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The brain and cranial nerves
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  1. The brain and cranial nerves

  2. Development of the brain

  3. Major parts of the brain • Brain stem • Medulla oblongaga, pons, midbrain • Cerebellum • Diencephalon • Thalmus, hypothalamus, and associated structures • Cerebrum • Largest and most distinctive part of brain

  4. Protective structures of brain • Skull • Meninges • Division of brain into hemispheres • Blood-brain barrier

  5. Distribution of cerebrospinal fluid (CSF) • Ventricles and subarachnoid space • Shock absorber • Chemical balance (electrolytes) • Circulation of nutrients and wastes • Formed in choroid plexuses • Reabsorbed through arachnoid villi

  6. The brain stem: medulla oblongata • White matter: ascending and descending tracts • Pyramids formed by motor tracts; neurons cross from one side to the other • Gray matter (nuclei); cardiovascular, rhythmicity area, various reflexes; cranial nerves

  7. What about the cranial nerves? • 12 pairs • Part of peripheral nervous system (PNS) • Numbered I through XII, in order of anterior to posterior emergence from the brain • Nose- I; eyes- II; inner ear (VIII); brain stem (III-XII); spinal cord (XI) • I and II are sensory; others are mixed • Sensory cell bodies are in ganglia; motor cell bodies are in brain • Motor function is somatic (skeletal) or autonomic

  8. Medulla oblongata and associated cranial nerves (inferior view) • Vestibulocochlear (VIII)-hearing • Glossopharyngeal (IX)- taste, chewing, salivation • Vagus (X)-multiple (digestive, heart rate, sensation) • Accessory (XI)-swallowing, head and neck movement • Hypoglossal (XII)-tongue movements during speech

  9. Pons is directly superior to medulla • Nuclei and tracts that connect one part of the brain with another • Pneumotaxic (limits inhalation) and apneustic (prolongs inhalation) centers • Associated with cranial nerves: • Trigeminal (V) chewing • Abducens (VI) movement of eyeballs • Facial (VII)- facial expression; secretion of saliva and tears • Vestibulcochlear (VIII) –balance, equilibrium, hearing

  10. Reflexes and tracts characterize the midbrain • Superior and inferior colliculi • Superior- eye reflexes • Inferior- auditory reflexes • substantia nigra • dopaminergic; motor coordination • Red nuclei • Tracts (cerebral peduncles) • Association with cranial nerves: • Oculomotor (III)- movement of eyeball, puil and lens • Trochlear (IV)- movement of eyeball

  11. What does the midbrain look like?

  12. Reticular formation • Netweork of cell bodies and myelinated axons • Extends from spinal cord to diencephalon • Helps maintain muscle tone • RAS (reticular activating system) extends to cerebral cortex; helps maintain wakefulness

  13. The cerebellum • Each hemisphere divided into lobes • Anterior, posterior- subconcscious skeletal movement • Flocculonodular- equilibrium • Peduncles organize transmission between cerebellum and rest of brain • Skilled movements • Posture and balance

  14. Diencephalon: thalamus and associated structures • Thalamus is major relay station of sensory information to cerebrum • Anterior nucleus • Medial • Lateral group • Ventral group • Intralaminar • Midline • Reticular • Integration, perception, learning, memory

  15. Hypothalamus • Control of ANS • Hormone production • Regulation of behavior (with limbic system) • Satiety and thirst • Thermoregulation • Epithalamus- pineal gland • Subthalamus-coordination

  16. Cerebrum- most recognizable part of the brain • Left and right hemispheres • Corpus callosum • Lobes formed by sulci and fissures • Insula is deep to the superficial lobes

  17. Basal ganglia • Globus pallidus, putamen, caudate nucleus • (motor) input from cerebral cortex and each other • Control of movement • Damage causes tremor, rigidity, involuntary movements • May intersect limbic system

  18. Limbic system, the emotional brain • Major components: • amygdala • Hippocampus • Various nuclei and tracts • Olfactory bulbs

  19. Organization of the cerebral cortex • Sensory areas (p. 607) • Generally in parietal or temporal lobe • Primary somatosensory area (postcentral gyrus) • Primary visual area, auditory, gustatory, olfactory • Motor areas • Primary motor area- precentral gyrus • Broca’s area

  20. Association areas • Association areas • Somatosensory-identify sensory input; memory • Visual- recognition, recall • Auditory- what do you hear? • Wernicke’s- what are you saying? • Common integrative area-full integration of sensory input • Premotor- learned motor skills • Frontal eye field area- taking in visual information

  21. Hemispheric lateralization • Each hemisphere controls the opposite side of the body • People tend to concentrate activities in one hemisphere • Left- speech, reasoning, numerical skills • Right- spatial awareness, pattern recognition, musical and artistic sensibility

  22. Summary • Brain grows rapidly during fetal and juvenile development; loses mass with aging • Organization of brain and functional areas is sophisticated with a considerable amount of overlap