1. Brain & Cranial Nerves Dr. Michael P. Gillespie

2. Major Parts of the Brain  Brain stem – continuous with the spinal cord. Medulla oblongata. Pons. Midbrain.  Cerebellum – posterior to the brain stem.

3. Major Parts of the Brain  Diencephalon – superior to the brain stem. Thalamus. Hypothalamus.  Cerebrum – supported on the diencephalon and brain stem. Largest part of the brain.

5. Brain Blood Supply  Arteries Internal carotid arteries Vertebral arteries  Veins Internal jugular veins

6. Brain Blood Flow  The brain consumes about 20% of the oxygen and glucose used at rest.  A brief slowing of blood flow may cause unconsciousness.

7. Brain Blood Flow  An interruption of blood flow for 1 to 2 minutes impairs neural function.  Total deprivation of oxygen for 4 minutes causes permanent injury.  If the blood entering the brain has a low level of glucose, mental confusion, dizziness, convulsions, and loss of consciousness may occur.

8. Blood Brain Barrier  The blood-brain barrier (BBB) protects the brain from harmful substances and pathogens.  It prevents the passage of many substances from the blood to the brain tissue.  Tight junctions seal together endothelial cells of brain capillaries.  Astrocytes selectively allow some substances through and not others.

9. Breaching the BBB  The BBB prevents the passage of harmful substances into the brain, but it also prevents the passage of useful drugs.  Drugs are injected in a concentrated sugar solution to facilitate passage. The high osmotic pressure causes cells lining the barrier to shrink and makes the membrane “leaky”.

10. Protective Coverings  Cranial Meninges. Dura mater. Arachnoid mater. Pia mater.

12. Cerebrospinal Fluid (CSF)  Clear colorless liquid.  Protects the brain and spinal cord from chemical and physical injuries.  Carries oxygen, glucose, and other needed chemicals from the blood to the neurons and neuroglia.  Circulates in the subarachnoid space (between the arachnoid mater and pia mater).

13. Protective Coverings  Extensions of the dura mater separate the parts of the brain. Falx cerebri – separates the two hemispheres of the cerebrum. Falx cerebelli – separates the two hemispheres of the cerebellum. Tentorium cerebelli – separates the cerebrum from the cerebellum.

14. Formation of CSF in the Ventricles  CSF is formed in the ventricles. Formed by ependymal cells that cover the choroid plexuses of the ventricles.

15. Formation of CSF in the Ventricles  There are 4 ventricles.  Functions of CSF. Mechanical protection. Shock absorption. Buoys the brain. Chemical protection – optimal chemical environment. Circulation – medium of exchange for wastes and nutrients.

20. Hydrocephalus  Abnormalities of the brain can interfere with drainage of CSF from the ventricles and subarachnoid space.  CSF pressure increases causing hydrocephalus.  In infants this causes the fontanels to budge.

21. Hydrocephalus  Tumors, inflammation, developmental malformations can all cause hydrocephalus.  Pressure buildup can damage the delicate nervous tissue.  A surgeon can implant a drain line called a shunt to divert CSF.  In adults, hydrocephalus may occur after head injury, meningitis, or subarachnoid hemorrhage.

22. Brain Stem  Between the brain and spinal cord.  3 regions. Medulla oblongata. Pons. Midbrain.

23. Medulla Oblongata  A continuation of the spinal cord.  Sensory (ascending) tracts and motor (descending) tracts travel through the white matter of the medulla.  Many nerves decussate (cross over) in the medulla.

24. Medulla Oblongata  Cardiovascular center regulates the heartbeat and the diameter of the blood vessels.

25. Medulla Oblongata  The medullary rhythmicity area adjusts the rhythm of the breathing and controls reflexes for vomiting, coughing, and sneezing.

26. Medulla Oblongata  The nuclei for the following cranial nerves reside in the medulla: VIII (vestibulocochlear). IX (glossopharyngeal). X (vagus). XI (accessory). XII (hypoglossal).

29. Pons  Pneumotaxic area and apneustic area regulate breathing.  Nuclei for cranial nerves V (trigeminal), VI (abducens), VII (facial), and VIII (vestibulocochlear).

30. Midbrain  The midbrain or mesencephalon contains the superior colliculi (visual actvities) and inferior colliculi (auditory pathways).  The midbrain contains the substantia nigra which release dopamine to help control subconscious muscle activities. Loss of these neurons results in Parkinson disease.  Cranial nerves III (oculomotor) and IV (trochlear) originate here.

32. Cerebellum  The second largest part of the brain.  A main function of the cerebellum is to evaluate how well movements are being carried out and correct for discrepancies. This helps to “smooth out” movements.

34. Diencephelon  Epithalamus. Contains the pineal gland which secretes melatonin.  Thalamus. Relays sensory information to the cortex. Provides crude perception of touch, pressure, pain, and temperature.

36. Diencephelon  Subthalamus. Controls body movements.  Hypothalamus. Controls and integrates activities of the ANS. Regulates emotional and behavioral patterns. Regulates cicadian rhythms. Regulates eating and drinking behavior. Produces hormones oxytocin and ADH.

38. Cerebrum  Sensory areas interpret sensory impulses.  Motor areas control muscular movement.  Association areas function in emotional and intellectual processes.  Basal areas regulate gross muscle movements and regulate muscle tone.  Limbic system functions in survival behaviors.

42. Brain Injuries  Concussion – an abrupt, temporary loss of consciousness following a blow to the head. Most common brain injury. Signs – headache, drowsiness, lack of concentration, confusion, amnesia.

43. Brain Injuries  Contusion – bruising of the brain due to trauma and includes leakage of blood. Signs - immediate loss of consciousness, transient cessation of respiration, decreased blood pressure.

44. Brain Injuries  Laceration – tear of the brain usually from a skull fracture or gunshot wound. Rupture of large blood vessels. Consequences – cerebral hematoma (localized pool of blood, usually clotted), edema, and increased intracranial pressure.

45. Cerebral Cortex Areas and Functions  Sensory areas – receive and interpret sensory information.

46. Cerebral Cortex Areas and Functions  Motor areas – initiate movements.  Association areas – deal with integrative functions: Memory. Emotions. Reasoning. Will. Judgement. Personality. Intelligence.

47. Sensory Areas  Primary somatosensory area – receives sensations for touch, proprioception, pain, itching, tickle, and thermal sensations. Located in the postcentral gyrus of the parietal lobes.  Primary visual area.  Primary auditory area.  Primary gustatory area – taste.  Primary olfactory area.

48. Motor Areas  Primary motor area – located in the precentral gyrus of the frontal lobe.  Broca’s speech area – coordinates the contractions of speech and breathing muscles.

49. Association Areas  Somatosensory association area – integrates and interprets sensations.  Visual association area – evaluates what is seen.  Auditory association area – evaluates sounds.

50. Association Areas  Wernicke’s (posterior language) area – interprets the meaning of speech.  Common integrative area.  Premotor area – controls learned skilled movements.  Frontal eye field area – controls voluntary scanning movements of the eyes.

52. Aphasia  An inability to use or comprehend words.

53. Aphasia  Damage to Broca’s area results in nonfluent aphasia. Inability to properly articulate to form words. These people know what they wish to say, but cannot speak.

54. Aphasia  Damage to the auditory association area results in fluent aphasia. Faulty understanding of spoken words. Word deafness – inability to understand spoken words. Word blindness – inability to understand written words.

55. Cranial Nerve I - Olfactory  Type: sensory.  Function: smell.  Anosmia – loss of sense of smell.

56. Cranial Nerve II – Optic Nerve  Type: sensory.  Function: vision.  Anopia – blindness in one or both eyes.

57. Cranial Nerve III - Oculomotor  Type: mixed (mainly motor).  Function: movement of the upper eyelid and eyeball. Accomodation of the lens for nearn vision and constriction of the pupil.  Strabismus – deviation of the eye in which both eyes don’t focus on the same object.  Ptosis – drooping of the upper eyelid.  Diploia – double vision.

58. Cranial Nerve IV – Trochlear Nerve  Type: mixed (mainly motor).  Function: movement of the eyeball.  Diplopia and strabismus occur with trochlear nerve damage.

60. Cranial Nerve V – Trigeminal Nerve  Type: mixed.  Function: conveys impulses for touch, pain, temperature and proprioception. Chewing.  Trigeminal neuralgia (tic douloureux) – pain to branches of the trigeminal nerve.  Dentists apply anesthetic to branches of this nerve.

62. Cranial Nerve VI - Abducens  Type: mixed (mainly motor).  Function: movement of the eyeball.  With damage to this nerve the eye cannot move laterally beyond the midpoint and usually points medially.

64. Cranial Nerve VII – Facial Nerve  Type: mixed.  Function: Propriception and taste. Facial expression. Secretion of saliva and tears.  Injury produces bell’s palsy (paralysis of facial muscles).

66. Cranial Nerve VIII – Vestibulocochlear Nerve  Type: mixed (mainly sensory).  Function: conveys impulses for equilibrium and hearing.  Injury can cause vertigo, ataxia (muscular incoordination), nystagmus (rapid movement of the eyeball), and tinnitus.

67. Cranial Nerve IX – Glossopharyngeal Nerve  Type: mixed.  Function: taste and somatic sensations from the posterior 1/3 of the tongue. Elevates the pharynx during swallowing and speech. Stimulates the secretion of saliva.  Injury causes decreased salivary secretion, loss of taste, and difficulty swallowing.

69. Cranial Nerve X – Vagus Nerve  Type: mixed.  Function: taste and somatic sensations. Swallowing, coughing, and voice production. Regulates GI tract and heart rate.  Injury interferes with swallowing, paralyzes vocal cords, and causes the heart rate to increase.

71. Cranial Nerve XI – Accessory Nerve  Type: mixed (mainly motor).  Function: Proprioception. Swallowing, movement of head and shoulders.  If the nerves are damaged the SCM and Trapezius become paralyzed.

73. Cranial Nerve XII – Hypoglossal Nerve  Type: mixed (mainly motor).  Function: Proprioception. Movement of the tongue during speech and swallowing.  Injury results in difficulty in chewing, speaking, and swallowing. When protruded, the tongue curls towards the affected side and atrophies on the affected side.

75. Cranial Nerves  On Old Olympus’ Towering Tops A Fin And German Viewed Some Hops.  This mnemonic device helps you memorize the names of the cranial nerves.  The first letter from each word corresponds to the first letter of each cranial nerve.