Transcript 29. The Senses

Chapter 29
The Senses
PowerPoint Lectures for
Biology: Concepts and Connections, Fifth Edition
– Campbell, Reece, Taylor, and Simon
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
An Animal's Senses Guide Its Movement
• Animals use sensory information gathered by
sensory receptors and processed in the brain
to guide behavior
– Salmon use their sense of smell to return to
a particular stream to reproduce
– Bears use their acute sense of smell to find
streams where salmon run
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
29.1 Sensory inputs become sensations and
perceptions in the brain
• Sensory receptor cells are tuned to internal
and external conditions
– Detect stimuli
– Trigger action potentials that go to central
nervous system
• Sensation: action potential received by brain
• Perception: brain's interpretation of the action
potential integrated with other information
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
SENSORY RECEPTION
29.2 Sensory receptors convert stimulus energy
to action potentials
• Sensory receptors are specialized cells or
neurons that detect stimuli
• All stimuli represent forms of energy
• Sensory transduction converts stimulus energy
into receptor potentials
• Receptor potentials trigger action potentials
that enter CNS for processing
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-2a-3
Taste pore
Taste
bud
Sensory neuron
Membrane of
sensory receptor
cell
Signal transduction
pathway
Ion
channels
Sensory
receptor
cell
Ion
Receptor
potential
Neurotransmitter
Sensory neuron
Action potential
mV
Tongue
Sugar
Sugar
molecule
molecule (stimulus)
Sensory
receptor
cells
No sugar
Sugar present
Action potentials
• Different sensory receptors respond to different
stimuli
– Synapse with interneurons in brain
• Brain distinguishes types of stimuli by patterns
of interneuron stimulation
• Action potential frequency reflects stimulus
intensity
• Repeated stimulus may lead to sensory
adaptation, a decrease in sensitivity
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-2b
“Sugar” interneuron
“Salt” interneuron
Sugar
receptor
Salt
receptor
Brain
Sensory
neurons
Taste
bud
No sugar
Taste
bud
No salt
Increasing sweetness
Increasing saltiness
29.3 Specialized sensory receptors detect five
categories of stimuli
•
Pain receptors detect dangerous stimuli
•
Thermoreceptors detect heat or cold and monitor
blood temperature deep in the body
•
Various mechanoreceptors respond to mechanical
energy such as touch, pressure, and sound
– Stretch receptors monitor the position of body parts
– Hair cells are cilia that detect movement in water;
important in hearing and balance
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-3a
Heat
Light
touch
Pain
Cold
Hair
Light
touch
Epidermis
Dermis
Nerve
Connective
tissue
Hair
movement
Strong
pressure
LE 29-3b
“Hairs” of
receptor cell
Neurotransmitter
at synapse
More
neurotransmitter
Less
neurotransmitter
Sensory
neuron
Action
potentials
Action
potentials
Receptor cell at rest
Fluid moving in one direction
Fluid moving in other direction
• Chemoreceptors respond to chemicals in the
external or internal environment
• Electromagnetic receptors detect energy
occurring as electricity, magnetism, or light
– Photoreceptors, including eyes, detect
varying visible or ultraviolet light
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-3d
Eye
Infrared
receptor
VISION
29.4 Several types of eyes have evolved among
invertebrates
• Eye cups
– Sense light intensity and direction but do
not form images
• Compound eyes
– Brain forms a mosaic image of data from
many tiny light-detecting omatidia
• Single-lens eye
– Works on the principle of a camera
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-4a
Eye cups
29.5 Vertebrates have single-lens eyes
• The vertebrate eye evolved independently of
the invertebrate single-lens eye and differs in
many details
• Structure of the human eye
– Sclera: tough, whitish outer surface
– Cornea: transparent thinning of sclera
– Choroid: pigmented layer that forms the iris
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
– Pupil: opening in center of the iris that lets
light into interior of eye
– Lens: focuses images on the retina
– Retina: photoreceptor cells
• Transduce light energy
• Send action potentials to the brain through
the optic nerve
• Concentrated in the fovea
• Blind spot cannot detect light
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Vitreous and aqueous humors make up bulk of
the eye
– Maintain shape
– Fluid secreted by ciliary body supplies
nutrients and oxygen and removes wastes
• Mucous membrane keeps outside of eye moist
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-5
Sclera
Choroid
Ciliary body
Retina
Ligament
Cornea
Fovea
(center of
visual field)
Iris
Pupil
Optic
nerve
Aqueous
humor
Lens
Vitreous
humor
Artery
and vein
Blind spot
29.6 To focus, a lens changes position or shape
• The lens focuses light onto the retina by
bending light rays
• Focusing can occur in two ways
– Muscles move rigid lens back and forth
– Lens changes shape
• Contraction of ciliary muscle produces
accommodation (near vision)
• Relaxation of ciliary muscle produces
distance vision
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LE 29-6
Choroid
Ciliary muscle contracted
Ligaments slacken
Retina
Light from a near object
(diverging rays)
Near vision (accommodation)
Ciliary muscle relaxed
Ligaments pull on lens
Light from a distant object
(parallel rays)
Distance vision
Lens
Animation: Near and Distance Vision
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CONNECTION
29.7 Artificial lenses or surgery can correct
focusing problems
• Visual acuity: ability to distinguish fine detail
• Nearsightedness (myopia): inability to focus on
far objects
– Eyeballs are elongated; focal point is in
front of retina
• Farsightedness (hyperopia): inability to focus
on near objects
– Eyeballs are too short; focal point is behind
retina
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Astigmatism: blurred vision caused by
misshapen lenses or corneas
• Compensating for deficient visual acuity
– Corrective lenses bend light rays to
compensate
– Surgery can reshape the cornea, reducing
bending of light rays
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-7a
Shape of
normal
eyeball
Lens
Retina
Focal
point
Diverging
corrective
lens
Focal
point
LE 29-7b
Shape of
normal
eyeball
Focal
point
Converging
corrective
lens
Focal
point
29.8 Our photoreceptors are rods and cones
• Rods
– Sensitive to dim light
– Distinguish shades of gray, not color
– Use light-absorbing pigment rhodopsin
• Cones
– Stimulated by bright light
– Distinguish color
• Blue, red, and green cones use three types
of the pigment photopsin
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-8a
Cell body
Rod
Cone
Synaptic
knobs
Membranous disks
containing visual pigments
•
Vision pathway
– Light absorbed by pigment in rods and cones
– Chemical changes trigger signal transduction
pathway, resulting in receptor potential
– Signals integrated in a layer of neurons on the
surface
– Signals combine and leave eye via the optic nerve
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-8b
Retina
Neurons
Photoreceptors
Cone Rod
Optic
nerve
fibers
Retina
Optic
nerve
HEARING AND BALANCE
29.9 The ear converts air pressure waves to
action potentials that are perceived as sound
• The human ear is composed of three regions
– Outer ear
• Pinna and auditory canal collect and
channel sounds
• Eardrum separating outer and middle ear
vibrates when sound waves strike
– Middle ear
• Hammer, anvil, and stirrup bones receive
vibrations
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• Vibrations pass through oval window in
skull to inner ear
• Opens into Eustachian tube, which connects
to pharynx and equalizes pressure
– Inner ear
• Contains three fluid-filled canals, including
cochlea
• Hair cells in organ of Corti are the ear's
sensory receptors
• Hair cells are embedded in basilar
membrane, contact tectorial membrane
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-9a
Outer Ear
Inner ear
Eardrum
Pinna
Auditory
canal
Middle ear
Eustachian
tube
LE 29-9b
Semicircular canals Auditory nerve,
Stirrup Skull bones (function in balance) to brain
Anvil
Hammer
Cochlea
Eardrum
Oval window
Eustachian tube
(behind stirrup)
LE 29-9c
Middle
canal
Bone
Hair cells Tectorial membrane
Auditory
nerve
Upper
canal
Sensory
neurons
Lower
canal
Cross section
through cochlea
Organ of Corti
Basilar
membrane
To auditory nerve
• Function of the ear in hearing
– Vibrations are amplified as sound
(pressure) waves are transferred through
middle ear
– Pressure waves produced by oval window
vibration pass into cochlear canals
– Vibrations of basilar membrane bend hair
cells, developing a receptor potential
– Action potentials travel from hair cells to
brain via auditory nerve
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-9d
Outer Ear
Pinna
One
vibration
Auditory
canal
Amplitude
Middle Ear
Eardrum
Hammer,
anvil, stirrup
Amplification
in middle ear
Inner Ear
Oval
window
Cochlear canals
Lower
Upper and middle
Organ of
Corti
stimulated
Time
• Volume and pitch
– Volume depends on the amplitude of
pressure waves
• Louder sounds generate higher amplitude
waves and thus more action potentials
– Pitch depends on the frequency of sound
waves
• High-pitched sounds generate highfrequency waves
• Different pitches stimulate different regions
of the organ of Corti
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
29.10 The inner ear houses our organs of
balance
• Several organs in the inner ear detect body
position and movement
– Semicircular canals detect changes in
head's rate of rotation or angular movement
– Utricle and saccule detect position of head
with respect to gravity
– All operate by bending of hairs on hair cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-10
Semicircular
canals
Nerve
Cochlea
Utricle
Saccule
Flow of fluid
Flow
of fluid
Cupula
Hairs
Hair
cell
Nerve fibers
Cupula
Direction of body movement
CONNECTION
29.11 What causes motion sickness?
• Motion sickness may be caused by conflicting
signals from the equilibrium receptors in the
inner ear and from the eyes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
TASTE AND SMELL
29.12 Taste and odor receptors detect chemicals
present in solution or air
• Taste receptors located in taste buds on the
tongue produce perceptions of sweet, sour,
salty, bitter, and umami
• Olfactory (smell) sensory neurons line the
nasal cavity
– Odorous substances bind to receptor
proteins on cilia
– Receptor potentials send impulses directly
to olfactory bulb of brain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 29-12
Brain
Olfactory
bulb
Bone
Nasal cavity
Epithelial
cell
Sensory
neuron
(chemoreceptor)
Cilia
Mucus
CONNECTION
29.13 Our sense of taste may change as we age
• Taste sensitivity declines with age
• Reduced sense of smell contributes to
diminishing flavor perception
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
29.14 Review: The central nervous system
couples stimulus with response
• Sensory receptors provide an animal's nervous
system with vital data that enable the animal to
survive
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings