LECTURE PRESENTATIONS

For CAMPBELL BIOLOGY, NINTH EDITION

Jane 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

Nervous Systems

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Chapter 49

Overview: Command and Control Center

• The human brain contains about 100 billion neurons, organized into circuits more complex than the most powerful supercomputers
• A recent advance in brain exploration involves a method for expressing combinations of colored proteins in brain cells, a technique called “brainbow”
• This may allow researchers to develop detailed maps of information transfer between regions of the brain

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Figure 49.1

Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells

• Each single-celled organism can respond to stimuli in its environment
• Animals are multicellular and most groups respond to stimuli using systems of neurons

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• The simplest animals with nervous systems, the cnidarians, have neurons arranged in nerve nets
• A nerve net is a series of interconnected nerve cells
• More complex animals have nerves

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• Nerves are bundles that consist of the axons of multiple nerve cells
• Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring

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Figure 49.2

Nerve net

(a) Hydra (cnidarian)

Radial�nerve

Nerve�ring

(b)

Sea star�(echinoderm)

Eyespot

Brain

Nerve�cords

Transverse�nerve

Brain

Ventral�nerve cord

Segmental�ganglia

(c)

Planarian�(flatworm)

(d) Leech (annelid)

(h)

Salamander�(vertebrate)

(e) Insect (arthropod)

(f) Chiton (mollusc)

(g) Squid (mollusc)

Brain

Brain

Brain

Ventral�nerve cord

Segmental�ganglia

Anterior�nerve ring

Longitudinal�nerve cords

Ganglia

Ganglia

Spinal�cord�(dorsal�nerve�cord)

Sensory�ganglia

Figure 49.2a

Nerve net

(a) Hydra (cnidarian)

Radial�nerve

Nerve�ring

(b) Sea star (echinoderm)

• Bilaterally symmetrical animals exhibit cephalization, the clustering of sensory organs at the front end of the body
• Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS)
• The CNS consists of a brain and longitudinal nerve cords

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Figure 49.2b

Eyespot

Brain

Nerve�cords

Transverse�nerve

Brain

Ventral�nerve cord

Segmental�ganglia

(c) Planarian (flatworm)

(d) Leech (annelid)

• Annelids and arthropods have segmentally arranged clusters of neurons called ganglia

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Figure 49.2c

(e) Insect (arthropod)

(f) Chiton (mollusc)

Brain

Ventral�nerve cord

Segmental�ganglia

Anterior�nerve ring

Longitudinal�nerve cords

Ganglia

• Nervous system organization usually 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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Figure 49.2d

(h) Salamander (vertebrate)

(g) Squid (mollusc)

Brain

Brain

Ganglia

Spinal�cord�(dorsal�nerve�cord)

Sensory�ganglia

• In vertebrates
• The CNS is composed of the brain and spinal cord
• The peripheral nervous system (PNS) is composed of nerves and ganglia

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Organization of the Vertebrate Nervous System

• The spinal cord conveys information from and to the brain
• The spinal cord also produces reflexes independently of the brain
• A reflex is the body’s automatic response to a stimulus
• For example, a doctor uses a mallet to trigger a knee-jerk reflex

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Figure 49.3

Quadriceps�muscle

Cell body of�sensory neuron in�dorsal root�ganglion

Gray �matter

White �matter

Hamstring�muscle

Spinal cord�(cross section)

Sensory neuron

Motor neuron

Interneuron

• Invertebrates usually have a ventral nerve cord while vertebrates have a dorsal spinal cord
• The spinal cord and brain develop from the embryonic nerve cord
• The nerve cord gives rise to the central canal and ventricles of the brain

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Figure 49.4

Central nervous�system (CNS)

Brain

Spinal cord

Peripheral nervous�system (PNS)

Cranial nerves

Ganglia outside�CNS

Spinal nerves

Figure 49.5

Gray matter

White�matter

Ventricles

• The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid
• The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord as well as to provide nutrients and remove wastes

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• The brain and spinal cord contain
• Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons
• White matter, which consists of bundles of myelinated axons

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Glia

• Glia have numerous functions to nourish, support, and regulate neurons
• Embryonic radial glia form tracks along which newly formed neurons migrate
• Astrocytes induce cells lining capilaries in the CNS to form tight junctions, resulting in a blood-brain barrier and restricting the entry of most substances into the brain

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Figure 49.6

CNS

PNS

VENTRICLE

Cilia

Neuron

Astrocyte

Oligodendrocyte

Capillary

Ependymal cell

LM

50 m

Schwann cell

Microglial cell

Figure 49.6a

CNS

PNS

VENTRICLE

Cilia

Neuron

Astrocyte

Oligodendrocyte

Capillary

Ependymal cell

Schwann cell

Microglial cell

Figure 49.6b

LM

50 m

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
• The motor system carries signals to skeletal muscles and is voluntary
• The autonomic nervous system regulates smooth and cardiac muscles and is generally involuntary

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Figure 49.7

Efferent neurons

Afferent neurons

Central Nervous�System�(information processing)

Peripheral Nervous�System

Sensory�receptors

Internal�and external�stimuli

Autonomic�nervous system

Motor�system

Control of�skeletal muscle

Sympathetic�division

Parasympathetic�division

Enteric�division

Control of smooth muscles,�cardiac muscles, glands

• The autonomic nervous system has sympathetic, parasympathetic, and enteric divisions
• The sympathetic regulates arousal and energy generation (“fight-or-flight” response)
• The parasympathetic system has antagonistic effects on target organs and promotes calming and a return to “rest and digest” functions

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• The enteric division controls activity of the digestive tract, pancreas, and gallbladder

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Figure 49.8

Parasympathetic division

Action on target organs:

Constricts pupil�of eye

Stimulates salivary�gland secretion

Constricts�bronchi in lungs

Slows heart

Stimulates activity�of stomach and�intestines

Stimulates activity�of pancreas

Stimulates�gallbladder

Promotes emptying�of bladder

Promotes erection�of genitalia

Cervical

Thoracic

Lumbar

Synapse

Sacral

Sympathetic�ganglia

Sympathetic division

Action on target organs:

Dilates pupil of eye

Accelerates heart

Inhibits salivary�gland secretion

Relaxes bronchi�in lungs

Inhibits activity of�stomach and intestines

Inhibits activity�of pancreas

Stimulates glucose�release from liver;�inhibits gallbladder

Stimulates�adrenal medulla

Inhibits emptying�of bladder

Promotes ejaculation�and vaginal contractions

Figure 49.8a

Parasympathetic division

Action on target organs:

Constricts pupil�of eye

Stimulates salivary�gland secretion

Constricts�bronchi in lungs

Slows heart

Stimulates activity�of stomach and�intestines

Stimulates activity�of pancreas

Stimulates�gallbladder

Cervical

Sympathetic�ganglia

Sympathetic division

Action on target organs:

Dilates pupil of eye

Inhibits salivary�gland secretion

Figure 49.8b

Parasympathetic division

Promotes emptying�of bladder

Promotes erection�of genitalia

Thoracic

Lumbar

Synapse

Sacral

Sympathetic division

Accelerates heart

Relaxes bronchi�in lungs

Inhibits activity of�stomach and intestines

Inhibits activity�of pancreas

Stimulates glucose�release from liver;�inhibits gallbladder

Stimulates�adrenal medulla

Inhibits emptying�of bladder

Promotes ejaculation�and vaginal contractions

Concept 49.2: The vertebrate brain is regionally specialized

• Specific brain structures are particularly specialized for diverse functions
• These structures arise during embryonic development

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Figure 49.9a

Figure 49.9b

Embryonic brain regions

Brain structures in child and adult

Forebrain

Midbrain

Hindbrain

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

Cerebrum (includes cerebral cortex, white�matter, basal nuclei)

Diencephalon (thalamus, hypothalamus,�epithalamus)

Midbrain (part of brainstem)

Pons (part of brainstem), cerebellum

Medulla oblongata (part of brainstem)

Midbrain

Forebrain

Hindbrain

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

Spinal �cord

Cerebrum

Diencephalon

Midbrain

Pons

Medulla�oblongata

Cerebellum

Spinal cord

Child

Embryo at 5 weeks

Embryo at 1 month

Figure 49.9ba

Midbrain

Forebrain

Hindbrain

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

Spinal �cord

Embryo at 5 weeks

Embryo at 1 month

Figure 49.9bb

Cerebrum

Diencephalon

Midbrain

Pons

Medulla�oblongata

Cerebellum

Spinal cord

Child

Figure 49.9c

Adult brain viewed from the rear

Cerebellum

Basal nuclei

Cerebrum

Left cerebral�hemisphere

Right cerebral�hemisphere

Cerebral cortex

Corpus callosum

Figure 49.9d

Diencephalon

Thalamus

Pineal gland

Hypothalamus

Pituitary gland

Spinal cord

Brainstem

Midbrain

Pons

Medulla�oblongata

Arousal and Sleep

• The brainstem and cerebrum control arousal and sleep
• The core of the brainstem has a diffuse network of neurons called the reticular formation
• This regulates the amount and type of information that reaches the cerebral cortex and affects alertness
• The hormone melatonin is released by the pineal gland and plays a role in bird and mammal sleep cycles

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Figure 49.10

Eye

Reticular formation

Input from touch,�pain, and temperature�receptors

Input from nerves�of ears

• Sleep is essential and may play a role in the consolidation of learning and memory
• Dolphins sleep with one brain hemisphere at a time and are therefore able to swim while “asleep”

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Figure 49.11

Low-frequency waves characteristic of sleep

High-frequency waves characteristic of wakefulness

Key

Location

Time: 0 hours

Time: 1 hour

Left�hemisphere

Right�hemisphere

Biological Clock Regulation

• Cycles of sleep and wakefulness are examples of circardian rhythms, daily cycles of biological activity
• Mammalian circadian rhythms rely on a biological clock, molecular mechanism that directs periodic gene expression
• Biological clocks are typically synchronized to light and dark cycles

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• 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

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Figure 49.12

Wild-type hamster

Wild-type hamster with�SCN from  hamster

 hamster

 hamster with SCN�from wild-type hamster

RESULTS

Before�procedures

After surgery�and transplant

Circadian cycle period (hours)

24

23

22

21

20

19

Emotions

• Generation and experience of emotions involves many brain structures including the amygdala, hippocampus, and parts of the thalamus
• These structures are grouped as the limbic system
• The limbic system also functions in motivation, olfaction, behavior, and memory

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Figure 49.13

Hypothalamus

Thalamus

Olfactory�bulb

Amygdala

Hippocampus

• Generation and experience of emotion also require interaction between the limbic system and sensory areas of the cerebrum
• The structure most important to the storage of emotion in the memory is the amygdala, a mass of nuclei near the base of the cerebrum

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Figure 49.14

Nucleus accumbens

Amygdala

Happy music

Sad music

Figure 49.14a

Nucleus accumbens

Happy music

Figure 49.14b

Amygdala

Sad music

Concept 49.3: The cerebral cortex controls voluntary movement and cognitive functions

• The cerebrum, the largest structure in the human brain, is essential for awareness, language, cognition, memory, and consciousness
• Four regions, or lobes (frontal, temporal, occipital, and parietal) are landmarks for particular functions

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Figure 49.15

Motor cortex�(control of�skeletal muscles)

Frontal lobe

Prefrontal cortex�(decision making,�planning)

Broca’s area�(forming speech)

Temporal lobe

Auditory cortex (hearing)

Wernicke’s area�(comprehending language)

Somatosensory cortex�(sense of touch)

Parietal lobe

Sensory association�cortex (integration of�sensory information)

Visual association�cortex (combining�images and object�recognition)

Occipital lobe

Cerebellum

Visual cortex�(processing visual�stimuli and pattern�recognition)

Language and Speech

• Studies of brain activity have mapped areas responsible for language and speech
• Broca’s area in the frontal lobe is active when speech is generated
• Wernicke’s area in the temporal lobe is active when speech is heard
• These areas belong to a larger network of regions involved in language

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Figure 49.16

Hearing�words

Speaking�words

Seeing�words

Generating�words

Max

Min

Lateralization of Cortical Function

• The two hemispheres make distinct contributions to brain function
• The left hemisphere is more adept at language, math, logic, and processing of serial sequences
• The right hemisphere is stronger at pattern recognition, nonverbal thinking, and emotional processing

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• The differences in hemisphere function are called lateralization
• Lateralization is partly linked to handedness
• The two hemispheres work together by communicating through the fibers of the corpus callosum

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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

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• Adjacent areas process features in the sensory input and integrate information from different sensory areas
• Integrated sensory information passes to the prefrontal cortex, which helps plan actions and movements
• In the somatosensory cortex and motor cortex, neurons are arranged according to the part of the body that generates input or receives commands

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Figure 49.17

Frontal lobe

Parietal lobe

Primary�motor cortex

Primary�somatosensory�cortex

Genitalia

Toes

Abdominal�organs

Tongue

Jaw

Lips

Face

Eye

Brow

Neck

Thumb

Fingers

Hand

Wrist

Forearm

Elbow

Shoulder

Trunk

Hip

Knee

Tongue

Pharynx

Jaw

Gums

Teeth

Lips

Face

Nose

Eye

Thumb

Fingers

Hand

Forearm

Elbow

Upper arm

Head

Neck

Trunk

Hip

Leg

Figure 49.17a

Primary�motor cortex

Toes

Tongue

Jaw

Lips

Face

Eye

Brow

Neck

Thumb

Fingers

Hand

Wrist

Forearm

Elbow

Shoulder

Trunk

Hip

Knee

Figure 49.17b

Primary�somatosensory�cortex

Genitalia

Abdominal�organs

Tongue

Pharynx

Jaw

Gums

Teeth

Lips

Face

Nose

Eye

Thumb

Fingers

Hand

Forearm

Elbow

Upper arm

Head

Neck

Trunk

Hip

Leg

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”

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Figure 49.UN01

Evolution of Cognition in Vertebrates

• Previous ideas that a highly convoluted neocortex is required for advanced cognition may be incorrect
• The anatomical basis for sophisticated information processing in birds (without a highly convoluted neocortex) appears to be the clustering of nuclei in the top or outer portion of the brain (pallium)

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Figure 49.18

Human brain

Avian brain

Thalamus

Midbrain

Hindbrain

Cerebellum

Avian brain�to scale

Thalamus

Midbrain

Hindbrain

Cerebellum

Cerebrum (including�cerebral cortex)

Cerebrum�(including pallium)

Concept 49.4 Changes in synaptic connections underlie memory and learning

• Two processes dominate embryonic development of the nervous system
• Neurons compete for growth-supporting factors in order to survive
• Only half the synapses that form during embryo development survive into adulthood

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Neural Plasticity

• Neural plasticity describes the ability of the nervous system to be modified after birth
• Changes can strengthen or weaken signaling at a synapse

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Figure 49.19

N₂

N₁

N₂

N₁

(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.

Memory and Learning

• The formation of memories is an example of neural plasticity
• Short-term memory is accessed via the hippocampus
• The hippocampus also plays a role in forming long-term memory, which is stored in the cerebral cortex
• Some consolidation of memory is thought to occur during sleep

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Long-Term Potentiation

• In the vertebrate brain, a form of learning called long-term potentiation (LTP) involves an increase in the strength of synaptic transmission
• LTP involves glutamate receptors
• If the presynaptic and postsynaptic neurons are stimulated at the same time, the set of receptors present on the postsynaptic membranes changes

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Figure 49.20

PRESYNAPTIC�NEURON

Glutamate

Mg^2

Ca^2

Na^

NMDA�receptor�(closed)

Stored�AMPA�receptor

NMDA receptor (open)

POSTSYNAPTIC�NEURON

(a) Synapse prior to long-term potentiation (LTP)

(b) Establishing LTP

(c) Synapse exhibiting LTP

Depolarization

Action�potential

2

1

3

1

2

3

4

Figure 49.20a

PRESYNAPTIC�NEURON

Glutamate

Mg^2

Ca^2

Na^

NMDA�receptor�(closed)

Stored�AMPA�receptor

NMDA receptor (open)

POSTSYNAPTIC�NEURON

(a) Synapse prior to long-term potentiation (LTP)

Figure 49.20b

(b) Establishing LTP

1

2

3

AMPA�receptor

NMDA receptor

Mg^2

Ca^2

Na^

Figure 49.20c

(c) Synapse exhibiting LTP

Depolarization

Action�potential

AMPA�receptor

NMDA receptor

1

3

4

2

Stem Cells in the Brain

• The adult human brain contains neural stem cells
• In mice, stem cells in the brain can give rise to neurons that mature and become incorporated into the adult nervous system
• Such neurons play an essential role in learning and memory

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Figure 49.21

Concept 49.5: Nervous system disorders can be explained in molecular terms

• Disorders of the nervous system include schizophrenia, depression, drug addiction, Alzheimer’s disease, and Parkinson’s disease
• Genetic and environmental factors contribute to diseases of the nervous system

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Figure 49.22

Genes shared with relatives of�person with schizophrenia

12.5% (3rd-degree relative)

25% (2nd-degree relative)

50% (1st-degree relative)

100%

50

40

30

20

10

0

Relationship to person with schizophrenia

Risk of developing schizophrenia (%)

Individual,�general�population

First cousin

Uncle/aunt

Nephew/�niece

Fraternal�twin

Identical�twin

Grandchild

Half sibling

Parent

Full sibling

Child

Schizophrenia

• About 1% of the world’s population suffers from schizophrenia
• Schizophrenia is characterized by hallucinations, delusions, and other symptoms
• Available treatments focus on brain pathways that use dopamine as a neurotransmitter

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Depression

• Two broad forms of depressive illness are known: major depressive disorder and bipolar disorder
• In major depressive disorder, patients have a persistent lack of interest or pleasure in most activities
• Bipolar disorder is characterized by manic (high-mood) and depressive (low-mood) phases
• Treatments for these types of depression include drugs such as Prozac

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Drug Addiction and the Brain’s Reward System

• The brain’s reward system rewards motivation with pleasure
• Some drugs are addictive because they increase activity of the brain’s reward system
• These drugs include cocaine, amphetamine, heroin, alcohol, and tobacco
• Drug addiction is characterized by compulsive consumption and an inability to control intake

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• Addictive drugs enhance the activity of the dopamine pathway
• Drug addiction leads to long-lasting changes in the reward circuitry that cause craving for the drug

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Figure 49.23

Nicotine�stimulates�dopamine-�releasing�VTA neuron.

Inhibitory neuron

Dopamine-�releasing�VTA neuron

Cerebral�neuron of�reward�pathway

Opium and heroin�decrease activity�of inhibitory�neuron.

Cocaine and�amphetamines�block removal�of dopamine�from synaptic�cleft.

Reward�system�response

Alzheimer’s Disease

• Alzheimer’s disease is a mental deterioration characterized by confusion and memory loss
• Alzheimer’s disease is caused by the formation of neurofibrillary tangles and amyloid plaques in the brain
• There is no cure for this disease though some drugs are effective at relieving symptoms

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Figure 49.24

Amyloid plaque

Neurofibrillary tangle

20 m

Parkinson’s Disease

• Parkinson’s disease is a motor disorder caused by death of dopamine-secreting neurons in the midbrain
• It is characterized by muscle tremors, flexed posture, and a shuffling gait
• There is no cure, although drugs and various other approaches are used to manage symptoms

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Figure 49.UN02

Nerve net

Hydra (cnidarian)

Salamander (vertebrate)

Sensory�ganglia

Spinal�cord�(dorsal�nerve�cord)

Brain

Figure 49.UN03

Capillary

Neuron

Microglial cell

Schwann�cells

Oligodendrocyte

Astrocyte

PNS

CNS

Cilia

VENTRICLE

Ependy-�mal�cell

Figure 49.UN04

Spinal�cord

Cerebral�cortex

Cerebellum

Medulla�oblongata

Pons

Hindbrain

Midbrain

Forebrain

Cerebrum

Thalamus

Hypothalamus

Pituitary gland

Figure 49.UN05