The brain stem functions in homeostasis, coordination of movement, and conduction of information to and from higher brain centers.

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1 Chapter 49 Nervus Systems Lecture Outline Cncept 49.2 The vertebrate brain is reginally specialized. In all vertebrates, three bilaterally symmetrical, anterir bulges f the neural tube the frebrain, midbrain, and hindbrain frm as the embry develps. By the fifth week f embrynic develpment in humans, the three primary bulges have frmed five brain regins. Three f these regins, derived frm the midbrain and the hindbrain, give rise t the brain stem, a set f structures that frm the lwer part f the brain. The hindbrain als gives rise t anther majr brain center, the cerebellum. As embrygenesis prceeds, the mst prfund changes in the human brain ccur in the telencephaln, the regin f the frebrain that gives rise t the adult cerebrum. Rapid grwth f the telencephaln causes the uter prtin f the cerebrum, called the cerebral crtex, t extend ver and arund much f the rest f the brain. Majr centers that develp frm the diencephaln are the thalamus, hypthalamus, and epithalamus. ETSU 3/31/ :19 PM Deleted: Overview: Cmmand and Cntrl System... [1] The brain stem functins in hmestasis, crdinatin f mvement, and cnductin f infrmatin t and frm higher brain centers. The adult brain stem cnsists f the midbrain, the pns, and the medulla blngata r medulla. The medulla and the pns transfer sensry infrmatin and mtr instructins between the PNS and the midbrain and frebrain. They als help crdinate large-scale bdy mvements, such as running r climbing. In carrying instructins abut the mvement frm cell bdies in the midbrain and frebrain t synapses in the spinal crd, mst axns crss in the medulla frm ne side f the CNS t the ther. As a result, the right side f the brain cntrls much f the mvement f the left side f the bdy, and vice versa. The midbrain cntains centers that receive and integrate different types f sensry infrmatin, sending cded sensry infrmatin alng neurns t specific regins f the frebrain. Sensry axns invlved in hearing terminate in r pass thrugh the midbrain n their way t the cerebrum. In nnmammalian vertebrates, prtins f the midbrain frm prminent ptic lbes that may be the nly visual centers. In mammals, visin is integrated in the cerebrum, nt the midbrain. The mammalian midbrain crdinates visual reflexes, such as the peripheral visin reflex, in which the head turns t an appraching bject withut frming an image f it. Lecture Outline fr Campbell/Reece Bilgy, 8 th Editin, Pearsn Educatin, Inc. 49-1

2 Signals frm the brain stem affect attentin, alertness, appetite, and mtivatin. The medulla cntains centers that cntrl several autmatic, hmestatic functins, including breathing, heart and bld vessel activity, swallwing, vmiting, and digestin. The pns als participates in sme f these activities; fr example, it regulates the breathing centers in the medulla. Axns frm the brain stem reach many areas f the cerebral crtex and cerebellum, releasing neurtransmitters such as nrepinephrine, dpamine, sertnin, and acetylchline. The brain stem and cerebrum cntrl arusal and sleep. Arusal is a state f awareness f the external wrld; sleep is a state in which external stimuli are received but nt cnsciusly perceived. Centers in the brain stem cntrl arusal and sleep. The reticular frmatin, a diffuse netwrk f neurns in the cre f the brain stem, acts as a sensry filter t chse which infrmatin reaches the cerebral crtex.! The brain ften ignres certain stimuli while actively prcessing ther inputs. The pns and medulla cntain centers that cause sleep when stimulated, and the midbrain has a center that causes arusal. All birds and mammals shw characteristic sleep/wake cycles regulated by melatnin, a hrmne prduced by the pineal gland. Peak melatnin secretin ccurs at night. Melatnin has been prmted as a dietary supplement t treat jet lag, insmnia, seasnal affective disrder, and depressin. Melatnin is synthesized frm sertnin, which itself may be the neurtransmitter f the sleep-prducing centers. Sertnin in turn is synthesized frm the amin acid tryptphan. Because tryptphan levels are relatively high in milk, drinking milk befre bedtime may prmte sleep by increasing the prductin f sertnin and melatnin. Sleep is essential fr survival. Furthermre, sleep is an active state, at least fr the brain. EEG recrdings shw that the frequency f brain waves changes as the brain prgresses thrugh the distinct stages f sleep. Sleep and dreams may be invlved in the cnslidatin f learning and memry. Regins f the brain activated during a learning task becme active again during sleep. Sme animals display evlutinary adaptatins that allw fr substantial activity during sleep. Bttlense dlphins, which sleep with ne eye pen and ne eye clsed, swim while sleeping, rising t the surface t breathe air. EEG recrdings frm the hemispheres f sleeping dlphins shw that dlphins sleep with nly ne brain hemisphere at a time. The cerebellum crdinates mvements and balance. The cerebellum receives sensry infrmatin abut jint psitin and muscle length, infrmatin frm the auditry and visual systems, and input abut mtr cmmands issued by the cerebrum. Infrmatin frm the cerebrum passes first t the pns and frm there t the cerebellum. The cerebellum integrates this sensry and mtr infrmatin as it carries ut crdinatin and errr checking during mtr and perceptual functins. Hand-eye crdinatin is an example f cerebellar cntrl; if the cerebellum is damaged, the eyes can fllw a mving bject, but they will nt stp at the same place as the bject. Lecture Outline fr Campbell/Reece Bilgy, 8 th Editin, Pearsn Educatin, Inc. 49-2

3 The cerebellum is als invlved in learning and remembering mtr skills. The embrynic diencephaln evlved int three adult brain regins: the thalamus, hypthalamus, and epithalamus. The embrynic diencephaln is the frebrain divisin that evlved earliest in vertebrate histry. The thalamus and hypthalamus are majr integrating centers that act as relay statins fr infrmatin flw in the bdy. The epithalamus includes the pineal gland, the surce f melatnin, and als cntains ne f several clusters f capillaries that generate cerebrspinal fluid frm bld. The thalamus is the main input center fr sensry infrmatin ging t the cerebrum. Incming infrmatin frm all the senses is srted in the thalamus and sent t the apprpriate cerebral centers fr further prcessing. The thalamus als receives input frm the cerebrum and ther parts f the brain that regulate emtin and arusal. The thalamus is frmed by tw masses, each rughly the size and shape f a walnut. The hypthalamus is ne f the mst imprtant brain regins fr the cntrl f hmestasis. The hypthalamus cntains the bdy s thermstat as well as centers fr regulating hunger, thirst, and ther basic survival mechanisms. The hypthalamus is the surce f psterir pituitary hrmnes and f releasing hrmnes that act n the anterir pituitary. Hypthalamic centers play a rle in sexual and mating behavirs, the fight-r-flight respnse, and pleasure. The hypthalamus regulates the bilgical clck. Specialized nerve cells within the hypthalamus regulate circadian rhythms, daily cycles f bilgical activity. Organisms frm bacteria and fungi t plants, insects, birds, and humans display these rhythms. In mammals, the cycles cntrlled by the hypthalamus influence a number f prcesses, including sleep, bdy temperature, hunger, and hrmne release. Circadian rhythms in mammals rely n a bilgical clck, a mlecular mechanism that directs peridic gene expressin and cellular activity. Bilgical clcks can maintain a 24-hur cycle even in the absence f envirnmental cues. Humans kept in a cnstant envirnment exhibit a cycle length f 24.2 hurs, with little variatin. In mammals, circadian rhythms are crdinated by a pair f hypthalamic structures called the suprachiasmatic nucleus, r SCN. In respnse t visual infrmatin, the SCN acts as a pacemaker t synchrnize the bdy s bilgical clcks t the natural cycles f day length. Animals whse SCN are remved lack rhythmicity in behavirs and brain activity. In 1990, Michael Menaker transplanted brain tissue between nrmal and mutant hamsters with faulty circadian rhythms and demnstrated that the SCN determines the circadian rhythm f the whle animal. In mammals, infrmatin prcessing is largely centered in the cerebrum. Lecture Outline fr Campbell/Reece Bilgy, 8 th Editin, Pearsn Educatin, Inc. 49-3

4 The cerebrum develps frm the embrynic telencephaln, an utgrwth f the frebrain that arse early in vertebrate evlutin as a regin supprting lfactry receptin as well as auditry and visual prcessing. The cerebrum is divided int right and left cerebral hemispheres. Each hemisphere cnsists f an uter cvering f gray matter, the cerebral crtex; internal white matter; and grups f neurns cllectively called basal nuclei lcated deep within the white matter. The basal nuclei are imprtant centers fr planning and learning mvement sequences. Damage in this brain regin during fetal develpment can result in cerebral palsy, a defect that disrupts the issuance f mtr cmmands t the muscles. The cerebral crtex is particularly extensive in mammals, where it is vital fr perceptin, vluntary mvement, and learning. In humans, the cerebral crtex accunts fr abut 80% f ttal brain mass and is highly cnvluted. Due t its cnvlutins, the cerebral crtex has a large surface area but still fits inside the skull: Less than 5 mm thick, it has a surface area f apprximately 1000 cm 2. The cerebral crtex is divided int right and left sides, each respnsible fr the ppsite half f the bdy. The left side f the crtex receives infrmatin frm, and cntrls the mvement f, the right side f the bdy, and vice versa. A thick band f axns knwn as the crpus callsum enables cmmunicatin between the right and left cerebral crtices. The cerebrum is very plastic, especially early in develpment, and areas f the brain can take n nvel functins. A dramatic example f this phenmenn results frm a treatment fr the mst extreme cases f epilepsy, a cnditin causing episdes f electrical disturbance, r seizures, in the brain. Infants with severe epilepsy may have a cerebral hemisphere surgically remved. Amazingly, recvery is nearly cmplete, as the remaining hemisphere assumes mst f the functins nrmally prvided by the entire cerebrum. Even in adults, damage t a prtin f the cerebral crtex can trigger the develpment r use f new brain circuits, leading in sme cases t recvery f functin. Sme vertebrates demnstrate cgnitin. In humans, the utermst part f the cerebral crtex frms the necrtex, six parallel layers f neurns arranged tangential t the brain surface. Such a large, highly cnvluted necrtex was thught t be required fr advanced cgnitin, the perceptin and reasning that frm knwledge. Bth primates and cetaceans pssess an extensively cnvluted necrtex. Birds lack a necrtex and were thught t have substantially lwer intellectual capacity. In fact, birds are capable f sphisticated infrmatin prcessing. Scrub jays can remember the relative perid f time that has passed since they stred and hid specific fd items. New Calednian crws are highly skilled at making and using tls, an ability therwise well dcumented fr nly humans and great apes. Lecture Outline fr Campbell/Reece Bilgy, 8 th Editin, Pearsn Educatin, Inc. 49-4

5 African gray parrts understand relatinal cncepts that are numerical r abstract, distinguishing between same and different and grasping the cncept f nne. The sphisticated cgnitive ability f birds is based n an evlutinary variatin n the architecture f the pallium, the tp r uter prtin f the brain. Whereas the human pallium the cerebral crtex cntains flat sheets f cells in six layers, the avian pallium cntains neurns clustered int nuclei. This rganizatin, likely ancestral in vertebrates, was transfrmed int a layered ne early in mammalian evlutin. Cnnectivity was maintained during this transfrmatin s that, fr example, the pallium f bth mammals and birds receives sensry input sights, sunds, and tuch frm the thalamus. The result was tw different arrangements, each supprting cmplex and flexible brain functin. ETSU 3/31/ :20 PM Deleted: Cncept 49.3 The cerebral crtex cntrls vluntary mvement and cgnitive functins.... [2] Lecture Outline fr Campbell/Reece Bilgy, 8 th Editin, Pearsn Educatin, Inc. 49-5

Topic 11: Nervous System

Topic 11: Nervous System Tpic 11: Nervus System Functin: Imprtant Definitins Neurns: Stimulus: anything that causes a nerve impulse t be sent Ex: Receptrs: sense rgans that detect Impulse: change alng the neurn Effectrs: any structure