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SENIOR INTER ZOOLOGY REFRESHER EXERCISE – 4 UNITS – I, II AND V

The unit-I includes prochordates, fishes and amphibia. The BIE weightage for unit-I is 6 marks. As such there is scope for one SAQ and one VSAQ from it. Apoda, Urochordata, differences between cartilaginous and bony fishes, cyclostomes are considered

to be important. The unit-II includes reptiles, birds and mammals. The BIE weightage of this unit is also 6 marks.

One can expect one SAQ and one VSAQ in this chapter also. Focus your attention on chelonia, rhyncocephalia, poisonous apparatus, feathers, ratitae,

Archaeopteryx, Prototheria and Metatheria for the SAQ. The unit-V is a big heterogenous chapter which includes nervous system, nerve impulse, endocrine

system, endocrine disorders and immunology. But the BIE weightage is only 10 marks. There is ample scope for one LAQ on brain or two SAQs (one on the diagram of T.S of spinal cord or

dorsal view of brain, pituitary gland, synaptic transmission, thyroid disorders, hepatitis, HIV and AIDS, cells of immune system, different types of immunities etc..,

Give top priority for the VSAQs given below in your final preparation.

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Concentrate on these VSAQs ::

UNIT-I (Phylum : Chordata) 1. What is anadromous migration? Give an example? (May 2005, March 2007, 2009, 2010) Ans: i ) The migration from the sea to rivers for spawning is called anadromous migration eg: Petromyzon, Hilsa and Salmon 2. Distinguish between Icthyopsida and sauropsida. (2010) Ans: Icthyopsida Sauropsida i) Fishes and amphibians are grouped i) Reptiles and Birds are grouped together as

together as Icthyopsida sauropsida 3. Define retrogressive metamorphosis and give an example [Mar-2006,May-2007] Ans: 1) The conversion of more advanced larva in to simple, degenerate adult is called retrogressive

metamorphosis 2) The larva of urochordates loses its nerve cord, notochord and tail during metamorphosis

Ex: Ascidia, Herdmania 4. What are neuromast organs of fishes ? What is their function ? [March-2005, 2008] Ans : The sense organs occur in lateral line canals that open at intervals by pores are called neuromast

organs or lateral line organs. They act as Rheoreceptors. 5. What is a living fossil? Name the fish that is considered as living fossil? (2005, 2007) Ans : 1) A living fossil is an animal which persists since ancient times with very little evolutionary

change. 2) Latimeria chalumnae is considered as a living fossil because it has been persisting since

Jurassic period with very little evolutionary change. 6. What are nuclei pulposi? Ans: i) In adult mammals the remnants of notochord occur as Nuclei pulposi ii) Nucleus pulposus is a small core of gel like material with in each intervertebral disc 7. What is branchial heart ? Name the Gnathostomes with branchial heart. Ans : The heart which pumps blood only to gills is called branchial heart. Fishes possess branchial heart. 8. Distinguish between pleurotrematic and hypotrematic Elasmobranchs. Ans : a) If, gill slits are present on the lateral sides of head, it is called pleurotrematic eg. Sharks. b) If, gill slits are present on the vertral sides of head, it is called hypotrematic eg. Rays and skates. 9. What is catadromous migration? Give an example you have studied. Ans : 1) The migration from fresh water to sea for breeding is called catadromous migration. 2) Anguilla (eel fish) it shows catadromous migration.

UNIT-II (Reptilia, Aves and Mammalia)

1. What are Jacobson’s organs? (March - 2009) Ans. In snakes and some lizards, Jacobson’s organs are present .These are also called vomeronasal

sense organs. These are vestigial or absent in turtles. 2. Which snakes are characterized by laterally compressed tail? Give an example. (2008) Ans. In sea snakes, the tail is laterally compressed. Ex: Hydrophis 3. What is ductus arteriosus? Name the group of extant reptiles having ductus arteriosus. (2009 & 2010) Ans. A small blood vessel that connects the systemic and pulmonary arches is called ductus arteriosus.

It is found in Chelonia. 4. Name the only reptile without copulatory organ. Why is it considered as a living fossil? (2010) Ans. Sphenodon is the only reptile without copulatory organ.

As Sphenodon retained many primitive characters since its origin, so it is referred to as a living fossil. 5. Name the three ear ossicles in mammals. By the modification of which bones of reptiles are

they formed? (2009) Ans. In the middle ear of a typical mammal, three ear ossicles are present. They are malleus, incus and

stapes. These are the modifications of articular, quadrate and hyomandibular bones of lower reptiles respectively.

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6. What is foramen of Panizza? Ans. A small opening that connects left and right systemic arches is called foramen of Panizza. It is

found in the members of Crocodilia. 7. Give four important points in which crocodiles resemble mammals. Ans. The mammalian features of crocodiles are 1. Presence of a complete bony secondary palate 2. Presence of thecodont dentition 3. Presence of diaphragm 4. Presence of four-chambered heart 8. Differentiate between altricial and precocial species. Ans. If, the young ones are dependent on parents, the condition is called altricial. Ex: Modern flying

birds If, the young ones are not dependent on parents, the condition is called precocial. Ex: Modern

flightless birds 9. What is foramen triosseum? What is its functional significance? Ans. Foramen triosseum is an aperture present at the junction of clavicle, scapula and coracoid of

pelvic girdle in birds. The tendon of pectoralis minor passes through foramen triosseum and acts as a pulley

10. How is synsacrum formed in birds? What is its significance? Ans. The last thoracic, lumbar, sacral and anterior few caudal vertebrae fused to form a synsacrum in

birds. It fuses with pelvic girdle and gives support to hind limbs 11. What is corpus callosum? Which group of mammals is characterized by it? Ans. The transverse band of nerve fibres that connects the two cerebral hemispheres is called corpus

callosum. It is well developed in eutherians. 12. What is a secondary palate in mammals? What is its functional significance? Ans. Palatine processes of premaxilla, maxilla and palatine bone form a complete secondary palate. As

it separates the nasal and oral passages, it enables a mammal to chew and breathe simultaneously 13. Which type of placenta is present in eutherians? Name a marsupial having this type of

placenta. Ans. In eutherians, chorioallantoic placenta is seen. A marsupial by name Parameles has this type of

placenta.

UNIT-V (Rabbit Functional Anatomy-III) 1. What is optic chiasma? Where is it located? [IPE 2008, 2009] Ans. The two optic nerves cross each other, infront of the infundibulum is called optic chiasma.It is

located on the ventral side of the diencepthalon. 2. What is insulin shock? (2010) Ans. Shock due to an insulin overdose is termed insulin shock in which these is severe hypoglycemia

leading to convulsions, un consciousness and if blood glucose level is not restored quickly, it can cause death.

3. Justify the Statement “action potentials are all-or-none events”. (2005) Ans. If, the level of depolarization is less than the threshold potential, the membrane potential will

normally drop back to resting levels without further consequences. When the depolarization is just equal to or above the threshold potential, an action potential of equal amplitude is initiated (The stimuli with strength below the threshold do not cause any impulse where as all stimuli having intensity above the threshold induce the same action potential).

4. What is the most commonly used screening test for HIV? (IPE 2006, 2007, 2010) Ans: ELISA ( Enzyme Linked Immunosorbent Assay ) test is the most commonly used screening test for HIV infection. 5. What is a corpus callosum? Ans. A broad transverse band of nerve fibres which connects the two cerebral hemispheres of the brain

called corpus callosum. 6. What do you know about arbor vitae? Ans. The white matter of cerebellum ramifies into grey matter forming branched, tree like appearance is

called arbor vitae.

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7. Name the largest and smallest cranial nerves of rabbit. Ans. 1) Vagus cranial nerve (X)– Largest 2) Pathetic or trochlear cranial nerve (IV)– Smallest 8. What is saltatory conduction? Ans. In a myelinated axon,the conduction of impulse from node to node is known as saltatory

conduction 9. Give two examples for inhibitory neurotransmitters. Ans. Gamma aminobutyric acid (GABA) and glycine. 10. What is tetany? Hyposecretion of which hormone is responsible for it? Ans. Tetany is the (sustained contraction) of a skeletal muscle. Hyposecretion of parathormone is

responsible for it. 11. What are natural killer cells? Ans: Natural killer cells (NK cells ) are large granular lymphocytes that do not express surface

markers.NK cells destroy virus infected cells and cancer cells by their cytotoxic activity. 12. What are Interferons? Ans: *Interferons are cytokines secreted by certain cells that induce an antiviral state in other cells. *Alpha-interferons & Beta interferons are produced by viral infected host cells. They induce

neighbouring cells to produce antiviral proteins (AVPs) *Gamma interferons are produced by T-lymphocytes. Concentrate on these SAQs ::

UNIT-I (Phylum : Chordata)

1. Give an account of general charcters of urochordates. (2006) Ans. a) Body is covered by a tunic or test. It is composed of tunicin similar to cellulose. b) Notochord and nervecord are present in larval stage but absent in adult stage. c) Nerve cord is reduced to a dorsal ganglion in the adult. d) Branchial aperture leads into pharynx e) Pharyngeal wall is perforated by many gill slits. f) Coelom is absent g) Pharynx is enclosed by atrial cavity h) Pharynx is ventrally lined by endostyle which helps in filter-feeding i) Circulatory system is open type, heart is tubular and unique in reversal of blood flow. j) Heart alternately functions as systemic heart and Branchial heart. k) Certain blood corpuscles are called Vanadocytes with Vanadium chromogen, a respiratory pigment having the vanadium which is extracted from the sea water. l) Excretion is by neural gland and nephrocytes. m) They are hermaphrodites. n) Fertilization is usually external and cross fertilisation. o) Development usually includes a larval stage that undergoes retrogressive metamorphosis. 2. Mention the general characters of chondrichthyes. [May-2005] Ans : 1) They are commonly called cartilagenous fishes. 2) The tail fin is heterocercal. 3) Mouth and nostrils are ventral in position. 4) Intestine has a spiral valve or scroll valve. 5) 4 to 7 pairs of gill slits are present without operculum. 6) Gills are lamelliform. 7) Air bladder is absent. 8) In males the pelvic fins are provided with claspers. 9) Fertilization is internal. 10) Most sharks and all rays are viviparous with yolksac placenta for nourishment of embryo. 11) Development is direct Ex : Scoliodon, Torpedo

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3. Write the general characters of osteichthyes. (2006, 2008 and 2010) Ans : 1) These are commonly called bony fishes 2) Caudal fin is diphycercal or homocercal 3) Scales are ganoid, cycloid or ctenoid. 4) Endoskeleton is bony. 5) Mouth is usually terminal 6) Alimentary canal opens out by anus 7) 4 pairs of filamentous gills are present. 8) Spiracles are absent 9) Gill slits are covered by operculum 10) Air bladder or swimbladder is present 11) Fertilization is external 12) Mostly they are oviparous and some are viviparous. 4. Mention eight important characters of Apoda.

[March-2005, March-2007, May-2007, March-2009 & 2010] Ans : 1. It includes caecilians or blind worms 2. They are found in India, Srilanka, Pakistan, Africa and Tropical America 3. Adults are terrestrial and fossorial. 4. Body is worm like with head and trunk 5. Limbs and limb girdles are absent 6. Tail is absent 7. Cloacal aperture is terminal. 8. Skin is embedded with minute dermal scales. 9. Vertebrae are amphicoelous, long ribs are present, sternum is absent. Teeth are present in both the jaws. 10. Gills and gill slits are absent in adults. 11. Lungs are asymmetrical (left lung is rudimentary) and vocal cords are absent. 12. Middle ear is absent, eyes are small, non-functional and buried under the skin or skull bones. 13. Sensory tentacle occur between nostril and eyes 14. In males cloacal wall is eversible and acts as a copulatory organ. 15. Fertilization is internal. 16. Development is direct or with larval stage having external gills. Eg. Icthyophis, Gegenophis 5. Write short notes on Dipnoi. [May-2006] Ans : 1) These are commonly called lung fishes 2) Exoskeleton consists of cycloid scales 3) Dorsal and ventral fins are confluent with caudal fin. 4) Spiracles are absent. 5) Internal nostrils are present. 6) Air bladder forms one (Neoceratodus) or two (Protopterus, Lepidosiren) lungs. 7) There are only three living genera which exhibit discontinuous distribution. 8) Romer described dipnoian fishes as “UNCLES OF AMPHIBIA”. Eg. Neoceratodus lives Burnett and mary rivers in queens land of Australia Protopterus (Rivers of tropical Africa) Lepidosiren (Rivers of tropical south America)

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UNIT-II (Reptilia, Aves and Mammalia) 1. Describe the poisonous apparatus of a venomous snake. (2007) Ans. A poisonous (venomous) apparatus is present in the head of a venomous snake. It has venom

glands, venom ducts and fangs Venom glands: 1. Venom gland is situated behind and below each eye 2. It is homologous to the Duvernoy’s gland (oral gland of some snakes) but not to parotid glands 3. Compressor muscle of lower jaw, sweeps upward around the venom gland and it inserted on the

gland’s surface Venom ducts: 1. Venom duct of venom gland opens at the base of the tongue Fangs: 1. These are the modified maxillary teeth 2. They act as hypodermic needles to inject the venom into the body of the prey 2. Describe the different types of feathers found in birds. (March – 2007, 2008) Ans: Body of birds covered by feathers. Feathers are epidermal in origin. There are different types of

feather covering the body of bird, like quill feathers, contour feathers, filoplumes and down feathers.

A. Quill Feathers : 1. The axis of quill feather has proximal quill/calamus and an expanded portion called vane or

vexillum. 2. Quill is hollow with a small opening at its base called inferior umbilicus through which nutrients

are supplied. 3. Second small opening which occurs at the junction of quill and the rachis is superior umbilicus. 4. There is a soft tuft of feathers near the superior umbilicus called after shaft/hyporachis. 5. The vane has a central axis namely rachis (or) shaft and interlocking arrangement. 6. The barbs associated with barbules and barbicels constitute an interlocking arrangement. 7. Feathers present on the tail are called rectrices 8. Feathers present on wings useful for flight are called remiges. B. Contour feathers: 1. They form the general covering of the body. 2. Each contour feather has a central axis and a vane. 3. Inter locking mechanism is poorly developed. C. Filoplumes : 1. They are small & delicate.. 2. Calamus is short and barbs are weak. 3. They are sparsely arranged in interspaces. D. Down Feathers : 1. These are small, soft and wooly feathers which differ from contour feathers in the absence of

rachis 2. The barbs are long and flexible with sharp barbules. 3. They cover the newly hatched birds and provide excellent insulation.

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***5. Mention differences between Palaeognathae and Neognathae or In what way the flightless

birds differ from flying birds? (2005 & 2008) Ans. Palaeognathae (Flightless birds) Neognathae (Flying birds) 1. Modern flightless running birds 1. Modern flying birds 2. Wings are reduced 2. Wings are well developed 3. Feathers without interlocking mechanism 3. Feathers are with interlocking mechanism 4. Rectrices are irregularly arranged 4. Rectrices are regularly arranged 5. Preen gland is absent 5. Preen gland is present 6. Vertebrae are usually free 6. Vertebrae are fused to form synsacrum and pygostyle 7. Pygostyle is rudimentary or absent 7. Pygostyle is well developed 8. Sternum is without keel 8. Sternum is with keel 9. Clavicles are absent 9. Clavicles and interclavicle fuse to form furcula 10. Syrinx is absent 10. Syrinx is present 11. Males have penis 11. Males are without copulatory organ 12. Young ones are precocial 12. Young ones are altricial

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13. They are discontinuous in distribution 13. They are world wide in distribution Ex: Struthio – Ostrich Ex: Columba – Pigeon Apteryx – Kiwi Pavo – Peafowl

UNIT-V (Rabbit Functional Anatomy-III)

1. Draw a labelled diagram of T.S. of the spinal cord. [IPE 2007, 08, 10]

2. Give an account of synaptic transmission. (2006) Ans. In a chemical synapse, the presynaptic neuron synthesizes the neurotransmitter and stores it in

synaptic vesicles of synaptic terminals. When an action potential reaches a synaptic terminal, it repolarizes the terminal membrane opening voltage-gated calcium channels in the membrane.Ca2+ then diffuse into the terminal. The rise in Ca2+ concentration in the terminal causes some of the synaptic vesicles to fuse with the terminal membrane releasing the neurotransmitter by

exocytosis. The neurotransmitter diffuses across the synaptic cleft. - The post synaptic membrane has Ligand-gated channels binding of the neurotransmitter to a

receptor of the channel opens the channel and allows specific ions to diffuse across the post synaptic membrane resulting in a post synaptic potential

- Excitatory neurotransmitters depolarize the post synaptic membrane. Those potentials are called EPSPs. - Inhibitory neurotransmitters cause hyperpolarisation of post synaptic membrane. These potentials are called inhibitory post synaptic potentials. - The neurotransmitter (e.g. acetycholine) is degraded by an enzyme (e.g. acetyl cholinesterase),

which resides in the synaptic cleft. 3. Write short notes on thyroid gland disorders. [IPE 2007, 2008,2009] Ans. i. Cretinism in children is due to congenital hypothyroidism. The child is mentally retarded, dwarf

and sterile. Hypothyroidism during the adult years produces myxoedema. A hallmark of this disorder is edema (accumulation of interstitial fluid) that causes the facial tissues to swell and look puffy.

ii. Hyperthyroidism The most common from of hyperthyroidism is Graves’s disease. Graves’s disease is an autoimmune

disorder in which the person produces antibodies for TSH-receptors that bind to the receptors and continually stimulate the thyroid gland to grow and produce thyroid hormones. Graves’s patients often have a peculiar edema behind the eyes, called exophthalmos, which causes the eyes to protrude

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iii. Endemic Goitre Endemic goitre (simple goiter) is the enlargement of thyroid gland. It may be associated with euthyroidism (normal secretion of thyroid hormone), hyperthyroidism or hypothyroidism. In some places in the world, dietary iodine intake is inadequate. The resultant low levels of thyroid hormone in the blood accelerates secretion of TSH, which causes thyroid gland enlargement.

4. Write notes on cells of immune system. (2008) Ans: Lymphocytes are responsible for adaptive immunity.The other types of cells play important roles,

such engulfing and destroying microorganisms, presenting antigens, and secreting cytokines. I. Lymphoid Cells *Lymphocytes circulate in the blood and lymph, and migrate into the tissue spaces and lymphoid

organs. * Lymphocytes can be broadly subdivided into three types B cells, T cells and Natural killer cells. i) B lymphocytes *Mature B cells have membrane-bound antibody molecules, called B cell receptors (BCR),

*Interaction between antigen and BCR,and interactions with TH cells induce activation and differentiation of immunocompetent B cell into memory cells and Plasma cells. *Plasma cells secrete antibodies. *B cells function, also as antigen - presenting cells. (APCs) ii) T lymphocytes * These cells also have membrane receptors for antigens called T-cell receptors(TCR). *Two T cell subpopulations can be distinguished by the type of CD markers. *T helper (TH) cells have CD4 marker (CD4+ cells) where as T cytotoxic (TC ) cells have CD8

marker (CD8+ cells) *TH cells are activated by antigen - class II MHC complex on an antigen - presenting cell. * After activation , the TH cell proliferates into a clone of effector cells. *These cells secrete various cytokines, which activate B cells, and other cells. *TC cells are activated when they interact with an antigen - class I MHC complex on the surface of

an altered self-cell (virus- infected cell or a tumor cell) in the presence of cytokines. *This activation results in proliferation of Tc cell into effector cell called cytotoxic

T lymphocyte(CTL). *CTLs recognize and eliminate altered self- cells. iii) Natural Killer Cells *Natural killer cells (NK cells) are large, granular lymphocytes that do not express the surface

markers. * NK cells exhibit cytotoxic activity against tumor cells and some virus infected cells. *

NK cells recognize target cells in two ways. 1. NK cell receptors recognize unusual surface antigens on tumor cells and virus infected cells. 2. Antibodies produced by the immune system bind to antigens on the surface of tumor and virus -

infected cells, *NK can attach to the FC end of these antibodies and destroy the targeted cells. Mononuclear Phagocytes * The mononuclear phagocytic system consists of monocytes in the blood and macrophages in the

tissues. *Monocytes differentiate into wandering macrophages or fixed macrophages. Eg.histiocytes in connective tissues, alveolar macrophages in the lung, Kupffer cells in the

liver, microglial cells in the brain, osteoclasts in bone. *Macrophages are capable of ingesting and digesting microorganisms, dead cells, cellular debris,

etc. * Activated macrophages function also as antigen-presenting cells. III Granulocytes Granulocytes are classified into neutrophils, eosinophils and basophils i) Neutrophils

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*Neutrophil is called polymorphonuclear leucocyte (PMN) for its multilobed nucleus.These are phagocytic.

ii)Eosinophils *These are also phagocytic but their phagocytic role is less important. They play a role in the

defence against parasitic organisms. iii) Basophils *Basophils are non-phagocytic. *They release inflammatory mediators like histamine and bradykinin. IV.Mast Cells Mast - cell precursors are formed in the bone marrow and are released into the blood. They differentiate in tissues. *These cells release inflammatory mediators such as histamine and bradykinin. V.Dendritic Cells *The dendritic cell has membrane extensions that resemble the dendrites of nerve cells. *They express class II MHC molecules and are the most potent antigen- presenting cells. 5. What is hepatitis? Explain any two types of viral hepatitis. (IPE 2005, 06, 08, 10) Ans: Hepatitis: *Hepatitis is inflammation of liver caused commonly by viruses. *It is also caused by bacteria and fungi. * Seven viruses are identified to cause hepatitis (HAV to HGV ). * Symptoms of viral hepatitis include anorexia ( loss of appetite), malaise ( general feeling of

discomfort), nausea, diarrhoea,abdominal discomfort, fever, chills, jaundice and cirrhosis (fibrosis of liver). i. Hepatitis A * It is caused by hepatitis A virus (HAV). *HAV contains single -stranded RNA and lacks an envelope around the capsid. * It infects through contaminated food and water. * Incubation period is 2-6 weeks. * Inactivated whole agent vaccine is available. ii.Hepatitis B * It is caused by hepatitis B virus (HBV). *It has double- stranded DNA and is enveloped. *Transmission is parenteral ( injections, blood transfusion), perinatal from mother to child, sexual

contact. *Incubation period is 4-26 weeks. *Vaccine consists of a portion of the viral protein coat produced by a genetically engineered yeast. Concentrate on these LAQs ::

UNIT-V (Rabbit Functional Anatomy-III)

1. Describe the structure and functions of the brain of rabbit. (IPE 2006, 2007, 2010) Ans. Brain

Olfactory lobes Prosencephalon Cerebral hemispheres Dien cephalon Brain Mesen cephalon Opticlobes Ponsvarolii

Metencephalon Rhombencephalon cerebellum

Myelencephalon Medulla

The brain lies in the cranium of the skull and is protected by it. The brain has outer grey matter and inner white matter. It is divided into three main regions.

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i. Forebrain or prosencephalon ii. Midbrain or mesencephalon iii. Hindbrain or rhombencephalon i. Forebrain or Prosencephalon It forms the anterior two-third of the brain. It consists of two olfactory lobes, two cerebral

hemispheres and a diencephalon. 1. Olfactory Lobes These are a pair of club-shaped bodies forming the anterior most part of the brain. Each olfactory lobe is differentiated into an olfactory bulb and an olfactory tract. Olfactory tracts are separated from hippocampal lobe of cerebral hemispheres by a rhinal fissure. The cavity of each lobe is called the rhinocoel or olfactory ventricle. Olfactory lobes are concerned with the sense of smell. 2. Cerebral Hemispheres - A pair of large cerebral hemispheres constitutes the cerebrum. Anteriorly they are narrow and Partly overlap olfactory lobes. They are posteriorly broad and cover the diencephalon and optic lobes. - The two cerebral hemispheres are separated from each other by a longitudinal median fissure. An oblique sylvian fissure separates each cerebral hemisphere into an anterior forntal lobe and a

and a posterolateral temporal lobe. The posteromedian of each cerebral hemisphere is called parietal lobe Ventrally a longitudinal rhinal fissure separates the hippocampal lobe from the olfactory tract. - Hippocampal sulcus demarcates the hippocampal lobe from the other lobes on the ventral side. - The two cerebral hemispheres are internally connected together by a broad transverse band of nerve fibres called corpus callosum. - The cavities of the cerebral hemispheres are I and II ventricles, or paracoels, or lateral ventricles. They are continuous with rhinocoels. - The two paracoels communicate with each other and with the diocoel by a transverse passage called foramen of Monro. - The roof and dorsolateral wall of the lateral ventricle are thick and are called neopallium. It is smooth in rabbit, but has deep grooves (sulci) and wrinkles (gyri) in primates. - The floor and ventrolateral wall of paracoel are thickened to form corpus striatum. - The two corpora striata are connected by a flat transverse fibrous strip called anterior commissure. - The cerebral hemispheres control voluntary movements. They are also the seat of thinking, reasoning, intelligence, memory, etc. 3. Diencephalon or Thalamencephalon - Diencephalon is a small posterior part of the forebrain. The cavity of the diencephalon is third ventricle or diocoel. - The roof of III ventricle is called epithalamus. Epithalamus and piamater fuse and project into III-ventricle to form anterior choroid plexus. - A pineal stalk arises from the roof of III ventricle. It terminates in a pineal body or epiphysis. The floor of III ventricle is called hypothalamus. Ventrally it has a median rounded projection

called infundibulum. - Infundibulum bears pituitary gland, or hypophysis. - The infundibulum and the hypophysis together form pituitary body. - In front of infundibulum, the optic nerves cross each other to form optic chiasma. A rounded

elevation present behind the infundibulum is called corpus mamillare. - The lateral walls of diencephalon are called optic thalami. They are thickened and meet across the

III ventricle forming the so – called median commissure. - Diencephalon provides perception of touch, pressure, pain and temperature. Hypothalamus controls autonomous nervous system and pituitary gland, and controls body temperature. ii. Midbrain or Mesencephalon - It is the small, middle region of the brain. Dorsally it has optic lobes.

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- A transverse groove divides each optic lobe into two parts thus forming four optic lobes, - collectively called corpora quadrigemina. - The two larger anterior optic lobes are called superior colliculi and the two smaller posterior lobes are called inferior colliculi. - The dorsal walls of the two anterior optic lobes are internally connected by a transverse strip called posterior commissure. - The midbrain has a narrow longitudinal passage called iter, or aqueduct of Sylvius. - It connects the III ventricle with the IV ventricle. - The floor of midbrain is formed by thick tracts of fibres called crura cerebri that link the cerebral hemispheres and medulla oblongata. - Superior colliculi are concerned with the sight whereas inferior colliculi are concerned with

hearing. iii. Hindbrain or rhombencephalon It is the posterior region of the brain and includes metencephalon and myelencephalon. 1. Metencephalon - Its anteroventral part is called pons Varolii and rest is called cerebellum. The pons Varolii and

cerebellum are without ventricles. A. Pons Varolii - This is a transverse band of nerve fibres. It connects the right and left halves of the cerebellum. B. Cerebellum - It is well developed and transversely elongated. It consists of a median lobe called vermis and two

lateral lobes, one on each side. - Each lateral lobe is with a ventrolateral extension called flocculus. - The surface of cerebellum is much folded. - The white matter of cerebellum is called arborvitae due to its branched, tree-like appearance. - Cerebellum coordinates the voluntary muscular movements that are initiated by cerebrum. It

regulates posture and balance. 2. Myelencephalon or Medulla Oblongata - It is anteriorly broad, and posteriorly tapers into the spinal cord. - It is the last part of the brain. The cavity of medulla oblongata is called myelocoel, or fourth

ventricle. - The vascular folds of its roof project into IV ventricle as posterior choroid plexus. - Medulla oblongata and Pons varolii control the involuntary activities in the body such as heartbeat, breathing, vomiting, swallowing, etc.

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2. Explain the impulse transmission through a nerve fibre. Ans. Virtually all cells maintain electrical potential across their plasma membrane, but nerve cells have special mechanisms for using this potential to transmit information over long distances. Nerve cells exhibit a special property called electrical excitability. The electrical excitability shows the following phases Resting membrane potential, Action potential, Depolarising phase, Repolarising phase, Hyper

polarising phase. Channels:The following channels are involved in nerve impulse transmission. 1) Many number of K+ leakage channels on axolemma 2) Small number of Na+ leakage channels on axolemma 3) Voltage gated Na+ channels on axolemma It has two gates, an activation gates and Inactivation gates. At resting condition the activated gates are closed and inactivated gates are open. At activated condition the activated gates are opened and inactivated gates are closed. At inactivation condition the activated gates are opened and inactivated gates are closed. Voltage gated Na+ channels are responsible for the generation of action potential 4) Voltage gated K+ channels on axolemma It has one gate.Voltage gated K+ channels are responsible for the generation of action potentials 5) Ligand -gated channels on post synaptic membrane : They are opened or closed in response to

chemical stimulus and are responsible for the generation of post synaptic potentials. Resting Membrane Potential The membrane potential of a neuron that is not transmitting signals is called the resting potential. Resting potential depends on the ionic gradients that exist across the axolemma and the differential permeability of the axolemma. - The concentration of Na+ in the ECF is ten times to its concentration in the axoplasm. - The concentration of K+ in the axoplasm is thirty times to its concentration in the ECF. - The Na+ and K+ gradients are maintained by Na+/K+ ATPase (sodium-potassium pump), which transports three Na+ into ECF and two K+ into the cell. - The principal anion in the ECF is Cl-. - The principal anions in the axoplasm are nondiffusible proteins, sulphate, phosphate and other

organic anions. - At the resting potential, the voltage-gated Na+ channels are in resting state. - Voltage- gated K+ channels are closed. - Because the axolemma has more K+ leakage channels than Na+ leakage channels, the cell is roughly 100 times more permeable to K+ than to Na+ at this point. - Consequently the resting potential is about -70mv, negative on the inner side of axolemma. - At resting phase, the axolemma is polarized. The membrane potential can change from its resting value when the membrane’s permeability to particular ions changes. - If the inner side becomes less negative, it is said to be depolarized. - If the inner side becomes more negative, it is said to be hyperpolarized. Action Potential - In nerve cells,a stimuli causes a rapid sequence of changes in membrane potential known as an action potential which infact termed as a nerve impulse. Depolarizing Phase (Rising Phase): - When the depolarization reaches the threshold level (–55mv), voltage-gated Na+ channels are activated. - Due to the rapid influx of Na+ the membrane potential shoots rapidly upto +45mV. - If the level of depolarization is less than the threshold potential, the membrane potential will

normally drop back to resting levels without further consequences. When the depolarization is just equal to or above the threshold potential, an action potential of equal amplitude is initiated. Thus action potential is an all-or-none phenomenon.

Repolarizing Phase (Falling Phase) : - Once the membrane potential has risen to its peak, the voltage-gated Na+

channels are inactivated and voltage-gated K+ channels open. Efflux of K+ repolarizes the axolemma.

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Hyperpolarizing Phase(Undershoot) During this phase, the membrane potential briefly becomes even more negative (-90mV) than it normally is at rest. This occurs because of the increased K+ permeability that exists while voltage-gated K+ channels remain open. Na+ channels come to resting state. The membrane

potential returns to its original resting state as the K+ channels close.

Propagation of action potentials - At the site where an action potential is initiated (usually the axon hillock). Na+ influx during the depolarizing phase creates an electrical current that depolarizes the neighbouring region of the axolemma. - The depolarization in the neighbouring region is large enough to reach the threshold, causing the action potential to be generated there. This processs is repeated many times as the action potential travels along the length of the axon. - The propagation of this cycle of events along the nerve fiber is called a nerve impulse. - The zone behind the travelling zone of depolarization is in refractory period. Hence the action

potential cannot be generated there. This prevents action potentials from travelling back and the action potentials move only toward the synaptic terminals.

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3. Give a detailed account of the pituitary gland Ans. The pituitary gland or hypophysis lies in sella tursica of the sphenoid bone. The pituitary - gland includes adenohypophysis and neurohypophysis. - Adenohypophysis of pituitary gland develops as an out growth of ectoderm called the Rathke’s

pouch in the roof of the buccal cavity. - Neurohypophysis develops from the terminal region of an ectodermal outgrowth that connects

neurohypophysis to the hypothalamus. - Several hormones secreted by adenohypophysis influence other endocrine glands and hence are

called tropic hormones. For many years, the pituitary gland was called the “master” endocrine gland because it secretes several hormones that control other endocrine glands.

- We know that release of hormones by adenohypophysis is stimulated by releasing hormones and suppressed by inhibiting hormones from the neurosecretory cells of the hypothalamus. Adenohypophysis secretes seven protein hormones.

Growth Hormone (GH) or Somatotropin: In response to human growth hormone, cells in the liver, skeletal muscle, cartilage, bone, and other tissues secrete insulin – like growth

factors (IGFs) that cause cells to grow and multiply. Thyroid-stimulating Hormone (TSH): Thyroid-stimulating hormone (TSH) stimulates the

synthesis and secretion of thyroid hormones by the thyroid gland. Adrenocorticotropic Hormone (ACTH): It controls the secretion of glucocorticoids by the

adrenal cortex. Follicle-stimulating Hormone (FSH): In females, FSH initiates the development of several

ovarian follicles. In males, FSH stimulates spermatogenesis in the seminiferous tubules of testes. Luteinizing Hormone (LH): In females, LH stimulates ovulation, formation of the corpus luteum,

and the secretion of progesterone by the corpus luteum. Together, FSH and LH also stimulate secretion of oestrogen by ovarian cells. In males, this hormone is called interstitial cell stimulating

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hormone(ICSH) as it stimulates the interstitial cells or Leydig cells in the testes to secrete testosterone. FSH and LH are termed gonadotropins because their target organs are gonads.

Prolactin (PRL) : Prolactin, together with other hormones initiates and maintains milk secretion by the mammary glands. The function of prolactin is not known in males.

Melanocyte-stimulating Hormone (MSH): MSH increases skin pigmentation in lower vertebrates by stimulating the dispersion of melanin granules in melanocytes. Its exact role in mammals is unknown.

Neurohypophysis Although the neurohypophysis does not synthesize hormones, it stores and releases two hormones –

oxytocin and vasopressin. These are peptide homones produced by neurosecretory cells of the hypothalamus. These hormones are transported to neurohypophysis through the axons of hypothalamohypophyseal tract from where they reach the target tissues through blood

Oxytocin : During delivery, oxytocin enhances contraction of smooth muscle cells in the wall of the uterus. After delivery, it stimulates milk ejection. The function of oxytocin in males and in non-pregnant females is not clearly known.

Vasopressin or Antidiuretic Hormone (ADH): ADH causes the kidneys to reabsorb more water into the blood. In the absence of ADH, urine output increases from the normal 1 to 2 liters to about 20 liters a day. ADH causes constriction of arterioles, which increases blood pressure. The amount of ADH secreted is regulated by osmoreceptors in hypothalamus. Secretion of ADH increases with an increase in blood osmotic pressure or decrease in blood volume.