1. Structure
• Free nerve ending: a form of peripheral ending of sensory nerve fibers in which
the terminal filaments end freely in the tissue.
Synonyms: terminationes nervorum liberae (40)
• Root Hair Plexuses: free nerve endings associated with hair follicle - very sensitive
to touch which moves the hair (41)
• Merkel Disks: Merkel's disks are located in the epidermis, where they are precisely
aligned with the papillae that lie beneath the dermal ridges. They account for
about 25% of the mechanoreceptors of the hand and are particularly dense in the
fingertips, lips, and external genitalia. (42)
• Meissner Corpuscle: enclosed in connective tissue capsule, just below epidermis in
hairless areas of skin such as lips, finger tips, nipples, external genitalia, palms of
hands and soles of feet - fine touch and pressure (41)
• Pacinian Corpuscles: enclosed in multilayered connective tissue capsule, in
deeper skin and tendons, sensitive to deep pressure and high pressure vibrations
(41)
• Muscle Spindles: small sensory organs that are enclosed within a capsule. They
are found throughout the body of a muscle, in parallel with typical muscle fibers.
There are several small, specialized muscle fibers known as intrafusal fibers. (43)
• Golgi tendon Organs: are in series with muscle fibers, located in the tendons that
attach muscle to bone. The sensory dendrites of the Golgi tendon organ afferent
are interwoven with collagen fibrils in the tendon. (43)

2. 44

4. SMELL
Smell (give diagram of nose indicating receptors)
Describe each
(1) smell, also called Olfaction, the detection and identification by sensory organs of
airborne chemicals. The concept of smell, as it applies to humans, becomes less distinct
when invertebrates and lower vertebrates (fish and amphibians) are considered, because
many lower animals detect chemicals in the environment by means of receptors in
various locations on the body, and no invertebrate possesses a chemoreceptive structure
resembling the vertebrate nasal cavity. For this reason, many authorities prefer to regard
smell as distance chemoreception and taste as contact chemoreception.
Left Right
receptor receptor
bulb bulb
(20)

5. Smell diagram! (7)

6. Olfactory receptors
olfactory receptor, also called
smell receptor, of binding odour
molecules that plays a central role
in the sense of smell (olfaction). In
terrestrial vertebrates, including
humans, the receptors are located
on olfactory receptor cells, which
are present in very large numbers
(millions) and are clustered within
a small area in the back of the
nasal cavity, forming an olfactory
epithelium. (2)
(20)
OLFACTORY RECEPTOR BULB

7. Olfactory pathways
Olfactory
OLFACTORY
straie
RECEPTOR
(yellow)
BULB (blue)
(20)
The sense of smell can create a powerful and long lasting memories.
These memories couples with unique sensory inputs especially ordor,
often persist from early child hood to death. New car, baby, kitchen and
people odors are all olfactory triggers that often bring back memories of
events that have occurred from the past. There is a huge relationship
between the olfactory and gustatory pathways because our sense of
smell and taste are closely related. (8)

8. Com paring human and canine olfaction
(5)Taste bud organ located on the tongue in terrestrial vertebrates that
functions in the perception of taste. In fish, taste buds occur on the lips, the
flanks, and the caudal (tail) fins of some species and on the barbells of
catfish. In most animals, including humans, taste buds are most prevalent on
small pegs of epithelium on the tongue called papillae The taste receptor
cells of other animals can often be characterized in ways similar to those of
humans, because all animals have the same basic needs in selecting food.
(4)

9. Neural pathway
The gustatory sensations or taste are closely associated with olfaction. Taste
receptors are located inside structures called taste buds that line the surface
of the tongue, and are found on the soft palate, pharynx, and larynx.
Nervous impulses generated in the anterior two thirds of the tongue travel
over the facial nerve where they are generated from the posterior one third
are conducted by fibers of the glossopharynegal.(10)
(9)

10. Taste
(20)
Taste buds:
bitter,
sweet,
papillaeh
sour,
salty
The taste buds are embedded in the epithelium of the tongue and make
contact with the outside environment through a taste pore.
Taste Buds are small organs located on the tongue in
terrestrial vertebrates that functions in the perception of taste
Taste buds are composed of groups of between 50 and 150 columnar taste receptor
cells bundled together like a cluster of bananas. The taste receptor cells within a bud
are arranged such that their tips form a small taste pore, and through this pore
extend microvilli from the taste cells. The microvilli of the taste cells bear taste
receptors.

11. (51)

12. The Mechanism of Hearing
 When one hears a sound or someone speaking, then an image
comes to mind that is called the cartilaginous tissue, or the pinna.
The pinna directs the sound energy into the ear canal. The eternal
meatus is about one inch in length and is closed at the inner end
near the ear drum; it forms a passage way in which sound energy
may be transmitted into the inner reaches of the ear. (30)
(45)

13. Neuronal pathway of Hearing
 Cochlear N. to the brain stem interneurons to multi-neuron pathway
to the thalamus then to the auditory cortex
 The Organ of Corti with its sound-sensitive hair cells and basilar
membrane are important parts of the sound transducing system for
hearing. Mechanical vibrations of the basilar membrane generate
membrane potentials in the hair cells which produce impulse
patterns in the cochlear portion of the vestibulocochlear nerve
(cranial nerve VIII). (53)

14. (49)

15. Vestibule and semicircular canals
 The vestibule has a round open space that accesses various passageways, it is
the central structure within the inner ear. The outer wall of the vestibule contains
the oval and round windows (which are the connection sites between the middle
and inner ear). Internally, the vestibule contains two membranous sacs, the
utricle and the saccule, which are lined with tiny hair cells. (47)
 The semicircular canals have three bony tubes that form loops. Each tube ends
in a bulge, or ampulla, containing sensors that detect the movement of fluid in
the loop—which depends on your body’s movement. Similar receptors called
maculae detect how upright you are. Your brain uses these signals to correct your
balance. (48)
 The vestibular system serves the bodily functions of balance and equilibrium. It
accomplishes this by assessing head and body movement and position in space,
generating a neural code representing this information, and distributing this
code to appropriate sites located throughout the central nervous system.
Vestibular function is largely reflex and unconscious in nature. (46)

16. Having a sense of balance is…
 The semicircular canals are three pretzel-like curved tubes arranged at
angles roughly perpendicular to each other, with the two vestibular sacs
located at their base. Both the canals and sacs contain fluid and tiny hair
cells, which act as receptors. When a person's head moves, the fluid
disturbs the hair cells, which stimulate a branch of the auditory nerve,
signaling the brain to make adjustments in the eyes and body. A
movement at any given angle will have its primary effect on one of the
three canals. Overstimulation from extreme movements will produce
dizziness and nausea. (32)

17. Dynamic Equilibrium…
 The special sense which interprets balance when one is moving, or
at least the head is moving; the semicircular canals contain the
receptors for dynamic equilibrium; within each semicircular canal
is a complex mechanoreceptor called a crista ampullaris which
contains the mechanoreceptors (Hair cells) for dynamic
equilibrium; when the perilymph in one of the semicircular canals
moves, the hair cells in the crista ampullaris are stimulated to send
nerve impulses to the brain; this advises the brain of whether or
not a person has their balance during body movements or if their
body is in motion, such as moving their head side-to-side.(50)

19. Cavities and humors of the eye
• Humors- is the clear gel that fills the space between the
lens and the retina of the eyeball of humans and other
vertebrates. It is often referred to as the vitreous body
or simply "the vitreous".
• Cavities of the eye- the anterior cavity is actually
divided into two subcategories.
• the anterior chamber ( from iris to cornea)
• the posterior chamber ( from iris to lens)

20. Muscles of the eye
Since only the fovea provides sharp distinct vision, the eye must move to
follow a target. It must be precise and fast. This is seen in scenarios like
reading, wherein the reader must shift gaze constantly, or following a small
object like a golf ball, in which the extraocular muscles must lead the eye to
follow the head movements. Although under voluntary control, most
movement is done without thinking, such as those based on head or other
body movement, or movement of objects in the area. Researchers still have
some work in order to find the parallel nature of the environment-based
(involuntary) and voluntary control

21. accessory structures
The site of accessory structures of
the eye are as follows: eyebrows,
eyelashes, eyelids, conjunctiva,
and lacrimal apparatus.

22. Photopigments
The photopigments that absorb light all have a
similar structure, which consists of a protein
called an opsin and a small attached molecule
known as the chromophore. The chromophore
absorbs photons of light, using a mechanism that
involves a change in its configuration. In
vertebrate rods the chromophore is retinal, the
aldehyde of vitamin A1

23. Retinal image
formation of focused images on the
photoreceptors of the retina depends on the
refraction (bending) of light by the cornea and the
lens . The corna is responsible for most of the
necessary refraction, a contribution easily
appreciated by considering the hazy out-of-focus
images experienced when swimming underwater.
Water, unlike air, has a refractive index close to
that of the cornea; as a result, immersion in water
virtually eliminates the refraction that normally
occurs at the air/cornea interface.

24. Rods & cones
Rods are responsible for vision at low light levels (scotopic vision). They do
not mediate color vision, and have a low spatial acuity.
Cones are active at higher light levels (photopic vision), are capable of color
vision and are responsible for high spatial acuity. The central fovea is
populated exclusively by cones. There are 3 types of cones which we will
refer to as the short-wavelength sensitive cones, the middle-wavelength
sensitive cones and the long-wavelength sensitive cones or S-cone, M-
cones, and L-cones for short

25. Questions
Why don't deer see Hunters who wear Bright orange?
Deer have no red-sensitive cone cells in their eyes, so they can't tell red or
orange from green and brown.
What is the difference between "nearsighted" and "farsighted"? How are
each of these corrected?
There are several differences between being nearsighted and being
farsighted, as these are two different vision problems. Nearsightedness is
called myopia, and farsightedness is known as hyperopia. The main
biological difference in the two is that in myopia, the images seen are
focused in front of the retina, rather than directly on the retina. In
hyperopia, the images are focused behind the retina, rather than on top of
it. You can fix these problems by simply getting eye glasses