ch28&29 notes nervous system and the eye

© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

PowerPoint Lectures forCampbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey

Chapter 28Chapter 28 Nervous Systems

Figure 28.0_1

Chapter 28: Big Ideas

Nervous SystemStructure and Function

The Human BrainAn Overview of AnimalThe Eye

Nerve Signals andTheir Transmission

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

The nervous system

– obtains sensory information, sensory input,

– processes sensory information, integration, and

– sends commands to effector cells (muscles) that carry out appropriate responses, motor output.

© 2012 Pearson Education, Inc.

Sensory neurons

– convey signals from sensory receptors

– to the CNS.

Interneurons

– are located entirely in the CNS,

– integrate information, and

– send it to motor neurons.

Motor neurons convey signals to effector cells.

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


Figure 28.1B

Sensoryreceptor

21

3

4

Sensoryneuron

Brain

Spinalcord

Interneuron

CNSPNS

NerveFlexormuscles

Quadricepsmuscles

Ganglion

Motorneuron

28.2 Neurons are the functional units of nervous systems

Neurons are

– cells specialized for carrying signals

– the functional units of the nervous system

A neuron consists of

– cell body

– extensions (fibers) that conduct signals,

– Dendrites (toward the cell body)

– Axons (away from the cell body)


28.2 Neurons are the functional units of nervous systems


Figure 28.2_2

Node of Ranvier

Layers of myelin

NucleusSchwann

cell

• Myelin sheaths• enclose axons,• form a cellular insulation, and speed up signal transmission.

28.3 Nerve function depends on charge differences across neuron membranes

At rest, a neuron’s plasma membrane has potential energy—the membrane potential, in which

– just inside the cell is slightly negative and

– just outside the cell is slightly positive.

The resting potential is the voltage across the plasma membrane of a resting neuron.

– The resting potential exists because of differences in ion concentration of the fluids inside and outside the neuron.


Figure 28.3

Neuron Axon

Plasmamembrane

Plasmamembrane

Na

channel

Outside of neuron

K channel

Inside of neuron

Na

Na

Na

Na

Na

KK

K

K

KK

K

K

K

K

K

Na Na

Na

Na

Na

Na Na

Na

Na

NaNa

NaNa

NaK

K

KKK

Na-K

pumpATP

K

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

A stimulus is any factor that causes a nerve signal to be generated. A stimulus

– alters the permeability of a portion of the membrane, which allows ions to pass through,

– Which then changes the membrane’s voltage.


A nerve signal, called an action potential, is

– a change in the membrane voltage, from the resting potential, to a maximum level, and then back to the resting potential.

Action potentials are

– self-propagated in a one-way chain reaction along a neuron

– all-or-none events.

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


Animation: Action Potential

Figure 28.5_s3

Na

1

Na

Na

Na

K

K

Action potential

2

Plasmamembrane

Axonsegment

Actionpotential

Action potentialNa

K

K3

Na

Animation

28.6 Neurons communicate at synapses

Synapses are junctions where signals are transmitted between

– two neurons or

– between neurons and other cells.


Electrical signals pass between cells at electrical synapses.

At chemical synapses

– the ending cell secretes a chemical signal, a neurotransmitter,

– the neurotransmitter crosses the synaptic cleft, and

– the neurotransmitter binds to a specific receptor on the surface of the receiving (postsynaptic) cell.

28.6 Neurons communicate at synapses


Animation: Synapse

Figure 28.6

Axon ofsendingcell

Synapticterminalof sendingcell

Dendriteof receiving cell

Sending cell

Synapticvesicles

Synapticterminal

Synapticcleft

Vesicle fuseswith plasmamembrane

Actionpotentialarrives

Neurotransmitteris released intosynaptic cleft

Neurotransmitterbinds to receptor

Neurotransmittermolecules

Neurotransmitter brokendown and released

Ion channel closes

Ions

Receptor

Receivingcell

Neurotransmitter

Ion channels

Ion channel opens5 6

4

32

1

Animation

28.7 Chemical synapses enable complex information to be processed

Neurotransmitters

– can excite a receiving cell

– can inhibit a receiving cell’s activity

– by decreasing its ability to develop action potentials.


28.8 A variety of small molecules function as neurotransmitters

Neurotransmitters:

– Acetylcholine is a neurotransmitter

– in the brain

– at synapses between motor neurons and muscle cells.

– Biogenic amines

– are important neurotransmitters in the CNS

– include serotonin and dopamine, which affect sleep, mood, and attention.

– Neuropeptides

– consist of relatively short chains of amino acids important in the CNS

– include endorphins, decreasing our perception of pain.


28.9 CONNECTION: Many drugs act at chemical synapses

Many psychoactive drugs

act at synapses

affect neurotransmitter action.

– Caffeine counters the effect of inhibitory neurotransmitters.

– Nicotine acts as a stimulant by binding to acetylcholine receptors.

– Alcohol is a depressant by increasing inhibitory effects.

– Antidepressants block the removal of serotonin, increasing the time this mood neurotransmitter is in the synapse.

– Tranquilizers (Valium & Xanax) increase inhibitors in synapses.

– Ritalin & Adderall block reuptake of dopamine and norepinephrine © 2012 Pearson Education, Inc.

In the vertebrates, the central nervous system (CNS)– consists of the brain and spinal cord and

– includes spaces filled with cerebrospinal fluid

The vertebrate peripheral nervous system (PNS) consists of– cranial nerves,

– spinal nerves, and

– ganglia.

28.11 Vertebrate nervous systems are highly centralized


Figure 28.11A

Centralnervoussystem(CNS)

Peripheralnervoussystem(PNS)

Spinalcord

Cranialnerves

GangliaoutsideCNS

Spinalnerves

Brain

Figure 28.11B

Brain Cerebrospinal fluid

Meninges

Gray matter

Whitematter

Dorsal rootganglion(part of PNS)

Spinal nerve(part of PNS)Central canal

Spinal cord(cross section)

Ventricles

Central canalof spinal cord

Spinal cord

The motor nervous system

– carries signals to and from skeletal muscles and

– mainly responds to external stimuli.

The autonomic nervous system

– regulates the internal environment and

– controls smooth and cardiac muscle and organs and glands of the digestive, cardiovascular, excretory, and endocrine systems.

28.12 The peripheral nervous system of vertebrates is a functional hierarchy


Figure 28.12A

Peripheral nervous system(to and from the central

nervous system)

Motor system(voluntary and

involuntary; to and fromskeletal muscles)

Autonomic nervous system(involuntary; smooth and

cardiac muscles, various glands)

Parasympatheticdivision

(“Rest and digest”)

Sympatheticdivision

(“Flight and fight”)

Enteric division(muscles and glands

of the digestive system)

28.14 The structure of a living supercomputer: The human brain

The human brain is

– more powerful than the most sophisticated computer and

– composed of three main parts:

1. forebrain,

2. midbrain, and

3. hindbrain.


Figure 28.14A

Cerebral cortex(outer regionof cerebrum)

Cerebrum

Thalamus

Hypothalamus

Pituitary gland

Midbrain

Forebrain

Hindbrain

Pons

MedullaoblongataCerebellum

Spinalcord

Figure 7.16a

Third ventricle

Anteriorcommissure

Hypothalamus

Optic chiasma

Pituitary gland

Mammillary bodyPonsMedulla oblongata

Spinal cord

Cerebral hemisphereCorpus callosumChoroid plexus of thirdventricleOccipital lobe ofcerebral hemisphere

Thalamus(encloses third ventricle)Pineal gland(part of epithalamus)

CorporaquadrigeminaCerebralaqueduct

Cerebral peduncleof midbrainFourth ventricleChoroid plexusCerebellum

Midbrain

(a)

The cerebrum is

– part of the forebrain and

– the largest and most complex part of the brain.

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

28.14 The structure of a living supercomputer: The human brain


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

The cerebral cortex

– accounts for 80% of the total human brain mass.

Specialized integrative regions of the cerebral cortex include

– the motor cortex

– the somatosensory cortex (touch, pain, pressure, and temperature)

– centers for vision, hearing, taste, and smell.


Association areas

– make up most of the cerebrum and

– are concerned with higher mental activities such as reasoning and language.

In a phenomenon known as lateralization, right and left cerebral hemispheres tend to specialize in different mental tasks.

– Left – language, logic, math, and motor control

– Right – spatial relations, patterns, nonverbal thinking

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


Figure 28.15

Frontal lobe Parietal lobe

Occipital lobeTemporal lobe

Frontalassociationarea

Speech

Smell

Speech

Mot

or c

orte

x

Hearing

Reading

Vision

Visualassociationarea

Somatosensoryassociationarea

Auditoryassociationarea

Som

atos

enso

ry c

ort

ex

Regions of the Brain

Hypothalamus

– Under the thalamus

– Important autonomic nervous system center

– Helps regulate body temperature

– Controls water balance

– Regulates metabolism

– Houses the limbic center for emotions

– Thirst, appetite, pain, pleasure, etc.


Medulla oblongata

– The lowest part of the brain stem

– Merges into the spinal cord

– Includes important fiber tracts

– Contains important control centers

– Heart rate control

– Blood pressure regulation

– Breathing

– Swallowing

– Vomiting


Cerebellum

– Two hemispheres with convoluted surfaces

– Provides involuntary coordination of body movements, balance and equilibrium.

28.20 CONNECTION: Changes in brain physiology can produce neurological disorders

Many neurological disorders can be linked to changes in brain physiology, including

– schizophrenia,

– major depression,

– Alzheimer’s disease, and

– Parkinson’s disease.



Schizophrenia

– a severe mental disturbance and

– characterized by psychotic episodes in which patients lose the ability to distinguish reality.

Depression

– Two broad forms of depressive illness have been identified:

1. major depression and

2. bipolar disorder, manic-depressive disorder.

– Treatments may include selective serotonin reuptake inhibitors (SSRIs), which increase the amount of time serotonin is available to stimulate certain neurons in the brain.


Figure 28.20A

Depressed brain

Normal brain

Alzheimer’s disease

– characterized by confusion, memory loss, and personality changes

Parkinson’s disease

– a motor disorder

– characterized by

– difficulty in initiating movements,

– slowness of movement, and

– rigidity.



The Eye and Vision

70 percent of all sensory receptors are in the eyes

Each eye has over a million nerve fibers

Protection for the eye

– Most of the eye is enclosed in a bony orbit

– A cushion of fat surrounds most of the eye

29.7 EVOLUTION CONNECTION: Several types of eyes have evolved independently among animals

The ability to detect light plays a central role in the lives of nearly all animals.

All animal light detectors are based on cells called photoreceptors that contain pigment molecules that absorb light.


29.7 EVOLUTION CONNECTION: Several types of eyes have evolved independently among animals

– In single-lens eyes– light enters the front center of the eye through a small opening, the

pupil,

– the amount of light that enters is controlled by the iris

– light passes through a single disklike lens

– light is focused onto the retina, which consists of many photoreceptor cells


Figure 29.7C

Sclera

Ciliary body

Ligament

Cornea

Iris

Pupil

Aqueoushumor

Lens

Vitreoushumor

Blind spot

Arteryand vein

Opticnerve

Fovea(center ofvisual field)

Retina

Choroid

29.8 Humans have single-lens eyes that focus by changing position or shape

The outer surface of the human eyeball is a tough, whitish layer of connective tissue called the sclera.

– At the front of the eye, the sclera becomes the transparent cornea

– lets light into the eye

– helps focus light



The lens and ciliary body divide the eye into two fluid-filled chambers.

1. The large chamber behind the lens is filled with a jellylike vitreous humor.

2. The smaller chamber in front of the lens contains the thinner aqueous humor.

– These humors

– help maintain the shape of the eyeball and

– circulate nutrients and oxygen to the lens, iris, and cornea.



In mammals, the lens focuses by changing shape using muscles attached to the choroid and ligaments that suspend the lens.


29.9 CONNECTION: Artificial lenses or surgery can correct focusing problems

Visual acuity is the ability of the eyes to distinguish fine detail.

– Visual acuity is measured by reading standardized eye charts from a distance of 20 feet.

– The ability to see normally at 20 feet is 20/20 vision.


29.10 The human retina contains two types of photoreceptors: rods and cones

The human retina contains two types of photoreceptors.

1. Rods

– contain the visual pigment rhodopsin, which can absorb dim light, and

– can detect shades of gray in dim light.

2. Cones

– contain the visual pigment photopsin, which absorbs bright colored light, and

– allow us to see color in bright light.


Figure 29.10B

Retina

Opticnerve

Retina

Neurons Photoreceptors

Rod Cone

Opticnervefibers

To the brain

Structure of the Eye: Sensory Layer

Signals leave the retina toward the brain through the optic nerve

Optic disc (blind spot) is where the optic nerve leaves the eyeball

– Cannot see images focused on the optic disc

ch28&29 notes nervous system and the eye

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sensory neurons

neurons plasma membrane

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