Transcript chapter30_Sensory Perception(1

Cecie Starr
Christine Evers
Lisa Starr
www.cengage.com/biology/starr
Chapter 30
Sensory Perception
(Sections 30.1 - 30.5)
Albia Dugger • Miami Dade College
30.1 A Whale of a Dilemma
• Animals use sensory systems to receive signals from inside
and outside the body, decode them, and become aware of
touches, sounds, sights, odors, and other sensations
• Whales rely heavily on their sense of hearing, and underwater
sound pollution puts them at risk
• 16 whales beached themselves when the US Navy tested a
new sonar system – autopsies revealed blood in their ears
and in acoustic fat
A Whale of a Dilemma
30.2 Detecting Stimuli
and Forming Perceptions
• The sensory portion of a vertebrate nervous system consists
of sensory neurons that detect stimuli, nerves that carry
information about the stimulus to the brain, and brain regions
that process the information
• stimulus
• Form of energy that a sensory receptor detects
Sensory Neurons
• Different types of sensory neurons respond to different
specific stimuli by producing action potentials
• Types of sensory receptors include, chemoreceptors,
thermoreceptors, pain receptors, mechanoreceptors, and
photoreceptors
Key Terms
• chemoreceptor
• Sensory receptor that responds to a chemical
• thermoreceptor
• Temperature-sensitive sensory receptor
• pain receptor
• Sensory receptor that responds to tissue damage
Key Terms
• mechanoreceptor
• Sensory receptor that responds to pressure, position, or
acceleration
• photoreceptor
• Sensory receptor that responds to light
Sensory Receptors in the Skin
Sensory Receptors in the Skin
detects touch,
tissue damage
detects
heat
detects
cold
detects
touch
epidermis
dermis
detects strong
pressure
detects hair
movement
Fig 30.2, p. 490
Sources of Information
About a Stimulus
• Three variables allow your brain to evaluate incoming action
potentials and determine the location and intensity of a
stimulus:
1. The nerve that delivers the action potentials
2. The frequency of action potentials
3. The number of sensory receptors firing
Frequency of Action Potentials
• Action potentials from a mechanoreceptor in skin; the
stronger the pressure, the more action potentials per second
Frequency of Action Potentials
Light touch,
low firing rate
Increased pressure,
higher firing rate
0
1
2
3
4
Time (seconds)
Fig 30.3, p. 490
Sources of Information
About a Stimulus
• Stimulus duration also affects response
• Continued stimulation of a receptor can lead to sensory
adaptation, in which sensory neurons cease firing in spite of
continued stimulation
• sensory adaptation
• Slowing or cessation of a sensory receptor’s response to
an ongoing stimulus
Sensation and Perception
• Sensation is the detection of sensory signals; perception
arises when the brain assigns meaning to those signals
• sensation
• Detection of a stimulus
• perception
• The meaning a brain derives from a sensation
Key Concepts
• Sensory Pathways
• Sensory systems consist of sensory receptors, nerves that
carry signals, and brain regions that receive and process
sensory input
• Each type of sensory receptor reacts to a specific stimulus
• Information about stimuli is encoded in the number and
frequency of action potentials
30.3 Somatic and
Visceral Sensations
• Our brain easily identifies the source of a somatic sensation
such as touch on skin; visceral sensations that originate at
receptors in walls of soft organs are less easily pinpointed
• somatic sensations
• Sensations such as touch and pain that arise when
sensory neurons in skin, muscle, or joints are activated
• visceral sensations
• Sensations that arise when sensory neurons associated
with organs inside body cavities are activated
The Somatosensory Cortex
• The human primary somatosensory cortex is a narrow strip of
cerebral cortex that runs from the top of the head to just
above the ear
• Somatic sensory signals from receptors in skin and skeletal
muscles reach sensory areas of the cerebral cortex, where
interneurons are organized like maps of individual parts of the
body surface
The Somatosensory Cortex
The
Somatosensory
Cortex
Fig 30.4, p. 491
Muscle Sense
• Sensory receptors report to the somatosensory cortex about
touch, pain, and temperature
• The fourth somatosensory sense is muscle sense, which
relates to the positioning of body parts
• Muscle spindles and mechanoreceptors near joints and
tendons contribute to muscle sense; the more a muscle
stretches, the more frequently receptors fire
Pain
• Injured or distressed body cells release local signaling
molecules (histamine and prostaglandins) that stimulate
neighboring pain receptors
• Various neuromodulators (including endorphins and
substance P) enhance or lessen pain signals
• pain
• Perception of tissue injury
Key Concepts
• Somatic and Visceral Sensation
• Somatic sensations include touch, pressure, pain,
temperature, and muscle sense
• They start at mechanoreceptors in skin, muscles, and near
joints
• Visceral sensations arise from stimulation of receptors in
walls of soft internal organs
Animation: Sensory Receptors in the Human
Skin
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BBC Video: Protected by Our Sense of Touch
BBC Video: Using Vision to Replace the
Sense of Touch
30.4 Do You See What I See?
• Most animals are sensitive to light, but only those with a
camera eye form images as humans do
• Eyes are sensory organs that contain a dense array of
photoreceptors
• Pigment molecules in photoreceptors absorb light energy,
which is converted to action potentials and sent to the brain
Requirements for Vision
• Vision requires eyes and a brain with the capacity to interpret
visual stimuli
• Formation of an image requires an eye with a lens
• lens
• Transparent, disk-shaped structure that bends light rays
so they fall on an eye’s photoreceptors
Types of Eyes
• Some invertebrates, such as earthworms, have
photoreceptors but do not have eyes
• Insects have compound eyes with many individual units,
each with a lens
• Cephalopods and vertebrates have camera eyes, with an
adjustable opening that lets in light, and a single lens that
focuses the light on a photoreceptor-rich retina
Key Terms
• compound eye
• Eye with many units each having its own lens
• camera eye
• Eye with an adjustable opening and a single lens that
focuses light on a retina
• retina
• Layer of eye that contains photoreceptors
Compound Eye of a Deerfly
Compound
Eye of a
Deerfly
lens
crystalline cone
cells (usually four)
screening pigment
photo receptor cell
sensory neuron
ommatidium
Fig 30.5a, p. 492
Camera Eye of Squid (Cephalopod)
Camera Eye
of Squid
(Cephalopod)
lens
retina
optic
tract
Fig 30.5b, p. 492
The Human Eye
• The eyeball is spherical with a three-layered structure:
• Outer layer includes a transparent cornea and white
sclera
• Middle layer includes a dark choroid layer, ciliary body,
two internal chambers, lens, iris and pupil
• Innermost layer (the retina) contains the photoreceptors
Key Terms
• cornea
• Clear, protective covering at front of vertebrate eye
• iris
• Circular muscle that adjusts the shape of the pupil to
regulate how much light enters the eye
• pupil
• Adjustable opening that allows light into a camera eye
Structure of the Human Eye
Structure of the Human Eye
sclera
choroid
retina
fovea
iris
lens
pupil
cornea
aqueous
humor
optic
disk
(blind
spot)
part of
optic
nerve
ciliary muscle
vitreous body
Fig 30.6, p. 493
Animation: Eye Structure
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Focusing Mechanisms
• Visual accommodation is the altering of lens shape to focus
on objects at different distances
• Contraction of ciliary muscle focuses the lens for reading;
relaxation allows the lens to flatten for distance vision
• visual accommodation
• Process of making adjustments to lens shape so light from
an object falls on the retina
Visual Accommodation
Visual Accommodation
contracted
ciliary
muscle
relaxed
ciliary
muscle
fibers
slack
fibers
taut
A Near vision
Contraction of ciliary muscle
allows fibers to slacken and the
lens becomes fatter and rounder.
B Distance vision
Relaxation of ciliary muscle pulls
fibers taut stretching the lens so it
becomes thinner and flatter.
Fig 30.7, p. 493
Animation: Focusing of Distant and Near
Sources of Light
Forming an Image
• The image on the retina is upside down and reversed left to
right – the brain interprets the image
BBC Video: The Anatomy of Sight
30.5 The Human Retina
• The retina has two types of photoreceptors (rods and cones),
each with stacks of membranous disks that contain pigment
• Visual pigments (opsins) are derived from vitamin A, which is
why vitamin A deficiency can impair vision
Rods Cells
• Rod cells detect dim light and are concentrated at the edges
of the retina
• All rods have the same pigment (rhodopsin), which is most
excited by exposure to green-blue light
• rod cell
• Photoreceptor that is active in dim light
• Provides coarse perception of image and detects motion
Cone Cells
• Three types of cone cells have different forms of the pigment
photopsin that absorb red, blue, and green light – they are
most abundant in the fovea
• cone cell
• Photoreceptor that provides sharp vision and allows
detection of color
• fovea
• Retinal region where cone cells are most concentrated
Rods and Cones
Rods and Cones
cone
cell
stacked, pigmented membrane
rod
cell
A The two types of photoreceptors in the retina
Fig 30.9a, p. 494
Vision Processing in the Retina
• Rods and cones lie at the very rear of the retina, beneath
layers of signal-processing neurons
• When a rod or cone photoreceptor absorbs light, signals flow
to neurons in the layer above, which process the signals and
send them to ganglion cells
•
Bundled axons of ganglion cells make up the optic nerve
Structure of the Retina
Structure
of the
Retina
horizontal cell
bipolar cell
cone cell
rod cell
amacrine cell
ganglion cell
incoming
rays of
light
B Multilayered structure of the retina
Fig 30.9b, p. 494
Structure of the Retina
Structure of the Retina
blood
vessel
start
of an
optic
nerve
fovea
(region
with
most
cones)
C Magnified view of the retina as seen through the pupil
Fig 30.9c, p. 494
Animation: Organization of Cells in the Retina
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Vision Processing in the Brain
• Signals from the visual field of each eye travel along an optic
nerve to the brain’s opposite hemisphere
• Each optic nerve ends in a brain region (lateral geniculate
nucleus) that processes the signals
• Signals are conveyed to the visual cortex where the final
integration process produces visual sensations
Key Concepts
• Vision
• Vision requires eyes with a dense array of photoreceptors
and a brain that integrates signals from them
• The vertebrate eye works like a film camera; a single
adjustable opening lets in light
• A sensory pathway starts at the eye’s retina and ends in
the visual cortex
Animation: Pathway to Visual Cortex
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