Sense Organs

Sense Organs: Specialized organs that detect changes in environment and send signals to brain.

Types: (1) Eyes (vision), (2) Ears (hearing and balance), (3) Nose (smell), (4) Tongue (taste), (5) Skin (touch, pressure, temperature, pain).

Receptors: Specialized cells or nerve endings that detect stimuli. Convert stimuli into electrical impulses.

Functions: (1) Detect environmental changes, (2) Send information to CNS, (3) Help in survival and adaptation.

Sensory Adaptation: Reduced sensitivity to constant stimulus. Example: Smell of room fades over time.

Diagram Importance: Overview diagram of human sensory system is essential for understanding.

Eye: Sense organ for vision. Spherical structure. Located in eye socket (orbit).

Parts: (1) Sclera (outer white layer), (2) Choroid (middle layer), (3) Retina (inner layer), (4) Cornea (transparent front), (5) Iris (colored part), (6) Pupil (opening), (7) Lens (focuses light), (8) Vitreous humor (gel-like).

Sclera: Tough, white outer coat. Maintains shape, protects inner parts.

Cornea: Transparent, curved. Refracts light. No blood vessels.

Iris: Colored muscular diaphragm. Controls pupil size (light regulation).

Pupil: Black opening in iris. Allows light entry.

Lens: Transparent, biconvex. Focuses light on retina. Changes shape for accommodation.

Retina: Inner layer with photoreceptors (rods and cones). Converts light to impulses.

Fovea: Area of sharpest vision. Contains only cones.

Blind Spot: Point where optic nerve exits. No photoreceptors.

Diagram Importance: Detailed labeled diagram of human eye (vertical section) is crucial for ICSE.

Image Formation: Light → Cornea → Pupil → Lens → Retina. Lens focuses image on retina.

Accommodation: Change in lens shape for near/far vision. Ciliary muscles contract for near vision.

Photoreceptors: (1) Rods - sensitive to dim light, black and white vision, (2) Cones - color vision, bright light, high acuity.

Distribution: Rods - periphery, Cones - fovea.

Color Vision: Three types of cones (red, green, blue). Color blindness - genetic defect.

Night Vision: Rods contain rhodopsin (visual purple). Regenerated by vitamin A.

Power of Accommodation: Ability to see objects at different distances.

Range of Vision: 25 cm (near point) to infinity (far point) for normal eye.

Myopia (Short-sightedness): Cannot see distant objects. Eyeball too long or lens too curved. Corrected by concave lens.

Hypermetropia (Long-sightedness): Cannot see near objects. Eyeball too short or lens too flat. Corrected by convex lens.

Astigmatism: Uneven curvature of cornea. Causes distorted vision. Corrected by cylindrical lens.

Presbyopia: Loss of accommodation with age. Bifocal lenses used.

Cataract: Clouding of lens. Treated by surgery (lens replacement).

Glaucoma: Increased intraocular pressure. Damages optic nerve. Can cause blindness.

Diagram Importance: Diagrams showing eye defects and corrections are frequently asked.

Ear: Sense organ for hearing and balance. Divided into external, middle, and internal ear.

External Ear: (1) Pinna (auricle) - collects sound waves, (2) Ear canal - directs sound, (3) Tympanic membrane (eardrum) - vibrates with sound.

Middle Ear: (1) Ossicles (malleus, incus, stapes) - amplify vibrations, (2) Eustachian tube - equalizes pressure.

Internal Ear: (1) Cochlea - hearing, (2) Semicircular canals - balance, (3) Vestibule - static balance.

Cochlea: Spiral structure. Contains organ of Corti with hair cells that detect sound vibrations.

Mechanism of Hearing: Sound waves → Eardrum → Ossicles → Oval window → Cochlear fluid → Hair cells → Auditory nerve → Brain.

Balance: Semicircular canals detect angular movements. Vestibule detects linear acceleration and gravity.

Diagram Importance: Labeled diagram of human ear showing all three parts is essential.

Nose (Olfaction): Detects smell. Olfactory receptors in nasal cavity. Impulses to brain via olfactory nerve.

Tongue (Gustation): Detects taste. Taste buds on tongue surface. Four basic tastes: sweet, sour, salty, bitter.

Skin (Somatosensory): Detects touch, pressure, temperature, pain. Receptors: Meissner's corpuscles (touch), Pacinian corpuscles (pressure), Krause's end bulbs (cold), Ruffini's corpuscles (heat).

Importance: All senses work together for complete perception of environment.

Sensory Pathways: Sensory nerves carry impulses from receptors to brain for interpretation.

Integration: Brain integrates information from all sense organs for coordinated response.

Example: Seeing food (eye), smelling aroma (nose), tasting (tongue) all contribute to eating experience.

Sensory Overload: Too much sensory input can cause confusion or stress.

Adaptation: Senses adapt to constant stimuli to focus on changes.

Eye Care: Regular checkups, protect from UV rays, avoid reading in dim light, eat vitamin A-rich foods.

Ear Care: Avoid loud noises, clean ears properly, treat infections promptly.

Common Disorders: (1) Conjunctivitis (eye infection), (2) Otitis media (ear infection), (3) Sinusitis (nose), (4) Glossitis (tongue).

Prevention: Healthy lifestyle, hygiene, protective gear (glasses, earplugs), balanced diet.