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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITIONJane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
© 2011 Pearson Education, Inc.
Lectures by
Erin Barley
Kathleen Fitzpatrick
Sensory and Motor Mechanisms
Chapter 50
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Overview: Sensing and Acting
• The star-nosed mole can catch insect prey in near
total darkness in as little as 120 milliseconds
• It uses the 11 appendages protruding from its
nose to locate and capture prey
• Sensory processes convey information about an
animal’s environment to its brain, and muscles and
skeletons carry out movements as instructed by
the brain
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Concept 50.1: Sensory receptors transduce
stimulus energy and transmit signals to the
central nervous system
• All stimuli represent forms of energy
• Sensation involves converting energy into a
change in the membrane potential of sensory
receptors
• When a stimulus’s input to the nervous system is
processed a motor response may be generated
• This may involve a simple reflex or more elaborate
processing
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Figure 50.2
Mole forages
along tunnel.
Food present
Food absent
Mole bites.
Mole
moves on.
Motor outputIntegrationSensory input
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Sensory Pathways
• Sensory pathways have four basic functions in
common
– Sensory reception
– Tranduction
– Transmission
– Integration
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Sensory Reception and Transduction
• Sensory reception - detection of stimuli by
sensory receptors
• Sensory receptors interact directly with stimuli,
both inside and outside the body
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(a) Receptor is afferent neuron. (b) Receptor regulates afferent neuron.
To CNS
Afferentneuron
Afferentneuron
To CNS
Receptorprotein
Sensoryreceptor
Stimulus
Neurotransmitter
Sensoryreceptorcell Stimulus
Stimulusleads toneuro-transmitterrelease.
Figure 50.3
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• Sensory transduction is the conversion of
stimulus energy into a change in the membrane
potential of a sensory receptor
• This change in membrane potential is called a
receptor potential
• Receptor potentials are graded potentials; their
magnitude varies with the strength of the stimulus
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Transmission
• After energy has been transduced into a receptor
potential, some sensory cells generate the
transmission of action potentials to the CNS
• Sensory neurons produce action potentials and
their axons extend into the CNS
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• The response of a sensory receptor varies with
intensity of stimuli
• If the receptor is a neuron, a larger receptor
potential results in more frequent action
potentials
• If the receptor is not a neuron, a larger receptor
potential causes more neurotransmitters to be
released
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Figure 50.4a
(a) Single sensory receptor activated
Gentle pressure
Sensory receptor
More pressure
Low frequency of
action potentials per receptor
High frequency of
action potentials per receptor
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Figure 50.4b
(b) Multiple receptors activated
Sensory receptor Gentle pressure
More pressure
Fewer
receptors
activated
More
receptors
activated
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Perception
• Perceptions are the brain’s construction of stimuli
• Stimuli from different sensory receptors travel as
action potentials along dedicated neural pathways
• The brain distinguishes stimuli from different
receptors based on the area in the brain where the
action potentials arrive
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Amplification and Adaptation
• Amplification is the strengthening of
stimulus energy by cells in sensory
pathways• Amplification of action potential from eye to brain is 100,000
greater than the energy of the photons that landed on the retina.
• Sensory adaptation is a decrease in
responsiveness to continued stimulation• Funny, this sweater doesn’t itch anymore….
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Types of Sensory Receptors
• Based on energy transduced, sensory receptors
fall into five categories
– Mechanoreceptors
– Chemoreceptors
– Electromagnetic receptors
– Thermoreceptors
– Pain receptors
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Mechanoreceptors
• Mechanoreceptors sense physical deformation
caused by stimuli such as pressure, stretch,
motion, and sound
• The knee-jerk response is triggered by the
vertebrate stretch receptor, a mechanoreceptor
that detects muscle movement
• The mammalian sense of touch relies on
mechanoreceptors that are dendrites of sensory
neurons
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Gentle pressure, vibration,and temperature
Connectivetissue
Hair Pain
Epidermis
Dermis
Hypodermis
Nerve
Hair movement
Strongpressure
Figure 50.5
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Chemoreceptors
• General chemoreceptors transmit information
about the total solute concentration of a solution
• Specific chemoreceptors respond to individual
kinds of molecules
• When a stimulus molecule binds to a
chemoreceptor, the chemoreceptor becomes
more or less permeable to ions
• The antennae of the male silkworm moth have
very sensitive specific chemoreceptors
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0.1
mm
Figure 50.6
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Electromagnetic Receptors
• Electromagnetic receptors detect
electromagnetic energy such as light, electricity,
and magnetism
• Some snakes have very sensitive infrared
receptors that detect body heat of prey against a
colder background
• Many animals apparently migrate using the Earth’s
magnetic field to orient themselves
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Figure 50.7
(a) Rattlesnake
(b) Beluga whales
Eye
Infraredreceptor
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• Thermoreceptors, which respond to heat or cold,
help regulate body temperature by signaling both
surface and body core temperature
• Mammals have a number of kinds of
thermoreceptors, each specific for a particular
temperature range
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Thermoreceptors
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Pain Receptors
• In humans, pain receptors, or nociceptors, are a
class of naked dendrites in the epidermis
• They respond to excess heat, pressure, or
chemicals released from damaged or inflamed
tissues
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Concept 50.3: Visual receptors on diverse
animals depend on light-absorbing pigments
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Light detectors all contain photoreceptors, cells that
contain light-absorbing pigment molecules
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The Vertebrate Visual System
• In vertebrates the eye detects color and light, but
the brain assembles the information and perceives
the image
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Sclera
Suspensoryligament
Cornea
Iris
Pupil
Aqueoushumor
Lens
Vitreous humor Optic disk
Centralartery andvein of the retina
Opticnerve
Fovea
Retina
Choroid Retina
NeuronsPhotoreceptors
Rod Cone
Opticnervefibers Ganglion
cell
Amacrinecell
Bipolarcell
Horizontal cell
Pigmentedepithelium
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Sclera
Suspensoryligament
Cornea
Iris
Pupil
Aqueoushumor
Lens
Vitreous humor Optic disk
Centralartery andvein of the retina
Opticnerve
Fovea
Retina
ChoroidFigure 50.17aa
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Retina
NeuronsPhotoreceptors
Rod Cone
Opticnervefibers Ganglion
cell
Amacrinecell
Bipolarcell
Horizontal cell
Pigmentedepithelium
Figure 50.17ab
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Rod
Synapticterminal
Cellbody
Outersegment
Disks
Cone
Cone
Rod
CYTOSOL
INSIDE OF DISK
Retinal: cis isomer
Light Enzymes
Retinal: trans isomer
Retinal
OpsinRhodopsin
Figure 50.17b
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Sensory Transduction in the Eye
• Transduction of visual information to the nervous
system begins when light induces the conversion
of cis-retinal to trans-retinal
• Trans-retinal activates rhodopsin, which activates
a G protein, eventually leading to hydrolysis of
cyclic GMP
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• When cyclic GMP breaks down, Na channels
close
• This hyperpolarizes the cell
• The signal transduction pathway usually shuts
off again as enzymes convert retinal back to the
cis form
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Figure 50.18
Light
Inactiverhodopsin
Activerhodopsin
Transducin
Phosphodiesterase
INSIDE OF DISK
Diskmembrane
CYTOSOL
GMP
cGMP
Na
Na
EXTRA-CELLULARFLUID
Plasmamembrane
Dark Light
Hyper-polarization
Time
0
40
70Mem
bra
ne
po
ten
tia
l (m
V)
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• The optic nerves meet at the optic chiasm near
the cerebral cortex
• Sensations from the left visual field of both eyes
are transmitted to the right side of the brain
• Sensations from the right visual field are
transmitted to the left side of the brain
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Processing of Visual Information in the Brain
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Figure 50.20
Rightvisualfield
Leftvisualfield
Righteye
Lefteye
Optic chiasm
Optic nerveLateralgeniculatenucleus
Primaryvisualcortex
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Color Vision
• Among vertebrates, most fish, amphibians, and
reptiles, including birds, have very good color
vision
• Humans and other primates are among the
minority of mammals with the ability to see color
well
• Mammals that are nocturnal usually have a high
proportion of rods in the retina
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• In humans, perception of color is based on three
types of cones, each with a different visual
pigment: red, green, or blue
• These pigments are called photopsins and are
formed when retinal binds to three distinct opsin
proteins
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• Abnormal color vision results from alterations in
the genes for one or more photopsin proteins
• In 2009, researchers studying color blindness in
squirrel monkeys made a breakthrough in gene
therapy
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Structure of striated skeletal muscle
• Muscle Fiber
– muscle cell• divided into sections = sarcomeres
• Sarcomere
– functional unit of muscle contraction
– alternating bands of thin (actin) & thick (myosin) protein filaments
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Muscle filaments & Sarcomere
• Interacting proteins
– thin filaments
• braided strands
– actin
– tropomyosin
– troponin
– thick filaments
• myosin
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Thin filaments: actin• Complex of proteins
– braid of actin molecules & tropomyosin fibers
• tropomyosin fibers secured with troponin molecules
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Thick filaments: myosin• Single protein
– myosin molecule• long protein with globular head
bundle of myosin proteins:
globular heads aligned
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Thick & thin filaments• Myosin tails aligned together & heads pointed
away from center of sarcomere
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Interaction of thick & thin filaments
• Cross bridges
– connections formed between myosin heads
(thick filaments) & actin (thin filaments)
– cause the muscle to shorten (contract)
sarcomere
sarcomere
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Where is ATP needed?
3
4
12
1
1
1
Cleaving ATP ADP allows myosin head to bind to actin filament
thin filament(actin)
thick filament(myosin)
ATP
myosin head
formcrossbridge
binding site
So that’s where those10,000,000 ATPs go!Well, not all of it!
ADP
releasecrossbridge
shortensarcomere
1
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Closer look at muscle cell
multi-nucleated
Mitochondrion
Sarcoplasmicreticulum
Transverse tubules(T-tubules)
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Muscle at rest• Interacting proteins
– at rest, troponin molecules hold tropomyosin fibers
so that they cover the myosin-binding sites on
actin
• troponin has Ca2+ binding sites
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The Trigger: motor neurons • Motor neuron triggers muscle contraction
– release acetylcholine (Ach) neurotransmitter
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• Nerve signal travels
down T-tubule
– stimulates
sarcoplasmic
reticulum (SR) of
muscle cell to
release stored Ca2+
– flooding muscle
fibers with Ca2+
Nerve trigger of muscle action
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• At rest, tropomyosin
blocks myosin-binding
sites on actin
– secured by troponin
• Ca2+ binds to troponin
– shape changecauses movement of troponin
– releasing tropomyosin
– exposes myosin-binding sites on actin
Ca2+ triggers muscle action
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How Ca2+ controls muscle• Sliding filament model
– exposed actin binds to
myosin
– fibers slide past each
other
• ratchet system
– shorten muscle cell
• muscle contraction
– muscle doesn’t relax
until Ca2+ is pumped
back into SR
• requires ATP
ATP
ATP
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Put it all together…1
ATP
2
3
4
5
7
6
ATP
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How it all works…• Action potential causes Ca2+ release from SR
– Ca2+ binds to troponin
• Troponin moves tropomyosin uncovering myosin binding site on actin
• Myosin binds actin– uses ATP to "ratchet" each time
– releases, "unratchets" & binds to next actin
• Myosin pulls actin chain along
• Sarcomere shortens– Z discs move closer together
• Whole fiber shortens contraction!
• Ca2+ pumps restore Ca2+ to SR relaxation!– pumps use ATP
ATP
ATP