (haemorrhagin) which damages the capillary endothelium and produces haemorrhages in various tissue. • Endotheliotoxin also produce some toxin which leads to failure of peripheral circulation with marked fall in blood pressure by paralysing the neuromuscular junction of vasoconstractor muscles.
  22. • Viper venom also contain a thromboidnase which causes intravascular clotting, if it happens to enter directly into the vein during the bite. • It also contains an enzyme an enzyme which help in formation of lysocythin which cause extensive local damage. • A cardiotoxin is also found in viper’s venom, which cause damage to heart. • Proteases cause local inflammation, necrosis and damage to vascular epithelium. • In general the venom of vipers act principally on the vascular system. • A class of enzymes Hyabronidases help in rapid absorption of venom.
  23. Neurotoxin • Venom of cobra, krait and sea snakes is neurotoxin type. • They cause death by paralysis of respiratory muscles and asphyxiation. • Neurotoxin (venom) attack CNS, the nerve centers and causing paralysis of muscles, especially those of respiratory muscles. • Due to neurotoxin coagulation of blood is reduced causing excessive bleeding. • Death occurs due to asphyxia as respiratory centers of brain are destroyed.
  24. Antivenom/Antivenin • The best cure for snake bite is an antivenom serum or antivenin, which is injected into the body of the victim to counteract snake venom. • Different antivenins are required against different snakes due to differences in the qualities of their venoms. • An antivenin is prepared by injecting a horse with gradually increasing dose of a snake venom until the horse becomes fully immunized to any amount of venom injected. • Now blood serum of horse is collected and preserved. • This is antivenom serum or antivenin which has developed sufficient antibodies to neutralize the effect of that particular snake venom.