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Vocabulary:
1,2,3,4,5,6,7,8,9,10,
11,12,13,14,15,
16,17,18,19,20,
21,22,23,24,25,
26,27,28,29,30,
31,32,33,34,35,
36,37,38,39,40,
41,42,43,44,45,
46,47,48,49,50,
51,52,53,54
Sensory Systems
I. Introduction A. Human Brain Requires Sensory Input
for Proper Functioning
B. Input to Central Nervous System (CNS) Via Afferent
Sensory Neurons
1. Information based on frequency
of impulses
2. Information based on identity of
transmitting neurons
II. The Nature Of Neurosensory Communication
A. Path of Sensory Information to the CNS
1. Stimulation: physical stimulus
on sensory receptor
2. Transduction: sensory receptor
initiates opening/closing of ion channel in sensory neuron
3. Transmission: sensory neuron conducts
action potential along afferent pathway to CNS
B. Comparison of Sensory Receptors
1. All initiate nerve impulses in
sensory neuron membranes
2. Differ as to the nature of the
stimulus that initiates this event
3. Four primary senses use different
classes of receptors
a) Mechanical receptors:
mechanoreceptors (hearing)
b) Chemical receptors:
chemoreceptors (taste and smell)
c) Photoreceptors
(vision)
d) Free nerve endings
(1)
Simplest sensory receptors
(2)
Respond to bending or stretching of sensory neuron membrane
(3)
Respond to changes in temperature or chemicals in extracellular fluid
4. More complex receptors involve
association with epithelial cells
C. Sensing the Exterior World
1. Defined as exteroception
2. Information depends on receptor,
medium in which stimulus travels
a) Most sensory
systems evolved in water, later adapted to air
b) Many senses operate
better in air than water, need no alteration
c) Other senses
required changes to work well in air: hearing
d) Few that work
in water do not work in air: electrical charges
e) Other senses
evolved in the air that cannot work in the sea: infrared vision
3. Sensory systems provide several
levels of information
a) Determine only
that an object is present, call attention to object
b) Location and
direction of object, can move in relation to it
c) Compose three-dimensional
image of object and surroundings
D. Sensing the Internal Environment of the Body
1. Defined as interoception, inner
perception
2. Receptors detect changes related
to muscle length and tension, limb position, pain, blood chemistry, blood
pressure, body temperature
3. Internal receptors are generally
simpler than exterior receptors
4. Comparison of interoceptors and
exteroceptors
III. The Mechanisms Of Sensory Transduction
A. Receptor Potentials
1. Cells possess stimulus-gated ion
channels in their membranes
a) Cause cells to
respond to stimuli
b) Application of
stimulus opens or closes channels
c) Resulting change
in membrane permeability produces shift in membrane potential
2. Generator potentials = receptor
potentials
a) Most stimulus-gated
ion channels pass Na+ and K+
b) Photoreceptors
are the exception
c) Resting potential
(-70 mV) closer to K+ equilibrium potential (-90 mV) than Na+ equilibrium
potential(+60 mV)
d) More Na+ enters
cell than K+ leaves cell
e) Results in depolarization
of sensory cell
f) One or more axon
action potentials initiated if depolarization reaches threshold
IV. Sensing Temperature
A. Skin Contains Two Populations of Thermoreceptors
1. Cold receptors stimulated by lowering
temperature
2. Heat receptors stimulated by increasing
temperature
B. Thermoreceptors in Hypothalamus
1. Monitor temperature of blood
2. Provide information about body's
internal, core temperature
V. Sensing Pain
A. Stimulus that Causes Tissue Damage Is Sensed as Pain
1. Cause changes in heartbeat and
blood pressure
2. Cause reflexive withdrawal of body
segments if from external source
B. Receptors Called Nociceptors
1. Mostly free nerve endings throughout
body, especially near surface
2. May respond to various stimuli
a) Extremes in temperature
b) Intense mechanical
stimulation
c) Specific chemicals
in extracellular fluid, including ones released by injured cells
3. Receptor thresholds vary
a) Some respond
only to actual tissue damage
b) Others respond
before damage has occurred
VI. Sensing Forces
A. Mechanoreceptors Sense Changes in Mechanical Force
on Membrane
1. Ion channels open in response to
mechanical distortion
2. Initiate depolarizing receptor
potential
3. Afferent nerve fires a series of
action potentials
B. Touch and Pressure
1. Receptors in epidermis, dermis
and subcutaneous tissue
2. Fine touch receptors located on
fingertips and face
a) Precisely localize
cutaneous stimuli
b) Phasic: hair
follicle receptors, Meissner`s corpuscles on hairless body surfaces
c) Tonic: Ruffini
endings, touch dome endings (Merkel cell s)
on surface of skin
3. Receptors measure duration of touch
and extent to which it is applied
4. Pacinian corpuscles are phasic
pressure-sensitive receptors
a) End of afferent
axon surrounded by capsule of layers of cells and extracellular fluid
5. Elastic capsule absorbs sustained
pressure, axon ceases to produce impulses
6. Monitor onset and removal of pressure,
as in vibrations
C. Muscle Length and Tension
1. Special muscle spindles are buried
in muscles, parallel with fibers
a) Stretch-sensitive
axon of sensory neuron wrapped around each spindle
b) Spindle functions
as stretch receptor, a type of proprioceptor
2. Muscle spindle elongates when muscle
is stretched
a) Associated sensory
neurons conduct action potentials to spinal cord
b) Synapse with
somatic motor neurons that innervate same muscle
c) Cause motor neurons
to produce action potentials, cause muscle to contract
d) Pathways is basis
for muscle stretch reflex and knee-jerk reflex
3. Functions as muscle length detector
a) If muscle stretched,
length detectors stimulated, muscle contracts
b) With contraction
tension removed, reduces activity of sensory neurons
4. Golgi tendon organs
a) Monitor tension
at tendon-muscle boundary of origin and insertion
b) If too high,
causes reflex to inhibit motor neuron innervating muscle
c) Ensures that
muscles do not contract too strongly, damaging their tendons
D. Blood Pressure
1. Receptors in carotid sinus (in
wall of carotid arterie s)
and in aortic arch
a) Baroreceptors
are highly branched network of afferent neurons
b) Detect tension
in blood artery walls
2. Rate of firing decreases with decrease
in blood pressure
a) CNS responds
by stimulating sympathetic division of autonomic system
b) Increases heart
rate and vasoconstriction
3. Rate of firing increases with increase
in blood pressure
a) Reduces sympathetic
activity, increases parasympathetic activity
b) Slows heart,
lowers blood pressure
E. Gravity
1. Statocysts help brain determine
orientation of body with respect to gravity
2. In vertebrates, receptors are in
hollow chambers in inner ear
a) Composed of saccule
and utricle fig 48.6
b) Walls lined by
sensory cells with projecting cilia, called hair cells
c) Each contains
gelatinous matrix containing calcium carbonate otoliths
d) Cilia of hair
cells beneath otolith bend with weight of otolith
3. Bent cilia exerts pressure on membrane
of hair cell, pressure depolarizes hair cell
a) Increases frequency
of action potentials in afferent axons from statocysts to brain
b) Movement causes
different set of hair cells to depolarize
c) Brain continually
apprised of orientation of statocysts
F. Angular Motion
1. Process similar to orientation
with respect to gravity
2. Three fluid-filled semicircular
canals located within the inner ear
a) Canals oriented
in different planes to detect motion in any direction
b) Sensory cells
protrude into canals in ampulla
c) Tips of cilia
embedded in gelatin-filled cupula
3. Rotation of head causes movement
of fluid, pushes against cupula
a) Deformation of
cupula bends cilia
b) Bending of cilia
depolarizes or hyperpolarizes hair cells
c) Converted into
a decrease or increase in frequency of nerve firing
d) Movement in any
direction sensed by at least one canal
e) Brain analyzes
complex movements
4. Vestibular apparatus: saccule,
utricle and semicircular canals
a) Saccule and utricle
sense linear acceleration
b) Semicircular
canals sense angular acceleration
c) Information from
all help maintain body's position in space, balance, equilibrium
G. Lateral Line Organs
1. Fish also have hair cells with
cilia embedded in cupulae
2. Cupulae extend into lateral line
organs, grooves along sides of fish
a) Water moving
past lateral line exerts pressure on cupula, bends cilia
b) Cilia oriented
so some sense movement of water in either direction
3. Receptors also indicate rate of
movement of water
a) Enable fish to
detect motionless objects by sensing deflection of pressure waves
b) Analogous to
a sense of hearing, similar cellular mechanism
c) Terrestrial vertebrate
hearing hair cells may have evolved from these organs
VII. Sensing Chemicals
A. Some Sensory Cell Membranes Contain Special Proteins
1. Bind to specific chemicals in environment
or extracellular fluid
2. With binding, membrane depolarizes
B. Taste
1. Mediated by taste buds, collection
of chemosensitive receptors
a) In fish, taste
buds are located all over body, used to locate food
b) Most sensitive
vertebrate chemoreceptors
2. In terrestrial vertebrates, taste
buds concentrated on papillae in mouth
a) Humans respond
to salt, sweet, sour and bitter tastes
b) Perception of
taste is a combination of impulses from these axons
C. Smell
1. In terrestrial vertebrates, located
in upper portion of nasal passage
2. Cell bodies in nasal epithelium,
dendrites extend into mucus layer
3. Sense of taste used like a fish`s
sense of taste
a) Sense chemical
environment around itself
b) Specialized to
detect airborne particles
c) Extremely acute
sense
d) Sense thousand's
of different smells
(1)
May be a thousand different genes to code for different smell receptor
proteins
(2)
Particular set of olfactory neurons respond to a given odor
(3)
That set serves as an odor fingerprint for identification
D. Blood Chemistry
1. Peripheral chemoreceptors, carotid
bodies embedded within walls of certain arteries
2. Central chemoreceptors in medulla
of brain
3. Sensitive to oxygen and carbon
dioxide concentration in blood and to blood pH
a) With low breathing
rate
(1)
O2 levels decrease slowly
(2)
pH decreases rapidly
(3)
CO2 levels increases rapidly
b) Receptors more
sensitive to changes in pH and CO2 concentration
c) Sensitivity to
O2 only important at high altitudes
VIII. Hearing
A. Terrestrial Vertebrates Detect Vibration in Air Via
Mechanical Receptors in the Ear
1. Analogous to and evolved from lateral
line organs in fish
2. Sense more accurate in water than
in air
3. Provides more information about
direction than chemoreceptors
4. Provide little information about
distance
B. Structure of the Ear
1. Terrestrial vertebrates evolved
ears for hearing
a) Sound waves are
weaker in air than in water
b) Terrestrial animals
need to amplify sound to use the same receptor
2. Sound waves beat against tympanic
membrane or eardrum
a) Membrane separates
outer ear from middle ear
b) Causes vibrations
of three small bones, ossicles: hammer, anvil and stirrup
c) Connected to
oval window, membrane that leads to cochlea
d) Cochlea is coiled,
fluid-filled chamber in inner ear
e) Stirrup pushes
on oval window causes it to vibrate
f) Vibrations set
up pressure waves in fluid of cochlea, actual site of hearing
3. System amplifies sound waves
a) Ossicles act
as lever system, increase force of vibration from tympanum to oval window
b) Oval window smaller
than tympanum, vibrations produce more force per unit
4. Middle ear connected to throat
by Eustachian tube
a) Equalizes pressure
in middle and outer ear
b) Ear pressure
changes with rapid change in altitude causes ear popping
C. Transduction in the Cochlea
1. Cochlea divided into upper and
lower chamber by cochlear duct
a) Both chambers
and duct are filled with fluid
b) Stirrup vibrations
on oval window produce pressure waves in upper chamber
c) Transmitted to
lower chamber
d) Cause vibrations
in basilar membrane, separates cochlear duct from lower chamber
2. Sensory hair cells located on top
of basilar membrane
a) Cilia project
into overhanging gelatinous structure called the tectorial membrane
b) Organ of Corti:
basilar and tectoral membranes plus hair cells
c) Basilar membrane
vibration bends hair cell cilia as it moves relative to the tectorial
membrane
d) Bending depolarizes
the hair cells
e) Hair cells cause
afferent neurons to transmit impulses to brain
f) Impulses interpreted
as sound
D. Frequency Localization in the Cochlea
1. Analysis of sound frequency based
on resonance
a) Vibrating tuning
fork or strings exhibit characteristic resonant frequency
b) String length
and taughtness determines resonant frequency in stringed instrument
2. Basilar membrane composed of elastic
fibers of varying length and stiffness
a) Short and stiff
at base of cochlea (near oval window) = high resonant frequency
b) Long and flexible
at apex (far en d)
= low resonant frequency
c) Sound wave energy
moves basilar membrane up and down
d) Energy imparted
to region with most similar resonant frequency
e) Causes maximum
deflection at that point
f) Depolarization
of hair cells greatest at that point
g) Action potentials
arriving in brain interpreted as sound of that frequency or pitch
3. Flexibility of basilar membrane
limits human hearing
a) Frequency range
of 20-20,000 cycles per second (Hz) in children
b) Hearing high-pitch
sounds declines with age
c) Other vertebrates
sense sounds lower than 20 Hz, higher than 20,000 Hz
4. Hair cells are innervated by efferent
axons from brain
a) Impulses can
make hair cells less sensitive
b) Increase individual's
ability to concentrate on one signal
c) Other sounds
effectively tuned-out by efferent axons
E. Sonar
1. Two ears of terrestrial vertebrates
enable localization of sound
a) Can be used to
determine direction
b) Not highly accurate
to provide measure of distance
2. Sonar circumvents limitations of
living in darkness
a) Bat can avoid
a wire less than 1 millimeter in diameter
b) Examples: shrew,
whale, dolphin
c) Emit sounds,
determine time for sound to reach object and return
d) Allows for three-dimensional
imaging
3. Allows bats to occupy birds environment,
but in darkness
IX. Vision
A. Visual Stimulus Is Electromagnetic Energy
1. Travels in straight line, arrives
almost instantaneously
2. Provides information to determine
direction and distance of objects
B. The Evolution of the Eye
1. Less advanced animals perceive
light with eyespots, but cannot construct visual image
2. Eyes evolved independently in many
different groups
3. All use same visual pigment
C. Structure of the Vertebrate Eye
1. Vertebrate eyes are lens-focused
a) Light passes
through transparent cornea, begins to focus it
b) Light continues
through lens completes focusing process
2. Lens is a fat disk, attached by
ligaments to ciliary muscles
a) Contraction of
muscles changes shape of lens
(1)
Fish and amphibian lenses have a constant shape
(2)
Focusing achieved by moving lens in and out
b) Alters point
of focus on retina at back of eye
3. Photoreceptors located on retina
4. Amount of light entering eye controlled
by iris
a) Sphincter muscle
that lies between cornea and lens
b) Light passes
through pupil, zone in iris
c) Bright light
reduces size of opening
d) Enlarges in dim
light to allow more light to enter eye
5. Lenses limited by chromatic aberration
a) Short wavelengths
refracted or bent more than longer wavelengths
b) Short wavelengths
focus at different point than long wavelengths
c) Vertebrate eye
thus filters out short-wavelength ultraviolet light
d) Insects do not
focus light and can perceive ultraviolet light
D. Vertebrate Photoreceptors
1. Vertebrate retina contains rods
and cones
a) Rods used for
black-and-white vision when illumination is dim
b) Cones are used
for color vision, are shorter than rods
c) Humans have 100
million rods and 3 million cones in each retina
d) Most cones found
in fovea
(1)
Location where eye forms its sharpest image
(2)
Almost no rods found here
2. Cellular structure of rods and
cones very similar
a) Inner segment
(1)
Rich in mitochondria
(2)
Contains numerous vesicles filled with neurotransmitter molecules
b) Outer segment:
connected to inner segment by narrow stalk
(1)
Packed with hundreds of flattened disks, stacked on one another
(2)
Light-capturing photopigment molecules on membranes of these disks
3. Rhodopsin is rod cell photopigment
a) Opsin protein
coupled to molecule of cis-retinal
b) Cis-retinal produced
from carotene
4. Photopsin is rod cell photopigment
a) Three kinds of
cones, each has cis-retinal plus opsin with slightly different amino acid
sequence
b) Sequence shifts
absorption maximum from 500 nanometers of rhodopsin
(1)
455 nm is blue-absorbing
(2)
530 nm is green-absorbing
(3)
625 nm is red absorbing
c) Different light-absorbing
properties account for different cone color sensitivities
E. Sensory Transduction in Photoreceptors
1. Rod or cone contains many Na+ channels
in plasma membrane of outer segment
a) In dark many
channels are open
b) Na+ ions continually
diffuse into outer segment, across stalk to inner segment
c) Small flow in
absence of light called the dark current
d) Causes membrane
to be somewhat depolarized in the dark
2. In the light, Na+ channels in outer
segment close rapidly
a) Reduces dark
current
b) Causes photoreceptor
to hyperpolarize
c) Only know receptor
to respond by hyperpolarizing rather than depolarizing
3. Light causes Na+ channels to close
a) Cis-retinal is
converted to trans-retinal when the photopigment absorbs light
b) Isomerization
causes retinal to dissociate from opsin: bleaching reaction
c) Opsin protein
changes shape
d) Shape change
activates G protein
e) In turn activates
hundreds of phosphodiester molecules
f) This breaks down
intracellular messenger cyclic guanosine monophosphate (cGMP)
4. Photopigments, G proteins and phosphodiesterase
embedded in outer segment disks
a) cGMP found in
cytoplasm between disks and plasma membrane
b) cGMP serves as
link between events in disk membrane and Na+ channels in plasma membrane
c) cGMP is required
to keep channels open
d) When light is
absorbed by photopigment, cGMP is broken down
e) Channels close
at rate of 1000 per second
f) Each photopigment
coupled to many G proteins each to many phosphodiesterases
g) Absorption of
one photon cascades to block entry of over a million Na+molecules
h) Photoreceptor
thus hyperpolarizes
F. Visual Processing in the Vertebrate Retina
1. Retina composed of three layers
of cells
a) Rods and cones
in layer closest to external surface of eyeball
b) Next layer contains
bipolar cells
c) Layer closest
to inside of eye composed of ganglion cells
2. Light must pass through ganglion
and bipolar cells to reach retina
a) Rods and cones
synapse with bipolar cells
b) Bipolar cells
synapse with ganglion cells
c) Flow of sensory
information is opposite the path of light
3. Ganglion cells are stimulated to
fire action potentials
a) When light is
absorbed by particular area of retina
b) Interpreted by
brain as light in specific areas of receptive field
c) Pattern of activity
encodes point-to point map
d) Retina and brain
image objects in visual space
4. Frequency of impulses indicates
light intensity at each point
5. Relative activity of ganglia cells
attached to three types of cones provides information about color
6. Relationship between receptors,
bipolar cells and ganglion cells differs within retina
a) In fovea
(1)
Each cone connects to one bipolar cell, each to one ganglion cell
(2)
Provides high visual acuity in fovea
b) Outside fovea
(1)
Transmission modified by other cells in middle layer
(2)
Horizontal cells channel output of many rods to single bipolar cells
(3)
Amacrine cells connect many ganglion cells outside the fovea
(4)
Carry out extensive processing of visual patterns
c) Peripheral vision
is less acute, more sensitive to low levels of light
d) Effects of many
rods summated on ganglion cells
7. Fovea serves as inspector, periphery
serves as detector
G. Binocular Vision
1. Visual images of vertebrate eyes
a) Eyes on opposite
sides of head, each sees object at different angle
b) Parallax permits
sensitive depth perception, stereoscopic vision
2. Predators have eyes set in front
of head to increase stereoscopic vision
3. Prey have eyes set on sides of
head to enlarge total receptive field
4. Must learn to perceive distance,
not inborn
X. Other Environmental Senses In Vertebrates
A. Heat
1. Electromagnetic radiation with
wavelengths longer than visible light
2. Infrared radiation (longer than
re d) detected as
radiant heat
3. Not possessed by aquatic animals
as water absorbs heat
4. Sensed by pit vipers (including
rattlesnake s)
a) Heat-detecting
pit organs located on either side of the head
b) Perceive heat
emanating from motionless animals in complete darkness
c) Two pit organs
provide stereoscopic information
B. Electricity
1. Not possessed by terrestrial animals,
air does not conduct electricity
2. Some fishes use weak electrical
charges to locate prey animals
3. Electrical discharges produced
by special organs of modified muscle
a) Forms columns
of disk-shaped electroplates
b) One surface has
nerve endings, the other does not
c) When axons generate
action potentials, release excitatory neurotransmitter
d) Causes electroplate
to produce own action potential on surface where they synapse
e) Transient voltage
difference of 150 millivolts on one electroplate
f) Electroplates
line up in series, voltages add up
g) Series arrangement
of disks can produce charges of 500 volts
4. Electric fishes produce weaker
charges to survey their surroundings
a) Sense an object
as it distorts the electrical field
b) Receptors include
ampullae of Lorenzini
C. Magnetism
1. Navigational, used by many birds,
eels, sharks and even bacteria
2. Birds in blind cages orient to
the earth`s magnetic fields
a) Orientation does
not occur in cages shielded by steel
b) Orientation improper
with artificially altered magnetic field
c) Nature of magnetic
receptor poorly understood
XI. An Overview Of Sensory Systems
A. Sensory Systems Utilize a Broad Variety of Cues
B. Individual Vertebrate Systems Differ from One Another