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Chapter 14 The Brain and Cranial Nerves

Chapter 14 The Brain and Cranial Nerves

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Chapter 14 The Brain and Cranial Nerves

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  1. Chapter 14The Brain and Cranial Nerves • Largest organ in the body at almost 3 lb. • Brain functions in sensations, memory, emotions, decision making, behavior Tortora & Grabowski 9/e 2000 JWS

  2. Principal Parts of the Brain • Cerebrum • Diencephalon • thalamus & hypothalamus • Cerebellum • Brainstem • medulla, pons & midbrain Tortora & Grabowski 9/e 2000 JWS

  3. Blood Supply to Brain • Arterial blood supply is branches from circle of Willis on base of brain (page 699) • Vessels on surface of brain----penetrate tissue • Uses 20% of our bodies oxygen & glucose needs • blood flow to an area increases with activity in that area • deprivation of O2 for 4 min does permanent injury • at that time, lysosome release enzymes • Blood-brain barrier (BBB) • protects cells from some toxins and pathogens • proteins & antibiotics can not pass but alcohol & anesthetics do • tight junctions seal together epithelial cells, continuous basement membrane, astrocyte processes covering capillaries Tortora & Grabowski 9/e 2000 JWS

  4. Cerebrospinal Fluid (CSF) • 80-150 ml (3-5oz) • Clear liquid containing glucose, proteins, & ions • Functions • mechanical protection • floats brain & softens impact with bony walls • chemical protection • optimal ionic concentrations for action potentials • circulation • nutrients and waste products to and from bloodstream Tortora & Grabowski 9/e 2000 JWS

  5. Origin of CSF • Choroid plexus = capillaries covered by ependymal cells • 2 lateral ventricles, one within each cerebral hemisphere • roof of 3rd ventricle • fourth ventricle Tortora & Grabowski 9/e 2000 JWS

  6. Drainage of CSF from Ventricles • One median aperture & two lateral apertures allow CSF to exit from the interior of the brain Tortora & Grabowski 9/e 2000 JWS

  7. Flow of Cerebrospinal Fluid Tortora & Grabowski 9/e 2000 JWS

  8. Reabsorption of CSF • Reabsorbed through arachnoid villi • grapelike clusters of arachnoid penetrate dural venous sinus • 20 ml/hour reabsorption rate = same as production rate Tortora & Grabowski 9/e 2000 JWS

  9. Hydrocephalus • Blockage of drainage of CSF (tumor, inflammation, developmental malformation, meningitis, hemorrhage or injury • Continued production cause an increase in pressure --- hydrocephalus • In newborn or fetus, the fontanels allow this internal pressure to cause expansion of the skull and damage to the brain tissue • Neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen Tortora & Grabowski 9/e 2000 JWS

  10. Medulla Oblongata • Continuation of spinal cord • Ascending sensory tracts • Descending motor tracts • Nuclei of 5 cranial nerves • Cardiovascular center • force & rate of heart beat • diameter of blood vessels • Respiratory center • medullary rhythmicity area sets basic rhythm of breathing • Information in & out of cerebellum • Reflex centers for coughing, sneezing, swallowing etc Tortora & Grabowski 9/e 2000 JWS

  11. VIII = Vestibulocochlear Nerve • Cochlear branch begins in medulla • receptors in cochlea • hearing • if damaged deafness or tinnitus (ringing) is produced • Vestibular branch begins in pons • receptors in vestibular apparatus • sense of balance • vertigo (feeling of rotation) • ataxia (lack of coordination) Tortora & Grabowski 9/e 2000 JWS

  12. Injury to the Medulla • Hard blow to the back of the head may be fatal • Cranial nerve malfunctions on same side as injury;loss of sensation or paralysis of throat or tongue; irregularities in breathing and heart rhythm Tortora & Grabowski 9/e 2000 JWS

  13. Pons • One inch long • White fiber tracts ascend and descend • Pneumotaxic & apneustic areas help control breathing • Middle cerebellar peduncles carry sensory info to the cerebellum • Cranial nerves 5 thru 7 Tortora & Grabowski 9/e 2000 JWS

  14. Reticular Formation • Scattered nuclei in medulla, pons & midbrain • Reticular activating system • alerts cerebral cortex to sensory signals (sound of alarm, flash light, smoke or intruder) to awaken from sleep • maintains consciousness & helps keep you awake with stimuli from ears, eyes, skin and muscles • Motor function is involvement with maintaining muscle tone Tortora & Grabowski 9/e 2000 JWS

  15. Cerebellum • 2 cerebellar hemispheres and vermis (central area) • Function • correct voluntary muscle contraction and posture based on sensory data from body about actual movements • sense of equilibrium Tortora & Grabowski 9/e 2000 JWS

  16. Cerebellum • Transverse fissure between cerebellum & cerebrum • Cerebellar cortex (folia) & central nuclei are grey matter • Arbor vitae = tree of life = white matter Tortora & Grabowski 9/e 2000 JWS

  17. Cerebellar Peduncles • Superior, middle & inferior peduncles attach to brainstem • inferior carries sensory information from spinal cord • middle carries sensory fibers from cerebral cortex & basal ganglia • superior carries motor fibers that extend to motor control areas Tortora & Grabowski 9/e 2000 JWS

  18. Thalamic Nuclei • Nuclei have different roles • relays auditory and visual impulses, taste and somatic sensations • receives impulses from cerebellum or basal ganglia • anterior nucleus concerned with emotions, memory and acquisition of knowledge (cognition) Tortora & Grabowski 9/e 2000 JWS

  19. Hypothalamus • Dozen or so nuclei in 4 major regions • mammillary bodies are relay station for olfactory reflexes;infundibulum suspends the pituitary gland • Major regulator of homeostasis • receives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood Tortora & Grabowski 9/e 2000 JWS

  20. Functions of Hypothalamus • Controls and integrates activities of the ANS which regulates smooth, cardiac muscle and glands • Synthesizes regulatory hormones that control the anterior pituitary • Contains cell bodies of axons that end in posterior pituitary where they secrete hormones • Regulates rage, aggression, pain, pleasure & arousal • Feeding, thirst & satiety centers • Controls body temperature • Regulates daily patterns of sleep Tortora & Grabowski 9/e 2000 JWS

  21. Epithalamus • Pineal gland • endocrine gland the size of small pea • secretes melatonin during darkness • promotes sleepiness & sets biological clock • Habenular nuclei • emotional responses to odors Tortora & Grabowski 9/e 2000 JWS

  22. Subthalamus & CVO • Subthalamus • small area just inferior to thalamus • work with basal ganglia, cerebrum & cerebellum to control body movements • Circumventricular organs • in walls of 3rd & 4th ventricles • monitor changes in blood chemistry because lack blood brain barrier (parts of hypothalamus, pineal & pituitary gland) • sites of entry of HIV virus into brain (dementia) Tortora & Grabowski 9/e 2000 JWS

  23. Cerebrum (Cerebral Hemispheres) • Cerebral cortex is gray matteroverlying white matter • 2-4 mm thick containing billionsof cells • grew so quickly formed folds(gyri) and grooves (sulci or fissures) • Longitudinal fissure separates left & right cerebral hemispheres • Corpus callosum is band of white matter connecting left and right cerebral hemispheres • Each hemisphere is subdivided into 4 lobes Tortora & Grabowski 9/e 2000 JWS

  24. Basal Ganglia • Connections to red nucleus, substantia nigra & subthalamus • Input & output with cerebral cortex, thalamus & hypothalamus • Control large automatic movements of skeletal muscles Tortora & Grabowski 9/e 2000 JWS

  25. Limbic System • Parahippocampal & cingulate gyri & hippocampus • Emotional brain--intense pleasure & intense pain • Strong emotions increase efficiency of memory Tortora & Grabowski 9/e 2000 JWS

  26. Brain Injuries • Causes of damage • displacement or distortion of tissue at impact • increased intracranial pressure • infections • free radical damage after ischemia • Concussion---temporary loss of consciousness • headache, drowsiness, confusion, lack of concentration • Contusion--bruising of brain (less than 5 min unconsciousness but blood in CSF) • Laceration--tearing of brain (fracture or bullet) • increased intracranial pressure from hematoma Tortora & Grabowski 9/e 2000 JWS

  27. Motor Areas of Cerebral Cortex • Voluntary motor initiation • Primary motor area = 4 = precentral gyrus • controls voluntary contractions of skeletal muscles on other side • Motor speech area = 44 = Broca’s area • production of speech -- control of tongue & airway Tortora & Grabowski 9/e 2000 JWS

  28. Association Areas of Cerebral Cortex • Somatosensory area = 5 & 7 (integrate & interpret) • Visual association area = 18 & 19 (recognize & evaluate) • Auditory association area(Wernicke’s) = 22(words become speech) • Gnostic area = 5,7,39 & 40 (integrate all senses & respond) • Premotor area = 6 (learned skilled movements such as typing) • Frontal eye field =8 (scanning eye movements such as phone book) Tortora & Grabowski 9/e 2000 JWS

  29. Aphasia • Language areas are located in the left cerebral hemisphere of most people • Inability to use or comprehend words = aphasia • nonfluent aphasia = inability to properly form words • know what want to say but can not speak • damage to Broca’s speech area • fluent aphasia = faulty understanding of spoken or written words • faulty understanding of spoken or written words • word deafness = an inability to understand spoken words • word blindness = an inability to understand written words • damage to common integrative area or auditory association area Tortora & Grabowski 9/e 2000 JWS

  30. Hemispheric Lateralization • Functional specialization of each hemisphere more pronounced in men • Females have larger connections between 2 sides • Damage to left side produces aphasia • Damage to same area on right side produces speech with little emotional inflection Tortora & Grabowski 9/e 2000 JWS

  31. Electroencephalogram (EEG) • Brain waves are millions of nerve action potentials in cerebral cortex • diagnosis of brain disorders (epilepsy) • brain death (absence of activity in 2 EEGs 24 hours apart) • Alpha -- awake & resting • Beta -- mental activity • Theta -- emotional stress • Delta -- deep sleep Tortora & Grabowski 9/e 2000 JWS

  32. Development of Principal Parts • By end of 4th week, 3 anterior enlargements occur • prosencephalon • mesencephalon • rhombencephalon Tortora & Grabowski 9/e 2000 JWS

  33. Aging & the Nervous System • Years 1 to 2 • rapid increase in size due to increase in size of neurons, growth of neuroglia, myelination & development of dendritic branches • Early adulthood until death • brain weight declines until only 93% by age 80 • number of synaptic contacts declines • processing of information diminishes • conduction velocity decreases • voluntary motor movements slow down • reflexes slow down Tortora & Grabowski 9/e 2000 JWS

  34. Cerebrovascular Accident (CVA) • Third leading cause of death after heart attacks and cancer • 2 types of strokes • ischemic due to decreased blood flow • hemorrhagic due to rupture of blood vessel • Risk factors • high blood pressure, high cholesterol, heart disease, diabetes, smoking, obesity, alcohol • Tissue plasminogen activator (t-PA) used within 3 hours of onset will decrease permanent disability Tortora & Grabowski 9/e 2000 JWS

  35. Transient Ischemic Attack (TIA) • Episode of temporary cerebral dysfunction • Cause • impaired blood flow to the brain • Symptoms • dizziness, slurred speech, numbness, paralysis on one side, double vision • reach maximum intensity almost immediately • persists for 5-10 minutes & leaves no deficits • Treatment is aspirin or anticoagulants; artery bypass grafting or carotid endarterectomy Tortora & Grabowski 9/e 2000 JWS

  36. Alzheimer Disease (AD) • Dementia = loss of reasoning, ability to read, write, talk, eat & walk • Afflicts 11% of population over 65 • Loss of neurons that release acetylcholine • Plaques of abnormal proteins outside neurons • Tangled protein filaments within neurons • Risk factors -- head injury, heredity • Beneficial effects of estrogen, vitamin E, ibuprofen & ginko biloba Tortora & Grabowski 9/e 2000 JWS