Sensory and Motor Mechanisms

1
Chapter 50
Sensory and Motor Mechanisms
2
Figure 50.1
3
Figure 50.2
Mole bites.
Food present
Mole foragesalong tunnel.
Molemoves on.
Food absent
Motor output
Integration
Sensory input
4
Sensory Pathways

• Sensory pathways have four basic functions in
  common
• Sensory reception
• Tranduction
• Transmission
• Integration

5
Figure 50.3
(a) Receptor is afferent neuron.
(b) Receptor regulates afferent neuron.
To CNS
To CNS
Afferentneuron
Afferentneuron
Receptorprotein
Neurotransmitter
Sensoryreceptor
Stimulusleads toneuro-transmitterrelease.
Stimulus
Sensoryreceptorcell
Stimulus
6
Figure 50.4a
(a) Single sensory receptor activated
Gentle pressure
Low frequency ofaction potentials per receptor
Sensory receptor
More pressure
High frequency ofaction potentials per receptor
7
Figure 50.4b
(b) Multiple receptors activated
Sensory receptor
Gentle pressure
Fewerreceptorsactivated
More pressure
Morereceptorsactivated
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Perception

• Perceptions are the brains 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

9
Amplification and Adaptation

• Amplification is the strengthening of stimulus
  energy by cells in sensory pathways
• Sensory adaptation is a decrease in
  responsiveness to continued stimulation

10
Types of Sensory Receptors

• Based on energy transduced, sensory receptors
  fall into five categories
• Mechanoreceptors
• Chemoreceptors
• Electromagnetic receptors
• Thermoreceptors
• Pain receptors

11
Figure 50.5
Connectivetissue
Gentle pressure, vibration,and temperature
Pain
Hair
Epidermis
Dermis
Strongpressure
Hypodermis
Nerve
Hair movement
12
CHEMORECEPTORS IN A MOTH
0.1 mm
13
ELECTROMAG-NETIC DETECTORS
Eye
Infraredreceptor
(a) Rattlesnake
(b) Beluga whales
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Concept 50.2 The mechanoreceptors responsible
for hearing and equilibrium detect moving fluid
or settling particles

• Hearing and perception of body equilibrium are
  related in most animals
• For both senses, settling particles or moving
  fluid is detected by mechanoreceptors

15
Sensing Gravity and Sound in Invertebrates

• Most invertebrates maintain equilibrium using
  mechanoreceptors located in organs called
  statocysts
• Statocysts contain mechanoreceptors that detect
  the movement of granules called statoliths

16
Figure 50.8
Ciliatedreceptorcells
Cilia
Statolith
Sensorynerve fibers(axons)
17
Figure 50.9
Tympanicmembrane
1 mm
18
Hearing and Equilibrium in Mammals

• In most terrestrial vertebrates, sensory organs
  for hearing and equilibrium are closely
  associated in the ear

19
Figure 50.10
Outer ear
Middle ear
Inner ear
Skullbone
Stapes
Semicircularcanals
Bone
Cochlearduct
Incus
Auditorynerve
Malleus
Auditory nerveto brain
Vestibularcanal
Tympaniccanal
Cochlea
Organof Corti
Ovalwindow
Eustachiantube
Auditorycanal
Pinna
Roundwindow
Tympanicmembrane
Tectorial membrane
1 ?m
Hair cells
Axons ofsensoryneurons
To auditorynerve
Basilarmembrane
Bundled hairs projecting from a hair cell
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Figure 50.10a
Outer ear
Middle ear
Inner ear
Skullbone
Stapes
Semicircularcanals
Incus
Malleus
Auditory nerveto brain
Cochlea
Ovalwindow
Eustachiantube
Auditorycanal
Pinna
Roundwindow
Tympanicmembrane
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Figure 50.11
Hairs ofhair cell
Moreneuro-trans-mitter
Neurotrans-mitter atsynapse
Lessneuro-trans-mitter
?50
?50
Sensoryneuron
?50
Receptor potential
?70
?70
?70
Membranepotential (mV)
Membranepotential (mV)
Membranepotential (mV)
Action potentials
0
0
0
Signal
Signal
Signal
?70
?70
?70
0
0
1
2
3
4
5
6
7
0
1
2
3
4
5
6
7
1
2
3
4
5
6
7
Time (sec)
Time (sec)
Time (sec)
(b) Bending of hairs in one direction
(c) Bending of hairs in other direction
(a) No bending of hairs
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Figure 50.12
C
A
B
Point C
6,000 Hz
Axons ofsensory neurons
3
Apex
Oval window
0
B
Vestibularcanal
Stapes
C
1,000 Hz
3
A
Relative motion of basilar membrane
Cochlea
0
Point B
100 Hz
Tympanicmembrane
3
Basilarmembrane
Base
Roundwindow
0
Tympaniccanal
10
30
20
0
Distance from oval window (mm)
Point A
(a)
(b)
23

• The ear conveys information about
• Volume, the amplitude of the sound wave
• Pitch, the frequency of the sound wave
• The cochlea can distinguish pitch because the
  basilar membrane is not uniform along its length
• Each region of the basilar membrane is tuned to a
  particular vibration frequency

24
Equilibrium

• Several organs of the inner ear detect body
  movement, position, and balance
• The utricle and saccule contain granules called
  otoliths that allow us to perceive position
  relative to gravity or linear movement
• Three semicircular canals contain fluid and can
  detect angular movement in any direction

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Figure 50.13
Semicircularcanals
PERILYMPH
Cupula
Fluidflow
Vestibularnerve
Hairs
Haircell
Vestibule
Nervefibers
Utricle
Body movement
Saccule
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Figure 50.14
Lateral line
Cross section
SURROUNDING WATER
Opening oflateral linecanal
Lateral line canal
Scale
Epidermis
Cupula
Sensoryhairs
Hair cell
Supportingcell
Segmental muscle
Lateral nerve
Nerve fiber
FISH BODY WALL
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Figure 50.15
LIGHT
DARK
(a)
Light
Photoreceptor
Ocellus
Nerve tobrain
Visualpigment
Screeningpigment
Ocellus
(b)
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Figure 50.16
2 mm
(a) Fly eyes
Cornea
Lens
Crystallinecone
Rhabdom
Photoreceptor
Axons
Ommatidium
(b) Ommatidia
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Figure 50.17a
Choroid
Retina
Sclera
Retina
Photoreceptors
Neurons
Suspensoryligament
Fovea
Rod
Cone
Cornea
Iris
Opticnerve
Pupil
Aqueoushumor
Centralartery andvein of the retina
Lens
Vitreous humor
Optic disk
Horizontal cell
Amacrinecell
Opticnervefibers
Pigmentedepithelium
Ganglioncell
Bipolarcell
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Figure 50.17b
CYTOSOL
Rod
Synapticterminal
Cellbody
Outersegment
Disks
Retinal cis isomer
Light
Enzymes
Cone
Rod
Retinal trans isomer
Cone
Retinal
Rhodopsin
Opsin
INSIDE OF DISK
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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

32

• 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

33
Figure 50.18
INSIDE OF DISK
EXTRA-CELLULARFLUID
Light
Diskmembrane
Activerhodopsin
Phosphodiesterase
Plasmamembrane
CYTOSOL
cGMP
Transducin
Inactiverhodopsin
GMP
Na?
Light
Dark
0
Hyper-polarization
Membranepotential (mV)
?40
Na?
?70
Time
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Figure 50.19
Dark Responses
Light Responses
Rhodopsin inactive
Rhodopsin active
Na? channels open
Na? channels closed
Rod depolarized
Rod hyperpolarized
Glutamate released
No glutamate released
Bipolar cell eitherdepolarized
orhyperpolarized,depending onglutamate
receptors
Bipolar cell eitherhyperpolarized
ordepolarized,depending onglutamate receptors
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Figure 50.20
Rightvisualfield
Optic chiasm
Righteye
Lefteye
Primaryvisualcortex
Optic nerve
Leftvisualfield
Lateralgeniculatenucleus
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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
• Why would so many mammals have deficient color
  seeing ability?

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Gene therapy for vision
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The Visual Field

• The brain processes visual information and
  controls what information is captured
• Focusing occurs by changing the shape of the lens
• The fovea is the center of the visual field and
  contains no rods, but a high density of cones

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Figure 50.22
(b) Distance vision
(a) Near vision (accommodation)
Ciliary musclesrelax, and borderof choroid
movesaway from lens.
Ciliary musclescontract, pullingborder of
choroidtoward lens.
Choroid
Retina
Suspensoryligaments pullagainst lens.
Suspensoryligamentsrelax.
Lens becomesthicker androunder, focusingon
nearby objects.
Lens becomesflatter, focusing ondistant objects.
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Concept 50.4 The senses of taste and smell rely
on similar sets of sensory receptors

• In terrestrial animals
• Gustation (taste) is dependent on the detection
  of chemicals called tastants
• Olfaction (smell) is dependent on the detection
  of odorant molecules
• In aquatic animals there is no distinction
  between taste and smell
• Taste receptors of insects are in sensory hairs
  called sensilla, located on feet and in mouth
  parts

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Figure 50.24
Papilla
Papillae
Tastebuds
(a) Tongue
Key
Taste bud
Sweet
Salty
Tastepore
Sour
Bitter
Umami
Sensoryneuron
Sensoryreceptor cells
Foodmolecules
(b) Taste buds
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Figure 50.25
Brain
Olfactorybulb
Odorants
Nasal cavity
Bone
Epithelialcell
Receptors for differentodorants
Chemo-receptor
Plasmamembrane
Cilia
Odorants
Mucus
43
Figure 50.26
Muscle
Bundle ofmuscle fibers
Nuclei
Single muscle fiber (cell)
Plasma membrane
Myofibril
Z lines
Sarcomere
TEM
0.5 ?m
Thickfilaments(myosin)
M line
Thinfilaments(actin)
Z line
Z line
Sarcomere
44
Figure 50.26a
Muscle
Bundle ofmuscle fibers
Nuclei
Single muscle fiber (cell)
Plasma membrane
Myofibril
Z lines
Sarcomere
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Figure 50.26b
Z lines
Sarcomere
TEM
0.5 ?m
Thickfilaments(myosin)
M line
Thinfilaments(actin)
Z line
Z line
Sarcomere
46
Figure 50.27
Sarcomere
0.5 ?m
Z
Z
M
Relaxedmuscle
Contractingmuscle
Fully contractedmuscle
Contractedsarcomere
47

• The sliding of filaments relies on interaction
  between actin and myosin
• The head of a myosin molecule binds to an actin
  filament, forming a cross-bridge and pulling the
  thin filament toward the center of the sarcomere
• Muscle contraction requires repeated cycles of
  binding and release

48
Figure 50.28
Thinfilaments
Thick filament
Thin filament
Myosin head (low-energy configuration)
ATP
ATP
Thickfilament
Myosin-binding sites
Thin filament movestoward center of sarcomere.
Actin
ADP
Myosin head (high-energy configuration
Myosin head (low-energy configuration)
P i
ADP
P i
Cross-bridge
ADP
P i
49
The Role of Calcium and Regulatory Proteins

• The regulatory protein tropomyosin and the
  troponin complex, a set of additional proteins,
  bind to actin strands on thin filaments when a
  muscle fiber is at rest
• This prevents actin and myosin from interacting

50
Figure 50.29
Ca2?-binding sites
Tropomyosin
Actin
Troponin complex
(a) Myosin-binding sites blocked
Ca2?
Myosin-binding site
(b) Myosin-binding sites exposed
51

• For a muscle fiber to contract, myosin-binding
  sites must be uncovered
• This occurs when calcium ions (Ca2) bind to the
  troponin complex and expose the myosin-binding
  sites
• Contraction occurs when the concentration of Ca2
  is high muscle fiber contraction stops when the
  concentration of Ca2 is low

52

• The stimulus leading to contraction of a muscle
  fiber is an action potential in a motor neuron
  that makes a synapse with the muscle fiber
• The synaptic terminal of the motor neuron
  releases the neurotransmitter acetylcholine
• Acetylcholine depolarizes the muscle, causing it
  to produce an action potential

53
Figure 50.30
Synapticterminal
Axon ofmotor neuron
T tubule
Mitochondrion
Sarcoplasmicreticulum (SR)
Myofibril
Plasmamembraneof muscle fiber
Ca2? released from SR
Sarcomere
Synaptic terminal of motor neuron
T tubule
Synaptic cleft
Plasma membrane
Sarcoplasmicreticulum (SR)
ACh
Ca2?
Ca2? pump
ATP
CYTOSOL
Ca2?
54
Figure 50.30a
Synapticterminal
Axon ofmotor neuron
T tubule
Mitochondrion
Sarcoplasmicreticulum (SR)
Myofibril
Plasmamembraneof muscle fiber
Ca2? released from SR
Sarcomere
55

• Action potentials travel to the interior of the
  muscle fiber along transverse (T) tubules
• The action potential along T tubules causes the
  sarcoplasmic reticulum (SR) to release Ca2
• The Ca2 binds to the troponin complex on the
  thin filaments
• This binding exposes myosin-binding sites and
  allows the cross-bridge cycle to proceed

56
Figure 50.30b
Synaptic terminal of motor neuron
T tubule
Plasma membrane
Synaptic cleft
Sarcoplasmicreticulum (SR)
ACh
Ca2?
Ca2? pump
ATP
CYTOSOL
Ca2?
57
Nervous Control of Muscle Tension

• There are two basic mechanisms by which the
  nervous system produces graded contractions
• Varying the number of fibers that contract
• Varying the rate at which fibers are stimulated
• In vertebrates, each motor neuron may synapse
  with multiple muscle fibers, although each fiber
  is controlled by only one motor neuron
• A motor unit consists of a single motor neuron
  and all the muscle fibers it controls

58
Figure 50.31
Spinal cord
Motorunit 1
Motorunit 2
Synaptic terminals
Nerve
Motor neuroncell body
Motor neuronaxon
Muscle
Muscle fibers
Tendon
59

• Recruitment of multiple motor neurons results in
  stronger contractions
• A twitch results from a single action potential
  in a motor neuron
• More rapidly delivered action potentials produce
  a graded contraction by summation

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Figure 50.32
Tetanus
Summation oftwo twitches
Tension
Singletwitch
Time
Actionpotential
Series of actionpotentials athigh frequency
Pair ofactionpotentials
61

• Oxidative and Glycolytic Fibers
• Oxidative fibers rely mostly on aerobic
  respiration to generate ATP
• These fibers have many mitochondria, a rich blood
  supply, and a large amount of myoglobin
• Myoglobin is a protein that binds oxygen more
  tightly than hemoglobin does

62

• Glycolytic fibers use glycolysis as their primary
  source of ATP
• Glycolytic fibers have less myoglobin than
  oxidative fibers and tire more easily
• In poultry and fish, light meat is composed of
  glycolytic fibers, while dark meat is composed of
  oxidative fibers

63

• Fast-Twitch and Slow-Twitch Fibers
• Slow-twitch fibers contract more slowly but
  sustain longer contractions
• All slow-twitch fibers are oxidative
• Fast-twitch fibers contract more rapidly but
  sustain shorter contractions
• Fast-twitch fibers can be either glycolytic or
  oxidative

64

• Most skeletal muscles contain both slow-twitch
  and fast-twitch muscles in varying ratios
• Some vertebrates have muscles that twitch at
  rates much faster than human muscles
• In producing its characteristic mating call, the
  male toadfish can contract and relax certain
  muscles more than 200 times per second

65
Figure 50.33
66
Other Types of Muscle

• In addition to skeletal muscle, vertebrates have
  cardiac muscle and smooth muscle
• Cardiac muscle, found only in the heart, consists
  of striated cells electrically connected by
  intercalated disks
• Cardiac muscle can generate action potentials
  without neural input

67

• In smooth muscle, found mainly in walls of hollow
  organs such as those of the digestive tract,
  contractions are relatively slow and may be
  initiated by the muscles themselves
• Contractions may also be caused by stimulation
  from neurons in the autonomic nervous system

68
Figure 50.34
Human forearm(internal skeleton)
Grasshopper tibia(external skeleton)
Extensormuscle
Biceps
Flexion
Flexormuscle
Triceps
Biceps
Extensormuscle
Extension
Flexormuscle
Triceps
Key
Relaxing muscle
Contracting muscle
69
Types of Skeletal Systems

• The three main types of skeletons are
• Hydrostatic skeletons (lack hard parts,
  pressurized, fluid-filled compartments, e.g.
  worms)
• Exoskeletons (external hard parts, chitin-based
  cuticle)
• Endoskeletons (internal, mineralized connective
  tissue)

70
Figure 50.35
Longitudinalmuscle relaxed(extended)
Circularmusclecontracted
Circularmusclerelaxed
Longitudinalmusclecontracted
Bristles
Head end
Head end
Head end
71
Figure 50.36
Typesof joints
Skull
Clavicle
Ball-and-socketjoint
Shoulder girdle
Scapula
Sternum
Rib
Hinge joint
Humerus
Vertebra
Pivot joint
Radius
Ulna
Pelvic girdle
Carpals
Phalanges
Metacarpals
Femur
Patella
Tibia
Fibula
Tarsals
Metatarsals
Phalanges
72
Figure 50.37
Ball-and-socket joint
Pivot joint
Hinge joint
Head ofhumerus
Humerus
Scapula
Ulna
Ulna
Radius
73
Is this possible?
74
Size and Scale of Skeletons

• An animals body structure must support its size
• The weight of a body increases with the cube of
  its dimensions while the strength of that body
  increases with the square of its dimensions

75
Energy-efficient locomotion on land stored
elastic potential energy in tendons. Same
energy at low speeds and high speeds
76
Energy costs of locomotion
RESULTS
Flying
Running
102
10
Energy cost (cal/kg? m)(log scale)
1
Swimming
10?1
1
106
10?3
103
Body mass (g) (log scale)