Reading Essentials for Biology Glencoe (794133), страница 100
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It also determines howmuch food you need to eat.The thyroid gland secretes calcitoninBlood calcium(kal suh TOH nun). This hormone regulates callevels decreasedcium levels in the blood. The body needs the mineral calcium for blood clotting, the formation ofbones and teeth, and for normal nerve and musclefunction. Calcitonin binds to the membranes ofkidney cells. Calcitonin then causes the kidneys toParathyroidsexcrete more calcium. Calcitonin also binds tobone-forming cells.
It causes these bone-formingcells to increase calcium absorption and to makenew bone.PTHREADING ESSENTIALSBlood calciumlevels increasedThyroidCalcitoninChapter 35439NameDateClassSection35.3The Endocrine System, continued5. What three minerals areregulated by PTH?________________________________________________________________________Parathyroid hormone (PTH) is involved in mineral regulation.This hormone is produced by the parathyroid glands.
Parathyroid glands are attached to the thyroid gland. The release of PTHleads to an increase in the rate that minerals are absorbed in theintestine. The three minerals affected are calcium, phosphate, andmagnesium. PTH causes the release of calcium and phosphatefrom bone tissue. PTH also increases the rate at which the kidneysremove calcium and magnesium from urine and return these twominerals to the blood. Hormones associated with the endocrinesystem control many different body functions.
Different hormones play more important roles during various stages of growthand development. They are the main biological influence on yourbehavior and on your development.◗ After You ReadMini Glossaryadrenal gland: located on top of the kidneys;outer portion secretes steroid hormones;inner portion secretes amino acid hormones; amino acid hormones are responsible for the fight-or-flight responseparathyroid gland: gland attached to the thyroid gland that is involved in mineral regulation in the bodyendocrine glands: glands that release chemicalsdirectly into the bloodstream; relay information to other parts of the bodyreceptors: the binding sites on target cellsnegative feedback system: type of internalfeedback mechanism that generally controlsadjustments to the endocrine systemtarget cells: cells to which hormones attachthemselves; contain specific binding siteseither on the plasma membranes, or inthe nucleithyroid gland: gland located in the neckthat regulates metabolism, growth, anddevelopment1.
Read the terms and their definitions in the Mini Glossary above. Use the lines below to listand describe the glands that belong to the endocrine system. Use your own words todescribe the glands.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________440Chapter 35READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.hypothalamus: the part of the brain thatconnects the endocrine system and thenervous systempituitary gland: the main gland of the endocrinesystem; controlled by the hypothalamusNameDateClassSection35.3The Endocrine System, continued2.
Use the flow diagram below to show how a negative feedback system in the endocrine system works to control the amount of hormones that are released into the body.Normal releaseof hormonesCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.A NegativeFeedbackSystemVisit the Glencoe Science Web site at science.glencoe.com to find yourbiology book and learn more about the endocrine system.READING ESSENTIALSChapter 35441NameDateClassSection36.1 The Nervous System◗ Before You ReadSC.F.1.4.6 The student knows that separate parts of the body communicate with each otherusing electrical and/or chemical signals. SC.F.1.4.7 The student knows that organismsrespond to internal and external stimuli.
Also covers SC.F.1.4.1, SC.F.1.4.8When you make a telephone call, telephone wires transmit messages electronically from location tolocation. In the same way, electrical impulses travel through the human body, allowing some parts tocommunicate with others.
On the lines below, list three examples of types of messages you thinkmay be transmitted within your body.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________◗ Read to LearnCreate a Quiz After youhave read this section, createa quiz based on what youhave learned.
After you havecompleted writing the quizquestions, be sure to answerthem.DendriteThe basic unit of structure and function in the nervous systemis called the neuron, or nerve cell. Neurons (NYU ronz) conductimpulses throughout the nervous system. As shown below, a neuron is a long cell that consists of three regions: a cell body, dendrites, and an axon.Dendrites (DEN drites) are branchlike extensions of the neuron that receive impulses and carry them toward the cell body.The axon is an extension of the neuron. It carries impulses awayfrom the cell body and toward other neurons, muscles, or glands.Neurons fall into three categories: sensory neurons, motorneurons, and interneurons. Sensory neurons carry impulses fromthe body to the spinal cord and brain. Interneurons are foundwithin the brain and spinal cord. They process incoming impulsesand pass response impulses on to motor neurons.
Motor neuronscarry the response impulses away fromMyelin sheaththe brain and spinal cord to a muscleor gland.NucleusHow are impulses relayed?AxonAxonendingsCell body442Chapter 36Imagine that you are in a crowded,noisy store and you feel a tap on yourshoulder. You turn your head, and yousee a friend standing behind you.
Whathappened in your body to cause the tapto get your attention? First, the touchstimulated sensory receptors located inREADING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Neurons: Basic Units of the Nervous SystemNameDateClassSection36.1The Nervous System, continuedthe skin of your shoulder. This produced a sensory impulse whichwas carried to the spinal cord and then to your brain.
From thebrain, an impulse was sent to your motor neurons, which transmitted the impulse to the muscles in your neck. The result? Yourneck muscles turned your head in response to the tap.Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.What occurs when the neuron is at rest?You have learned that the plasma membrane controls the concentration of ions in a cell. Because the plasma membrane of aneuron is more permeable to potassium ions (K+) than to sodiumions (Na+), more potassium ions are inside the cell membranethan outside it. Similarly, more sodium ions are outside the cellmembrane than inside it.The neuron membrane also contains an active transport system, called the sodium/potassium (Na+/K+) pump.
The pump usesATP (the cell’s energy storing molecules) to pump three sodiumions out of the cell for every two potassium ions it pumps in. Thisincreases the concentration of positive charges on the outside ofthe membrane. In addition, the presence of many negativelycharged proteins and organic phosphates means that the inside ofthe membrane is more negatively charged than the outside.Under these conditions, which exist when the cell is at rest, theplasma membrane is said to be polarized. A polarized membranehas the potential to transmit an impulse.1. Analyze When someonetaps you on the shoulder,which neuron goes intoaction?________________________________________________________________________2. In order for an impulseto be transmitted, whatstate must the restingcell’s membrane be in?________________________________________________________________________How are impulses transmitted?When a stimulus excites a neuron, gated sodium channels inthe membrane open up.
That allows sodium ions to enter the cell.As the positive sodium ions build up inside the membrane, theinside of the cell becomes more positively charged than the outside. This is called depolarization. The change in the chargemoves down the length of the axon like a wave.
As the diagram onpage 444 shows, the gated channels and the Na+/K+ pump thenreturn the neuron to its resting state.An impulse can only move down the complete length of anaxon when stimulation of the neuron is strong enough. If thethreshold level—the level at which depolarization occurs—is notreached, the impulse will die out quickly.What are white and gray matter?Most axons are surrounded by a white covering of cells calledthe myelin sheath.
The myelin sheath is like the plastic coatingon an electric wire. It insulates the axon, hindering the movementREADING ESSENTIALSChapter 36443NameDateClassSectionThe Nervous System, continuedKGated KchannelOutside cellImpulseNaNaGated NachannelInside cellNa+A Gated sodium channels open, allowing sodium ions toenter and make the inside of the cell positively chargedand the outside negatively charged.KKGated K channelGated K channelImpulseGated NachannelGated NachannelNaNa/KpumpNaB As the impulse passes, gated sodium channels close,stopping the influx of sodium ions. Gated potassiumchannels open, letting potassium ions out of the cell.This action repolarizes the cell.3NaGated K channelImpulseNa/Kpump2KGated NachannelC As gated potassium channels close, the Na/K pumprestores the ion distribution.444Chapter 36of ions across its plasma membrane. Theions move quickly down the axon untilthey reach a gap in the sheath.
Here, theions pass through the plasma membraneof the nerve cell and depolarizationoccurs. As a result, the impulse jumpsfrom gap to gap, greatly increasing thespeed at which it travels.The myelin sheath gives axons a whiteappearance. In the brain and spinal cord,masses of myelinated axons make up whatis called “white matter.” The absence ofmyelin in masses of neurons accounts forthe grayish color of “gray matter” in thebrain.What are the spaces betweenneurons called?Neurons lie end to end—axons todendrites—but they do not actuallytouch. There is a tiny space between oneneuron’s axon and another neuron’s dendrites. This space is called a synapse.Impulses traveling to and from the brainmust move across this space. How doimpulses make this leap?As an impulse reaches the end of anaxon, calcium channels open, allowing calcium to enter the end of the axon. The calcium causes vesicles in the axon to fusewith the plasma membrane, releasing theirchemicals into the synaptic space.
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