Chapter 14

1. Chapter 14 The Brain and Cranial Nerves

2. An Introduction to the Brain and Cranial Nerves • The Adult Human Brain • Ranges from 750 cc to 2100 cc • Contains almost 97% of the body’s neural tissue • Average weight about 1.4 kg (3 lb)

3. The Brain • Six Regions of the Brain • Cerebrum • Cerebellum • Diencephalon • Mesencephalon • Pons • Medulla oblongata

4. The Brain • Cerebrum • Largest part of brain • Controls higher mental functions • Divided into left and right cerebral hemispheres • Surface layer of gray matter (neural cortex)

5. The Brain • Cerebrum • Neural cortex • Also called cerebral cortex • Folded surface increases surface area • Elevated ridges (gyri) • Shallow depressions (sulci) • Deep grooves (fissures)

6. The Brain • Cerebellum • Second largest part of brain • Coordinates repetitive body movements • Two hemispheres • Covered with cerebellar cortex

7. The Brain • Diencephalon • Located under cerebrum and cerebellum • Links cerebrum with brain stem • Three divisions • Left thalamus • Right thalamus • Hypothalamus

8. The Brain • Diencephalon • Thalamus • Relays and processes sensory information • Hypothalamus • Hormone production • Emotion • Autonomic function • Pituitary gland • Major endocrine gland • Connected to hypothalamus • Via infundibulum (stalk) • Interfaces nervous and endocrine systems

9. The Brain • The Brain Stem • Processes information between • Spinal cord and cerebrum or cerebellum • Includes • Mesencephalon • Pons • Medulla oblongata

10. The Brain • The Brain Stem • Mesencephalon • Also called midbrain • Processes sight, sound, and associated reflexes • Maintains consciousness • Pons • Connects cerebellum to brain stem • Is involved in somatic and visceral motor control

11. The Brain • The Brain Stem • Medulla oblongata • Connects brain to spinal cord • Relays information • Regulates autonomic functions: • heart rate, blood pressure, and digestion

12. The Brain Figure 14–1 An Introduction to Brain Structures and Functions.

13. The Brain • Embryological Development • Determines organization of brain structures • Neural tube • Origin of brain • Enlarges into three primary brain vesicles • prosencephalon • mesencephalon • rhombencephalon

14. The Brain • Five Secondary Brain Vesicles • Telencephalon • Diencephalon • Mesencephalon • Metencephalon • Myelencephalon

15. The Brain • Origins of Brain Structures • Diencephalon and mesencephalon persist • Telencephalon: • Becomes cerebrum • Metencephalon • Forms cerebellum and pons • Myelencephalon • Becomes medulla oblongata

16. The Brain

17. The Brain • Ventricles of the Brain • Origins of ventricles • Neural tube encloses neurocoel • Neurocoel expands to form chambers (ventricles) lined with ependymal cells • Each cerebral hemisphere contains one large lateral ventricle • Separated by a thin medial partition (septum pellucidum)

18. The Brain • Ventricles of the Brain • Third ventricle • Ventricle of the diencephalon • Lateral ventricles communicate with third ventricle: • via interventricular foramen (foramen of Monro)

19. The Brain • Ventricles of the Brain • Fourth ventricle • Extends into medulla oblongata • Becomes continuous with central canal of the spinal cord • Connects with third ventricle: • via narrow canal in mesencephalon • aqueduct of midbrain

20. The Brain Figure 14–2 Ventricles of the Brain.

21. The Brain • The brain is a large, delicate mass of neural tissue containing internal passageways and chambers filled with cerebrospinal fluid • Each of the six major brain regions has specific functions • Ascending from the medulla oblongata to the cerebrum, brain functions become more complex and variable • Conscious thought and intelligence are produced in the neural cortex of the cerebral hemispheres

22. Brain Protection and Support • Physical protection • Bones of the cranium • Cranial meninges • Cerebrospinal fluid • Biochemical isolation • Blood–brain barrier

23. Brain Protection and Support • The Cranial Meninges • Have three layers: • Dura mater • Arachnoid mater • Pia mater • Are continuous with spinal meninges • Protect the brain from cranial trauma

24. Brain Protection and Support • The Cranial Meninges • Dura mater • Inner fibrous layer (meningeal layer) • Outer fibrous layer (endosteal layer) fused to periosteum • Venous sinuses between two layers • Arachnoid mater • Covers brain • Contacts epithelial layer of dura mater • Subarachnoid space: between arachnoid mater and pia mater • Pia mater • Attached to brain surface by astrocytes

25. Brain Protection and Support • Dural Folds • Folded inner layer of dura mater • Extend into cranial cavity • Stabilize and support brain • Contain collecting veins (dural sinuses) • Falx cerebri, tentorium cerebelli, and falx cerebelli

26. Brain Protection and Support • Dural Folds • Falx cerebri • Projects between the cerebral hemispheres • Contains superior sagittal sinus and inferior sagittal sinus • Tentorium cerebelli • Separates cerebellum and cerebrum • Contains transverse sinus • Falx cerebelli • Divides cerebellar hemispheres below the tentorium cerebelli

27. Brain Protection and Support Figure 14–3a The Relationship among the Brain, Cranium, and Meninges.

28. Brain Protection and Support Figure 14–3b The Relationship among the Brain, Cranium, and Meninges.

29. Brain Protection and Support • Cerebrospinal Fluid (CSF) • Surrounds all exposed surfaces of CNS • Interchanges with interstitial fluid of brain • Functions of CSF • Cushions delicate neural structures • Supports brain • Transports nutrients, chemical messengers, and waste products

30. Brain Protection and Support • Cerebrospinal Fluid (CSF) • Choroid plexus • Specialized ependymal cells and capillaries: • secrete CSF into ventricles • remove waste products from CSF • adjust composition of CSF • Produces about 500 mL of CSF/day

31. Brain Protection and Support • Cerebrospinal Fluid (CSF) • CSF circulates • From choroid plexus • Through ventricles • To central canal of spinal cord • Into subarachnoid spacearound the brain, spinal cord, and cauda equina

32. Brain Protection and Support • Cerebrospinal Fluid (CSF) • CSF in subarachnoid space • Arachnoid villi: • extensions of subarachnoid space • extend through dura mater to superior sagittal sinus • Arachnoid granulations: • large clusters of villi • absorb CSF into venous circulation

33. Brain Protection and Support Figure 14–4 The Formation and Circulation of Cerebrospinal Fluid.

34. Brain Protection and Support Figure 14–4a The Formation and Circulation of Cerebrospinal Fluid.

35. Brain Protection and Support Figure 14–4b The Formation and Circulation of Cerebrospinal Fluid.

36. Brain Protection and Support • Blood Supply to the Brain • Supplies nutrients and oxygen to brain • Delivered by internal carotidarteries and vertebral arteries • Removed from dural sinuses by internal jugular veins

37. Brain Protection and Support Figure 21–22 Arteries of the Neck and Head.

38. Brain Protection and Support Figure 21–23 Arteries of the Brain.

39. Brain Protection and Support Figure 21–28 Major Veins of the Head, Neck, and Brain.

40. Brain Protection and Support Figure 21–28 Major Veins of the Head, Neck, and Brain.

41. Brain Protection and Support • Cerebrovascular Disease • Disorders interfere with blood circulation to brain • Stroke or cerebrovascular accident (CVA) • Shuts off blood to portion of brain • Neurons die

42. Brain Protection and Support • Blood–Brain Barrier • Isolates CNS neural tissue from general circulation • Formed by network of tight junctions • Between endothelial cells of CNS capillaries • Lipid-soluble compounds (O2, CO2), steroids, and prostaglandins diffuse into interstitial fluid of brain and spinal cord • Astrocytes control blood–brain barrier by releasing chemicals that control permeability of endothelium

43. Brain Protection and Support • Blood–CSF Barrier • Formed by special ependymal cells • Surround capillaries of choroid plexus • Limits movement of compounds transferred • Allows chemical composition of blood and CSF to differ

44. Brain Protection and Support • Four Breaks in the BBB • Portions of hypothalamus • Secrete hypothalamic hormones • Posterior lobe of pituitary gland • Secretes hormones ADH and oxytocin • Pineal glands • Pineal secretions • Choroid plexus • Where special ependymal cells maintain blood–CSF barrier

45. Brain Protection and Support • Meninges stabilize brain in cranial cavity • Cerebrospinal fluid protects against sudden movement • CSF provides nutrients and removes wastes • Blood–brain barrier and blood–CSF barrier • Selectively isolate brain from chemicals in blood that might disrupt neural function

46. The Medulla Oblongata • The Medulla Oblongata • Allows brain and spinal cord to communicate • Coordinates complex autonomic reflexes • Controls visceral functions • Nuclei in the Medulla • Autonomic nuclei: control visceral activities • Sensory and motor nuclei: of cranial nerves • Relay stations: along sensory and motor pathways

47. The Medulla Oblongata Figure 14–5a The Diencephalon and Brain Stem.

48. The Medulla Oblongata Figure 14–5b The Diencephalon and Brain Stem.

49. The Medulla Oblongata Figure 14–5c The Diencephalon and Brain Stem.

50. The Medulla Oblongata • The Medulla Oblongata • Includes three groups of nuclei • Autonomic nuclei • Sensory and motor nuclei of cranial nerves • Relay stations along sensory and motor pathways