PowerLecture: Chapter 13 The Nervous System. Learning Objectives Describe the visible structure of neurons, neuroglia, nerves, and ganglia, both separately

PowerLecture:PowerLecture:Chapter 13Chapter 13

The Nervous SystemThe Nervous System

Learning ObjectivesLearning Objectives

Describe the visible structure of neurons, Describe the visible structure of neurons, neuroglia, nerves, and ganglia, both neuroglia, nerves, and ganglia, both separately and together as a system.separately and together as a system.

Describe the distribution of the invisible Describe the distribution of the invisible array of proteins, ions, and other molecules array of proteins, ions, and other molecules in a neuron, both at rest and as a neuron in a neuron, both at rest and as a neuron experiences a change in potential.experiences a change in potential.

Understand how a nerve impulse is Understand how a nerve impulse is received by a neuron, conducted along a received by a neuron, conducted along a neuron, and transmitted across a synapse neuron, and transmitted across a synapse to a neighboring neuron, muscle, or gland.to a neighboring neuron, muscle, or gland.

Learning Objectives (cont’d)Learning Objectives (cont’d)

Outline some of the ways by which Outline some of the ways by which information flow is regulated and integrated information flow is regulated and integrated in the human body.in the human body.

Describe the organization of peripheral Describe the organization of peripheral versus central nervous systems.versus central nervous systems.

Summarize the major parts of the human Summarize the major parts of the human brain and the principal functions of each.brain and the principal functions of each.

Characterize the major groups of drugs, Characterize the major groups of drugs, emphasizing their effects on the nervous emphasizing their effects on the nervous system.system.

Impacts/IssuesImpacts/Issues

In Pursuit of EcstasyIn Pursuit of Ecstasy


Ecstasy is a drug that can make you feel Ecstasy is a drug that can make you feel really good, at least for a time.really good, at least for a time.

The active ingredient is MDMA, an The active ingredient is MDMA, an amphetamine-like drug that interferes with the amphetamine-like drug that interferes with the function of serotonin in the brain.function of serotonin in the brain.

Excess serotonin can relieve anxiety, sharpen Excess serotonin can relieve anxiety, sharpen the senses, and make you feel socially the senses, and make you feel socially accepted; it can also kill.accepted; it can also kill.


How we function as How we function as individuals depends individuals depends on whether we nurture on whether we nurture or abuse our nervous or abuse our nervous system. system.

How Would You Vote?How Would You Vote?To conduct an instant in-class survey using a classroom response To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main system, access “JoinIn Clicker Content” from the PowerLecture main menu. menu.

Would you support legislation that forces Would you support legislation that forces nonviolent drug offenders to enter drug rehab nonviolent drug offenders to enter drug rehab programs as an alternative to jail?programs as an alternative to jail? a. Yes, treatment is more effective than jail at a. Yes, treatment is more effective than jail at

reducing drug use, and it is more cost effective reducing drug use, and it is more cost effective too.too.

b. No, easing penalties will lead to more drug b. No, easing penalties will lead to more drug use. use.

Section 1Section 1

Neurons—The Neurons—The Communication Communication

SpecialistsSpecialists

NeuronsNeurons

The role of the The role of the nervous systemnervous system is to detect is to detect and integrate information about external and integrate information about external and internal conditions and carry out and internal conditions and carry out responses.responses.

NeuronsNeurons form the basis of the system’s form the basis of the system’s

communication network.communication network.

Figure 13.2Figure 13.2

NeuronsNeurons

There are three types of neurons:There are three types of neurons:• Sensory neuronsSensory neurons are receptors for specific sensory are receptors for specific sensory

stimuli (signals).stimuli (signals).• InterneuronsInterneurons in the brain and spinal cord integrate in the brain and spinal cord integrate

input and output signals.input and output signals.• Motor neuronsMotor neurons send information from integrator to send information from integrator to

muscle or gland cells (effectors).muscle or gland cells (effectors).

NeuronsNeurons

Neurons have several functional zones.Neurons have several functional zones. Neurons form extended cells with several Neurons form extended cells with several

zones:zones:• The The cell bodycell body contains the nucleus and organelles. contains the nucleus and organelles.• The cell body has slender extensions called The cell body has slender extensions called

dendritesdendrites; the cell body and the dendrites form the ; the cell body and the dendrites form the input zoneinput zone for receiving information. for receiving information.

• Next comes the Next comes the trigger zonetrigger zone, called the , called the axon axon hillockhillock in motor neurons and interneurons; the in motor neurons and interneurons; the trigger zone leads to the trigger zone leads to the axonaxon, which is the neuron’s , which is the neuron’s conducting zoneconducting zone..

• The axon’s endings are The axon’s endings are output zonesoutput zones where where messages are sent to other cells.messages are sent to other cells.

dendrites

cell body

trigger zone

conducting zone

axon

output zone

axon endings

Fig. 13.1, p. 226

input zone

NeuronsNeurons

Only 10% of the nervous system consists of Only 10% of the nervous system consists of neurons; the rest of the 90% is composed of neurons; the rest of the 90% is composed of support cells called support cells called neuroglianeuroglia, or , or gliaglia..

Neurons function well in communication Neurons function well in communication because they are because they are excitableexcitable (produce electrical (produce electrical signals in response to stimuli).signals in response to stimuli).

NeuronsNeurons

Properties of a neuron’s plasma membrane Properties of a neuron’s plasma membrane allow it to carry signals.allow it to carry signals.

The plasma membrane prevents charged The plasma membrane prevents charged substances (Ksubstances (K++ and Na and Na++ ions) from moving ions) from moving freely across, but both ions can move through freely across, but both ions can move through channels.channels.

• Some channel proteins are always open, others are Some channel proteins are always open, others are gated.gated.

• In a resting neuron, gated sodium channels are In a resting neuron, gated sodium channels are closed; sodium does not pass through the closed; sodium does not pass through the membrane, but potassium does.membrane, but potassium does.

• According to the gradients that form, sodium diffuses According to the gradients that form, sodium diffuses into the cell, potassium diffuses out of the cell.into the cell, potassium diffuses out of the cell.

Passive transporters with open channels let ions steadily leak across the membrane.

Other passive transporters have voltage-sensitive gated channels that open and shut. They assist diffusion of Na+ and K+ across the membrane as the ions follow concentration gradients.

Active transporters pump Na+ and K+ across the membrane, against their concentration gradients. They counter ion leaks and restore resting membrane conditions.

lipid bilayer of neuron membrane

cytoplasm Na+/K+ pump

Fig. 13.3b, p. 227

fluid outside cell

NeuronsNeurons

The difference across the membrane that forms The difference across the membrane that forms because of the Kbecause of the K++ and Na and Na++ gradients results in a gradients results in a resting membrane potential of ‒70 millivolts resting membrane potential of ‒70 millivolts (cytoplasmic side of the membrane is negative).(cytoplasmic side of the membrane is negative).

Fig. 13.3a, p. 227

K+

Na+ outside

inside

K+

Na+

Plasma membrane

Section 2Section 2

Action Potentials = Action Potentials = Nerve ImpulsesNerve Impulses

Action Potentials = Nerve ImpulsesAction Potentials = Nerve Impulses

Sufficient signals at the input zone of a Sufficient signals at the input zone of a resting neuron can trigger reversal of the resting neuron can trigger reversal of the voltage difference across the membrane.voltage difference across the membrane.

The signal opens gated sodium channels, The signal opens gated sodium channels, allowing Naallowing Na++ to rush into the neuron. to rush into the neuron.

The internal charge near the membrane The internal charge near the membrane becomes less negative, stimulating more becomes less negative, stimulating more channels to open (positive feedback).channels to open (positive feedback).


When the voltage difference crosses a key When the voltage difference crosses a key thresholdthreshold level of stimulation, an level of stimulation, an actionaction potentialpotential (nerve impulse) occurs. (nerve impulse) occurs.

• Thresholds can only be reached in areas of the Thresholds can only be reached in areas of the neuron where there are voltage-sensitive sodium neuron where there are voltage-sensitive sodium channels.channels.

• Stimuli must be strong enough to trigger the Stimuli must be strong enough to trigger the potential.potential.

fluid outsideneuron

gated sodiumchannel

Fig. 13.4a, p. 228

In a membrane at rest, the inside of the neuron is negative relative to the outside. An electrical disturbance (yellow arrow) spreads from an input zone to an adjacent trigger zone of the membrane, which has a large number of gated sodium channels.

©2007 Thomson Higher Education

Na+

Na+

Na+

Fig. 13.4b, p. 228

A strong disturbance initiates an action potential. Sodium gates open. Sodium flows in, reducing the negativity inside the neuron. The change causes more gates to open, and so on until threshold is reached and the voltage difference across the membrane reverses.

voltage reversed


Action potentials spread by themselves.Action potentials spread by themselves. The action potential is self-propagating and The action potential is self-propagating and

moves away from the stimulation site.moves away from the stimulation site. Potentials can self-propagate because the Potentials can self-propagate because the

changes to the membrane potential don’t lose changes to the membrane potential don’t lose strength.strength.


Na+

Na+

Na+

K+

K+

K+

Fig. 13.4c, p. 229

At the next patch of membrane, another group of gated sodium channels open. In the previous patch, some K+ moves out through other gated channels. That region becomes negative again.


Na+Na+

K+ K+K+

Na+

K+

Fig. 13.4d, p. 229

After each action potential, the sodium and potassium concentration gradients in a patch of membrane are not yet fully restored. Active transport at sodium–potassium pumps restores them.

Na+/K+ pump

propagating action potential


A neuron can’t “fire” again until ion pumps A neuron can’t “fire” again until ion pumps restore its resting potential.restore its resting potential.

By diffusion, some potassium ions will always By diffusion, some potassium ions will always leak out of the cell and some sodium will always leak out of the cell and some sodium will always leak in.leak in.

The The sodium-potassium pumpsodium-potassium pump uses ATP to uses ATP to actively pump potassium ions in and sodium actively pump potassium ions in and sodium ions out of the neuron to keep the concentration ions out of the neuron to keep the concentration of sodium ions higher outside, ready for another of sodium ions higher outside, ready for another action potential to form.action potential to form.


Action potentials are “all-or-nothing.”Action potentials are “all-or-nothing.” Action potentials are all-or-nothing events.Action potentials are all-or-nothing events.

• Once a positive-feedback cycle starts, nothing stops Once a positive-feedback cycle starts, nothing stops the full “spiking” of a potential.the full “spiking” of a potential.

• If threshold is not reached, however, the membrane If threshold is not reached, however, the membrane disturbance will subside when the stimulus is disturbance will subside when the stimulus is removed.removed.

action potential

thresholdlevel

resting level

Time (milliseconds)1 2 3 4 5

Fig. 13.6, p. 229

6


When the action potential is terminated, the When the action potential is terminated, the sodium gates close, potassium gates open, and sodium gates close, potassium gates open, and the sodium-potassium membrane pumps the sodium-potassium membrane pumps become operational to fully restore the resting become operational to fully restore the resting potential.potential.

Na+ pumped out

K+

leaks out

Na+ leaks in

K+ pumped in

fluidoutside plasma membrane

neuron’s plasma membrane

cytoplasmnext to the membrane

Fig. 13.5, p. 229

Section 3Section 3

Chemical Synapses: Chemical Synapses: Communication JunctionsCommunication Junctions


Action potentials can stimulate the release Action potentials can stimulate the release of of neurotransmittersneurotransmitters..

Neurotransmitters diffuse across a Neurotransmitters diffuse across a chemical chemical

synapsesynapse, the junction between a neuron and , the junction between a neuron and an adjacent cell (between neurons and other an adjacent cell (between neurons and other neurons, or between neurons and muscle or neurons, or between neurons and muscle or gland cells).gland cells).


The neuron that releases the transmitter is The neuron that releases the transmitter is called the called the presynaptic cellpresynaptic cell..

• In response to an action potential, gated calcium In response to an action potential, gated calcium

channels open and allow calcium ions to enter the channels open and allow calcium ions to enter the

neuron from the synapse.neuron from the synapse.• Calcium causes the synaptic vesicles to fuse Calcium causes the synaptic vesicles to fuse

with the membrane and release the transmitter with the membrane and release the transmitter substance into the synapse.substance into the synapse.

The transmitter binds to receptors on the The transmitter binds to receptors on the membrane of the membrane of the postsynaptic cellpostsynaptic cell. .

plasma membrane of an axon ending of a presynaptic cell

vesicle containing

neurotransmitter

membrane receptor for neurotransmitter

plasma membrane of a

postsynaptic cellFig. 13.7a, p. 230

synapse

molecule of neurotransmitter in synapse

receptor for the neurotransmitter on gated channel protein in plasma membrane of postsynaptic cell

Fig. 13.7b, p. 230

ions (black) that now can diffuse through channel


Neurotransmitters can excite or inhibit a Neurotransmitters can excite or inhibit a receiving cell.receiving cell.

How a postsynaptic cell responds to a How a postsynaptic cell responds to a transmitter depends on the type and amount of transmitter depends on the type and amount of transmitter, the receptors it has, and the types transmitter, the receptors it has, and the types of channels in its input zone.of channels in its input zone.

• Excitatory signalsExcitatory signals drive the membrane toward an drive the membrane toward an action potential.action potential.

• Inhibitory signalsInhibitory signals prevent an action potential. prevent an action potential.


Examples of neurotransmitters:Examples of neurotransmitters:• AcetylcholineAcetylcholine (ACh) can excite or inhibit target cells (ACh) can excite or inhibit target cells

in the brain, spinal cord, glands, and muscles.in the brain, spinal cord, glands, and muscles.• SerotoninSerotonin acts on brain cells to govern sleeping, acts on brain cells to govern sleeping,

sensory perception, temperature regulation, and sensory perception, temperature regulation, and emotional states.emotional states.

• Some neurons secrete Some neurons secrete nitric oxidenitric oxide (NO), a gas that (NO), a gas that controls blood vessel dilation, as in penis erection.controls blood vessel dilation, as in penis erection.

Fig. 13.8a, p. 231

axon endingsmuscle fiber


Motor end plate(troughs in muscle cell membrane)

gapaxon ending

muscle cell membrane

Fig. 13.8b, p. 231


NeuromodulatorsNeuromodulators can magnify or reduce the can magnify or reduce the effects of a neurotransmitter.effects of a neurotransmitter.

• One example includes the natural painkillers called One example includes the natural painkillers called endorphinsendorphins..

• Release of endorphins prevents sensations of pain Release of endorphins prevents sensations of pain from being recognized.from being recognized.

• Endorphins may also play a role in memory, learning, Endorphins may also play a role in memory, learning, and sexual behavior.and sexual behavior.


Competing signals are “summed up.”Competing signals are “summed up.” Excitatory and inhibitory signals compete at the Excitatory and inhibitory signals compete at the

input zone.input zone.• An excitatory postsynaptic potential (An excitatory postsynaptic potential (EPSPEPSP) )

depolarizesdepolarizes the membrane to bring it closer to the membrane to bring it closer to threshold.threshold.

• An inhibitory postsynaptic potential (An inhibitory postsynaptic potential (IPSPIPSP) either ) either drives the membrane away from threshold by a drives the membrane away from threshold by a hyperpolarizinghyperpolarizing effect or maintains the membrane effect or maintains the membrane potential at the resting level.potential at the resting level.


In In synaptic integrationsynaptic integration, competing signals that , competing signals that reach the input zone of a neuron at the same reach the input zone of a neuron at the same time are summed; summation of signals time are summed; summation of signals determines whether a signal is suppressed, determines whether a signal is suppressed, reinforced, or sent onward to other body cells. reinforced, or sent onward to other body cells.


Neurotransmitter molecules must be Neurotransmitter molecules must be removed from the synapse.removed from the synapse.

Neurotransmitters must be removed from the Neurotransmitters must be removed from the synaptic cleft to discontinue stimulation.synaptic cleft to discontinue stimulation.

There are three methods of removal:There are three methods of removal:• Some neurotransmitter molecules simply diffuse out Some neurotransmitter molecules simply diffuse out

of the cleft.of the cleft.• Enzymes, such as acetylcholinesterase, break down Enzymes, such as acetylcholinesterase, break down

the transmitters.the transmitters.• Membrane transport proteins actively pump Membrane transport proteins actively pump

neurotransmitter molecules back into the presynaptic neurotransmitter molecules back into the presynaptic cells.cells.

Section 4Section 4

Information PathwaysInformation Pathways

Nerves are long-distance lines.Nerves are long-distance lines. Signals between the brain or spinal cord and Signals between the brain or spinal cord and

body regions travel via body regions travel via nervesnerves..• Axons of sensory neurons, motor neurons, or both, Axons of sensory neurons, motor neurons, or both,

are bundled together in a nerve.are bundled together in a nerve.• Within the brain and spinal cord, bundles of Within the brain and spinal cord, bundles of

interneuron axons are called interneuron axons are called nerve tractsnerve tracts..


Axons are covered by a Axons are covered by a myelin sheathmyelin sheath derived derived from from Schwann cellsSchwann cells..

• Each section of the sheath is separated from Each section of the sheath is separated from adjacent ones by a region where the axon adjacent ones by a region where the axon membrane, along with gated sodium channels, is membrane, along with gated sodium channels, is exposed.exposed.

• Action potentials jump from node to node (Action potentials jump from node to node (saltatory saltatory

conductionconduction); such jumps are fast and efficient.); such jumps are fast and efficient.• There are no Schwann cells in the central nervous There are no Schwann cells in the central nervous

system; here processes from system; here processes from oligodendrocytesoligodendrocytes form the sheaths of myelinated axons.form the sheaths of myelinated axons.


blood vessels

outer connective tissue of one nerve

unsheathed node containing gated Na+ channels

axon

myelin sheath formed by Schwann cells

Fig. 13.9, p. 232

many neurons bundled together inside a connective tissue sheath

axon of one neuron

Table 13.1, p. 232

Reflex arcs are the simplest nerve Reflex arcs are the simplest nerve pathways.pathways.

A A reflexreflex is a simple, stereotyped movement in is a simple, stereotyped movement in response to a stimulus.response to a stimulus.

In the simplest In the simplest reflex arcsreflex arcs, sensory neurons , sensory neurons synapse directly with motor neurons; an synapse directly with motor neurons; an example is the example is the stretch reflexstretch reflex, which contracts , which contracts a muscle after that muscle has been stretched.a muscle after that muscle has been stretched.

In most reflex pathways, the sensory neurons In most reflex pathways, the sensory neurons also interact with several interneurons, which also interact with several interneurons, which excite or inhibit motor neurons as needed for a excite or inhibit motor neurons as needed for a coordinated response.coordinated response.


RESPONSEBiceps contracts.

Fig. 13.10, p. 233

STIMULUSBiceps stretches.

muscle spindle

neuromuscularjunction

a Fruit being loaded into a bowlputs weight on an arm muscle andstretches it.

b Stretching stimulates sensoryreceptor endings in this musclespindle.

c Axon endings of the sensory neuron release a neuro-transmitterd The stimulation is strong

enough to generate actionpotentials

e Axon endings of the motorneuron synapse with musclecells in the stretched muscle.

f ACh released from the motor neuron’s axon endings stimulates muscle cells.

g Stimulation makes the stretched muscle contract.

Fig. 13.27, p. 248

muscle spindle

extensor muscle of knee (quadriceps femoris)

reflex arc

motor neuron

patellar tendon

In the brain and spinal cord, neurons In the brain and spinal cord, neurons interact in circuits.interact in circuits.

The overall direction of flow in the nervous The overall direction of flow in the nervous system: sensory neurons >>> spinal cord and system: sensory neurons >>> spinal cord and brain >>> interneurons >>> motor neurons.brain >>> interneurons >>> motor neurons.


In-text Fig., p. 233

axon

axon endings

cell body

dendrites

axon

cell bodyaxon

endingaxon

receptor endings

sensory neuron motor neuroninterneuron

cell body axon

dendrites

Interneurons in the spinal cord and brain are Interneurons in the spinal cord and brain are grouped into blocks, which in turn form circuits; grouped into blocks, which in turn form circuits; blocks receive signals, integrate them, and then blocks receive signals, integrate them, and then generate new ones.generate new ones.

• Divergent circuits fan out from one block into Divergent circuits fan out from one block into another.another.

• Other circuits funnel down to just a few neurons.Other circuits funnel down to just a few neurons.• In reverberating circuits, neurons repeat signals In reverberating circuits, neurons repeat signals

among themselves.among themselves.


Section 5Section 5

Overview of the Nervous Overview of the Nervous SystemSystem

Overview of the Nervous SystemOverview of the Nervous System

The The central nervous systemcentral nervous system (CNS) is (CNS) is composed of the brain and spinal cord; all composed of the brain and spinal cord; all of the interneurons are contained in this of the interneurons are contained in this system.system.

Nerves that carry sensory input to the CNS are Nerves that carry sensory input to the CNS are called the called the afferent nervesafferent nerves..

Efferent nervesEfferent nerves carry signals away from the carry signals away from the CNS.CNS.

Overview of the Nervous SystemOverview of the Nervous System

The The peripheral nervous systemperipheral nervous system (PNS) (PNS) includes all the nerves that carry signals to includes all the nerves that carry signals to and from the brain and spinal cord to the and from the brain and spinal cord to the rest of the body.rest of the body.

The PNS is further divided into the The PNS is further divided into the somaticsomatic and and autonomicautonomic subdivisions. subdivisions.

The PNS consists of 31 pairs of spinal nerves The PNS consists of 31 pairs of spinal nerves and 12 pairs of cranial nerves.and 12 pairs of cranial nerves.

At some sites, cell bodies from several neurons At some sites, cell bodies from several neurons cluster together in cluster together in gangliaganglia..

brain

cranial nerves

spinal cord

ulnar nerve

lumbar nerves(five pairs)

sacral nerves (five pairs)

coccygeal nerves(one pair)

cervical nerves(eight pairs) thoracic nerves(twelve pairs)

sciatic nerve

Fig. 13.11, p. 234

sympatheticnerves

para-sympathetic

nerves

sensorynerves

axons ofmotor nerves

somaticsubdivision

(motor functions)

autonomicsubdivision

(visceralfunctions)

peripheral nervous system

Fig. 13.12, p. 235

CENTRAL NERVOUS SYSTEM

brain

spinal cord

© 2007 Thomson Higher Education Fig. 13.13, p. 235

I Olfactory nerve

II Optic nerve (from the retina)

III To eye muscles

IV To eye muscles

V To jaw muscles; from mouth

VII To facial muscles, glands; from the taste buds

IX To/from pharynx

VIII From inner ear

VI To eye muscles

X To tongue muscles

XI To/from internal organs

XII To neck and back muscles

Section 6Section 6

Major Expressways: Major Expressways: Peripheral Nerves and Peripheral Nerves and

the Spinal Cordthe Spinal Cord

Major Expressways: Peripheral Nerves Major Expressways: Peripheral Nerves and the Spinal Cord and the Spinal Cord

The peripheral nervous system consists of The peripheral nervous system consists of somatic and autonomic nerves.somatic and autonomic nerves.

Somatic nervesSomatic nerves carry signals related to carry signals related to movement of the head, trunk, and limbs; signals movement of the head, trunk, and limbs; signals move to and from skeletal muscles for voluntary move to and from skeletal muscles for voluntary control.control.


Autonomic nervesAutonomic nerves carry signals between carry signals between internal organs and other structures; signals internal organs and other structures; signals move to and from smooth muscles, cardiac move to and from smooth muscles, cardiac muscle, and glands (involuntary control).muscle, and glands (involuntary control).

• The cell bodies of The cell bodies of preganglionic neuronspreganglionic neurons lie within lie within the CNS and extend their axons to ganglia outside the CNS and extend their axons to ganglia outside the CNS.the CNS.

• Postganglionic neuronsPostganglionic neurons receive the messages receive the messages from the axons of the preganglionic cells and pass from the axons of the preganglionic cells and pass the impulses on to the effectors.the impulses on to the effectors.


Autonomic nerves are divided into Autonomic nerves are divided into parasympathetic and sympathetic groups.parasympathetic and sympathetic groups.

They normally work antagonistically towards They normally work antagonistically towards each other.each other.

• Parasympathetic nervesParasympathetic nerves slow down body activity slow down body activity when the body is not under stress.when the body is not under stress.

• Sympathetic nervesSympathetic nerves increase overall body activity increase overall body activity during times of stress, excitement, or danger; they during times of stress, excitement, or danger; they also call on the hormone norepinephrine to increase also call on the hormone norepinephrine to increase the the fight-flight responsefight-flight response..

When sympathetic activity drops, When sympathetic activity drops, parasympathetic activity may rise in a parasympathetic activity may rise in a rebound rebound effecteffect. .

5© 2007 Thomson Higher Education

eyes

salivary glands

heart

larynxbronchilungs

stomach

liverspleen

pancreas

kidneysadrenal glands

small intestineupper colonlower colon

rectum

bladder

uterus

genitals

(most ganglia

near spinalcord)

(all ganglia

in walls of organs)

midbrainmedulla oblongata

cervical nerves(8 pairs)

thoracic nerves(12 pairs)

lumbar nerves(5 pairs) sacral nerves(5 pairs)

sympathetic parasympathetic

Fig. 13.14, p. 236

pelvic nerve

Vagusnerve

optic nerve


The spinal cord is the pathway between the The spinal cord is the pathway between the PNS and the brain.PNS and the brain.

The The spinal cordspinal cord lies within a closed channel lies within a closed channel formed by the bones of the vertebral column.formed by the bones of the vertebral column.

Signals move up and down the spinal cord in Signals move up and down the spinal cord in nerve tracts.nerve tracts.

• The myelin sheaths of these tracts are white; thus, The myelin sheaths of these tracts are white; thus, they are called they are called white matterwhite matter..

• The central, butterfly-shaped area (in cross-section) The central, butterfly-shaped area (in cross-section) consists of dendrites, cell bodies, interneurons, and consists of dendrites, cell bodies, interneurons, and neuroglia cells; it is called neuroglia cells; it is called gray mattergray matter..


The spinal cord and brain are covered with The spinal cord and brain are covered with three tough membranes—the three tough membranes—the meningesmeninges..

The spinal cord is a pathway for signal travel The spinal cord is a pathway for signal travel between the peripheral nervous system and the between the peripheral nervous system and the brain; it also is the center for controlling some brain; it also is the center for controlling some reflex actions.reflex actions.

• Spinal reflexesSpinal reflexes result from neural connections made result from neural connections made within the spinal cord and do not require input from within the spinal cord and do not require input from the brain, even though the event is recorded there.the brain, even though the event is recorded there.

• Autonomic reflexesAutonomic reflexes, such as bladder emptying, are , such as bladder emptying, are also the responsibility of the spinal cord.also the responsibility of the spinal cord.

© 2007 Thomson Higher Education

spinal cord

ganglion

spinal nerve

vertebra

meninges(protectivecoverings)

Fig. 13.15, p. 237

intervertebral disk

white matter

central canal

grey matter

Section 7Section 7

The Brain—Command The Brain—Command CentralCentral

The Brain – Command CentralThe Brain – Command Central

The spinal cord merges with the body’s The spinal cord merges with the body’s master control center, the master control center, the brainbrain..

The brain is protected by bone and meninges.The brain is protected by bone and meninges.• The tough outer membrane is the The tough outer membrane is the dura materdura mater; it is ; it is

folded double around the brain and divides the brain folded double around the brain and divides the brain into its right and left halves.into its right and left halves.

• The thinner middle layer is the The thinner middle layer is the arachnoidarachnoid; the ; the delicate delicate pia materpia mater wraps the brain and spinal cord wraps the brain and spinal cord as the innermost layer.as the innermost layer.

The meninges also enclose fluid-filled spaces The meninges also enclose fluid-filled spaces that cushion and nourish the brain.that cushion and nourish the brain.

Fig. 13.16, p. 238

Fig. 13.16a, p. 238

cerebrospinal fluid

ventricles

arachnoid mater

pia mater

cerebrospinal fluid in spinal canal

spinal chord

three m

enin

ges

dura mater


Fig. 13.16b, p. 238

scalp

skull bone

dura mater

arachnoidmater

pia mater

cerebrospinal fluid


The brain is divided into a hindbrain, The brain is divided into a hindbrain, midbrain, and forebrain.midbrain, and forebrain.

The The hindbrainhindbrain and and midbrainmidbrain form the form the brain brain stemstem, responsible for many simple reflexes., responsible for many simple reflexes.

Hindbrain.Hindbrain.• The The medulla oblongatamedulla oblongata has influence over has influence over

respiration, heart rate, swallowing, coughing, and respiration, heart rate, swallowing, coughing, and sleep/wake responses.sleep/wake responses.

• The The cerebellumcerebellum acts as a reflex center for acts as a reflex center for maintaining posture and coordinating limbs.maintaining posture and coordinating limbs.

• The The ponspons (“bridge”) possesses nerve tracts that (“bridge”) possesses nerve tracts that pass between brain centers.pass between brain centers.


The The midbrainmidbrain coordinates reflex responses to coordinates reflex responses to sight and sound.sight and sound.

• It has a roof of gray matter, the It has a roof of gray matter, the tectumtectum, where visual , where visual and sensory input converges before being sent to and sensory input converges before being sent to higher brain centers.higher brain centers.

The The forebrainforebrain is the most developed portion of is the most developed portion of the brain in humans.the brain in humans.

• The The cerebrumcerebrum integrates sensory input and selected integrates sensory input and selected motor responses; motor responses; olfactory bulbsolfactory bulbs deal with the deal with the sense of smell.sense of smell.


• The The thalamusthalamus relays and coordinates sensory relays and coordinates sensory signals through clusters of neuron cell bodies called signals through clusters of neuron cell bodies called nucleinuclei; Parkinson’s disease occurs when the ; Parkinson’s disease occurs when the function of function of basal nucleibasal nuclei in the thalamus is disrupted. in the thalamus is disrupted.

• The The hypothalamushypothalamus monitors internal organs and monitors internal organs and influences responses to thirst, hunger, and sex, thus influences responses to thirst, hunger, and sex, thus controlling homeostasis.controlling homeostasis.

Cerebrospinal fluid fills cavities and canals Cerebrospinal fluid fills cavities and canals in the brain.in the brain.

The brain and spinal cord are surrounded by The brain and spinal cord are surrounded by the the cerebrospinal fluidcerebrospinal fluid (CSF), which fills (CSF), which fills cavities (ventricles) and canals within the brain.cavities (ventricles) and canals within the brain.


A mechanism called the A mechanism called the blood-brain barrierblood-brain barrier controls which substances will pass to the fluid controls which substances will pass to the fluid and subsequently to the neurons.and subsequently to the neurons.

• The capillaries of the brain are much less permeable The capillaries of the brain are much less permeable than other capillaries, forcing materials to pass than other capillaries, forcing materials to pass through the cells, not around them.through the cells, not around them.

• Lipid-soluble substances, such as alcohol, nicotine, Lipid-soluble substances, such as alcohol, nicotine, and drugs, diffuse quickly through the lipid bilayer of and drugs, diffuse quickly through the lipid bilayer of the plasma membrane.the plasma membrane.

Section 8Section 8

A Closer Look at the A Closer Look at the CerebrumCerebrum

A Closer Look at the Cerebrum A Closer Look at the Cerebrum

There are two cerebral hemispheres.There are two cerebral hemispheres. The human cerebrum is divided into left and The human cerebrum is divided into left and

right right cerebral hemispherescerebral hemispheres, which , which communicate with each other by means of the communicate with each other by means of the corpuscorpus callosumcallosum..

• Each hemisphere can function separately; the left Each hemisphere can function separately; the left hemisphere responds to signals from the right side of hemisphere responds to signals from the right side of the body, and vice versa.the body, and vice versa.

• The left hemisphere deals The left hemisphere deals mainly with speech, analytical mainly with speech, analytical skills, and mathematics; skills, and mathematics; nonverbal skills such as music nonverbal skills such as music and other creative activities reside in the right.and other creative activities reside in the right.



The thin surface (The thin surface (cerebral cortexcerebral cortex) is gray ) is gray matter, divided into lobes by folds and fissures; matter, divided into lobes by folds and fissures; white matter and basal nuclei (gray matter in white matter and basal nuclei (gray matter in the thalamus) underlie the surface.the thalamus) underlie the surface.

Each hemisphere is divided into frontal, Each hemisphere is divided into frontal, occipital, temporal, and parietal lobes.occipital, temporal, and parietal lobes.


The cerebral cortex controls thought and The cerebral cortex controls thought and other conscious behavior.other conscious behavior.

Motor areasMotor areas are found in the frontal lobe of are found in the frontal lobe of each hemisphere.each hemisphere.

• The The motor cortexmotor cortex controls the coordinated controls the coordinated movements of the skeletal muscles.movements of the skeletal muscles.

• The The premotor cortexpremotor cortex is associated with learned is associated with learned pattern or motor skills.pattern or motor skills.

• Broca’s areaBroca’s area is involved in speech. is involved in speech.• The The frontal eye fieldfrontal eye field controls voluntary eye controls voluntary eye

movements.movements.

frontal lobe (planning movements; some aspects of memory; inhibition of inappropriate behavior)

primarymotorcortex

primarysomatosensory

cortex

parietallobe (body sensations)

temporal lobe(hearing; advanced visual processing)

occipital lobe(vision)

Fig. 13.19a, p. 241

Fig. 13.19b, p. 241

Motor cortex activitywhen speaking

Prefrontal cortex activitywhen generating words

Visual cortex activitywhen observing words

Fig. 13.20, p. 241


Several Several sensory areassensory areas are found in the parietal are found in the parietal lobe:lobe:

• The The primary somatosensory cortexprimary somatosensory cortex is the main is the main receiving center for sensory input from the skin and receiving center for sensory input from the skin and joints, while the joints, while the primary cortical areaprimary cortical area deals with deals with taste.taste.

• The The primary visual cortexprimary visual cortex, which receives sensory , which receives sensory input from the eyes, is found in the occipital lobe.input from the eyes, is found in the occipital lobe.

• Sound and odor perception arises in Sound and odor perception arises in primary primary cortical areascortical areas in each temporal lobe. in each temporal lobe.


Association areasAssociation areas occupy all parts of the occupy all parts of the cortex except the primary motor and sensory cortex except the primary motor and sensory regions: regions:

• Each area integrates, analyzes, and responds to Each area integrates, analyzes, and responds to many inputs.many inputs.

• Neural activity is the most complex in the prefrontal Neural activity is the most complex in the prefrontal cortex, the area of the brain that allows for complex cortex, the area of the brain that allows for complex learning, intellect, and personality.learning, intellect, and personality.


The limbic system: Emotions and more.The limbic system: Emotions and more. Our emotions and parts of our memory are Our emotions and parts of our memory are

governed by the governed by the limbic systemlimbic system, which consists , which consists of several brain regions.of several brain regions.

Parts of the thalamus, hypothalamus, Parts of the thalamus, hypothalamus, amygdala, amygdala, and the hippocampus form the and the hippocampus form the limbic system and contribute to producing our limbic system and contribute to producing our “gut” “gut” reactions.reactions.

(olfactory tract) cingulate gyrus thalamus

amygdala

hippocampus

hypothalamus

Fig. 13.21, p. 241

Section 9Section 9

Memory and Memory and ConsciousnessConsciousness


Memory is how the brain stores and Memory is how the brain stores and retrieves information.retrieves information.

Learning and adaptive modifications to Learning and adaptive modifications to behavior are possible because of behavior are possible because of memorymemory, the , the storage information.storage information.

• Short-term memoryShort-term memory lasts from seconds to hours lasts from seconds to hours and is limited to a few bits of information.and is limited to a few bits of information.

• Long-term memoryLong-term memory is more permanent and seems is more permanent and seems to be limitless.to be limitless.


Emotional state, having timeto repeat (or rehearse) input,and associating the input with stored categories ofmemory influence transferto long-term storage

Recallof storedinput

Input irretrievable

Input forgotten

Fig. 13.22, p. 242

Sensory stimuli; as fromthe nose, eyes, and ears

Temporary storage inthe cerebral cortex

SHORT-TERM MEMORY

LONG-TERM MEMORY


Facts are processed separately from skills Facts are processed separately from skills using separate memory circuits.using separate memory circuits.

• FactsFacts, such as names or faces, are forgotten or , such as names or faces, are forgotten or stored in long term memory where they can be stored in long term memory where they can be recalled through association.recalled through association.

• SkillsSkills, such as playing the piano, can only be , such as playing the piano, can only be recalled by doing them.recalled by doing them.

Figure 13.23bFigure 13.23b

touch

hearing

vision

thalamus and hypothalamus

basal nuclei

prefrontal cortex

amygdala

smell

hippocampus

Fig. 13.23a, p. 242


AmnesiaAmnesia is a loss of fact memory; the severity is a loss of fact memory; the severity of loss depends on the extent of damage to the of loss depends on the extent of damage to the brain, but amnesia does not prevent a person brain, but amnesia does not prevent a person from learning new skills.from learning new skills.


States of consciousness include alertness States of consciousness include alertness and sleeping.and sleeping.

ConsciousnessConsciousness ranges from being wide awake ranges from being wide awake and alert to drowsiness, sleep, and coma.and alert to drowsiness, sleep, and coma.

• The constant electrical The constant electrical

activity of the brain can activity of the brain can

be measured by an be measured by an

electroencephalogram (EEG).electroencephalogram (EEG).• PET scans can show PET scans can show

the precise location of brain activity.the precise location of brain activity.



Neurons of the Neurons of the reticular formationreticular formation control the control the changing levels of consciousness by releasing changing levels of consciousness by releasing serotonin from sleep centers in the neural serotonin from sleep centers in the neural network.network.

• High serotonin levels trigger drowsiness and sleep.High serotonin levels trigger drowsiness and sleep.• Sleep has two major stages: slow-wave, “normal” Sleep has two major stages: slow-wave, “normal”

sleep and REM (sleep and REM (rapid eye movementrapid eye movement) sleep.) sleep.

Fig. 13.24a, p. 243

Fig. 13.24b, p. 243

The Central The Central Nervous Nervous SystemSystem

Section 10Section 10

Disorders of the Nervous Disorders of the Nervous System System

Disorders of the Nervous SystemDisorders of the Nervous System

Some diseases attack and damage Some diseases attack and damage neurons.neurons.

Alzheimer’s diseaseAlzheimer’s disease involves the progressive involves the progressive degeneration of brain neurons, while at the degeneration of brain neurons, while at the same time there is an abnormal buildup of same time there is an abnormal buildup of amyloid protein, leading to the loss of memory.amyloid protein, leading to the loss of memory.


Parkinson’s diseaseParkinson’s disease (PD) is characterized by (PD) is characterized by the death of neurons in the thalamus that the death of neurons in the thalamus that normally make dopamine and norepinephrine normally make dopamine and norepinephrine needed for normal muscle function.needed for normal muscle function.

Figure 13.25aFigure 13.25a


MeningitisMeningitis is an often fatal inflammatory is an often fatal inflammatory disease caused by a virus or bacterial infection disease caused by a virus or bacterial infection of the meninges covering the brain and/or of the meninges covering the brain and/or spinal cord.spinal cord.

EncephalitisEncephalitis is very dangerous inflammation of is very dangerous inflammation of the brain, often caused by a virus.the brain, often caused by a virus.

Multiple sclerosisMultiple sclerosis (MS) is an autoimmune (MS) is an autoimmune disease that results in the destruction of the disease that results in the destruction of the myelin sheath of neurons in the CNS.myelin sheath of neurons in the CNS.


The CNS can also be damaged by injury or The CNS can also be damaged by injury or seizure.seizure.

A A concussionconcussion can result from can result from

a severe blow to the head, a severe blow to the head,

resulting in blurred vision and resulting in blurred vision and

brief loss of consciousness.brief loss of consciousness. Damage to the spinal cord can Damage to the spinal cord can

result in lost sensation, muscle result in lost sensation, muscle

weakness, or weakness, or paralysisparalysis below below

the site of the injury.the site of the injury. Figure 13.25bFigure 13.25b


EpilepsyEpilepsy is a is a seizure disorderseizure disorder, often inherited , often inherited but also caused by brain injury, birth trauma, or but also caused by brain injury, birth trauma, or other assaults on the brain.other assaults on the brain.

HeadachesHeadaches occur when the brain registers occur when the brain registers tension in muscles or blood vessels of the face, tension in muscles or blood vessels of the face, neck, and scalp as pain; neck, and scalp as pain; migrainemigraine headaches headaches are extremely painful and can be triggered by are extremely painful and can be triggered by hormonal changes, fluorescent lights, and hormonal changes, fluorescent lights, and certain foods, particularly in women.certain foods, particularly in women.

Section 11Section 11

The Brain on DrugsThe Brain on Drugs


Drugs can alter mind and body functions. Drugs can alter mind and body functions. Psychoactive drugs exert their influence on Psychoactive drugs exert their influence on

brain regions that govern states of brain regions that govern states of consciousness and behavior.consciousness and behavior.

There are four categories of psychoactive There are four categories of psychoactive drugs:drugs:

• StimulantsStimulants (caffeine, cocaine, nicotine, (caffeine, cocaine, nicotine, amphetamines) increase alertness or activity for a amphetamines) increase alertness or activity for a time, and then depress you.time, and then depress you.

Fig. 13.26, p. 245


• DepressantsDepressants (alcohol) depress brain activity, limit (alcohol) depress brain activity, limit judgment, and interfere with coordinated movement; judgment, and interfere with coordinated movement; blood alcohol concentration (BAC) measures alcohol blood alcohol concentration (BAC) measures alcohol in the blood to determine the level of intoxication.in the blood to determine the level of intoxication.

• AnalgesicsAnalgesics (pain relievers) include morphine and (pain relievers) include morphine and OxyContin, a synthetic derivative; analgesics block OxyContin, a synthetic derivative; analgesics block pain signals and some may produce euphoria.pain signals and some may produce euphoria.

• HallucinogensHallucinogens, such as marijuana, act like , such as marijuana, act like depressants at low levels, but may also skew depressants at low levels, but may also skew perception and performance of complex tasks.perception and performance of complex tasks.


Drug use can lead to addiction.Drug use can lead to addiction. As the body develops As the body develops tolerancetolerance to a drug, to a drug,

larger and more frequent doses are needed to larger and more frequent doses are needed to produce the same effect; this reflects physical produce the same effect; this reflects physical drug dependence.drug dependence.

Psychological drug dependence, or Psychological drug dependence, or habituationhabituation, develops when a user begins to , develops when a user begins to crave the feelings associated with using a crave the feelings associated with using a particular drug and cannot function without it.particular drug and cannot function without it.

Habituation and tolerance are evidence of Habituation and tolerance are evidence of addictionaddiction..

Table 13.2, p. 245

Documents

PowerLecture: Chapter 13 The Nervous System. Learning Objectives Describe the visible structure of neurons, neuroglia, nerves, and ganglia, both separately