The Nervous SystemThe Nervous System

Nervous systemsNervous systems

Perform the three overlapping functions of Perform the three overlapping functions of sensory input, integration, and motor sensory input, integration, and motor outputoutput

Peripheral nervous system (PNS).Peripheral nervous system (PNS). Sensory receptors a responsive to external Sensory receptors a responsive to external

and internal stimuli.and internal stimuli. Such sensory input is conveyed to integration Such sensory input is conveyed to integration

centers.centers. Where in the input is interpreted an associated with a Where in the input is interpreted an associated with a

response.response.

Fig. 48.1

Motor outputMotor output is the conduction of signals is the conduction of signals from integration centers to effector cells.from integration centers to effector cells. Effector cellsEffector cells carry out the body’s response carry out the body’s response

to a stimulus.to a stimulus.

The The central nervous system (CNS)central nervous system (CNS) is is responsible for integration.responsible for integration.

The signals of the nervous system are The signals of the nervous system are conducted by conducted by nervesnerves..

Networks of neuronsNetworks of neurons

Neuron Structure and Synapses.Neuron Structure and Synapses. The neuron is the structural and functional The neuron is the structural and functional

unit of the nervous system.unit of the nervous system. Nerve impulses are conducted along a neuron.Nerve impulses are conducted along a neuron.

Dentrite Dentrite cell body cell body axon hillock axon hillock axon axon Some axons are insulated by a myelin sheath.Some axons are insulated by a myelin sheath.

Fig. 48.2

Axonal EndingsAxonal Endings

Axon endings are called synaptic Axon endings are called synaptic terminals.terminals. They contain neurotransmitters which conduct They contain neurotransmitters which conduct

a signal across a synapse.a signal across a synapse. A synapse is the junction between a presynaptic A synapse is the junction between a presynaptic

and postsynaptic neuron.and postsynaptic neuron.

A Simple Nerve Circuit – the Reflex Arc.A Simple Nerve Circuit – the Reflex Arc. A A reflexreflex is an autonomic response. is an autonomic response.

Fig. 48.3

A A ganglionganglion is a cluster of nerve cell is a cluster of nerve cell bodies within the PNS.bodies within the PNS.

A A nucleusnucleus is a cluster of nerve cell bodies is a cluster of nerve cell bodies within the CNS.within the CNS.

Neurons differ in terms of both Neurons differ in terms of both function and shapefunction and shape

Fig. 48.4

Types of Nerve CircuitsTypes of Nerve Circuits

Single presynaptic neuron Single presynaptic neuron several several postsynaptic neurons.postsynaptic neurons.

Several presynaptic neurons Several presynaptic neurons single single postsynaptic neuron.postsynaptic neuron.

Circular paths.Circular paths.

Supporting Cells (Glia)Supporting Cells (Glia)

There are several types of glia.There are several types of glia. Astrocytes are found within the CNS.Astrocytes are found within the CNS.

Structural and metabolic support.Structural and metabolic support. By inducing the formation of tight junctions By inducing the formation of tight junctions

between capillary cells astrocytes help form the between capillary cells astrocytes help form the blood-brain barrier.blood-brain barrier.

Like neurons, astrocytes communicate with one Like neurons, astrocytes communicate with one another via chemical signals.another via chemical signals.

Myelin SheathMyelin Sheath Oligodendrocytes Oligodendrocytes are found within the CNS.are found within the CNS.

Form a myelin sheath by insulating axons.Form a myelin sheath by insulating axons.

Schwann cellsSchwann cells are found within the PNS. are found within the PNS. Form a myelin sheath by insulating axons.Form a myelin sheath by insulating axons.

Fig. 48.5

Every cell has a voltageEvery cell has a voltage

Membrane potential, across its plasma Membrane potential, across its plasma membrane membrane

A membrane potential is a localized A membrane potential is a localized electrical gradient across membrane.electrical gradient across membrane. Anions are more concentrated within a cell.Anions are more concentrated within a cell. Cations are more concentrated in the Cations are more concentrated in the

extracellular fluid.extracellular fluid.

Measuring Membrane Potentials.Measuring Membrane Potentials.

Fig. 48.6a

An unstimulated cell usually have a An unstimulated cell usually have a resting resting potentialpotential of -70mV. of -70mV.

Maintaining a Maintaining a Membrane PotentialMembrane Potential

Cations.Cations. K+ the principal intracellular cation.K+ the principal intracellular cation. Na+ is the principal extracellular cation.Na+ is the principal extracellular cation.

Anions.Anions. Proteins, amino acids, sulfate, and phosphate Proteins, amino acids, sulfate, and phosphate

are the principal intracellular anions.are the principal intracellular anions. Cl– is principal extracellular anion.Cl– is principal extracellular anion.

Ungated ion channels allow ions to diffuse Ungated ion channels allow ions to diffuse across the plasma membrane.across the plasma membrane. These channels are always open.These channels are always open.

This diffusion does not achieve an This diffusion does not achieve an equilibrium since sodium-potassium pump equilibrium since sodium-potassium pump transports these ions against their transports these ions against their concentration gradients.concentration gradients.

Fig. 48.7

Changes in the Changes in the membrane potentialmembrane potential

Excitable cells have the ability to generate Excitable cells have the ability to generate large changes in their membrane large changes in their membrane potentials.potentials. Gated ion channels open or close in response Gated ion channels open or close in response

to stimuli.to stimuli. The subsequent diffusion of ions leads to a change The subsequent diffusion of ions leads to a change

in the membrane potential.in the membrane potential.

Gated ChannelsGated Channels

Types of gated ions.Types of gated ions. Chemically-gated ion channelsChemically-gated ion channels open or open or

close in response to a chemical stimulus.close in response to a chemical stimulus. Voltage-gated ion channelsVoltage-gated ion channels open or close in open or close in

response to a change in membrane potential.response to a change in membrane potential.

At the DendritesAt the Dendrites

Graded Potentials: Hyperpolarization and Graded Potentials: Hyperpolarization and DepolarizationDepolarization Graded potentialsGraded potentials are changes in membrane are changes in membrane

potentialpotential

Hyperpolarization.Hyperpolarization. Gated KGated K++ channels channels

open open K K++ diffuses diffuses out of the cell out of the cell the the membrane potential membrane potential becomes more becomes more negative.negative.

Fig. 48.8a

Depolarization.Depolarization. Gated NaGated Na++ channels channels

open open Na Na++ diffuses diffuses into the cell into the cell the the membrane potential membrane potential becomes less becomes less negative.negative.

Fig. 48.8b

The Action Potential: The Action Potential: All or Nothing All or Nothing Depolarization.Depolarization. If graded potentials If graded potentials

sum to sum to -55mV a -55mV a threshold potentialthreshold potential is achieved.is achieved. This triggers an This triggers an action action

potentialpotential.. Axons only.Axons only.

Fig. 48.8c

Chemical or electrical communication Chemical or electrical communication between cells occurs at synapsesbetween cells occurs at synapses

Electrical Synapses.Electrical Synapses. Action potentials travels directly from the Action potentials travels directly from the

presynaptic to the postsynaptic cells via gap presynaptic to the postsynaptic cells via gap junctions.junctions.

Chemical Synapses.Chemical Synapses. More common than electrical synapses.More common than electrical synapses. Postsynaptic chemically-gated channels exist Postsynaptic chemically-gated channels exist

for ions such as Nafor ions such as Na++, K, K++, and Cl, and Cl--.. Depending on which gates open the postsynaptic Depending on which gates open the postsynaptic

neuron can depolarize or hyperpolarize.neuron can depolarize or hyperpolarize.

Fig. 48.12

Neural integration occurs at the cellNeural integration occurs at the cell

Excitatory postsynaptic potentials Excitatory postsynaptic potentials (EPSP) (EPSP) depolarize the postsynaptic depolarize the postsynaptic neuron.neuron. The binding of neurotransmitter to The binding of neurotransmitter to

postsynaptic receptors open gated channels postsynaptic receptors open gated channels that allow Nathat allow Na++ to diffuse into and K to diffuse into and K++ to diffuse to diffuse out of the cell.out of the cell.

Inhibitory postsynaptic potentialInhibitory postsynaptic potential

Inhibitory postsynaptic potential (IPSP) Inhibitory postsynaptic potential (IPSP) hyperpolarize the postsynaptic neuron.hyperpolarize the postsynaptic neuron. The binding of neurotransmitter to The binding of neurotransmitter to

postsynaptic receptors open gated channels postsynaptic receptors open gated channels that allow K+ to diffuse out of the cell and/or that allow K+ to diffuse out of the cell and/or Cl- to diffuse into the cell.Cl- to diffuse into the cell.

SummationSummation: graded potentials (EPSPs and : graded potentials (EPSPs and IPSPs) are summed to either depolarize or IPSPs) are summed to either depolarize or hyperpolarize a postsynaptic neuron.hyperpolarize a postsynaptic neuron.

Fig. 48.14

Acetylcholine.Acetylcholine. Excitatory to skeletal muscle.Excitatory to skeletal muscle. Inhibitory to cardiac muscle.Inhibitory to cardiac muscle. Secreted by the CNS, PNS, and at Secreted by the CNS, PNS, and at

vertebrate neuromuscular junctions.vertebrate neuromuscular junctions.

Same neurotransmitter can produce Same neurotransmitter can produce different effects on different types of cellsdifferent effects on different types of cells

Biogenic AminesBiogenic Amines.. EpinephrineEpinephrine and and norepinephrinenorepinephrine..

Can have excitatory or inhibitory effects.Can have excitatory or inhibitory effects.Secreted by the CNS and PNS.Secreted by the CNS and PNS.Secreted by the adrenal glands.Secreted by the adrenal glands.

DopamineDopamine

Generally excitatory; may be inhibitory at Generally excitatory; may be inhibitory at some sites.some sites. Widespread in the brain.Widespread in the brain. Affects sleep, mood, attention, and learning.Affects sleep, mood, attention, and learning.

Secreted by the CNS and PNS.Secreted by the CNS and PNS. A lack of dopamine in the brain is A lack of dopamine in the brain is

associated with Parkinson’s disease.associated with Parkinson’s disease. Excessive dopamine is linked to Excessive dopamine is linked to

schizophrenia.schizophrenia.

SerotoninSerotonin

Generally inhibitory.Generally inhibitory. Widespread in the brain.Widespread in the brain. Affects sleep, mood, attention, and learningAffects sleep, mood, attention, and learning

Secreted by the CNS.Secreted by the CNS.

Amino AcidsAmino Acids

Gamma aminobutyric acid (GABA).Gamma aminobutyric acid (GABA). Inhibitory.Inhibitory. Secreted by the CNS and at invertebrate Secreted by the CNS and at invertebrate

neuromuscular junctions.neuromuscular junctions.

Glycine.Glycine. Inhibitory.Inhibitory. Secreted by the CNS.Secreted by the CNS.

Amino AcidsAmino Acids

Glutamate.Glutamate. Excitatory.Excitatory.

Secreted by the CNS and at invertebrate Secreted by the CNS and at invertebrate neuromuscular junctions. neuromuscular junctions.

Aspartate.Aspartate. Excitatory.Excitatory. Secreted by the CNSSecreted by the CNS

NeuropeptidesNeuropeptides

Substance P.Substance P. Excitatory.Excitatory. Secreted by the CNS and PNS.Secreted by the CNS and PNS.

Met-enkephalin (an endorphin).Met-enkephalin (an endorphin). Generally inhibitory.Generally inhibitory. Secreted by the CNS.Secreted by the CNS.

GassesGasses

Gasses that act as local regulators.Gasses that act as local regulators. Nitric oxide.Nitric oxide. Carbon monoxide.Carbon monoxide.

Vertebrate nervous systemsVertebrate nervous systems

Central nervous system (CNS).Central nervous system (CNS). Brain and spinal cord.Brain and spinal cord.

Both contain fluid-filled spaces which Both contain fluid-filled spaces which contain cerebrospinal fluid (CSF).contain cerebrospinal fluid (CSF).The central canal of the spinal cord The central canal of the spinal cord

is continuous with the ventricles of is continuous with the ventricles of the brain.the brain.

Vertebrate nervous systemsVertebrate nervous systems

White matter is composed of bundles of White matter is composed of bundles of myelinated axonsmyelinated axons

Gray matter consists of unmyelinated Gray matter consists of unmyelinated axons, nuclei, and dendrites.axons, nuclei, and dendrites.

Peripheral nervous system.Peripheral nervous system. Everything outside the CNS.Everything outside the CNS.

Divisions of the Divisions of the peripheral nervous systemperipheral nervous system

Structural composition of the PNS.Structural composition of the PNS. Paired Paired cranial nervescranial nerves that originate in that originate in

the brain and innervate the head and the brain and innervate the head and upper body.upper body.

Paired Paired spinal nervesspinal nerves that originate in that originate in the spinal cord and innervate the entire the spinal cord and innervate the entire body.body.

Ganglia associated with the cranial and Ganglia associated with the cranial and spinal nerves.spinal nerves.

Functional composition of PNSFunctional composition of PNS

Fig. 48.17

A closer look A closer look at the (often at the (often antagonistic) antagonistic) divisions of divisions of

the the autonomic autonomic

nervous nervous system system (ANS).(ANS).

Fig. 48.18

Embryonic development of the vertebrate brain Embryonic development of the vertebrate brain reflects its evolution from three anterior bulges of reflects its evolution from three anterior bulges of

the neural tubethe neural tube

Fig. 48.19

Fig. 48.20

The Brainstem.The Brainstem. The “lower brain.”The “lower brain.” Consists of the Consists of the medulla oblongatamedulla oblongata, , ponspons, ,

and and midbrainmidbrain.. Derived from the embryonic hindbrain and Derived from the embryonic hindbrain and

midbrain.midbrain. Functions in homeostasis, coordination of Functions in homeostasis, coordination of

movement, conduction of impulses to higher movement, conduction of impulses to higher brain centers.brain centers.

Evolutionary older structures of the Evolutionary older structures of the vertebrate brain regulate essential vertebrate brain regulate essential

autonomic and integrative functionsautonomic and integrative functions

The MedullaThe Medulla and Pons.and Pons. Medulla oblongata.Medulla oblongata.

Contains nuclei that control visceral (autonomic Contains nuclei that control visceral (autonomic homeostatic) functions.homeostatic) functions. Breathing.Breathing. Heart and blood vessel activity.Heart and blood vessel activity. Swallowing.Swallowing. Vomiting.Vomiting. Digestion.Digestion.

Relays information to and from higher brain Relays information to and from higher brain centers.centers.

Pons.Pons. Contains nuclei involved in the regulation Contains nuclei involved in the regulation

of visceral activities such as breathing.of visceral activities such as breathing. Relays information to and from higher Relays information to and from higher

brain centers.brain centers.

The Midbrain.The Midbrain. Contains nuclei involved in the integration Contains nuclei involved in the integration

of sensory information.of sensory information.Superior colliculi are involved in the regulation Superior colliculi are involved in the regulation

of visual reflexes.of visual reflexes. Inferior colliculi are involved in the regulation of Inferior colliculi are involved in the regulation of

auditory reflexes.auditory reflexes.

Relays information to and from higher Relays information to and from higher brain centers.brain centers.

The Reticular System, Arousal, and Sleep.The Reticular System, Arousal, and Sleep. The reticular activating systemThe reticular activating system (RAS)(RAS) of of

the the reticular formation.reticular formation.Regulates sleep Regulates sleep

and arousal.and arousal.Acts as a Acts as a

sensory filter.sensory filter.

Fig. 48.21

Sleep and wakefulness produces patterns Sleep and wakefulness produces patterns of electrical activity in the brain that can be of electrical activity in the brain that can be recorded as an recorded as an electroencephalogram electroencephalogram (EEG).(EEG).Most dreaming Most dreaming

occurs during occurs during REM (rapid REM (rapid eye movement) eye movement) sleep.sleep.

Fig. 48.22b-d

The CerebellumThe Cerebellum

Develops from part of the metencephalon.Develops from part of the metencephalon. Functions to error-check and coordinate Functions to error-check and coordinate

motor activities, and perceptual and motor activities, and perceptual and cognitive factors.cognitive factors.

Relays sensory information about joints, Relays sensory information about joints, muscles, sight, and sound to the cerebrum.muscles, sight, and sound to the cerebrum.

Coordinates motor commands issued by the Coordinates motor commands issued by the cerebrum.cerebrum.

The The thalamusthalamus and and hypothalamushypothalamus..The epithalamus, thalamus, and The epithalamus, thalamus, and

hypothalamus are derived from the hypothalamus are derived from the embryonic diencephalon.embryonic diencephalon.

EpithalamusEpithalamus.. Includes a choroid plexus and the pineal Includes a choroid plexus and the pineal

gland.gland.

ThalamusThalamus..Relays all sensory information to the Relays all sensory information to the

cerebrum.cerebrum. Contains one nucleus for each type of sensory Contains one nucleus for each type of sensory

information.information.

Relays motor information from the cerebrum.Relays motor information from the cerebrum.Receives input from the cerebrum.Receives input from the cerebrum.Receives input from brain centers involved in Receives input from brain centers involved in

the regulation of emotion and arousal.the regulation of emotion and arousal.

HypothalamusHypothalamus..Regulates autonomic activity.Regulates autonomic activity.

Contains nuclei involved in thermoregulation, Contains nuclei involved in thermoregulation, hunger, thirst, sexual and mating behavior, etc.hunger, thirst, sexual and mating behavior, etc.

Regulates the pituitary gland.Regulates the pituitary gland.

The Hypothalamus and Circadian The Hypothalamus and Circadian Rhythms.Rhythms. The The biological clockbiological clock is the internal timekeeper. is the internal timekeeper.

The clock’s rhythm usually does not exactly match environmental The clock’s rhythm usually does not exactly match environmental events.events.

Experiments in which humans have been deprived of external cues Experiments in which humans have been deprived of external cues have shown that biological clock has a period of about 25 hours.have shown that biological clock has a period of about 25 hours.

In mammals, the hypothalamic In mammals, the hypothalamic suprachiasmatic suprachiasmatic nuclei (SCN)nuclei (SCN) function as a biological clock. function as a biological clock. Produce proteins in response to light/dark cycles.Produce proteins in response to light/dark cycles.

•• This, and other biological clocks, may This, and other biological clocks, may be responsive to hormonal release, be responsive to hormonal release, hunger, and various external stimuli.hunger, and various external stimuli.

The The cerebrumcerebrum is is derived from the derived from the embryonic embryonic telencephalon.telencephalon.

The cerebrum is the most highly evolved The cerebrum is the most highly evolved structure of the mammalian brainstructure of the mammalian brain

Fig. 48.24a

The cerebrum is divided into left and right The cerebrum is divided into left and right cerebrum hemispherescerebrum hemispheres.. The The corpus callosumcorpus callosum is the major connection is the major connection

between the two hemispheres.between the two hemispheres. The left hemisphere is primarily responsible for The left hemisphere is primarily responsible for

the right side of the body.the right side of the body. The right hemisphere is primarily responsible for The right hemisphere is primarily responsible for

the left side of the body.the left side of the body. Cerebral cortex: outer covering of gray Cerebral cortex: outer covering of gray

matter.matter. NeocortexNeocortex: region unique to mammals.: region unique to mammals.

The more convoluted the surface of the neocortex the The more convoluted the surface of the neocortex the more surface area the more neurons.more surface area the more neurons.

Basal nucleiBasal nuclei: internal clusters of nuclei.: internal clusters of nuclei.

The The cerebrum is cerebrum is divided into divided into frontal, frontal, temporal, temporal, occipital, occipital, and parietal and parietal lobes.lobes.

Regions of the cerebrum are specialized for Regions of the cerebrum are specialized for different functionsdifferent functions

Fig. 48.24b

Frontal lobe.Frontal lobe. Contains the primary motor cortex.Contains the primary motor cortex.

Parietal lobe.Parietal lobe. Contains the primary somatosensory cortex.Contains the primary somatosensory cortex.

Fig. 48.25

Integrative Function of the Association Integrative Function of the Association Areas.Areas. Much of the cerebrum is given over to Much of the cerebrum is given over to

association areas.association areas.Areas where sensory information is Areas where sensory information is

integrated and assessed and motor integrated and assessed and motor responses are planned.responses are planned.

The brain exhibits plasticity of function.The brain exhibits plasticity of function. For example, infants with intractable For example, infants with intractable

epilepsy may have an entire cerebral epilepsy may have an entire cerebral hemisphere removed.hemisphere removed.The remaining hemisphere can provide the The remaining hemisphere can provide the

function normally provided by both function normally provided by both hemispheres.hemispheres.

Lateralization of Brain FunctionLateralization of Brain Function The left hemisphere.The left hemisphere.

Specializes in language, math, logic operations, and Specializes in language, math, logic operations, and the processing of serial sequences of information, the processing of serial sequences of information, and visual and auditory details.and visual and auditory details.

Specializes in detailed activities required for motor Specializes in detailed activities required for motor

controlcontrol..

The right hemisphere.The right hemisphere. Specializes in pattern recognition, spatial Specializes in pattern recognition, spatial

relationships, nonverbal ideation, emotional relationships, nonverbal ideation, emotional processing, and the parallel processing of information.processing, and the parallel processing of information.

Language and SpeechLanguage and Speech

Broca’s area.Broca’s area. Usually located in the left hemisphere’s frontal lobeUsually located in the left hemisphere’s frontal lobe Responsible for speech production.Responsible for speech production.

Wernicke’s area.Wernicke’s area. Usually located in the right hemisphere’s temporal Usually located in the right hemisphere’s temporal

lobelobe Responsible for the comprehension of speech.Responsible for the comprehension of speech.

Other speech areas are involved generating verbs to Other speech areas are involved generating verbs to match nouns, grouping together related words, etc.match nouns, grouping together related words, etc.

Emotions.Emotions. In mammals, the In mammals, the limbic systemlimbic system is is

composed of the hippocampus, olfactory composed of the hippocampus, olfactory cortex, inner portions of the cortex’s lobes, cortex, inner portions of the cortex’s lobes, and parts of the thalamus and and parts of the thalamus and hypothalamus.hypothalamus. Mediates basic emotions (fear, anger), involved Mediates basic emotions (fear, anger), involved

in emotional bonding, establishes emotional in emotional bonding, establishes emotional memorymemory For example, For example,

the amygdala the amygdala is involved in is involved in recognizing recognizing the emotional the emotional content of content of facial expression.facial expression.

Fig. 48.27

Memory and LearningMemory and Learning

Short-term memory stored in the frontal lobes.Short-term memory stored in the frontal lobes. The establishment of long-term memory The establishment of long-term memory

involves the hippocampus.involves the hippocampus. The transfer of information from short-term to long-The transfer of information from short-term to long-

term memory.term memory. Is enhanced by repetition (remember that when you are Is enhanced by repetition (remember that when you are

preparing for an exam).preparing for an exam). Influenced by emotional states mediated by the Influenced by emotional states mediated by the

amygdala.amygdala. Influenced by association with previously stored Influenced by association with previously stored

information.information.

Different types of long-term memories Different types of long-term memories are stored in different regions of the are stored in different regions of the brain.brain.

Memorization-type memory can be Memorization-type memory can be rapid.rapid. Primarily involves changes in the strength Primarily involves changes in the strength

of existing nerve connections.of existing nerve connections. Learning of skills and procedures is Learning of skills and procedures is

slower.slower. Appears to involves cellular mechanisms Appears to involves cellular mechanisms

similar to those involved in brain growth similar to those involved in brain growth and development.and development.

Functional changes in synapses in synapses Functional changes in synapses in synapses of the hippocampus and amygdala are of the hippocampus and amygdala are related to memory storage and emotional related to memory storage and emotional conditioning.conditioning. Long-term depression (LTD)Long-term depression (LTD) occurs when a occurs when a

postsynaptic neuron displays decreased postsynaptic neuron displays decreased responsiveness to action potentials.responsiveness to action potentials. Induced by repeated, weak stimulation.Induced by repeated, weak stimulation.

Long-term potentiation (LTP)Long-term potentiation (LTP) occurs when a occurs when a postsynaptic neuron displays increased postsynaptic neuron displays increased responsiveness to stimuli.responsiveness to stimuli. Induced by brief, repeated action potentials that Induced by brief, repeated action potentials that

strongly depolarize the postsynaptic membrane.strongly depolarize the postsynaptic membrane. May be associated with memory storage and learning.May be associated with memory storage and learning.

Human ConsciousnessHuman Consciousness

Brain imaging can show neural Brain imaging can show neural activity associated with:activity associated with: Conscious perceptual choiceConscious perceptual choice Unconscious processingUnconscious processing Memory retrievalMemory retrieval Working memory.Working memory.

Consciousness appears to be a Consciousness appears to be a whole-brain phenomenon.whole-brain phenomenon.

The mammalian PNS has the ability to repair The mammalian PNS has the ability to repair itself, the CNS does not.itself, the CNS does not. Research on nerve cell development and Research on nerve cell development and

neural stem cells may be the future of neural stem cells may be the future of treatment for damage to the CNS.treatment for damage to the CNS.

Research on neuron development and Research on neuron development and neural stem cells may lead to new neural stem cells may lead to new

approaches for treating CNS injuries and approaches for treating CNS injuries and

diseasesdiseases

Nerve Cell Development.Nerve Cell Development.

Fig. 48.28

Neural Stem CellsNeural Stem Cells

The adult human brain does produce The adult human brain does produce new nerve cells.new nerve cells. New nerve cells have been found in the New nerve cells have been found in the

hippocampus.hippocampus. Since mature human brain cells cannot Since mature human brain cells cannot

undergo cell division the new cells must undergo cell division the new cells must have arisen from stem cells.have arisen from stem cells.