Special Senses Question And Answers

Question 1. Name the receptors for light. Give their specific functions. Draw and explain visual pathway. (or) Describe the visual pathway. (or) What are the receptors for vision? Draw and label visual pathway. (or) Receptors of vision/rods and cones.
Answer:

Visual receptors and their functions:

Read And Learn More: BDS Previous Examination Question And Answers

Visual pathway:

• It consist of a 6 components.

1. Optic nerve:

• It is formed by the axons of ganglionic cells.
  1. The fibres from the temporal part of retina and present in the lateral half of the nerve.
• They carry impulses from nasal feild of same eye.
  1. The fibres from the nasal part of retina are present in the medial half of the nerve they carry impulses from temporal field of same eye.

2. Optic chiama:

• It is formed by the crossing of medial fibres of both the optic nerve.

3. Optic tract:

• The medial fibers of each optic nerve cross the midline and join the uncrossed lateral fibers of opposite side to form the optic tract.
• The fibers run backwards towards the cerebral peduncle and reach the lateral geniculate nucleus.

4. Lateral geniculate nucleus:

• It is a part of thalamus.
  1. Majority of the fibers synapse and forms subcortical center for visual sensation.
     • From here, the geniculocalcarine tract or optic radiation arises.
     • It is last relay of visual pathway.
  2. Some fibres do not synapse and pass through to terminate in any one of the following centres.
     • Superior colliculus.
     • Pretectal nucleus.
     • Supraoptic nucleus of hypothalamus.

5. Optic radiation:

• Fibers from lateral geniculate body pass through internal capsule and form optic radiation.
• It terminates in primary visual area of visual cortex.

6. Visual cortex:

• It is located on the medial surface of the occipital lobe along the wells and lips of calcarine fissure.
• The macular representation occupies the posterior part while peripheral representation occupies the anterior part of visual cortex.

Question 2. What are primary tastes? Describe pathway of sensation of taste. (or) Primary tastes.
Answer:

Primary Tastes:

There are 4 primary taste sensations they are:

Taste pathway:

• It is bilateral pathway.

1. First order neurons of it are in the nuclei of three different cranial nerves.

1. Chorda tympani branch of the facial nerve runs from anterior 2/3rd of the tongue.
2. Glossopharyngeal nerve – runs from posterior 1/3rd of the tongue.
3. Vagus nerve runs from epiglottis and pharynx.
   • On each side the fibres of these nerves unite in the medulla to form tractus solitaris.

2. Second order neuron.

• Present in the nucleus of tractus solitaris.
• Axon of its ascend and join the medial lemiscus and terminate in posteroventral nucleus of thalamus.

3. Third order neuron.

• Present in the posteroventral nucleus of thalamus.
• Axons of this neuron project into parietal lobe of the cerebral cortex.
• It ends in the lower part of post central gyrus, which forms the center for taste sensation.

Question 3. Give an account of the structure and functions of skin. (or) Functions of skin. 
Answer:

Structure of skin:

• Skin is made up of two layers.

1. Epidermis:

• It is outermost layer formed by stratified epithelium.
• It consists of 5 layers.

• From this layer, projections called rete ridges extend down upto dermis.

2. Dermis:

• It is a connective layer.
• It is made up of

Collagen fibers:

• Exhibits elastic property
• Capable of storing water
• Contains collagenase enzyme which helps in wound healing.

Cells:

• Fibroblasts.
• Histiocytes.

Layers:

• Superificial papillary layer.
• Deeper reticular layer.

Functions of skin:

1. Protective function:

1. Protection against bacteria and toxic substances.
   • Skin covers the organs of the body and protects the organs from having direct contact with external environment and prevents in infections.
   • During injury, keratinocytes in skin secretes cytokines and antimicrobial peptides.
2. Protection from mechanical blow.
   • Skin is placed loosely over subcutaneous tissue thus prevents transmission of any below to the underlying tissues.
3. Protection from ultraviolet rays.
   • Exposure to sunlight or UV radiation increase melanin production in skin.
   • This absorbs ultraviolet rays.

2. Sensory function:

• Skin has many nerve ending forming cutaneous receptors.

3. Storage function:

• Skin stores fat, water, chloride and sugar.

4. Synthetic function:

• Vit D3 is synthesized in skin

5. Regulation of body temperature:

• Excess heat from the body is lost by radiation conduction, convection and evaporation through skin.

6. Regulation of water and electrolyte balance:

• Skin excrete water and salts through sweat and maintains balance.

7. Excretory function:

• It excretes urea, salts, fatty substances in small amounts.

8. Absorptive function:

• It absorbs fat soluble substances and some ointments.

9. Secretory function:

• Skin secretes.
• Sweat-through sweat glands
• Sebum-through sebaceous glands.

Question 4. Explain role of skin in temperature regulation.
Answer:

• Skin helps in temperature regulation by maintain balance between heat production and heat loss.

1. Heat production:

• By following mechanism heat is produced and thus heat is gain in the body.

Shivering:

• Exposure to cold causes rapid involuntary muscular contractions called shivering.
• During this enormous heat is produced.

Cutaneous vasoconstriction:

• When cutaneous blood vessels are cooled, they become more sensitive to catecholamines and the arterioles and venules constrict.
• This direct blood away from the skin into deeper veins.
• Therefore, heat is transferred from the warm arterial blood to the cold venous blood coming from the extremities.

2. Heat loss:

• Heat loss occurs in skin by.

Increased sweating:

• This, in turn, decreases body temperature.

Cutaneous vasodilation:

• When the sympathetic centers are inhibited, there is vasodilation.
• This increases blood flow through skin causing increased sweating.
• This, in turn, causes heat loss.

Question 5. Accommodation of eye.  (or) Accommodation reflex.
Answer:

Definition:

The ability of the eye to focus an object at varying distances is called accommodation.

Mechanism:

• Accommodation can be achieved by.
  1. Change in the length of the eyeball.
  2. Changing the curvature of the cornea.
  3. Moving the lens.
  4. Changing the curvature of the lens.

Pathway:

• Visual impulses from retina pass through visual pathway to visual cortex of occipital lobe.
• From here, association fibers carry the impulses to frontal lobe to frontal eye field – area 8.
• Corticonuclear fibers from here pass in the anterior limb of the internal capsule to reach the III nerve nucleus.
• This supplies following muscles.

Summary: Pathways for light reflex (direct and consensual)

Question 6. Describe the refractory errors of the eye and how they are corrected.
Answer:

Refractory errors: Type

Question 7. What are the contents and functions of middle ear? Explain tympanic reflex.
Answer:

Tympanic reflex:

• It can be activated either by sounds or one’s speech mechanism.
• When loud sounds are transmitted through the ossicular system into the CNS, a reflex occurs after a latent period of 40 – 80 milliseconds.
• It causes contraction of.

• As these two forces oppose each other, it causes stiffness of ossicles and thereby the transmission of sound is decreased.
• This helps in the following.
  1. Protects cochlea from damaging vibrations.
  2. Filters low frequency sounds.
  3. Protects tympani membrane from being ruptured by loud sound.
  4. Prevents fixation of footplate of stapes, against oval window during exposure to loud sound.

Question 8. Taste receptors.
Answer:

• The taste receptors are the chemoreceptors which are stimulated by substances dissolved in the oral fluids.
• They are the type III cells of taste buds.
• They are located on the edges and dorsum of the tongue, on the epiglottis, soft palate and pharynx.
• The taste buds are located in the walls of the papillae.

Types of Papillae:

• The cells within the laste buds are of two types.
  • Gustatory receptor cells.
  • Supporting cells.

Question 9. Trace the pathway for taste sensation with the help of a diagram. (or) Taste pathway.
Answer:

Question 10. Write short notes on sense of smell. (or) Sensation of smell.
Answer:

• The sensation of smell is called olfaction.
• The olfactory receptors are situated in olfactory mucous membrane located in the roof of the nasal cavity.

Olfactor pathway:

Abnormalities:

Question 11. Aqueous humour.
Answer:

• It is a thin fluid in front of retina and fills the space between the lens and cornea.
• It is secreted from the epithelial cell lining of the ciliary body
• It is drained by the ciliary veins and the canal of schiemm.

Properties:

• Volume – 0.13 ml.
• pH 7.5, Alkaline.
• Viscocity – 1.029
• Refractory index. 1.34

Composition:

1. Water-98.7%

2. Solids – 1.3%

1. Organic substances
2. Inorganic substances.

Question 12. Functions of aqueous humour.
Answer:

• It maintains shape of the eyeball.
• It maintains intraocular pressure.
• Provides nutrition to the avascular structures like lens and cornea.
• Removes metabolities.
• Acts as a reflective medium.

Question 13. Dark adaptation.
Answer:

Defintion:

• The process by which the person is able to see the objects in dim light is called dark adaptation.

Duration:

• The maximum duration of it is about 20 min.

Causes:

• Increased sensitivity of rods.
• Dilatation of pupil.

Question 14. Light adaptation. (or) Presbyopia. (or) Myopia. (or) Refractory error of eye.
Answer:

Definition:

• The process by which the person is adapted to bright light after entering from dim light area is called light adaptation.

Duration:

• Its maximum duration is 5 min.

Causes:

• Reduced sensitivity of rods
• Constriction of pupil.

Question 15. Acuity of vision.
Answer:

Definition:

• The ability of the eye to determine the precise shape and details of the object is called acuity of vision.
• Cones of the retina are responsible for acuity of vision.
• It is reduced during the refractory errors.

Test for visual acuity:

• Visual acuity is tested for distant as well as nearby objects.
• Sneller’s chart is used to test the acuity of vision for distant vision.
• Jaeger’s chart is used to test the visual acuity for near vision.

Question 16. Visual pathway.
Answer:

Question 17. Colour blindness.
Answer:

Definition:

• Inability to distinguish colour is called colour blindness.
• It is more common in males than in females.

Causes:

1. Herediatary

2. Acquired conditions.

• Trauma
• Chronic diseases
• Drugs like barbiturates
• Toxins like carbon monoxide.
• Alcoholism.
• Aging.

Classification:

• Based on Young-Helmholtz trichromatic theory, colour blindness is classified into.

1. Monochromatism.

• In this condition, the person cannot appreciate any of the primary colour.

2. Dichromatism.

• In it, the subject can appreciate only two primary colours.

3. Trichromatism.

• Subject are able to perceive all the three colours but the intensity of one of the primary colors cannot be appreciated correctly.

Question 18. Organ of corti.
Answer:

• It is the located on the basilar membrane extending from the apex to the base of the cochlea.

Cells of it:

• It consists of
  1. Border cells.
  2. Inner hair cells.
  3. Inner phalangeal cells.
  4. Inner pillar cells.
  5. Outer piller cells.
  6. Outer phalangeal cells.
  7. Outer hair cells
  8. Cells of Hensen.
  9. Cell of Claudius
  10. Tectorial membrane and lamina reticularis.

Question 19. Enumerate the heat gain mechanism occurring in the body when the body is exposed to cold environment.
Answer:

• Heat production is increased in the body by the following mechanism when the body is exposed to cold environment.
  1. Shivering
  2. Increased metabolic reactions.
  3. Increased sympathetic activity.
  4. Increased adrenaline secretion.
  5. Radiation.

Question 20. Heat loss mechanism.
Answer:

• Heat is loss from the body by.
  • Conduction
  • Convection
  • Radiation
  • Evaporation
  • Panting in animals.

Question 21. What is normal body temperature? Enumerate thermal regulation organs of the body.
Answer:

Normal body temperature:

• The normal body temperature in human is 37°C when measured by placing the clinical thermometer in the mouth.
• Thermal regulating organs of the body:

1. Hypothalamus.

• It contains heat gain and heat loss center.

2. Skin.

• It regulates body temperature by vasoconstriction or vasodilation of blood vessels.

3. Hair.

• Erection of the hairs over skin causes increase in thickness of the trapped air.
• Thus, heat transfer across the layer is reduced and heat loss is decreased.

Question 22. Taste buds
Answer:

• Taste buds are located in the walls of the papillae
• They are oval clusters of cells in the epithelial layer with a small pore opening on the surface.
• This allows substances to reach the interior of the taste buds

Cells Within Taste Buds:

• Cells within the taste buds are of two types
  1. Gustatory receptor cells
  2. Supporting or sustentacualar cells

Question 23. Hypermetropia
Answer: