Eye aur ear: blind spot vs fovea, rods vs cones, aqueous vs vitreous humour, perilymph vs endolymph confusion

8 answers & replies

• [+][–]Sara Fernandes11thSample· 7d ago

  Class 11 here too, I think I know #1. The blind spot has only rods, so we can't see in dim light there, and the fovea has only cones, so it's the best at colour and detail? Is this right, or did I mess it up?

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  • [+][–]Siddharth RaoDropperSample· 7d ago

    Sara, the fovea part is right, but the blind spot is not "only rods". The blind spot is where the optic nerve (and the blood vessels) leaves the eye, and there are no photoreceptors at all there, neither rods nor cones, so no image is formed. That's why it's blind. Next to it, towards the side, is the macula lutea, a yellow pigmented spot with a small central pit, the fovea, which is thinned out and has only cones densely packed. That's the point of maximum visual acuity (sharpest vision). So Yash, "rods mostly in fovea" in your notes is wrong, you were right to doubt it.

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    • [+][–]Yash Tiwari11thSample· 7d agoAuthor

      Haan fovea me sirf cones, blind spot me kuch nahi. Notes me sudhaar kar diya. Thanks bhaiya!

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    • [+][–]Sara Fernandes11thSample· 7d ago

      Got it, thanks Siddharth 🙏 mistakes are how we learn lol

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• [+][–]Zoya Khan12thSample· 7d ago

  Rods and cones, the quick version:

  • Rods: contain rhodopsin (visual purple), a pigment made of opsin protein + retinal (a derivative of vitamin A). Work in dim light (twilight vision). Vitamin A deficiency → trouble in dim light, i.e., night blindness.
  • Cones: contain photopsins, work in bright light, give colour vision. There are three types, sensitive to red, green and blue light. The brain mixes the three signals to make all colours.

  A fun consequence: the fovea has no rods, so in the dark a very faint star seems to vanish when you look straight at it, and reappears when you look slightly to the side. That's rods working outside the fovea.

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• [+][–]Tanvi Deshmukh12thSample· 7d ago

  For the fluids and layers of the eye, a small diagram in words:

  Cornea → aqueous humour (thin watery fluid in the space between the cornea and the lens) → pupil, lens → vitreous humour (in the vitreous chamber, between the lens and the retina) → retina.

  So the aqueous is in front of the lens and the vitreous is behind. The iris (the coloured part) controls the size of the pupil. The lens is held in place by ligaments attached to the ciliary body. And the retina has three layers of cells: ganglion cells, bipolar cells, and the photoreceptor cells (rods and cones).

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• [+][–]Rahul DubeyDropperSample· 7d ago

  Ear, as a journey of sound:

  pinna → external auditory canal → tympanic membrane (eardrum) → three ear ossicles: malleus, incus, stapes → stapes pushes on the oval window → fluid (perilymph) in the cochlea moves → basilar membrane vibrates → hair cells of the organ of Corti bend against the tectorial membrane → impulses go through the auditory nerve → brain.

  Answering your confusing ones:

  • Eustachian tube connects the middle ear to the pharynx, and it equalises the pressure on both sides of the eardrum. That's why your ears "pop" when you yawn on a bus going uphill.
  • The cochlea is divided into the upper scala vestibuli, the lower scala tympani (both filled with perilymph, and the scala vestibuli ends at the oval window, the scala tympani at the round window) and the middle scala media, filled with endolymph. The organ of Corti sits on the basilar membrane inside the scala media.
  • Vestibular apparatus: the three semicircular canals and the otolith organ (utricle and saccule) for balance and posture.

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  • [+][–]Yash Tiwari11thSample· 7d agoAuthor

    Rahul bhaiya ye journey wali list ekdum chaapne wali hai 🔥 samajh aa gaya, testing kal subah. Thanks sab ko!

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