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Free nerve ending- a receptor
nerve ending that is not enclosed
in a capsule. A typical free nerve
ending consists of a bare axon that
may be myelinated or unmyelinat-
ed. It is often found in fibrous
capsules, ligaments, or synovial
spaces and may be sensitive to
mechanical or biochemical stimuli.
(2) root hair plexuses- Are Deli-
cate, weblike arrangements of free
nerve endings that surround hair
follicles and detect hair movement.
(2) Merkel discs- Flattened or disc
-shaped variations of free nerve
endings, called Merkel Discs, are
responsible for mediating sensa-
tions of light or discriminative
touch. (2) Meissner Corpuscle-
Mediates sensations of discrimina-
tive touch and low-frequency vi-
bration. (2) Pacinian Corpuscles-
mediate sensations to crude touch.
(2) Muscle Spindles- consists of a
discrete grouping of about 5 to 10
modified muscle fibers called intra
-fusal fibers, which are surrounded
by a delicate capsule. (2) Golgi
tendon Organs- Like muscle spin-
dles, are proprioceptors. They are
located ar the point of junction
between muscle tissue and tendon.
(2)
© (14)
Written by Colton Goudie
Written by—Agron Mena
Sense of smell: Sense of smell is
made up of olfactory receptors
which are yellow colored epithelial
support cells, basal cells, and spe-
cialized bipolar type olfactory
receptor neurons. The olfactory
epithelial is located in the most
superior portion of the nasal cavi-
ty. The location of these receptors
explains the necessity for sniffing,
or drawing air forcefully up into
the nose to smell delicate odors.
Sense of taste= Taste buds are the
most important part of this sense,
they house the chemoreceptors
responsible for taste. The sense of
taste of taste depends on the crea-
tion of a receptor potential in gus-
tatory cells. Only then can an ac-
tion potential be generated and
nerve impulse relayed to the brain
for interpretation
Sense hearing= the ear has dual
sensory functions. In addition to its
role in hearing, it also functions as
the sense organ of balanced, or equi-
librium. The stimulation, of trigger,
responsible for hearing and balance
involves activation of specialized
mechanoreceptors called hair cells.
Sound waves movement are physi-
cal forces that act on hair cells to
generate receptor potentials, and
then nerve impulses, which are
eventually perceived in the brain as
sound or balance. The ear is divided
into three anatomical parts: external
ear, middle ear and inner ear.
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Exteroceptors: Somatic sense receptor locat-
ed on the body surface. A sense organ, such
as the ear, that receives and responds to
stimuli originating from outside the body.
Visceroceptors: Somatic sense receptors
located in the internal visceral organs. locat-
ed in blood vessels and viscera. It arises
from within the body and may be felt as
pain, taste, fatigue, hunger, thirst and nau-
sea.
Proprioceptors: receptors located in the
muscles tendons, and joints. It allows the
body to recognize its position.
Mechanoreceptors: receptors the respond to
physical movements in the environment
such as sound waves like equilibrium and
balance sensors in the ears.
Thermoreceptors: Receptors
activated by heat or
cold. The body will either vaso-
constrict the blood vessels, in-
crease the metabolic rare, or
cause you. Heat-Loss the body
will dilate the blood vessels or
make you sweat.
Nociceptors: receptors activated
by intense stimuli of any type the
results in tissue damages. A
group of cells that senses painful
stimuli and sends these nerve
signals to the brain and the spi-
nal cord.
Photoreceptors: receptors only in
the eye, it responds to light stim-
uli if the intensity is great
enough to generate a receptor
potential. Their distinguishing
feature is the presence of large
amounts of tightly packed mem-
brane that contains the photopig-
ment rhodopsinor a related mole-
cule
retinal to change shape and the
opsin molecule to expand. This
signal travels to the brain to be
interpreted, and objects are seen in
shades of gray. (2)
There are 3 types of cones in the
retina and contain a different pho-
topigment than rhodopsin. Each
cone is acted on by a different
wavelength or color. Cones are less
sensitive to light so brighter light is
needed for the break down. Cones
contribute more to sharper images.
(2)
Nearsightedness, or myopia and
farsightedness, or hyperopia is both
refraction disorders. Nearsighted-
ness is when the eyes are elongated
and the image focuses in front of
There are 4 processes that focus a clear
image on the retina; refraction of the light
rays, accommodation of the lens, con-
striction of the pupil, and convergence of
the eyes. Refraction is the bending of
light. The refracting media of the eye are
the cornea, aqueous humor, lens, and vitreous humor. These 4
refracting media together bend light rays to bring focus on the
retina from an object 20 feet away. But an eye can also focus
on object much closer than 20 feet away and this is achieved
by accommodation. Accommodation is for near vision and it
causes an increase in the curvature of the lens, constriction of
the pupils, and convergence of the eyes. The constriction of the
pupil prevents divergent rays from the object from entering the
eye through the periphery of the cornea and lens. Convergence
is the movement of the two eyeballs inward so that their visual
axes come together at the object viewed. (2)
Rods and cones contain photopigments. The photopigment
found in rods is called rhodopsin. Rhodopsin is very light
sensitive so even dim light is broken down. Light causes the
the retina instead of on it, caus-
ing the image to be blurry. This
can be corrected by using con-
cave contact lenses, glasses, or
refractive eye surgery. Farsight-
edness is caused when the eyes
are shorter than normal, and the
image focuses behind the retina
also making the image blurry. It
can be corrected by convex con-
tact lenses, glasses, and refrac-
tive eye surgery. (2)
Deer’s don’t see hunters who
wear bright orange because they
have dichromatic vision; only
seeing hues of blue and yellow,
but they are red and green color-
blind. They can also see uv light.
(13)
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Anatomy and Physiology Weekly
ISSUE 3