Special Senses in Human Anatomy PDF

1 SPECIAL SENSES GROUP  SENSATION The senses are the means by which the brain receives information about the environment and the body. Sensation is the process initiated by stimulating sensory receptors, and perception is the conscious awareness of those sti...

1 SPECIAL SENSES GROUP  SENSATION The senses are the means by which the brain receives information about the environment and the body. Sensation is the process initiated by stimulating sensory receptors, and perception is the conscious awareness of those stimuli. The brain constantly receives a wide variety of stimuli from both inside and outside the body, but stimulation of sensory receptors does not immediately result in perception. Sensory receptors respond to stimuli by generating action potentials that are propagated to the spinal cord and brain. Perception results when action potentials reach the cerebral cortex. Some other parts of the brain are also involved in perception. For example, the thalamus plays a role in the perception of pain.  SENSORY RECEPTORS Sensory receptors are sensory nerve endings or specialized cells capable of responding to stimuli by developing action potentials. Several types of receptors are associated with both the general and the special senses, and each responds to a different type of stimulus: Mechanoreceptors (MEK-an-noh-ree-SEP-ters) respond to mechanical stimuli, such as the bending or stretching of receptors. Chemoreceptors (kee-moh-ree-SEP-ters) respond to chemicals. For example, odor molecules bind to chemoreceptors, allowing us to perceive smells. Photoreceptors (foh-toh-ree-SEP-tors) respond to light. Thermoreceptors (thur-moh-ree-SEP-ters) respond to temperature changes. Nociceptors (NOH-see-sep-ters; noceo, to injure) respond to stimuli that result in the sensation of pain.  SPECIAL SENSES 1. THE EYE AND VISION 2. THE EAR: HEARING AND BALANCE 3. CHEMICAL SENSES: TASTE AND SMELL 4. DEVELOPMENTAL ASPECTS 1 THE EYE AND VISION  EYE & VISION - ANATOMY OF THE EYE Accessory structures of the eye include extrinsic eye muscles, eyelids, conjunctiva, and lacrimal appratus. Eyes are protected by eyelids anteriorly, also by medial commissure. Palpebra fissures are the space between eyelids. Eyelashes are associated with tarsal glands protecting from each border of eyelid lubricates the eye. Ciliary glands duct open at the eyelash follicles. Lacrimal caruncle’s produce whitish secretions lubricating eyes. Conjunctiva is delicate membrane, which covers the eyelid and the outer surface of the eyeball. It ends at the edge of transparent cornea by fusing with cornea epithelium.  ANATOMY OF EYE Lacrimal apparatus containing lacrimal glands are located above the lateral end of the eye. They released tears, which flushes across the eyeball, into the lacrimal calculi medially, then into the lacrimal SAC, and finally into nasolacrimal duct, which empties into the inferior meatus of the nasal cavity. Tears contains mucus antibodies and lysosomes and enzymes that destroys bacteria day cleanse and protect the eye surface as their moisture in and lubricate. Six extrinsic eye muscles are attached to the outer surface plays a role in eye movement.  ANATOMY OF EYE Name Action Controlling cranial nerves Lateral rectus Moves eye laterally VI (abducens) Medial rectus Moves eye medially III (oculomotor) Superior rectus Elevates eye and turns it medially III (oculomotor) Inferior rectus Depresses eye and turns it medially III (oculomotor) Inferior oblique Elevates eye and turns it laterally III (oculomotor) Superior oblique Depresses eye and turns it laterally IV (trochlea)  INTERNAL STRUCTURES OF EYE The eye walls are composed of three tunics and its interior is filled with fluid called humors which maintain the shape. The layer forming the walls of eyeball: 1. Fibrous layer 2. Vascular layer 3. Sensory layer  LAYERS OF EYEBALL THE OUTERMOST FIBROUS LAYER consists of protective sclera and transparent cornea. Sclera is the white of eye interior. Central anterior portion of fibrous layer, is crystal clear. Light enters through cornea, the only tissue which is never rejected for transplant.  LAYERS OF EYEBALL THE MIDDLE VASCULAR LAYER Posterior is choroid which contain dark pigment which prevent light from scattering inside the eye. The Ciliary body, which is attached to lens by ciliary ligament, called Ciliary zonules and the iris, the pigment iris has rounded opening, the pupil through light passes. In close vision, circular muscles contract pupil constrict in distant vision, radial fibers contract. To enlarge the pupil, which allows light to enter eye. Cranial nerve 3 controls the muscles of iris.  LAYERS OF EYEBALL THE INNERMOST SENSORY LAYER is the two-layered retina. The outer pigmented layer of retina prevent light from scattering, act as phagocytes to remove dead cell and store vitamin A for vision The neural layer contains rods and cones, which are photoreceptors. Electrical signal pass from photoreceptor via two nueron chain bipolar cells before leaving the retina via optic nerve and then interpreted by optic cortex. there are no photoreceptors at optic disc with result in the blind spot in our vision.  CONES Allow us to the details of the world. Densest in the center of retina. Decrease in number towards the retinal edge. Fovea Centralis only contain cones - greatest visual activity. There are 3 types of cones: Type 1: vigorously respond to blue light Type 2: respond to green light Type 3: respond to range including both green and red wavelength of light (also known as red cones)  LENS Light is focused on retina by flexible biconvex lens. Held upright in eye by Ciliary zonules and attached to ciliary body. Lens divide eye into anterior chamber (contain aqueous humor) & posterior chambers (contain vitreous humor). Vitreous humor prevent eyeball from maintain intraocular pressure & provide nutrients for lens and cornea. Aqueous humor is reabsorbed by venous blood through the scleral venous sinus located at junction of sclera and cornea.  PATHWAY OF LIGHT & REFRACTION Refraction: bending of light rays in eye through cornea, aqueous humor, lens and vitreous humor. Greater the lens convexity = more it bends light, flatter the lens = lens it bends light. Light from distance approach eye as parallel rays, however, light from close object diverge to make vision possible. Accommodation - ability of eye to focus specific object. Reversed and inverted image form at retina due to light bending is a real image.  VISUAL FIELDS & PATHWAYS TO BRAIN Axons carrying impulses from the retina are bundied together at the posterior aspect of the eyeball and leave the back of the eye as the optic nerve. At the optic chiasma the fibers from the medial side of each eye cross over to the opposite side of the brain. The fiber tracts result are the optic tracts. Each optic tract contains fibers from the lateral side of the eye on the same side and the medial side of the opposite eye. The optic tract fibers synapse with neurons in the thalamus, whose axons from the optic radiation, which runs to the occipital lobe of the brain. There they synapse with the cortical cells, and visual interpretation, or seeing, occurs. Humans have binocular vision. Binocular vision, literally “two-eyed vision”, providers for depth perception, also called “three-dimensional” vision, as our visual cortex fuses the two slightly different images delivered by the two eyes into one “picture”.  EYE REFLEXES Internal muscles are controlled by the autonomic nervous system. Bright light causes pupils to constrict through action of radial (iris) and ciliary muscles (photopupillary reflex) Viewing close objects causes accommodation pupillary reflex. External muscles control eye movement to follow objects- voluntary, controlled at the frontal eye field. Viewing close objects causes convergence (eyes moving medially).  EYE PATHOLOGIES Inflammation of the conjunctiva, called conjunctivitis, results in redeemed, irritated eyes. Pinkeye, its infectious form caused by bacteria or viruses, is highly contagious. Lack of all three cone types results in total color blindness, whereass lack of one cone type leads to partial color blindness. Cataracts, the loss of lens transparency, cause vision to become hazy and distorted and can eventually cause blindness. If drainage of aqueous humor is blocked, fluid backs up like a clogged sink. Pressure within the eye may increase to dangerous levels and compress the delicate retina and optic nerve. The resulting condition, glaucoma. Hemianopia is the loss the same side of the visual field of the of both eyes, which results from damage to the visual cortex on one side only. Nearsightedness, or myopia occurs when the parallel light rays from distant objects fall to reach the retina and instead are focused in front of it. Farsightedness, or hyperopia occurs when the parallel light rays from distatnt objects are focused behind the retina - at least in the resting eye, in which the lens is flat and the ciliary muscle is relaxed. 2 THE EAR: HEARING & BALANCE  THE EAR: HEARING & BALANCE Houses two senses. Hearing (interpreted in the auditory cortex of the temporal lobe). Equilibrium (balance) interpreted in the cerebellum). Receptors are mmechanoreceptors. Different organs house receptors for each sense.  ANNATOMY OF EAR THE OUTER EAR Composed of the auricle and the the external acoustic meatus. The auricle, or pinna is the shell-shaped structure surrounding the auditory canal opening. The external acoustic meatus (or auditory canal) is a short, narrow chamber carved into the temporal bone of the skull. The ceruminous glands secrete waxy yellow cerumen, or earwax, which provides a sticky trap for foreign bodies and repels insects. Sound waves entering the auditory canal eventually hit the tympanic membrane, or eardrum, and cause it to vibrate. The canal ends at the eardrum, which separates the external from the middle ear.  ANNATOMY OF EAR THE MIDDLE EAR CAVITY Tympanic cavity, is a small, air-filled, mucosa-lined cavity within the temporal bone. It 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. The pharyngotympanic tube (equalize pressure runs obliquely downward to link the middle ear cavity with the throat, and the mucosae lining the two regions are continous. When the pressures are unequal, the eardrum bulges inward or outward, causing hearing difficulty and sometimes earaches. 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, the anvil and the stirrup.  ANNATOMY OF EAR THE MIDDLE EAR CAVITY When the eardrum moves, it moves the hammer and transfers the vibration to the anvil. The anvil, in turn, passes the vibration on the stirrup, which passes on the oval window of the inner ear. The movement at the oval window sets the fluids of the ear. The movement at the oval window sets the fluids of the inner ear into motion, eventually exciting the hearing receptors.  ANNATOMY OF EAR THE INTERNAL EAR Is a maze of bony chambers called bone labyrinth, or osseous labyrinth, located deep within the temporal bone behind the eye socket. The three subdivisions of the bony labyrinth are the spiraling, pea-sized cochlea, the vestibule, and the semicircular canal. The vestibule is situated between the semicircular canals and the cochlea. The bony labyrinth is filled with a plasma like fluid called perilymph. Suspended in the perilymph is a membranous labyrinth, a system of membrane sacs that follows the shape of the bony labyrinth. The membranous labyrinth itself contains a thicker called endolymph. ANNATOMY OF EAR  STATIC EQUILIBRIUM Within the membrane sacs of the vestibule are receptors called maculae. The maculae report on changes in the position of the head in space. Provide information on which way is up or down. Help us keep our head erect. Each macula is a patch of receptor cells with their “hairs” embedded in the otolithic membrane, a gelatinous mass studded with otoliths, tiny stones made of calcium salts. 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 turn bends the hairs of the hair cells. Bending activates the hair cells, which send impulses along the vestibular nerve (a division of cranial nerve) to the cerebellum of the brain, informing it of the position of the head in space.  DYNAMIC EQUILIBRIUM Dynamic equilibrium receptors, found in the semicircular canals, respond to angular or rotational movement of the head. The semicircular canals are oriented in the three planes of space. Within the ampullae, swollen regions at the base of each membranous semicircular canal, are multiple receptor regions, each called a crista ampullaris which consists of a tuft of hair cells covered with a gelatinous cap called the cupula. When your head moves in an archlike or angular direction, the endolymph in the canal legs the movement. Then, as the cupula drags against the stationary endolymph, the cupula bends with the body’s motion. This stimulates the hair cells, and impulses are transmitted up the vestibular nerve to the cerebellum. Bending the cupula in the opposite in the opposite direction reduces impulse. HEARING  HEARING & EQUILIBRIUM DEFICIT Deafness is defined as hearing loss of any degree-from a slight loss to a total inability to hear sound. Temporary or permanent conduction deafness results when something interferes with the conduction of sound vibrations to the fluids of the inner ear Conduction deafness include fusion of the ossicles (a problem called otosclerosis, a ruptured eardrum, and otitis media (inflammation of the middle ear). Sensorineural deafness occurs when there is degeneration or damage to the receptor cells in the spiral organ of Corti, to the cochlear nerve, or to neurons of the auditory cortex Equilibrium problems are usually obvious. Nausea, dizziness, and problems in maintaining balance are common symptoms, particularly when impulses from the vestibular apparatus "disagree" with what we see (visual input). Ménière's syndrome, suspected causes are arteriosclerosis, degeneration of cranial nerve VIII, and increased pressure of the inner ear fluids. Affected individuals become nauseated and often have howling or ringing sounds in their ears and vertigo 3 CHEMICAL SENSES: TASTE & SMELL  CHEMICAL SENSES: SMELL The receptors for taste and olfaction are classified as chemoreceptors they respond to chemicals in solution. The olfactory receptor cells are neurons equipped with olfactory hairs, bathed by a layer of mucus secreted by underlying glands. When the olfactory receptors located on the cilia are stimulated by chemicals dissolved in the mucus, they transmit impulses along the olfactory filaments, which are bundled axons of olfactory neurons that collectively make up the olfactory nerve (cranial nerve I). The olfactory nerve conducts the impulses to the olfactory cortex of the brain. There the odor is interpreted, and an "odor snapshot" is made. The olfactory pathways are closely tied into the limbic system (emotional-visceral part of the brain)  CHEMICAL SENSES: TASTE The dorsal tongue surface is covered with small peg like projections, or papillae. The taste buds are found on the sides of the large round vallate papillae, or circumvallate papillae, on the tops of the more numerous fungiform papillae and in the foliate papillae on the sides of the tongue. The specific receptor cells that respond to chemicals dissolved in the saliva are epithelial cells called gustatory cells. Their long microvilli-the gustatory hairs--protrude through the taste pore; and when they are stimulated, they depolarize, and impulses are transmitted to the brain. Three cranial nerves-VII, IX, and X-carry taste impulses from the various taste buds to the gustatory cortex. The facial nerve (VII) serves the anterior part of the tongue. The other two cranial nerves-the glossopharyngeal nerve and vagus nerve-serve the other taste bud-containing areas. Taste buds are replaced every 7 to 10 days by basal cells (stem cells) found in the deeper regions of the taste buds.  TASTE RECEPTORS There are five basic taste sensations, each corresponding to stimulation of one of the five major types of taste buds. THE SWEET RECEPTORS respond to substances such as sugars, saccharine, some amino acids, and some lead salts. SOUR RECEPTORS respond to hydrogen ions (H+), or the acidity of the solution. BITTER RECEPTORS to alkaloids; and salty receptors to metal ions in solution. UMAMI, a taste discovered by the Japanese, is elicited by the amino acid glutamate, which appears to be responsible for the "beef taste" of steak and the flavor of monosodium glutamate, a food additive. Historically, the tip of the tongue was believed to be most sensitive to sweet and salty substances, its sides to sour, the back of the tongue to bitter, and the pharynx to umami. Most taste buds respond to two, three, four, or even all five taste modalities. 4 DEVELOPMENTAL ASPECTS DEVELOPMENT ASPECT OF SPECIAL SENSES Special sense organs are formed early in embryonic development. Maternal infections during the first 5 or 6 months of pregnancy may cause visual abnormalities as well as sensorineural deafness in the developing child. An important congenital eye problem is strabismus. The most important congenital ear problem is lack of the external acoustic meatus. Vision requires the most learning. The infant has poor visual acuity (is farsighted) and lacks color vision and depth perception at birth. The eye continues to grow and mature until age 8 or 9. Problems of aging associated with vision include presbyopia, glaucoma, cataracts, and arteriosclerosis of the eye's blood vessels. The newborn infant can hear sounds, but initial responses are reflexive. By the toddler stage, the child is listening critically and beginning to imitate sounds as language development begins. Sensorineural deafness (presbycusis) is a normal consequence of aging. Taste and smell are most acute at birth and decrease in sensitivity after age 40 as the number of olfactory and gustatory receptors decreases.  REFERENCES Seeley’s Essentials of Anatomy & Physiology (11th Edition) Sciencera. (2022, April 11). LESSON 16 - The Special Senses [Video]. YouTube. https://www.youtube.com/watch?v=2KekHzmoXnY THANK YOU