Does that Make Sense?

Why do we leave cookies

out for Santa? The answer is that he feels hungry after traveling the

world and through the chimney. He senses this hunger with his sensory receptors.

Why are Christmas songs different than Halloween songs? The music sets a tone that

affects the way people feel. Without hearing it would be hard to understand the different moods.

These are just a few examples of how sensory receptors are used during the Christmas holiday. Let’s explore what they are and what else they do.

Sensory receptors-

•· Include our “special senses (vision, hearing, balance, taste, and smell)” (2).

•· Have receptor potential which is what causes a reflex (2). It is like a tea pot that heats and once it hits a certain point causes the whistling sound. Once the potential is at its climax, it causes the body to react.

•· Allows the brain to interpret sensations with the special senses (registering heat, cold) (2).

•· Receptors adapt after a period of time. An example from Anthony’s Textbook of Anatomy and Physiology 17th Edition is how when a person first puts on clothes he can feel the material but after a while does not sense it at all.

Distribution

•· Receptors are not distributed equally throughout the body.

•· Receptors in the general source organs produce somatic senses (2).

•· The two-point discrimination test proves that there are more receptors in some areas of the body than others (receptors in finger tips > receptors of skin on the back) (2).

Location

1.Exteroceptors

•· Superficial or near the surface.

•· React to stimuli from outside of the body (2).

Examples: receptors that sense the heat from picking up a hot cookie sheet, the cold from licking an ice sickle, a paper cut from opening a holiday card, and the pressure from the inside a plane during take-off or landing while visiting family.

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4.Visceroceptors

•· Internal and “within body organs” (2).

•· Internal stimuli cause a reaction (2).

Examples: receptors that sense the craving of gingerbread men, wanting eggnog, and realizing you can’t eat anymore cookies or drink anymore apple cider.

3. Proprioceptors

•· Are a type of visceroceptors.

•· Located in “skeletal muscle, joint capsules, and tendons” (2).

•· Identify body movement.

Examples: Help us to realize when we walk, when we raise our hands, sit still, and stand tall.

Stimulus Detected1.Mechanoreceptors

•· Activate or start the receptor potential (2).

•· Caused by a change of location of receptor (2).

Examples: While exercising our muscles and skin are being stretched and causes a shift in the receptors positions.

2. Chemoreceptors

•· Depends on chemical concentration (2). Examples: The differences between certain smells and

tastes. It is a reaction of the different chemical make-up of what is being smelt and tasted (vegetables vs. candy).

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3. Thermoreceptors

•· “Activated by change in temperature” (2).

Examples: Why we wear jackets in the winter and shorts in the summer, and why Santa has long sleeves, long pants, snow boots, and a hat. His cheeks are always rosy because the winds in the air whip against his cheeks as he flies over neighborhoods.

4. Nociceptors

•· Senses pain (2).

Examples: What Tim Allen experienced after falling of the roof trying to tie up Frosty in Christmas with the Kranks.

5. Photoreceptors

•· “Found only in the eye” (2).

•· “Responds to light” (2).

Examples: When your eyes adjust on Christmas morning after being in the dark to waking up in the bright early morning.

Structure Free nerve ending: Simplest, most common, and most

widely distributed sensory receptors. Located both on the surface of the body and in the deep visceral organs. (1)

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Root hair plexuses: Delicate, web-like arrangements of free nerve endings that surround hair follicles and detect variations of free nerve endings called merkel discs. (1)

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Merkel discs: Responsible for mediating sensations of light or discriminative touch. Delicate mechanoreceptors that are more easily “deformed” than pacinian corpuscles and thus are capable of generating an action potential when exposed to minimal stimulation. (1)

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Meissner Corpuscle: Numerous in hairless skin areas, such as nipples, fingertips and lips. These structures are large and superficially placed ovoid or egg shaped mechanoreceptors. (1)

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Pacinian Corpuscles: Large mechanoreceptors that show thick laminated connective tissue capsules. Found in the deep dermis of the skin, mainly in the hands and feet. Respond quickly to sensations of deep pressure, high frequency, and stretch. They are sensitive and quick to respond, adapt quickly, and the sensations they evoke seldom last long. (1)

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Muscle Spindles: Consist of a discrete grouping of about 5 to 10 modified muscle fibers called intrafusal fibers. Found lying between and parallel to the regular muscle fibers. Both ends of spindle are connected or anchored to connective tissue elements within the muscle mass. (1)

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Golgi tendon Organs: Operate to provide the body with information concerning muscle length and the strength of muscle contraction. (1)

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Smell

The olfactory receptors are embedded in a specialized (20 ©) patch of yellow-tinted mucous membrane in the roof of the nasal cavity. The olfactory receptor neurons are chemoreceptors. Receptor potentials are generated in olfactory receptor neurons when gas molecules or chemicals are dissolved in mucus covering the nasal epithelium.

The Olfactory Pathways; the Olfactory Bulb, the Olfactory Tract, Olfactory Recess, and the Nasal cavity are a few of the Olfactory Pathways. These pathways basically are the ways that help you breathe in and out of our nose (2).

Taste

Taste Buds are the sense organs that respond to gustatory, or taste, stimuli. They are located in the lining of the mouth and on the soft palate, most are on the small elevated projections of the tongue called papillae. As chemoreceptors, the taste buds, like olfactory receptors, tend to be quite sensitive but fatigue easily.

Neural Pathway connects one part of the nervous system with another and usually consists of bundles of elongated, myelin-insulated neurons. Neural pathways serve to connect relatively distant areas of the brain or nervous system. Nervous impulses generated in the anterior two thirds of the tongue travel over the facial nerve (2).

Hearing The Pressure Wave:

The sound waves we hear travel through air just like the waves travel through the slinky. The above illustration shows the relative conformations of air molecules as they transmit a sound wave downward. Soud travels through the air and along the outer and middle ear as a series of compressions (crests) and rarefractions (troughs) of air molecules. These patterns of molecules stimulate parts of the ear as described below to create the perception of sound.

How the Ear Perceives Sound:

The audirory canal (a.k.a. the outer auditory meatus) brings what you hear from the outside of the ear to the middle ear. At the end of the auditory canal, there is a thin layer of skin called the tympanic membrane (more commonly called the ear drum). The waves of sound hit the ear drum, and get further transferred onto the three small bones in the middle ear collectively known as the auditory ossicles: incus (anvil), stapes (stirrup), and malleus (hammer).

These structures act as a chain, which lead through an opening in the bone between the middle and the inner ears. The middle ear is filled with air, and the inner ear is filled with fluid, so this opening is covered by a thin membrane to keep them separate. This membrane allows the sound waves to be transmitted into the inner ear, and finally to a bundle of 30,000 nerve fibers each representing a different frequency. Noise is filtered out of this signal and the brain interprets the signal.

The brain’s interpretation of sound gives it an added property: pitch. This is basically how the brain interprets the frequency. The higher the frequency, the higer the pitch. Since frequency is the inverse of the period, the longer the wavelength, the lower the pitch. The amplitude of the wave translates into how loud the brain takes the sound to be.

Wave addition contributes to the rich complex sounds the we hear each day. A voice is just the addition of many simpler waves to give a unique sound. If two waves are added together, and they happen to have the same amplitude, the compressions of one are in the same position as the rarefractions of the other (and vice versa) the end result is no sound. This is how your noise cancelling headphones work. They take in sounds from the outside, and emit a wave that has just the right properties to cancel them out.

Inner Ear(20 ©)

Middle Ear(20 ©)

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Balance:(21 ©)

• Proprioception — from Latin proprius, meaning "one's own," and perception — is one of the human senses. There are between nine and 21 in all, depending on which sense researcher you ask. Rather than sensing external reality, proprioception is the sense of the orientation of one's limbs in space. This is distinct from the sense of balance, which derives from the fluids in the inner ear, and is called equilibrioception. Proprioception is what police officers test when they pull someone over and suspect drunkenness. Without proprioception, we'd need to consciously watch our feet to make sure that we stay upright while walking. (21)

• Proprioception doesn't come from any specific organ, but from the nervous system as a whole. Its input comes from sensory receptors distinct from tactile receptors — nerves from inside the body rather than on the surface. Proprioceptive ability can be trained, as can any motor activity. (21)

Without proprioception, drivers would be unable to keep their eyes on the road while driving, as they would need to pay attention to the position of their arms and legs while working the pedals and steering wheel. And I would not be able to type this article without staring at the keys. If you happen to be snacking while reading this article, you would be unable to put food into your mouth without taking breaks to judge the position and orientation of your hands. (21)

VISION: THE EYE

The eye is the body’s sensory organ for vision. This organ converts the energy of light into electrical nerve impulses that are interpreted by the brain. Approximately five sixths of the eyeball is hidden in the socket. There are three layers of tissue in the eye. The three layers of tissue are the sclera, the choroid, and the retina (2).

The anterior layer of the sclera is called the cornea and lies over the iris, the colored part of the eye. The middle or choroid part of the eye contains many blood vessels and large amounts of pigment. The iris or the colored part of the eye, consists of circular and radial smooth muscle fibers arranged to form a doughnut shaped structure. The hole in the middle is called the pupil. The iris attaches to the ciliary body (2).

The retina is the innermost coat of the eyeball. Three

layers of neurons make up the major portion of the retina; the photoreceptor, bipolar neurons, and ganglion neurons. Rods and cones are our visual receptors (2).

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Process of seeing

Formation of retinal Image Refraction of light rays

Accommodation of lens

Constriction of pupil

Convergence of eyes

Role of Photopigments Rods- photopigment in rods is rhodopsin; highly light

sensitive; breaks down into opsin and retinal; separation of opsin and retinal in the presence of light causes an action potential in rod cells; energy is needed to reform rhodopsin retina

Cones- three types of cones are present in the retina, with each having a different photopigment; cone pigments are less light sensitive than rhodophsin and need brighter light to breakdown

Questions

Deer can’t see color so wearing bright orange vests don’t scare them off. It keeps other hunters from shooting people with those vests instead of mistaking their movements as an animal.

Nearsighted means you cant see very good far and farsighted means you cant see very well near.