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THE BRAIN

THE BRAIN. Chapter 14. Brain Basics:. 100 billion neurons in the adult brain 1000 billion neuroglia adult brain weighs almost 3 lbs 4 basic parts of the brain: Brain stem Cerebellum Diencephalon Cerebrum. 4 Parts of the Brain. - brain stem *continuous with the spinal cord

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THE BRAIN

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  1. THE BRAIN Chapter 14

  2. Brain Basics: • 100 billion neurons in the adult brain • 1000 billion neuroglia • adult brain weighs almost 3 lbs • 4 basic parts of the brain: • Brain stem • Cerebellum • Diencephalon • Cerebrum

  3. 4 Parts of the Brain • -brain stem • *continuous with the spinal cord • *medulla oblongata • *pons • *midbrain • -cerebellum • -diencephalon • *thalamus • *hypothalamus • -cerebrum • *largest part • *2 hemispheres

  4. COVERINGS OF THE BRAIN: • Meninges: • dura mater = outer layer • arachnoid = middle layer • pia mater =inner layer

  5. Fig. 14-3a, top, p. 456

  6. Fig. 14-3, p. 456

  7. BRAIN BLOOD FLOW AND THE BLOOD BRAIN BARRIER • Basics: • Blood supply to the brain is mainly from the cerebral arterial circle –or the circle of Willis at the base of the brain. • Brain is 2% of body weight but consumes 20% of oxygen and glucose used at rest. • Brain metabolizes glucose using oxidative respiration to generate ATP

  8. And….. • There is a corresponding increase in blood supply when there is a localized increase in brain activity • An interruption of blood flow can cause unconsciousness, 1-2 minutes can impair neuronal function, 4 minutes can result in permanent injury • No glucose is stored in the brain so it must be continually supplied

  9. Ventricles of the Brain and CSF • Ventricles: • There are 4 ventricles filled with CSF -2 lateral, one in each cerebral hemisphere *separated by the septum pellucidum -Third ventricle *narrow cavity superior to the hypothalamus -Fourth ventricle *between the brain stem and the cerebellum

  10. Fig. 14-2a, p. 454

  11. CSF –Cerebral Spinal Fluid • Clear, colorless liquid • Carries oxygen, glucose proteins, lactic acid, urea, cations (Na+, K+ , Ca2+, Mg2+) and anions (Cl- and HCO3-) and some white blood cells • Circulates continually through the super-arachnoid space and around the brain and spinal cord • Total volume: 80-150 mL

  12. Contributes to homeostasis in 3 ways • mechanical protection –shock absorber, the brain “floats” • chemical protection –optimal chemical environment for accurate neuronal signaling • Circulation –medium for exchange of nutrients and wastes between blood and nervous tissue

  13. Fig. 14-2b, p. 454

  14. THE BRAIN STEM • Basics: • Between spinal cord and diencephalon • Reticula formation • -netlike gray and white matter • -extends through the brain stem • -RAS Reticular activating system • *awakening from sleep • *maintaining level of consciousness • *arouses cerebral cortex in response to stimuli • *maintains muscle tone

  15. Fig. 14-1, part 2, p. 453

  16. 3 parts of the brain stem: • 1. Medulla Oblongata • continuation of the upper part of the spinal cord • begins at the foramen magnum and extends to the pons -3 cm • pyramids –anterior aspect -formed by largest motor tracts from spinal cord -conspicuous external bulges -cross over each other –decussation of pyramids

  17. inferior olivary nucleus (oval shaped swelling (olive) -relay stations to the thalamus -nucleus gracilis - -nucleus cuneatus Autonomic Nuclei -regulation of vital functions -reflex centers receive inputs from cranial nerves, brain stem, and cerebral cortex -adjust activities of peripheral systems cardiovascular centers -cardiac -vasomotor respiratory rhythmicity centers -activity regulated by the pons

  18. Fig. 14-5b, p. 460

  19. Fig. 14-5a, p. 460

  20. 2. Pons (bridge) • -nuclei -control breathing with medulla • pneumatoaxic area • apneustic area

  21. 1. nuclei for cranial nerves Trigeminal (V) -mixed -largest cranial nerve -somatosensory info for head and neck -motor for chewing -Trigeminal neuralgia (Tic Douloureux) affects CV Abducens (VI) -motor -eye movements

  22. More…… • Facial (VII) • -mixed • -taste, secretion of saliva, tears, muscles for facial expression • -Bell’s palsy- inflammation of CVII • Vestibulocochlear (VIII) • -special sensory • -balance and equilibrium

  23. Cranial Nerves • To help you remember the cranial nerves: • On occasion, our trusty truck acts funny—very good vehicle any how. • 1. Olfactory, 2. optic, 3. oculomotor, 4. trochlear, 5. trigeminal, 6. abducens, 7. facial, 8. vestibulocochlear, 9. glossopharangeal, 10. vagus, 11. accessory, 12. hypoglossal

  24. 3. Midbrain (or mesencephalon) reflex centers • superior colliculi -movement of eyes, head, and neck in response to visual and other stimuli • Inferior colliculi -movement of head and trunk in response to auditory stimuli

  25. 2. Specialized nuclei • a. Substantianigra -subconscious muscle activities -fluidity of movement -secretes dopamine -Parkinson’s disease- decrease in dopamine secreting cells • b. red nuclei • -control of skeletal muscle tone

  26. Fig. 14-1, part 1, p. 453

  27. CEREBELLUM Basics: Second largest part of the brain Shape is like a butterfly Vermis =central constriction Cerebellar hemispheres -anterior and posterior lobe *govern subconscious movements of skeletal muscles -Flocculonodular lobe *inferior surface *sense of equilibrium

  28. Fig. 14-7a, left, p. 463

  29. Main functions: • -compares intended movements with what is actually happening • -coordinates complex, skilled movements • -regulates posture and balance • Affected by drugs and trauma • -alcohol affects cerebellum causing ataxia

  30. DIENCEPHALON 1. Thalamus –2 halves • 80% of diencephalon –3 cm long • principal relay station for sensory impulses • “the secretary” • sends sensory input to cerebral cortex • assorted nuclei and their roles: • -medial geniculate nucleus –auditory • -lateral geniculate nucleus -visual • -ventral posterior nucleus -taste, touch, pressure, vibration, temperature, pain • -anterior nucleus -emotions and memory • functions in cognition and awareness

  31. Fig. 14-8b, p. 465

  32. 2. HypothalamusSmall, inferior to thalamus (in position) 4 major regions: 1. mammillary region -mammillary bodies -relay stations for reflexes related to sense of smell 2. tuberal region -widest part

  33. 3. infindibulum connects hypothalamus with the pituitary gland -supraoptic region -superior to optic chiasm (where optic nerves cross) -contains suprachiasmatic nucleus 4. preoptic region -contains medial and lateral preoptic nuclei -regulates certain autonomic activities

  34. Fig. 14-10b, p. 467

  35. Functions: • major regulator of homeostasis a. Control of ANS -axons from hypothalamus to parasympathetic and sympathetic -regulates visceral activities -regulates heart rate

  36. Controls Pituitary gland (master gland) -hypothalamic regulating hormones *stimulate or inhibit secretion of hormones from the anterior pituitary -axons from paraventricular and supraoptic nuclei *nerve cell bodies make oxytocin and ADH which are transported and stored in the posterior pituitary

  37. Regulation of emotional and behavioral patterns • -works with the limbic system *rage *aggression *pain *pleasure *behavior patterns related to sexual arrousal

  38. And…… *Feeding center –hunger *Satiety center –fullness *Thirst center –cells stimulated by rising osmotic pressure -sensation of thirst

  39. Control of Body Temperature *monitors blood temperature *promotes cooling or warming up • Regulation of circadian rhythms and states of consciousness *sleep patterns of circadian rhythm

  40. 3. Epithalamus–superior and posterior to thalamus pineal gland -pea size -secretes melatonin -may promote sleepiness -may set biological clock habenular nuclei -olfaction -emotional responses to odors

  41. CEREBRUM • - bulk of the brain • Geographic basics of the Cerebrum: • Cerebral cortex is the 2-4 mm layer of gray matter on the surface of the cerebrum –billions of neurons • Cerebral white matter is underneath • Folds or convolutions of the cerebrum are due to the rapid growth of gray matter during development which is faster than white matter • Fissures are the deepest grooves

  42. Fig. 14-12c, p. 471

  43. Sulci the shallower grooves Longitudinal fissure separates the right and left cerebral hemispheres Corpus callosum connects the two hemispheres –nerve net Cerebrum divided into lobes named for the bones that lie over them.

  44. Lobes of the Cerebrum • -Frontal • -central sulcus • -parietal • -pre-central gyrus –in front of the central sulcus- motor area • -post-central gyrus –primary somatosensory area • -Lateral cerebral sulcus • -Temporal lobe • -parieto-occipital sulcus • -occipital lobe • -insula (deep within the lateral cerebral fissure)

  45. Fig. 14-9a, p. 466

  46. Fig. 14-12b, p. 471

  47. BASAL GANGLIA • Function: -receive input from and provide output to: -cerebral cortex -thalamus -hypothalamus

  48. Structures included:(paired nuclei) • -corpus striatum • -largest nuclei • -includes: • 1. -caudate nucleus *autonomic movement of skeletal muscles • 2. -lentiform nucleus (2 parts) • *putamen (lateral part) - autonomic movement of skeletal muscles -swinging of arms while walking, laughing • *globus pallidus (medial) -muscle tone for specific body movements

  49. Huntington’s Disease • Genetic Disease –dominant gene • Affects the basal ganglia • Progresses slowly over a period of 20 years • Affects the coordination (chorea) controlled by the basal ganglia and the cortex involved in memory and thought • Unsteady gait, lack of coordination, impaired reasoning and memory. • Abnormal protein -Huntingtin • Killed Woodie Guthrie

  50. Parkinson’s Disease • Etiology: idiopathic (most do not know), head trauma, MDMA • Cells of sustantia nigra no longer make dopamine • Symptoms • Tremor –(pill rolling) • Slowed movement (bradykinesia) • Muscle rigidity • Loss of facial expression • mumbling

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