Exercise 19

1. Exercise 19 The Brain & Cranial Nerves

2. Ventricles of the Brain Figure 12.5

3. Fiber Tracts in White Matter Figure 12.10a

4. Basal Nuclei Figure 12.11a

5. Basal Nuclei Figure 12.11b

6. Meninges • Three connective tissue membranes lie external to the CNS – dura mater, arachnoid mater, and pia mater • Functions of the meninges • Cover and protect the CNS • Protect blood vessels and enclose venous sinuses • Contain cerebrospinal fluid (CSF) • Form partitions within the skull

7. Meninges Figure 12.23a

8. Dura Mater • Leathery, strong meninx composed of two fibrous connective tissue layers • The two layers separate in certain areas and form dural sinuses

9. Dura Mater • Three dural septa extend inward and limit excessive movement of the brain • Falx cerebri – fold that dips into the longitudinal fissure • Falx cerebelli – runs along the vermis of the cerebellum • Tentorium cerebelli – horizontal dural fold extends into the transverse fissure

10. Dura Mater Figure 12.24

11. Arachnoid Mater • The middle meninx, which forms a loose brain covering • It is separated from the dura mater by the subdural space • Beneath the arachnoid is a wide subarachnoid space filled with CSF and large blood vessels • Arachnoid villi protrude superiorly and permit CSF to be absorbed into venous blood

12. Arachnoid Mater Figure 12.23a

13. Pia Mater • Deep meninx composed of delicate connective tissue that clings tightly to the brain

14. Cerebrospinal Fluid (CSF) • Watery solution similar in composition to blood plasma • Contains less protein and different ion concentrations than plasma • Forms a liquid cushion that gives buoyancy to the CNS organs • Prevents the brain from crushing under its own weight • Protects the CNS from blows and other trauma • Nourishes the brain and carries chemical signals throughout it

15. Choroid Plexuses • Clusters of capillaries that form tissue fluid filters, which hang from the roof of each ventricle • Have ion pumps that allow them to alter ion concentrations of the CSF • Help cleanse CSF by removing wastes

16. Choroid Plexuses Figure 12.25a

17. Blood-Brain Barrier • Protective mechanism that helps maintain a stable environment for the brain • Bloodborne substances are separated from neurons by: • Continuous endothelium of capillary walls • Relatively thick basal lamina • Bulbous feet of astrocytes

18. Blood-Brain Barrier: Functions • Selective barrier that allows nutrients to pass freely • Is ineffective against substances that can diffuse through plasma membranes • Absent in some areas (vomiting center and the hypothalamus), allowing these areas to monitor the chemical composition of the blood • Stress increases the ability of chemicals to pass through the blood-brain barrier

19. Cranial Nerves • Twelve pairs of cranial nerves arise from the brain • They have sensory, motor, or both sensory and motor functions • Each nerve is identified by a number (I through XII) and a name • Four cranial nerves carry parasympathetic fibers that serve muscles and glands

20. Cranial Nerves Figure 13.5a

21. Summary of Function of Cranial Nerves Figure 13.5b

22. Cranial Nerve I: Olfactory • Arises from the olfactory epithelium • Passes through the cribriform plate of the ethmoid bone • Fibers run through the olfactory bulb and terminate in the primary olfactory cortex • Functions solely by carrying afferent impulses for the sense of smell

23. Cranial Nerve I: Olfactory Figure I from Table 13.2

24. Cranial Nerve II: Optic • Arises from the retina of the eye • Optic nerves pass through the optic canals and converge at the optic chiasm • They continue to the thalamus where they synapse • From there, the optic radiation fibers run to the visual cortex • Functions solely by carrying afferent impulses for vision

25. Cranial Nerve II: Optic Figure II Table 13.2

26. Cranial Nerve III: Oculomotor • Fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles • Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape • Parasympathetic cell bodies are in the ciliary ganglia

27. Cranial Nerve III: Oculomotor Figure III from Table 13.2

28. Cranial Nerve IV: Trochlear • Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle • Primarily a motor nerve that directs the eyeball

29. Cranial Nerve IV: Trochlear Figure IV from Table 13.2

30. Cranial Nerve V: Trigeminal • Composed of three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3) • Fibers run from the face to the pons via the superior orbital fissure (V1), the foramen rotundum (V2), and the foramen ovale (V3) • Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication

31. Cranial Nerve V: Trigeminal Figure V from Table 13.2

32. Cranial Nerve VI: Abdcuens • Fibers leave the inferior pons and enter the orbit via the superior orbital fissure • Primarily a motor nerve innervating the lateral rectus muscle Figure VI from Table 13.2

33. Cranial Nerve VII: Facial • Fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face • Mixed nerve with five major branches • Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands • Sensory function is taste from the anterior two-thirds of the tongue

34. Cranial Nerve VII: Facial Figure VII from Table 13.2

35. Cranial Nerve VIII: Vestibulocochlear • Fibers arise from the hearing and equilibrium apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border • Two divisions – cochlear (hearing) and vestibular (balance) • Functions are solely sensory – equilibrium and hearing

36. Cranial Nerve VIII: Vestibulocochlear Figure VIII from Table 13.2

37. Cranial Nerve IX: Glossopharyngeal • Fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat • Nerve IX is a mixed nerve with motor and sensory functions • Motor – innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland • Sensory – fibers conduct taste and general sensory impulses from the tongue and pharynx

38. Cranial Nerve IX: Glossopharyngeal Figure IX from Table 13.2

39. Cranial Nerve X: Vagus • The only cranial nerve that extends beyond the head and neck • Fibers emerge from the medulla via the jugular foramen • The vagus is a mixed nerve • Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs • Its sensory function is in taste

40. Cranial Nerve X: Vagus Figure X from Table 13.2

41. Cranial Nerve XI: Accessory • Formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord • The spinal root passes upward into the cranium via the foramen magnum • The accessory nerve leaves the cranium via the jugular foramen

42. Cranial Nerve XI: Accessory • Primarily a motor nerve • Supplies fibers to the larynx, pharynx, and soft palate • Innervates the trapezius and sternocleidomastoid, which move the head and neck

43. Cranial Nerve XI: Accessory Figure XI from Table 13.2

44. Cranial Nerve XII: Hypoglossal • Fibers arise from the medulla and exit the skull via the hypoglossal canal • Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech

45. Cranial Nerve XII: Hypoglossal Figure XII from Table 13.2