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Support, Movement, Senses… The Brain…
References- chapters 48, 49
© 2014 Pearson Education, Inc.
Nervous systems consist of circuits of neurons
and supporting cells
§  By the Cambrian explosion, specialized systems of
neurons enabled animals to sense and respond to
their environments
§  The simplest nervous systems (in cnidarians) have
neurons arranged in nerve nets- a series of
interconnected nerve cells
§  More complex animals have nerves, in which axons
of multiple neurons are bundled together
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Figure 49.2
Eyespot
Nerve net
(a) Hydra (cnidarian)
Brain
Ventral
nerve
cord
Segmental
ganglia
(e) Insect (arthropod)
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Brain
Brain
Nerve
cords
Radial
nerve
Nerve
ring
Ventral
nerve cord
Transverse
nerve
(b) Sea star (echinoderm)
(c) Planarian (flatworm)
Ganglia
Anterior
nerve ring
Segmental
ganglia
Brain
Ganglia
(d) Leech (annelid)
Brain
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
Longitudinal
nerve cords
(f) Chiton (mollusc)
(g) Squid (mollusc)
(h) Salamander
(vertebrate)
§  Bilaterally symmetrical animals exhibit cephalization,
clustering of sensory organs at the front end of body
§  The simplest cephalized animals, flatworms, have a
central nervous system (CNS)- consisting of a brain
and longitudinal nerve cords
§  The peripheral nervous system (PNS) consists of
neurons carrying information into and out of the CNS
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Figure 49.6
Central
nervous
system
(CNS)
Brain
Spinal
cord
Cranial nerves
Ganglia
outside CNS
Spinal nerves
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Peripheral
nervous
system
(PNS)
§  Nervous system organization correlates with lifestyle
§  Sessile molluscs (for example, clams and chitons)
have simple systems, whereas more complex
molluscs (for example, octopuses and squids) have
more sophisticated systems
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The Central Nervous System
§  The spinal cord conveys information to and from the
brain and generates basic patterns of locomotion
§  Spinal cord also produces reflexes independently of
the brain
§  A reflex is the body’s automatic response to a
stimulus
§  Ex: mallet triggers a knee-jerk reflex
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Figure 49.7
Cell body of
sensory neuron in
dorsal root ganglion
Gray
matter
Quadriceps
muscle
Spinal cord
(cross section)
Hamstring
muscle
Key
Sensory neuron
Motor neuron
Interneuron
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White
matter
The Peripheral Nervous System
§  The PNS transmits information to and from the CNS
and regulates movement and the internal
environment
§  In the PNS, afferent neurons transmit information to
the CNS and efferent neurons transmit information
away from the CNS
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§  The PNS has two efferent components: the motor
system and the autonomic nervous system
§  Motor system carries signals to skeletal muscles and
is voluntary
§  Autonomic nervous system regulates smooth and
cardiac muscles and is generally involuntary
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§  The autonomic nervous system has sympathetic and
parasympathetic divisions
§  Sympathetic division regulates arousal and energy
generation (“fight-or-flight” response)
§  Parasympathetic division has antagonistic effects on
target organs and promotes calming and a return to
“rest and digest” functions
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Figure 49.9
Parasympathetic division
Sympathetic division
Constricts pupil of eye
Dilates pupil of eye
Stimulates salivary
gland secretion
Inhibits salivary
gland secretion
Constricts
bronchi in lungs
Cervical
Sympathetic
ganglia
Relaxes bronchi in lungs
Slows heart
Accelerates heart
Stimulates activity of
stomach and intestines
Inhibits activity of
stomach and intestines
Stimulates activity
of pancreas
Thoracic
Inhibits activity
of pancreas
Stimulates glucose
release from liver;
inhibits gallbladder
Stimulates gallbladder
Lumbar
Stimulates
adrenal medulla
Promotes emptying
of bladder
Promotes erection
of genitalia
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Inhibits emptying
of bladder
Sacral
Synapse
Promotes ejaculation and
vaginal contractions
The vertebrate brain is regionally specialized
§  Brain structures are specialized for diverse functions
§  Forebrain has activities
including processing
olfactory input, regulating
sleep, learning
§  Midbrain coordinates
routing of sensory input
§  Hindbrain controls
involuntary activities,
coordinates motor activities
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§  Comparison of vertebrates shows that relative sizes
of particular brain regions vary
§  These size differences reflect the relative importance
of the particular brain function
§  Evolution has resulted in a close match between
structure and function
Lamprey
ANCESTRAL
VERTEBRATE
Shark
Ray-finned
fish
Amphibian
Crocodilian
Key
Forebrain
Midbrain
Hindbrain
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Bird
Mammal
Figure 49.11b
Embryonic brain regions
Brain structures in child and adult
Telencephalon
Cerebrum (includes cerebral cortex, basal nuclei)
Diencephalon
Diencephalon (thalamus, hypothalamus, epithalamus)
Forebrain
Midbrain
Mesencephalon
Midbrain (part of brainstem)
Metencephalon
Pons (part of brainstem), cerebellum
Myelencephalon
Medulla oblongata (part of brainstem)
Hindbrain
Cerebrum
Mesencephalon
Metencephalon
Midbrain
Hindbrain
Embryo at 1 month
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Diencephalon
Myelencephalon
Midbrain
Pons
Medulla
oblongata
Telencephalon
Cerebellum
Spinal
cord
Embryo at 5 weeks
Spinal cord
Child
Brainstem
Forebrain
Diencephalon
Arousal and Sleep
§  The brainstem and cerebrum control arousal and
sleep; sleep also regulated by biological clock
§  Sleep is essential for learning and memory
§  Some animals have evolutionary adaptations allowing
substantial activity during sleep
§  Dolphins sleep with one brain hemisphere at a time
and are therefore able to swim while “asleep”
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Biological Clock Regulation
§  Cycles of sleep and wakefulness are examples of
circadian rhythms, daily cycles of biological activity
§  Such rhythms rely on a biological clock, a molecular
mechanism that directs periodic gene expression and
cellular activity
§  Biological clocks are typically synchronized to light
and dark cycles
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Emotions
§  Generation and experience of emotions involve many
brain structures- the amygdala, hippocampus,
thalamus- grouped as the limbic system
Thalamus
Hypothalamus
Olfactory
bulb
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Amygdala
Hippocampus
The cerebral cortex controls voluntary
movement and cognitive functions
§  The cerebrum, the largest structure in the human brain, is
essential for language, cognition, memory, consciousness,
and awareness of our surroundings
Skeletal muscle control
Sense of touch
Frontal lobe
Integration of sensory information
Parietal lobe
Decision making, planning
Combining images and object recognition
Forming speech
Temporal lobe
Occipital lobe
Hearing
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Cerebellum
Language comprehension
Processing visual stimuli, pattern recognition
Figure 49.18
Max
Hearing
words
Seeing
words
Min
Speaking
words
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Generating
words
Lateralization of Function
§  The two hemispheres make distinct
contributions to brain function
§  Left hemisphere more adept at
language, math, logic
§  Right hemisphere stronger at
facial and pattern recognition,
spatial relations, nonverbal
thinking
§  The two hemispheres work together
by communicating through fibers of
the corpus callosum
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Many nervous system disorders can be
explained in molecular terms
§  Disorders of the nervous system include
schizophrenia, depression, drug addiction,
Alzheimer’s disease, Parkinson’s disease
§  Genetic and environmental factors contribute to
diseases of the nervous system
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The Brain’s Reward System and Drug Addiction
§  Some drugs are addictive because they increase
activity of the brain’s dopamine reward (“pleasure”)
system
§  Cocaine, amphetamine, heroin, alcohol, and tobacco
§  Drug addiction is characterized by compulsive
consumption and an inability to control intake
§  Drug addiction leads to long-lasting changes in the
reward circuitry that cause craving for the drug
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Alzheimer’s Disease
§  Mental deterioration characterized by confusion and
memory loss- caused by formation of neurofibrillary
tangles and amyloid plaques in the brain
§  No cure for this disease- some drugs relieve symptoms
Amyloid plaque
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Neurofibrillary tangle
20 µm
Parkinson’s Disease
§  A motor disorder caused by death of dopaminesecreting neurons in the midbrain
§  Characterized by muscle tremors, flexed posture, and
a shuffling gait
§  No cure, although drugs and various other
approaches may manage symptoms
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Senses
§  The star-nosed mole can catch insect prey in near total
darkness in as little as 120 milliseconds
§  Uses 11 pairs of appendages protruding from its nose to
locate and capture prey
§  Sensory processes convey information about an animal’s
environment to its brain; muscles carry out movements
as instructed by the brain
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Sensory receptors transduce stimulus energy
and transmit signals to the CNS
§  All stimuli represent forms
of energy
§  When a stimulus’s input to
the nervous system is
processed, a motor
response may be
generated
§  May involve a simple reflex
or elaborate processing
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Mole forages
along tunnel
Mole
moves on
Food absent
OR
Mole bites
Food present
Sensory input
Integration
Motor output
§  Sensory pathways have four basic functions in
common:
§  Sensory reception- detection of stimuli by sensory
receptors
§  Transduction- conversion of stimulus energy;
magnitude varies with stimuli intensity
§  Transmission- to the CNS
§  Integration- brain distinguishes stimuli from different
receptors based on where they arrive in the brain
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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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Hearing and Equilibrium in Mammals
§  In most terrestrial
vertebrates, sensory
organs for hearing and
equilibrium are closely
associated in the ear
§  For both senses, settling
particles or moving fluid
is detected by
mechanoreceptors
Ciliated
receptor
cells
Cilia
Statolith
Sensory
nerve fibers
(axons)
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The statocyst is used to sense equilibrium
Hearing
§  Vibrating objects create
percussion waves in air, causing
tympanic membrane vibration
Sensory neurons
§  The three bones of the middle
ear transmit vibrations of moving
air to the cochlea
§  Vibrations create pressure waves
in fluid in the cochlea that travel
through the vestibular canal
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Cochlea
Tympanic
membrane
Hearing
§  The ear conveys information about
§  Volume- the amplitude of the sound wave
§  Pitch- the frequency of the sound wave
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Hearing and Equilibrium in Other Vertebrates
§  Unlike mammals, fishes have only inner ears (near the brain)
§  Fishes also have a lateral line system that contains
mechanoreceptors with hair cells to detect water movement
SURROUNDING WATER
Lateral line
epidermis
Side view
Lateral
line
Top view
Lateral line canal
Water flow
Opening of
lateral line canal
Cross
section
Nerve
Lateral nerve
FISH BODY WALL
Scale
Segmental
muscle
Water
flow
Cupula
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Supporting
cell
Nerve fiber
Action
potentials
Sensory
hairs
Hair cell
Diverse visual receptors of animals depend on
light-absorbing pigments
§  Animals use diverse organs for vision, but the
underlying mechanism for capturing light is the
same, suggesting a common evolutionary origin
§  Light detectors range from simple clusters of cells
that detect direction and intensity of light, to complex
organs that form images
§  Light detectors all contain photoreceptors, cells that
contain light-absorbing pigment molecules
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Light-Detecting Organs
§  Most invertebrates have a light-detecting organ
§  One of the simplest light-detecting organs is that of
planarians
§  A pair of ocelli called eyespots are located near the head
§  These allow planarians to move away from light and seek
shaded locations
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Compound Eyes
§  Insects and crustaceans have compound eyes,
which consist of up to several thousand light
detectors called ommatidia
§  Compound eyes are effective at detecting movement
§  Insects have excellent color vision, and some can
see into the ultraviolet range
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Single-Lens Eyes
§  Among invertebrates, single-lens eyes are found in
some jellies, polychaetes, spiders, and molluscs
§  Work like a camera- iris changes the pupil diameter
to control how much light enters
§  Eyes of all vertebrates have a single lens- eye
detects color and light, but brain assembles
information and perceives an image
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Figure 50.17a
Retina
Choroid
Sclera
Photoreceptors
Retina
Suspensory
ligament
Fovea
Neurons
Rod Cone
Cornea
Iris
Optic
nerve
Pupil
Aqueous
humor
Lens
Vitreous
humor
Optic
disk
Central
artery and
vein of
the retina
Optic
nerve
fibers
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Horizontal
Amacrine
cell
cell
Bipolar
Ganglion
cell
cell
Pigmented
epithelium
Color Vision
§  Among vertebrates, most fish, amphibians, and
reptiles, including birds, have good color vision
§  In humans, perception of color is based on three
types of cones (photoreceptors), each with a
different visual pigment: red, green, or blue
§  Mammals that are nocturnal usually have a high
proportion of rods (photoreceptors that differentiate
objects in low light) in the retina
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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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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; In mammals, there are five
taste perceptions: sweet, sour, salty, bitter, umami
§  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
located on feet and in mouth parts
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The physical interaction of protein filaments is
required for muscle function
Muscle
§  Muscle activity is a response
to input from the nervous
system
§  Vertebrate skeletal muscle
moves bones and the body
Bundle of
muscle fibers
Nuclei
Single muscle fiber (cell)
Plasma membrane
§  Glycolysis and aerobic
respiration generate the
energy (ATP) needed to
sustain muscle contraction
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Myofibril
§  Amyotrophic lateral sclerosis (ALS), formerly called
Lou Gehrig’s disease, interferes with the excitation
of skeletal muscle fibers; this disease is usually fatal
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Nervous 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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Figure 50.31
Spinal cord
Motor
unit 1
Motor
unit 2
Synaptic terminals
Nerve
Motor neuron
cell body
Motor
neuron
axon
Muscle
Muscle fibers
Tendon
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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
§  Smooth muscle is 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
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Skeletal systems transform muscle contraction
into locomotion
Human forearm
(internal skeleton)
§  Skeletons function in
support, protection, and
movement
Flexor
muscle
Triceps
Extension
Biceps
Triceps
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Extensor
muscle
Flexion
§  The skeleton provides a
rigid structure to which
muscles attach
Biceps
Grasshopper tibia
(external skeleton)
Key
Contracting muscle
Extensor
muscle
Flexor
muscle
Relaxing muscle
Types of Skeletal Systems
§  The three main types of skeletons are
§  Hydrostatic skeletons (lack hard parts)
§  Exoskeletons (external hard parts)
§  Endoskeletons (internal hard parts)
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§  The skeletons of small and large animals have
different proportions, underlying function
§  In mammals and birds, the position of legs relative
to the body is very important in determining how
much weight the legs can bear
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Types of Locomotion
§  Most animals are capable of locomotion- active
travel from place to place
§  In locomotion, energy is expended to overcome
friction and gravity
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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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§  Air poses relatively little resistance for land
locomotion
§  Maintaining balance is a prerequisite to walking,
running, or hopping
§  Crawling poses a different challenge; a crawling
animal must exert more energy to overcome friction
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Swimming
§  In water, friction is a bigger problem than gravity
§  Fast swimmers usually have a sleek, torpedo-like
shape to minimize friction
§  Animals swim in diverse ways
§  Paddling with their legs as oars
§  Jet propulsion
§  Undulating their body and tail from side to side, or up
and down
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Flying
§  Active flight requires that wings develop enough lift
to overcome the downward force of gravity
§  Many flying animals have adaptations that reduce
body mass
§  Ex: birds have no urinary bladder or teeth, and have
relatively large bones with air-filled regions
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Energy cost (cal/kg ・ m)
(log scale)
Figure 50.UN01a
Flying
Running
102
10
1
Swimming
10-1
10-3
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1
103
Body mass (g) (log scale)
106