chapter 28 nervous systems

BIOLOGYCONCEPTS & CONNECTIONS

Fourth Edition

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor

From PowerPoint® Lectures for Biology: Concepts & Connections

CHAPTER 28Nervous Systems

Modules 28.1 – 28.9


• The spinal cord is the central communication conduit between the brain and the body

– It consists of a bundle of nerves

Can an Injured Spinal Cord Be Fixed?


• Spinal cord injury disrupts communication between the central nervous system and the rest of the body

– Paraplegia is paralysis of the lower half of the body

– Quadriplegia is paralysis from the neck down

– Research on nerve cells is leading to new therapies


• The nervous system has three interconnected functions

– Sensory input

– Integration

– Motor output

28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands

NERVOUS SYSTEM STRUCTURE AND FUNCTION


Figure 28.1A

Sensory receptor

SENSORY INPUT

INTEGRATION

MOTOR OUTPUT

Effector

Peripheral nervoussystem (PNS)

Central nervoussystem (CNS)

Brain and spinal cord


• The nervous system can be divided into two main divisions– The central nervous system (CNS) :

the brain the spinal cord (in vertebrates)

– The peripheral nervous system (PNS) : nerves ganglia (carry signals into/out of the CNS)


A. Central nervous system B. Peripheral nervous systemB1. Somatic nervous systemB2. Autonomic nervous system 1. Cerebrum2. Brainstem3. Cerebellum4. Spinal cord


• Three types of neurons correspond to the nervous system’s three main functions

– Sensory neurons convey signals from sensory receptors into the CNS

– Interneurons integrate data and relay signals

– Motor neurons convey signals to effectors


Figure 28.1B

Brain

1 Sensoryreceptor 2 Sensory neuron

3

4

Ganglion

Motorneuron Spinal

cord

Interneuron

CNS

Nerve

PNS

Quadricepsmuscles

Flexormuscles


• Neurons are cells specialized to transmit nervous impulses

• They consist of

– a cell body

– dendrites (highly branched fibers)

– an axon (long fiber)

28.2 Neurons are the functional units of nervous systems


• Supporting cells protect, insulate, and reinforce neurons

• The myelin sheath is the insulating material in vertebrates

– It is composed of a chain of Schwann cells linked by nodes of Ranvier

– It speeds up signal transmission

– Multiple sclerosis (MS) involves the destruction of myelin sheaths by the immune system


Figure 28.2

Signal direction Dendrites

Cellbody

Cell body

Nucleus

Axon

Schwann cell

Signalpathway

Myelin sheath

Nodes ofRanvier

Synaptic knobs

Node of Ranvier

Myelin sheath

Schwann cell

Nucleus


• The resting potential of a neuron’s plasma membrane is caused by the cell membrane’s ability to maintain

– a positive charge on its outer surface

– a negative charge on its inner (cytoplasmic) surface

28.3 A neuron maintains a membrane potential across its membrane

NERVE SIGNALS AND THEIR TRANSMISSION

Plasmamembrane

Microelectrodeinside cell

Axon

Neuron

Microelectrodeoutside cell

Voltmeter

–70 mV

Figure 28.3A


• Resting potential is generated and maintained with help from sodium-potassium pumps– These pump K+ into the cell and Na+ out

of the cell

Figure 28.3B

OUTSIDE OF CELL

Na+

Na+

channel

Na+

Na+

Na+

Na+K+ K+

Na+

Na+

Na+

Na+

Na+

K+Plasmamembrane

Protein

Na+

K+

K+

K+

K+

K+ K+

K+

K+

K+

K+

Na+ - K+

pump

Na+

Na+

K+

channel

INSIDE OF CELL


• A stimulus alters the permeability of a portion of the plasma membrane

– Ions pass through the plasma membrane, changing the membrane’s voltage

– It causes a nerve signal to be generated

28.4 A nerve signal begins as a change in the membrane potential


• An action potential is a nerve signal

– It is an electrical change in the plasma membrane voltage from the resting potential to a maximum level and back to the resting potential


Figure 28.4

Resting state: voltage gated Na+

and K+ channels closed; restingpotential is maintained.

1

2

3

4

A stimulus opens some Na+channels; if threshold is reached,action potential is triggered.

Additional Na+ channels open,K+ channels are closed; interior ofcell becomes more positive.

5 The K+ channels closerelatively slowly, causinga brief undershoot.

Na+ channels close andinactivate. K+ channelsopen, and K+ rushesout; interior of cell morenegative than outside.

Neuroninterior

Actionpotential

Thresholdpotential

Resting potential

1

2

3

4

5

Na+

Na+

Na+

Na+

1 Return to resting state.

1

Neuroninterior

K+

K+


28.5 The action potential propagates itself along the neuron

Figure 28.5

1

2

3

Axon

Action potential

Axonsegment

Action potential

Na+

Na+

K+

K+

Action potential

Na+

K+

K+


• An action potential is an all-or-none event– Its size is not affected by the stimulus

strength

– However, the frequency changes with the strength of the stimulus


• The synapse is a key element of nervous systems

– It is a junction or relay point between two neurons or between a neuron and an effector cell

• Synapses are either electrical or chemical

– Action potentials pass between cells at electrical synapses

– At chemical synapses, neurotransmitters cross the synaptic cleft to bind to receptors on the surface of the receiving cell

28.6 Neurons communicate at synapses


Figure 28.6

1

Actionpotentialarrives

2

Vesicle fuses with plasma membrane

3

Neurotransmitteris released intosynaptic cleft

Axon ofsendingneuron

Vesicles

SENDINGNEURON

Synapticknob SYNAPSE

SYNAPTICCLEFT

RECEIVINGNEURON

Ion channels

Neurotransmittermolecules

4

Neuro-transmitterbinds to receptor

Receivingneuron

5 Ion channel opens

Receptor

Ions

Neurotransmitter

6 Ion channel closes

Neurotransmitter brokendown and released


• Excitatory neurotransmitters trigger action potentials in the receiving cell

• Inhibitory neurotransmitters decrease the cell’s ability to develop action potentials

• The summation of excitation and inhibition determines whether or not the cell will transmit a nerve signal

28.7 Chemical synapses make complex information processing possible


• A neuron may receive input from hundreds of other neurons via thousands of synaptic knobs

Figure 28.7

Dendrites Synaptic knobs

Myelinsheath

Receivingcell body

AxonSynapticknobs


• Most neurotransmitters are small, nitrogen-containing organic molecules

– Acetylcholine

– Biogenic amines (epinephrine, norepinephrine, serotonin, dopamine)

– Amino acids (aspartate, glutamate, glycine, GABA)

– Peptides (substance P and endorphins)

– Dissolved gases (nitric oxide)

28.8 A variety of small molecules function as neurotransmitters


• Drugs act at synapses and may increase or decrease the normal effect of neurotransmitters

– Caffeine

– Nicotine

– Alcohol

– Prescription and illegal drugs

28.9 Connection: Many drugs act at chemical synapses

Figure 28.9


• Radially symmetrical animals have a nervous system arranged in a nerve net

– Example: Hydras

28.10 Nervous system organization usually correlates with body symmetry

NERVOUS SYSTEMS

Figure 28.10A

A. Hydra (cnidarian)

Nervenet

Neuron


• Most bilaterally symmetrical animals exhibit– cephalization, the concentration of the

nervous system in the head end

– centralization, the presence of a central nervous system

Figure 28.10B-E

B. Planarian (flatworm)

Eye

Brain

Nervecord

Transversenerve

C. Leech (annelid)

Brain

Ventralnervecord

Segmentalganglion

D. Insect (arthropod)

Brain

Ventralnervecord

Ganglia

Brain

Giantaxon

E. Squid (mollusk)


28.11 Vertebrate nervous systems are highly centralized and cephalized

Figure 28.11A

CENTRAL NERVOUSSYSTEM (CNS)

PERIPHERALNERVOUSSYSTEM (PNS)

Brain

Spinal cord

Cranialnerve

GangliaoutsideCNS

Spinalnerves


• The brain and spinal cord contain fluid-filled spaces

Figure 28.11B

BRAIN Meninges

Ventricles

Central canalof spinal cord

Spinal cord

White matter

Gray matterDorsal rootganglion(part of PNS)

Central canal Spinal nerve(part of PNS)

SPINAL CORD(cross section)


28.12 The peripheral nervous system of vertebrates is a functional hierarchy

Figure 28.12A

Peripheralnervous system

Sensorydivision

Motordivision

Sensingexternal

environment

Sensinginternal

environment

Autonomicnervous system

(involuntary)

Somaticnervous system

(voluntary)

Sympatheticdivision

Parasympatheticdivision


• Referred pain is when we feel pain from an internal organ on the body surface

– This happens because neurons carrying information from the skin and those carrying information from the internal organs synapse with the same neurons in the CNS

Figure 28.12B

Liver

Gallbladder

Liver

Small intestine

Appendix

Colon

Urinarybladder

Heart

Lungs anddiaphragmLungs anddiaphragm

Heart

Stomach

Pancreas

Ovaries

Kidney

Ureters


• The motor division of the PNS

– The autonomic nervous system exerts involuntary control over the internal organs

– The somatic nervous system exerts voluntary control over skeletal muscles


• The autonomic nervous system consists of two sets of neurons that function antagonistically on most body organs

– The parasympathetic division primes the body for activities that gain and conserve energy

– The sympathetic division prepares the body for intense, energy-consuming activities

28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment


Figure 28.13

PARASYMPATHETIC DIVISION SYMPATHETIC DIVISION

Brain

Constrictspupil

Stimulatessalivaproduction

Constrictsbronchi

Slowsheart

Stimulatesstomach,pancreas,and intestines

Stimulatesurination

Promoteserection ofgenitals

Spinalcord

Eye

Salivaryglands

Lung

Heart

LiverStomach

Adrenalgland

Pancreas

Intestines

Bladder

Genitals

Dilatespupil

Inhibitssalivaproduction

Relaxesbronchi

Acceleratesheart

Stimulatesepinephrineand norepi-nephrine release

Stimulatesglucoserelease

Inhibitsstomach,pancreas,and intestines

Inhibitsurination

Promotes ejacu-lation and vaginalcontractions


• The vertebrate brain evolved by the enlargement and subdivision of three anterior bulges of the neural tube

– Forebrain

– Midbrain

– Hindbrain

• Cerebrum size and complexity in birds and mammals correlates with sophisticated behavior

28.14 The vertebrate brain develops from three anterior bulges of the neural tube

THE HUMAN BRAIN


Figure 28.14

EmbryonicBrain Regions

Brain StructuresPresent in Adult

Forebrain

Cerebrum (cerebral hemispheres; includescerebral cortex, white matter, basal ganglia)

Diencephalon (thalamus, hypothalamus,posterior pituitary, pineal gland)

Midbrain (part of brainstem)Midbrain

Hindbrain

Pons (part of brainstem), cerebellum

Medulla oblongata (part of brainstem)

Midbrain

Hindbrain

Forebrain

Cerebralhemisphere

Diencephalon

Midbrain

Pons

Cerebellum

Medullaoblongata

Spinal cord

Embryo one month old Fetus three months old


28.15 The structure of a living supercomputer: The human brain

Table 28.15


Figure 28.15A

Forebrain

Cerebrum

Thalamus

Hypothalamus

Pituitary gland

Midbrain

Hindbrain

Pons

Medullaoblongata

Cerebellum

Spinal cord

Cerebralcortex


• Most of the cerebrum’s integrative power resides in the cerebral cortex of the two cerebral hemispheres

Figure 28.15B

Left cerebralhemisphere

Right cerebralhemisphere

Corpuscallosum

Basalganglia


• The motor cortex sends commands to skeletal muscles

• The somatosensory cortex receives information about pain, pressure, and temperature

• Several regions receive and process sensory information (vision, hearing, taste, smell)

28.16 The cerebral cortex is a mosaic of specialized, interactive regions


• The association areas are the sites of higher mental activities (thinking)

– Frontal association area (judgment, planning)

– Auditory association area

– Somatosensory association area (reading, speech)

– Visual association area


Figure 28.16

PARIETAL LOBE

OCCIPITAL LOBETEMPORAL LOBE

Frontalassociationarea

Speech

Mo

tor

cort

ex

Som

atos

enso

ry c

orte

x

Speech

Taste

Smell

Hearing

Auditoryassociationarea

Somatosensoryassociationarea

Reading

Visualassociationarea

Vision

FRONTAL LOBE


• In lateralization, areas in the two hemispheres become specialized for different functions– “Right-brained” vs. “left-brained”


• Much knowledge about the brain has come from individuals whose brains were altered through injury, illness, or surgery

– The rod that pierced Phineas Gage’s skull left his intellect intact but altered his personality and behavior

28.17 Connection: Injuries and brain operations have provided insight into brain function

Figure 28.17A


• A radical surgery called hemispherectomy removes almost half of the brain– It demonstrates the

brain’s remarkable plasticity

Figure 28.17B


• Sleep and arousal are controlled by

– the hypothalamus

– the medulla oblongata

– the pons

– neurons of reticular formation

28.18 Several parts of the brain regulate sleep and arousal

Figure 28.18A

Eye

Reticular formation

Input from touch,pain, and temperaturereceptors

Input from ears

Motoroutput tospinal cord


• An electroencephalogram (EEG) measures brain waves during sleep and arousal• Two types of deep sleep alternate

– Slow-wave (delta waves) and REM sleep

Figure 28.18B, C

Awake but quiet (alpha waves)

Awake during intense mental activity (beta waves)

Asleep

Delta waves REM sleep Delta waves


• The limbic system is a functional group of integrating centers in the cerebral cortex, thalamus, and hypothalamus

• It is involved in emotions, memory (short-term and long-term), and learning

– The amygdala is central to the formation of emotional memories

– The hippocampus is involved in the formation of memories and their recall

28.19 The limbic system is involved in emotions, memory, and learning


Figure 28.19

Thalamus

Hypothalamus

Prefrontalcortex

Smell

Olfactorybulb

Amygdala Hippocampus

CEREBRUM


• Memory and learning involve structural and chemical changes at synapses

– Long-term depression (LTD)

– Long-term potentiation (LTP)

28.20 The cellular changes underlying memory and learning probably occur at synapses


Figure 28.20

Repeatedactionpotentials

1

2

3

4

Synapticcleft

Ca2+Cascade ofchemical changes

Sendingneuron

Sendingneuron

3

Ca2+

LTPReceiving neuron

2

chapter 28 nervous systems

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