KERALA PSC / CDPO / BIOLOGY / SENSE ORGANS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY

 

KERALA PSC / CDPO / BIOLOGY / SENSE ORGANS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY

KERALA PSC / CDPO / BIOLOGY / SENSE ORGANS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY

SENSE ORGANS

The organs which receive the external and internal stimuli and convey the same to the central nervous system are called sense organs.

 

NOSE: SMELL

·      Receptors for smell occur in nasal mucosa and are made up of modified pseudo stratified epithelium. This epithelium is known as olfactory epithelium

·      Olfactory epithelium is more extensive in dogs with an acute olfactory sense.

·      This epithelium is composed of three types of cells – olfactory receptor cells, supporting cells and basal cells.

·      Olfactory receptor cells function as chemo receptors

·      In order for a substance to be smelled, the substance must be capable of entering to a gaseous state to reach nostrils and it must be water soluble to dissolve in the mucus to make contact with olfactory cells.

 

TONGUE: TASTE

·      Taste buds are sense crayons for taste sensation.

·      Taste buds are oval bodies found as some elevation in tongue called papillae.

·      Human beings recognize four basic modalities or tastes-sweet, sour, salty and bitter.

·      They are principally perceived at the tip, along lateral edges, on upper surface of front half and on the back of the tongue, respectively.

·      Sour taste is evoked by H+ ions, produced by ionization of acids.

·      Sweet taste is evoked by organic substances viz., sugar, dextrin, glycerol, chloroform, aspartame and saccharine.

·      Bitter taste is evoked by quinine, morphine, caffeine, nicotine, urea and cation of many inorganic salts like Magnesium salts.

·      Salty taste is evoked from cations of Na+

·      Aspartame & saccharine are widely used as artificial sweetening agents.

·      Loss of smell reduces the perception of taste also. That is why people suffering from cold (rhinitis) often complain that they cannot taste their food.

·      Taste of chillies, black pepper and hot sauces are not true sensation. It is mainly a sensation of pain receptors.

·      Many insects such as honey bee, flies, butterflies and moth possess chemoreceptors for taste sensation at their feet.

·      Some mammals like rhesus monkey, dogs, pig and cat possess taste sensation for water.

·      Man doesn’t possess taste buds for tasting water.

 

SKIN: TOUCH

·      Skin: Touch corpuscle in the skin responds to physical sensations of pressure, heat, cold, contact and pain.

·      Skin is our tactile (sense of touch) sense organ.

·      It is the largest organ of the human body

·      In an adult man skin covers the muscles of about 1.9m² (20 sq.ft) and a woman has about 1.6m² (17sq.ft)

·      The outer layer of the skin is termed as epidermis, which has no nerves or blood vessels and is continuously renewed.

·      Inner layer, called dermis, is a thick layer below the epidermis which contain nerves, blood vessels, hair follicles, sebaceous gland and sweat glands.

·      Colour of the skin is due to the presence of the pigment, melanin, in epidermis.

·      The main function of human skin is excretion.

·      Sweat serves to regulate the body temperature.

·      Sweat glands seen in dermis layer help to eliminate excess heat from the body.

·      Dermatology is the branch of science that deals with the study of skin and its diseases.

 

EYE: VISION

·      The eye (photoreceptor) is a globular ball like organ situated in a bony cavity, the orbit, of the skull.

·      The eyeball has a diameter of 2.5cm

·      The eyeball has 3 coatings

·      Outer most layer is an opaque, white, fibro elastic capsule called sclera. This is continuous with a transparent layer called Cornea (bulging white part of the eye)

·      The membrane that covers cornea is conjunctiva

·      In case of eye transfer only cornea is used.

·      Middle layer is called choroid, is a highly vascular, pigmented layer.

·      Ciliary body is the thickest portion of vascular tissue, arising from a point just behind the junction of sclera and cornea. It consists of ciliary process and ciliary muscles.

·      A pigmented, muscular, opaque diaphragm called, Iris, extend from ciliary body in front of lens. It can be seen as a black screen through the cornea and has a small central aperture called ‘Pupil’

·      The iris has two sets of smooth muscles arranged circularly. The pupil is constricted and dilated respectively by their construction, to reduce and increase the amount of light falling on the lens.

·      In bright light the iris automatically shuts tighter, reducing the amount of light entering the pupil.

·      In front of the eye there is a convex lens. The lens is attached to the ciliary bodies by suspensory ligaments.

·      Retina is the inner most layer, sensitive and made up of many cells and fibres.

·      Retina acts like the film in camera. In order to form an image on the retina, light must pass through all the media of eye (cornea, aqueous humour, lens, vitreous humour) and it must be brought to focus on the retina to form an upside down image on it.

·      The interpretation takes place in the brain

·      The image formed on the retina of the human eye is real and inverted

·      Eye contain receptors called photoreceptors viz., ‘rods’ and ‘cone’ cells, which convert the energy of specific wavelength into action potential of nerve fibre.

·      Cone cells are responsible for day vision.

·      Rode cells are responsible for night vision.

·      Nerve impulses are carried from rods and cones by bipolar nerve cells to the ganglion cells. The axon of the ganglion cells converges and leave the eye ball to form ‘optic nerve’

·      The spot at the back of eye, from where the optic nerve fibre leaves is covered by a zone of retina free from rods and cones. So this spot is devoid of ability for vision and is called Blind Spot.

·      Lateral to blind spot, there is a depressed area of retina, called Fovea, which contains only cones and no rods. Ability of vision is highest is fovea.

·      The anterior compartment is filled with aqueous humour. It supplies nutrients to lens and cornea having no blood supply, maintain shape of cornea and support the lens.

·      The posterior compartment is filled with transparent gelatinous material called vitreous humour, which supports the lens and retina.

·      Squint eye is another eye defect which can be corrected by an operation

·      The parts of eye involved in eye transplantation surgery are cornea, sclera and vitreous humour.

·      Twenty-twenty means perfect vision.

 

EAR- HEARING

·      The ears have two main functions:

Ø Detection and analysis of sound

Ø Maintenance of balance of the body

·      Ear has three main regions – the outer ear, the middle ear and the inner ear

·      External ear consists of pinna and external auditory canal.

·      Pinna is a funnel shaped cartilaginous flap. It collects and directs sound waves into ear canal.

·      The external canal ends at a delicate membranous diaphragm, called eardrum or tympanic membrane.

·      The middle ear is an air-filled chamber. It communicates with that of the pharynx through an air filled tube called, Eustachian tube.

·      Eustachian tube helps to equalize air pressures on either side of ear drum and thus allows it to vibrate freely, when sound waves impinge on it.

·      The vibrating eardrum transmits the vibration to the ear ossicles. Ear ossicles consists of the hammer (malleus), the anvil (incus) and the strip (stapes). The stapes is the smallest bone in the body.

·      The ossicles transmit the vibration t the inner ear, where they cause waves in the fluid called perilymph

·      Perilymph is filled in the coiled, tube called cochlea, in the middle ear.

·      Cochlea is a tube coiled, like a small snail shell, of 2½ turns.

·      The sensory structures respond to different frequency, found on basilar membrane is the rods or corti

·      The internal ear is made up of bony labyrinth and membranous labyrinth. The bony labyrinth contains a fluid called perilymph.

KERALA PSC / CDPO / BIOLOGY / SENSE ORGANS / NOTES / OBJECTIVE QUESTIONS / STUDY MATERIALS / GENERAL KNOWLEDGE / KERALA PSC PRELIMINARY