Biting mechanism of snake

A short note on Biting mechanism of snake:-

The skull and jaw bones of poisonous snakes are very flexible. They are loosely 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. Thus the mechanism of biting serves two main purposes-
a. Erection of fangs and
b. Injection of poison into victim’s body
During a strike a series of movements occur in chain. Contraction of diagastric muscles lowers the mandibles so that mouth opens and lower end of quadrate thrusts forward. This in turn pushes the pterygoid forward. The forward pull of pterygoid in turn pushes the ectopterygoid upwards. This causes the maxilla bearing fangs to rotate through 900. As a result fangs become vertically erect and in the most effective position to strike. A simultaneous stretching of constrictor muscles around the poison gland forces its poison through poison duct into the canal of fang to be injected into the victim. When mouth is closed by the contraction of temporal muscles, the above movements are reversed. The fangs embed in the prey which is drawn in the mouth. At the same time the vertical fangs rotate to become horizontal.

Detailed note:- 

The skull and jaw bones in poisonous snakes are loosely and movably articulated, thus, allowing an enormous gape and swallowing whole of large prey. In cobras fangs are small and remain permanently erect, but in vipers the fangs are large and curved and lie against the root of mouth cavity when closed. Premaxilla, usually toothless and the bones of the upper jaw are loosely attached to rest of the skull. Quadrate jointed to the squamosal.

There are movable joints between the frontals behind and prefrontals and nasals in front and also between several other bones of brain case, palate and jaws. These joints have loose ligaments and allow movement in several directions and so permit a huge gap. The two halves of the lower jaw are connected together by elastic ligamentous tissue. So they are capable of being widely separated from one another.

The mechanism of biting is a complicated process and it can be described in the following four steps:

(i) Opening of the Mouth:

By the contraction of digastric muscles the mouth is opened (lower jaw moves down).

(ii) Rotation of Maxilla:

As the mouth opens the lower jaw moves down and the lower end of quadrate moves forward. Quadrate and squamosal are very movable. The pterygoid is movably attached to the palatine. Quadrate pushes the pterygoid forward and the pterygo-palatine joint bent.

This forward movement of the pterygoid is conveyed by the transpalatine bone to the maxilla and causes it to rotate through about 90° upon its prefrontal articulation in such a way that the surface to which the fang is attached is carried forwards and ventralwards, and the fang is erected, i.e., is made to project downwards at the front end of the mouth. The contraction of sphenopterygoid muscles also helps in the movement of pterygoid forward.

(iii) Closing of Mouth:

The closing of the mouth is brought about by the contraction of the temporalis and sphenopterygoid muscles. The point of fang is directed backward while the mouth is closed. It takes longer time to open the mouth than to close it.

(iv) Transference of Venom:

During the contraction of the digastric muscle the posterior ligament is relaxed and during the rotation of the squamosal bone the fan-shaped ligaments are stretched to squeeze the wall of the poison gland. This makes the poison to come out of the poison gland through the poison duct and the fang.

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Poisonous apparatus in snakes

Poison apparatus includes- 

               a. A pair of poison gland
               b. Their ducts
               c. Fangs and
               d. Muscles

a. Poison gland

Two sac-like poison glands are situated one on either innerside of the upper jaw, below the eye. These are possibly modified superior labial or parotid glands. The glands may be small and oval (sea snakes) or large and tubular (vipers). Each gland is covered by fan shaped constrictor muscle, often referred to as temporal. It’s stretching during biting squeezes poison from gland into its duct.

b. Poison duct
A narrow poison duct leads anteriorly from each poison gland to the base of a poison fang to enter its groove or canal.

c. Fangs
Fangs are certain specialized teeth attached to maxillary bones. They are long curved, sharp and pointed. They serve for injecting poison into the body of victim. When a functional fang is lost, it is replaced by one of the reserved fangs. On the basis of structure and position 3 types of fangs occur in poisonous snakes: Solenoglyphous, Proteroglyphous and Opisthoglyphous.

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DNA fingerprinting

A short idea about DNA fingerprinting

DNA profiling or DNA fingerprinting is a sophisticated technique which is used often by experts which are helpful in identification of individuals by their respective DNA profiles.

Some interesting salient features of DNA fingerprinting are:

• DNA fingerprinting is a technique to identify a person based on his/her DNA.
• DNA fingerprinting is specific to a person and it cannot be changed by any treatment.
• It is also known as genetic fingerprinting or DNA profiling.
• DNA fingerprinting is a very quick way to compare the DNA sequence of two living organisms.
• Sir Alec Jeffrey (1984) invented the technique of DNA fingerprinting.
• 99.9 per cent DNA is identical between individuals, but 0.1 per cent that differs can be used to distinguish one individual from another.
• DNA fingerprinting uses a specific type of DNA sequence, known as microsatellite.
• Microsatellites are short pieces of DNA, which repeat many times in a given person’s DNA.
• In a given area, microsatellites tend to be highly variable that make them ideal for DNA fingerprinting.
• In a given area, microsatellites tend to highly variable that make them ideal for DNAfingerprinting.
• By comparing a number of microsatellites in a particular area, a person can be identified easily.

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AIDS

Acquired Immuno Deficiency Syndrome (AIDS): An Overview

AIDS stands for Acquired Immuno Deficiency Syndrome, first described in 1981. AIDS is the result of damage of the immune system. A damaged immune system is unable to protect the body against certain specific, ‘opportunistic’ infections and tumours. These are called opportunistic because they are caused by organisms which are normally controlled by the immune system but which take the opportunity to cause disease if the immune system has been damaged.
AIDS patients are sensitive to opportunistic infection by agents like viruses, bacteria, fungi and protozoans. AIDS victims also suffer a high frequency of some type of cancer especially lymphomas and Kaposis sarcoma.
AIDS is caused by a retrovirus (human immuno deficiency virus or HIV) was first described by Robert Gallo and Luc Montagnier in 1983.
HIV stands for Human Immuno Deficiency Virus. It belongs to a group of viruses, called retroviruses. Viruses copy their genetic material into the genetic material of human cells.
Through mechanisms which are not still fully understood, HIV prevents the immune system from working properly. Normally the body’s immune system would fight off infection. But HIV is able to infect cells (called CD4 cells) which coordinate the immune system’s fight against infection. Many are actually destroyed by being infected, others, including CD4 cells which are not themselves infected, no, longer work properly. HIV infects principally a specific type of lymphocytes, the T4 lymphocytes, which is required for a normal immune response.

Structure of HIV: HIV is an encapsulated circular virus having an average diameter of 90-120 nm (nanometer). In the centre of the capsule there is a single stranded RNA as genome and core proteins. The enzyme reverse transcriptase remains associated with the genomic RNA. With the help of this enzyme the RNA replicated and transformed into DNA genome (single stranded) and then into double stranded DNA. This stage is called provirus. Provirus may remain in an inactive form for a long time. RNA is synthesized from the provirus with the activity of viral promoter gene. The core of the virus remains covered with nuceo-caspid shell. When the naked virus comes in contact with the outer covering of the host cell membrane bilayered lipoprotein membrane is developed. This lipoprotein is synthesized from the lipid layer of the host cell but the glycoprotein is made by the viral gene codes. A portion of this protein is spike cell. The extended portion is called pedicles. The spikes make the infrastructure of the virus and binds with the CD-4 receptor of the host.

Stages of HIV infection:

Cell tropism: The receptor antigen of viral spike protein is CD4. So the virus can attack and infest those cells having CD4. T-4 is commonly infected by the virus due to presence of CD4 in T-lymphocytes. B-lymphocytes possess 5-10 %, Monocyte 10-20 % CD4, therefore, they are also attacked by the virus.

Pathogenesis: HIV enters into the blood or any tissue and attacks the T-4 lymphocytes. The pathogen can enter through blood transfusion and sexual mating. After enter into the host nucleus the viral genome may remain in a dormant state for a number of years or infect the cell. HIV usually destroys the T-4 cells. The infected T-4, then cannot secretes interleukin 2 gamma interferon or other lymphokines. As a result, the cells losses their immunity.
AIDS infected patients do not give responses to any other antigen. On the other hand, hypergamma globulineaemia can be developed due to polyclonal activation of B-lymphocyte. This increases the rate of IgG and IhA level. In this way the HIV destroys the humoral sanctity. Since T-lymphocyte cannot secrete the active secretory substances. So, the macrophage cannot destroy antigen anymore. Therefore, the immune response is totally destroyed.

Stages of HIV infection:

Becoming HIV antibody positive: Most people who become infected with HIV do not immediately notice that they have been infected. Some have a short illness soon after they become infected. This is called ‘seroconservation illness’, because it coincides with the time that blood testes for HIV antibodies will become positive. The illness may take the form of sore throat, a fever or a rash, or rarely more severe illness.

Asymptomatic HIV infection: Initially any damage caused by HIV has not outward effect. This is called asymptomatic infection, which may last for many months or years. Sometimes, people with asymptomatic HIV infection may have swollen lymph nodes, which is called PGL (persistent generalized lymphadenopathy).

Symptomatic HIV infection: Statistical studies of people with HIV have shown that more time passes, the, more likely it is than the damage will become more severe and opportunistic infections or tumors may develop.
HIV can also have direct effects upon the body. For instance, the virus can also attack immune cells in the brain. In such case, the brain or nervous system may not work properly. This is called HIV associated dementia. If people become ill because of these infections or tumours, they are said to have symptomatic HIV infection.

AIDS:
The last stage of HIV infection is the development of AIDS. AIDS completely destroys the immune system of the infected person. This may lead to various diseases. AIDS damage the following systems of man.

(i) Respiratory system: AIDS patients suffer from dry cough, and fever. The patients may be secondarily infected by tuberculosis bacteria.
(ii) Gastro-intestinal disorders: AIDS patients suffer from various types of gastro-intestinal problems.
(iii) Central nervous system: AIDS infected patients may be infected by toxoplasmosis, cryptococcosis. Patients may develop cerebral lymphonoma.
(iv) Malignancies: AIDS patients may become the victim of many types of cancers.
(v) Dementia: HIV may destroy the brain cells, thereby, leading to dementia.
(vi) Infection among newborn: HIV infected mother usually produce HIV infected babies. Among the born babies, 50 % gets infected and usually dies within one year. Children may get the HIV from the transfusion of blood.

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Classification of Phylum Nematoda according to Ruppert & Barnes(1994)

Classification of Phylum Nematoda according to Ruppert &

Barnes(1994)

Phylum :- Nematoda

Characters :-

(i) They have perfectly cylindrical body adapted for living in minutes place.

(ii) Body cavity is pseudocoel, Cuticle thick & tough.

(iii) Circular muscle is absent, longitudinal muscles in 4 groups.

(iv) Anterior end bear sense organ amphid & posterior phasmid present. 

Class :- Aphasmida

Characters :-

(i) Anterior end of body bear chemo receptor amphids, phasmid absent posteriorly.

(ii) Most are free living animal.

(iii) Excretory system relatively simple types.

(iv) Presence of cephalic setae & papillae.

Examples :- Trichurus; Trichenella;

Class :- Phasmida

Characters :-

(i) Possess anteriorly Amphids & posteriorly Phasmid.

(ii) Most are parasitic.

(iii) In the caudal region there is the presence of a pair of Phasmid.

Examples :- Ascaris; Wuchereria; Ancylostoma;

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Classification of Phylum Echinodermata

Classification of Phylum Echinodermata

Phylum :- Echinodermata

Characters :-

(i) Adult with radial & five rayed symmetry, while the larvae are bilaterally symmetrical.

(ii) The body is covered by calcareous ossicles or plates, often bearing projecting tubercles or

spines.

SubPhylum :- Crinozoa

Characters :-

(i) Madriporite absent.

(ii) Radially symmetrical, possessing a cup shaped theca.

Class :- Crinoidea

Characters :-

(i) Arms are branched & bearing pinnules.

(ii) The ambulacral grooves radiates from the mouth & extend to the tip of the pinnules.

Examples :- Antedon (sea lily); Metacrinus;

SubPhylum :- Asterozoa

Characters :-

(i) Body is star shaped & remain unattached.

(ii) On the oral surface in the ambulacral groove, tube feet are present.

Class :- Asteroidea

Characters :-

(i) Arms are not sharply set off from the cetral dosc.

(ii) Anus & madriporite are present on the aboral surface.

Examples :- Asterias ; Asteropectin;

Class :- Ophiuroidea

Characters :-

(i) Arm sharply set off from the central disc.

(ii) Absence of ambulacral groove & arms are filled by vertebral ossicles.

Example :- Ophiura

SubPhylum :- Echinozoa

Characters :-

(i) Radially symmetrical, globoid or discoid without arms or brachioles.

(ii) Madriporite & anus remain on the aboral surface.

Class :- Echinoidea

Characters :-

(i) Body more or less spherical, flattened orally/ aborally.

(ii) Aristotle's lantern, a apparatus used in feeding is mostly present.

Examples :- Echinus ; Arbacia;

Class :- Holothuroidea

Characters :-

(i) Body elongated along oral/ aboral axis.

(ii) The surface of body may exhibit five ambulacral groove.

Examples :- Holothuria; Cucumaria;

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Classification of Phylum Platyhelminthes

Classification of Phylum Platyhelminthes

Phylum :- Platyhelminthes

Characters :-

(i) Body bilaterally symmetrical & dorsoventrally flattened.

(ii) Digestive system had a single opening or mouth, that leads to a well developed gastrovascular

cavity absent & anus absent.

Class :- Tubellaria

Characters :-

(i) Turbellarian are mainly free living, aquatic, but there are some terristrial sp.

(ii) Hermaphrodite, with internal fertilization.

Example :- Planeria (free living)

Class :- Trematoda

Characters :-

(i) Body cylindrical or leaf shaped & parasitic.

(ii) Body is covered by cuticle, which provides protection against host enzyme action & defence

Mechanism

Examples :- Fasciola; Schistosoma; Aspidogaster;

Class :- Cestoidea

Characters :-

(i) Endoparasitic helminth, whose body is covered by a syncytial tegument.

(ii) Organs of attachment in the form of hooks & suckers are present.

Examples :- Taenia; Echinococcus;

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Classification of Phylum Arthropoda

Classification of Phylum Arthropoda

Phylum :- Arthropoda

Characters :-

(i) A pair of externally jointed appendages is usually present in each segment.
(ii) Body is externally covered by thick, tough & chitinous cuticle, forming the exoskeleton.

SubPhylum :- Crustacea

Characters :-

  (i) Head bears five pairs of appendages which comprises of two pairs of antennae & two pairs of
   maxilla.
  (ii) Respiration usually through gills.

Class :- Branchiopoda

Characters:-

                            (i) Trunk appendages are flattened leaf like structure.
                            (ii) Coxa is provided with a flattened epipod.

                             Examples :- Triopes(tadpole shrimp); Daphnia; Artemia;

Class :- Ciripedia

Characters :-

(i)Body enclosed within a bivalve carapace.
(ii) Body is poorly segmented & most lack abdomen.

Examples :- Lepas; Balanus; Sacculina;

Class :- Malacostraca

Characters :-

(i)Body comprises of head, an eight segmented thorax & six segmented abdomen.
(ii) The posterior thoracic limbs being walking legs, the 1st five pairs of abdominal ones forming
swimming organs.

Examples :- Squilla; Hippa; Macrobrachium(prawn); Cancer;

SubPhylum :- Uniramia

Characters :-

  (i)   Appendages are uniramous

       Class :- Diplopoda

Characters :-

(i)Presence of double trunk segments, which are either cylindrical or somewhat flattened.
(ii) Presence of calcified exoskeleton.

Example :- Julus

Class :- Insecta

Characters :-

(i)Head formed by the fusion of 6 segments, typically bears a single pairs of antennae & two pairs of
maxillae.
(ii) The trunk in insects subdevided into three segmented thorax & an abdomen of 11 segments
without walking legs.

Examples :- Lepisma(silver fish); Periplaneta; Carausias(stick insect);Bombyx; Anopheles;

SubPhylum :- Chelicerata

Characters :-

(i)Body divided into an anterior cephalothorax or prosoma, which wholly or partially covered by a
dorsal carapace & a posterior abdomen or opsthosoma.
(ii) Lack of antennae.

Class :- Merostomata

Characters :-

(i)A prominent spike like caudal spine or telson is present at the end of the body.
(ii) Prosoma is covered by a large, horse shoe shaped carapace.

Example :- Limulus

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Classification of Protozoa by Levine et al

Classification of Protozoa by Levine et al(1980)

Subkingdom :- Protozoa

Characters :-

(i) They are usually microscopic & single celled animal & the single cells performs all the vital

activities of the body.

(ii) Body may be naked or covered by pellicle or enclosed in a shell.

(iii) Main locomotory organs are pseudopodia, flagella or cilia (in sporozoa well define locomotory

organs are absent).

(iv) Nucleus single or multiple, which in sac like, oval or biconvex & contains a thick endosome.

Phylum :- Sarcomastigophora

Characters :-

(i) Locomotory organs pseudopodia or flagella.

(ii Nucleus monomorphic.

(iii)Reproduction by fission or syngamy.

Examples :- Amoeba; Trypanosoma; Euglena; Opalina; Entamoeba; Leishmania;

Phylum :- Apicomplexa

Characters :-

(i) It possess an apical complex which can be seen under electron microscope.

(ii) All are generally inter cellular parasite & lack locomotory organ.

(iii) Micropore may be present at certain stage.

Examples :- Plasmodium; Monocystis;

Phylum :- Ciliophora

Characters :-

(i) Locomotory organs are simple cilia or complex ciliated organelles.

(ii) Nucleus are of two types, one micro nucleus & other macro nucleus.

(iii) Presence of cytostome & cytopyge.

Examples :- Paramoecium; Balantidium; Nyctotherus; Tetrahymena;

Phylum :- Myxozoa

Characters :-

(i) Multicellular origin of spore.

(ii) Polar capsule one to many.

(iii) All are parasites in the blood or coelom or cells of cold blood vertebrates.

Example :- Myxozoa

Phylum :- Microspora

Characters :-

(i) Spore single celled, spore wall is without any pore.

(ii) Sporoplasm is with one or two nuclei.

(iii)Polar cap & polar tubules are always present.

Example :- Microspora;

Phylum :- Ascetospora

Characters :-

(i) Spores are generally multicellular, may be single celled.

(ii) All are parasite.

(iii) Sporoplasm may be one or two or many types.

Example :-Ascetospora;

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