sense organs

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RATIONAL: In order to get around in this world, we depend upon our various sense organs to receive surrounding internal and external stimuli in which our brains then evaluate for producing the proper response. Without our sense organs we would not be able to evaluate our surroundings.


UNIT OBJECTIVES The Students will be able to: Define key terms Investigate possible careers Understand the role of sensory receptors Be able to classify the sensory receptors Investigate the senses (smell, taste, hearing, vision, touch) Investigate the cycle of life Define some mechanisms of diseases related to the sense organs Labs: Eye dissection; and two-point discrimination test

Warm up : 

Warm up Why are senses important to all living things? Which sense do you utilize for the following situations: Eating your favorite food? Someone is whispering to you? When using a mirror in the morning? When purchasing perfume?

Sequence of Study: : 

Sequence of Study: Writing key terms and defining as we go along in our study Description of receptors Information related to special senses Diseases Careers Lab: dissection of “Cow Eye” Lab: “two-point discrimination test”

Key terms for the chapter : 

Key terms for the chapter Adaptation Chemoreceptor Cochlea Equilibrium Exteroceptors Gustatory Labyrinth Macula Mechanoreceptor Nocieptor Olfactory Photoreceptor Proprioceptor Refraction Retina Rhodospin Thermoreceptor visceroceptors

Introduction : 

Introduction The body has millions of sense organs Fall into two main categories: GENERAL SENSE ORGANS: Most numerous such as: touch, temperature, and pain: and to initiate various reflexes necessary for maintaining homeostasis SPECIAL SENSE ORGANS: function to produce vision, hearing, balance, taste, and smell; and to initiate reflexes important for homeostasis.


SENSORY RECEPTORS SENSORY RECEPTORS: make it possible for the body to respond to stimuli caused by changes occurring in our external or internal environment. Critical to survival (external environment) Hearing, seeing danger coming Helps us to maintain homeostasis (internal environment) Pain and pressure; hunger and thirst.


RECEPTOR RESPONSE FUNCTION OF RECEPTORS: Is to respond to stimuli by converting them to nerve impulses via special sensory neurons ADAPTATION: receptors often exhibit a functional characteristic known as adaptation. Meaning that the magnitude of the receptors potential decreases over a period in response to a continuous stimulus. Example olfactory nerve becoming desensitized to perfume.


DISTRUBUTION OF RECEPTORS Special senses of smell taste, vision hearing are grouped into localized areas General senses consist of microscopic receptors distributed throughout the body in the skin, mucosa, tissues, muscles, etc…commonly termed our “somatic senses” There are more receptors in the fingertips then say on your back. WHY? LETS FIND OUT Two-point discrimination test demonstration


CLASSIFCATION OF RECEPTORS Classified according to: Location; Stimulus detected; and Structure.

Classification by location : 

Classification by location Three groups/classes of receptors that are identified by their location: Exteroceptors: (cutaneous receptors) Located on or very near the body surface Respond mostly to external stimuli Detect pressure, touch, pain, and temperature Visceroceptors (interoceptors): Located internally, often within the body organs (viscera) provide information about the internal environment Activated by pressure, stretching, and chemical changes Involved in sensations of hunger and thirst. Proprioceptors: (effects space astronauts) (or intoxicated) Specialized type of visceroceptors Less numerous and more specialized Limited to skeletal muscles, joint capsules, and tendons Gives us information about body movement, orientation in space and muscle stretch

Classification by stimulus detected : 

Classification by stimulus detected Five categories based on the types of stimuli that activate them: Mechanoreceptors: Chemoreceptors: Thermoreceptors: Nociceptors: Photoreceptors:

mechanoreceptor : 

mechanoreceptor Activated by mechanical stimuli that some way “deform” or change the position of the receptor, resulting in the generation of a receptor potential Examples: pressure applied to the skin or a blood vessel. Or by stretch or pressure in muscle, tendon, or lung tissue

chemoreceptors : 

chemoreceptors Activated by either the amount or the changing concentration of certain chemicals Taste and smell depend on chemoreceptors Special chemoreceptors in the body also sense the concentration of chemicals such as pH, glucose, etc.

thermoreceptors : 

thermoreceptors Activated by changes in temperature

nociceptors : 

nociceptors Activated by intense stimuli of any type that results in tissue damage Can by a toxic chemical, intense light, sound, pressure, or heat The sensation produced is one of pain Serve as the primary sensory receptors for pain as free nerve endings.

photoreceptors : 

photoreceptors Found only in the eye Respond to light stimuli if the intensity is great enough to generate a receptor potential.


CLASSIFICATION BY STRUCTURE General sensory receptors may be classified anatomically as either: FREE NERVE ENDING: are the simplest, most common and most widely distributed sensory receptors Located both on the surface (exteroceptors) and in the deep visceral organs (visceroceptors) The term nociceptor is used to describe these fibers. ENCAPSULATED NERVE ENDINGS: there are 6 types that all have some type of connective tissue capsule that surrounds their terminal ends are specialized receptors that are mechanoreceptors Deal with touch and pressure; and stretch receptors


SPECIAL SENSES Are characterized by receptors grouped closely together or located in specialized organs Special senses are: Smell (olfaction) Taste Hearing Equilibrium Vision




OLFACTORY RECEPTORS Olfactory: Consist of a yellow-colored epithelial support cells (BASAL CELLS) Located in the most superior portion of the nasal cavity (fig 15-2) This is a poor location b/c a great deal of inspired air flows around and down the passageway without contacting the receptor cells. This is why “sniffing” in needed to smell delicate odors. Have olfactory cilia which touch the surface of the lining of the upper surface of the nasal cavity The receptor neurons are chemoreceptors Are replaced on a regular basis by germinative basal cells


OLFACTORY PATHWAY As air enters the nasal passageway the level of odor-producing chemicals dissolve in the mucus membrane With in the mucus membrane the olfactory cilia capture the chemicals After reaching a threshold level it is passed to the olfactory nerves located in the olfactory bulb The impulse passes through the olfactory tract and into the thalamic and olfactory centers of the brain for interpretation, integration, and memory storage. The sense of smell can create powerful and long-lasting memories. That often persist from early childhood to death New car smell; dental office; kitchen; baby smells and so on.




TASTE BUDS Blue food coloring to show filiform papillae on tongue TASTE BUDS: are the sense organs that respond to GUSTATROY (TASTE) stimuli A few taste buds are located in the lining of the mouth and on the soft palate, most are associated with small, elevated projections on the tongue PAPILLAE: are the small elevated projections on the tongue Fungiform, circumvallate, and foliate papillae contain taste buds Filiform papillae do not contain taste buds but allow us to experience food texture and feel It was once thought that the taste buds of the tongue were located in specific regions (bitter in the posterior portion and sweet at the anterior portion) HOWEVER, this is NOT TRUE. There is no known taste “map” all tastes can be detected in all areas of the tongue that contain taste buds.

Taste bud receptors : 

Taste bud receptors Taste buds house the chemoreceptors responsible for taste. Stimulated by chemicals termed TESTANTS that are dissolved in saliva Each grapelike taste bud contains 50-125 chemorecptors termed GUSTATORY CELLS which are surrounded by supportive capsules Tiny cilia-like structures extend from each gustatory cell and project into an opening called TASTE PORES which are bathed in saliva

What can we taste? : 

What can we taste? All taste cells can respond at least to most taste-producing chemicals Functionally however, there are five “primary’ taste sensation: Sour Sweet Bitter Salty Umami (from glutamate) four primary sensation + sense of smell = ability to detect many different flavors. Recently, METALLIC TASTE may be a fifth primary taste Japanese researcher recently have suggested that another primary taste called umami from protein rich meat and fish. Yet this is still under study. (bitter cheese)

Neuronal pathway for taste : 

Neuronal pathway for taste Begins with creation of a receptor potential in the gustatory cells of a taste bud It is then transmitted via sensory input to the brain anterior 2/3 of the tongue cells travel over the facial VII nerve. The posterior 1/3 are conducted by the fibers of the glossopharyngeal IX nerve The III cranial nerve and the vagus X nerve plays minor role in taste except form the taste buds located on the walls of the pharynx and epiglottis The three cranial nerves carry impulses into the medulla, into the thalamus and then into the taste area of the cerebral cortex in the parietal lobe



External Ear : 

External Ear Two divisions: Auricle (pinna) Flap (modified trumpet) External auditory meatus (ear canal) The tube leading from the auricle into the temporal bone Approximately 3cm lone travels inward, forward and downward direction In adults the first portion of the tube slants upward and then curves downward this is why the auricle is pulled up and back for examining the ear. Modified sweat glands secrete cerumen (wax) which can become impacted causing pain and temporary deafness. Tympanic membrane (eardrum) stretches across the inner end of the auditory canal, separating it from the middle ear.

Middle Ear : 

Middle Ear The middle ear termed tympanic cavity Is a tiny epithelial lined cavity that is hallowed out of the temporal bone Contains three auditory ossicles: Malleus (hammer) The handle is attached to the inner surface of the tympanic membrane and the head attaches to the incus Incus (anvil) Attaches from the head of the malleus and then to the stapes Stapes (stirrup)


OPENINGS OF THE MIDDLE EAR There are several openings into the middle ear: One from the external auditory meatus, covered with the tympanic membrane; Two into the internal ear, the oval window (into which the stapes fits) and the round window which is covered by a membrane; and One into the auditory (eustachian) tube Clinical importance of these openings is that they provide routes for infection to travel (head colds which lead to ear infections that are common in children

Eustachian tube : 

Eustachian tube Composed partly of bone and partly of cartilage and fibrous tissue and lined with mucosa Extends downward, forward, and inward from the middle ear to the nasopharynx or pharyngotypanic tube Serves as a useful function: it makes possible equalization of pressure against inner and outer surfaces of the tympanic membrane (prevents rupture) performed by swallowing or yawning, the air spreads through the open tube, atmospheric pressure then presses against the inner surface of the tympanic membrane


INNER EAR Also termed labyrinth Consist of two main parts: Bony labyrinth consisting of three parts: vestibule, cochlea, and semicircular canals Membranous labyrinth consists of the: utricle and saccule inside the vestibule, the cochlear duct inside the cochlea, and the membranous semicircular canals inside the bony ones


INNER EAR FLUIDS The vestibule, (containing the utricle and saccule) and the semicircular canals are involved in balance The cochlea is involved in hearing Endolymph is the clear potassium-rich fluid that fills the membranous labyrinth Perilymph similar to CSF, surrounds the membranous labyrinth and fills the space between this membranous tunnel, its contents, and the bony walls

Cochlea and cochlear duct : 

Cochlea and cochlear duct Cochlea means snail In the center is a cone-shaped core termed modiolus The modiolus houses the spiral ganglion that has cell bodies of the first sensory neurons in the auditory relay Cochlear ducts are the only part of the internal ear concerned with hearing Cochlear implants are used to correct some forms of nerve deafness if the hairs on the organ of corti are damaged. Electrodes wired to the organ of corti stimulates the vestibulocochlear nerve.


SENSE OF BALANCE Controlled by the vestibule and semicircular canals Static equilibrium Needed to sense the position of the head relative to gravity or to sense acceleration or deceleration of the body Dynamic equilibrium Needed to maintain balance when the head or body itself is rotated or suddenly moved





overview : 

overview Converts the energy of light into electrical nerve impulses that are interpreted by the brain as sight


STRUCTURE OF THE EYECOATS OF THE EYEBALL 5/6 of the eye lies recessed in the orbit Only the small anterior surface of the eyeball is exposed Three layers compose the eyeball, from outside in they are: Sclera Choroid Retina The sclera and choroid consist of an anterior and posterior portion. The sclera is made of tough white fibrous tissue

The Sclera (outer layer) : 

The Sclera (outer layer) Anterior portion of the sclera is termed cornea and lies over the colored part of the eye termed iris The cornea is transparent whereas the rest of the sclera is white normally referred to as the “whites of the eye” No blood vessels are found in the cornea or in the lens

Choroid (middle layer) : 

Choroid (middle layer) Contains many blood vessels and a large amount of pigment The anterior portion is modified into three separate structures: Ciliary body Suspensory ligament Iris

Slide 48: 

The ciliary body is formed by thickening of the choroid. holds the suspensory ligaments which controls the pupil and hold the lens and iris. Iris is the colored part of the eye. The hole in the middle is the pupil Between the cornea and iris is the anterior chamber which contains aqueous humor The lens covers the pupil and retains the posterior chamber containing the vitreous humor

Retina (inner layer) : 

Retina (inner layer) Is the incomplete innermost coat of the eyeball (it has no anterior part like the choroid and sclera) Three layers of neurons make up a major portion of the retina. Named in the order in which the conduct impulses: Photoreceptor neurons Bipolar neurons Ganglion neurons

photorecptors : 

photorecptors Rods and cones constitute our visual receptors. They differ in number, distribution and function Cones are less numerous Rods

Rods : 

Rods are absent entirely form the fovea and macula and increase in density toward the periphery of the retina The single photopigment found in rods is rhodopsin Rhodopsin is highly sensitive to light that even dim light causes a rapid breakdown of the pigment into its opsin and retinal components Objects are seen in shades of gray not color

Cons : 

Cons Densely concentrated in the fovea centralis which is a small depression in the center of a yellowish area known as the macula lutea found near the center of the retina they become less dense as they move away from the fovea Three types present: red, green, and blue Each contain photopigment different from the rhodopsin found in rod cells Do not breakdown in presence of light like rods

Neurons : 

Neurons All axons of ganglion neurons extend posteriorly to the part of the eyeball known as the optic disc (also called the blind spot)

Cavities and humors : 

Cavities and humors Eye is divided into two cavities: Anterior cavity Lies in front of the lens which has two subdivisions Anterior chamber Posterior chamber Aqueous humor fills both chambers of the anterior cavity, which leaks out during an injury Posterior cavity Occupies all space posterior to the lens Vitreous humor (like soft gelatin) which along with the aqueous humor maintains intraocular pressure to prevent the eyeball from collapsing

Eye pressure : 

Eye pressure Normally 20-25 mm Hg Above 25mm Hg an individual has glaucoma which if untreated can lead to retinal damage and blindness Pressure can increase due to decreased drainage or excess drainage of the aqueous humor which is normally re-circulated via vessels into vitreous humor




MUSCLES Two types: Extrinsic Are skeletal muscles Move the eye voluntarily Four are straight and two are oblique muscles Their names describe their location Superior rectus Inferior rectus Medial rectus Lateral rectus Superior oblique Inferior oblique Intrinsic Are smooth involuntary muscles Located within the eye Iris muscle Ciliary muscle



Accessory structures : 

Accessory structures Consist of the Eyebrows Eyelashes Eyelids (palpebrae) Mucous membrane termed conjunctiva which lines the undersides of the eyelids and continues over the surface of the eyeball Conjunctivitis is inflammation, fairly common, produces a pinkish discoloration (pinkeye) Lacrimal apparatus Consist of structures that secrete tears and drain them from the surface of the eyeball. Consist of Lacrimal glands Lacrimal ducts Lacrimal sacs Nasolacrimal ducts

Process of vision : 

Process of vision

How do we see? : 

How do we see? For vision to occur: An image must be formed on the retina to stimulate the rods and cones Nerve impulses must be conducted to the visual areas of the cerebral cortex Interpretation occurs

Formation of a retinal image : 

Formation of a retinal image Four processes focus light rays so that they form clear images on the retina Refraction of light rays Accommodation of the lens Constriction of the pupils Convergence of the eyes

Refraction of light rays : 

Refraction of light rays Bending of light rays Refractor media of the eyes are Cornea aqueous humor Lens Vitreous humor Health eyes are able to distinguish objects 20 or more feet away (6 meter) anything further requires “accommodation” Common errors of refraction: Nearsightedness (myopia) Farsightedness (hyperopia) astigmatism

Accommodation of lens : 

Accommodation of lens For near vision necessitates three changes: Increase in the curvature of the lens Constriction of the pupils Convergence of the two eyes Light rays from objects 20 ft or more are practically parallel Therefore the eye must increase in its curvature to achieve greater refraction for objects nearer

Contraction or relaxation of the ciliary muscle : 

Contraction or relaxation of the ciliary muscle Contraction pulls the choroid layer closer to the lens which loosens the tension of the suspensory ligaments and allowing the lens to bulge Near vision the ciliary muscles is contracted Far vision the ciliary muscle is relaxed and the lens is comparatively flat Continual use of eyes for near work produces eyestrain b/c of the prolonged contraction of the ciliary muscle (so take breaks to relax muscle) Older people tend to become farsighted because lenses lose their elasticity and therefore their ability to bulge and to accommodate for near vision

Constriction of pupil : 

Constriction of pupil Iris muscle plays a major role in the formation of clear retinal images This prevents divergent rays from the object from entering the eye through the periphery of the cornea and lens The pupil constricts also in bright light to protect the retina from stimulation that is too intense or too sudden

Convergence of eyes : 

Convergence of eyes Binocular vision (seeing one object instead of two) occurs when light rays from an object fall on corresponding points of the two retinas Whenever the eyeballs move in unison light rays strike corresponding points of the two retinas Convergence is the movement of the two eyeballs inward so that their visual axes come together The nearer the object the greater the convergence Simple demonstration: Gently press one eyeball out of line while viewing an object. Instead of one object you will see two

Visual acuity : 

Visual acuity Is the clearness or sharpness of visual perception Affected by our focusing ability Measure of visual acuity is determined by a chart on which letters or objects of various sizes are printed from a distance of 20 feet (6.1m) Normal is 20/20 the first number represents the distance in feet the second number represents the number of feet a person with normal acuity would have to stand to see the same objects clearly A vision acuity of 20/100 means a person can see objects at his 20 feet that a normal person can see at 100 feet. People with greater than 20/200 after correction are considered to be legally blind


COLOR BLINDNESS Usually an inherited condition from the mother on the X chromosome Caused by mistakes in producing three chemicals (photopigments) in the cons Each are sensitive to one of three primary colors Green Blue Red

The cycle of life : 

The cycle of life

Cycle of life : 

Cycle of life The ability of the sense organs to respond varies during life Age, disease, structural defects, or lack of maturation all affect our ability to identify and respond to sensory input Newborns have limited sight, hearing, and tactile identification capabilities As maturation occurs and normal development progresses the senses b/c more acute By late adulthood, presbyopia, progressive hearing loss and reduced senses of taste and smell are common Some loss of sensory capability in old age is directly related to structural changes in receptor cells. The lens of the eye b/c harder, taste buds become less functional

Mechanisms of disease : 

Mechanisms of disease

Disorders of hearing : 

Disorders of hearing Divided into two basic categories Conduction impairment: Blocking of sound waves Most common is wax build up, foreign objects, tumors etc. Nerve impairment: Due to inherited or acquired nerve damage Otosclerosis is an inherited bone disorder which impairs conduction due to irregularities in the stapes. Occur during childhood as tinnitus (ringing of the ears) Otitis common ear infection. Otitis media produces swelling and pus formation that block the conduction of sound through the middle ear

Disorders of the eye : 

Disorders of the eye Most common the use of glasses. Conjunctivitis Chlamydia trachomatis commonly infects the reproductive tract (STD) and infects newborns from infected mothers. Common for newborns to have antibiotics applied to eyes shortly after birth Bacterial conjunctivitis seen with drainage of a mucous pus caused by Staphylococcus or Haemophilus can lead to damage or blindness Diabetes mellitus: involving insulin causes small hemorrhages in retinal blood vessels that disrupt the oxygen supply to the photoreceptors Nyctalopia: night blindness due to degeneration of the retina or deficiency of vitamin A that impairs the function of rod cells which are need for deem light.


RESOURCES CLASSROOM CLIPART, October 30, 2005, Thibodeau, Gary; Patton, Kevein. “Anthony’s Textbook of Anatomy & Physiology”. 17th edition. Mosby

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