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Chapter 12Lecture Outline

See separate PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes.

12.1: Introduction to Sensory Function

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• Senses maintain homeostasis, by providing information about the outside world and the internal environment

• Sensory receptors collect information from the environment, and relay it to the CNS on sensory neurons

• Sensory receptors link nervous system to internal and external changes or events

• Sensory receptors can be specialized cells or multicellular structures

• General senses:• Receptors that are widely distributed throughout the body• Skin, various organs and joints

• Special senses:• Specialized receptors confined to structures in the head • Eyes, ears, nose and mouth

12.2: Receptors, Sensation, and Perception

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Sensory receptors:• Respond to specific stimuli

• Particularly sensitive to a certain type of environmental change, and less sensitive to other stimuli

Sensation:• A feeling that occurs when brain becomes aware of sensory information

Perception:• The way the brain interprets the sensory information

5 types of sensory receptors in the body:

• Chemoreceptors:Respond to changes in chemical concentrations (smell, taste, oxygen

concentration)

• Pain receptors (nociceptors):Respond to tissue damage (mechanical, electrical, thermal energy)

• Thermoreceptors:Respond to moderate changes in temperature

• Mechanoreceptors:Respond to mechanical forces that distort receptor (touch, tension, blood

pressure, stretch)

• Photoreceptors:Respond to light (eyes)

Receptor Types

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• Sensory receptors can take the form of ends of neurons or cells near extensions of the neurons

• Stimulation of receptor causes local change in its membrane potential, causing graded potential according to stimulus intensity

• If receptor is part of a neuron, the membrane potential may generate an action potential

• If receptor is not part of a neuron, the receptor potential must be transferred to a neuron to trigger an action potential

• Peripheral nerves transmit impulses to CNS where they are analyzed and interpreted in the brain

Sensory Impulses

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• Sensation occurs when action potentials make the brain aware of a sensory event (such as pain)

• Perception occurs when brain interprets sensory impulses (realizing that the pain is a result of stepping on a tack)

• Projection:• Process in which cerebral cortex interprets sensation as being derived

from certain receptors

• Brain projects the sensation back to the apparent source

• It allows a person to pinpoint the region of stimulation

Sensation and Perception

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Information Flow Through the Nervous System

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Sensory Adaptation:Ability to ignore unimportant (or continuous) stimuli

• Involves a decreased response to a particular stimulus from the receptors (peripheral adaptation) or along the CNS pathways leading to the cerebral cortex (central adaptation)

• When sensory adaptation occurs, sensory impulses become less frequent and may cease

• Stronger stimulus is then required to trigger impulses

• Best accomplished by thermoreceptors and olfactory receptors

Sensory Adaptation

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12.3: General Senses

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General Senses:

Senses with small, widespread sensory receptors, associated with skin, muscles, joints and viscera

General Senses are divided into 3 groups:• Exteroceptive senses:

Senses associated with body surface, such as touch, pressure, temperature, and pain

• Interoceptive (visceroceptive) senses:Senses associated with changes in the viscera, such as blood pressure stretching blood vessels

• Proprioceptive senses:Senses associated with changes in muscles, tendons, and joints, as when changing position or exercising

3 types of mechanoreceptors provide touch and pressure senses:• Free nerve endings:

• Common in epithelial tissues

• Simplest receptors

• Sense itching

• Tactile (Meissner’s) corpuscles:

• Abundant in hairless portions of skin and lips

• Detect fine touch and texture

• Distinguish between 2 points on skin

• Lamellated (Pacinian) corpuscles:

• Large oval structures

• Common in deeper subcutaneous tissues, tendons and ligaments

• Detect heavy pressure and vibrations

Touch and Pressure Senses

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Touch and Pressure Receptors

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Temperature receptors (thermoreceptors):

Free nerve endings in skin; 2 types:

• Warm receptors:

• Sensitive to temperatures above 25oC (77o F)

• Unresponsive to temperature above 45oC (113oF)

• Cold receptors:

• Sensitive to temperatures between 10oC (50oF) and 20oC (68oF)

• Pain receptors:

• Respond to temperatures below 10oC; produce freezing sensation

• Respond to temperatures above 45oC; produce burning sensation

Temperature Senses

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• Pain receptors/nociceptors consist of free nerve endings

• Widely distributed

• Nervous tissue of brain lacks pain receptors

• Stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature

• Adapt very little, if at all

Sense of Pain

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• Pain receptors are the only receptors in viscera whose stimulation produces sensations

• Pain receptors in viscera respond differently to stimulation than those of surface tissues

• Visceral pain may feel as if coming from some other part of the body; this is called referred pain

• Example of referred pain: Heart pain often feels like it is coming from the left shoulder or medial portion of left arm

• Referred pain results from common nerve pathways, in which sensory impulses from the visceral organ and a certain area of the skin synapse with the same neuron in the CNS

Visceral Pain

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Referred pain may occur due to sensory impulses from two regions following a common nerve pathway to brain:

Referred Pain

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Referred Pain

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2 types of axons/fibers that conduct impulses away from pain receptors:• Fast pain (A-delta) fibers:

• Myelinated• Conduct impulses rapidly (up to 30 m/sec)• Associated with sharp (acute) pain in localized skin area• Usually stops as soon as stimulus stops

• Slow pain (C) fibers:• Unmyelinated• Conduct impulses slowly (up to 2 m/sec)• Associated with dull, aching (chronic) pain• Difficult to localize• Pain often continues after stimulus stops

In the brain, most pain fibers synapse in reticular formation, and proceed to the thalamus, hypothalamus, and cerebral cortex

Pain Pathways

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• Thalamus:

Begins sensation of pain

• Cerebral cortex:

• Judges intensity of pain

• Locates source of pain

• Produces emotional and motor responses to pain

• Gray matter in brainstem:

Regulates flow of impulses from spinal cord

• Pain-inhibiting substances produced in the body:

• Enkephalins

• Serotonin

• Endorphins

Regulation of Pain Pathways

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Treating Pain

About 25% of people have moderate or severe pain. Treatments for pain:• Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin,

ibuprofen: can cause GI irritation• Opiates: can be addicting• Acetaminophen: non-addicting, no GI irritation, but can damage liver

Reformulation efforts are producing smaller particles, that dissolve faster and relieve pain faster

Chronic pain treatments:NSAIDs, exercises, injection of anesthetics into cramping muscles, antidepressants, transcutaneous electrical nerve stimulation (TENS), invasive nerve block

Clinical Application 12.1

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Proprioceptors: Mechanoreceptors that send information to CNS about body position, and length and tension of skeletal muscles

Main types of proprioceptors:• Lamellated (Pacinian) corpuscles:

Pressure receptors in joints• Muscle spindles:

- Stretch receptors in skeletal muscles- Initiate stretch reflexes, in which spindle stretch causes muscle contraction

• Golgi tendon organs: - Stretch receptors in tendons- Stimulate reflexes that oppose stretch reflexes- Help maintain posture, protect tearing of muscles away from insertions

Proprioception

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Stretch Receptors

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• Visceral senses have receptors in internal organs

• Examples of visceral receptors: lamellated corpuscles, free nerve endings

• Convey information that includes the sense of fullness after eating a meal as well as the discomfort of intestinal gas and the pain that signals a heart attack

Visceral Senses

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Receptors Associated with General Senses

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12.4: Special Senses

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Special Senses:Senses that have sensory receptors are within large, complex sensory

organs in the head:

• Smell: olfactory organs in nasal cavity

• Taste: taste buds in oral cavity

• Hearing and equilibrium: inner ears

• Sight: eyes

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Synesthesia

Synesthesia (joined sensation):• Condition in which brain interprets a stimulus for one sense as coming

from another• Example: “The paint smelled blue”• 1 in 1,000 people have this condition, and it lasts a lifetime• Common in creative people• Caused by genetic mutation; 4 genes have been identified

• Most common form is grapheme-color type synesthesia:Letters, numbers or time evoke certain colors

• Lexical-gustatory synesthesia:A name evokes perception of strong taste or smell

Clinical Application 12.2

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Olfaction: the sense of smell

• Olfactory receptors:

• Olfactory receptor cells are chemoreceptors

• Respond to chemicals dissolved in liquids

• Sense of smell provides 75-80% of sense of taste

• Olfactory organs:

• Contain olfactory receptor cells (bipolar neurons) and supporting epithelial cells

• Cover upper parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum

• Odorants may bind to any of almost 400 types of olfactory membrane receptors, resulting in depolarization and action potentials

Sense of Smell

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Olfactory Receptors

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• Once olfactory receptors are stimulated, nerve impulses travel through openings in cribriform plates of ethmoid bone

• Olfactory nerves olfactory bulbs olfactory tracts limbic system (for emotions) and olfactory cortex (for interpretation)

• Olfactory bulbs analyze sensory impulses

• Limbic system, center for memory and emotion, provides emotional responses to certain odorant molecules

Olfactory Pathways

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Leading hypothesis for encoding specific smells:

• Each olfactory receptor cell contains only 1 type of membrane protein

• Each type of membrane protein can bind several types of odorants

• Brain interprets binding as an olfactory code

• Olfactory organs located high in the nasal cavity, above the pathway of inhaled air

• Olfactory receptors undergo sensory adaptation rapidly

• Sense of smell drops by 50% within 1 second after stimulation

• Olfactory receptor neurons are the only ones in direct contact with environment, and can be damaged

• Receptors are replaced regularly (very unusual for neurons to be replaced in the human adult)

Olfactory Stimulation

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Gustation is the sense of taste.

• Taste buds:• Organs of taste

• Located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx

• About 10,000 taste buds, each with 50-150 taste cells

• Taste receptors:• Chemoreceptors

• Taste cells: modified epithelial cells that function as receptors

• Taste hairs: microvilli that protrude from taste cells through pores of taste buds; sensitive parts of taste cells

• Taste cells are replaced every 3 days

Gustation: Sense of Taste

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Taste Receptors

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• 5 primary taste sensations:• Sweet: stimulated by carbohydrates

• Sour: stimulated by acids (H+)

• Salty: stimulated by salts (Na+ or K+)

• Bitter: stimulated by many organic compounds, Mg and Ca salts

• Umami: stimulated by some amino acids, MSG

• Each flavor results from 1 primary taste sensation or a combination

• Spicy foods activate pain receptors

• Taste receptors undergo rapid adaptation

Taste Sensations

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• Sensory impulses from taste receptor cells travel on fibers of 3 different cranial nerves, according to the location of the taste cells:

Facial nerve (VII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)

• Cranial nerves conduct impulses into medulla oblongata

• Impulses then proceed to the thalamus

• Impulses are interpreted in the gustatory cortex in the insula

Taste Pathways

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Smell and Taste Disorders

• Disorders of smell and taste can be caused by colds, flu, allergies, nasal polyps, swollen mucous membranes in the nose, head injury, toxic chemical exposure, nutritional or metabolic problem, a disease

• Often, cause cannot be identified

• Drugs and medications can also alter smell or taste

Clinical Application 12.3

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• Ear:

Organ of hearing

• 3 sections of the ear:

• Outer/external ear

• Middle ear

• Inner/internal ear

Sense of Hearing

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Parts of the Outer Ear:• Auricle (Pinna):

• Funnel-shaped• Collects sounds waves

• External acoustic meatus:• S-shaped tube• Lined with ceruminous glands• Carries sound to tympanic

membrane• Terminates at tympanic

membrane• Tympanic membrane

(Eardrum): • Vibrates in response to

sound waves

Outer (External) Ear

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Parts of the Middle Ear:• Tympanic cavity:

• Air-filled space intemporal bone

• Auditory ossicles:• 3 tiny bones• Vibrate in response to

tympanic membrane vibrations; amplify force

• Malleus, incus and stapes• Hammer, anvil and stirrup

• Oval window: • Opening in wall of tympanic

cavity• Stapes vibrates against it to

move fluids in inner ear

Middle Ear

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Tympanic Reflex:• Muscle contractions that occur during loud sounds, to lessen the

transfer of sound vibrations to inner ear, and prevent damage to hearing receptors

• Muscles involved are tensor tympani and stapedius

Middle Ear: Tympanic Reflex

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Auditory (eustachian) tube:• Connects middle ear to throat

• Helps maintain equal pressure

on both sides of tympanic

membrane

• Usually closed by valve-like

flaps in throat

Middle Ear: Auditory Tube

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Inner ear is a complex system

of labyrinths:• Osseous (bony) labyrinth:

• Bony canal in temporal bone

• Filled with perilymph fluid

• Membranous labyrinth:

• Tube within osseous labyrinth

• Filled with endolymph fluid

Inner (Internal) Ear

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3 parts of labyrinths:• Cochlea:

Functions in hearing

• Semicircular canals:

Function in dynamic

equilibrium

• Vestibule:

Functions in static

equilibrium

Inner Ear

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Cochlea:• Spiral, snail-shaped tube

• Coiled around bony core,

the modiolus

• Spiral lamina is a bony

shelf that coils around

the cochlea

Cochlea

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There are 2 membrane-covered “windows” in the wall of the bony labyrinth:• Oval window:

Opening in the wall of the tympaniccavity, through which the stapestransfers vibrations to the fluidof the inner ear; these vibrationsstimulate hearing receptors

• Round window: Window in the wall of the innerear facing the tympanic cavity,through which excess vibrations dissipate into the tympaniccavity

Windows of the Inner Ear

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The cochlea contains 3 compartments:• Scala vestibuli:

• Upper compartment• Leads from oval window

to apex of spiral• Part of bony labyrinth

• Scala tympani:• Lower compartment• Extends from apex of the

cochlea to round window• Part of bony labyrinth

• Cochlear duct:• Middle compartment• Portion of membranous

labyrinth in cochlea

Cochlea

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The cochlea contains these

membranes:

• Vestibular membrane:Separates scala vestibuli

from cochlear duct

• Basilar membrane:Separates cochlear duct

from scala tympani

• Tectorial membrane:Extends partially into cochlear duct; part of the

hearing receptor organ,

the Spiral Organ

Cochlea

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Getting a Cochlear Implant

• Hearing aids amplify sound, but cochlear implants directly stimulate auditory nerve

• Enables a person to hear certain sounds

• Best time is before age 3, as brain is rapidly processing speech and hearing

Clinical Application 12.4

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Spiral Organ:• Organ for sense of hearing• Sits on upper surface of basilar

membrane• Contains hearing receptor cells,

called hair cells• Hair cells contain stereovilli

(or stereocilia)• Tectorial membrane passes like

a roof over the hair cell stereovilli• Sound vibrations cause

stereocilia to contact and bend against the tectorial membrane

• Different frequencies of vibration move different parts of basilar membrane

• Nerve impulses are generated

Spiral Organ (Organ of Corti)

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Sound reception occurs as

the basilar membrane vibrates,

vibrating the hair cells of the

spiral organ, and putting them

in contact with the tectorial membrane.

Spiral Organ (Organ of Corti)

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This is a “straightened out” view of the cochlea. Receptor cells in different regions of the cochlear duct detect different frequencies of vibration (cycles/sec or cps).

Spiral Organ (Organ of Corti)

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Cochlear branch of

vestibulocochlear

nerve

Medulla oblongata

Midbrain

Thalamus

Auditory cortex in

temporal lobe of

cerebrum

Auditory Pathways

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Hearing Loss• About 8% of people have some decree of hearing loss• 2 major types of hearing loss: Conductive and SensorineuralConductive Deafness: • Interference with conduction of sound vibrations to inner ear• 95% of cases of hearing loss• Caused by accumulation of ear wax, hardening or injury of tympanic

membrane, injury to auditory ossicles, otosclerosis• Diagnostic tests: Rinne test and Weber testSensorineural Deafness:• Damage to cochlea, auditory (vestibulocochlear) nerve, or nerve

pathways• Can be caused by long-term exposure to very loud sounds, such as

factory noise, loud music, explosions• Also caused by CNS tumors, brain damage resulting from a stroke, use of

certain drugs

Clinical Application 12.5

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Steps in Generation of Sensory Impulses from the Ear

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Feeling of equilibrium/balance is derived from 2 senses:

• Static equilibrium:• Senses position of head when body is not moving

• Receptors are found in vestibule of inner ear

• Dynamic Equilibrium:• Senses rotation and movement of head and body

• Receptors are found in semicircular canals

Sense of Equilibrium

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• Utricle and saccule are

expanded chambers of the

membranous labyrinth of

the vestibule

• Each contains a Macula,an organ of static equilibrium

• A macula is a patch of hair

cells and supporting cells

Static Equilibrium

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• A macula has hair cells embedded in gelatinous material, with otoliths(calcium carbonate crystals) on its surface

• Gravity pulls on gelatinous mass when head changesposition

• Otoliths shift position, andpull on gelatinous mass andcilia of hair cells

• Bending of hairs results in generation of nerve impulsesin vestibular branch of thevestibulocochlear nerve

Static Equilibrium

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• Receptors for dynamic equilibriumare found in 3 semicircularcanals

• 3 canals sit at right angles toeach other

• Each canal contains an ampulla:a swelling of the membranous labyrinth that communicates with the vestibule

• Crista ampullaris:• Sensory organ for dynamic

equilibrium• Hair cells and supporting cells• Located in ampulla of each

semicircular canal• Consists of hair cells whose hairs extend upward into dome-shaped

gelatinous mass (cupula)• Rotation of head or body bends cupula, stimulates hair cells• Nerve impulses are sent over vestibular branch of vestibulocochlear n.

Dynamic Equilibrium

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Dynamic Equilibrium: Crista Ampullaris

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• Visual receptors are found in the eye

• Accessory organs for sense of sight:

- Eyelids (palpebrae, protection)

- Eyelashes (protection)

- Lacrimal apparatus (tear production)

- Extrinsic eye muscles (eye movement)

Sense of Sight

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• Eyelids = Palpebrae• Composed of 4 layers:

• Skin• Muscle • Connective tissue• Conjunctiva

• Orbicularis oculi musclecloses eyelid

• Levator palpebrae superiorismuscle opens eyelid

• Tarsal glands secrete oil onto eyelashes

• Conjunctiva: mucous membrane; lines eyelid and covers portion of eyeball

Visual Accessory Organs: Eyelids

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Lacrimal Apparatus:• Lacrimal gland:

• In orbit, lateral to eye

• Secretes tears

• Canaliculi:

• 2 ducts that collect tears

• Lacrimal sac:

• Collects tears from canaliculi

• Lies in groove in lacrimal bone

• Nasolacrimal duct:

• Collects from lacrimal sac

• Empties tears into nasal cavity

• Lysozyme:

Antibacterial component of tears

Visual Accessory Organs:Lacrimal Apparatus

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• Superior rectus:

Rotates eye up and medially

• Inferior rectus:

Rotates eye down and medially

• Medial rectus:

Rotates eye medially

• Lateral rectus:

Rotates eye laterally

• Superior oblique:

Rotates eye down and laterally

• Inferior oblique:

Rotates eye up and laterally

Visual Accessory Organs:Extrinsic Eye Muscles

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• Hollow, spherical organ

of sight

• Wall has 3 layers:

• Outer (fibrous) tunic

• Middle (vascular) tunic

• Inner (nervous) tunic

Structure of the Eye

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• Outer (fibrous) tunic:Cornea + Sclera

• Cornea:• Anterior sixth• Transparent• Helps focus light rays• Transmits and refracts light

• Sclera:• Posterior five sixths• White, opaque• Protects eye, attaches

muscles• Pierced by optic nerve and blood vessels

The Outer (Fibrous) Tunic

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Middle (vascular) tunic: Choroid coat + Ciliary body + Iris

• Choroid coat:• Posterior five-sixths• Provides blood supply• Contains melanocytes• Melanin absorbs extra light

• Ciliary body:• Anterior portion• Thickest portion, pigmented• Forms ring to hold lens• Changes lens shape for focusing

• Iris: • Anterior to ciliary body• In front of lens• Pigmented• Controls light entering eye

Middle (Vascular) Tunic

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• Anterior cavity of eye, between cornea and lens, is filled with a watery fluid, aqueous humor

• Lens: Transparent, biconvex, lies behind iris, elastic, held in place by suspensory ligaments of ciliary body; helps focus light rays, and changes shape for long-distance or close vision

Anterior Portion of the Eye

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Ciliary body forms internal ring around the front of the eye

• Ciliary processes are the radiating folds

• Ciliary muscles contract and relax to move lens

• Suspensory ligaments hold lens in position

Lens lies just behind iris and pupil

Ciliary Body and Lens

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Accommodation:A change in the shape of

the lens, to view close

objects

• Lens thickens and becomes

more convex when

focusing on close object

• Lens thins and becomes

flatter when focusing on

distant objects

Accommodation

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• Iris controls amount of light entering the eye

• Iris consists of connective tissue and smooth muscle(colored portion of eye)

• Pupil is window or opening in center of iris

• Dim light stimulates radial muscles and pupil dilates

• Bright light stimulates circular muscles and pupil constricts

• Amount and distribution of melanin determines eye color

Iris

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Aqueous Humor:• Fluid in anterior cavity of eye

• Secreted by epithelium on inner surface of the ciliary body

• Provides nutrients and maintains shape of anterior portion of eye

• Leaves cavity through scleral venous sinus

Aqueous Humor

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• Inner tunic consists of retina

• Retina contains visual receptors (photoreceptors)

• Continuous with optic nerve in back of eye

• Ends just behind margin of the ciliary body toward front of eye

• Composed of several layers

• Macula lutea: yellowish spot in retina

• Fovea centralis: center of macula lutea; produces sharpest vision

• Optic disc: blind spot; contains no visual receptors; found where nerve fibers from retina leave eye to become optic nerve

• Vitreous humor: thick gel that holds retina flat against choroid coat

Inner (Nervous) Tunic

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• Posterior cavity: space enclosed by lens, ciliary body, and retina

• Contains vitreous humor: thick gel that supports internal structures and maintains shape of eye

Posterior Cavity

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• Photoreceptor cells, bipolar cells, and ganglion cells:  provide pathway for impulses triggered by photoreceptors to reach the optic nerve

• Horizontal cells and amacrine cells: modify, integrate impulses 

Major Groups of Retinal Neurons

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Summary: Layers of the Eye

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• Refraction:

Bending of light, which occurs when light waves pass at an angle

between mediums of different densities

Light Refraction

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Convex lenses cause Concave lenses cause

light waves to converge light waves to diverge

Types of Lenses

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• As light enters eye, it is refracted by:

• Convex surface of cornea

• Convex surface of lens

• Image focused on retina is upside down and reversed from left to right

• Visual cortex corrects the reversals

Focusing on the Retina

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Refraction Disorders

• Concave lens corrects nearsightedness• Convex lens corrects farsightedness

Clinical Application 12.6

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Photoreceptors are modified neurons of retina that sense light:• Rods:

• Long, thin projections• Contain light sensitive pigment, called rhodopsin• Hundreds of times more sensitive to light than cones• Provide vision in dim light• Produce colorless vision• Produce outlines of objects

• Cones:• Short, blunt projections• Contain light sensitive pigments, called erythrolabe, chlorolabe, and

cyanolabe• Provide vision in bright light• Produce sharp images• Produce color vision• Fovea centralis contains only cones

Photoreceptors

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Rods and cones are named for shape of receptive ends:

rods are cylindrical and cones are conical

Rods and Cones

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Rods and cones contain light-sensitive pigments that decompose upon absorption of light:

• Rhodopsin (Visual purple):

• Light-sensitive pigment in rods

• In presence of light, decomposes into Opsin and Retinal

• Triggers a complex series of reactions that initiates nerve impulses

• Impulses travel along optic nerve

• Iodopsins (pigments in cones):

• Each type of cone contains different light-sensitive pigment

• Each type of cone is sensitive to different wavelengths

• Color perceived depends on which types of cones are stimulated

• Erythrolabe: responds to red light

• Chlorolabe: responds to green light

• Cyanolabe: responds to blue light

Visual Pigments

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Rhodopsin is embedded

in the many discs of

membrane at the end of

the rod.

Rhodopsin in a Rod

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• Provides perception of distance, depth, height and width of objects

• Results from formation of two slightly different retinal images from eyes

Stereoscopic Vision

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• The visual pathway proceeds

from the ganglion cells of the

retina to the optic nerve, optic

chiasma, optic tracts, the

thalamus, optic radiations, and

visual cortex in occipital lobe

of cerebrum.

• A few fibers branch off before

reaching the thalamus, and

enter nuclei for visual reflexes.

Visual Pathways

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12.5: Life-Span Changes

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• Age-related hearing loss due to:

• Damage to hair cells in spiral organ

• Degeneration of nerve pathways to the brain

• Tinnitus

• Age-related visual problems include:

• Dry eyes

• Floaters (crystals in vitreous humor)

• Loss of elasticity of lens, decreasing accommodation (presbyopia)

• Glaucoma

• Cataracts

• Macular degeneration

• Age-related smell and taste problems due to:

• Loss of olfactory receptors (anosmia)