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1. 12 The Central Nervous System: Part C

2. Functional Brain Systems • Networks of neurons that work together and span wide areas of the brain • Limbic system • Reticular formation

3. Limbic System • Includes parts of the diencephalon and some cerebral structures that encircle the brain stem

4. Fiber tracts connecting limbic system structures Septum pellucidum Diencephalic structures of the limbic system Corpus callosum •Fornix •Anterior thalamic nuclei (flanking 3rd ventricle) •Anterior commissure Cerebral struc- tures of the limbic system •Hypothalamus •Mammillary body •Cingulate gyrus •Septal nuclei •Amygdala •Hippocampus •Dentate gyrus •Parahippocampal gyrus Olfactory bulb Figure 12.18

5. Limbic System • Emotional or affective brain • Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response • Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict • Puts emotional responses to odors • Example: skunks smell bad

6. Limbic System: Emotion and Cognition • The limbic system interacts with the prefrontal lobes, therefore: • We can react emotionally to things we consciously understand to be happening • We are consciously aware of emotional richness in our lives • Hippocampus and amygdala—play a role in memory

7. Reticular Formation • Three broad columns along the length of the brain stem • Raphe nuclei • Medial (large cell) group of nuclei • Lateral (small cell) group of nuclei • Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord

8. Reticular Formation: RAS and Motor Function • RAS (reticular activating system) • Sends impulses to the cerebral cortex to keep it conscious and alert • Filters out repetitive and weak stimuli (~99% of all stimuli!) • Severe injury results in permanent unconsciousness (coma)

9. Reticular Formation: RAS and Motor Function • Motor function • Helps control coarse limb movements • Reticular autonomic centers regulate visceral motor functions • Vasomotor • Cardiac • Respiratory centers

10. Radiations to cerebral cortex Visual impulses Auditory impulses Reticular formation Descending motor projections to spinal cord Ascending general sensory tracts (touch, pain, temperature) Figure 12.19

11. Electroencephalogram (EEG) • Records electrical activity that accompanies brain function • Measures electrical potential differences between various cortical areas

12. (a) Scalp electrodes are used to record brain waveactivity (EEG). Figure 12.20a

13. Brain Waves • Patterns of neuronal electrical activity

14. 1-second interval Alpha waves—awake but relaxed Beta waves—awake, alert Theta waves—common in children Delta waves—deep sleep (b) Brain waves shown in EEGs fall intofour general classes. Figure 12.20b

15. Epilepsy • A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking • Epilepsy occurs in 1% of the population • not associated with intellectual impairments

16. Control of Epilepsy • Anticonvulsive drugs

17. Consciousness • Conscious perception of sensation

18. Consciousness • Clinically defined on a continuum that grades behavior in response to stimuli • Alertness • Drowsiness (lethargy) • Stupor • Coma

19. Sleep • State of partial unconsciousness from which a person can be aroused by stimulation • Two major types of sleep (defined by EEG patterns) • Nonrapid eye movement (NREM) • Rapid eye movement (REM)

20. Awake REM: Skeletal muscles (except ocular muscles and diaphragm) are actively inhibited; most dreaming occurs. NREM stage 1: Relaxation begins; EEG shows alpha waves, arousal is easy. NREM stage 2: Irregular EEG with sleep spindles (short high- amplitude bursts); arousal is more difficult. NREM stage 3: Sleep deepens; theta and delta waves appear; vital signs decline. NREM stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur. (a) Typical EEG patterns Figure 12.21a

21. Sleep Disorders • Narcolepsy • Lapsing abruptly into sleep from the awake state • Insomnia • Chronic inability to obtain the amount or quality of sleep needed • Sleep apnea • Temporary cessation of breathing during sleep

22. Language • Language implementation system • Broca’s area and Wernicke’s area (in the association cortex on the left side)

23. Memory • Storage and retrieval of information • Two stages of storage • Short-term memory (STM, or working memory)—temporary holding of information; limited to seven or eight pieces of information • Long-term memory (LTM) has limitless capacity

24. Outside stimuli General and special sensory receptors Afferent inputs Temporary storage (buffer) in cerebral cortex Data permanently lost Data selected for transfer Automatic memory Forget Short-term memory (STM) Forget Data transfer influenced by: Excitement Rehearsal Association of old and new data Retrieval Long-term memory (LTM) Data unretrievable Figure 12.22

25. Transfer from STM to LTM • Factors that affect transfer from STM to LTM • Emotional state—best if alert, motivated, surprised, and aroused • Rehearsal—repetition and practice • Association—tying new information with old memories • Automatic memory—subconscious information stored in LTM

26. Protection of the Brain • Bone (skull) • Membranes (meninges) • Watery cushion (cerebrospinal fluid) • Blood-brain barrier

27. Meninges • Cover and protect the CNS • Protect blood vessels and enclose venous sinuses • Contain cerebrospinal fluid (CSF) • Form partitions in the skull

28. Meninges • Three layers • Dura mater • Arachnoid mater • Pia mater

29. Cerebrospinal Fluid (CSF) • Composition • Watery solution • Less protein and different ion concentrations than plasma • Constant volume

30. Cerebrospinal Fluid (CSF) • Functions • Gives buoyancy to the CNS organs • Protects the CNS from blows and other trauma • Nourishes the brain and carries chemical signals

31. Superior sagittal sinus 4 Choroid plexus Arachnoid villus Interventricular foramen Subarachnoid space Arachnoid mater Meningeal dura mater Periosteal dura mater 1 Right lateral ventricle (deep to cut) Choroid plexus of fourth ventricle 3 Third ventricle 1 CSF is produced by the choroid plexus of each ventricle. Cerebral aqueduct Lateral aperture 2 CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord. Fourth ventricle Median aperture 2 Central canal of spinal cord 3 CSF flows through the subarachnoid space. (a) CSF circulation 4 CSF is absorbed into the dural venous sinuses via the arachnoid villi. Figure 12.26a

32. Choroid Plexuses • Hang from the roof of each ventricle • Clusters of capillaries enclosed by pia mater and a layer of ependymal cells

33. Ependymal cells Capillary Section of choroid plexus Connective tissue of pia mater Wastes and unnecessary solutes absorbed CSF forms as a filtrate containing glucose, oxygen, vitamins, and ions (Na+, Cl–, Mg2+, etc.) Cavity of ventricle (b) CSF formation by choroid plexuses Figure 12.26b

34. Blood-Brain Barrier • Helps maintain a stable environment for the brain • Separates neurons from some bloodborne substances

35. Capillary Neuron Astrocyte (a) Astrocytes are the most abundantCNS neuroglia. Figure 11.3a

36. Homeostatic Imbalances of the Brain • Cerebrovascular accidents (CVAs)(strokes) • Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot • Typically leads to hemiplegia, or sensory and speed deficits • Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia • Tissue plasminogen activator (TPA) is the only approved treatment for stroke

37. Homeostatic Imbalances of the Brain • Degenerative brain disorders • Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia • Parkinson’s disease: degeneration of the dopamine-releasing neurons of the substantia nigra • Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex