Sense organs BSC nursing 1 st sem, Assignments of Anatomy

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Ms. K. GOWRI. M.Pharm

Lecture

Physiology of vision

:

The eye is the organ of the sense of sight in the orbital cavity and is supplied by optic nerve. Structure : •

There are 3 layers of tissue in the walls of the eye. They are •

outer fibrous layer : sclera and cornea.

middle vascular layer or ureal tract : choroid, ciliary body and iris.

inner nervous tissue layer : retina. Physiology :

Light waves travel at a speed of 186000 miles per second. Light is reflected into the eyes by objects in the field of vision.

White light is a combination of all the colours of the visual spectrum (rainbow).

i.e. red, orange, yellow, green, blue, indigo and violet.

This range of colour is the spectrum of visible light. Electromagnetic spectrum

:

Electromagnetic spectrum is broad but only a small part is visible to the human eye. Beyond the long end there are IR waves, microwaves andradiowaves.

Size of the pupils : Pupil size influences accomdation by controlling the amount of light entering the eye. In a blight the pupils are constricted. •

In dim light dilated.

The size of the pupil is controlled by autonomic nervous system.

Sympathetic stimulation dilates the pupils and parasympathetic stimulation causes constric Accomodation of the eyes to light : Close vision :

In order to focus on near objects, i.e. within about 6 meters, the eye must make

following adjustments. •

Constriction of the pupil

Convergence of the eyeballs.

Changing the power of the lens. Distant vision :

objects more than 6 metres away from the eyes are focussed on the retina ou

adjustment of the lens or convergence of the eyes. Function of retina

:

Retina is the photosensitive part of the eye.

Light sensitive nerve cells are the rods and cones.

Rods are more sensitive than the cones.

They are stimulated by low intensity or dim light. Eg : by the dim light in the interior of a darkened room. •

Cones are sensitive to bright light and colour. The different wavelengths of visible light stim photosensitive pigments in the cones, resulting in the perception of different colours. •

Rods are more numerous towards the periphery of the retina. Visual purple (rhodopsin) is a photosensitive pigment present only in rods. •

It is bleached by bright light and is quickly regenerated when an adequate supply of vitami available.

Dark adaptation : When exposed to bright light, the rhodopsin in the sensitive rods is completely degraded. •

When regeneration of rhodopsin occurs, normal sight returns.

In dim evening light different colours cannot be distinguished because the light intensity is insufficient to stimulate colour-sensitive pigments in cones. •

Breakdown and regeneration of the visual pigments in cones is similar to that of rods. Binocular vision : Each eye sees a scence slightly different. It provides a much more accurateassessment of one object relative to another. Eg : distance, depth, height & width. Audition : Physiology of hearing : •

Ear is the organ of hearing. It is supplied by the 8

th

cranial nerve. i.e. the coculear part of the

vestibulocochlear nerve which is stimulated by vibrations caused by sound waves. Structure : Ear is divided into three distinct parts •

Outer ear

Middle ear

Inner ear. Physiology of hearing : •

Every sound produces sound waves or vibrations in the air, which travel at about 332 mts p second. •

The auricle, because of its shape, concentrates the waves and directs them along the auditor meatus causing the sympanic membrane to vibrate. •

The nerve impulses generated pass to the brain in the coculear portion of the vestibulococu nerve. •

The vestibulococulear nerve transmits the impulses to the hearing area in the cerebrum whe sound is perceived and to various nuclei in the pons & mid brain. •

Sound waves have properties of pitch and volume or intensity.

Pitch is determined by frequency of the sound waves & is measured in hertz (HZ). The volu

All odorous material give off volatile molecules, which are carried into the nose the inhaled and stimulate the olfactory chemoreceptors when dissolved in mucus. •

The air entering the nose is warmed and convection currents carry eddies of inspired air to roof of the nasal cavity. •

‘sniffing’ concentrates volatile molecules in the roof of nose. This t’es the no. of olfactory re stimulated & thus the perception of the smell. The sense of smell may affect appetite. If the odours are pleasant the appetite may improve and vice versa. •

When accompanied by the sight of food, an appetising smell t’es salivation and stimulates t digestive system. •

The senses of smell may create long – lasting memories, especially to distinctive odours. Eg : hospital smells, favourite or least liked foods. •

Inflammation of the nasal mucusa prevents odorous substances from reaching the olfactory the nose causing loss of sense of smell (anosmia). The usual cause is the common cold. Adaptation :

when an individual is continuously exposed to an odour, perception of the odo

and ceases in a few min. this loss of perception only affects specific odour and adaptation proccurs both in the cerebrum & in the sensory receptors in the nasal cavity.

Taste :

Taste buds contain sensory receptors that are found in the papillae of the tongue widely distributed in the epithelia of the tongue, soft plate, pharynx and epiglottis •

They consists of small sensory nerve endings of the glossopharyngeal, facial and nerves. •

The sensory receptors are stimulated by chemicals that enter the pores dissolved saliva. •

Nerve impulses are generated and conducted along the glossopharyngeal, facial vagus nerves before synapsing in the medulla & thalamus. •

Physiology :

four fundamental sensations of taste described are sweet , sour , bitt

salt. •

This is probable over simplification because perception varies widely and many t cannnot be easily classified. •

Some tastes consistently stimulate taste buds in specific parts of tongue.

Sweet and salty mainly at the tip.

Sour, at the sides.

Bitter, at the back. The sense of taste triggers salivation and the secretion of gastric juice. •

It also has a protective fun, Eg : when foul – tasting food is eaten then reflex gagging or vomiting may be indu •

The sense of taste is impaired when the mouth is dry because substances can be t only if they are in solution.

Dermis : It is tough and elastic. Formed from connective tissue and the matrix contains collfibres interlaced with elastic fibres. The structures in the dermis are : •

Blood vessels

Lymph vessels

Sensory nerve endings

Sweat glands and their ducts

Hairs, arrector pilimuscles and sebaceous glands. functions of skin : It acts as a barrier against •

Invasion by microbes

Chemicals

Physical agents eg : mild trauma , uv light

Dehydration Dermis contains specialised immune cells called langerhans cells •

Due to presence of sensory nerve endings in the skin body reacts by reflex action unpleasant or painful stimuli, protecting it from further injury. Regulation of body temperature

The temp. of the body remains at about 36.8c (98.4f) across a wide range of environmental temperature.

Heat production : The principal organs involved are •

The muscles - contraction of skeletal muscles produces a large amt of heat.

The liver -chemically active, heat is produced a by product. Metabolic rate and he production are increased. •

Digestive organs - produce heat during peristalsis and by the chemical reactions involved in digestion. Heat loss : Most of the heat loss occurs through skin •

Small amts in expired air, urine & faeces.

Only heat lost through the skin can be regulated to maintain a constant body temperature. •

Heat loss through the skin is affected by difference between the body and environmental temperatures, the amt of the body surface exposed to the air and thtypes of clothes worn. Mechanism of heat loss : in evaporation, body is cooled when heat is used to convwater in sweat to water vapour. •

In radiation, exposed parts of the body radiate heat away from the body.

In conduction, clothes & other objects in contact with skin take up heat.

In convection, air passing over the exposed parts of the body.