Download File

CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
38
Nervous and
Sensory Systems
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
© 2014 Pearson Education, Inc.
Aim: How can we describe the peripheral and central
nervous system?
Do Now: Describe the main differences between the
peripheral and central nervous system.
Homework: Read chapter 38 and complete concept
questions.
© 2014 Pearson Education, Inc.
Concept 38.1: Nervous systems consist of circuits
of neurons and supporting cells
 The ability to sense and react originated billions of
years ago in prokaryotes
 Hydras, jellies, and cnidarians are the simplest
animals with nervous systems
 In most cnidarians, interconnected nerve cells form
a nerve net, which controls contraction and
expansion of the gastro-vascular cavity
© 2014 Pearson Education, Inc.
Figure 38.2
Eyespot
Brain
Nerve
cords
Nerve net
Transverse
nerve
(a) Hydra (cnidarian)
(b) Planarian (flatworm)
Brain
Brain
Ventral
nerve cord
Spinal
cord
(dorsal
nerve
cord)
Sensory
ganglia
Segmental
ganglia
(c) Insect (arthropod)
© 2014 Pearson Education, Inc.
(d) Salamander (vertebrate)
 In more complex animals, the axons of multiple
nerve cells are often bundled together to form
nerves
 These fibrous structures channel and organize
information flow through the nervous system
 Animals with elongated, bilaterally symmetrical
bodies have even more specialized systems
© 2014 Pearson Education, Inc.
 Cephalization is an evolutionary trend toward a
clustering of sensory neurons and interneurons at
the anterior
 Nonsegmented worms have the simplest clearly
defined central nervous system (CNS), consisting
of a small brain and longitudinal nerve cords
© 2014 Pearson Education, Inc.
 Annelids and arthropods have segmentally arranged
clusters of neurons called ganglia
 In vertebrates:
 The CNS is composed of the brain and spinal cord
 The peripheral nervous system (PNS) is composed
of nerves and ganglia
© 2014 Pearson Education, Inc.
Glia
 Glia have numerous functions to nourish, support,
and regulate neurons:
 Embryonic radial glia form tracks along which newly
formed neurons migrate
 Astrocytes (star-shaped glial cells) induce cells
lining capillaries in the CNS to form tight junctions,
resulting in a blood-brain barrier
© 2014 Pearson Education, Inc.
Figure 38.3
CNS
PNS
Neuron
VENTRICLE
Cilia
Oligodendrocyte
Schwann cell
Microglial cell
Capillary
Ependymal
cell
Astrocytes
50 m
Intermingling of
astrocytes with
neurons (blue)
© 2014 Pearson Education, Inc.
LM
Figure 38.3a
Astrocytes
50 m
Intermingling of
astrocytes with
neurons (blue)
© 2014 Pearson Education, Inc.
LM
Organization of the Vertebrate Nervous System
 The spinal cord runs lengthwise inside the vertebral
column (the spine)
 The spinal cord conveys information to and from the
brain
 It can also act independently of the brain as part of
simple nerve circuits that produce reflexes, the
body’s automatic responses to certain stimuli
© 2014 Pearson Education, Inc.
Figure 38.4
Central nervous
system (CNS)
Brain
Spinal cord
Peripheral nervous
system (PNS)
Cranial
nerves
Ganglia
outside
CNS
Spinal
nerves
© 2014 Pearson Education, Inc.
 The brain and spinal cord contain:
 Gray matter, which consists mainly of neuron cell
bodies and glia
 White matter, which consists of bundles of
myelinated axons
© 2014 Pearson Education, Inc.
 The CNS contains fluid-filled spaces called ventricles
in the brain and the central canal in the spinal cord
 Cerebrospinal fluid is formed in the brain and
circulates through the ventricles and central canal
and drains into the veins
 It supplies the CNS with nutrients and hormones and
carries away wastes
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
 The PNS has two efferent components:
 The motor system carries signals to skeletal
muscles and can be voluntary or involuntary
 The autonomic nervous system regulates smooth
and cardiac muscles and is generally involuntary
© 2014 Pearson Education, Inc.
 The autonomic nervous system has sympathetic,
parasympathetic, and enteric divisions
 The enteric division controls activity of the
digestive tract, pancreas, and gallbladder
 The sympathetic division regulates the “fight-orflight” response
 The parasympathetic division generates opposite
responses in target organs and promotes calming
and a return to “rest and digest” functions
© 2014 Pearson Education, Inc.
Aim: How can we describe the various parts of the
brain and how they function?
Do Now: Describe the different functions of the left and
right hemispheres of the brain?
© 2014 Pearson Education, Inc.
Concept 38.2: The vertebrate brain is regionally
specialized
 The human brain contains 100 billion neurons
 These cells are organized into circuits that can
perform highly sophisticated information processing,
storage, and retrieval
© 2014 Pearson Education, Inc.
Figure 38.6b
Brain structures in child and adult
Embryonic brain regions
Telencephalon
Cerebrum (includes cerebral cortex,
white matter, basal nuclei)
Diencephalon
Diencephalon (thalamus,
hypothalamus, epithalamus)
Mesencephalon
Midbrain (part of brainstem)
Metencephalon
Pons (part of brainstem), cerebellum
Myelencephalon
Medulla oblongata (part of brainstem)
Forebrain
Midbrain
Hindbrain
Midbrain
Hindbrain
Mesencephalon
Metencephalon
Diencephalon
Cerebrum
Diencephalon
Myelencephalon
Midbrain
Pons
Forebrain
Embryo at 1 month
© 2014 Pearson Education, Inc.
Telencephalon
Medulla
oblongata
Cerebellum
Spinal cord
Spinal
cord
Embryo at 5 weeks
Child
Figure 38.6c
Left cerebral
hemisphere
Right cerebral
hemisphere
Cerebral
cortex
Corpus
callosum
Cerebrum
Basal
nuclei
Cerebellum
Adult brain viewed from the rear
© 2014 Pearson Education, Inc.
Figure 38.6d
Diencephalon
Thalamus
Pineal gland
Hypothalamus
Pituitary gland
Brainstem
Midbrain
Pons
Medulla
oblongata
Spinal cord
© 2014 Pearson Education, Inc.
Arousal and Sleep
 Arousal is a state of awareness of the external world
 Sleep is a state in which external stimuli are
received but not consciously perceived
 Arousal and sleep are controlled in part by clusters
of neurons in the midbrain and pons
© 2014 Pearson Education, Inc.
 Sleep is an active state for the brain and is regulated
by the biological clock and regions of the forebrain,
which regulate the intensity and duration of sleep
 Some animals have evolutionary adaptations that
allow for substantial activity during sleep
 For example, in dolphins, only one side of the brain
is asleep at a time
© 2014 Pearson Education, Inc.
Biological Clock Regulation
 Cycles of sleep and wakefulness are examples of
circadian rhythms, daily cycles of biological activity
 Mammalian circadian rhythms rely on a biological
clock, a molecular mechanism that directs periodic
gene expression
 Biological clocks are typically synchronized to light
and dark cycles and maintain a roughly 24-hour
cycle
© 2014 Pearson Education, Inc.
 In mammals, circadian rhythms are coordinated by
a group of neurons in the hypothalamus called the
suprachiasmatic nucleus (SCN)
 The SCN acts as a pacemaker, synchronizing the
biological clock
© 2014 Pearson Education, Inc.
Emotions
 Generation and experience of emotions involve
many brain structures including the amygdala,
hippocampus, and parts of the thalamus
 These structures are grouped as the limbic system
 Generation and experience of emotion also require
interaction between the limbic system and sensory
areas of the cerebrum
 The brain structure that is most important for
emotional memory is the amygdala
© 2014 Pearson Education, Inc.
The Brain’s Reward System and Drug Addiction
 The brain’s reward system provides motivation for
activities that enhance survival and reproduction
 The brain’s reward system is dramatically affected
by drug addiction
 Drug addiction is characterized by compulsive
consumption and an inability to control intake
© 2014 Pearson Education, Inc.
 Addictive drugs such as cocaine, amphetamine,
heroin, alcohol, and tobacco enhance the activity of
the dopamine pathway
 Drug addiction leads to long-lasting changes in the
reward circuitry that cause craving for the drug
© 2014 Pearson Education, Inc.
Functional Imaging of the Brain
 Functional imaging methods are transforming our
understanding of normal and diseased brains
 In positron-emission tomography (PET) an injection
of radioactive glucose enables a display of metabolic
activity
© 2014 Pearson Education, Inc.
 In functional magnetic resonance imaging, fMRI, the
subject lies with his or her head in the center of a
large, doughnut-shaped magnet
 Brain activity is detected by changes in local oxygen
concentration
 Applications of fMRI include monitoring recovery
from stroke, mapping abnormalities in migraine
headaches, and increasing the effectiveness of brain
surgery
© 2014 Pearson Education, Inc.
Concept 38.3: The cerebral cortex controls
voluntary movement and cognitive functions
 The cerebrum is essential for language, cognition,
memory, consciousness, and awareness of our
surroundings
 The cognitive functions reside mainly in the cortex,
the outer layer
 Four regions, or lobes (frontal, temporal, occipital,
and parietal), are landmarks for particular functions
© 2014 Pearson Education, Inc.
Figure 38.11
Motor cortex (control
of skeletal muscles)
Frontal lobe
Somatosensory cortex
(sense of touch)
Parietal lobe
Prefrontal cortex
(decision
making,
planning)
Broca’s area
(forming speech)
Temporal lobe
Auditory cortex
(hearing)
Cerebellum
Wernicke’s area
(comprehending language)
© 2014 Pearson Education, Inc.
Sensory association
cortex (integration
of sensory
information)
Visual association
cortex (combining
images and object
recognition)
Occipital lobe
Visual cortex
(processing visual
stimuli and pattern
recognition)
Language and Speech
 The mapping of cognitive functions within the cortex
began in the 1800s
 Broca’s area, in the left frontal lobe, is active when
speech is generated
 Wernicke’s area, in the posterior of the left frontal
lobe, is active when speech is heard
© 2014 Pearson Education, Inc.
Lateralization of Cortical Function
 The left side of the cerebrum is dominant regarding language,
math, and logical operations
 The right hemisphere is dominant in recognition of faces and
patterns, spatial relations, and nonverbal thinking
 The establishment of differences in hemisphere function is
called lateralization
 The two hemispheres exchange information through the
fibers of the corpus callosum
 Severing this connection results in a “split brain” effect, in
which the two hemispheres operate independently
© 2014 Pearson Education, Inc.
Information Processing
 The cerebral cortex receives input from sensory
organs and somatosensory receptors
 Somatosensory receptors provide information
about touch, pain, pressure, temperature, and the
position of muscles and limbs
 The thalamus directs different types of input to
distinct locations
© 2014 Pearson Education, Inc.
Frontal Lobe Function
 Frontal lobe damage may impair decision making
and emotional responses but leave intellect and
memory intact
 The frontal lobes have a substantial effect on
“executive functions”
© 2014 Pearson Education, Inc.
Evolution of Cognition in Vertebrates
 In nearly all vertebrates, the brain has the same
number of divisions
 The hypothesis that higher order reasoning requires
a highly convoluted cerebral cortex has been
experimentally refuted
 The anatomical basis for sophisticated information
processing in birds (without a highly convoluted
neocortex) appears to be a cluster of nuclei in the
top or outer portion of the brain (pallium)
© 2014 Pearson Education, Inc.
Aim: How can we explain how organisms maintain
equilibrium?
Do Now: What human structure/organ contributes to
maintaining equilibrium the most?
© 2014 Pearson Education, Inc.
Neural Plasticity
 Neural plasticity is the capacity of the nervous
system to be modified after birth
 Changes can strengthen or weaken signaling at a
synapse
 Autism, a developmental disorder, involves a
disruption of activity-dependent remodeling at
synapses
 Children with autism display impaired communication
and social interaction, as well as stereotyped and
repetitive behaviors
© 2014 Pearson Education, Inc.
Figure 38.14
N1
N1
N2
N2
(a) Synapses are strengthened or weakened in response to
activity.
(b) If two synapses are often active at the same time, the strength
of the postsynaptic response may increase at both synapses.
© 2014 Pearson Education, Inc.
Memory and Learning
 Neural plasticity is essential to formation of memories
 Short-term memory is accessed via the
hippocampus
 The hippocampus also plays a role in forming longterm memory, which is stored in the cerebral cortex
 Some consolidation of memory is thought to occur
during sleep
© 2014 Pearson Education, Inc.
Concept 38.4: Sensory receptors transduce
stimulus energy and transmit signals to the central
nervous system
 Much brain activity begins with sensory input
 A sensory receptor detects a stimulus, which alters
the transmission of action potentials to the CNS
 The information is decoded in the CNS, resulting in
a sensation
© 2014 Pearson Education, Inc.
Sensory Reception and Transduction
 A sensory pathway begins with sensory reception,
detection of stimuli by sensory receptors
 Sensory receptors, which detect stimuli, interact directly
with stimuli, both inside and outside the body
 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; their magnitude varies with
the strength of the stimulus
© 2014 Pearson Education, Inc.
Figure 38.15
(a) Receptor is afferent neuron.
(b) Receptor regulates afferent neuron.
To CNS
To CNS
Afferent
neuron
Afferent
neuron
Receptor
protein
Neurotransmitter
Sensory
receptor
Stimulus
© 2014 Pearson Education, Inc.
Sensory
receptor
cell
Stimulus
leads to
neurotransmitter
release.
Stimulus
Transmission
 Sensory information is transmitted as nerve impulses
or action potentials
 Neurons that act directly as sensory receptors
produce action potentials and have an axon that
extends into the CNS
 Non-neuronal sensory receptors form chemical
synapses with sensory neurons
 They typically respond to stimuli by increasing the
rate at which the sensory neurons produce action
potentials
© 2014 Pearson Education, Inc.
 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 neurotransmitter to be
released
© 2014 Pearson Education, Inc.
Perception
 Perception is the brain’s construction of stimuli
 Action potentials from sensory receptors travel
along neurons that are dedicated to a particular
stimulus
 The brain thus distinguishes stimuli, such as light or
sound, solely by the path along which the action
potentials have arrived
 Amplification is the strengthening of stimulus
energy by cells in sensory pathways
 Sensory adaptation is a decrease in
responsiveness to continued stimulation
© 2014 Pearson Education, Inc.