Transcript Chapter 1 A Perspective on Human Genetics

Chapter 6B
The Peripheral Nervous System:
Special Senses
Outline
• Pathways, perceptions, sensations
• Receptor Physiology
– Receptors have differential sensitivities to various stimuli.
– A stimulus alters the receptor’s permeability, leading to a graded
receptor potential.
– Receptor potentials may initiate action potentials in the afferent
neuron.
– Receptors may adapt slowly or rapidly to sustained stimulation.
– Each somatosensory pathway is “labeled” according to modality
and location.
– Acuity is influenced by receptive field size and lateral inhibition.
– PAIN
– Stimulation of nociceptors elicits the perception of pain plus
motivational and emotional responses.
– The brain has a built-in analgesic system.
• Cortex
– Higher processing
• Basal nuclei
– Control of movement, inhibitory, negative
• Thalamus
– Relay and processing of sensory information
– Awareness, a positive screening center for information
• Hypothalamus
– Hormone secretion, regulation of the internal environment
• Cerebellum
– Important in balance and in planning and executing voluntary
movement
• Brain Stem
– Relay station (posture and equilibrium), cranial nerves,
control centers, reticular integration, sleep control
What did you learn from the vision lab?
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Color blindness
Rod and cone function
What an astigmatism is
After imaging? positive and negative after images
Vision outline
• Anatomy
• Muscles and light control
• Refraction and refractive structures
– Refractive problems
• Retina, photoreceptors, transduction
• Visual cortical processing
Countercurrent exchange
• Found in many animal systems
– thermoregulation, and in the kidney
• The transfer of a substance flowing in one direction
to another moving in the opposite direction
• Efficient - gill can remove 80 % of O2
Anatomy
Eye protection
Eyelids
Act like shutters to protect eye from
environmental hazards
Eyelashes
Trap fine, airborne debris such as dust
before it can fall into eye
Tears
Continuously produced by lacrimal glands
Lubricate, cleanse, bactericidal
Eyesocket
Eye
middle layer underneath
sclera which
contains blood vessels
that nourish retina
tough outer layer of
connective tissue;
forms visible white
part of the eye
Circular and radial muscle
controlling the amt. of
light entering eye
opening
anterior, transparent outer layer through
which light rays pass into interior of eye
•Maintains eye shape
Aqueous humor is formed by capillary network in
ciliary body, then drains into the
canal of Schlemm, and eventually enters the blood.
Nutrients for cornea and lense
Eye
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Interior consists of two fluid-filled cavities separated by the lens
– Posterior cavity
• Larger cavity between lens and retina
• Contains vitreous humor
– Important in maintaining the spherical shape of eyeball
– Anterior cavity
• Anterior cavity between cornea and lens
• Contains aqueous humor
– Carries nutrients for cornea and lens
– Produced by capillary network within ciliary body
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Fovea
– Pinhead-sized depression in exact center of retina
– Point of most distinct vision
– Has only cones
Macula lutea
– Area immediately surrounding fovea
– Fairly high acuity
Macular degeneration
– Leading cause of blindness in western hemisphere
Vision outline
• Anatomy
• Light and muscle control
• Refraction and refractive structures
– Refractive problems
• Retina, photoreceptors, transduction
• Visual cortical processing
Eye
• Convex structures of eye produce convergence of
diverging light rays that reach eye
Eye
Focusing on
Distant and Near
Light Sources
What happens to
light rays when
they leave the
light source?
Eye
• Two structures most important in eye’s refractive ability are
– Cornea
• Contributes most extensively to eye’s total refractive ability
• Refractive ability remains constant because curvature never
changes
– Lens
• Refractive ability can be adjusted by changing curvature as needed
for near or far vision
• Accommodation
– Change in strength and shape of lens
– Accomplished by action of ciliary muscle and suspensory
ligaments
– Age-related reduction in accommodation ability - presbyopia
Mechanics of Accommodation
Far vision
* Light moves towards thick part of lens
Near vision
Fig. 6-11, p. 193
Vision outline
• Anatomy
• Muscles and light control
• Refraction and refractive structures
– Refractive problems
• Retina, photoreceptors, transduction
• Visual cortical processing
Emmetropia, Myopia, and Hyperopia
Vision outline
• Anatomy
• Muscles and light control
• Refraction and refractive structures
– Refractive problems
• Retina, photoreceptors, transduction
• Visual cortical processing
Retinal Layers
• Retina – receptor containing portion is actually an extension of the
CNS
• Neural portion of retina consists of three layers of excitable cells
– Outermost layer containing rods and cones
– Middle layer of bipolar cells
– Inner layer of ganglion cells
• Axons of ganglion cells join to form optic nerve
– Point on retina at which optic nerve leaves is the optic disc
» Region often called the blind spot because no image can be
detected here because of lack of rods and cones
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Rod and cone cells
Consist of three parts
– Outer segment
Photoreceptors
• Detects light stimulus
– Inner segment
• Contains metabolic
machinery of cell
– Synaptic terminal
• Transmits signal generated in
photoreceptor on light
stimulation to next cells in
visual pathway
Photopigments
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Undergo chemical alterations when activated by light
Consists of two components
– Opsin
• Protein that is integral part of disc membrane
– Retinene
• Derivative of vitamin A
• Light-absorbing part of photopigment
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Four different photopigments
– Rod pigment
• Provide vision only in shades of gray
• Rhodopsin
– Absorbs all visible wavelengths
– Cone pigments
• Respond selectively to various wavelengths of light
• Make color vision possible
– Red cones
– Green cones
– Blue cones
Fig. 6-25, p. 202
Properties of Rod Vision and Cone Vision
Rods
Cones
100 million per retina
3 million per retina
Vision in shades of gray
Color vision
High sensitivity
Low sensitivity
Low acuity
High acuity
Night vision
Day vision
Much convergence in retinal
pathways
Little convergence in retinal
pathways
More numerous in periphery
Concentrated in fovea
The sensitivity of the eyes varies
through dark and light
adaptation.
•Dark adaptation
•Can gradually distinguish objects as you enter a
dark area.
•Due to the regeneration of rod photopigments that
had been broken down by previous light exposure.
•Light adaptation
•Can gradually distinguish objects as you enter an
area with more light.
•Due to the rapid breakdown of cone
photopigments.
Vision outline
• Anatomy
• Muscles and light control
• Refraction and refractive structures
– Refractive problems
• Retina, photoreceptors, transduction
• Visual fields
• Visual cortical processing
Visual Processing
• Blending color
– 3 cone types – blue, green, red
– Stimulated in a ratio to produce blends % max
• Distinguishing contours
– On center and off center ganglion cells
• Images on the retina are upside down and
backwards.
• Depth perception
Hearing outline
• Anatomy
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– Outer, middle, inner
Hearing
Transmission of sound waves
Hair cells and transduction
Cochlea and canals/ducts
Pitch and loudness
Auditory cortical processing
Ear
• Consists of three parts
– External ear
• Consists of pinna, external auditory meatus, and tympanum
• Transmits airborne sound waves to fluid-filled inner ear
• Amplifies sound energy
– Middle ear
• Transmits airborne sound waves to fluid-filled inner ear
• Amplifies sound energy
– Inner ear
• Houses two different sensory systems
– Cochlea
» Contains receptors for conversion of sound waves into
nerve impulses which makes hearing possible
– Vestibular apparatus
» Necessary for sense of equilibrium
Ear
Hearing outline
• Anatomy
– Outer, middle, inner
• Hearing
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Transmission of sound waves
Pitch and loudness
Hair cells and transduction
Cochlea and canals/ducts
Auditory cortical processing
• Neural perception of sound energy
• Involves two aspects
– Identification of the sounds (“what”)
– Localization of the sounds (“where”)
• Sound waves
– Traveling vibrations of air
– Consist of alternate regions of compression
and rarefaction of air molecules
Hearing
Hearing
• Pitch (tone) of sound
– Depends on frequency of air waves 20-20,000 cps, 1000-4000
• Intensity (loudness)
– Depends on amplitude of air waves
• Timbre (quality)
– Determined by overtones
Hearing outline
• Anatomy
– Outer, middle, inner
• hearing
• Transmission of sound waves
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Pitch and loudness
Hair cells and transduction
Cochlea and canals/ducts
auditory cortical processing
Transmission of Sound Waves
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Tympanic membrane
vibrates when struck by
sound waves
Middle ear transfers
vibrations through ossicles
(malleus, incus, stapes) to
oval window (entrance into
fluid-filled cochlea)
Waves in cochlear fluid set
basilar membrane in motion
Receptive hair cells are bent
as basilar membrane is
deflected up and down
Mechanical deformation of
specific hair cells is
transduced into neural
signals that are transmitted
to auditory cortex in temporal
lobe of brain for sound
perception
Fig. 6-33, p. 213
Hearing outline
• Anatomy
– Outer, middle, inner
• Hearing
• Transmission of sound waves
• Pitch and loudness
• Hair cells and transduction
• Cochlea and canals/ducts
• Auditory cortical processing
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Inner
– Deformation and rubbing on the tectoral
membrane hyper or depolarizes the cells
resulting in a signal.
Outer
– Do not signal the brain
– Fine tuning
– Accentuates movement of basilar
membrane
• (lengthening and shortening)
Transduction to
Auditory nerve
amplification
Fig. 6-33c, p. 213
Fig. 6-34a, p. 214
Fig. 6-35, p. 215
Sound waves
Bending of hairs of receptor
hair cells of organ of Corti
as basilar membrane movement displaces these hairs
in relation to overlying
tectorial membrane in which
the hairs and embedded
Vibration of
tympanic membrane
Vibration of
middle ear bones
Graded potential
changes
(receptor potential) in
receptor cells
Vibration of
oval window
Fluid movement
within cochlea
Vibration of
round
window
Changes in rate of
action
potentials generated in
auditory nerve
In ear
Vibration of
basilar membrane
Dissipation of
energy (no
sound
perception)
Propagation of action
potentials to auditory cortex
in temporal lobe of brain for
sound perception
Fig. 6-36, p. 216
Hearing outline
• Anatomy
– Outer, middle, inner
• hearing
• Transmission of sound waves
• Pitch and loudness
• Hair cells and transduction
• Cochlea and canals/ducts
• auditory cortical processing
Auditory Cortical Processing
– Primary auditory cortex is tonotopically organized
– Locations on basilar membrane map to locations
in the cortex
– Pathway
• Hair cells-afferent auditory nerve- synapses in
brainstem and thalamus (LGN)-higher auditory cortex
• Cortex
– Higher processing
• Basal nuclei
– Control of movement, inhibitory, negative
• Thalamus
– Relay and processing of sensory information
– Awareness, a positive screening center for information
• Hypothalamus
– Hormone secretion, regulation of the internal environment
• Cerebellum
– Important in balance and in planning and executing voluntary
movement
• Brain Stem
– Relay station (posture and equilibrium), cranial nerves,
control centers, reticular integration, sleep control
Equilibrium outline
• Anatomy
– Semicircular canals
• otoliths
Equilibrium
• Vestibular apparatus
– In inner ear
– Consists of
• Semicircular canals
– Detect rotational acceleration or deceleration in any
direction
• Utricle and saccule
– Detect changes in rate of linear movement in any
direction
– Provide information important for determining head
position in relation to gravity
Fig. 6-38a, p. 219
Equilibrium
• Neural signals generated in response to mechanical
deformation of hair cells by specific movement of
fluid and related structures
• Vestibular input goes to vestibular nuclei in brain
stem and to cerebellum for use in maintaining
balance and posture, controlling eye movement,
perceiving motion and orientation
• Cortex
– Higher processing
• Basal nuclei
– Control of movement, inhibitory, negative
• Thalamus
– Relay and processing of sensory information
– Awareness, a positive screening center for information
• Hypothalamus
– Hormone secretion, regulation of the internal environment
• Cerebellum
– Important in balance and in planning and executing voluntary
movement
• Brain Stem
– Relay station (posture and equilibrium), cranial nerves,
control centers, reticular integration, sleep control
Equilibrium
Receptive hair cells
Ampulla
Cupula – moves in the
Direction of movement
Inertia!
XYZ
Kino –
Stero-ionchannels
Hair cells-affarent neurons-vestibular nerve-vestibulocochlear nerveFig. 6-38, p. 219
Fig. 6-38b, p. 219
Fig. 6-38c, p. 219
Otoliths
Fig. 6-38a, p. 219
Body moves
Head moves
Fig.
Fig.6-38a,
6-40, p. 219
221
Fig. 6-40a, p. 221
Chemical Senses
Taste and smell
• Receptors are chemoreceptors
• In association with food intake, influence flow of
digestive juices and affect appetite
• Stimulation of receptors induces pleasurable or
objectionable sensations and signals presence of
something to seek or to avoid
Taste (Gustation)
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Chemoreceptors housed in taste buds
Present in oral cavity and throat
Taste receptors have life span of about 10 days
Taste bud consists of
– Taste pore
• Opening through which fluids in mouth come into
contact with surface of receptor cells
– Taste receptor cells
• Modified epithelial cells with surface folds called
microvilli
• Plasma membrane of microvilli contain receptor sites
that bind selectively with chemical molecules
Location and Structure of Taste Buds
Taste
• Tastant (taste-provoking chemical)
• Binding of tastant with receptor cell alters cell’s ionic
channels to produce depolarizing receptor potential
• Receptor potential initiates action potentials within
terminal endings of afferent nerve fibers with which
receptor cell synapses
• Terminal afferent endings of several cranial nerves
synapse with taste buds in various regions of mouth
• Signals conveyed via synaptic stops in brain stem
and thalamus to cortical gustatory area
Receptor cell-afferent nerve-cranial nerves- brain stem- thalamus- cortical gustatory area
Taste
• Five primary tastes
– Salty
• Stimulated by chemical salts, especially NaCl
– Direct entry of sodium ions thru sodium channels
– Sour
• Caused by acids which contain a free hydrogen ion, H+
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hydrogen ions block potassium channels (depolarization)
– Sweet
• Evoked by configuration of glucose
– G protein - cAMP pathway blockage of potassium channels
(depolarization)
– Bitter
• Brought about by more chemically diverse group of tastants
• Examples – alkaloids, toxic plant derivatives, poisonous substances
– G protein linked
– Umani
• Meaty or savory taste
– G protein linked
Taste Perception
• Influenced by information derived from other
receptors, especially odor
• Temperature and texture of food influence taste
• Psychological experiences associated with past
experiences with food influence taste
• How cortex accomplishes perceptual processing of
taste sensation is currently unknown
Smell (Olfaction)
• Olfactory receptors in nose are specialized endings of
renewable afferent neurons
• Olfactory mucosa
– 3cm2 of mucosa in ceiling of nasal cavity
– Contains three cell types
• Olfactory receptor cell
– Afferent neuron whose receptor portion is in olfactory mucosa
in nose and afferent axon traverses into brain
– Axons of olfactory receptor cells collectively form olfactory
nerve
• Supporting cells
– Secrete mucus
• Basal cells
– Precursors of new olfactory receptor cells (replaced about
every two months)
Smell (Olfaction)
• Odorants
– Molecules that can be smelled
• To be smelled, substance must be
– Sufficiently volatile that some of its molecules can
enter nose in inspired air
– Sufficiently water soluble that it can dissolve in
mucus coating the olfactory mucosa
Smell (Olfaction)
• 1000 different types of olfactory receptors
• Odorants act through second-messenger systems to
trigger action potentials
• Afferent signals are sorted according to scent
component by glomeruli within olfactory bulb
Fig. 6-43, p. 225
Olfactory receptor cells
• Enlarged knob bearing several cilia
• Have olfactory receptors
• Odorants
– Must be volatile
– Water soluble
Processing of Scents in Olfactory Bulb
Olfactory processing
• Odors dissected into components
• Each part of a n odor detected by one of a thousand
receptor
• G protein, cAMP, Na channel transduction
• Olfactory bulb
– Above bone layer
– Glomeruli and mitral cells together
• Limbic system in the primary olfactory cortex of the
temporal lobe
• Through the thalamus to the cortex
Processing
• Each odorant molecule activates multiple receptors
and glomeruli
• Odor discrimination based on “patterns” of
glomerular excitation
Vomeronasal Organ (VNO)
• Common in mammals but until recently was thought
to nonexistent in humans
• Located about half an inch inside human nose next
to vomer bone
• Detects pheromones
– Nonvolatile chemical signals passed
subconsciously from one individual to another
• Role in human behavior has not been validated