special senses (eye)

8/14/2019 Special Senses (EYE)

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3.INNER NERVOUS TISSUE LAYER Inner most layer Consists of retina Externally delicate layer Composed several nerve cell bodies and

axon

- lying on pigmented layer attached to choroid

Light sensitive layer- consists sensory cells

Sensory cells are two types1. Rod to view object in black andwhite image.


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Cones to view object in color image Retina thickest layer at posterior of the

eye ball Near the centre of posterior yellow spot Yellow spot also known macula lutea

In the centre of the macula lutea foveacentralis

Fovea centralis consists only cones cells Rods and cones contains photosensitive

pigments


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Photosensitive pigments convert light raysinto nerve impulse

Nerve fiber in retina from optic nerve Optic nerve leaves eyes from small area The small area known as optic disc / blind

spot Optic disc no light sensitive cells- cannotdetect image fall on optic disc


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PICTURE OF CONS AND RODS


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F.PHYSIOLOGY OF SIGHT Retina is the photosensitive part of the eyes Light sensitive cells rod and cones Light rays cause chemical changes in

photosensitive pigments Photosensitive pigments generate nerve impulse

Impulse conduct through optic nerve tooccipital lobe in cerebrum Cones are sensory cells

- sensitive to bright light and color- bright light rays focus on macula

lutea


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Rods are sensory cells- More sensitive than cones

- Stimulated by low intensity/ bim light- Contain Rhodopsin- Rhodopsin photosensitive pigment

- Bright light bleached Rhodopsin- Rhodopsin quickly regenerated in present

of vitamin A


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G. ACCESORY ORGANS OF THE EYE Eye delicate organ Has 3 main accessory organ

1. Eye brows2. Eye lids and eye lashes

3. Lacrimal apparatus1.EYE BROWS-Two arched ridges of super orbital margins

- Located at frontal bone-Numerous hair- Protect the eye ball from sweat ,

dust and foreign bodies


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2.EYE LIDS Two movable folds of tissues Situated above and below front of each eye Free edges has short curved hairs eye

lashes

Has 4 layers forms eye lidsa. Thin skinb. Thin sub cutaneous connective

c. Has 2 muscle orbicularis oculi- contracteye to close- Levator palpebrae

contract eye to open


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d. Lining conjunctiva fine transparentmembrane

- lines eye lid- consists columnar epithelium- protect delicate cornea front of eye

Functions of eye lidsa. Corneal reflex

- reflex closure of eye lids- occurs when conjunctiva eye lashes

touches/ object gets closure/ bright lightshines in to eyes


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b. Prevent drying- tarsal gland secretes oily material

- spread over conjunctiva blinking- delay evaporation3.LACRIMAL APPARATUS

Consists 4 structures of lacrimal apparatusa. 1 lacrimal glandb. 2 lacrimal caanaliculic. 1 lacrimal sacd. 1 nasolacrimal duct


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Lacrimal gland exocrine glands Situated in frontal bone

- behind super orbital margin Consists secretory cells Secretory cells secretes tears

Tears contains of lysozyme bactericidalenzyme

- antibodies- mineral salts sodium- water


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Tears secretion increased whena. Foreign material direct contact

b. Irritant substantc. Emotional status Function of tears

a. Washing away irritant materialb. Prevent microbial infection- bactericidalc. Prevent dryness of conjunctiva


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H. STRUCTURE AND FUNCTIONS OF NOSE Nose Organ of sense of smell

Originate nasal cavity Nasal cavity also acts as a passage way dorrespiration

Olfactory nerve sensory nerve for smell- originate as specialized

olfactory nerve endings

- located - in mucousmembrane

- on roof of the nasal cavity- above superior nasalconcha


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Picture of the olfactory structures


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On each side of nasal septum nerve fiberPass through cribriform to olfactory bulb

In olfactory bulb interconnection andsynapses occur Olfactory bulb bundles and nerve fiber

form Olfactory tract Olfactory tract pass impulses to

olfactory area in temporal lobe

1. PHYSIOLOGY OF SMELL Odorous material give off volatile

molecule


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Volatile molecule carried in to nosetogether with inhaled air

Molecule dissolved in mucus stimulateolfactory chemoreceptor

Air entering nose warmed and conventionoccur

Air convention carried inspired air to theroof of nasal cavity

Olfactory receptor stimulated generate

impulse- impulse conducted through olfactory nerve to temporal lobe to

detect perception of smell


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J. STRUCTURE AND FUNCTIONS OFTONGUE

Tongue organ sense of taste Sense of taste also known - gustation Closely linked to sense of smell

Stimulation of chemoreceptor by dissolvedchemical Taste bud contain chemoreceptor

Chemoreceptor has 3 small nerve ending1. Glossopharyngeal nerve

2. Facial nerve3. Vagus nerve


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Location of chemoreceptor are1. Papillae of tongue

2. Soft palate3. Pharynx4. Epiglottis

Some cells has microvilli projectingtowards tiny pores dissolved in saliva

Nerve impulse generated conduct along CN7,9 and 10 to parietal lobe to detect

perception of taste


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K. PHYSIOLOGY OF TASTE Has 4 sense of taste

1. Sweet2. Sour3. Bitter

4. Salt Tongue divided in 3 sections

1. Tip2. Side3. Back


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Sense of taste stimulate taste buds inspecific part of the tongue

1. Sweet and salty at the tip2. Sour at the sides3. Bitter at the back

Sense of taste trigger salivation andsecretion of gastric juice


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The taste buds of the circumvallate papillaeare made up of a taste pore with sensitivemicrovilli (hair like structures) at the top.Inside the taste bud are taste receptor cellsconnected to nerve fiber.


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special senses (eye)

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