ICSE 10 Biology Sense Organs Short

⚡ Quick Revision: The Human Eye (Anatomy)

🔹 Outer and Middle Coats

• ✔ Sclera & Cornea: The white protective layer (Sclera) becomes the transparent Cornea in front to admit light.
• ✔ Choroid: Rich in blood vessels and melanin (dark pigment) to prevent internal reflection of light.
• ✔ Iris & Pupil: The muscular Iris regulates the size of the Pupil to control light entry.

Internal Structure of the Eye

🔹 Inner Coat: The Retina

• ✔ Rods: Sensitive to dim light; do not perceive colors (contain Rhodopsin).
• ✔ Cones: Sensitive to bright light and responsible for color vision (contain Iodopsin).
• ✔ Yellow Spot (Macula): Area of brightest vision; contains maximum cones.

Term Card

Blind Spot: The point on the retina where the optic nerve leaves the eye; no photo-receptors are present here.

❌ Don't Confuse:

Aqueous Humour with Vitreous Humour. Remember: Aqueous is watery and in front of the lens; Vitreous is jelly-like and fills the space behind the lens.

⚡ Quick Revision: Accommodation & Eye Defects

🔹 Power of Accommodation

• ✔ Distant Vision: Ciliary muscles relax → Suspensory ligaments pull tight → Lens becomes thin/flat.
• ✔ Near Vision: Ciliary muscles contract → Suspensory ligaments relax → Lens becomes thick/convex.

🔹 Common Vision Defects

Defect	Description	Correction
Myopia (Short-sight)	Cannot see far; image forms in front of retina.	Concave Lens
Hyperopia (Long-sight)	Cannot see near; image forms behind retina.	Convex Lens
Astigmatism	Uneven curvature of cornea; blurred vision.	Cylindrical Lens

[attachment_1](attachment)

Term Card

Presbyopia: A condition in elderly people where the lens loses flexibility, making near vision difficult (corrected by bifocal lenses).

❌ Don't Confuse:

Cataract with Glaucoma. Remember: Cataract is the lens becoming opaque (milky); Glaucoma is increased pressure in the eye due to blocked drainage of aqueous humour.

⚡ Quick Revision: The Human Ear

🔹 Parts of the Ear

• ✔ Outer Ear: Pinna collects sound; Auditory canal leads to the Eardrum (Tympanum).
• ✔ Middle Ear: Contains three ossicles (Malleus, Incus, Stapes) that amplify sound vibrations.
• ✔ Inner Ear (Membranous Labyrinth): Contains Cochlea (for hearing) and Semicircular canals (for balance).

Labeled Diagram of the Human Ear

🔹 Dual Function: Hearing & Balance

• ✔ Organ of Corti: Located inside the cochlea; contains sensory hair cells that convert vibrations into nerve impulses.
• ✔ Dynamic Balance: Managed by sensory cells in the Semicircular Canals.
• ✔ Static Balance: Managed by the Utriculus and Sacculus (Vestibule).

Term Card

Eustachian Tube: Connects middle ear to the throat; equalizes air pressure on both sides of the eardrum.

❌ Don't Confuse:

Perilymph with Endolymph. Remember: Perilymph is the fluid outside the membranous labyrinth; Endolymph is the fluid inside it.

⚡ Quick Revision: Chemical Senses & Sensory Summary

🔹 Taste and Smell (Chemoreceptors)

• ✔ Tongue: Contains Taste Buds (Sensory papillae) for Sweet, Sour, Salty, and Bitter.
• ✔ Nose: Contains Olfactory Receptors in the upper nasal cavity to detect chemical vapors.
• ✔ Skin: Contains Mechanoreceptors (Touch/Pressure), Thermoreceptors (Heat/Cold), and Nociceptors (Pain).

🔹 Sensory Receptors Summary

Sense Organ	Type of Receptor	Stimulus
Eye	Photoreceptors	Light
Ear	Phonoreceptors	Sound/Gravity
Nose/Tongue	Chemoreceptors	Chemicals

Term Card

Stereoscopic Vision: The ability to perceive depth and distance because our eyes see the same object from slightly different angles.

❌ Exam Tip:

If asked about the Stapes, always mention it is the smallest bone in the human body and it vibrates against the Oval Window.