Week 5 Flashcards

Question

Homeostasis

Answer 1

For cells to function efficiently and interact properly, internal body conditions must be relatively constant Temperature, pH, concentrations of glucose and oxygen

Answer 2

Mechanisms Changing conditions are detected by sensors (cells or membrane receptors) Information is fed to an integrating center (brain, spinal cord, or endocrine gland) Compares conditions to a set point If conditions deviate too far from a set point, biochemical reactions are initiated to change conditions back toward the set point

Answer 3

Humans have set points for body temperature, blood glucose concentrations, electrolyte (ion) concentration, tendon tension, etc. Integrating center is often a particular region of the brain or spinal cord Effectors (muscles or glands) change the value of the condition in question back toward the set point value

Answer 4

Mammals and birds are endothermic Maintain a relatively constant body temperature independent of the environmental temperature Humans 37°C or 98.6°F Changes in body temperature are detected by the hypothalamus in the brain

Answer 5

Negative feedback mechanisms often oppose each other to produce finer degree of control Many internal factors are controlled by antagonistic effectors Have “push–pull” action Increasing activity of one effector is accompanied by decrease in the other

Answer 6

Antagonistic effectors are involved in the control of body temperature If hypothalamus detects high temperature Promotes heat dissipation via sweating and dilation of blood vessels in skin If hypothalamus detects low temperature Promotes heat conservation via shivering and constriction of blood vessels in skin

Answer 7

Mechanisms Enhance a change – not common These do not in themselves maintain homeostasis Important components of some physiological mechanisms. Blood clotting Contraction of uterus during childbirth

Answer 8

Temperature is one of the most important aspects of the environment Some organisms have a body temperature that conforms to the environment Other organisms regulate their body temperature Q(10) is a measure of temperature sensitivity The rate of any chemical reaction is affected by temperature The rate increases with increasing temperature Every 10°C increase in temperature doubles the reaction rate Q(10)=R(t+10)/R(T) (root)

Answer 9

Temperature determined by internal and external factors Overall metabolic rate and body temperature are interrelated Organisms must deal with external and internal factors that relate body heat, metabolism, and the environment body heat = heat produced + heat transferred

Answer 10

Radiation- transfer of heat by electromagnetic radiation Conduction- direct transfer of heat from hotter object to a colder one Convection- transfer of heat brought about by the movement of a gas or liquid Evaporation- heat of vaporization or the amount of energy needed to change them from a liquid to a gas phase

Answer 11

Ectotherms regulate temperature using behavior Low metabolic rates Regulate their temperature using behavior

Answer 12

Endotherms create internal metabolic heat Conservation or dissipation Heat transfer is controlled by amount of blood flow to the surface of the animal Countercurrent exchange Allows sustained high-energy activity Tradeoff is the high metabolic rate

Answer 13

Changes in body mass have a large effect on metabolic rate Smaller animals consume much more energy per unit of body mass than larger animals Summarized in the “mouse to elephant” curve

Answer 14

Mammalian thermoregulation is controlled by the hypothalamus Neurons in the hypothalamus detect the temperature change Stimulation of the heat-losing center Peripheral blood vessel dilation Sweating Stimulation of heat-promoting center Thermogenesis Constriction of blood peripheral blood vessels Epinephrine production by adrenal glands Anterior pituitary produces T S H

Answer 15

All animals must be able to respond to environmental stimuli In most invertebrate phyla and in all vertebrate classes, animals use: Sensory receptors – detect stimulus Motor effectors – respond to it Nervous system links the two Consists of neurons and supporting cells

Answer 16

The brain Spinal cord

Answer 17

Vertebrates have three types of neurons Sensory neurons (afferent neurons) carry impulses to central nervous system (C N S) Motor neurons (efferent neurons) carry impulses from C N S to effectors (muscles and glands) Interneurons (association neurons) provide more complex reflexes and associative functions (learning and memory)

Answer 18

P N S consists of: Sensory and motor neurons Somatic N S stimulates skeletal muscles Autonomic N S stimulates smooth and cardiac muscles, as well as glands Sympathetic and parasympathetic N S Counterbalance each other

Answer 19

Neurons have the same basic structure Cell body Enlarged part containing nucleus Dendrites Short, cytoplasmic extensions that receive stimuli Axon Single, long extension that conducts impulses away from cell body

Answer 20

Neuroglia Support neurons both structurally and functionally Schwann cells and oligodendrocytes produce myelin sheaths surrounding axons In the C N S, myelinated axons form white matter Dendrites/cell bodies form gray matter In the P N S, myelinated axons are bundled to form nerves

Answer 21

A potential difference exists across every cell’s plasma membrane Negative pole − cytoplasmic side Positive pole − extracellular fluid side When a neuron is not being stimulated, it maintains a resting potential Ranges from −40 to −90 millivolts (mV) Average about −70 mV

Answer 22

The inside of the cell is more negatively charged than the outside Sodium-Potassium Pump - 2 K+ in, three Na in Ion Leakage Channels - More K+ out than Na+ in Differential distribution of other ions and molecules across the pm Especially negatively charged proteins

Answer 23

Sodium–potassium pump creates significant concentration gradient K+ concentration much higher in the cell Membrane not permeable to negative ions Leads to buildup of positive charges outside and negative charges inside cell Attractive force to bring K+ back inside cell Equilibrium potential – balance between diffusional force and electrical force

Answer 24

Uniqueness of neurons compared with other cells is not the production and maintenance of the resting membrane potential Rather the sudden temporary disruptions to the resting membrane potential that occur in response to stimuli 2 types of changes Graded potentials Action potentials.

Answer 25

Graded potentials Small consistent changes in membrane potential due to activation of gated ion channels Action potentials Transient disruptions triggered by a threshold change in potential The actual signals that move along an axon

Answer 26

Chemically-gated or ligand-gated channels Ligands are chemical signals hormones or neurotransmitters Induce opening and cause changes in cell membrane permeability

Answer 27

Depolarization makes the membrane potential more positive Hyperpolarization makes it more negative These small changes result in graded potentials Size depends on either the strength of the stimulus or the amount of ligand available to bind with their receptors Can reinforce or negate each other Summation is the ability of graded potentials to combine

Answer 28

Result when depolarization reaches the threshold potential (−55 mV) Voltage-gated Depolarizations bring a neuron closer to the threshold Hyperpolarizations move the neuron further from the threshold

Answer 29

Voltage-Gated Na+ and K+ Channels

Answer 30

The action potential has three phases Rising, falling, and undershoot Action potentials are always separate, all-or-none events with the same amplitude Do not add up or interfere with each other Intensity of a stimulus is coded by the frequency, not amplitude, of action potentials

Answer 31

Propagation of action potentials Each action potential, in its rising phase, reflects a reversal in membrane polarity Positive charges due to influx of Na+ can depolarize the adjacent region to threshold And so, the next region produces its own action potential Meanwhile, the previous region repolarizes back to the resting membrane potential Signal does not go back toward cell body

Answer 32

Two ways to increase velocity of conduction Axon has a large diameter. Less resistance to current flow. Found primarily in invertebrates Axon is myelinated Action potential is only produced at the nodes of Ranvier Impulse jumps from node to node Saltatory conduction

Answer 33

Specialized intercellular junctions with the other neurons, with muscle cells, or with gland cells Presynaptic cell transmits action potential Postsynaptic cell receives it Two basic types: electrical and chemical

Answer 34

Electrical synapses Involve direct cytoplasmic connections between the two cells formed by gap junctions Relatively rare in vertebrates Chemical synapses Have a synaptic cleft between the two cells End of presynaptic cell contains synaptic vesicles packed with neurotransmitters

Answer 35

Action potential triggers influx of Ca^2+ Synaptic vesicles fuse with cell membrane Neurotransmitter is released by exocytosis Diffuses to other side of cleft and binds to chemical- or ligand-gated receptor proteins Produces graded potentials in the postsynaptic membrane Neurotransmitter action is terminated by enzymatic digestion or cellular uptake

Answer 36

Acetylcholine (ACh) Crosses the synapse between a motor neuron and a muscle fiber Neuromuscular junction Binds to receptor in the postsynaptic membrane Causes ligand-gated ion channels to open Produces a depolarization called an excitatory postsynaptic potential (E P S P) Stimulates muscle contraction Acetylcholinesterase (AChE) degrades ACh Causes muscle relaxation

Answer 37

Glutamate Major excitatory neurotransmitter in the vertebrate C N S Glycine and G A B A (γ-aminobutyric acid) are inhibitory neurotransmitters Open ligand-gated channels for Cl- Produce a hyperpolarization called an inhibitory postsynaptic potential (I P S P)

Answer 38

Epinephrine (adrenaline) and norepinephrine are responsible for the “fight or flight” response Dopamine is used in some areas of the brain that control body movements Serotonin is involved in the regulation of sleep

Answer 39

Neuropeptides Substance P is released from sensory neurons activated by painful stimuli Intensity of pain perception depends on enkephalins and endorphins Nitric oxide (NO). A gas – produced as needed from arginine Causes smooth muscle relaxation

Answer 40

Integration of E P S Ps (depolarization) and I S P Ss (hyperpolarization) occurs on the neuronal cell body Small E P S Ps add together to bring the membrane potential closer to the threshold I P S Ps subtract from the depolarizing effect of E P S Ps Deter the membrane potential from reaching threshold

Answer 41

Spatial summation Many different dendrites produce E P S Ps Temporal summation One dendrite produces repeated E P S Ps

Answer 42

Prolonged exposure to a stimulus may cause cells to lose the ability to respond to it Cell decreases the number of receptors because there is an abundance of neurotransmitters In long-term drug use, means that more of the drug is needed to obtain the same effect

Answer 43

Affects neurons in the brain’s “pleasure pathways” (limbic system) Binds dopamine transporters and prevents the reuptake of dopamine Dopamine survives longer in the synapse and fires pleasure pathways more and more

Answer 44

Binds directly to a specific receptor on postsynaptic neurons of the brain Binds to a receptor for acetylcholine Brain adjusts to prolonged exposure by “turning down the volume” by Making fewer receptors to which nicotine binds Altering the pattern of activation of the nicotine receptors

Answer 45

Sponges are only major phylum without nerves Cnidarians have the simplest nervous system Neurons linked to each other in a nerve net No associative activity Free-living flatworms (phylum Platyhelminthes) are simplest animals with associative activity Two nerve cords run down the body Permit complex muscle control All of the subsequent evolutionary changes in nervous systems can be viewed as a series of elaborations on the characteristics already present in flatworms

Answer 46

All vertebrate brains have three basic divisions: Hindbrain or rhombencephalon Midbrain or mesencephalon Forebrain or prosencephalon In fishes, Hindbrain – largest portion Midbrain – processes visual information Forebrain – processes olfactory information

Answer 47

Forebrain is composed of two elements Diencephalon Thalamus – integration and relay center Hypothalamus – participates in basic drives and emotions, controls pituitary gland Telencephalon (“end brain”) Devoted largely to associative activity Called the cerebrum in mammals

Answer 48

The increase in brain size in mammals reflects the great enlargement of the cerebrum Split into right and left cerebral hemispheres, which are connected by a tract called the corpus callosum Each hemisphere receives sensory input from the opposite side Hemispheres are divided into: frontal, parietal, temporal, and occipital lobes

Answer 49

Cerebral cortex Outer layer of the cerebrum Contains about 10% of all neurons in brain Highly convoluted surface Increases threefold the surface area of the human brain Activities are motor, sensory, or associative

Answer 50

Primary motor cortex – movement control Primary somatosensory cortex – sensory control Association cortex – higher mental functions Basal nuclei Aggregates of neuron cell bodies – gray matter Participate in the control of body movements

Answer 51

Integrates visual, auditory, and somatosensory information

Answer 52

Integrates visceral activities Controls pituitary gland

Answer 53

Hypothalamus, hippocampus, and amygdala Responsible for emotional responses

Answer 54

Sleep and arousal One section of reticular formation is the reticular-activating system Controls consciousness and alertness Brain state can be monitored by means of an electroencephalogram (E E G) Records electrical activity

Answer 55

Language Left hemisphere is “dominant” hemisphere Different regions control various language activities Adept at sequential reasoning Right hemisphere is adept at spatial reasoning Primarily involved in musical ability Nondominant hemisphere is also important for the consolidation of memories of nonverbal experiences

Answer 56

Appears dispersed across the brain Short-term memory is stored in the form of transient neural excitations Long-term memory appears to involve structural changes in neural connections Two parts of the temporal lobes, the hippocampus and the amygdala, are involved in both short-term memory and its consolidation into long-term memory

Answer 57

Cellular basis of learning and memory Long-term changes in the strength of synaptic connection Two examples of synaptic plasticity Long-term potentiation (L T P) Long-term depression (L T D)

Answer 58

Condition where memory and thought become dysfunctional Two causes have been proposed Nerve cells are killed from the outside in External protein: β-amyloid Nerve cells are killed from the inside out Internal proteins: tau (τ)

Answer 59

Cable of neurons extending from the brain down through the backbone Enclosed and protected by the vertebral column and the meninges

Answer 60

Two zones Inner zone is gray matter Primarily consists of the cell bodies of interneurons, motor neurons, and neuroglia Outer zone is white matter Contains cables of sensory axons in the dorsal columns and motor axons in the ventral columns

Answer 61

It serves as the body’s “information highway” Relays messages between the body and the brain It also functions in reflexes The knee-jerk reflex is monosynaptic. However, most reflexes in vertebrates involve a single interneuron

Answer 62

Consists of nerves and ganglia Nerves are bundles of axons bound by connective tissue Ganglia are aggregates of neuron cell bodies Function is to receive info from the environment, convey it to the C N S, and to carry responses to effectors such as muscle cells

Answer 63

Sensory neurons Axons enter the dorsal surface of the spinal cord and form dorsal root of spinal nerve Cell bodies are grouped outside the spinal cord in dorsal root ganglia Motor neurons Axons leave from the ventral surface and form ventral root of spinal nerve Cell bodies are located in the spinal cord

Answer 64

Somatic motor neurons stimulate the skeletal muscles to contract In response to conscious command or reflex actions Antagonist of the muscle is inhibited by hyperpolarization (I P S Ps) of spinal motor neurons

Answer 65

Composed of the sympathetic and parasympathetic divisions, plus the medulla oblongata In both, efferent motor pathway has two neurons Preganglionic neuron – exits the C N S and synapses at an autonomic ganglion Postganglionic neuron – exits the ganglion and regulates visceral effectors Smooth or cardiac muscle or glands

Answer 66

Sympathetic division Preganglionic neurons originate in the thoracic and lumbar regions of spinal cord Most axons synapse in two parallel chains of ganglia right outside the spinal cord Parasympathetic division Preganglionic neurons originate in the brain and sacral regions of spinal cord Axons terminate in ganglia near or even within internal organs

Answer 67

Twelve pairs of cranial nerves arise from the underside of the brain They carry sensory neurons for the special and general senses as well as somatic and autonomic motor neurons

Answer 68

Vision Hearing Taste Smell Touch

Answer 69

Sensory receptors provide information from our internal and external environments that is crucial for survival and success Exteroceptors sense external stimuli Interoceptors sense internal stimuli

Answer 70

Stimulation Transduction Transmission Interpretation

Answer 71

Sensory cells respond to stimuli via stimulus-gated ion channels in their membranes Open or close depending on the sensory system involved In most cases, a depolarization of the receptor cell occurs Analogous to the excitatory postsynaptic potential (E P S P) Referred to as receptor potential

Answer 72

Receptor potential like a graded potential The larger the sensory stimulus, the greater the degree of depolarization The greater the sensory stimulus, the greater the depolarization of the receptor potential and the higher the frequency of action potentials

Answer 73

Mechanoreceptors are stimulated by physical or mechanical forces pressure that results from “pushing” or “pulling” or from vibrations through water or air Give rise to the senses of touch and hearing Provide input for balance and body position

Answer 74

Several types of mechanoreceptors in the skin detect the sense of touch Contain sensory cells with ion channels that open in response to membrane distortions Two types Phasic – intermittently activated Hair follicle receptors, Meissner corpuscles, Pacinian corpuscles Tonic – continuously activated Ruffini corpuscles, Merkel’s disks

Answer 75

Monitor muscle length and tension Provide information about the relative position or movement of animal’s body parts Examples Muscle spindles – monitor stretch on muscle – receptors that lie in parallel with muscle fibers – knee jerk reflex Golgi tendon organs – monitor tension on tendons – reflex inhibits motor neurons – prevents damage to tendons

Answer 76

Monitor blood pressure Located at carotid sinus and aortic arch Detect tension or stretch in the walls of these blood vessels When blood pressure decreases, the frequency of impulses produced by baroreceptors decreases Results in increased heart rate and vasoconstriction

Answer 77

These receptors are also stimulated by physical or mechanical forces detecting: Vibrations through water or air—hearing and lateral line system Gravity and acceleration—balance and body position

Answer 78

Detection of sound waves Sound is the result of vibration, or waves, traveling through a medium Detection of sound waves is possible through the action of specialized mechanoreceptors that first evolved in aquatic organisms

Answer 79

Sense objects that reflect pressure waves and low-frequency vibrations Supplements hearing Consists of hair cells within a longitudinal canal in the fish’s skin that extends along each side of the body and within several canals in the head Hair cells’ surface processes project into a gelatinous membrane called a cupula Hair cells are innervated by sensory neurons that transmit impulses to the brain

Answer 80

Hearing structures in fish Called otoliths- composed of calcium carbonate crystals. Contained in the otolith organs of the membranous labyrinth Otoliths vibrate against stereocilia projecting from hair cells Produces action potentials

Answer 81

Air vibrations are channeled through the ear canal of the outer ear Vibrations reach the tympanic membrane causing movement of three small bones (ossicles) in the middle ear Malleus (hammer), incus (anvil), and stapes (stirrup) The stapes vibrates against the oval window, which leads into the inner ear

Answer 82

The inner ear consists of the cochlea Bony structure containing part of the cochlear duct The vestibular canal lies above this duct, while the tympanic canal lies below it All three chambers are filled with fluid Pressure waves travel down the tympanic canal to the round window, which is another flexible membrane Transmits pressure back to middle ear

Answer 83

As pressure waves are transmitted through the cochlea to the round window, they cause the cochlear duct to vibrate Organ of Corti Basilar membrane contains sensory hair cells Stereocilia from hair cells project into tectorial membrane Bending of stereocilia depolarizes hair cells Hair cells send action potentials to the brain

Answer 84

Basilar membrane of the cochlea consists of elastic fibers that respond to different frequencies, or pitch, of sound Hair cell depolarization is greatest in region that responds to a particular frequency Afferent axons from that region stimulated more Brain interprets that as representing sound of a particular frequency or pitch

Answer 85

A few mammals have the ability to perceive presence and distance of objects by sound Bats, shrews, whales, dolphins They emit sounds and then determine the time it takes these sounds to return This process is called echolocation The invention of sonar and radar are based on the same principles

Answer 86

Most invertebrates can orient themselves with respect to gravity using a statocyst Consists of ciliated hair cells embedded in a membrane with calcium carbonate stones (statoliths) In vertebrates, the gravity receptors consist of two chambers in the membranous labyrinth Utricle and saccule

Answer 87

Within the utricle and saccule are hair cells with stereocilia and a kinocilium Processes embedded in the calcium carbonate-rich otolith membrane Utricle more sensitive to horizontal acceleration Saccule more sensitive to vertical acceleration Both types of accelerations cause cilia to bend, thus producing an action potential in an associated sensory neuron

Answer 88

The utricle and saccule are continuous with three semicircular canals that detect angular acceleration in any direction At the ends of the canals are swollen chambers called ampullae Groups of cilia protrude into them Tips of cilia are embedded within a gelatinous cupula that protrudes into the endolymph fluid of each canal

Answer 89

When the head rotates, the semicircular canal fluid pushes against the cupula, causing the cilia to bend Bending in the direction of the kinocilium causes a receptor potential Stimulates an action potential in the associated sensory neuron Saccule, utricle, and semicircular canals are collectively called the vestibular apparatus

Answer 90

Bind to particular chemicals in the extracellular fluid Membrane of sensory neuron becomes depolarized and produces action potentials Chemoreceptors are used in the senses of taste and smell Also important in monitoring the chemical composition of blood

Answer 91

Mixture of physical and psychological factors Broken down into five categories Sweet, sour, salty, bitter, and umami (hearty) Taste buds are collections of chemosensitive cells associated with afferent neurons

Answer 92

In fish, taste buds are scattered all over the body surface In land vertebrates, taste buds are located in the epithelium of the tongue and oral cavity within raised areas called papillae Salty and sour tastes act directly through ion channels Other tastes act indirectly by binding to specific G protein–coupled receptors

Answer 93

Many arthropods have taste chemoreceptors Flies have them in sensory hairs located on their feet

Answer 94

In land vertebrates, involves neurons located in the upper portion of the nasal passages Receptors project into the nasal mucosa, and their axons project directly into the cerebral cortex Particles must first dissolve in extracellular fluid before they can activate the olfactory receptors Humans can detect thousands of different smells

Answer 95

Peripheral chemoreceptors Found in the aortic and carotid bodies Sensitive primarily to the pH of plasma Central chemoreceptors Found in the medulla oblongata of the brain Sensitive to the pH of cerebrospinal fluid Increased CO2 in blood lowers pH Stimulates respiratory control center

Answer 96

Nonspecialized sensory receptors that are sensitive to changes in temperature Warm and cold receptors Vertebrates have most of their thermoreceptors in the dermis layer of the skin

Answer 97

Some snakes use thermoreception for detection of prey Pit vipers Have a pair of heat-detecting pit organs on either side of the head between the eye and nostril Locate heat sources in the environment, including prey in darkness Paired pits appear to be stereoscopic To some extent can form a thermal image

Answer 98

Transmit impulses perceived as pain Sensitive to tissue damage Most consist of free nerve endings located throughout the body, especially near surfaces Vertebrate nociceptors use neurotransmitters, substance P, and glutamate Endorphins and enkephalins block the release of substance P

Answer 99

Detect electrical currents Elasmobranchs (sharks, rays, and skates) have electroreceptors called the ampullae of Lorenzini Can sense electrical currents generated by the muscle contractions of their prey Detect magnetic fields Eels, sharks, bees, and many birds appear to navigate along the magnetic field lines of the Earth

Answer 100

Begins with the capture of light energy by photoreceptors Can be used to determine both the direction and distance of an object Invertebrates have simple visual systems with photoreceptors clustered in an eyespot Flatworms can perceive the direction of light but cannot construct a visual image

Answer 101

Members of four phyla have evolved well-developed, image-forming eyes Annelids, mollusks, arthropods, and chordates Although these eyes are similar in structure, they have evolved independently Example of convergent evolution

Answer 102

Sclera White portion of the eye, formed of tough connective tissue Cornea Transparent portion through which light enters; begins to focus light Iris Colored portion of the eye Contraction of iris muscles in bright light decreases the size of its opening, the pupil Lens Transparent structure that completes focusing of light onto the retina

Answer 103

The lens is attached to the ciliary muscles by the suspensory ligament Changes shape of lens In near vision, ciliary muscles contract Lens becomes more rounded and bends light more strongly In distance vision, ciliary muscles relax Lens becomes more flattened and bends light less

Answer 104

Vertebrate retina contains two types of photoreceptors Rods Responsible for black-and-white vision when illumination is dim Cones Responsible for color vision and high visual acuity (sharpness) Most are located in the central region of the retina known as the fovea Sharpest image is formed

Answer 105

Rods and cones have same basic structure Both have inner segment rich in mitochondria and vesicles filled with neurotransmitter molecules Connected by narrow stalk to the outer segment Packed with hundreds of flattened disks which contain photopigments

Answer 106

Photopigment in rods is rhodopsin Photopigments of cones are photopsins Humans have three kinds of cones Each possesses a photopsin consisting of a cis-retinal bound to a protein with a slightly different amino acid sequence These shift the absorption maximum, the region of the electromagnetic spectrum that the pigment best absorbs

Answer 107

The retina consists of three layers of cells External layer contains the rods and cones Middle layer contain bipolar cells Layer closest to eye cavity contains ganglion cell Once photoreceptors are activated, they stimulate bipolar cells, which in turn stimulate ganglion cells Ganglion cells transmit impulses to brain via optic nerve

Answer 108

In the dark Photoreceptor cells release an inhibitory neurotransmitter that hyperpolarizes the bipolar neurons Prevents the bipolar neurons from releasing excitatory neurotransmitter to the ganglion cells that signal to the brain In the presence of light Photoreceptor cells stop releasing their inhibitory neurotransmitter, in effect, stimulating bipolar cells Bipolar cells in turn stimulate the ganglion cells, which transmit action potentials to the brain

Answer 109

Action potentials in the optic nerves are relayed from the retina to the lateral geniculate nuclei of the thalamus They are then projected to the occipital lobes of the cerebral cortex Each hemisphere of the cerebrum receives input from both eyes

Answer 110

Relationship between receptors, bipolar cells, and ganglion cells varies in different parts of the retina Fovea – one-to-one connections = high acuity Outside of fovea, many rods converge on a single bipolar cell and many bipolar cells converge on a single ganglion cell More sensitive to dim light At the expense of acuity and color vision

Answer 111

Color blindness is due to an inherited lack of one or more types of cones People with normal vision are trichromats Have all three cones Color blind individuals are dichromats Sex-linked recessive trait More common in men

Answer 112

Primates and most predators have two eyes, one located on each side of the face Two fields of vision overlap Parallax permits binocular vision Ability to perceive 3-D images and depth. In contrast, prey animals generally have eyes located to the sides of the head Prevents binocular vision, but enlarges the overall receptive field

Answer 113

Explaining complicated structures was one of Darwin’s greatest challenges Incremental improvements in function could build a complex structure through natural selection Morphologists concluded that eyes are an example of convergent evolution

Answer 114

Genes discovered that code for transcription factor important in lens development Pax6 in mice, eyeless in flies Sequence of genes highly similar – homologues Walter Gehring inserted mouse Pax6 into genome of a fruit fly Created transgenic fly Pax6 gene turned on by regulatory factors in the fly’s leg Eye formed on leg of fly Replacement of fly Pax6 with mouse Pax6 results completely unexpected Insects and vertebrates diverged more than 500 M Y A Large differences in eye structure Expected eye development to be controlled by completely different genes Pax6 and eyeless cave fish Pax6 gene expression reduced Eyes start to develop, then degenerate

Answer 115

Ribbon worms, Lineus sanguineus, also rely on Pax6 for eyespot development Pax6 homologue has been cloned and has been shown to express at the sites where eyespots develop In contrast, planarian worms do not rely on Pax6 for eyespot development

Answer 116

Pax genes involved in eye development much earlier in evolutionary history than imagined Jellyfish PaxA gene can make a compound eye on a fly leg Different Pax genes have been recruited by different animal lineages for eye development after early gene duplications

Answer 117

Eyes in different types of animals evolved truly independently, as originally believed Possible Pax6 had role in forehead development and this role has been co-opted time and time again for eye development Many think this unlikely since gene sequences and functional roles so similar Suggests to many that Pax6 acquired its eye development role only a single time in the ancestor to all organisms using Pax6 for eye development

Answer 118

Four mechanisms of cell communication Direct contact Synaptic signaling Endocrine signaling Paracrine signaling

Answer 119

Hormone Regulatory chemical that is secreted into extracellular fluid and carried by the blood Can act at a distance from source Endocrine system Organs and tissues that produce hormones Only targets with receptor can respond

Answer 120

Paracrine regulators do not travel in blood Allow cells of organ to regulate each other Pheromones are chemicals released into the environment to communicate among individuals of a single species Not involved in normal metabolic regulation within an animal

Answer 121

Some neurotransmitters are distributed by the blood and act as a hormone Norepinephrine coordinates the activity of heart, liver, and blood vessels during stress Neurons can also secrete a class of hormones called neurohormones that are carried by blood Antidiuretic hormone is secreted by neurons of the brain

Answer 122

The endocrine system includes all the organs that secrete hormones Endocrine – product secreted into extracellular fluid and carried in blood Exocrine – secrete product into a duct Two basic hormone characteristics Must be sufficiently complex to convey regulatory information to their target cells Must be adequately stable to resist destruction before reaching their target cells

Answer 123

Peptides and proteins Glycoproteins Amino acid derivatives Catecholamines Thyroid hormones Melatonin Steroids Sex steroids Corticosteroids

Answer 124

Hormones may be categorized as: Lipophilic (nonpolar) – fat-soluble Steroid hormones and thyroid hormones Travel on transport proteins in blood Bind to intracellular receptors Tend to act over brief time period Hydrophilic (polar) – water-soluble All other hormones Freely soluble in blood Bind to extracellular receptors Tend to have much longer active period

Answer 125

Paracrine regulation occurs in most organs Growth factors Proteins that promote growth and cell division in specific organs Epidermal growth factor Activates mitosis in skin Nerve growth factor Stimulates growth and survival of neurons Insulin-like growth factor Stimulates cell division in developing bone Cytokines Specialize in control of cell division and differentiation in immune system

Answer 126

Nitric oxide (N O) Function as neurotransmitter Produced by endothelium of blood vessels Dilates arteries to control blood pressure. Endothelin stimulates vasoconstriction Bradykinin promotes vasodilation Paracrine regulation supplements autonomic nervous system

Answer 127

Diverse group of fatty acids that are produced in almost every organ Regulate a variety of functions Smooth muscle contraction, lung function, labor, and inflammation Synthesis is inhibited by nonsteroidal anti-inflammatory drugs (N S A I Ds) such as aspirin and ibuprofen

Answer 128

Lipophilic hormones include the steroid hormones and the thyroid hormones Also retinoids, or vitamin A Can enter cells through plasma membrane

Answer 129

Circulate in the blood bound to transport proteins Dissociate from carrier at target cells Pass through the cell membrane Bind to an intracellular receptor, either in the cytoplasm or the nucleus Hormone-receptor complex binds to hormone response elements in D N A Regulate gene expression

Answer 130

Peptide, protein, glycoprotein, and catecholamine hormones Too large or polar to cross cell membrane Bind to receptors on plasma membrane Initiate signal transduction pathways Activation of protein kinases Activate or deactivate intracellular proteins by phosphorylation Production of second messengers

Answer 131

For some peptide hormones (like insulin) the receptor itself is a kinase Can directly phosphorylate intracellular proteins that alter cellular activity For other peptide hormones (like growth hormone) the receptor itself is not a kinase Rather, it activates intracellular kinases

Answer 132

Second-messenger systems Many hydrophilic hormones work through second messenger systems Two have been described One involving cyclic adenosine monophosphate (cAMP) One that generates 2 lipid messengers: inositol triphosphate (IP3) and diacyl glycerol (D A G)

Answer 133

Second-messenger systems Receptors are linked to a second-messenger-generating enzyme via membrane proteins called G proteins G protein–coupled receptors (G P C Rs) When the G protein activates the enzyme, the second-messenger molecules increase Cellular response depends on the type of G protein activated Some activate while others inhibit their second-messenger-generating system Single hormone can have distinct actions in two different cells

Answer 134

Also known as the hypophysis Hangs by a stalk from the hypothalamus Consists of two parts Anterior pituitary (adenohypophysis) Appears glandular Posterior pituitary (neurohypophysis) Appears fibrous Different embryonic origins Different hormones

Answer 135

Appears fibrous because it contains axons that originate in cell bodies within the hypothalamus and that extend along the stalk of the pituitary as a tract of fibers Develops from outgrowth of the brain Stores and releases two hormones Both are produced by neuron cell bodies in the hypothalamus Neuroendocrine reflex

Answer 136

Antidiuretic hormone (A D H) Peptide hormone that stimulates water reabsorption by the kidney, and thus inhibits diuresis (urine production) Oxytocin Like A D H, composed of 9 amino acids In mammals, it stimulates the milk ejection reflex and uterine contractions during labor, and it regulates reproductive behavior

Answer 137

Develops from a pouch of epithelial tissue of the embryo’s mouth Not part of the nervous system Produces at least 7 essential hormones Tropic hormones or tropins Act on other endocrine glands. Can be categorized into three families Peptide hormones, protein hormones, and glycoprotein hormones.

Answer 138

Peptide hormones Cleaved from a single precursor protein Fewer than 40 amino acids in size Adrenocorticotropic hormone (A C T H) Melanocyte-stimulating hormone (M S H) Protein hormones A single chain of about 200 amino acids Growth hormone (G H) Prolactin (P R L)

Answer 139

Glycoprotein hormones Dimers, containing alpha (α) and beta (β) subunits, each around 100 amino acids Thyroid-stimulating hormone (T S H) Luteinizing hormone (L H) Follicle-stimulating hormone (F S H) F S H and L H Function in both men and women Referred to as gonadotropins

Answer 140

Anterior pituitary is controlled by hormones from hypothalamus Neurons secrete releasing hormones and inhibiting hormones, which diffuse into blood capillaries at the hypothalamus’ base Each hormone delivered by the hypothalamo-hypophyseal portal system regulates a specific anterior pituitary hormone Portal system has 2 capillary beds (not 1)

Answer 141

The hypothalamus and the anterior pituitary are partially controlled by the very hormones whose secretion they stimulate Negative feedback or feedback inhibition Acts to maintain relatively constant levels of the target cell hormone Positive feedback not as common Causes deviations from homeostasis Control of ovulation

Answer 142

Pituitary gland was referred to as the “master gland” Hypophysectomy caused a number of deficits Effects may be direct or indirect Direct: activation of nonendocrine targets Growth hormone, prolactin, and M S H. Indirect: activation of other endocrine glands Tropic hormones A C T H, T S H, L H, and F S H

Answer 143

Growth Hormone Stimulates protein synthesis and growth of muscles and connective tissues Stimulates production of insulin-like growth factors that stimulate cell division in epiphyseal growth plates – elongation of bone Gigantism versus pituitary dwarfism Also functions in adults to regulate protein, lipid, and carbohydrate metabolism Acromegaly

Answer 144

Prolactin Acts on glands that are not endocrine glands Actions appear diverse Milk production in mammals, “crop milk” and brood patch in birds, electrolyte balance in kidneys T S H stimulates thyroid A C T H stimulates only adrenal cortex F S H and L H act only on the gonads M S H regulates melanophores or melanocytes that contain melanin

Answer 145

In humans, the thyroid gland is shaped like a bow tie, and lies just below the Adam’s apple in the front of the neck Secretes Thyroid hormones Thyroxine Triiodothyronine Calcitonin

Answer 146

Thyroid hormones bind to nuclear receptors Regulates enzymes controlling carbohydrate and lipid metabolism Hypothyroidism vs hyperthyroidism in adults Often functions synergistically with other hormones Trigger metamorphosis in tadpoles

Answer 147

Peptide hormone Stimulates the uptake of calcium (Ca^2+) into bones - lowering blood Ca^2+ levels Appears less important in day-to-day regulation of Ca^2+ levels in adult humans

Answer 148

Four small glands attached to the thyroid Produce parathyroid hormone (P T H) Raises blood Ca^2+ levels Stimulates osteoclasts to dissolve calcium phosphate crystals in the bone matrix and release Ca^2+ into blood Stimulates the kidneys to reabsorb Ca^2+ from urine Vitamin D activated by a P T H controlled enzyme Stimulates the intestinal absorption of

Answer 149

Medulla (inner portion) Stimulated by the sympathetic division of the autonomic nervous system Secretes the catecholamines epinephrine and norepinephrine Cortex (outer portion) Stimulated by anterior pituitary hormone A C T H Corticosteroids Glucocorticoids (like cortisol) act on various cells to maintain glucose homeostasis Aldosterone (mineralocorticoid) helps regulate mineral balance

Answer 150

Exocrine and endocrine glands Connected to the duodenum of the small intestine by the pancreatic duct Islets of Langerhans are scattered clusters of cells throughout the pancreas These govern blood glucose levels through two hormones with antagonistic functions

Answer 151

Insulin Secreted by beta (β) cells of the islets Stimulates cellular uptake of blood glucose and its storage as glycogen in the liver and muscle cells, or as fat in fat cells Glucagon Secreted by alpha () cells of the islets Promotes the hydrolysis of glycogen in the liver and fat in adipose tissue

Answer 152

Diabetics cannot take up glucose from blood Type 1 (insulin-dependent diabetes) Individuals lack insulin-secreting b cells Treated by daily injections of insulin Type 2 (noninsulin-dependent diabetes) Most patients have this form Very low number of insulin receptors Treated by diet and exercise

Answer 153

Ovaries and testes in vertebrates Produce sex steroids that regulate reproductive development Estrogen and progesterone “Female” hormones Androgens “Male” hormones Testosterone and its derivatives

Answer 154

Located in the roof of the third ventricle of the brain Secretes hormone melatonin Functions of melatonin Reduces dispersal of melanin granules Synchronizes various body processes to a circadian rhythm Secretion of melatonin activated in the dark

Answer 155

Some hormones are secreted by organs that are not exclusively endocrine glands Atrial natriuretic hormone is secreted by the right atrium of the heart Promotes salt and water excretion Erythropoietin is secreted by the kidney Stimulates the bone marrow to produce red blood cells

Answer 156

Insects undergo two types of transformations during post-embryonic development Molting Shedding of old exoskeleton and secretion of a new larger one Metamorphosis Radical transformation from the larval to the adult form

Answer 157

Hormonal secretions influence both molting and metamorphosis Brain hormone stimulates prothoracic gland to produce ecdysone, or molting hormone High levels cause molting Corpora allata produces juvenile hormone Low levels result in metamorphosis