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3/14/2017
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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)