Chapter 2: The Anatomy and Evolution of the

The road to our current understanding of the structure and function of the nervous systemhas had its share of twists and turns. Concepts that we now take for granted werenot easy to establish. In some cases, students of the brain got a lot of things right, only toundo their credibility by the errors they made. A classic example of the ups and downsof brain science is the work of Franz Joseph Gall (17581828), the Austrian physician wemet in Chapter 1 as the developer of phrenology. Phrenology was a pseudoscience thatargued that a persons character could be determined by feeling the lumps on the skull.Phrenologists reasoned that parts of the brain that were related to a particular trait would be exercised through expression of that trait, leading to increases in brain size reflected inbumps on the skull. Phrenology became wildly popular in Europe and in the United States,and numbered among its fans were such notables as Walt Whitman, Edgar Allan Poe, andRalph Waldo Emerson. Employers would insist that job candidates undergo a phrenologyexam, and engaged couples would consult phrenologists to see whether their characterswere compatible. Candidates for public office would challenge their rivals to see whichperson had the best reading. Todays political debates begin to look better.Gall actually got a few things right in spite of not subjecting his ideas to controlledexperimentation. Gall was correct in assuming that the brain is the organ of the mind, andhe was right again in suggesting that the brain was not a single entity but a collection ofstructures with different functions. Gall was substantially ahead of his time in suggestingthat certain functions were localized in the brain. Where Gall fell completely off track wasin his suggestion that the external contours of the skull had anything whatsoever to dowith the functions of the brain beneath it.In this chapter, we will preview many topics that will later be explained in greater detailin their own chapters. Feel free to look ahead. Similarly, as you read later chapters, you mayfind it helpful to return to sections of this chapter as a reminder of how the various partsof this miraculous structure work together. Perhaps 200 years from now, our understandingof brain science will have advanced so far that some of the material in this chapter willseem as wrong as Galls phrenology. I dont think this will be the case. Our advantage overGall is the painstaking and carefully controlled research that has pieced together our currentunderstanding of the structures, functions, and evolutionary history of the brain.1Chapter 2: The Anatomy and Evolution of the

L E A R N I N GO B J ECTI V E SAfter this chapter,you should be able to:LO1 Identify the majoranatomical directional terms andplanes of section.LO2 Describe the three layersof the meninges, the circulationof cerebrospinal fluid, and themajor sources of blood supply tothe brain.LO3 Describe the majordivisions and functions of thespinal cord.

LO4 Identify the majorstructures and functions of thehindbrain, midbrain, andforebrain.LO5 Describe the outerappearance and layeredstructure of the cerebral cortexand the location and function ofthe four cortical lobes.LO6 Differentiate the sensory,motor, and association cortices.

LO7 Describe the structureand function of the cranial andspinal nerves.LO8 Summarize the majorstructural and functionalfeatures of the peripheralnervous system.LO9 Trace the evolution of thehuman nervous system.

CHAP T E R O U T L INEAnatomical Directions and Planes of SectionProtecting and Supplying the Nervous SystemThe MeningesThe Cerebrospinal FluidThe Blood SupplyThe Central Nervous SystemThe Spinal CordThe HindbrainThe MidbrainThe Forebrain

The Peripheral Nervous SystemThe Cranial NervesThe Spinal NervesThe Autonomic Nervous SystemEvolution of the Human Brain and Nervous SystemNatural Selection and EvolutionEvolution of the Nervous SystemEvolution of the Human BrainAnatomical Directions and Planes and Section

Head of the dog is rostral to its shouldersThe dogs ear is caudal to its nose, and its hips are caudal to its shouldersInferior or ventral- towards the bellySuperior or dorsal- toward the back

Anatomical Directions and Planes and Section

N/B: an illustration of an animal

Rostral or anterior- toward the end of the animal e.g. head of the dog is rostral to its shoulders

Caudal or posterior- toward the tail end of the animale.g. the dogs ears are caudal to its nose, and its hips are caudal to its shoulders

Inferior or ventral- toward the belly side

Superior or dorsal- toward the backe.G dorsal shark fin

N/B: like geographical terms, anatomical terms are relative to another place.Just as Luzon is north of Visayas but Mindanao is south.

Dogs ears is caudal to its nose but rostral to its shoulders

Why are anatomical directions different in people?Our two-legged stance puts a 90-degree bend in the neuraxisNeuraxis- an imaginary line that runs the length of the spinal cord through the brain.

In the four-legged animal Neuraxis forms a straight line running parallel to the ground.Dorsal parts of the animals brain are in line with the dorsal parts of the spinal cord.

In humansDorsal parts of our brain form a 90-degree angle with the dorsal parts of the spinal cord.

Midline- imaginary line that divides us into approximately equal halves.Ipsilateral- they are both on the same side of the midlinee.g. left arm and leg Contralateral- structures are opposite sides of the midlinee.g. left arm and right legMedial- structures close to the centerLateral- side of the midlinee.g.. Heart is medial to my arms, whereas my ears are lateral to my nose.

Similar termsProximal- close to the centere.g. my shoulders are proximal relative to my elbowsDistal- far away from the centere.g. toes are distal relative to my knees-Use to refer to the limbs

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Anatomical Directions and Planes and Section

N/B: an illustration of an animal

Rostral or anterior- toward the end of the animal e.g. head of the dog is rostral to its shoulders

Caudal or posterior- toward the tail end of the animale.g. the dogs ears are caudal to its nose, and its hips are caudal to its shoulders

Inferior or ventral- toward the belly side

Superior or dorsal- toward the backe.G dorsal shark fin

N/B: like geographical terms, anatomical terms are relative to another place.Just as Luzon is north of Visayas but Mindanao is south.

Dogs ears is caudal to its nose but rostral to its shoulders

Why are anatomical directions different in people?Our two-legged stance puts a 90-degree bend in the neuraxisNeuraxis- an imaginary line that runs the length of the spinal cord through the brain.

In the four-legged animal Neuraxis forms a straight line running parallel to the ground.Dorsal parts of the animals brain are in line with the dorsal parts of the spinal cord.

In humansDorsal parts of our brain form a 90-degree angle with the dorsal parts of the spinal cord.

Midline- imaginary line that divides us into approximately equal halves.Ipsilateral- they are both on the same side of the midlinee.g. left arm and leg Contralateral- structures are opposite sides of the midlinee.g. left arm and right legMedial- structures close to the centerLateral- side of the midlinee.g.. Heart is medial to my arms, whereas my ears are lateral to my nose.

Similar termsProximal- close to the centere.g. my shoulders are proximal relative to my elbowsDistal- far away from the centere.g. toes are distal relative to my knees-Use to refer to the limbs

8MAP OF THE WORLDPlanes and Sections

3 major planes of section, along with representative images of the brain slicesCoronal sections- frontal sectionsThe ns from front to backLooking the brain in the face

Sagittal sections- parallel to the midlineSide of the brainMidsagittal section- relatively equal halves

Horizontal or axial section- divides the brain from top to bottom10Protecting and Supplying the Nervous SystemMeninges- layers of membranes that cover the central nervous system and the peripheral nerves.Meningitis3 layers:Dura materArachnoid layerPia materSub arachnoid space

Brain- the most protected organsInfants- not fully mature skull bonesThe skull bones are like tectonic plates that can overlapThis _______ of the brain enables the baby to go through the birth canal.There is also pulse at the top of the head between the skull bones, known as soft spot or fontanel

18 months for the bones to fuse completely.

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Dura Mater- hard motherDurableComposed of the leather-like tissue that follows the outlines of the skull bones

mother

Arachnoid layer or memberane-below the dura mater-The more delicate layer which structure looks like a spiders web in cross-section.

Pia mater-Pious motherNearly transparent membrane sticks closely to the outside of the brain.

Subarachnoid space- sub meaning below

Only dura and pia mater cover the nerves (peripheral ns) that exit the brain and spinal cord

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Meningitis- meninges become infected- life-threatening disease caused by various viruses and bacteria13Cerebrospinal fluid (CSF)- is secreted within hollow spaces in the brain known as ventricles.The choroid plexus converts material from the nearby blood supply into cerebrospinal fluid.

Cerebrospinal fluid (CSF)- is secreted within hollow spaces in the brain known as ventricles.The choroid plexus converts material from the nearby blood supply into cerebrospinal fluid.

Characteristics: similar to the composition to the clear plasma of the blood.If you bump- this will serve as a cushion to soften the blow to your brain.

The neurons responds to appropriate input, not to pressure on the brain.If there is a lot of pressure, the neurons can fire in maladaptive ways. E.g. tumor- seizures

So the CSF makes the brain float and prevents neurons from responding to pressure and false information

CSF circulates through the central canal of the spinal cord and four ventricles inthe brain: the two lateral ventricles, one in each hemisphere, and the third and fourthventricles in the brainstem. The fourth ventricle is continuous with the central canalof the spinal cord, which runs the length of the cord at its midline. The ventriclesand the circulation of CSF are illustrated in Figure 2.5. Below the fourth ventricle,there is a small opening that allows the CSF to flow into the subarachnoid spacethat surrounds both the brain and spinal cord. New CSF is made constantly, with theentire supply being turned over about three times per day. The old CSF is reabsorbedinto the blood supply at the top of the head.

Because there are several narrow sections in this circulation system, blockagessometimes occur. This condition, known as hydrocephalus, is apparent at birth inaffected infants, such as the one depicted in Figure 2.6. Hydrocephalus literallymeans water on the brain. Left untreated, hydrocephalus can cause mental retardation,as the large quantity of CSF prevents the normal growth of the brain. Currently,however, hydrocephalus can be treated by the installation of a shunt to drain offexcess fluid. When the baby is old enough, surgery can be used to repair the obstruction.Some adults also experience blockages of the CSF circulatory system. They, too,must be treated with shunts and/or surgery.CSF moves through a completely self-contained and separate circulation systemthat never has direct contact with the blood supply. Because the composition of thecerebrospinal fluid is often important in diagnosing diseases, a spinal tap is a common,though extremely unpleasant, procedure. In a spinal tap, the physician withdrawssome fluid from the subarachnoid space through a needle.14Cerebrospinal Fluid

15Blood Supply

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Blood SupplyThe brain has enormous energy requirements, so its blood supply is generous. Thebrain receives its nutrients through the carotid arteries on either side of the neckas well as through the vertebral arteries that travel up through the back of theskull. Once inside the skull, these major arteries, as shown in Figure 2.7, branchto form the anterior, middle, and posterior cerebral arteries, which serve most ofthe brain.Because the brain is unable to store energy, any interruption of the blood supplyproduces damage very quickly. Significant brain damage occurs less than three minutesafter the stopping of a persons heart. Other structures in the body will not beaffected so quickly. With life support, other organs are able to continue almost indefinitely.Thats why we currently view brain death as our working definition of death.

17Murder Case The sirens stopped. Then, people went out of the van to investigate a cadaver found. According to the residents they had found him stealing tons of gold from a treasures chest in an old mansion house.You are one of the forensic team who will investigate the cadaver, then for you be able to learn the root cause of the death of the person you have to study about the different structures of the nervous systemPpt at least 5 slidesAnatomical directions help us locate structures in thenervous system. In four-legged animals, rostral or anteriorstructures are located toward the head, caudal orposterior structures are located toward the tail, dorsal orsuperior structures are located toward the back, and ventralor inferior structures are located toward the belly. Inhumans, the dorsal parts of our brain form a 90-degreeangle with the dorsal parts of the spinal cord. (LO1)2. Ipsilateral structures are on the same side of the midline,and contralateral structures are on opposite sides of themidline. Structures near the midline are medial, andstructures away from the midline are lateral. In limbs,proximal structures are closer to the body center, anddistal structures are farther away. (LO1)3. Coronal sections divide the brain from front to back.Sagittal sections are parallel to the midline and give usa side view of the brain. Horizontal sections divide thebrain from top to bottom. (LO1)4. Three layers of meninges protect the central nervous system:the dura mater, the arachnoid, and the pia mater.Only the dura mater and pia mater layers are present inthe peripheral nervous system. Cerebrospinal fluid floatsand cushions the brain. Cerebrospinal fluid circulatesthrough the four ventricles of the brain, the central canalof the spinal cord, and the subarachnoid space. (LO2)5. The brain is supplied with blood through the carotidand vertebral arteries.19What we think, we become.Buddha

We divide the entire nervous system into two components, the central nervous system(CNS) and the peripheral nervous system (PNS).

The central nervous system includesthe brain and spinal cord.

The peripheral nervous system contains all the nerves thatexit the brain and spinal cord, carrying sensory and motor messages to and from theother parts of the body.

DIFFERENCES BET CNS AND PNSStructure of the of the membraneCNS- CSF while PNS noneDamageCNS- permanentPNS- Temporary21The Central Nervous SystemThe Spinal CordThe HindbrainThe MidbrainThe Forebrain

Spinal Corda long cylinder of nerve tissue that extends from the medulla, the most caudal structure of the brain, down to the first lumbar vertebra (a bone in the spine, or vertebral column)

The spinal cord is the original information superhighway.Vertebral column- where majority of the neurons are found in the sc

The spinal cord is shorter than the vertebralcolumn because the cord itself stops growing before the bones in the vertebral columndo. Running down the center of the spinal cord is the central canal.23

the spinal nerves exit between the bones of the vertebralcolumn. The bones are cushioned from one another with disks.

If any of these disks degenerate, pressure is exerted on the adjacent spinal nerves, producing a painful pinched nerve.

Based on the points of exit, we divide the spinal cord into 31 segments.

Starting closest to the brain, there are eight cervical nerves that serve the area of thehead, neck, and arms. We refer to the neck brace used after a whiplash injury as acervical collar.

Below the cervical nerves are the 12 thoracic nerves, which serve mostof the torso.thoracic surgeon used to identify a surgeonwho specializes in operations involving the chest, such as heart or lung surgeries.

Fivelumbar nerves come next, serving the lower back and legs. If somebody complainsof lower back pain, this means he or she has lumbar problems.

The five sacral nervesserve the backs of the legs and the genitals.

Finally, we have the single coccygeal nerve.

Although the spinal cord weighs only 2 percent as much as the brain, it is responsiblefor several essential functions.24

White matter is made up of nerve fibers known as axons, the parts ofneurons that carry signals to other neurons. The tissue looks white due to a fatty materialknown as myelin, which covers most human axons

When the tissue is preservedfor study, the myelin repels staining and remains white, looking much like the fat ona steak. These large bundles or tracts of axons are responsible for carrying informationto and from the brain.

Axons from sensory neurons that carry information abouttouch, position, pain, and temperature travel up the dorsal parts of the spinal cord.

Axons from motor neurons, responsible for movement, travel in the ventral parts ofthe cord.

Gray matter consists of areas primarily made up of cell bodies. The tissue appears gray because the cell bodies absorb some of the chemicalsused to preserve the tissue, which stains them gray.

The neurons found in thedorsal horns of the H receive sensory input, whereas neurons in the ventral horns ofthe H pass motor information on to the muscles. These ventral horn cells participatein either voluntary movement or spinal reflexes.25make some pop ups white and gray matter--------------------------the spinal cord neurons are capable of someimportant reflexes. The knee jerk, or patellar reflex, that your doctor checks bytapping your knee, is an example of one type of spinal reflex.

This reflex is managedby only two neurons. One neuron processes sensory information coming tothe cord from muscle stretch receptors

This neuron communicateswith a spinal motor neuron that responds to input by contracting a muscle, causing your foot to kick.--------------------------------------Spinal reflexes also protect us from injury. If you touch somethinghot or step on something sharp, your spinal cord produces a withdrawal reflex. Youimmediately pull your body away from the source of the pain.

This time, three neuronsare involved: a sensory neuron, a motor neuron, and an interneuron betweenthem. Because so few neurons are involved, the withdrawal reflex produces very rapidmovement.

_________________________________The spinal cord also manages a number of more complex postural reflexesthat help us stand and walk. These reflexes allow us to shift our weight automaticallyfrom one leg to the other.

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Damage to the spinal cord results in loss of sensation (of both the skin and internal organs) and loss of voluntary movement in parts of the body served by nerveslocated below the damaged area.

Some spinal reflexes are usually retained. Musclescan be stimulated, but they are not under voluntary control.

E.g.

A person with cervicaldamage, such as the late actor Christopher Reeve, is a quadriplegic (quad meaningfour, indicating loss of control over all four limbs).

All sensation and ability to movethe arms, legs, and torso are lost. A person with lumbar-level damage is a paraplegic.Use of the arms and torso is maintained, but sensation and movement in the lowertorso and legs are lost.

In all cases of spinal injury, bladder and bowel functions are nolonger under voluntary control, as input from the brain to the sphincter muscles doesnot occur. Currently, spinal damage is considered permanent, but significant progressis being made in repairing the spinal cord27The Hindbrainlocated just above the spinal cord.Early in embryological development, the brain divides into three parts:the hindbrain, midbrain (or mesencephalon), and forebrain.

the hindbrainand midbrain make up the brainstem.

Later in embryological development, the midbrainmakes no further divisions, but the hindbrain divides into the myelencephalon,or medulla, and the metencephalon.

Cephalon, by the way, refers to the head.28

Later in embryological development, the midbrainmakes no further divisions, but the hindbrain divides into the myelencephalon,or medulla, and the metencephalon.

The medulla, like the spinal cord, contains large quantities of white matter.The vast majority of all information passing to and from higher structures of the brainmust still pass through the medulla.

Instead of the butterfly appearance of the gray matter in the spinal cord, themedulla contains a number of nuclei, or collections of cell bodies with a shared function.These nuclei are suspended within the white matter of the medulla. Some ofthese nuclei contain cell bodies whose axons make up several of the cranial nervesserving the head and neck area.

Other nuclei manage essential functions such asbreathing, heart rate, and blood pressure. Damage to the medulla is typically fatal dueto its control over these vital functions.29The Myelencephalon (Medulla)- The gradual swelling of tissue above the cervicalspinal cord marks the most caudal portion of the brain, the myelencephalon, ormedulla.

Along the midline of the upper medulla, we see the caudal portion of a structureknown as the reticular formation.

The reticular formation, shown in Figure 2.10, isa complex collection of nuclei that runs along the midline of the brainstem from themedulla up into the midbrain.

The structure gets its name from the Latin reticulum,or network.

The reticular formation plays an important role in the regulation of sleepand arousal30The MetencephalonThe metencephalon contains two major structures, the pons and the cerebellum.Pons means bridge in Latin, and one of the roles of the pons is to form connections between the medulla and higher brain centers as well as with the cerebellum.cerebellum, actually means little brain in Latin. emphasizes its role in coordinating voluntary movements, maintaining muscle tone, and regulating balance.

large fiber pathways with embedded nuclei are found inthe pons. Among the important nuclei found at this level of the brainstem are thecochlear nucleus and the vestibular nucleus.

The fibers communicating with these nuclei arise in the inner ear.

The cochlear nucleus receives informationabout sound, and the vestibular nucleus receives information about the position andmovement of the head. This vestibular input helps us keep our balance (or makes usfeel motion sickness on occasion)._____________________________The reticular formation, which begins in the medulla, extends through the ponsand on into the midbrain. The pons contains a number of other important nuclei thathave wide-ranging effects on the activity of the rest of the brain. Nuclei located withinthe pons are necessary for the production of rapid-eye-movement (REM) sleep,

_______________________________The raphe nuclei and the locuscoeruleus project widely to the rest of the brain and influence mood, states of arousal,and sleep.

_____________________________The second major part of the metencephalon, the cerebellumThe cerebellum looks almost like a second little brain attached to the dorsalsurface of the brainstem

Its name, cerebellum, actually means little brain in Latin.The use of little is misleading because the cerebellum actually contains more nervecells (neurons) than the rest of the brain combined. When viewed with a sagittal section,the internal structure of the cerebellum resembles a tree. White matter, or axons,forms the trunk and branches, while gray matter, or cell bodies, forms the leaves.

HOW THE CEREBELLUM WORKS1. Input from the spinalcord tells the cerebellum about the current location ofthe body in three- dimensional space.2. Input from the cerebralcortex, by way of the pons, tells the cerebellum aboutthe movements you intend to make.3. The cerebellum thenprocesses the sequences and timing of muscle movementsrequired to carry out the plan.31Damages to the cerebellumAlthough neuroscientists do not agree on its exact function, most theories propose a cerebellum that can use past experience to make corrections and automate behaviors, whether they involve motor systems or not.Considerable data support this role for the cerebellumin movement.

Damage to the cerebellum affects skilledmovements, including speech production.

Because the cerebellumis one of the first structures affected by the consumptionof alcohol, most sobriety tests, such as walking astraight line or pointing in a particular direction, are actuallytests of cerebellar function.

Along with the previouslymentioned vestibular system, the cerebellum contributesto the experience of motion sickness.

___________________More contemporary views see the cerebellum asresponsible for much more than balance and motor coordination.

In spite of its lowly position in the hindbrain, thecerebellum is involved in some of our more sophisticatedprocessing of information

In the course of evolution, thesize of the cerebellum has kept pace with increases in thesize of the cerebral cortex. One of the embedded nuclei ofthe cerebellum, the dentate nucleus, has become particularlylarge in monkeys and humans. A part of the dentatenucleus, known as the neodentate, is found only in humans.In addition to language difficulties, patients with cerebellar damage also experiencesubtle deficits in cognition and perception.

As we will see in Chapter 12, the cerebellumalso participates in learning (Albus, 1971; Marr, 1969). In cases of autism, a disorderin which language, cognition, and social awareness are severely afflicted, the mostreliable anatomical marker is an abnormal cerebellum (Courchesne, 1997). Althoughneuroscientists do not agree on its exact function, most theories propose a cerebellumthat can use past experience to make corrections and automate behaviors, whetherthey involve motor systems or not.32The Midbrainhas a dorsal or top half known as the tectum, or roof, and a ventral, or bottom half, known as the tegmentum, or covering. In the midbrain, cerebrospinal fluid is contained in a small channel at the midline known as the cerebral aqueduct.

On the dorsal surface of the midbrain are four prominent bumps. The upper pairis known as the superior colliculi. The superior colliculi receive input from the opticnerves leaving the eye. Although the colliculi are part of the visual system, they areunable to tell you what youre seeing. Instead, these structures allow us to make visuallyguided movements, such as pointing in the direction of a visual stimulus. Theyalso participate in a variety of visual reflexes, including changing the size of the pupilsof the eye in response to light conditions (see Chapter 6).

The other pair of bumps is known as the inferior colliculi. These structures areinvolved with hearing, or audition. The inferior colliculi are one stop along the pathwayfrom the ear to the auditory cortex. These structures are involved with auditoryreflexes such as turning the head in the direction of a loud noise. The inferiorcolliculi also appear to participate in the localization of sounds in the environment bycomparing the timing of the arrival of sounds at the two ears (see Chapter 7).34

The Forebrainthe most advanced and most recently evolved structures of the brain.divisions are the diencephalon (The Thalamus and Hypothalamus) and the telencephalon (symmetrical left and right cerebral hemispheres).Like the hindbrain, the forebrain divides again later in embryological development.The two resulting divisions are the diencephalon and the telencephalon.The diencephalon contains the thalamus and hypothalamus, which are located atthe midline just above the mesencephalon or midbrain. The telencephalon containsthe bulk of the symmetrical left and right cerebral hemispheres

The upper portion of the diencephalonconsists of the thalamus.36Thalamus- structure in the diencephalonthat processes sensoryinformation, contributes tostates of arousal, and participatesin learning and memory.

The diencephalon, depicted in Figure 2.12,is located at the rostral end of the brainstem. The upper portion of the diencephalonconsists of the thalamus.LOCATIONWe actually have two thalamic nuclei, one on either side of the midline. These structures appear to be just about in the middle of the brain, asviewed in a midsagittal section.HOW IT WORKSInputs from most of our sensory systems convergeon the thalamus, which then forwards the information on to the cerebral cortexfor further processing. It appears that the thalamus does not change the nature ofthe sensory information, so much as it filters the information passed along to thecortex, depending on the organisms state of arousal and consciousness.

DAMAGEDamage to the thalamus typically results in coma,and disturbances in circuits linking the thalamus and cerebral cortex are involvedin some seizures (see Chapter 15). The thalamus has also been implicated in learningand memory (see Chapter 12).37Hypothalamus- A structure found in thediencephalon that participates inthe regulation of hunger, thirst,sexual behavior, and aggression;part of the limbic system.

The name hypothalamus literallymeans below the thalamus. The hypothalamus is a major regulatory center for suchbehaviors as eating, drinking, sex, biorhythms, and temperature control

COMPONENTSRather thanbeing a single, homogeneous structure, the hypothalamus is a collection of nuclei. Forexample, the aforementioned ventromedial nucleus of the hypothalamus (VMH) participatesin the regulation of feeding behavior. The suprachiasmatic nucleus receivesinput from the optic nerve and helps set daily rhythms according to the rising of thesun. The hypothalamus is directly connected to the pituitary gland, from whichmany important hormones are released (see Chapter 10). Finally, the hypothalamusdirects the autonomic nervous system, the portion of the peripheral nervous systemthat controls our glands and organs.38The Basal GangliaA collection of nuclei (caudate nucleus, theputamen, the globus pallidus, and the subthalamic nucleus) within the cerebral hemispheres that participate in the control of movement.A ganglion (ganglia is plural) is a general term for a collection of cell bodies.

RELATED STRUCTURESBecause these structures are so closelyconnected with the substantia nigra of the midbrain, some anatomists include thesubstantia nigra as part of the basal ganglia. Also associated with the basal ganglia isthe nucleus accumbens, which plays an important role in the experience of reward39

The basal ganglia are an important part of our motor system. Degeneration of thebasal ganglia, which occurs in Parkinsons disease and in Huntingtons disease, producescharacteristic disorders of movement. The basal ganglia have also been implicated in a number of psychological disorders, including attention deficit/ hyperactivitydisorder (ADHD) and obsessive-compulsive disorder (OCD; see Chapter 16).41The Limbic Systemcollection of forebrain structures that participate in emotional behavior and learning.Different anatomists propose different sets of forebrain structuresfor inclusion in the limbic system, illustrated in Figure 2.14. Limbic means borderand describes the location of these structures on the margins of the cerebral cortex.42

hippocampus (hip-oh-KAMPus) A structure deep within the cerebral hemispheres that is involved with the formation of long-term declarative memories; part of the limbic system.amygdala (uh-MIG-duh-luh) An almond-shaped structure in the rostral temporal lobes that is part of the limbic system.ORIGINThe hippocampus, named after the Greek word for seahorse, curves aroundwithin the cerebral hemispheres from close to the midline out to the tip of the temporallobe.

FUNCTION AND DAMAGEThe hippocampus participates in learning and memory. Damage to thehippocampus in both hemispheres produces a syndrome known as anterogradeAmnesia. People with this type of memory loss have difficulty formingnew long-term declarative memories, which are memories for facts, language, andpersonal experience.

STUDIESIn studies of patients with hippocampal damage, it was foundthat memories formed prior to the damage remained relatively intact; however, thepatients were able to learn and remember procedures for solving a puzzle requiringmultiple steps, like the Tower of Hanoi (

_________________FUNCTIONThe amygdala plays important roles in fear, rage, and aggression (see Chapter 14).In addition, the amygdala interacts with the hippocampus during the encoding andstorage of emotional memories

DAMAGE AND STUDIESDamage to the amygdala specificallyinterferes with an organisms ability to respond appropriately to dangerous situations.In laboratory studies, rats with damaged amygdalas were unable to learn to fear tonesthat reliably predicted electric shock

Rhesus monkeys with damagedamygdalas were overly friendly with unfamiliar monkeys, a potentially dangerousway to behave in a species that enforces strict social hierarchies. Stimuli that normally elicit fear in monkeys, such as rubber snakes or unfamiliarhumans, failed to do so in monkeys with lesions in their amygdalas

In humans, autism, which produces either extreme and inappropriate fear and anxiety or a complete lack of fear, might involve abnormalitiesof the amygdala44

In very rare cases, abnormalities affecting theamygdala result in irrational violence. Charles Whitman( Figure 2.15), the sniper who killed 15 people andwounded 31 from the clock tower at the University ofTexas, Austin, in 1966, had a cancerous tumor that waspressing against his amygdala.

In a case described by Markand Ervin (1970), a woman experiencing a seizure originatingin her amygdala stabbed another person for simplybrushing against her on the way out of a restroom. Thecontroversial solution suggested by these researchers, andagreed to by the woman, was the lesioning of the womansamygdala, which seemed to reduce her violent behavior.Nonetheless, most cases of human violence are extremelycomplex, and the number of violent acts resulting fromabnormalities of the amygdala is quite small.45cingulate cortex (SING-you-let) A segment of older cortex just dorsal to the corpus callosum that is part of the limbic system.septal area An area anterior to the thalamus and hypothalamus that is often included as part of the limbic system.olfactory bulb (ole-FAC-to-ree) A structure extending from the ventral surface of the brain that processes the sense of smell; part of the limbic system.