Structure

Free nerve ending: simplest, most common sensory receptors located on the surface of the body known as exteroceptors and in internal organs known as visce receptors. Nociceptor are slen-der sensory fibers that are responsible for pain. Brain tissue lack free sensory nerve endings and are incapable of sensing painful stimuli. Nerve endings are also responsible for sensation and touch and also sensations of heat cold.

Root hair plexuses: delicate, web-like arrangements of free nerve endings that surround hair follicles that can detect any type of hair movement.

Merkel disks: disc-shaped or flattened and are responsible for mediating sensations of light or discriminative touch that is lo-cated on the surface of the skin.

Meissner Corpuscle: when “deformed” by a mechanical type of stimulus, this type of receptor, sometimes called a tactile corpus-cle, mediates sensations of discriminative touch and low-frequency vibration. (especially numerous in hairless skin areas, such as the nipples, fingertips, and lips)

Pacinian Corpuscles: large mechanoreceptors, which when sec-tioned, show thick laminated connective tissue capsules. (found in deep dermis of the skin-especially in the hands and feet-and are also numerous in joint capsules throughout the body).

Muscle Spindles- the most important stretch receptors are asso-ciated with muscles and tendons and are classified as proprio-ceptors. Two types of stretch receptors, called muscle spindles and golgi tendon receptors, operate to provide the body with information concerning muscle length and the strength of mus-cle contraction. (the result of stimulation is a stretch reflex that shortens a muscle or muscle group, thus aiding in the mainte-nance of posture or the positioning of the body or one of its ex-tremities in a way that may be opposed by the force of gravity).

Golgi tendon Organs- like muscle spindles, are proprioceptors. They are located at the point of junction between muscle tissue and tendon. These receptors act in a way opposite that of mus-cle spindles.

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Also in this issue... • Locations of receptors……………………….……page 12

• Stimulus detected…………………………………..page 13

• Structure……………………………………………….page 14

We’ll tell you how to spot some great deals with the help of your vision! (Page 2-3)

The minty smell of that peppermint candle… ah, it’s the smell of Christmas. (page 7-8)

How are we able to see all the bright Christmas lights? We’ll tell you how! (page 4-5)

We all love the cinnamon taste of snickerdoodle cookies! (page 10-11)

Remember to keep your balance while hanging up your Christmas lights! (page 9)

It’s beginning to look a lot like Christmas, everywhere you go…(page 6)

Christmas edition

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Page 2

With the help of your vision

Your vision plays an important part when spotting some good deals. There are 3 layers of tissue that compose the eyeball: the sclera (a tough outer coat), the cornea (the transparent anteri-or portion that lies over the iris), and the canal of schlemm (a ring-shaped venous sinus found deep within the anterior portion of the sclera). The choroid is the middle coat of the eye and it contains many blood vessels and a large amount of pigment . The ciliary body , suspensory ligament, and the iris are all part of this layer: Ciliary body– the thickening of choroid, fits between anterior

margin of retina and posterior margin of iris. Suspensory ligament– attached to the ciliary processes and

blends with the elastic capsule of the lens to hold it in. Iris– colored part of the eye. The retina is the incomplete innermost coat of the eyeball. Three layers of neurons make up the sensory retina. Photoreceptor neurons are the visual receptors, highly specialized for stimulation by light rays. Bipolar neurons are the second layer and ganglion neurons are the third layer. All axons of these neurons extend back to the optic disc; part of the sclera, which contains perforations through which the fibers emerge from the eyeball as the optic nerve. (5)

HOW TO SPOT KILLER DEALS

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Page 13

Stimulus Detected

Mechanoreceptors: are activated by mechanical stimuli that in some way “deform” or change the position of the receptor, re-sulting in the generation of a receptor potential. Examples of this is pressure applied to the skin or to blood vessels, or cause by stretch or pressure in the muscle, tendon, or lung tissue.

Chemoreceptors: activated by either the amount or the changing concentration of certain chemicals. Examples are our senses of taste and smell depend on these.

Thermoreceptors: activated by change in temperature. Examples are when the outside temperature is colder than your body; your brain tells your body to warm up.

Nociceptors: the relatively unspecialized nerve cell endings that initiate the sensation of pain are called Nociceptors. They trans-duce a variety of stimuli into receptor potentials, which in turn trigger afferent action potentials. They arise from cell bodies in dorsal root ganglia that send one axonal process to the periphery and the other into the spinal cord or brainstem. (20)

Photoreceptors: the retina is the back part of the eye that con-tains the cells that respond to light. These specialized cells are called photoreceptors. There are two types of photoreceptors (rods and cones) in the retina. (9)

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Page 12

Locations of receptors

Exteroceptors: are near the surface of the body. The extero-ceptors located in the skin provide the sensations of pain, touch, temperature, and pressure.

Visceroceptors: located in the blood vessels and viscera. Proprioceptors: receptors located in muscles, tendons,

joints, and the external ear.

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Page 3 Cavities & Humors

The eyeball has a large interior space divided into two cavities. The anterior cavity lies in front of the lens and has two subdivisions: The anterior chamber– the space anterior to the iris and posterior

to the cornea. The posterior chamber– the small space posterior to the iris and

anterior to the lens. The posterior cavity is larger than the anterior cavity and it occupies the entire space posterior to the lens, suspensory ligament, and ciliary body.

Muscles There are two types of eye muscles. The extrinsic eye muscle is the skeletal muscles that attach to the outside of the eyeball and to the bones of the orbit, and its named according to their position on the eyeball. The muscles are superior, inferior, medial, and lateral rectus muscles and the superior and inferior oblique muscles. (5)

Accessory Structures

Eyebrows and eyelashes give some protection against foreign objects entering the eye. Eyelids consist of voluntary muscle and skin with a tarsal plate, lined with conjunctiva, a mucous membrane, and a pal-pebral fissure where the upper and lower eyelids join together. Lacri-mal glands are about the size and shape of an almond, and are locat-ed at the upper, outer margin of each orbit. Approximately a dozen small ducts lead from each gland and drain tears onto the conjunctiva. Lacrimal canals are small channels that empty into lacrimal sacs. Lacrimal sacs are located in a groove in the lacrimal bone. Nasolacrimal ducts are small tubes that extend from the lacrimal sac into the inferior meatus of the nose. (5)

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Take a gander at the Christmas lights

Process of seeing

The cornea, pupil, iris, and lens work together to refract light rays so that the rays from the Christmas lights focus directly on the retina. Light rays first touch the cornea. The cornea has 2 purposes: 1) it bends light rays as they pass through it in order to focus them through the lens and towards the back of the eye. 2) its smooth, reflective surface serves to protect the eye from external damage. Once light passes the cornea, it hits the aqueous humor, a clear watery fluid. The purpose of the aqueous humor is to keep a constant pressure within the eye. Behind the aqueous humor are the iris and the pupil. They both work together to control the amount of light that enters the eye. The iris consists of two muscles on either side of the pupil that can dilate or constrict to ad-just the size of the pupil. Behind the iris and the pupil is the lens, and elastic structure that becomes thinner to focus on distant objects and thick to focus on nearby objects. All these parts of the eye work together to allow you to see all the Christmas lights.

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Why don’t deer see hunters who are wearing bright orange?

Deer have under-developed cones. They have no red-sensitive cones in their eyes, which prohibit them from distinguishing red or orange from green and brown.

Page 11

Taste cont. (23)

The Neural Pathway

The Taste Pathway Transduction occurs when different taste substances cause a change in the flow of ions across the membrane of a taste cell. Different substances affect the membrane in different ways: Bitter and sweet substances bind into receptor sites which

release other substances into the cell. Sour substances contain H+ ions that block channels in the

membrane. Salty substances break up into Na+ ions which flow through

the membrane directly into the cell. Electrical signals generated in the taste cells are transmitted in 3 pathways: The chorda tympani nerve conducts signals from the front and

sides of the tongue. The glosso-pharyngeal nerve conducts signals from the back of

the tongue. The vagus nerve conducts taste signals from the mouth and

the larynx. These three nerves make connections in the brain stem in the nu-cleus of the solitary tract (NST) before going on to the thalamus and then to two regions of the frontal lobe (the insula and the frontal operculum cortex).

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All the tasty treats...yum! (23)

Taste buds- describe

Anatomy of taste The tongue contains many ridges and valleys called papillae. There are four types of papillae: 1) Filiform papillae– cone shaped and found all over the tongue

(why gives the tongue its rough appearance). 2) Fungiform papillae– mushroom shaped and found at the tip

and sides of the tongue. 3) Foliate papillae– a series of folds along the sides of the tongue. 4) Circumvallate papillae– shaped like flat mounds surrounded by

a trench and found at the back of the tongue. All papillae except filiform contain taste buds, so the very center of your tongue (which only has filiform papillae) is “taste blind.” Each taste bud contains a number of taste cells which have tips that pro-trude into the taste pore.

PROCESS OF SEEING CONT.

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Describe the role of Photopigments

Both rods and cones contain photopigments, or light sensitive pig-ments compounds that are found in the distal area of both types of photoreceptors near the pigments retina. A derivative called reti-nal acts as the light-absorbing portion of all photopigments. Rods– the single photopigment found in rods is rhodopsin.

Rhodopsin is highly light sensitive that a dim light can cause a rapid breakdown of the photopigment into its opsin and retinal components. Light causes retinal to change shape and the op-sin molecule to expand or open.

Cones– 3 types of cones are present in the retina. Each con-tains a photopigment different from the rhodopsin found in rod cells. Each of the 3 primary colors (red, green, and blue) reflect light rays of a different wavelength. Each wavelength acts primarily on one type of cone, causing its particular pho-topigment to break down and initiate impulse conduction by the cone. Brighter light is necessary for the breakdown of cone photopigments. (5)

Describe between nearsighted and farsighted. How is it corrected?

People with farsightedness (hyperopia) can see distant objects well, but have difficulty focusing on objects close up. People with nearsightedness (myopia) can focus well on objects close up, but have trouble seeing distant objects. Glasses and contacts are the most common ways of cor-recting either nearsightedness or farsightedness. Glasses help for the abnormal shape of the eye so that rays can hit the retina properly. Contact lenses also work by refocusing light, and may improve vision more than glasses because the lenses sit directly on the eyes.

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CAN YOU HEAR THE SONGS OF THE SEASON?

Oh the weather outside is frightful, but the fire is so delightful...

Describe mechanism of hearing

Sound is created by vibrations that can occur in air. Fluid or solid material. For example, when we speak, our vocal cords create sound waves that produce vibrations. Amplitude of a sound wave determines its loudness or volume. The number of sound waves during a specific time (frequency) determines pitch. This allows us to hear about Elvis’ blue Christmas. (5)

Detail Neuronal pathway of hearing

Dendrites of neurons terminate around bases of hair cells of the organ name corti. Movement of hair cells against adherent tec-torial membrane stimulates dendrites and initiates impulse con-duction by cochlear nerve to the brainstem. Impulses pass through “relay stations” in the nuclei of the medulla, pons, mid-brains, and thalamus before reaching auditory area of temporal lobe. (5)

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Remember to keep your balance!

Describe sense of balance

Balance is maintained by the visual system, the vestibule system, and proprioception. The vestibular system detects changes in static equilibrium, and the movements of fluid in the semicircular canals detect which direction we’re facing. The brain receives signals from these parts of the body to determine how to keep balanced.

Dynamic equilibrium

Dynamic equilibrium is responsible for maintaining the position of the head when the body rotates. This especially comes in handy when hanging up Christmas lights on your house.

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Page 8

The smells of Christmas time cont.

Olfactory Pathways

When the level of odor-producing chemicals reaches a threshold level, the following occurs: receptor potential, and then action po-tential, is generated and passed to the olfactory nerves in the olfac-tory bulb. The impulse then passes through the olfactory tract and into the thalamic and olfactory centers of the brain for interpreta-tion, integration, and memory storage.

Compare Olfaction in a human with a canine.

Genes between a dog and a human, suggest that our genes evolved from a common mammalian ancestral repertoire by successive duplications.

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The smells of Christmas time

Olfactory Receptors Olfactory receptors are unique because they are replaced on a regular basis by germinative basal cells in the olfactory epithelium. They are located in the most superior portion of the nasal cavity. They also con-sist of epithelial support cells and specialized olfactory receptor neu-rons. Olfactory cilia– located on olfactory receptor neurons that touch

the olfactory epithelium linin the upper surface of the nasal cavity. Olfactory cells– chemoreceptors; gas molecules or chemicals dis-

solved in the mucus over covering the nasal epithelium stimulate the olfactory cells.

Olfactory epithelium– located in the most superior portion of the nasal cavity.

Olfactory receptors– extremely sensitive and easily fatigued

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