Power Points Sidesfor Test2

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

PowerPoint® Lecture Presentations for

Biology Eighth Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp

Chapter 45Chapter 45

Hormones and theEndocrine System


Overview: The Body’s Long-Distance Regulators

• Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body

• Hormones reach all parts of the body, but only target cells are equipped to respond

• Insect metamorphosis is regulated by hormones


• Two systems coordinate communication throughout the body: the endocrine system and the nervous system

• The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior

• The nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells


Concept 45.1: Hormones and other signaling molecules bind to target receptors, triggering specific response pathways

• Chemical signals bind to receptor proteins on target cells

• Only target cells respond to the signal


Types of Secreted Signaling Molecules

• Secreted chemical signals include

– Hormones

– Local regulators

– Neurotransmitters

– Neurohormones

– Pheromones


Hormones

• Endocrine signals (hormones) are secreted into extracellular fluids and travel via the bloodstream

• Endocrine glands are ductless and secrete hormones directly into surrounding fluid

• Hormones mediate responses to environmental stimuli and regulate growth, development, and reproduction

• Exocrine glands have ducts and secrete substances onto body surfaces or into body cavities (for example, tear ducts)


Local Regulators

• Local regulators are chemical signals that travel over short distances by diffusion

– help regulate blood pressure, nervous system function, and reproduction

• Local regulators are divided into two types

– Paracrine signals act on cells near the secreting cell

– Autocrine signals act on the secreting cell itself


Neurotransmitters and Neurohormones

• Neurons (nerve cells) contact target cells at synapses

• At synapses, neurons often secrete chemical signals called neurotransmitters that diffuse a short distance to bind to receptors on the target cell

• Neurotransmitters play a role in sensation, memory, cognition, and movement


• Neurohormones are a class of hormones that originate from neurons in the brain and diffuse through the bloodstream


Pheromones

• Pheromones are chemical signals that are released from the body and used to communicate with other individuals in the species

• Pheromones mark trails to food sources, warn of predators, and attract potential mates


Chemical Classes of Hormones

• Three major classes of molecules function as hormones in vertebrates:

– Polypeptides (proteins and peptides)

– Amines derived from amino acids

– Steroid hormones

• Lipid-soluble hormones (steroid hormones) pass easily through cell membranes

– travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells

• water-soluble hormones (polypeptides and amines) do not

– secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors

• The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells


Pathway for Water-Soluble Hormones

• Binding of a hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoplasm, enzyme activation, or a change in gene expression

Animation: Water-Soluble HormoneAnimation: Water-Soluble Hormone


• The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress

• Epinephrine binds to receptors on the plasma membrane of liver cells

• This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream

Fig. 45-6-2

cAMP Secondmessenger

Adenylylcyclase

G protein-coupledreceptor

ATP

GTP

G protein

Epinephrine

Inhibition ofglycogen synthesis

Promotion ofglycogen breakdown

Proteinkinase A


Pathway for Lipid-Soluble Hormones

• The response to a lipid-soluble hormone is usually a change in gene expression

• Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus

• Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes

Animation: Lipid-Soluble HormoneAnimation: Lipid-Soluble Hormone

Fig. 45-7-2

Hormone(estradiol)

Hormone-receptorcomplex

Plasmamembrane

Estradiol(estrogen)receptor

DNA

VitellogeninmRNA

for vitellogenin


Multiple Effects of Hormones

• The same hormone may have different effects on target cells that have

– Different receptors for the hormone

– Different signal transduction pathways

– Different proteins for carrying out the response

• A hormone can also have different effects in different species

Fig. 45-8-2

Glycogendeposits

receptor

Vesseldilates.

Epinephrine

(a) Liver cell

Epinephrine

receptor

Glycogenbreaks downand glucoseis released.

(b) Skeletal muscle blood vessel

Same receptors but differentintracellular proteins (not shown)

Epinephrine

receptor

Different receptors

Epinephrine

receptor

Vesselconstricts.

(c) Intestinal blood vessel


Concept 45.2: Negative feedback and antagonistic hormone pairs are common features of the endocrine system

• Hormones are assembled into regulatory pathways


Simple Hormone Pathways

• Hormones are released from an endocrine cell, travel through the bloodstream, and interact with the receptor or a target cell to cause a physiological response


• A negative feedback loop inhibits a response by reducing the initial stimulus

• Negative feedback regulates many hormonal pathways involved in homeostasis


Insulin and Glucagon: Control of Blood Glucose

• Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis

• The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin

Fig. 45-12-5

Homeostasis:Blood glucose level

(about 90 mg/100 mL)

Glucagon

STIMULUS:Blood glucose level

falls.

Alpha cells of pancreasrelease glucagon.

Liver breaksdown glycogenand releasesglucose.

Blood glucoselevel rises.

STIMULUS:Blood glucose level

rises.

Beta cells ofpancreasrelease insulininto the blood.

Liver takesup glucoseand stores itas glycogen.

Blood glucoselevel declines.

Body cellstake up moreglucose.

Insulin


Target Tissues for Insulin and Glucagon

• Insulin reduces blood glucose levels by

– Promoting the cellular uptake of glucose

– Slowing glycogen breakdown in the liver

– Promoting fat storage

• Glucagon increases blood glucose levels by

– Stimulating conversion of glycogen to glucose in the liver

– Stimulating breakdown of fat and protein into glucose


Concept 45.3: The endocrine and nervous systems act individually and together in regulating animal physiology

• Signals from the nervous system initiate and regulate endocrine signals


Coordination of Endocrine and Nervous Systems in Vertebrates

• The hypothalamus receives information from the nervous system and initiates responses through the endocrine system

• Attached to the hypothalamus is the pituitary gland composed of the posterior pituitary and anterior pituitary

– The posterior pituitary stores and secretes hormones that are made in the hypothalamus

– The anterior pituitary makes and releases hormones under regulation of the hypothalamus


• The posterior pituitary stores and secretes hormones that are made in the hypothalamus

• The anterior pituitary makes and releases hormones under regulation of the hypothalamus

• Table 45-1 gives a list of


Fig. 45-15

Posteriorpituitary

Anteriorpituitary

Neurosecretorycells of thehypothalamus

Hypothalamus

Axon

HORMONE OxytocinADH

Kidney tubulesTARGET Mammary glands,uterine muscles

Posterior Pituitary Hormones

• The two hormones released from the posterior pituitary act directly on nonendocrine tissues


• Oxytocin induces uterine contractions and the release of milk

• Suckling sends a message to the hypothalamus via the nervous system to release oxytocin, which further stimulates the milk glands

• This is an example of positive feedback, where the stimulus leads to an even greater response

• Antidiuretic hormone (ADH) enhances water reabsorption in the kidneys


Anterior Pituitary Hormones

• Hormone production in the anterior pituitary is controlled by releasing and inhibiting hormones from the hypothalamus

• For example, the production of thyrotropin releasing hormone (TRH) in the hypothalamus stimulates secretion of the thyroid stimulating hormone (TSH) from the anterior pituitary


Hormone Cascade Pathways

• A hormone can stimulate the release of a series of other hormones, the last of which activates a nonendocrine target cell; this is called a hormone cascade pathway

• The release of thyroid hormone results from a hormone cascade pathway involving the hypothalamus, anterior pituitary, and thyroid gland

• Hormone cascade pathways are usually regulated by negative feedback


Tropic Hormones

• A tropic hormone regulates the function of endocrine cells or glands

• The four strictly tropic hormones are

– Thyroid-stimulating hormone (TSH)

– Follicle-stimulating hormone (FSH)

– Luteinizing hormone (LH)

– Adrenocorticotropic hormone (ACTH)


Growth Hormone

• Growth hormone (GH) is secreted by the anterior pituitary gland and has tropic and nontropic actions

• It promotes growth directly and has diverse metabolic effects

• It stimulates production of growth factors

• An excess of GH can cause gigantism, while a lack of GH can cause dwarfism


Adrenal Hormones: Response to Stress

• The adrenal glands are adjacent to the kidneys

• Each adrenal gland actually consists of two glands: the adrenal medulla (inner portion) and adrenal cortex (outer portion)

• Epinephrine and norepinephrine

– Trigger the release of glucose and fatty acids into the blood

– Increase oxygen delivery to body cells

– Direct blood toward heart, brain, and skeletal muscles, and away from skin, digestive system, and kidneys

• The release of epinephrine and norepinephrine occurs in response to nerve signals from the hypothalamus

Fig. 45-21

Stress

Adrenalgland

Nervecell

Nervesignals

Releasinghormone

Hypothalamus

Anterior pituitary

Blood vessel

ACTH

Adrenal cortex

Spinal cord

Adrenal medulla

Kidney

(a) Short-term stress response (b) Long-term stress response

Effects of epinephrine and norepinephrine:

2. Increased blood pressure

3. Increased breathing rate

4. Increased metabolic rate

1. Glycogen broken down to glucose; increased blood glucose

5. Change in blood flow patterns, leading to increased alertness and decreased digestive, excretory, and reproductive system activity

Effects ofmineralocorticoids:

Effects ofglucocorticoids:

1. Retention of sodium ions and water by kidneys

2. Increased blood volume and blood pressure

2. Possible suppression of immune system

1. Proteins and fats broken down and converted to glucose, leading to increased blood glucose


Gonadal Sex Hormones

• The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins

• All three sex hormones are found in both males and females, but in different amounts


• The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system

• Testosterone causes an increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks


You should now be able to:

1. Distinguish between the following pairs of terms: hormones and local regulators, paracrine and autocrine signals

2. Describe the evidence that steroid hormones have intracellular receptors, while water-soluble hormones have cell-surface receptors

3. Explain how the antagonistic hormones insulin and glucagon regulate carbohydrate metabolism


4. Explain how the hypothalamus and the pituitary glands interact and how they coordinate the endocrine system

5. Explain the role of tropic hormones in coordinating endocrine signaling throughout the body

6. List and describe the functions of hormones released by the following: anterior and posterior pituitary lobes, thyroid glands, parathyroid glands, adrenal medulla, adrenal cortex, gonads, pineal gland


Chapter 46

Animal Reproduction

Animal ReproductionChapter 46


Concept 46.1: Both asexual and sexual reproduction occur in the animal kingdom

• Sexual reproduction is the creation of an offspring by fusion of a male gamete (sperm) and female gamete (egg) to form a zygote

• Asexual reproduction is creation of offspring without the fusion of egg and sperm

– Mechanisms of asexual reproduction

• Many invertebrates reproduce asexually by fission, separation of a parent into two or more individuals of about the same size


• In budding, new individuals arise from outgrowths of existing ones

• Fragmentation is breaking of the body into pieces, some or all of which develop into adults

• Fragmentation must be accompanied by regeneration, regrowth of lost body parts

• Parthenogenesis is the development of a new individual from an unfertilized egg


Sexual Reproduction: An Evolutionary Enigma

• Sexual females have half as many daughters as asexual females; this is the “twofold cost” of sexual reproduction

• Despite this, almost all eukaryotic species reproduce sexually


• Sexual reproduction results in genetic recombination, which provides potential advantages:

– An increase in variation in offspring, providing an increase in the reproductive success of parents in changing environments

– An increase in the rate of adaptation

– A shuffling of genes and the elimination of harmful genes from a population


Reproductive Cycles and Patterns

• Animals may reproduce asexually or sexually, or they may alternate these methods

• Several genera of fishes, amphibians, and lizards reproduce only by a complex form of parthenogenesis that involves the doubling of chromosomes after meiosis

• Asexual whiptail lizards are descended from a sexual species, and females still exhibit mating behaviors

• Individuals of some species undergo sex reversals

• Some species exhibit male to female reversal (for example, certain oysters), while others exhibit female to male reversal (for example, a coral reef fish)


• Sexual reproduction is a special problem for organisms that seldom encounter a mate

• One solution is hermaphroditism, in which each individual has male and female reproductive systems

• Some hermaphrodites can self-fertilize


Concept 46.4: The timing and pattern of meiosis in mammals differ for males and females

• Gametogenesis, the production of gametes by meiosis, differs in females and males

• Sperm are small and motile and are produced throughout the life of a sexually mature male

• Spermatogenesis is production of mature sperm


• Eggs contain stored nutrients and are much larger

• Oogenesis is development of mature oocytes (eggs) and can take many years


• Spermatogenesis differs from oogenesis:

– In oogenesis, one egg forms from each cycle of meiosis; in spermatogenesis four sperm form from each cycle of meiosis

– Oogenesis ceases later in life in females; spermatogenesis continues throughout the adult life of males

– Oogenesis has long interruptions; spermatogenesis produces sperm from precursor cells in a continuous sequence


Fig. 46-12g

Primordial germ cell

Mitotic divisions

Oogonium

Mitotic divisions

Primary oocyte(present at birth), arrestedin prophase of meiosis I

Completion of meiosis I and onset of meiosis II

Secondary oocyte,arrested at metaphase of meiosis II

Firstpolarbody

Ovulation, sperm entry

Completion of meiosis IISecondpolarbody

Fertilized egg

2n

2n

nn

n

n

In embryo


Fig. 46-12c

Primordial germ cell in embryo

Mitotic divisions

Spermatogonialstem cell

Mitotic divisions

Spermatogonium

Mitotic divisions

Primary spermatocyte

Meiosis I

Secondary spermatocyte

Meiosis II

Earlyspermatid

Differentiation (Sertolicells provide nutrients)

Sperm

2n

2n

2n

n n

n n n n

n n n n


Chapter 47 Animal Development


Concept 47.1: After fertilization, embryonic development proceeds through cleavage, gastrulation, and organogenesis

• Important events regulating development occur during fertilization and the three stages that build the animal’s body

– Cleavage: cell division creates a hollow ball of cells called a blastula

– Gastrulation: cells are rearranged into a three-layered gastrula

– Organogenesis: the three layers interact and move to give rise to organs


Fertilization

• Fertilization brings the haploid nuclei of sperm and egg together, forming a diploid zygote

• The sperm’s contact with the egg’s surface initiates metabolic reactions in the egg that trigger the onset of embryonic development


The Acrosomal Reaction

• The acrosomal reaction is triggered when the sperm meets the egg

• The acrosome at the tip of the sperm releases hydrolytic enzymes that digest material surrounding the egg


• Gamete contact and/or fusion depolarizes the egg cell membrane and sets up a fast block to polyspermy


Activation of the Egg

• The sharp rise in Ca2+ in the egg’s cytosol increases the rates of cellular respiration and protein synthesis by the egg cell

• With these rapid changes in metabolism, the egg is said to be activated

• The sperm nucleus merges with the egg nucleus and cell division begins


• In mammals the first cell division occurs 12–36 hours after sperm binding

• The diploid nucleus forms after this first division of the zygote


Cleavage

• Fertilization is followed by cleavage, a period of rapid cell division without growth

• Cleavage partitions the cytoplasm of one large cell into many smaller cells called blastomeres

• The blastula is a ball of cells with a fluid-filled cavity called a blastocoel


Fig. 47-6

(a) Fertilized egg (b) Four-cell stage (c) Early blastula (d) Later blastula


• The eggs and zygotes of many animals, except mammals, have a definite polarity

• The polarity is defined by distribution of yolk (stored nutrients)

• The vegetal pole has more yolk; the animal pole has less yolk


• Cleavage planes usually follow a pattern that is relative to the zygote’s animal and vegetal poles


Fig. 47-8-6

Blastula(crosssection)

BlastocoelAnimal pole

4-cellstageforming

2-cellstageforming

Zygote 8-cellstage

Vegetalpole

0.25 mm 0.25 mm


Gastrulation

• Gastrulation rearranges the cells of a blastula into a three-layered embryo, called a gastrula, which has a primitive gut


• Gastrulation in the frog

– The frog blastula is many cell layers thick

– Cells of the dorsal lip originate in the gray crescent and invaginate to create the archenteron

– Cells continue to move from the embryo surface into the embryo by involution

– These cells become the endoderm and mesoderm


• Gastrulation in the frog

– The blastopore encircles a yolk plug when gastrulation is completed

– The surface of the embryo is now ectoderm, the innermost layer is endoderm, and the middle layer is mesoderm


Fig. 47-10-4

Future ectoderm

Key

Future endoderm

Future mesoderm

SURFACE VIEW

Animal pole

Vegetal poleEarlygastrula

Blastopore

Blastocoel

Dorsal lipof blasto-pore

CROSS SECTION

Dorsal lipof blastopore

Lategastrula

Blastocoelshrinking Archenteron

Blastocoelremnant

Archenteron

Blastopore

Blastopore Yolk plug

Ectoderm

Mesoderm

Endoderm


Chapter 48

Neurons, Synapses, and Signaling


Overview: Lines of Communication

• The cone snail kills prey with venom that disables neurons

• Neurons are nerve cells that transfer information within the body

• Neurons use two types of signals to communicate: electrical signals (long-distance) and chemical signals (short-distance)


• The transmission of information depends on the path of neurons along which a signal travels

• Processing of information takes place in simple clusters of neurons called ganglia or a more complex organization of neurons called a brain


Introduction to Information Processing

• Nervous systems process information in three stages: sensory input, integration, and motor output


• Sensors detect external stimuli and internal conditions and transmit information along sensory neurons

• Sensory information is sent to the brain or ganglia, where interneurons integrate the information

• Motor output leaves the brain or ganglia via motor neurons, which trigger muscle or gland activity


• Many animals have a complex nervous system which consists of:

– A central nervous system (CNS) where integration takes place; this includes the brain and a nerve cord

– A peripheral nervous system (PNS), which brings information into and out of the CNS


Neuron Structure and Function

• Most of a neuron’s organelles are in the cell body

• Most neurons have dendrites, highly branched extensions that receive signals from other neurons

• The axon is typically a much longer extension that transmits signals to other cells at synapses

• An axon joins the cell body at the axon hillock


Fig. 48-4

Dendrites

Stimulus

Nucleus

Cellbody

Axonhillock

Presynapticcell

Axon

Synaptic terminalsSynapse

Postsynaptic cellNeurotransmitter


• A synapse is a junction between an axon and another cell

• The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters


• Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell)

• Most neurons are nourished or insulated by cells called glia


Concept 48.2: Ion pumps and ion channels maintain the resting potential of a neuron

• Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential

• Messages are transmitted as changes in membrane potential

• The resting potential is the membrane potential of a neuron not sending signals


Formation of the Resting Potential

• In a mammalian neuron at resting potential, the concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell

• Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane

• These concentration gradients represent chemical potential energy


• The opening of ion channels in the plasma membrane converts chemical potential to electrical potential

• A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell

• Anions trapped inside the cell contribute to the negative charge within the neuron

Animation: Resting PotentialAnimation: Resting Potential


Production of Action Potentials

• Voltage-gated Na+ and K+ channels respond to a change in membrane potential

• When a stimulus depolarizes the membrane, Na+ channels open, allowing Na+ to diffuse into the cell

• The movement of Na+ into the cell increases the depolarization and causes even more Na+ channels to open

• A strong stimulus results in a massive change in membrane voltage called an action potential

• Ligand gated sodium channels

– Acetylcholine released into the junction between a motor neuron and a skeletal muscle binds to a sodium channe and opens it


Conduction Speed

• The speed of an action potential increases with the axon’s diameter

• In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase

• Myelin sheaths are made by glia— oligodendrocytes in the CNS and Schwann cells in the PNS


Fig. 48-12

Axon

Schwanncell

Myelin sheathNodes ofRanvier

Node of Ranvier

Schwanncell

Nucleus ofSchwann cell

Layers of myelinAxon

0.1 µm


Fig. 48-12a

Axon Myelin sheath

Schwanncell

Nodes ofRanvier

Schwanncell

Nucleus ofSchwann cell

Node of Ranvier

Layers of myelinAxon


• Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found

• Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction


Concept 48.4: Neurons communicate with other cells at synapses

• At electrical synapses, the electrical current flows from one neuron to another

• At chemical synapses, a chemical neurotransmitter carries information across the gap junction

• Most synapses are chemical synapses


• The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal

• The action potential causes the release of the neurotransmitter

• The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell

Animation: SynapseAnimation: Synapse


Fig. 48-15

Voltage-gatedCa2+ channel

Ca2+12

3

4

Synapticcleft

Ligand-gatedion channels

Postsynapticmembrane

Presynapticmembrane

Synaptic vesiclescontainingneurotransmitter

5

6

K+Na+


Generation of Postsynaptic Potentials

• Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell

• Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential


Chapter 49

Nervous Systems


Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells

• The simplest animals with nervous systems, the cnidarians, have neurons arranged in nerve nets

• A nerve net is a series of interconnected nerve cells

• More complex animals have nerves


• Nerves are bundles that consist of the axons of multiple nerve cells

• Sea stars have a nerve net in each arm connected by radial nerves to a central nerve ring


• Bilaterally symmetrical animals exhibit cephalization

• Cephalization is the clustering of sensory organs at the front end of the body

• Relatively simple cephalized animals, such as flatworms, have a central nervous system (CNS)

• The CNS consists of a brain and longitudinal nerve cords


Concept 49.2: The vertebrate brain is regionally specialized

• All vertebrate brains develop from three embryonic regions: forebrain, midbrain, and hindbrain

• By the fifth week of human embryonic development, five brain regions have formed from the three embryonic regions


The Brainstem

• The brainstem coordinates and conducts information between brain centers

• The brainstem has three parts: the midbrain, the pons, and the medulla oblongata


• The midbrain contains centers for receipt and integration of sensory information

• The pons regulates breathing centers in the medulla

• The medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion


Arousal and Sleep

• The brainstem and cerebrum control arousal and sleep

• The core of the brainstem has a diffuse network of neurons called the reticular formation

• This regulates the amount and type of information that reaches the cerebral cortex and affects alertness

• The hormone melatonin is released by the pineal gland and plays a role in bird and mammal sleep cycles


Chapter 50

Sensory and Motor Mechanisms


Concept 50.1: Sensory receptors transduce stimulus energy and transmit signals to the central nervous system

• All stimuli represent forms of energy

• Sensation involves converting energy into a change in the membrane potential of sensory receptors

• Sensations are action potentials that reach the brain via sensory neurons

• The brain interprets sensations, giving the perception of stimuli


Sensory Pathways

• Functions of sensory pathways: sensory reception, transduction, transmission, and integration

• For example, stimulation of a stretch receptor in a crayfish is the first step in a sensory pathway


Sensory Reception and Transduction

• Sensations and perceptions begin with sensory reception, detection of stimuli by sensory receptors

• Sensory receptors can detect stimuli outside and inside the body


• Sensory transduction is the conversion of stimulus energy into a change in the membrane potential of a sensory receptor

• This change in membrane potential is called a receptor potential

• Many sensory receptors are very sensitive: they are able to detect the smallest physical unit of stimulus

– For example, most light receptors can detect a photon of light


Transmission

• After energy has been transduced into a receptor potential, some sensory cells generate the transmission of action potentials to the CNS

• Sensory cells without axons release neurotransmitters at synapses with sensory neurons

• Larger receptor potentials generate more rapid action potentials


• Integration of sensory information begins when information is received

• Some receptor potentials are integrated through summation


Perception

• Perceptions are the brain’s construction of stimuli

• Stimuli from different sensory receptors travel as action potentials along different neural pathways

• The brain distinguishes stimuli from different receptors by the area in the brain where the action potentials arrive


Amplification and Adaptation

• Amplification is the strengthening of stimulus energy by cells in sensory pathways

• Sensory adaptation is a decrease in responsiveness to continued stimulation


Hearing

• Vibrating objects create percussion waves in the air that cause the tympanic membrane to vibrate

• Hearing is the perception of sound in the brain from the vibration of air waves

• The three bones of the middle ear transmit the vibrations of moving air to the oval window on the cochlea


• These vibrations create pressure waves in the fluid in the cochlea that travel through the vestibular canal

• Pressure waves in the canal cause the basilar membrane to vibrate, bending its hair cells

• This bending of hair cells depolarizes the membranes of mechanoreceptors and sends action potentials to the brain via the auditory nerve


• The fluid waves dissipate when they strike the round window at the end of the tympanic canal


Equilibrium

• Several organs of the inner ear detect body position and balance:

– The utricle and saccule contain granules called otoliths that allow us to detect gravity and linear movement

– Three semicircular canals contain fluid and allow us to detect angular acceleration such as the turning of the head


Hearing and Equilibrium in Other Vertebrates

• Unlike mammals, fishes have only a pair of inner ears near the brain

• Most fishes and aquatic amphibians also have a lateral line system along both sides of their body

• The lateral line system contains mechanoreceptors with hair cells that detect and respond to water movement


Chapter 43

The Immune System


Overview: Reconnaissance, Recognition, and Response

• Barriers help an animal to defend itself from the many dangerous pathogens it may encounter

• The immune system recognizes foreign bodies and responds with the production of immune cells and proteins

• Two major kinds of defense have evolved: innate immunity and acquired immunity


• Innate immunity is present before any exposure to pathogens and is effective from the time of birth

• It involves nonspecific responses to pathogens

• Innate immunity consists of external barriers plus internal cellular and chemical defenses


• Acquired immunity, or adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances

• It involves a very specific response to pathogens


Concept 43.2: In acquired immunity, lymphocyte receptors provide pathogen-specific recognition

• White blood cells called lymphocytes recognize and respond to antigens, foreign molecules

• Lymphocytes that mature in the thymus above the heart are called T cells, and those that mature in bone marrow are called B cells


• Lymphocytes contribute to immunological memory, an enhanced response to a foreign molecule encountered previously

• Cytokines are secreted by macrophages and dendritic cells to recruit and activate lymphocytes


Acquired Immunity: An Overview

• B cells and T cells have receptor proteins that can bind to foreign molecules

• Each individual lymphocyte is specialized to recognize a specific type of molecule


Antigen Recognition by Lymphocytes

• An antigen is any foreign molecule to which a lymphocyte responds

• A single B cell or T cell has about 100,000 identical antigen receptors


• All antigen receptors on a single lymphocyte recognize the same epitope, or antigenic determinant, on an antigen

• B cells give rise to plasma cells, which secrete proteins called antibodies or immunoglobulins


The Antigen Receptors of B Cells and T Cells

• B cell receptors bind to specific, intact antigens

• The B cell receptor consists of two identical heavy chains and two identical light chains

• The tips of the chains form a constant (C) region, and each chain contains a variable (V) region, so named because its amino acid sequence varies extensively from one B cell to another


• Secreted antibodies, or immunoglobulins, are structurally similar to B cell receptors but lack transmembrane regions that anchor receptors in the plasma membrane


• Each T cell receptor consists of two different polypeptide chains

• The tips of the chain form a variable (V) region; the rest is a constant (C) region

• T cells can bind to an antigen that is free or on the surface of a pathogen

Video: T Cell ReceptorsVideo: T Cell Receptors


• T cells bind to antigen fragments presented on a host cell

• These antigen fragments are bound to cell-surface proteins called MHC molecules

• MHC molecules are so named because they are encoded by a family of genes called the major histocompatibility complex


The Role of the MHC

• In infected cells, MHC molecules bind and transport antigen fragments to the cell surface, a process called antigen presentation

• A nearby T cell can then detect the antigen fragment displayed on the cell’s surface

• Depending on their source, peptide antigens are handled by different classes of MHC molecules


• Class I MHC molecules are found on almost all nucleated cells of the body

• They display peptide antigens to cytotoxic T cells


• Class II MHC molecules are located mainly on dendritic cells, macrophages, and B cells

• Dendritic cells, macrophages, and B cells are antigen-presenting cells that display antigens to cytotoxic T cells and helper T cells


Cytotoxic T Cells: A Response to Infected Cells

• Cytotoxic T cells are the effector cells in cell-mediated immune response

• Cytotoxic T cells make CD8, a surface protein that greatly enhances interaction between a target cell and a cytotoxic T cell

• Binding to a class I MHC complex on an infected cell activates a cytotoxic T cell and makes it an active killer

• The activated cytotoxic T cell secretes proteins that destroy the infected target cell

Animation: Cytotoxic T CellsAnimation: Cytotoxic T Cells


B Cells: A Response to Extracellular Pathogens

• The humoral response is characterized by secretion of antibodies by B cells

• Activation of B cells is aided by cytokines and antigen binding to helper T cells

• Clonal selection of B cells generates antibody-secreting plasma cells, the effector cells of humoral immunity


Active and Passive Immunization

• Active immunity develops naturally in response to an infection

• It can also develop following immunization, also called vaccination

• In immunization, a nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory


• Passive immunity provides immediate, short-term protection

• It is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk

• It can be conferred artificially by injecting antibodies into a nonimmune person

Date post:	19-Oct-2014
Category:	Technology
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