Sly Senses: Adding Knowledge About Sight, Hearing, and Taste

This article will provide supplementary and detailed information about the senses: sight, hearing, and taste.

I. Sight

1. Structure of the Eye

• Structure: The eye consists of 3 layers: outer layer, middle layer, inner layer.
• Outer layer:
  • Cornea (GM): Transparent, with a certain degree of curvature, is the outermost membrane, plays a role in refracting light.
  • Conjunctiva: Thin membrane covering the front of the eyeball and the inside of the eyelid.
  • Ciliary body: Smooth muscle ring, plays a role in changing the curvature of the lens (TTT) to adjust for near and far vision.
• Middle layer:
  • Iris: Colored, with a hole in the middle called the pupil, adjusts the diameter of the pupil, controls the amount of light entering the eye.
  • Lens (TTT): Transparent layer, with variable curvature, plays a role in refracting light and adjusting for near and far vision.
  • Vitreous humor: Transparent fluid, occupies most of the volume of the eyeball, plays a role in keeping the eyeball from collapsing.
• Inner layer:
  • Retina: Thin membrane, receives and processes light, consisting of 10 layers of cells.
    • Outermost layer: Pigment and vitamin A layer:
      • Pigment: Prevents light reflection throughout the eyeball.
      • Vitamin A: Helps form visual pigment.
    • Next layers: Rod cells, cone cells, bipolar cells, horizontal cells, amacrine cells, ganglion cells.
  • Optic nerve: Where the axons of ganglion cells converge, transmitting visual information to the brain.
  • Macula: Where cone cells are concentrated, the region of sharpest vision in the retina.
  • Blind spot: Where the optic nerve exits the retina, no light-sensitive cells are present.

Note:

• Aqueous humor: Transparent fluid located between the GM and TTT.
• Vitreous humor: Transparent fluid located between the TTT and retina.
• Ciliary body: Changes the curvature of the TTT, not the pupil diameter.
• Iris muscle: Changes the pupil diameter, not the curvature of the TTT.
• Retina: Composed of 10 layers of cells, not 6 layers.
• Macula: Has no rod cells, only cone cells.
• Blind spot: No light-sensitive cells are present, not light-sensing cells.
• In the retina, the convergence is 100:1, at the macula, especially the central fovea: 1:1. The area with the highest visual acuity in the retina.

2. Light Refraction

• Light refraction: The phenomenon of light being deflected when passing through a medium with a different refractive index.
• Factors affecting:
  • Characteristics of light rays: parallel light, convergent light, divergent light.
  • Characteristics of the lens: curvature, refractive index of the lens.

3. Mechanism of Adjusting for Near and Far Vision

• Far vision:
  • Ciliary body relaxes.
  • Suspensory ligament of the TTT stretches.
  • TTT flattens.
• Near vision:
  • Ciliary body contracts.
  • Suspensory ligament of the TTT slackens.
  • TTT bulges.

Note:

• Maximum limit of ciliary body contraction: 12 diopters.
• Presbyopia: Degeneration of lens protein causes the fibers to become less elastic, making it difficult to adjust for near vision.

4. Light-sensitive Receptor Cells

• Light-sensitive receptor cells: Rod cells and cone cells.
• Structure:
  • Outer segment: Many discs containing visual pigment (rhodopsin).
  • Inner segment: Mitochondria.
  • Synaptic terminal: Contact with horizontal and ganglion cells.

5. Visual Pigment

• Role: Changes membrane potential to create receptor potential.
• Structure: Opsin + retinal 1 (aldehyde of vitamin A1).
• Visual pigment of rod cells: Rhodopsin.
• Visual pigment of cone cells: 3 types: red, green, blue.

Note:

• The visual pigments only differ in the opsin component, retinal 1 remains unchanged.
• Vitamin A deficiency causes night blindness, which can lead to permanent blindness if left untreated.

6. Pupil

• Pupil diameter: Changes from 1.5-8mm.
• Adjustment:
  • Dark: Pupil dilates.
  • Light: Pupil constricts.
• Mechanism:
  • Sympathetic nervous system: Contracts the dilator pupillae muscle, pupil dilates (alpha receptors).
  • Parasympathetic nervous system: Contracts the sphincter pupillae muscle, pupil constricts (M3 receptors).

Note:

• The greatest depth of focus occurs when the pupil diameter is smallest.
• Large depth of focus: Clear image.
• Small depth of focus: Blurred image.

7. Optical Center of the Eye

• Nodal point: The optical center of the eye.
• Light rays passing through the nodal point: Not refracted.
• Image on the retina: Reversed compared to the object being observed.

8. Visual Pathology

• Emmetropia: Normal eye, parallel light rays converge on the retina.
• Hyperopia: Due to the eyeball having a shorter diameter than normal.
  • Parallel light rays converge behind the retina.
  • Corrected by wearing a convex lens.
• Myopia: Due to the eyeball having a longer diameter than normal.
  • Parallel light rays converge in front of the retina.
  • Corrected by wearing a concave lens.
• Astigmatism: Due to uneven corneal curvature, causing the point of convergence on the retina to differ, resulting in a blurred image.
• Presbyopia: Due to the loss of elasticity of the transparent protein layer, the TTT loses its ability to adjust.
• Optic nerve damage: Blindness on the side of the damage.

II. Hearing

1. Structure of the Ear

• Outer ear: Consists of the pinna, external auditory canal.
  • Pinna: Collects sound.
  • External auditory canal: Conducts sound to the tympanic membrane.
• Middle ear: Consists of the tympanic cavity, Eustachian tube, ossicles (malleus, incus, stapes).
  • Tympanic cavity: Located in the temporal bone, filled with air.
  • Eustachian tube: Connects the middle ear to the nasopharynx, helps balance pressure on both sides of the tympanic membrane.
  • Ossicles: Transmit vibrations from the tympanic membrane to the oval window.
• Inner ear: Consists of the bony labyrinth, membranous labyrinth.
  • Bony labyrinth: Encases the membranous labyrinth, filled with perilymph.
  • Membranous labyrinth: Consists of the semicircular canals, saccule, utricle, cochlea.
    • Semicircular canals: Sense angular acceleration.
    • Saccule, utricle: Sense linear acceleration.
    • Cochlea: Senses sound.

Note:

• Parts that conduct sound: Outer ear, middle ear, skull.
• Cochlea: Contains endolymph.
• Saccule and utricle: Belong to the inner ear, function to maintain balance.

2. Mechanism of Sound Transmission

• Outer ear: Collects sound, conducts sound to the tympanic membrane.
• Middle ear: Sound acts on the tympanic membrane, transmitted through the ossicles, causing the oval window to be pulled outward (if the tympanic membrane bulges) or inward (if the tympanic membrane retracts), causing perilymph in the vestibule to vibrate.
• Inner ear: Perilymph vibration causes the basilar membrane to move, stimulating the Organ of Corti, generating an electrical signal.
• Auditory nerve: Transmits the signal to the auditory cortex.

Note:

• Ossicles: Amplify sound 22 times.
• Tympanic membrane: Located between the external auditory canal and the middle ear.
• Oval window: Located between the middle ear and the vestibule.
• Round window: Located between the middle ear and the scala tympani.
• Vestibule: Contains perilymph, located at the top of the cochlea.
• Scala media: Contains endolymph, located in the middle.
• Scala tympani: Contains perilymph, located at the bottom.
• Organ of Corti: Located on the basilar membrane of the scala media, is the sound-sensing organ.

3. Sound Perception

• Pitch: Frequency of sound, unit Hz.
• Intensity: Loudness of sound, unit dB.
• Human hearing threshold: 2-20k Hz.
• Clear hearing threshold: 2k-4k Hz.
• Auditory stimulation threshold (standard sound): 3k Hz.
• Ear damage threshold: From 140 dB or higher (10^14 standard intensity).

4. Organ of Corti

• Structure:
  • Hair cells: 3 rows of outer hair cells and 1 row of inner hair cells.
  • Corti’s arch: Supports the reticular lamina.
  • Reticular lamina: Attached to the tops of the inner hair cells, moves with the basilar membrane.

Note:

• Outer hair cells: Amplify sound.
• Inner hair cells: Primary auditory function.
• Basilar membrane: Made of basilar fibers, originating from the bony cochlear axis, vibrates when receiving sound waves.
• Tectorial membrane: Very thin membrane, located on top of the reticular lamina.
• Endolymph: Contained in the scala media.
• Perilymph: Contained in the vestibule and scala tympani.

5. Mechanism of Organ of Corti Function

• Sound waves stimulate the basilar membrane: Causing basilar fibers to vibrate.
• Basilar membrane movement: Pulls the reticular lamina, bending the cilia of the hair cells.
• Cilia bending: Opens ion channels, K+ flows into the top of the hair cell, causing membrane depolarization.
• Membrane depolarization: Stimulates the release of neurotransmitter into the synaptic cleft.
• Electrical signal transmitted to auditory neurons: Transmitted to the auditory cortex.

Note:

• Basilar fibers: Closer to the apex of the cochlea, the fibers are shorter and stiffer, vibrating at lower frequencies.
• Basilar fibers: Closer to the base of the cochlea, the fibers are longer and smaller in diameter, vibrating at higher frequencies.
• Cilia: The tops of the outer cilia are located on the tectorial membrane, the tops of the inner cilia touch the tectorial membrane.

6. Hearing Pathology

• Sensorineural deafness: Due to damage to the cochlea or the auditory nerve pathway.
  • Causes: Long-term use of drugs that damage hair cells (aminoglycoside antibiotics), excessive noise, acoustic neuroma.
• Conductive deafness: Due to obstruction of sound conduction from the external auditory canal, tympanic membrane to the cochlea.
  • Causes: Blockage of the external auditory canal (foreign objects, earwax), destruction of ossicles, thickening of the tympanic membrane, perforation of the tympanic membrane, adhesions that reduce elasticity between the ossicles, stapes fixation to the oval window.

Note:

• Detection of middle ear blockage, Eustachian tube blockage: Impedance measurement using tympanometry.
• Detection of simulated deafness: Measurement of the stapedius reflex.
• Using a tuning fork frequency: 128Hz or 256Hz.
• Using speech: The normal distance for hearing clear speech is 5m, for whispered speech is 0.5m.

III. Taste

1. Structure of the Taste Organ

• Taste buds: Taste receptor organs, scattered on the tongue, palate, and pharynx.
• Taste cells: Located in taste buds, have taste hairs protruding outwards, contacting substances dissolved in saliva.

2. Mechanism of Taste Perception

• Substances dissolved in saliva: Stimulate taste hairs.
• Taste cells send signals: Transmitted to taste neurons.
• Taste neurons: Transmit signals to the gustatory cortex.

3. Types of Taste

• Sweet taste: Due to organic substances, mainly sucrose.
• Sour taste: Due to acids.
• Salty taste: Due to ionized salts, cations (represented by NaCl).
• Bitter taste: Due to many substances, especially nitrogenous and alkaloid substances (caffeine, nicotine).

Note:

• Taste: Perceived by specific taste receptors, coupled to G protein systems, activating second messenger systems.
• Sweet and bitter tastes: Perceived by taste receptors coupled to G protein systems, activating second messenger systems.
• Salty taste: Due to Na+ entering the cell through channels at the apex.
• Sour taste: Due to H+ closing calcium channels or entering the cell through ion channels.

4. Taste Pathology

• Dysgeusia: Due to viral infection.
• Ageusia: Due to damage to the chorda tympani nerve.
• Taste degeneration: Due to sclerosis.
• Taste hallucination: Due to drug addiction, central nervous system disorders.
• Hypogeusia: Due to radiation therapy or found in some elderly people.

Note:

• Ageusia: Can be “taste blindness” in some cases.
• Taste degeneration: A condition of decreased taste perception due to brain damage.
• Taste hallucination: A condition of perceiving unreal taste due to central nervous system disorders.

Conclusion

This article has provided supplementary and detailed information about the senses: sight, hearing, and taste. You can use this article to look up and learn about the senses.

Note:

• This article is just a part of the knowledge about the senses.
• For more complete and accurate information, you should consult more specialized materials.
• You should pay attention to protecting your senses by avoiding contact with harmful agents.