Reading Essentials for Biology Glencoe (794133), страница 101
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Thesechemicals are called neurotransmitters.They diffuse across the space to the dendrites of the next neuron. As the neurotransmitters reach the dendrites, they signalreceptor sites to open the ion channels.This process is illustrated on page 445.The open channels change the polarityin the neuron, starting a new impulse.Enzymes in the synapse typically breakdown the neurotransmitters shortly aftertransmission.
This prevents the continualfiring of impulses.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.36.1NameDateClassSection36.1The Nervous System, continuedVesicle withneurotransmittersinsideAxonDendriteVesicle fuseswithmembrane(exocytosis)AxonImpulseCa 2+CalciumchannelSynapseCa 2+Ca 2+Neurotransmitterdiffuses acrosssynapse and bindswith receptor ondendriteSynapticspaceNeurotransmittersreleased intosynapseDendriteImpulseIon channelCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.AxonDendriteThe Central Nervous SystemWhen you make a telephone call to a friend, your call travelsthrough wires to a control center. There it is switched over towires that connect with a friend’s telephone.
In the same way, animpulse travels through the neurons in your body. The impulseusually reaches the control center of the nervous system—yourbrain—before being rerouted. The brain and the spinal cordtogether make up the central nervous system, which coordinates all your body’s activities.Another division of your nervous system is called the peripheral(puh RIH frul) nervous system.
It is made up of all the nervesthat carry messages to and from the central nervous system. It issimilar to the telephone wires that run between a phone system’scontrol center and the phones in individual homes. Together, thecentral nervous system (CNS) and the peripheral nervous system(PNS) respond to stimuli from the external environment.READING ESSENTIALS3. What two parts of thebody make up the centralnervous system?________________________________________________Chapter 36445NameDateClassSection36.1The Nervous System, continuedHow does the brain work?________________________________________________________________________The Peripheral Nervous System5.
What two divisions makeup the peripheral nervoussystem?________________________________________________Remember that the PNS carries impulses between the body andthe CNS. For example, when a stimulus is picked up by receptorsin your skin, it initiates an impulse in the sensory neurons.
Theimpulse is carried to the CNS. There, the impulse transfers to themotor neurons, which carry the impulse to a muscle.The PNS can be separated into two divisions—the somaticnervous system and the autonomic nervous system.What is the somatic nervous system?The somatic nervous system is made up of 12 pairs of cranialnerves from the brain, 31 pairs of spinal nerves from the spinalcord, and all of their branches. These nerves are actually bundlesof neuron axons bound together by connective tissue. The cellbodies of the neurons are found in clusters along the spinal column. Most nerves contain both sensory and motor axons.The nerves of the somatic system relay information mainlybetween your skin, the CNS, and skeletal muscles.
This pathway446Chapter 36READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.4. Apply When you are trying to balance on onefoot, which part of yourbrain are you using?The brain is the control center for the entire nervous system.The brain can be divided into three main sections. They are thecerebrum, the cerebellum, and the brain stem.The cerebrum (suh REE brum) is divided into two halves thatare connected by bundles of nerves. The sections are called hemispheres. The cerebrum controls all conscious activities, intelligence, memory, language, skeletal muscle movements, and senses.The outer surface of the cerebrum, called the cerebral cortex, ismade up of gray matter.
The cerebral cortex contains numerousfolds and grooves that increase its total surface area. This increasein surface area played an important role in the evolution ofhuman intelligence. Greater surface area allowed more and morecomplex thought processes.The cerebellum (ser uh BE lum) is located at the back of thebrain. It controls balance, posture, and coordination. If the cerebellum is injured, movements can become jerky.The brain stem is made up of the medulla oblongata, thepons, and the midbrain.
The medulla oblongata (muh DU luh •ah blon GAH tuh) is the part of the brain that controls involuntary activities such as breathing and heart rate. The pons andmidbrain act as pathways connecting various parts of the brain toeach other.NameDateClassSection36.1The Nervous System, continuedSensory neuronInterneuronDirection of impulseSpinalcordMotorneuronFlexor muscle contractsand withdraws partbeing stimulatedCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Pain receptors in skinis voluntary, meaning that you can decide whether or not to movebody parts under the control of the system.Sometimes a stimulus results in an automatic, unconsciousresponse within the somatic system.
When you touch somethinghot, you automatically jerk your hand away. Such an action is areflex, an automatic response to a stimulus. As illustrated above, areflex impulse travels to the spinal column or brain stem where itcauses an impulse to be sent directly back to a muscle. It does notgo to the brain for interpretation. The brain becomes aware ofthe reflex only after it occurs.What is the autonomic nervous system?Have you ever heard scary sounds in the middle of the night?Maybe your heart began to pound or your palms got sweaty.These internal reactions to being scared are controlled by theautonomic nervous system. The autonomic nervous system carries impulses from the CNS to internal organs.
These impulsesproduce responses that are involuntary, meaning they are notunder conscious control.There are two divisions of the autonomic nervous system—thesympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system controls many internalREADING ESSENTIALSChapter 36447NameDateClassSection36.1The Nervous System, continued6. What are the two divisions of the autonomicnervous system?________________________________________________functions during times of stress. When something scares you, thesympathetic nervous system causes the release of hormones, suchas epinephrine and norepinephrine, which results in a fight-orflight response.The parasympathetic nervous system controls many of thebody’s internal functions when it is at rest.
It is in control whenyou are reading quietly in your room. Both the sympathetic andparasympathetic systems send signals to the same internal organs.The resulting activity of the organ depends on the intensities ofthe opposing signals.◗ After You ReadMini Glossaryaxon: extension of a neuron; carries impulsesaway from a nerve cellcentral nervous system (CNS): in humans, thecentral control center of the nervous systemmade up of the brain and spinal cordcerebellum (ser uh BE lum): rear portion ofthe brain; controls balance, posture, andcoordinationcerebrum (suh REE brum): largest part of thebrain, composed of two hemispheres connected by bundles of nerves; controls conscious activities, intelligence, memory,language, skeletal muscle movements, andthe sensesdendrite (DEN drite): branchlike extension ofa neuron; transports impulses toward thecell bodymedulla oblongata (muh DU luh • ah blon GAHtuh): part of the brain stem that controlsinvoluntary activities such as breathing andheart rateneuron (NYU ron): basic unit of structure andfunction in the nervous system; conductsimpulses throughout the nervous system;composed of dendrites, a cell body, andan axon448Chapter 36neurotransmitters: chemicals released from anaxon that diffuse across a synapse to the nextneuron’s dendrites to initiate a new impulseparasympathetic nervous system (PNS): divisionof the autonomic nervous system that controls many of the body’s internal functionswhen the body is at restperipheral (puh RIH frul) nervous system: division of the nervous system made up of allthe nerves that carry messages to and fromthe central nervous systemreflex (REE fleks): simple, automatic response inan animal that involves no conscious control, usually acts to protect an animal fromserious injury, automatic response to a stimulus; reflex stimulus travels to the spinal column or brain stem and is sent directly backto the musclesomatic nervous system: portion of the nervous system composed of cranial nerves,spinal nerves, and all of their branches; voluntary pathway that relays informationmainly between the skin, the CNS, andskeletal musclessympathetic nervous system: division of theautonomic nervous system that controlsmany of the body’s internal functions during times of stresssynapse: tiny space between one neuron’s axonand another neuron’s dendrites over whicha nerve impulse must passREADING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.autonomic nervous system (ANS): in humans,portion of the peripheral nervous systemthat carries impulses from the central nervous system to internal organs; producesinvoluntary responsesNameDateClassSection36.1The Nervous System, continued1.
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