Download Sensory & Motor Mechanism

Chapter 49
Sensory and Motor
Mechanisms
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Sensing and Acting
• Bats use sonar to detect their prey
• Moths, a common prey for bats, can detect the
bat’s sonar and attempt to flee
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Both organisms have complex sensory systems
that facilitate survival
• These systems include diverse mechanisms that
sense stimuli and generate appropriate movement
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Concept 49.1: Sensory receptors transduce stimulus
energy and transmit signals to the central nervous system
• Sensations are action potentials that reach the
brain via sensory neurons
• The brain interprets sensations, giving the
perception of stimuli
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• Sensations and perceptions begin with sensory
reception, detection of stimuli by sensory
receptors
• Exteroreceptors detect outside stimuli
• Interoreceptors detect internal stimuli
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Functions Performed by Sensory Receptors
• All stimuli represent forms of energy
• Sensation involves converting energy into change
in the membrane potential of sensory receptors
• Functions of sensory receptors: sensory
transduction, amplification, transmission, and
integration
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• The stretch receptor in a crayfish is an example of
a sensory receptor
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LE 49-2a
Weak
muscle stretch
Muscle
Stretch
receptor
Membrane
potential (mV)
Dendrites
Strong
muscle stretch
–50 Receptor potential
–50
–70
–70
Action potentials
0
0
–70
–70
Axon
0 1 2 3 4 5 6 7
Time (sec)
Crayfish stretch receptors have
dendrites embedded in abdominal
muscles. When the abdomen bends,
muscles and dendrites stretch, producing a
receptor potential in the stretch receptor. The
receptor potential triggers action potentials
0 1 2 3 4 5 6 7
Time (sec)
in the axon of the stretch receptor. A stronger
stretch produces a larger receptor potential
and higher frequency of action potentials.
• Another sensory receptor is the hair cell, which
detects motion in the vertebrate ear and lateral
line systems of fishes and amphibians
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LE 49-2b
No fluid
movement
“Hairs” of
hair cell
Fluid moving in
one direction
More
neurotransmitter
Neurotransmitter at
synapse
Less
neurotransmitter
–50
–50
–70
Action potentials
0
–70
Membrane
potential (mV)
–50 Receptor potential
Membrane
potential (mV)
Membrane
potential (mV)
Axon
Fluid moving in
other direction
–70
0
Vertebrate hair cells have specialized cilia
or microvilli (“hairs”) that bend when
surrounding fluid moves. Each hair cell
releases an excitatory neurotransmitter
0
–70
–70
0 1 2 3 4 5 6 7
Time (sec)
–70
0 1 2 3 4 5 6 7
Time (sec)
at a synapse with a sensory neuron, which
conducts action potentials to the CNS.
Bending in one direction depolarizes the
hair cell, causing it to release more
0 1 2 3 4 5 6 7
Time (sec)
neurotransmitter and increasing frequency of
action potentials in the sensory neuron. Bending
in the other direction has the opposite effects.
Thus, hair cells respond to the direction of motion
as well as to its strength and speed.
Sensory Transduction
• 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
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• Many sensory receptors are very sensitive, able to
detect the smallest physical unit of stimulus
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Amplification
• Amplification is the strengthening of stimulus
energy by cells in sensory pathways
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Transmission
• After energy has been transduced into a receptor
potential, some sensory cells generate action
potentials, which are transmitted to the CNS
• Sensory cells without axons release
neurotransmitters at synapses with sensory
neurons
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Integration
• Integration of sensory information begins when
information is received
• Integration occurs at all levels of the nervous
system
• Some receptor potentials are integrated through
summation
• Another integration is sensory adaptation,
decreased responsiveness during stimulation
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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 sense of touch in mammals relies on
mechanoreceptors that are dendrites of sensory
neurons
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LE 49-3
Heat
Light
touch
Pain
Cold
Hair
Epidermis
Dermis
Hypodermis
Nerve
Connective
tissue
Hair
movement
Strong
pressure
Chemoreceptors
• General chemoreceptors transmit information
about the total solute concentration of a solution
• Specific chemoreceptors respond to individual
kinds of molecules
• The antennae of the male silkworm moth have
very sensitive specific chemoreceptors
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0.1 mm
LE 49-4
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
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LE 49-5
Eye
Infrared
receptor
This rattlesnake and other pit vipers have a pair of infrared
receptors, one between each eye and nostril. The organs
are sensitive enough to detect the infrared radiation
emitted by a warm mouse a meter away.
Some migrating animals, such as these beluga whales,
apparently sense Earth’s magnetic field and use the
information, along with other cues, for orientation.
• Many mammals appear to use Earth’s magnetic
field lines to orient themselves as they migrate
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Thermoreceptors
• Thermoreceptors, which respond to heat or cold,
help regulate body temperature by signaling both
surface and body core temperature
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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 49.2: The mechanoreceptors involved with hearing
and equilibrium detect settling particles or moving fluid
• Hearing and perception of body equilibrium are
related in most animals
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Hearing and Equilibrium in Mammals
• In most terrestrial vertebrates, sensory organs for
hearing and equilibrium are closely associated in
the ear
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LE 49-8
Middle
ear
Inner ear
Outer ear
Semicircular canals
Stapes
Middle
ear
Incus
Skull bones
Auditory nerve,
to brain
Malleus
Pinna
Tympanic
Auditory membrane
canal
Eustachian
tube
Tympanic
membrane
Oval
window
Cochlea
Round
window
Eustachian tube
Tectorial
membrane
Hair cells
Bone
Cochlea duct
Vestibular
canal
Basilar
membrane
Axons of
To auditory
sensory neurons nerve
Auditory
nerve
Tympanic
canal
Organ of Corti
Hearing
• Vibrating objects create percussion waves in the
air that cause the tympanic membrane to vibrate
• The three bones of the middle ear transmit the
vibrations to the oval window on the cochlea
• These vibrations create pressure waves in the
fluid in the cochlea that travel through the
vestibular canal and strike the round window
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LE 49-9
Cochlea
Stapes
Vestibular
canal
Oval
window
Perilymph
Apex
Base
Round
window
Tympanic
canal
Axons of
sensory
neurons
Basilar
membrane
• Pressure waves in the canal cause the basilar
membrane to vibrate, bending its hair cells
• This bending of hair cells depolarizes their
membranes, sending action potentials that travel
via the auditory nerve to the brain
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• The cochlea can distinguish pitch because the
basilar membrane is not uniform along its length
• Each region vibrates most vigorously at a
particular frequency and leads to excitation of a
specific auditory area of the cerebral cortex
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LE 49-10
Cochlea
(uncoiled)
Basilar
membrane
Apex
(wide and
flexible)
500 Hz (low pitch)
1 kHz
2 kHz
4 kHz
8 kHz
16 kHz
(high pitch)
Base
(narrow and stiff)
Frequency
producing
maximum vibration
Equilibrium
• Several organs of the inner ear detect body
position and balance: the utricle, saccule, and
semicircular canals
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LE 49-11
Semicircular canals
Ampulla
Flow
of endolymph
Flow
of endolymph
Vestibular nerve
Cupula
Hairs
Hair
cell
Vestibule
Nerve fibers
Utricle
Saccule
Body movement
Hearing and Equilibrium in Other Vertebrates
• Like other vertebrates, fishes and amphibians
have inner ears near the brain
• Most fishes and aquatic amphibians also have a
lateral line system along both sides of their body
• The lateral line system contains
mechanoreceptors with hair cells that respond to
water movement
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LE 49-12
Lateral line
Lateral line canal
Scale
Neuromast
Epidermis
Segmental muscles of body wall
Opening of
lateral line canal
Lateral nerve
Cupula
Sensory
hairs
Supporting
cell
Nerve fiber
Hair cell
Concept 49.3: The senses of taste and smell are
closely related in most animals
• Gustation (taste) and olfaction (smell) are
dependent on chemoreceptors that detect specific
chemicals in the environment
• Taste receptors of insects are in sensory hairs
called sensilla, located on feet and in mouthparts
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Number of action potentials
in first second of response
LE 49-13b
Chemoreceptors
50
30
10
0
0.5 M
NaCl
Meat
0.5 M
Sucrose
Stimulus
Honey
Taste in Humans
• In humans, receptor cells for taste are modified
epithelial cells organized into taste buds
• Five taste perceptions: sweet, sour, salty, bitter,
and umami (elicited by glutamate)
• Transduction in taste receptors occurs by several
mechanisms
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LE 49-14
Taste pore
Sugar
molecule
Sensory
receptor
cells
Taste
bud
Tongue
Sensory
neuron
G protein
Adenylyl cyclase
Sugar
Sugar receptor
ATP
cAMP
Protein
kinase A
SENSORY
RECEPTOR
K+
CELL
Synaptic
vesicle
Ca2+
Neurotransmitter
Sensory neuron
Smell in Humans
• Olfactory receptor cells are neurons that line the
upper portion of the nasal cavity
• Binding of odorant molecules to receptors triggers
a signal transduction pathway, sending action
potentials to the brain
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LE 49-15
Brain
Olfactory bulb
Nasal cavity
Bone
Odorant
Epithelial cell
Odorant
receptors
Chemoreceptor
Plasma
membrane
Odorant
Cilia
Mucus
Concept 49.4: Similar mechanisms underlie vision
throughout the animal kingdom
• Many types of light detectors have evolved in the
animal kingdom and may be homologous
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Vision in Invertebrates
• Most invertebrates have a light-detecting organ
• One of the simplest is the eye cup of planarians,
which provides information about light intensity
and direction but does not form images
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The Vertebrate Visual System
• The eyes of vertebrates are camera-like, but they
evolved independently and differ from the singlelens eyes of invertebrates
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Structure of the Eye
• Main parts of the vertebrate eye:
– The sclera: white outer layer, including cornea
– The choroid: pigmented layer
– The conjunctiva: covers outer surface of sclera
– The iris: regulates the pupil
– The retina: contains photoreceptors
– The lens: focuses light on the retina
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LE 49-18
Sclera
Choroid
Retina
Ciliary body
Fovea (center
of visual field)
Suspensory
ligament
Cornea
Iris
Optic
nerve
Pupil
Aqueous
humor
Lens
Vitreous humor
Central artery and
vein of the retina
Optic disk
(blind spot)
• Humans and other mammals focus light by
changing the shape of the lens
Animation: Near and Distance Vision
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LE 49-19
Front view of lens
and ciliary muscle
Choroid
Lens (rounder)
Retina
Ciliary
muscle
Suspensory
ligaments
Near vision (accommodation)
Lens (flatter)
Distance vision
• The human retina contains two types of
photoreceptors: rods and cones
• Rods are light-sensitive but don’t distinguish
colors
• Cones distinguish colors but are not as sensitive
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Sensory Transduction in the Eye
• Each rod or cone contains visual pigments
consisting of a light-absorbing molecule called
retinal bonded to a protein called opsin
• Rods contain the pigment rhodopsin, which
changes shape when absorbing light
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LE 49-20
Rod
Outer
segment
Disks
Inside
of disk
Cell body
cis isomer
Light
Enzymes
Synaptic
terminal
Cytosol
Retinal
Rhodopsin
Opsin
trans isomer
Processing Visual Information
• Processing of visual information begins in the
retina
• Absorption of light by retinal triggers a signal
transduction pathway
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LE 49-21
Light
Active
rhodopsin
INSIDE OF DISK
EXTRACELLULAR
FLUID
PDE
Plasma
membrane
Inactive
rhodopsin
Transducin
Disk
membrane
Membrane
potential (mV)
0
Dark Light
cGMP
–40
GMP
Na+
Hyperpolarization
–70
Time
CYTOSOL
Na+
• In the dark, rods and cones release the
neurotransmitter glutamate into synapses with
neurons called bipolar cells
• Bipolar cells are either hyperpolarized or
depolarized
• In the light, rods and cones hyperpolarize, shutting
off release of glutamate
• The bipolar cells are then either depolarized or
hyperpolarized
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LE 49-22
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 either
depolarized or
hyperpolarized,
depending on
glutamate receptors
Bipolar cell either
hyperpolarized or
depolarized,
depending on
glutamate receptors
• Three other types of neurons contribute to
information processing in the retina: ganglion
cells, horizontal cells, and amacrine cells
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LE 49-23
Retina
Optic nerve
To
brain
Retina
Photoreceptors
Neurons
Cone Rod
Amacrine
cell
Optic
nerve Ganglion
fibers cell
Horizontal
cell
Bipolar
cell
Pigmented
epithelium
• Signals from rods and cones travel from bipolar
cells to ganglion cells
• Axons of ganglion cells form the optic nerves that
transmit sensations from the eyes to the brain
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LE 49-24
Left
visual
field
Left
eye
Optic nerve
Optic chiasm
Lateral
geniculate
nucleus
Primary
visual cortex
Right
visual
field
Right
eye
• Most ganglion cell axons lead to the lateral
geniculate nuclei of the thalamus
• The thalamus relays information to the primary
visual cortex
• Several integrating centers in the cerebral cortex
are active in creating visual perceptions
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Concept 49.5: Animal skeletons function in
support, protection, and movement
• The various animal movements result from
muscles working against a skeleton
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Endoskeletons
• An endoskeleton consists of hard supporting
elements, such as bones, buried in soft tissue
• Endoskeletons are found in sponges,
echinoderms, and chordates
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• A mammalian skeleton has more than 200 bones
• Some are fused; others are connected at joints by
ligaments that allow freedom of movement
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LE 49-26_6
Key
Axial skeleton
Appendicular
skeleton
Shoulder
girdle
Sternum
Rib
Humerus
Skull
Examples
of joints
Head of
humerus
Scapula
Clavicle
Scapula
Ball-and-socket joints, where the humerus
contacts the shoulder girdle and where the femur
contacts the pelvic girdle, enable us to rotate our
arms and legs and move them in several planes.
Vertebra
Radius
Ulna
Humerus
Pelvic
girdle
Carpals
Ulna
Phalanges
Metacarpals
Femur
Hinge joints, such as between the humerus
and the head of the ulna, restrict movement
to a single plane.
Patella
Tibia
Fibula
Ulna
Radius
Pivot joints allow us to rotate our forearm at the
elbow and to move our head from side to side.
Tarsals
Metatarsals
Phalanges
Physical Support on Land
• In addition to the skeleton, muscles and tendons
help support large land vertebrates
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Concept 49.6: Muscles move skeletal parts by
contracting
• The action of a muscle is always to contract
• Skeletal muscles are attached in antagonistic
pairs, with each member of the pair working
against each other
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LE 49-27
Human
Grasshopper
Extensor
muscle
relaxes
Biceps
contracts
Biceps
relaxes
Extensor
muscle
contracts
Forearm
extends
Triceps
contracts
Flexor
muscle
contracts
Forearm
flexes
Triceps
relaxes
Tibia
flexes
Tibia
extends
Flexor
muscle
relaxes
Vertebrate Skeletal Muscle
• Vertebrate skeletal muscle is characterized by a
hierarchy of smaller and smaller units
• A skeletal muscle consists of a bundle of long
fibers running parallel to the length of the muscle
• A muscle fiber is itself a bundle of smaller
myofibrils arranged longitudinally
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• The myofibrils are composed to two kinds of
myofilaments:
– Thin filaments consist of two strands of actin
and one strand of regulatory protein
– Thick filaments are staggered arrays of myosin
molecules
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• Skeletal muscle is also called striated muscle
because the regular arrangement of myofilaments
creates a pattern of light and dark bands
• Each unit is a sarcomere, bordered by Z lines
• Areas that contain the myofilments are the I band,
A band, and H zone
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LE 49-28
Muscle
Bundle of
muscle fibers
Single muscle fiber
(cell)
Nuclei
Plasma membrane
Myofibril
Light
Z line
band Dark band
Sarcomere
TEM
I band
A band
M line
0.5 µm
I band
Thick filaments
(myosin)
Thin filaments
(actin)
Z line
H zone
Sarcomere
Z line
The Sliding-Filament Model of Muscle Contraction
• According to the sliding-filament model, filaments
slide past each other longitudinally, producing
more overlap between thin and thick filaments
• As a result of sliding, the I band and H zone shrink
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LE 49-29
0.5 µm
Z
H
A
Sarcomere
Relaxed muscle fiber
Contracting muscle fiber
Fully contracted muscle fiber
I
• The sliding of filaments is based on interaction
between actin and myosin molecules of the thick
and thin filaments
• 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
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LE 49-30–4
Thick filament
Thin filaments
Thin filament
Myosin head (low-energy
configuration)
Thick
filament
Thin filament moves
toward center of sacomere.
Actin
Myosin head (lowenergy configuration)
Cross-bridge
binding site
Myosin head (highenergy configuration)
Cross-bridge
The Role of Calcium and Regulatory Proteins
• A skeletal muscle fiber contracts only when
stimulated by a motor neuron
• When a muscle is at rest, myosin-binding sites on
the thin filament are blocked by the regulatory
protein tropomyosin
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LE 49-31
Tropomyosin
Ca2+-binding sites
Actin
Troponin complex
Myosin-binding sites blocked.
Ca2+
Myosinbinding site
Myosin-binding sites exposed.
• For a muscle fiber to contract, myosin-binding
sites must be uncovered
• This occurs when calcium ions (Ca2+) bind to a set
of regulatory proteins, the troponin complex
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• 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
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LE 49-32
Motor
neuron axon
Mitochondrion
Synaptic
terminal
T tubule
Ca2+ released
from sarcoplasmic
reticulum
Sarcoplasmic
reticulum
Myofibril
Plasma membrane
of muscle fiber
Sarcomere
• The synaptic terminal of the motor neuron
releases the neurotransmitter acetylcholine
• Acetylcholine depolarizes the muscle, causing it to
produce an action potential
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• Action potentials travel to the interior of the muscle
fiber along transverse (T) tubules
• The action potential along T tubules causes the
sarcoplasmic reticulum to release Ca2+
• The Ca2+ binds to the troponin-tropomyosin
complex on the thin filaments
• This binding exposes myosin-binding sites and
allows the cross-bridge cycle to proceed
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LE 49-33
Synaptic terminal
of motor neuron
Synaptic cleft
PLASMA
MEMBRANE
T TUBULE
SR
ACh
Ca2+
CYTOSOL
Ca2+
Neural Control of Muscle Tension
• Contraction of a whole muscle is graded, which
means that the extent and strength of its
contraction can be voluntarily altered
• 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
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• In a vertebrate skeletal muscle, each branched
muscle fiber is innervated by one motor neuron
• Each motor neuron may synapse with multiple
muscle fibers
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LE 49-34
Spinal cord
Motor
unit 1
Motor
unit 2
Synaptic terminals
Nerve
Motor neuron
cell body
Motor neuron
axon
Muscle
Muscle fibers
Tendon
• A motor unit consists of a single motor neuron and
all the muscle fibers it controls
• 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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LE 49-35
Tension
Tetanus
Summation of
two twitches
Single
twitch
Action
potential
Time
Pair of
action
potentials
Series of action
potentials at
high frequency
• Tetanus is a state of smooth and sustained
contraction produced when motor neurons deliver
a volley of action potentials
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Types of Muscle Fibers
• Skeletal muscle fibers are classified as slow
oxidative, fast oxidative, and fast glycolytic
• These categories are based on their contraction
speed and major pathway for producing ATP
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Other Types of Muscle
• Cardiac muscle, found only in the heart, consists
of striated cells electrically connected by
intercalated discs
• Cardiac muscle can generate action potentials
without neural input
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• In smooth muscle, found mainly in walls of hollow
organs, 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
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Concept 49.7: Locomotion requires energy to
overcome friction and gravity
• Movement is a hallmark of all animals and usually
necessary for finding food or evading predators
• Locomotion is active travel from place to place
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Swimming
• Overcoming friction is a major problem for
swimmers
• Overcoming gravity is easier for swimmers than
for animals that move on land or fly
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Locomotion on Land
• Walking, running, hopping, or crawling on land
requires an animal to support itself and move
against gravity
• Diverse adaptations for locomotion on land have
evolved in vertebrates
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Flying
• Flight requires that wings develop enough lift to
overcome the downward force of gravity
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Comparing Costs of Locomotion
• The energy cost of locomotion depends on the
mode of locomotion and the environment
• Animals specialized for swimming expend less
energy per meter traveled than equivalently sized
animals specialized for flying or running
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LE 49-37
Flying
Running
102
10
1
Swimming
10–1
10–3
1
103
Body mass (g)
106
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