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)

Article One

Article Two

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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