Chapter 49 Nervous Systems - biolympiads.com · Central Nervous System (information processing) Peripheral Nervous System Sensory receptors Internal and external stimuli Autonomic

Chapter 49

Nervous Systems

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

© 2011 Pearson Education, Inc.

Figure 49.1

• Each single-celled organism can respond to

stimuli in its environment

• Animals are multicellular and most groups

respond to stimuli using systems of neurons


Concept 49.1: Nervous systems consist of

circuits of neurons and supporting cells

• 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


• 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


Figure 49.2

Nerve net

(a) Hydra (cnidarian)

Radialnerve

Nervering

(b) Sea star(echinoderm)

Eyespot

Brain

Nervecords

Transversenerve

Brain

Ventralnerve cord

Segmentalganglia

(c) Planarian(flatworm)

(d) Leech (annelid)

(h) Salamander(vertebrate)

(e) Insect (arthropod) (f) Chiton (mollusc) (g) Squid (mollusc)

Brain

Brain

Brain

Ventralnerve cord

Segmentalganglia

Anteriornerve ring

Longitudinalnerve cords

Ganglia

Ganglia

Spinalcord(dorsalnervecord)

Sensoryganglia

Figure 49.2a

Nerve net

(a) Hydra (cnidarian)

Radialnerve

Nervering

(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


Figure 49.2b

Eyespot

Brain

Nervecords

Transversenerve

Brain

Ventralnerve cord

Segmentalganglia

(c) Planarian (flatworm) (d) Leech (annelid)

• Annelids and arthropods have segmentally

arranged clusters of neurons called ganglia


Figure 49.2c

(e) Insect (arthropod) (f) Chiton (mollusc)

Brain

Ventralnerve cord

Segmentalganglia

Anteriornerve ring

Longitudinalnerve 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


Figure 49.2d

(h) Salamander (vertebrate)(g) Squid (mollusc)

Brain

Brain

Ganglia

Spinalcord(dorsalnervecord)

Sensoryganglia

• In vertebrates

– The CNS is composed of the brain and spinal

cord

– The peripheral nervous system (PNS) is

composed of nerves and ganglia


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


Quadricepsmuscle

Cell body ofsensory neuron indorsal rootganglion

Gray matter

White matter

Hamstringmuscle

Spinal cord(cross section)

Sensory neuron

Motor neuron

Interneuron

Figure 49.3

• 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


Figure 49.4Central nervoussystem (CNS)

Brain

Spinal cord

Peripheral nervoussystem (PNS)

Cranial nerves

Ganglia outsideCNS

Spinal nerves

Figure 49.5

Gray matter

Whitematter

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


• 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


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 capillaries in the

CNS to form tight junctions, resulting in a

blood-brain barrier and restricting the entry of

most substances into the brain


Figure 49.6CNS 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

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


• 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


Efferent neuronsAfferent neurons

Central NervousSystem

(information processing)

Peripheral NervousSystem

Sensoryreceptors

Internaland external

stimuli

Autonomicnervous system

Motorsystem

Control ofskeletal muscle

Sympatheticdivision

Parasympatheticdivision

Entericdivision

Control of smooth muscles,cardiac muscles, glands

Figure 49.7

• The autonomic nervous system has

sympathetic, parasympathetic, and enteric

divisions

• The sympathetic division regulates arousal

and energy generation (“fight-or-flight”

response)

• The parasympathetic division has

antagonistic effects on target organs and

promotes calming and a return to “rest and

digest” functions

• The enteric division controls activity of the

digestive tract, pancreas, and gallbladder


Parasympathetic division

Action on target organs:

Constricts pupilof eye

Stimulates salivarygland secretion

Constrictsbronchi in lungs

Slows heart

Stimulates activityof stomach and

intestines

Stimulates activityof pancreas

Stimulatesgallbladder

Promotes emptyingof bladder

Promotes erectionof genitalia

Cervical

Thoracic

Lumbar

Synapse

Sacral

Sympatheticganglia

Sympathetic division

Action on target organs:

Dilates pupil of eye

Accelerates heart

Inhibits salivarygland secretion

Relaxes bronchiin lungs

Inhibits activity ofstomach and intestines

Inhibits activityof pancreas

Stimulates glucoserelease from liver;inhibits gallbladder

Stimulatesadrenal medulla

Inhibits emptyingof bladder

Promotes ejaculationand vaginal contractions

Figure 49.8

Concept 49.2: The vertebrate brain is

regionally specialized

• Specific brain structures are particularly

specialized for diverse functions

• These structures arise during embryonic

development


Figure 49.9a

Embryonic brain regions Brain structures in child and adult

Forebrain

Midbrain

Hindbrain

Telencephalon

Diencephalon

Mesencephalon

Metencephalon

Myelencephalon

Cerebrum (includes cerebral cortex, whitematter, 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

Medullaoblongata

Cerebellum

Spinal cord

ChildEmbryo at 5 weeksEmbryo at 1 month

Figure 49.9b

Figure 49.9c

Adult brain viewed from the rear

Cerebellum

Basal nucleiCerebrum

Left cerebralhemisphere

Right cerebralhemisphere

Cerebral cortex

Corpus callosum

Figure 49.9d

Diencephalon

Thalamus

Pineal gland

Hypothalamus

Pituitary gland

Spinal cord

Brainstem

Midbrain

Pons

Medullaoblongata

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


Figure 49.10

Eye

Reticular formation

Input from touch,pain, and temperaturereceptors

Input from nervesof 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”


Figure 49.11

Low-frequency waves characteristic of sleep

High-frequency waves characteristic of wakefulness

Key

Location Time: 0 hours Time: 1 hour

Lefthemisphere

Righthemisphere

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, molecular mechanism that

directs periodic gene expression

• Biological clocks are typically synchronized to

light and dark cycles


• 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


Figure 49.12

Wild-type hamster

Wild-type hamster withSCN from hamster

hamster

hamster with SCNfrom wild-type hamster

RESULTS

Beforeprocedures

After surgeryand transplant

Cir

cad

ian

cycle

pe

rio

d (

ho

urs

)

24

23

22

21

20

19

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

• The limbic system also functions in motivation,

olfaction, behavior, and memory


Figure 49.13

Hypothalamus

Thalamus

Olfactorybulb

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


Figure 49.14

Nucleus accumbens Amygdala

Happy music 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


Figure 49.15

Motor cortex(control ofskeletal 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 associationcortex (integration ofsensory information)

Visual associationcortex (combiningimages and objectrecognition)

Occipital lobe

Cerebellum

Visual cortex(processing visualstimuli and patternrecognition)

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


Figure 49.16

Hearingwords

Speakingwords

Seeingwords

Generatingwords

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


• 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


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


• 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


Figure 49.17

Frontal lobe Parietal lobe

Primarymotor cortex

Primarysomatosensorycortex

GenitaliaToes

Abdominalorgans

Tongue

Jaw

Hip

Kn

ee

Tongue

Pharynx

Head

Neck

Tru

nk

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”


Figure 49.UN01

Phineas Gage

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)


Human brain

Avian brain

Thalamus

Midbrain

Hindbrain Cerebellum

Avian brainto scale

Thalamus

Midbrain

Hindbrain

Cerebellum

Cerebrum (includingcerebral cortex)

Cerebrum(including pallium)

Figure 49.18

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


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


Figure 49.19

N2

N1

N2

N1

(a) Synapses are strengthened or weakened in response toactivity.

(b) If two synapses are often active at the same time, thestrength of the postsynaptic response may increase atboth synapses.

Neural

plasticity

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


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


Figure 49.20PRESYNAPTIC

NEURON

GlutamateMg2

Ca2

Na

NMDAreceptor(closed)

StoredAMPAreceptor

NMDA receptor (open)

POSTSYNAPTICNEURON

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

(b) Establishing LTP

(c) Synapse exhibiting LTP

Depolarization

Actionpotential

2

1

3

1

2

3

4

Figure 49.20a

PRESYNAPTICNEURON

GlutamateMg2

Ca2

Na

NMDAreceptor(closed)

StoredAMPAreceptor

NMDA receptor (open)

POSTSYNAPTICNEURON

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

Figure 49.20b

(b) Establishing LTP

1

23

AMPAreceptor

NMDA receptor

Mg2

Ca2

Na

Figure 49.20c

(c) Synapse exhibiting LTP

Depolarization

Actionpotential

AMPAreceptor

NMDA receptor

13

42

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


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


Figure 49.22

Genes shared with relatives ofperson 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

Ris

k o

f d

eve

lop

ing

sc

hiz

op

hre

nia

(%

)

Ind

ivid

ua

l,g

en

era

lp

op

ula

tio

n

Fir

st

co

usin

Un

cle

/au

nt

Ne

ph

ew

/n

iec

e

Fra

tern

al

twin

Ide

nti

ca

ltw

in

Gra

nd

ch

ild

Ha

lf s

iblin

g

Pa

ren

t

Fu

ll s

iblin

g

Ch

ild

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


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


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


• 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


Figure 49.23Nicotinestimulatesdopamine-releasingVTA neuron.

Inhibitory neuron

Dopamine-releasingVTA neuron

Cerebralneuron ofrewardpathway

Opium and heroindecrease activityof inhibitoryneuron.

Cocaine andamphetaminesblock removalof dopaminefrom synapticcleft.

Rewardsystemresponse

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


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


Documents

Chapter 49 Nervous Systems - biolympiads.com · Central Nervous System (information processing) Peripheral Nervous System Sensory receptors Internal and external stimuli Autonomic