General & Special Senses

The Senses

  • Sensory info

    • Continuously surrounds us

    • Gives info abt the internal and external environ

    • Detected by receptors and sent to the brain

    • Comes in multiple forms

      • General—touch, pressure, pain, stretch, temperature)

      • Special—taste, smell, sight, hearing, balance

Sensory Receptors Have Receptive Fields

  • Receptive field—the area of distribution of sensitive ends of the receptor

  • There is an inverse relationship btwn field size and the ability to ID stimulus location

    • Small field = precise location is easily determined

    • Broad field = only general region can be determined

General Sense Organs

  • Often exist as individ cells or receptor units

  • Widely distributed

  • Examples

    • Free nerve ending—pain, temperature, and pressure

    • Tactile (Meissner’s) corpuscle—light touch and discriminative touch

      • Touch receptors closer to the surface are more sensitive to lighter touch compared to receptors deeper in the skin (which will be more sensitive to deeper sensations, like a hard press or smth)

    • Bulbous (Ruffini’s) corpuscle—deep pressure

    • Lamellated (Pacinian) corpuscle—pressure & vibration

    • (Krause’s) end bulb—light pressure & vibration

    • Tactile (Merkel) disc—light touch



Special Sense Organs

  • Large and complex organs

  • Localized grouping of specialized receptors

  • Five special senses

    • Gustation (taste)

    • Olfaction (smell)

    • Vision (sight)

    • Hearing (audition)

    • Equilibrium (balance & acceleration)

Gustation: Sense of Taste

  • Works w/ olfaction

  • Gustatory cells

    • Taste receptors are located in specialized organs, the taste buds (~40 per taste bud)

    • Taste buds lie alongside epithelial projections called papillae (4 types)

  • Involves mechanoreceptors and thermoreceptors

    • Provide info abt texture and temp



4 Types of Papillae on Tongue

  • Filiform—short spikes on anterior 2/3 of tongue that lack taste buds

    • Detect food texture and manipulate food

  • Fungiform—blocklike projections on top and sides of tongue that have a few taste buds

  • Vallate—large papillae in a V formation on the posterior surface of tongue that contain most of the taste buds

  • Foliate—extend as ridges on the lateral tongue; only contain a few taste buds during childhood


5 Taste Sensations

  • Sweet—organic compounds, such as sugar

  • Salt—metal ions, such as sodium or potassium

  • Sour—acids, scu

  • Bitter—alkaloid substances, such as unsweetened chocolate, nicotine, and caffeine

  • Umami—savory substances w/ a meaty or cheesy flavor; related to amino acids, such as glutamate and aspartate

Olfaction: Sense of Smell

  • Yellowish olfactory epithelium lines the superior region of the nasal cavity

  • Olfactory receptor cells detect dissolved odor molecules; replaced every 40-60 days by basal cells

  • Humans can distinguish one odor among thousands

  • Olfactory receptors are extremely sensitive, but easily adapt (become fatigued)

    • When you start using a new shampoo, you are very aware of it but over time, you don’t smell it as much anymore. Your brain no longer deems the new scent important/dangerous, so it picks up on it less


Vision: Sense of Sight

  • Major anterior eye structures

    • Sclera—”white” of the eye

    • Cornea—transparent covering over iris

    • Conjunctiva—mucous membrane covering the sclera (except cornea)

    • Lacrimal gland—contains tear-producing cells

    • Aqueous humor—chamber containing watery fluid

    • Iris—colored part of the eye containing the pupil

    • Lens—transparent body behind the pupil that focuses light on the retina



  • Major posterior eye structures

    • Vitreous humor—chamber of gel-like fluid that causes the eye to be a round shape

    • Retina—innermost layer of the eye containing photoreceptors that detect the light

      • Rods—detect greyscale lightwaves

      • Cones—detect color lightwaves



  • Optic disc—lacks photoreceptors; cannot form an image

  • Macula lutea—contains the fovea centralis, which forms the sharpest color images


  • Image Formation

    • Images are not single point, but rather consist of large numbers of individual points (like pixels on computer screen) each focused on the retina

    • Image is inverted and reversed; brain compensates—learned from experience


Audition: Sense of Hearing

  • Three ear regions

    • External ear (air-filled)—funnels sound waves into the canal to the tympanic membrane

    • Middle ear (air-filled)—transmits and amplifies sound waves; connects to the nasopharynx through the auditory tube

    • Inner ear (fluid-filled)—cochlea creates nerve impulses in response to sound waves that move cochlear hair cells

  • The auditory tube allows air pressure to equalize on both sides of the tympanic membrane for optimal hearing




Senses of Equilibrium and Acceleration

  • Receptors in the fluid-filled semicircular canals detect rotation and acceleration

  • Fluid mvmt pushes on hair cells that respond by creating nerve impulses

  • Vision is important to maintaining equilibrium