Five Senses Science Presentation PDF

SPECIAL SENSES olfaction gustation vision hearing equilibrium  SPECIAL SENSES Sensory organs have special receptors that allow us to smell, taste, see, hear, and maintain equilibrium or balance. Information conveyed from these receptors to the central nervous system is used to help maintain...

SPECIAL SENSES olfaction gustation vision hearing equilibrium  SPECIAL SENSES Sensory organs have special receptors that allow us to smell, taste, see, hear, and maintain equilibrium or balance. Information conveyed from these receptors to the central nervous system is used to help maintain homeostasis.  SPECIAL SENSES Receptors for the special senses— smell, taste, vision, hearing, and equilibrium—are anatomically distinct from one another and are concentrated in specific locations in the head. OLFACTION The sense of smell, or olfaction, is caused by the detection of chemicals inhaled through a small region of your nasal cavity. This region is the olfactory epithelium and it contains the olfactory sensory neurons.  ANATOMY OF OLFACTORY RECEPTORS OLFACTORY EPITHELIUM The nose contains 10–100 million receptors for the sense of smell or olfaction (ol-FAK-shun; olfact-  smell), contained within an area called the olfactory epithelium. OLFACTORY EPITHELIUM The olfactory epithelium consists of three kinds of cells: olfactory receptors, supporting cells, and basal cells.  OLFACTORY RECEPTORS Olfactory receptors are the first-order neurons of the olfactory pathway. Each olfactory receptor is a bipolar neuron with an exposed knob-shaped dendrite and an axon projecting through the cribriform plate and ending in the olfactory bulb. OLFACTORY RECEPTORS Chemicals that have an odor and can therefore stimulate the olfactory hairs are called odorants. Olfactory receptors respond to the chemical stimulation of an odorant molecule by producing a generator potential, thus initiating the olfactory response.  SUPPORING CELLS Are columnar epithelial cells of the mucous membrane lining the nose. They provide physical support, nourishment, and electrical insulation for the olfactory receptors, and they help detoxify chemicals that come in contact with the olfactory epithelium.  BASAL CELLS Are stem cells located between the bases of the supporting cells. They continually undergo cell division to produce new olfactory receptors, which live for only a month or so before being replaced.  OLFACTORY GLANDS Within the connective tissue that supports the olfactory epithelium are olfactory (Bowman’s) glands, which produce mucus that is carried to the surface of the epithelium by ducts.  OLFACTORY GLANDS The secretion moistens the surface of the olfactory epithelium and dissolves odorants so that transduction can occur.  OLFACTORY GLANDS Within the connective tissue that supports the olfactory epithelium are olfactory (Bowman’s) glands, which produce mucus that is carried to the surface of the epithelium by ducts. GUSTATION The sense of taste. Taste or gustation, like olfaction, is a chemical sense. However, it is much simpler than olfaction in that only five primary tastes can be distinguished: sour, sweet, bitter, salty, and umami. ANATOMY OF TASTE BUDS AND PAPILLAE ANATOMY OF PAPILLAE  ANATOMY OF TASTE BUDS The supporting cells surround about 50 gustatory receptor cells in each taste bud. A single, long microvillus, called a gustatory hair, projects from each gustatory receptor cell to the external surface through the taste pore, an opening in the taste bud.  ANATOMY OF TASTE BUDS Basal cells, stem cells found at the periphery of the taste bud near the connective tissue layer, produce supporting cells, which then develop into gustatory receptor cells.  ANATOMY OF TASTE BUDS Each gustatory receptor cell has a life span of about 10 days. At their base, the gustatory receptor cells synapse with dendrites of the first-order neurons that form the first part of the gustatory pathway. The dendrites of each first-order neuron branch profusely and contact many gustatory receptor cells in several taste buds.  ANATOMY OF PAPILLAE Taste buds are found in elevations on the tongue called papillae (pa-PIL-e¯; singular is papilla), which provide a rough texture to the upper surface of the tongue. Three types of papillae contain taste buds.  ANATOMY OF PAPILLAE 1. About 12 very large, circular vallate (circumvallate) papillae (VAL-a¯t - wall-like) form an inverted V- shaped row at the back of the tongue. Each of these papillae houses 100–300 taste buds.  ANATOMY OF PAPILLAE 2. Fungiform papillae (FUN-ji-form  mushroomlike) are mushroom-shaped elevations scattered over the entire surface of the tongue that contain about five taste buds each.  ANATOMY OF PAPILLAE In addition, the entire surface of the tongue has filiform papillae (FIL-i-form  threadlike). These pointed, threadlike structures contain tactile receptors but no taste buds. They increase friction between the tongue and food, making it easier for the tongue to move food in the oral cavity. The relationship of gustatory receptor cells in taste buds to tongue papillae. The relationship of gustatory receptor cells in taste buds to tongue papillae. Structure of a taste bud Histology of a taste bud from vallate papilla. VISION Sight or vision is extremely important to human survival. More than half the sensory receptors in the human body are located in the eyes, and a large part of the cerebral cortex is devoted to processing visual information. VISION In this section of the chapter, we examine electromagnetic radiation, the accessory structures of the eye, the eyeball itself, and the visual pathway from the eye to the brain. ELECTROMAGNETIC RADIATION The energy in the form of waves that radiates from the sun. There are many types of electromagnetic radiation, including gamma rays, x-rays, UV rays, visible light, infrared radiation, microwaves, and radio waves. This range of electromagnetic radiation is known as the electromagnetic spectrum. ELECTROMAGNETIC SPECTRUM ELECTROMAGNETIC SPECTRUM The distance between two consecutive peaks of an electromagnetic wave is the wavelength. Wavelengths range from short to long; for example, gamma rays have wavelengths smaller than a nanometer, and most radio waves have wavelengths greater than a meter. ELECTROMAGNETIC WAVE ELECTROMAGNETIC RADIATION The eyes are responsible for the detection of visible light, the part of the electromagnetic spectrum with wavelengths ranging from about 400 to 700 nm. Visible light exhibits colors. The color of visible light depends on its wavelength. For example, light that has a wavelength of 400 nm is violet, and light that has a wavelength of 700 nm is red. ELECTROMAGNETIC RADIATION An object appears white because it reflects all wavelengths of visible light. An object appears black because it absorbs all wavelengths of visible light. ANATOMY OF THE EYE External and Accessory Structures The accessory structures of the eye include the extrinsic eye muscles, eyelids, conjunctiva, and lacrimal apparatus.  External and Accessory Structures The accessory structures of the eye include the extrinsic eye muscles, eyelids, conjunctiva, and lacrimal apparatus.  EYELIDS The space between the upper and lower eyelids that exposes the eyeball is the palpebral fissure. Its angles are known as the lateral commissure, which is narrower and closer to the temporal bone, and the medial commissure, which is broader and nearer the nasal bone.  EYELIDS In the medial commissure is a small, reddish elevation, the lacrimal caruncle, which contains sebaceous (oil) glands and sudoriferous (sweat) glands. The whitish material that sometimes collects in the medial commissure comes from these glands.  EYELIDS From superficial to deep, each eyelid consists of epidermis, dermis, subcutaneous tissue, fibers of the orbicularis oculi muscle, a tarsal plate, tarsal glands, and conjunctiva.  EYELASHES AND EYEBROWS The eyelashes, which project from the border of each eyelid, and the eyebrows, which arch transversely above the upper eyelids, help protect the eyeballs from foreign objects, perspiration, and the direct rays of the sun.  CONJUCTIVA A delicate membrane, the conjunctiva, lines the eyelids and covers part of the outer surface of the eyeball; it ends at the edge of the cornea by fusing with the corneal epithelium.  THE LACRIMAL APPARATUS The lacrimal apparatus consists of the lacrimal gland and a number of ducts that drain the lacrimal secretions into the nasal cavity.  LACRIMAL GLANDS The lacrimal glands are located above the lateral end of each eye; they continually release a salt solution (tears) onto the anterior surface of the eyeball through several small ducts.  LACRIMAL CANALICULI The tears flush across the eyeball into the lacrimal canaliculi medially, then into the lacrimal sac, and finally into the nasolacrimal duct, which empties into the nasal cavity.  LYSOZYME Lacrimal secretion also contains antibodies and lysozyme, an enzyme that destroys bacteria; thus, it cleanses and protects the eye surface as it moistens and lubricates it.  FLOW OF TEARS Lacrimal gland >> Lacrimal ducts >> Superior or Inferior lacrimal canal >> Lacrimal Sac >> Nasolacrimal duct >> Nasal cavity  EXTRINSIC EYE MUSCLE Six extrinsic, or external, eye muscles are attached to the outer surface of the eye; these muscles produce gross eye movements and make it possible for the eyes to follow a moving object;  EXTRINSIC EYE MUSCLE These are the lateral rectus, medial rectus, superior rectus, inferior rectus, inferior oblique, and superior oblique. Internal Structures: The Eyeball The eye itself, commonly called the eyeball, is a hollow sphere; its wall is composed of three layers, and its interior is filled with fluids called humors that help to maintain its shape. Layers Forming the Wall of the Eyeball Fibrous layer. The outermost layer, called the fibrous layer, consists of the protective sclera and the transparent cornea. Sclera. The sclera, thick, glistening, white connective tissue, is seen anteriorly as the “white of the eye”. Layers Forming the Wall of the Eyeball Cornea. The central anterior portion of the fibrous layer is crystal clear; this “window” is the cornea through which light enters the eye. Vascular layer. The middle eyeball of the layer, the vascular layer, has three distinguishable regions: the choroid, the ciliary body, and the iris. Layers Forming the Wall of the Eyeball Choroid. Most posterior is the choroid, a blood-rich nutritive tunic that contains a dark pigment; the pigment prevents light from scattering inside the eye. Layers Forming the Wall of the Eyeball Ciliary body. Moving anteriorly, the choroid is modified to form two smooth muscle structures, the ciliary body, to which the lens is attached by a suspensory ligament called ciliary zonule, and then the iris. Layers Forming the Wall of the Eyeball Pupil. The pigmented iris has a rounded opening, the pupil, through which light passes. Sensory layer. The innermost sensory layer of the eye is the delicate two-layered retina, which extends anteriorly only to the ciliary body.  VISUAL RODS AND CONES Pigmented layer. The outer pigmented layer of the retina is composed pigmented cells that, like those of the choroid, absorb light and prevent light from scattering inside the eye.  VISUAL RODS AND CONES Neural layer. The transparent inner neural layer of the retina contains millions of receptor cells, the rods and cones, which are called photoreceptors because they respond to light.  VISUAL RODS AND CONES Two-neuron chain. Electrical signals pass from the photoreceptors via a two-neuron chain- bipolar cells and then ganglion cells– before leaving the retina via optic nerve as nerve impulses that are transmitted to the optic cortex; the result is vision.  VISUAL RODS AND CONES Optic disc. The photoreceptor cells are distributed over the entire retina, except where the optic nerve leaves the eyeball; this site is called the optic disc, or blind spot.  VISUAL RODS AND CONES Fovea centralis. Lateral to each blind spot is the fovea centralis, a tiny pit that contains only cones. LENS Light entering the eye is focused on the retina by the lens, a flexible biconvex, crystal-like structure.  LENS Chambers. The lens divides the eye into two segments or chambers; the anterior (aqueous) segment, anterior to the lens, contains a clear, watery fluid called aqueous humor;  LENS the posterior (vitreous) segment posterior to the lens, is filled with a gel-like substance called either vitreous humor, or the vitreous body.  LENS Vitreous humor. Vitreous humor helps prevent the eyeball from collapsing inward by reinforcing it internally.  LENS Aqueous humor. Aqueous humor is similar to blood plasma and is continually secreted by a special of the choroid; it helps maintain intraocular pressure, or the pressure inside the eye.  LENS Canal of Schlemm. Aqueous humor is reabsorbed into the venous blood through the scleral venous sinus, or canal of Schlemm, which is located at the junction of the sclera and cornea.  LENS Canal of Schlemm. Aqueous humor is reabsorbed into the venous blood through the scleral venous sinus, or canal of Schlemm, which is located at the junction of the sclera and cornea. EYE REFLEXES Both the external and internal eye muscles are necessary for proper eye function.  EYE REFLEXES Photopupillary reflex. When the eyes are suddenly exposed to bright light, the pupils immediately constrict; this is the photopupillary reflex; this protective reflex prevents excessively bright light from damaging the delicate photoreceptors.  EYE REFLEXES Accommodation pupillary reflex. The pupils also constrict reflexively when we view close objects; this accommodation pupillary reflex provides for more acute vision. HEARING AND EQUILIBRIUM ANATOMY OF THE EAR Anatomically, the ear is divided into three major areas: the external, or outer, ear; the middle ear, and the internal, or inner, ear. External (Outer) Ear The external, or outer, ear is composed of the auricle and the external acoustic meatus.  Auricle The auricle, or pinna, is what most people call the “ear”- the shell-shaped structure surrounding the auditory canal opening.  External acoustic meatus The external acoustic meatus is a short, narrow chamber carved into the temporal bone of the skull; in its skin-lined walls are the ceruminous glands, which secrete waxy, yellow cerumen or earwax, which provides a sticky trap for foreign bodies and repels insects.  Tympanic membrane Sound waves entering the auditory canal eventually hit the tympanic membrane, or eardrum, and cause it to vibrate; the canal ends at the ear drum, which separates the external from the middle ear. Middle Ear The middle ear, or tympanic cavity, is a small, air-filled, mucosa-lined cavity within the temporal bone.  Openings The tympanic cavity is flanked laterally by the eardrum and medially by a bony wall with two openings, the oval window and the inferior, membrane-covered round window.  Pharyngotympanic tube The pharyngotympanic tube runs obliquely downward to link the middle ear cavity with the throat, and the mucosae lining the two regions are continuous.  Ossicles The tympanic cavity is spanned by the three smallest bones in the body, the ossicles, which transmit the vibratory motion of the eardrum to the fluids of the inner ear; these bones, named for their shape, are the hammer, or malleus, the anvil, or incus, and the stirrup, or stapes. Internal (Inner) Ear The internal ear is a maze of bony chambers, called the bony, or osseous, labyrinth, located deep within the temporal bone behind the eye socket.  Subdivisions The three subdivisions of the bony labyrinth are the spiraling, pea-sized cochlea, the vestibule, and the semicircular canals.  Perilymph The bony labyrinth is filled with a plasma-like fluid called perilymph.  Membranous labyrinth Suspended in the perilymph is a membranous labyrinth, a system of membrane sacs that more or less follows the shape of the bony labyrinth.  Endolymph The membranous labyrinth itself contains a thicker fluid called endolymph. Mechanisms of Equilibrium The equilibrium receptors of the inner ear, collectively called the vestibular apparatus, can be divided into two functional arms- one arm responsible for monitoring static equilibrium and the other involved with dynamic equilibrium. Static Equilibrium Within the membrane sacs of the vestibule are receptors called maculae that are essential to our sense of static equilibrium.  Maculae The maculae report on changes in the position of the head in space with respect to the pull of gravity when the body is not moving.  Otolithic hair membrane Each macula is a patch of receptor (hair) cells with their “hairs” embedded in the otolithic hair membrane, a jelly-like mass studded with otoliths, tiny stones made of calcium salts.  Otoliths As the head moves, the otoliths roll in response to changes in the pull of gravity; this movement creates a pull on the gel, which in turn slides like a greased plate over the hair cells, bending their hairs.  Vestibular nerve This event activates the hair cells, which send impulses along the vestibular nerve (a division of cranial nerve VIII) to the cerebellum of the brain, informing it of the position of the head in space. Dynamic Equilibrium The dynamic equilibrium receptors, found in the semicircular canals, respond to angular or rotatory movements of the head rather than to straight-line movements.  Semicircular canals The semicircular canals are oriented in the three planes of space; thus regardless of which plane one moves in, there will be receptors to detect the movement.  Crista ampullaris Within the ampulla, a swollen region at the base of each membranous semicircular canal is a receptor region called crista ampullaris, or simply crista, which consists of a tuft of hair cells covered with a gelatinous cap called the cupula.  Head movements When the head moves in an arclike or angular direction, the endolymph in the canal lags behind. Bending of the cupulaents Then, as the cupula drags against the stationary endolymph, the cupula bends- like a swinging door- with the body’s motion.  Vestibular nerve This stimulates the hair cells, and impulses are transmitted up the vestibular nerve to the cerebellum.