Hockenbury Discovering Psychology 5th txtbk

A Guided Tour of the Brain67their body. Our friend Asha, for example, suffered only minor damage to motorcontrol areas in her brain. However, because the stroke occurred on the left side ofher brain, what muscle weakness she did experience was localized on the right sideof her body, primarily in her right hand.Three structures make up the hindbrain—the medulla, the pons, and the cerebellum.The medulla is situated at the base of the brain directly above the spinalcord. It is at the level of the medulla that ascending sensory pathways and descendingmotor pathways crisscross to the contralateral side of the body.The medulla plays a critical role in basic life-sustaining functions. It contains centersthat control such vital autonomic functions as breathing, heart rate, and bloodpressure. The medulla also controls a number of vital reflexes, including swallowing,coughing, vomiting, and sneezing. Because the medulla is involved in such criticallife functions, damage to this brain region can rapidly prove fatal.Above the medulla is a swelling of tissue called the pons, which represents the uppermostlevel of the hindbrain. Bulging out behind the pons is the large cerebellum.On each side of the pons, a large bundle of axons connects it to the cerebellum. Theword pons means “bridge,” and the pons is a bridge of sorts: Information from variousother brain regions located higher up in the brain is relayed to the cerebellumvia the pons. The pons also contains centers that play an important role in regulatingbreathing.The cerebellum functions in the control of balance, muscle tone, and coordinatedmuscle movements. It is also involved in the learning of habitual or automaticmovements and motor skills, such as typing, writing, or backhanding a tennisball.Jerky, uncoordinated movements can result from damage to the cerebellum.Simple movements, such as walking or standing upright, may become difficult orimpossible. The cerebellum is also one of the brain areas affected by alcohol consumption,which is why a person who is intoxicated may stagger and have difficultywalking a straight line or standing on one foot. (This is also why a policeofficer will ask a suspected drunk driver to execute these normally effortlessmovements.)At the core of the medulla and the pons is a network of neurons called thereticular formation, or the reticular activating system, which is composed ofmany groups of specialized neurons that project up to higher brain regions anddown to the spinal cord. The reticular formation plays an important role in regulatingattention and sleep.The MidbrainThe midbrain is an important relay station that contains centers involved in theprocessing of auditory and visual sensory information. Auditory sensations from theleft and right ears are processed through the midbrain, helping you orient towardthe direction of a sound. The midbrain is also involved in processing visual information,including eye movements, helping you visually locate objects and track theirmovements. After passing through the midbrain level, auditory and visual informationis relayed to sensory processing centers farther up in the forebrain region,which will be discussed shortly.A midbrain area called the substantia nigra is involved in motor control andcontains a large concentration of dopamine-producing neurons. Substantia nigrameans “dark substance,” and as the name suggests, this area is darkly pigmented.The substantia nigra is part of a larger neural pathway that helps prepare other brainregions to initiate organized movements or actions. In the section on neurotransmitters,we noted that Parkinson’s disease involves symptoms of abnormal movement,including difficulty initiating or starting a particular movement. Many ofthose movement- related symptoms are associated with the degeneration ofdopamine-producing neurons in the substantia nigra.medulla(meh-DOOL-uh) A hindbrain structure thatcontrols vital life functions such as breathingand circulation.ponsA hindbrain structure that connects themedulla to the two sides of the cerebellum;helps coordinate and integrate movementson each side of the body.cerebellum(sare-uh-BELL-um) A large, two-sidedhindbrain structure at the back of the brain;responsible for muscle coordination andmaintaining posture and equilibrium.reticular formation(reh-TICK-you-ler) A network of nerve fiberslocated in the center of the medulla thathelps regulate attention, arousal, and sleep;also called the reticular activating system.midbrainThe middle and smallest brain region,involved in processing auditory and visualsensory information.substantia nigra(sub-STAN-she-uh NYE-gruh) An area of themidbrain that is involved in motor controland contains a large concentration ofdopamine-producing neurons.