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Anatomy & Physiology: Special Senses

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  • General senses

    Touch, pain, temperature, pressure, vibration, proprioception

  • Special senses

    Smell, vision, taste, hearing, equilibrium

  • Difference between general and special senses

    General senses are widespread and simple receptors; special senses are located in specific organs with complex receptors.

  • Location of olfaction (smell)

    Nasal cavity, specifically the olfactory epithelium.

  • Layers of olfactory region

    Olfactory epithelium and lamina propria.

  • Type of cells olfactory receptors are

    Modified neurons

  • How smell works

    Odorants bind receptors → Na⁺ channels open → depolarization → signal sent.

  • Nerve for smell

    Olfactory nerve (CN I)

  • Olfactory pathway

    Receptor → olfactory bulb → olfactory tract → brain

  • Unique feature of smell pathway

    Only sense that goes directly to cortex without passing through the thalamus.

  • Cells that regenerate olfactory receptors

    Basal cells

  • Anosmia

    Loss of smell, e.g., due to COVID-19.

  • Location of taste buds

    On tongue papillae

  • Papillae without taste buds

    Filiform papillae (function in friction)

  • Papillae with few taste buds

    Fungiform papillae (3–5 taste buds each)

  • Papillae with many taste buds

    Vallate and foliate papillae (~100 taste buds each)

  • Taste detection mechanism

    Taste hairs (microvilli) detect chemicals in food.

  • Nerves carrying taste signals

    Cranial nerves VII (facial) and IX (glossopharyngeal)

  • Taste signal pathway

    Signal → medulla → thalamus → cortex

  • Primary tastes

    Sweet, salty, sour, bitter

  • Umami taste

    Detects protein/amino acids

  • How salt and sour tastes are detected

    Via ion channels for Na⁺ and H⁺ ions.

  • How sweet, bitter, and umami tastes are detected

    Via G-protein coupled receptors (gustducins).

  • Final step in taste signal transduction

    Neurotransmitter release triggers nerve signal.

  • Taste sensitivity

    More sensitive to bitter than sweet tastes.

  • Lifespan of taste buds

    Replaced approximately every 10 days.

  • Effect of aging on taste

    Taste sensitivity declines after age 50.

  • Layers of the eyeball

    Fibrous (sclera + cornea), vascular (uvea) (iris, ciliary body, choroid), and neural (retina).

  • Function of iris

    Controls pupil size to regulate light entry.

  • Effect of sympathetic stimulation on pupil

    Dilates the pupil.

  • Effect of parasympathetic stimulation on pupil

    Constricts the pupil.

  • Function of ciliary body

    Controls lens shape for accommodation and produces aqueous humor.

  • Function of rods in retina

    Detect dim light and do not detect color.

  • Function of cones in retina

    Detect color and provide high visual acuity.

  • Fovea

    Area of highest cone density and best vision.

  • Fluids in the eye

    Aqueous humor in anterior cavity; vitreous humor in posterior cavity.

  • Glaucoma

    Increased intraocular pressure causing optic nerve damage.

  • Cataract

    Cloudy lens causing vision impairment.

  • Myopia

    Near-sightedness: focus is in front of the retina.

  • Hyperopia

    Far-sightedness: focus is behind the retina.

  • Presbyopia

    Age-related lens stiffening causing difficulty focusing.

  • Outer ear components

    Auricle (pinna) and external auditory canal.

  • Function of tympanic membrane

    Separates outer ear from middle ear and transmits sound vibrations.

  • Auditory ossicles

    Malleus, incus, stapes bones that amplify sound vibrations.

  • Function of auditory tube

    Equalizes pressure between middle ear and atmosphere.

  • Function of semicircular canals

    Detect rotational movement for balance.

  • Function of vestibule

    Detects position and linear movement.

  • Function of cochlea

    Responsible for hearing.

  • Hair cells in vestibular system

    Mechanoreceptors that detect movement.

  • Utricle function

    Detects horizontal movement.

  • Saccule function

    Detects vertical movement.

  • Otoliths

    Calcium crystals that aid balance by stimulating hair cells.

  • Benign paroxysmal positional vertigo (BPPV)

    Displaced otolith crystals causing dizziness.

  • Function of oval window

    Receives vibrations from the stapes to transmit into inner ear.

  • Function of round window

    Relieves pressure within the cochlea.

  • What determines pitch of sound

    Location of stimulation on the basilar membrane.

  • What determines loudness of sound

    Number of hair cells activated.