1. The Senses Nestor T. Hilvano, M.D., M.P.H.
(Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain, Textbook, 2012.)

2. Learning Objectives State the functions of sensory pathways.
Define sensory receptors and describe the 5 general categories of sensory receptors.
Describe the human eye and its function.
Compare the rods and cones of retina.
Explain myopia, hyperopia, presbyopia and astigmatism.
List the structure of ear in the order in which they participate in hearing.
Explain how body position and movement are sense in the ear.
Discuss how odor and taste receptors function.

3. Sensations All stimuli represent forms of energy
Sensation involves converting energy into a change in the membrane potential of sensory receptors
The brain interprets sensations, giving the perception of stimuli
General senses (Somatic)- skin, muscles, joint, and viscera (internal organs)
Special senses- sight (vision), smell (olfaction), taste (gustation), hearing (audition), and vestibular (balance/equilibrium)

4. Fig. 50-2
Functions of Sensory Pathways: sensory reception, transduction, transmission, and integration (brain perception)
Weak receptor potential
Action potentials
Membrane potential (mV)
–50
Membrane potential (mV)
–70
Slight bend: weak stimulus
–70
Brain perceives slight bend.
Dendrites
Stretch receptor
Time (sec) 1 2 4
Axon 3
Brain
Muscle
Brain perceives large bend.
Action potentials
Large bend: strong stimulus
Strong receptor potential
Membrane potential (mV)
Figure 50.2 A simple sensory pathway: Response of a crayfish stretch receptor to bending
Membrane potential (mV)
–50
–70 1
Reception
–70
Time (sec) 2
Transduction 3
Transmission 4
Perception

5. Sensory Receptors: Transduce Stimuli into Action Potential
Classification of Receptors:
Pain (nociceptors) receptors – inflame/damage tissues
Thermoreceptors – change in temp., hot or cold
Mechanoreceptors – change in pressure or fluid movement; touch, pressure, stretching of muscles, motion, sound
Chemoreceptors – change in odor and taste
Electromagnetic receptors – electricity, magnetism, and light (photoreceptors)
Receptors for General senses:
Pain - free nerve endings
Temperature –Ruffini (hot); Kraus End Bulb (cold)
Crude (light) touch -Meissner’s corpuscle
Proprioception (deep touch and pressure) -pacinian corpuscle
Receptors for Special senses:
Vision – rods and cones
Audition – organ of corti
Vestibular – maculae, cristae
Olfaction- olfactory cell
Gustation- taste bud

6. Figure 30.13 Some Mechanoreceptors in Human Skin
Human skin contains many different types of neurons and sensory cells that provide detailed information about mechanical stimuli.

7. Eyeball - Vision Fibrous (outermost) layer = sclera and cornea
Vascular (middle) layer = choroid, ciliary body, and iris
*pupil – central opening
* Light passes through a transparent
lens that focuses images on the retina
Nervous (innermost) layer = retina,
photoreceptor layer (rods and cones)
Rods - sensitive to low level of light; night vision
Cones - detect colors of light; day vision
_____ - center of sharpest vision (cones only)
_____ - Blind spot (w/ nerve & b.v.)
a. optic disc b. fovea centralis
Aqueous humor filled the chamber in front of the lens
Vitreous humor filled the chamber behind the lens

8. Figure 30.14 Major Features of the Human Eye
A pupil adjusts the amount of light entering through the lens. The lens focuses images on the retina, where photoreceptor cells generate nerve impulses in sensory neurons that are closely associated with them.

9. Figure 30.17 Sensory Neurons in the Retina Send Visual Information to the Brain
Layers of sensory neurons stacked above the rods and cones process visual information to some degree before sending it to the brain via the optic nerve.

10. Copyright © 2009 Pearson Education, Inc
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

11. Visual Problems Passage of light:
Light cornea aqueous humor pupil lens
vitreous humor retina
Nearsightedness (myopia)- Can’t see far distance; eyeball is longer; focus distant objects in front of retina; corrective lenses that are thinner in the middle
Farsightedness (hyperopia)- Can’t see near distance; eyeball is short; focal point is behind the retina; corrective lenses that are thicker in the middle
*presbyopia – hyperopia in old age, inelasticity of lens
Astigmatism – blurred vision caused by misshapen lens or cornea; corrective asymetrical lens

12. Clinical Correlation ___ = clouding of lens
aging, diabetes, smoking, and UV light
___ = death of retinal cells due to elevated pressure within the eye
___ = pink eye, results from damage or irritation of conjunctival surface.
a. glaucoma b. conjunctivitis c. cataract

13. Ear: Hearing Mechanoreceptor (change in pressure due to sound waves)
Outer ear = pinna and auditory canal
* tympanic membrane
Middle ear = contain ossicles
(malleus, incus, stapes)
* oval window
Inner ear = cochlea (contains organ of corti)
Auditory nerve
Sound volume (loudness) ranging
from 0 to 120 db. (long exposure to
90 db can cause hearing loss)
Pitch (frequency) from 20 – 20,00 Hz.
Sound at pinna auditory canal tympanic membrane middle ear oval window cochlea (organ of corti) send impulses to the brain (auditory cortex)

14. Semicircular canals (function in balance) Skull bones Oval window
Figure 29.4B
Semicircular canals
(function in balance)
Skull bones
Oval
window
(behind
the
stirrup)
Auditory
nerve,
to the brain
Hammer
Anvil
Stirrup
Eardrum
Figure 29.4B The middle ear and the inner ear
Cochlea
Eustachian
tube
(connects to
the pharynx) 14

15. Ear: Vestibular Sense: (Body Position and Balance)
Inner ear – houses organs of balance
a) Semicircular canals = crista ampullaris, receptor for changes in head’s rate of rotation
b) Utricle and saccule – maculae, receptor for head position relative to the force of gravity and linear motion

16. Semicircular canals Flow of fluid Vestibular nerve Cupula Hairs
Fig
Semicircular canals
Flow of fluid
Vestibular nerve
Cupula
Hairs
Hair cells
Vestibule
Figure Organs of equilibrium in the inner ear
Axons
Utricle
Body movement
Saccule

17. Taste Receptors Chemoreceptors in taste buds 4 types a) sweet b) sour
c) salty
d) bitter
A fifth taste perception called umami (elicited by glutamate)
Taste perception varies with individuals and may be related to genetic traits

18. Figure Taste in Humans
Taste buds consist of groups of chemoreceptor cells and supporting cells. The receptor cells respond to chemicals that lodge in the tongue during eating.

19. Smell Receptors
Chemoreceptors in nose (olfactory mucosa) – olfactory (bipolar) cells
Integration of signals in the brain results in an odor perception
Smell is tied with limbic system, evoking emotions and memories.

20. Figure 30.12 The Human Sense of Smell

21. Homework
Define terms: rods, cones, presbyopia, myopia, hyperopia, astigmatism, cornea, lens, tympanic membrane, semicircular canals, utricle and saccule, cataract, glaucoma, conjunctivitis, optic disc, fovea centralis, macula, cristae ampullaris.
Give the sensory receptors of the following:
__ pain a. bipolar (olfactory) cells
__ pressure and deep touch b. organ of corti
__ taste c. free nerve endings
__ olfaction d. pacinian corpuscle
__ hearing e. taste bud
Classify the receptors of the items listed below:
__ change in pressure or fluid movement a. chemoreceptor
__ change in light perception b. thermoreceptor
__ change in smell of CO2 c. photoreceptor
__ change in climate’s temperature d. mechanoreceptor