1. The Brain & Cranial Nerves
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
Arachnoid Mater

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
Cranial Nerve VII: Facial

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
Cranial Nerve IX: Glossopharyngeal

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