Detection of Environmental Conditions in Mammals.
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Transcript of Detection of Environmental Conditions in Mammals.
Detection of Environmental Conditions in Mammals
Irritability
• The ability to respond to stimuli
• Stimuli (external or internal) are detected by receptors or sense organs
• Receptors generate nerve impulses after being stimulated
• Nerve impulses are sent to the brain for interpretation
• The brain then generates nerve impulses carrying suitable responses to the effectors
• The effectors (muscles or glands) then produces suitable responses
Eye
• Sense organ for receiving light
• Protected by the skull
Structures around the eye-ball
• Tear glands: secrete tears which– wash away dust– contain lyzozyme which kills bacteria– moisten the eye surface
• Eyelids– protect eye from damage
• Eyelashes– protect the eye from large particles to enter it
Internal structure of the eye-ball
• Wall of eye-ball consists of 3 layers
1. Sclera• maintain the shape
of the eye-ball• protects the inner
structures• provides anchorage
to eye muscles
Internal structure of the eye-ball
2. Choroid• With many blood
vessels and pigment
• Blood vessels supplies oxygen and nutrients to the eyes, and to remove metabolic wastes from them
• Pigment absorbs extra light to prevent reflection of light inside the eyeball which may blur the image
Internal structure of the eye-ball
3. Retina• Contains light
sensitive cells (photo-receptors) and nerves• Rods for black-
and-white vision• Cones for colour
vision
Internal structure of the eye-ball
Yellow spot• densely packed with
cones• no rod is present• gives the most
distinct image and the greatest colour discrimination
Internal structure of the eye-ball
Blind spot• the point where the
nerve fibres leave the eye-ball
• no photo-receptorscannot detect any
image
Internal structure of the eye-ball
Cornea• Continuous with sclera• Protected by
conjunctiva• To allow light to enter• To refract light onto
the retina
Internal structure of the eye-ball
Pupil• The opening which
allows light to enter the eye-ball
Iris• To control the size of
the pupil
Change in the pupil size
• Iris is made of circular muscles and radial muscles –antagonistic pair
Increase in the pupil size
• At dim light : circular muscles relax; radial muscles contract• increase in size of pupil
Decrease in the pupil size
• At bright light : circular muscles contract; radial muscles relax• decrease in size of pupil
Internal structure of the eye-ball
Lens
• Transparent, elastic, biconvex structure
• To focus light rays on the retina by changing its convexity
Internal structure of the eye-ball
Suspensory ligaments
• Hold the lens in position
Ciliary body
• Regulates the curvature of the lens by contraction and relaxation of the ciliary muscles
Accommodation
• The ability of the eye to focus objects at varying distances onto the retina
• Light entering the eye is refracted successively at the cornea, the aqueous humour, the lens and the vitreous humour.
• The image is formed on the retina and the retina sends signal along the optical nerve to the brain, causing the sensation of sight.
• The image formed on the retina is inverted but is interpreted as erect.
Focusing near object
Light from near object
Focusing on near objects
Ciliary muscles contract Decrease in circumferenceTension of suspensory ligaments is decreasedLens become more convex
Focusing far away object
Light from far away object
Focusing on distant objects
Ciliary muscles relax Increase in circumferenceTension of suspensory ligaments is increasedLens become less convex
Accommodation
Object CiliaryMuscle
Shape Focal length
Near Contract Thicker Shortened
Distant Relax Thinner Lengthened
Near Point and Far Point
• The average normal eye can focus objects easily from about 25 cm, i.e., the near point, to infinity, i.e. the far point.
• This range of distance of clear vision varies from one person to another and decreases with age.
Short sight
Light from distant object
• The eyeball is a bit too long.
• The lens lacks the ability to accommodate for a distant object.
Correction of short sight
Light from distant object
Diverging lens
( Concave lens )
Long sight
Light from near object
• The eyeball is a bit too short.
• The lens lacks the ability to accommodate for a near object.
Correction of long sight
Light from near object
Converging lens
( Convex lens )
Causes
Defect Eye lens Eye ball Correction
Short sight Too thick Too long Concave lens
Long sight Too thin Too short Convex lens
Eye defects
• Short-sighted– Image of a distant object formed in front of the
retina– Lens too thick– Eye-ball too long– Correction: wear concave lens
Eye defects
• Long-sighted– Image of a near object formed behind the retina– Lens too thin– Eye-ball too short– Correction: wear conves lens
Eye defects
• Colour blindness– Defect of one or more of the three types of cone
cells– Unable to distinguish between colours– Inherited
Class Practice
1. Which of the following statements about the lens is/are correct ?
(1) The image formed on the retina is real.(2) The pupil is smaller in bright light than in dim light.(3) When the object distance changes, the eye focuses an object by chaning the focal length of the eye lens.
Internal structure of the eye-ball
Anterior chamber• Filled with aqueous
humour– to refract light onto the
retina
– to maintain the shape of the eye-ball
– to supply nutrients to the conjunctiva, conera and lens
Internal structure of the eye-ball
Posterior chamber• Filled with vitreous
humour– to refract light onto the
retina
– to maintain the shape of the eye-ball
Internal structure of the eye-ball
Optic nerve• To transmit nerve
impulses to the optic centre in the cerebral cortex of the brain for interpretation
Basic Fact of EAR
• Ears are used to detect SOUND in environment.
• Ears help to detect movement & position.
• Ear is divided into Outer Ear, Middle Ear & Inner Ear.
Structure of EAR
• Outer Ear: EAR PINNA, EAR CANAL & EAR DRUM.
• Middle Ear: EAR BONES
• Inner Ear: EUSTACHIAN TUBE & ADENOIDS.
Outer Ear
• It is the part which is visible and is made of folds of skin and cartilage.
• It leads into the ear canal, which is about one inch long in adults and is closed at the inner end by the eardrum.
• The eardrum is a thin, fibrous, circular membrane covered with a thin layer of skin.
• It vibrates in response to changes in the air pressure that constitute sound.
• The eardrum separates the outer ear from the middle ear.
Middle Ear• It is a small cavity which
conducts sound to the inner ear by means of three tiny, linked, movable bones called "ossicles."
• These are the smallest bones in the human body and are named for their shape.
• The hammer (malleus) joins the inside of the eardrum.
• The incus joint with the hammer and to the stapes.
• The base of the stapes fills the oval window which leads to the inner ear.
Inner Ear
• The inner ear is a very delicate series of structures deep within the bones of the skull.
• It consists of a maze of winding passages, called the "labyrinth".
• The front (see cochlea) is a tube resembling a snail's shell and is concerned with hearing.
• The rear part is concerned with balance.
Detection of SOUND
1. Sound waves (air vibrations) are collected by the OUTER EAR.
2. Sound waves vibrate the EAR DRUM.
3. Vibrations are amplified by the EAR BONES.
4. Vibrations change the pressure of the FLUID of the INNER EAR.
5. Vibrations are transmitted to signals to the brain via nerve impulses.
Intensity Cues in Stereo
• When the volume of two speakers are equal, we will hear the sound as come from the centre.
Structure of the ear
• Three regions:• Outer ear• Middle ear• Inner ear
Process of hearing
• Sound waves are collected by the ear pinna
Process of hearing
• Sound waves pass along the external auditory canal to the ear drum
Process of hearing
• Sound waves make the ear drum to vibrate• Ear drum converts sound waves into mechanical vibrations
Process of hearing
• Ear drum transmits vibration to the ear bones
• Ear bones transmit and amplify vibrations
Process of hearing
• Ear bones transmit vibration to the oval windows
Process of hearing
• Oval window causes the perilymph in the upper canal of the cochlea to vibrate
Process of hearing
• Perilymph transmits vibrations to the endolymph in the middle canal
Process of hearing
• The sensory hair cells on the bottom membrane of the middle canal are stimulated
• The sensory hair cells send off nerve impulses
Process of hearing
• The auditory nerve transmits the impulses to the auditory centre of the cerebral cortex
• The auditory centre interprets the nerve impulses and produce the sensation of hearing
Process of hearing
• The vibrations of perilymph are transmitted to the round window
• Round window bulges outwards into the middle ear cavity to release pressure
Equalizing the pressure on both sides of the eardrum
• The middle ear is air-filled– The atmospheric pressure may become higher
or lower than the air pressure in the middle ear– This causes the ear drum to curve inwards or
outwards– The ear drum cannot vibrate properly and
causes pain and temporarily deaf
Equalizing the pressure on both sides of the eardrum
• The pressure on both sides of the ear drum can be equalized by the Eustachian tube• Eustachian tube is connected to the pharynx• It is opened only during swallowing or yawning
Detection of movement by the ear
• Above the cochlea are three semi-circular canals– They are responsible for detecting head movement
• At the base of each canal is a swelling called ampulla
• The semi-circular canals are perpendicular to each other to detect head movement in all planes
Detection of movement by the ear
• Semi-circular canals are filled with endolymph • Gelatinous mass (cupula) is found inside each ampulla
Detection of movement by the ear
• When the head move, the semi-circular canals will move in the same direction
• However, the endolymph in the canals will move in opposite direction due to inertia
• The endolymph displaces the gelatinous mass inside the ampulla
• The sensory hair cells under the gelatinous mass is stimulated
• Nerve impulses are generated and transmitted along the auditory nerve
Detection of movement by the ear
• Nerve impulses are generated and transmitted along the auditory nerve to• the cerebrum: aware of the direction of head
movement
• the cerebellum: leads to appropriate responses of the muscles to maintain body balance
Nose - the olfactory organ
• For detection of smell
• By olfactory cells on the upper part of nasal cavity
• Covered with mucus– to dissolve chemicals in air which stimulate the
olfactory cells to produce nerve impulses to the cerebrum
Tongue - the taste organ
• Detected by taste buds on the upper surface of the tongue which are stimulated by chemicals dissolved in saliva
• Different regions detect different tastes
sweetsalty
sour
bitter• Flavour of food is
given by both the sense of taste and odour of it
The skin
• Contains many receptors for the sensation of touch, cold, hot, pain and pressure
• The distribution of them are uneven throughout the skin