Essentials of Human Anatomy & Physiology PDF

Essentials of Human Anatomy & Physiology Thirteenth Edition Global Edition Chapter 8 Special Senses Lecture Presentation by...

Essentials of Human Anatomy & Physiology Thirteenth Edition Global Edition Chapter 8 Special Senses Lecture Presentation by Patty Bostwick-Taylor Florence-Darlington Technical College Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Special Senses Special senses include: – Smell – Taste – Sight – Hearing – Equilibrium Special sense receptors – Large, complex sensory organs (eye and ear) – Localized clusters of receptors (taste buds and olfactory epithelium) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Concept Link Recall the three basic functions of the nervous system (Figure 7.1, p. 243). Each of the special senses gathers unique sensory information that, once integrated, will influence motor output. For example, if you saw a ball moving toward your head, this sensory input might result in a motor output that would move your body out of the path of the ball. Additionally, recall that each type of sensory information is processed in a specialized area of the cerebrum (Figure 7.13c, p. 259). Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Part I : The Eye and Vision one 70 percent of all sensory receptors are in the eyes Each eye has over 1 million nerve fibers carrying information to the brain Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Anatomy of the Eye Accessory structures include the: – Extrinsic eye muscles – Eyelids – Conjunctiva – Lacrimal apparatus Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.1 Surface Anatomy of the Eye and Accessory Structures Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. External and Accessory Structures (1 of 5) Eyelids – Meet at the medial and lateral commissure (canthus) Eyelashes – Tarsal glands produce an oily secretion that lubricates the eye – Ciliary glands are located between the eyelashes Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. External and Accessory Structures (2 of 5) Conjunctiva – Membrane that lines the eyelids and eyeball – Connects with the transparent cornea – Secretes mucus to lubricate the eye and keep it moist Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. External and Accessory Structures (3 of 5) Lacrimal apparatus = lacrimal gland + ducts – Lacrimal gland—produces lacrimal fluid (tears); situated on lateral end of each eye – Tears drain across the eye into the lacrimal canaliculi, then the lacrimal sac, and into the nasolacrimal duct, which empties into the nasal cavity Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. External and Accessory Structures (4 of 5) Tears contain: – Dilute salt solution – Mucus – Antibodies – Lysozyme (enzyme that destroys bacteria) Function of tears – Cleanse, protect, moisten, lubricate the eye Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.2a Accessory Structures of the Eye Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.2b Accessory Structures of the Eye Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. External and Accessory Structures (5 of 5) Extrinsic eye muscles – Six muscles attach to the outer surface of the eye – Produce gross eye movements Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.3a Extrinsic Muscles of the Eye Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.3b Extrinsic Muscles of the Eye Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.3c Extrinsic Muscles of the Eye Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (1 of 13) Three layers, or tunics, form the wall of the eyeball – Fibrous layer: outside layer – Vascular layer: middle layer – Sensory layer: inside layer Humors are fluids that fill the interior of the eyeball Lens divides the eye into two chambers Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.4a Internal Anatomy of the Eye (Sagittal Section) (1 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.4b Internal Anatomy of the Eye (Sagittal Section) (1 of 2) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (2 of 13) Fibrous layer = sclera + cornea – Sclera ▪ White connective tissue layer ▪ Seen anteriorly as the “white of the eye” – Cornea ▪ Transparent, central anterior portion ▪ Allows for light to pass through ▪ Repairs itself easily ▪ The only human tissue that can be transplanted without fear of rejection due to lack of blood vessels Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (3 of 13) Vascular layer – Choroid is a blood-rich nutritive layer that contains a pigment (prevents light from scattering) – Choroid is modified anteriorly into two smooth muscle structures ▪ Ciliary body—attached to lens by a suspensory ligament called the ciliary zonule ▪ Iris—regulates amount of light entering eye – Pigmented layer that gives eye color – Pupil—rounded opening in the iris Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (4 of 13) Sensory layer – Retina contains two layers 1. Outer pigmented layer absorbs light and prevents it from scattering 2. Inner neural layer contains receptor cells (photoreceptors) – Rods – Cones Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (5 of 13) Sensory layer – Electrical signals pass from photoreceptors via a two-neuron chain ▪ Bipolar cells ▪ Ganglion cells – Signals leave the retina toward the brain through the optic nerve – Optic disc (blind spot) is where the optic nerve leaves the eyeball ▪ Cannot see images focused on the optic disc Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.5a The Three Major Types of Neurons Composing the Retina Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.5b The Three Major Types of Neurons Composing the Retina Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (6 of 13) Sensory layer – Rods ▪ Most are found toward the edges of the retina ▪ Allow vision in dim light and peripheral vision ▪ All perception is in gray tones Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (7 of 13) Sensory layer – Cones ▪ Allow for detailed color vision ▪ Densest in the center of the retina ▪ Fovea centralis–lateral to blind spot – Area of the retina with only cones – Visual acuity (sharpest vision) is here – No photoreceptor cells are at the optic disc, or blind spot Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (8 of 13) Sensory layer – Cone sensitivity ▪ Three types of cones ▪ Each cone type is sensitive to different wavelengths of visible light Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.6 Sensitivities of the Three Cone Types to Different Wavelengths of Visible Light Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (9 of 13) Lens – Flexible, biconvex crystal-like structure – Held in place by a suspensory ligament attached to the ciliary body Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.4a Internal Anatomy of the Eye (Sagittal Section) (2 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (10 of 13) Lens divides the eye into two segments, or chambers 1. Anterior (aqueous) segment ▪ Anterior to the lens ▪ Contains aqueous humor, a clear, watery fluid 2. Posterior (vitreous) segment ▪ Posterior to the lens ▪ Contains vitreous humor, a gel-like substance Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.4a Internal Anatomy of the Eye (Sagittal Section) (3 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.4b Internal Anatomy of the Eye (Sagittal Section) (2 of 2) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (11 of 13) Aqueous humor – Watery fluid found between lens and cornea – Similar to blood plasma – Helps maintain intraocular pressure – Provides nutrients for the lens and cornea – Reabsorbed into venous blood through the scleral venous sinus, or canal of Schlemm Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (12 of 13) Vitreous humor – Gel-like substance posterior to the lens – Prevents the eye from collapsing – Helps maintain intraocular pressure Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Internal Structures: The Eyeball (13 of 13) Ophthalmoscope – Instrument used to illuminate the interior of the eyeball and fundus (posterior wall) – Can detect diabetes, arteriosclerosis, degeneration of the optic nerve and retina Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.7 The Posterior Wall (Fundus) of the Retina as Seen With an Ophthalmoscope Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Physiology of Vision (1 of 7) Pathway of light through the eye and light refraction – Light must be focused to a point on the retina for optimal vision – Light is bent, or refracted, by the cornea, aqueous humor, lens, and vitreous humor – The eye is set for distant vision (over 20 feet away) – Accommodation—the lens must change shape to focus on closer objects (less than 20 feet away) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.8 Relative Convexity of the Lens During Focusing for Distant and Close Vision Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Physiology of Vision (2 of 7) Pathway of light through the eye and light refraction – Image formed on the retina is a real image – Real images are: ▪ Reversed from left to right ▪ Upside down ▪ Smaller than the object Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.9 Real Image (Reversed Left to Right, and Upside Down) Formed on the Retina Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Physiology of Vision (3 of 7) Visual fields and visual pathways to the brain – Optic nerve ▪ Bundle of axons that exit the back of the eye carrying impulses from the retina – Optic chiasma ▪ Location where the optic nerves cross ▪ Fibers from the medial side of each eye cross over to the opposite side of the brain Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Physiology of Vision (4 of 7) Visual fields and visual pathways to the brain – Optic tracts ▪ Contain fibers from the lateral side of the eye on the same side and the medial side of the opposite eye ▪ Synapse with neurons in the thalamus – Optic radiation ▪ Axons from the thalamus run to the occipital lobe ▪ Synapse with cortical cells, and vision interpretation (seeing) occurs Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Physiology of Vision (5 of 7) Summary of the pathway of impulses from the retina to the point of visual interpretation 1. Optic nerve 2. Optic chiasma 3. Optic tract 4. Thalamus 5. Optic radiation 6. Visual cortex in occipital lobe of brain Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.10 Visual Fields of the Eyes and Visual Pathway to the Brain (Inferior View) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Physiology of Vision (6 of 7) Visual fields – Each eye “sees” a slightly different view – Field of view overlaps for each eye Binocular vision results and provides: – Depth perception (three-dimensional vision) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. A Closer Look (1 of 3) Emmetropia—eye focuses images correctly on the retina Myopia (nearsightedness) – Distant objects appear blurry – Light from those objects fails to reach the retina and are focused in front of it – Results from an eyeball that is too long Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. A Closer Look (2 of 3) Hyperopia (farsightedness) – Near objects are blurry, whereas distant objects are clear – Distant objects are focused behind the retina – Results from an eyeball that is too short or from a “lazy lens” Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. A Closer Look (3 of 3) Astigmatism – Images are blurry – Results from light focusing as lines, not points, on the retina because of unequal curvatures of the cornea or lens Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. A Closer Look 8.2 Bringing Things Into Focus Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Physiology of Vision (7 of 7) Eye reflexes – Convergence: reflexive movement of the eyes medially when we focus on a close object – Photopupillary reflex: bright light causes pupils to constrict – Accommodation pupillary reflex: viewing close objects causes pupils to constrict Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Part II : The Ear: Hearing and Balance Two Ear houses two senses 1. Hearing 2. Equilibrium (balance) Receptors are mechanoreceptors Different organs house receptors for each sense Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Anatomy of the Ear (1 of 6) The ear is divided into three areas 1. External (outer) ear 2. Middle ear 3. Internal (inner) ear Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.11 Anatomy of the Ear (1 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Anatomy of the Ear (2 of 6) External (outer) ear – Auricle (pinna) – External acoustic meatus (auditory canal) ▪ Narrow chamber in the temporal bone ▪ Lined with skin and ceruminous (earwax) glands – Glands secrete cerumen (earwax) – Cerumen traps foreign objects and repels insects ▪ Ends at the tympanic membrane (eardrum) – External ear is involved only in collecting sound waves Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Anatomy of the Ear (3 of 6) Middle ear cavity (tympanic cavity) – Air-filled, mucosa-lined cavity within the temporal bone – Involved only in the sense of hearing – Located between tympanic membrane (laterally) and medially by a bony wall with two openings: ▪ Oval window ▪ Round window Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Anatomy of the Ear (4 of 6) Middle ear cavity (tympanic cavity) – Pharyngotympanic tube (auditory tube) ▪ Links middle ear cavity with the throat ▪ Equalizes pressure in the middle ear cavity so the eardrum can vibrate Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Anatomy of the Ear (5 of 6) Middle ear cavity (tympanic cavity) – Three bones (ossicles) span the cavity 1. Malleus (hammer) 2. Incus (anvil) 3. Stapes (stirrup) – Function ▪ Transmit and amplify vibrations from tympanic membrane to the fluids of the inner ear ▪ Vibrations travel from the hammer anvil stirrup oval window of inner ear Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.11 Anatomy of the Ear (2 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Anatomy of the Ear (6 of 6) Internal (inner) ear – Includes sense organs for hearing and balance – Bony labyrinth (osseous labyrinth) consists of: ▪ Cochlea ▪ Vestibule ▪ Semicircular canals – Bony labyrinth is filled with perilymph ▪ Membranous labyrinth is suspended in perilymph and contains endolymph Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.11 Anatomy of the Ear (3 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Hearing (1 of 4) Spiral organ of Corti – Located within the cochlear duct – Receptors = hair cells on the basilar membrane – Gel-like tectorial membrane is capable of bending hair cells – Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.12a Anatomy of the Cochlea Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.12b Anatomy of the Cochlea Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Hearing (2 of 4) Pathway of vibrations from sound waves 1. Auricle (pinna) 2. External acoustic meatus (auditory canal) 3. Tympanic membrane 4. Ossicles amplify the sound waves 5. Oval window 6. Basilar membrane in the spiral organ of Corti 7. Hair cells of the tectorial membrane are bent when the basilar membrane vibrates against it Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Hearing (3 of 4) Pathway of vibrations from sound waves 8. An action potential starts in the cochlear nerve (cranial nerve VIII) 9. Impulse travels to the auditory cortex in the temporal lobe Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.13 Route of Sound Waves Through the Ear Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Hearing (4 of 4) High-pitched sounds disturb the short, stiff fibers of the basilar membrane – Receptor cells close to the oval window are stimulated Low-pitched sounds disturb the long, floppy fibers of the basilar membrane – Specific hair cells further along the cochlea are affected Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.14 Activation of the Cochlear Hair Cells Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Equilibrium Equilibrium receptors of the inner ear are called the vestibular apparatus Vestibular apparatus has two functional parts 1. Static equilibrium 2. Dynamic equilibrium Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Static Equilibrium Maculae—receptors in the vestibule – Report on the position of the head – Help us keep our head erect – Send information via the vestibular nerve (division of cranial nerve VIII ) to the cerebellum of the brain Anatomy of the maculae – Hair cells are embedded in the otolithic membrane – Otoliths (tiny stones) float in a gel around hair cells – Movements cause otoliths to roll and bend hair cells Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.15a Structure and Function of Maculae (Static Equilibrium Receptors) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.15b Structure and Function of Maculae (Static Equilibrium Receptors) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Dynamic Equilibrium Crista ampullaris – Responds to angular or rotational movements of the head – Located in the ampulla of each semicircular canal – Tuft of hair cells covered with cupula (gelatinous cap) – If the head moves, the cupula drags against the endolymph – Hair cells are stimulated, and the impulse travels the vestibular nerve to the cerebellum Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.16a Structure and Function of the Crista Ampullaris (Dynamic Equilibrium Receptor Region) (1 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.16b Structure and Function of the Crista Ampullaris (Dynamic Equilibrium Receptor Region) (2 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.16c Structure and Function of the Crista Ampullaris (Dynamic Equilibrium Receptor Region) (3 of 3) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Hearing and Equilibrium Deficits Deafness is any degree of hearing loss – Conduction deafness results when the transmission of sound vibrations through the external and middle ears is hindered – Sensorineural deafness results from damage to the nervous system structures involved in hearing – Ménière’s syndrome affects the inner ear and causes progressive deafness and perhaps vertigo (sensation of spinning) Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Part III : Chemical Senses: Smell and Three Taste Chemoreceptors – Stimulated by chemicals in solution – Taste has five types of receptors – Smell can differentiate a wider range of chemicals Both senses complement each other and respond to many of the same stimuli Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Olfactory Receptors and the Sense of Smell Olfactory receptors are in roof of nasal cavity – Olfactory receptor cells (neurons) with long cilia known as olfactory hairs detect chemicals – Chemicals must be dissolved in mucus for detection by chemoreceptors called olfactory receptors Impulses are transmitted via the olfactory filaments to the olfactory nerve (cranial nerve I) Smells are interpreted in the olfactory cortex Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.17 Location and Cellular Makeup of the Olfactory Epithelium Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Taste Buds and the Sense of Taste (1 of 5) Taste buds house the receptor organs Locations of taste buds – Most are on the tongue – Soft palate – Superior part of the pharynx – Cheeks Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Taste Buds and the Sense of Taste (2 of 5) The tongue is covered with projections called papillae that contain taste buds – Vallate (circumvallate) papillae – Fungiform papillae – Filiform papillae Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.18a Location and Structure of Taste Buds Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.18b Location and Structure of Taste Buds Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Taste Buds and the Sense of Taste (3 of 5) Gustatory cells are the taste receptors – Possess gustatory hairs (long microvilli) – Gustatory hairs protrude through a taste pore – Hairs are stimulated by chemicals dissolved in saliva Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Figure 8.18c Location and Structure of Taste Buds Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Taste Buds and the Sense of Taste (4 of 5) Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas – Facial nerve (cranial nerve VII) – Glossopharyngeal nerve (cranial nerve IX) – Vagus nerve (cranial nerve X) Taste buds are replaced frequently by basal cells Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Taste Buds and the Sense of Taste (5 of 5) Five basic taste sensations – Sweet receptors respond to sugars, saccharine, some amino acids – Sour receptors respond to H ions or acids – Bitter receptors respond to alkaloids – Salty receptors respond to metal ions – Umami receptors respond to the amino acid glutamate or the beefy taste of meat Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Part Four IV : Developmental Aspects of the Special Senses (1 of 5) Special sense organs are formed early in embryonic development Maternal infections during the first 5 or 6 weeks of pregnancy may cause visual abnormalities as well as sensorineural deafness in the developing child Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Part Four IV : Developmental Aspects of the Special Senses (2 of 5) 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 Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Part Four IV : Developmental Aspects of the Special Senses (3 of 5) Age-related eye issues – Presbyopia—“old vision” results from decreasing lens elasticity that accompanies aging ▪ Causes difficulty to focus for close vision – Lacrimal glands become less active – Lens becomes discolored – Dilator muscles of iris become less efficient, causing pupils to remain constricted Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Part Four IV : Developmental Aspects of the Special Senses (4 of 5) 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 Age-related ear problems – Presbycusis—type of sensorineural deafness that may result from otosclerosis ▪ Otosclerosis—ear ossicles fuse – Congenital ear problems usually result from missing pinnas and closed or missing external acoustic meatuses Copyright © 2022 Pearson Education, Ltd. All Rights Reserved. Part Four IV : Developmental Aspects of the Special Senses (5 of 5) Taste and smell are most acute at birth and decrease in sensitivity after age 40 as the number of olfactory and gustatory receptors decreases Copyright © 2022 Pearson Education, Ltd. All Rights Reserved.