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


• Three interconnected functions

– Sensory input (sensory neurons)

– Integration (interneurons)

– Motor output (motor neurons)

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


• NS: 2 divisions

– CNS: brain & spinal cord

– PNS: nerves that carry info into and out of CNS


Figure 28.1B

Brain

1 Sensoryreceptor 2 Sensory neuron

3

4

Ganglion

Motorneuron Spinal

cord

Interneuron

CNS

Nerve

PNS

Quadricepsmuscles

Flexormuscles


• Neurons - cells transmit nervous impulses

• Made 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

• Myelin sheath - insulating material in vertebrates

– Made of Schwann cells linked by nodes of Ranvier

– 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


• Resting potential

• (+) outside and (- 70 mv) inside

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


• Stimulus changes permeability of part of plasma membrane

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

– Causes nerve signal (electrical) to be generated

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


• Action potential - nerve signal

– Electrical change in plasma membrane voltage (charge) from the resting potential to maximum level and back to resting potential


Ions and channels involved

• Sodium (Na+) outside, Potassium (K+) inside

• Voltage gated (Na+) and (K+) channels where specific ions go through are found in EACH node

• Change in voltage opens channels, and ions go from hi-lo concn

• Sodium/Potassium pump restores 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, resulting In REFRACTORY periodWhere the node is unable To be stimulated

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+


Polarized / Depolarized / Repolarized / Hyperpolarized

• POLARIZED

resting potential – opposite sides of membranes have opposite charges ( - inside / + outside)

• DEPOLARIZED

when membrane reaches threshold – 50 mV, Na+ gates open and Na+ rush in, changing inside to +++


Polarized / Depolarized / Repolarized / Hyperpolarized

• REPOLARIZED

Na+ gates close, K+ gates open and K+ rush out, making inside membrane (-) again

• HYPERPOLARIZED

K+ gates stay open longer; more K+ rush out and cell becomes – 90 mV = REFRACTORY PERIOD (node is temp unstimulatable)


HYPERPOLARIZED -> RESTING POTENTIAL

• Na+ / K+ pump pumps Na+ out and K+ in to restore RP (-70 mV)

• Some Na+ move to next node to change charge if reach – 50 mV, next Na+ gate opens


Figure 28.4

RESTING POTENTIAL1

2

3

4

REACHING THRESHOLD

DEPOLARIZATION

5 HYPERPOLARIZATIONRefractory Period

REPLORIZATION

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+


• Action potential: all-or-none event

– Stronger the stimulus = more AP coming through nodes (instead of stronger AP)

ex. Tap on finger versus hammer hitting finger


• Synapse:

– Space between two neurons or between a neuron and target (muscle) cell

• Synapses - either electrical or chemical

– Electrical: Action potentials pass between cells w/o neurotransmitter

– Chemical: neurotransmitters cross synaptic cleft to bind to receptors on 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 NT: open Na+ gates for AP to move forward

• Inhibitory NT: open Cl- gates = decrease next cell’s ability to develop AP

• Summation: total excitation and inhibition determines whether or not next cell will move signal forward (AP go forward)

28.7 Chemical synapses make complex information processing possible


• Neuron receiving input from 100s other neurons

Figure 28.7

Dendrites Synaptic knobs

Myelinsheath

Receivingcell body

AxonSynapticknobs


• Radially symmetrical animals = 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:concentration of nervous

system in head region

– Centralization: presence of CNS

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

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


• Motor division of the PNS

– Autonomic nervous system: involuntary control over the internal organs

– Somatic nervous system: voluntary control over skeletal muscles


• Autonomic NS:

– Parasympathetic division: resting / digesting

– Sympathetic division: fight / flight

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

Spinalcord

Eye

Salivaryglands

Lung

Heart

LiverStomach

Adrenalgland

Pancreas

Intestines

Bladder

Dilatespupil

Inhibitssalivaproduction

Relaxesbronchi

Acceleratesheart

Stimulatesepinephrineand norepi-nephrine release

Stimulatesglucoserelease

Inhibitsstomach,pancreas,and intestines

Inhibitsurination


Figure 28.15A

Forebrain

Cerebrum

Thalamus

Hypothalamus

Pituitary gland

Midbrain

Hindbrain

Pons

Medullaoblongata

Cerebellum

Spinal cord

Cerebralcortex


• Hemisphere – left/right

Figure 28.15B

Left cerebralhemisphere

Right cerebralhemisphere

Corpuscallosum

Basalganglia


• Cerebral cortex: voluntary motion; higher function (memory and creativity); conscious mind; speech; problem solving; sensations – smell, sights, temperature, etc

• Olfactory lobe: smell

• Thalamus: relay sensory input and distribute to appropriate part of cerebral cortex

• Hypothalamus: body homeostasis – hormone level, temperature, hunger, thirst, pain, etc

28.16 Parts of CNS / Brain


• Pons: relay center cerebellum

• Medulla (oblongata): vital functions – breathing, heart rate, CO2 level

• Cerebellum: muscle movement and balance

• Spinal cord: brain to body – reflex arc

BIOLOGYCONCEPTS & CONNECTIONS

Fourth Edition


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

From PowerPoint® Lectures for Biology: Concepts & Connections

CHAPTER 29The Senses

Modules 29.1 – 29.3


• Sensation

– Awareness of sensory stimuli

• Perception

– Brain’s full integration of sensory data

29.1 Sensory inputs become sensations and perceptions in the brain

Figure 29.1


• Sensory receptors (sight, touch, sound, smell, taste)

29.2 Sensory receptor cells convert stimuli into electrical energy

SENSORY RECEPTION


Figure 29.2A

Taste bud anatomy1

2 Sugarbinding

Tongue Taste pore

Taste bud

Sugarmolecule

Sensoryreceptorcells

Sensory neuron

Receptor cellmembrane

Sugar molecule

Ionchannels

Ion

3 Receptorpotential

4 Synapse

Sensoryreceptorcell

Neuro-transmittermolecules

Sensoryneuron

Action potential

5 Action potentials

No sugar Sugar present

mV


• Action potentials transmitted to CNS via sensory neurons

• Brain distinguishes different types of stimuli


Figure 29.2B

Sugarreceptor

BRAIN

Interneurons

Saltreceptor

Sensoryneurons

TASTEBUD

No salt

Increasing sweetness Increasing saltiness

No sugar


• Pain receptors

– Sense dangerous stimuli

• Thermoreceptors

– Detect heat or cold

• Mechanoreceptors

– Respond to mechanical energy (touch, pressure, and sound)

29.3 Specialized sensory receptors detect five categories of stimuli


Figure 29.3A

Heat Lighttouch

Pain Cold (Hair) Lighttouch

Epidermis

Dermis

Nerve Touch Strongpressure


• Stretch receptors and hair cells are two types of mechanoreceptors

Figure 29.3B

“Hairs” ofreceptor cell

Neurotransmitterat synapse

Sensoryneuron

Actionpotentials

Moreneurotransmitter

(1) Receptor cell at rest (2) Fluid moving in one direction

Lessneurotransmitter

(3) Fluid moving in other direction


• Electromagnetic receptors

– Respond to electricity, magnetism, and light

• Photoreceptors sense light

– They are the most common electromagnetic receptors

Figure 29.3D

Eye

Infraredreceptor


29.5 Vertebrates have single-lens eyes

Figure 29.5

Sclera

Muscle

Ligament

Iris

Pupil

Cornea

Aqueoushumor

Lens

Vitreoushumor

Choroid

Retina

Fovea(center ofvisual field)

Opticnerve

Arteryand vein

Blind spot


• Human eye

– Cornea and lens focus light on photoreceptor cells in the retina

– Photoreceptors most concentrated in fovea

– two eyes compensates for blind spot

– blind spot optic nerve passes through retina


Figure 29.6

Muscle contracted

Ligaments

Light from anear object Lens

Choroid

Retina

NEAR VISION(ACCOMMODATION)

DISTANCE VISION

Muscle relaxed

Light from adistant object


• photoreceptor cells

• Rods (contrast – black/white)

– Cones (color)

29.8 Our photoreceptor cells are rods and cones

Figure 29.8A

Cell body

Synapticknobs

Membranous discscontaining visual pigments

ROD

CONE


Figure 29.8B

Retina

Opticnerve

Fovea

Opticnervefibers

Retina

Photoreceptors

Neurons Cone Rod


– outer ear channels sound waves to eardrum

29.9 The ear converts air pressure waves into action potentials that are perceived as sound

HEARING AND BALANCE

Figure 29.9A

OUTER EARMIDDLE

EAR INNER EAR

Pinna Auditorycanal Eustachian

tube


– The eardrum passes vibrations to chain of bones in middle ear

Figure 29.9B

Stirrup

Anvil

Hammer

Skull bones

Semicircular canals(function in balance)

Auditory nerve,to brain

Cochlea

EardrumOval window(behind stirrup)

Eustachian tube


– bones transmit vibrations to fluid in cochlea, which houses organ of Corti

– Vibrations in cochlear fluid move hair cells (mechanoreceptors) against overlying membrane

– Bending hair cells trigger nerve signals to brain via the auditory nerve


Middlecanal

Bone

Cross sectionthrough cochlea ORGAN OF CORTI

Lowercanal

Uppercanal

Auditorynerve

Hair cells

Overlying membrane

Sensoryneurons

Basilarmembrane To auditory nerve

Figure 29.9C


• Louder sounds generate

– more action potentials are generated


Figure 29.9D

OUTER EAR MIDDLE EAR INNER EAR

Pinna Auditorycanal

Ear-drum

Hammer,anvil, stirrup

Ovalwindow

Cochlear canal

Upper and middle Lower

Time

Organ of Cortistimulated

Amplificationin middle ear

Onevibration

Amplitude

Pre

ss

ure


• Organs of balance located in inner ear

– Semicircular canals

29.10 The inner ear houses our organs of balance


• Equilibrium structures in the inner ear

Figure 29.10

Semicircularcanals

Nerve

Cochlea

Utricle

Saccule

Flow of fluid

Cupula

Flowof fluid

Cupula

Hairs

Haircell

Nerve fibers

Direction of body movement


• Smell and taste depend on chemoreceptors sending nerve signals to the brain

– Specific molecules binding to chemoreceptors determine signals

29.12 Odor and taste receptors detect categories of chemicals

TASTE AND SMELL


• Olfactory (smell) receptors are sensory neurons that line the upper part of the nasal cavity

Figure 29.12A

BRAIN

NASAL CAVITY

Action potentials

Bone

Chemo-receptorcell

Cilia

Epithelialcell

MUCUS


• Taste receptors - sensory neurons located in back of the throat and tongue (taste buds)

• types of taste receptors

– Sweet, sour, salty, bitter, umami


• Insects have taste receptors located in sensory hairs on feet– can taste food

by stepping on it

Figure 29.12B

To brain

Chemo-receptorcells

Sensoryhair

Pore at tip

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CHAPTER 28 Nervous Systems

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