1. The Brain & Cranial Nerves
Chapter 12
The CNS
The Brain & Cranial Nerves
Part B

2. Diencephalon Central core of the forebrain
Consists of three paired structures
Thalamus
Hypothalamus
epithalamus
Encloses the third ventricle

3. Thalamus Paired, egg-shaped masses (nuclei) Forms:
The superolateral walls of the 3rd ventricle
Connected at the midline by:
The intermediate mass

4. Epithalamus
Figure 12.12

5. Thalamic Function
It is the location where afferent impulses from all senses converge and synapse
All other inputs ascending to the cerebral cortex pass through it (gateway to the cerebral cortex)
Plays a key role in mediating:
Sensation
Motor activities
Learning
Memory

6. Hypothalamus Located below the thalamus
Forms the inferolateral walls of the 3rd ventricle
Extends:
From the optic chiasma
To the posterior margin of mammillary bodies
Mammillary bodies (paired nuclei) :
Relay-station for the olfactory pathways
Infundibulum:
Hypothalamic stalk connecting the pituitary gland

7. Epithalamus
Figure 12.12

8. Hypothalamic Function
Important to overall body homeostasis
Regulates ANS activities:
Blood pressure
Heartbeat
Digestive tract motility
Eye pupil
Many other visceral activities
Involved with perception of:
Pleasure
Fear
Rage

9. Hypothalamic Function (cont’d)
Regulates:
Normal body temperature
Water balance & thirst (ADH release)
Feelings of hunger & satiety
Sleep & the sleep cycle
Controls:
Endocrine system functioning

10. Epithalamus Most dorsal portion of the diencephalon
Form the roof of the 3rd ventricle
Pineal gland:
Extends from the epithalamus posterior border
Secretes melatonin:
Sleep-inducing hormone
Involved with sleep-wake cycle regulation
An antioxidant

11. Epithalamus
Figure 12.12

12. Brain Stem Consists of three regions:
Midbrain
Pons
Medulla oblongata
Located between the cerebrum & the spinal cord
Similar to spinal cord, but has nuclei embedded in its white matter
Associated with 10 of the 12 pairs of the cranial nerves

13. Human Brain: Ventral Aspect
Figure 12.14

14. Brain Stem
Figure 12.15a

15. Midbrain Located between the diencephalon & the pons
Midbrain structures include:
Cerebral peduncles:
Two bulging structures containing descending pyramidal motor tracts
Cerebral aqueduct:
Tube connecting the third and fourth ventricles
Visual reflex centers & auditory relay (corpora quadrigemina)

16. Pons (Bridge): Bulging brainstem region Located between:
The midbrain & the medulla oblongata
Fibers of the pons:
Longitudinal (deep):
Connect higher brain centers and the spinal cord
Transverse (superficial):
Relay impulses between the motor cortex and the cerebellum
Regional cranial nerves:
Include:
Trigeminal (V), abducens (VI), & facial (VII)

17. Brain Stem
Figure 12.15b

18. Medulla Oblongata The most inferior part of the brain stem
Forms, with the pons, the ventral floor of the 4th ventricle
Comprises:
The decussation (crossover) point of the cortico-spinal tracts (pyramids)
The cardiovascular center, which includes:
Cardiac center (force & rate of contraction)
Vasomotor center (blood pressure regulation)
The respiratory center (rate & depth of breathing)
Other centers:
Vomiting, hiccupping, swallowing, coughing, and sneezing

19. The Cerebellum Makes up 11% of the brain’s mass
Made of two hemispheres connected by:
The vermis (wormlike structure)
Has a distinct branching white matter called:
Arbor vitae (tree of life)
Involved in:
Maintaining equilibrium and posture
Skeletal muscle contraction (timing & patterns)
Its activity occurs subconsciously

20. Protection of the Brain
The brain is protected by:
Bony skull
Meninges
Cerebrospinal fluid
Substances harmful to brain are shielded by:
The blood-brain barrier

21. Biol2401.3248 Break Slide Mon, April 01, ‘13

22. Meninges Connective tissue membranes Lie external to the CNS Include:
Dura mater
Arachnoid mater
Pia mater

23. Meninges (Cont’d) Functions of the meninges: Cover and protect the CNS
Protect blood vessels
Enclose venous sinuses
Contain cerebrospinal fluid (CSF)
Form partitions within the skull

24. Meninges
Figure 12.24a

25. Dura Mater A leathery, strong meninx
Made of two fibrous connective tissue layers:
Periosteal layer
Meningeal layer
These layers separate in certain areas forming:
Dural venous sinuses
The meningeal layer extends inward into three sickle-shaped (falx) septa:
A fold dips into the longitudinal fissure (attached to crista galli)
Another runs along the vermis of the cerebellum
A 3rd fold extending into the transverse fissure
These septa limit excessive brain movement

26. Dura Mater
Figure 12.25

27. Arachnoid Mater Aloose brain covering (middle meninx )
Secured to the pia mater by weblike extensions
Separated from the dura by the subdural space
Separated from the pia by a subarachnoid space
The subarachnoid space is filled with CSF & contains large blood vessels
Arachnoid villi protrude superiorly thru the dura into the superior sagittal sinus
These villi permit absorption of CSF into venous blood

28. Arachnoid Mater
Figure 12.24a

29. Pia Mater Richly supplied with tiny blood vessels Deep meninx
Composed of delicate connective tissue
Richly supplied with tiny blood vessels
Clings tightly to the brain tissue

30. Cerebrospinal Fluid (CSF)
Watery solution
Similar to plasma in composition but has:
less protein &
different ion concentrations
Has a total volume of 150 ml
Replaced every 8 hr (500 ml formed per day)

31. Cerebrospinal Fluid (CSF) Functions
A liquid cushion giving buoyancy to the CNS organs
Prevents brain from crushing under its own weight
Protects the CNS from blows & other trauma
Nourishes the brain
Carries chemical signals throughout the brain

32. Circulation of CSF
Figure 12.26b

33. Choroid Plexuses Clusters of capillaries Form tissue-fluid filters
Hang from the roof of each ventricle
Have ion pumps allowing them to alter ion concentrations of the CSF
Help cleanse CSF by removing wastes

34. Choroid Plexuses

35. Blood-Brain Barrier A protective mechanism
Helps maintain a stable brain environment
Blood-borne substances are separated from extracellular space & neurons by:
Continuous endothelium of capillary walls
Relatively thick basal lamina of capillaries
Bulbous feet of astrocytes clinging to capillaries

36. Blood-Brain Barrier: Functions
Selective:
Not absolute barrier
Allows nutrients (glucose, E-aa, Ions) to pass freely
Ineffective against:
Membrane diffusible (fat soluble) substances
Absent in some areas (blood composition monitors):
Medulla vomiting center (poisonous substances)
Hypothalamus (blood chemical composition)
Stress:
Increases passage of chemicals through the blood-brain barrier

37. Chapter 13
The CNS The Spinal Cord

38. The Spinal Cord The other component of the CNS
Enclosed within the vertebral column
Extends from foramen magnum to end of L1
Provides two-way communication (to & from the brain)
Protected by:
Bone
Meninges
CSF

39. The Spinal Cord
Has a single (meningeal) dura mater layer(no periosteal dura)
Meningeal dura matter doesn’t attach to the bony vertebral wall
Epidural space:
The space between the vertebral wall & the meningeal dura mater
Filled with:
Fat
Network of veins

40. Cross-Sectional Anatomy of the Spinal Cord
Figure 12.31a

41. The Spinal Cord The dural & arachnoid membranes extend to:
Conus medullaris:
Terminal portion of the spinal cord (between L1-L2)
Filum terminale:
Fibrous extension of pia mater beyond the conus
Anchors the spinal cord to the coccyx
Denticulate ligaments:
Delicate saw-toothed extensions of pia mater
Attach the spinal cord to the tough dura mater

42. Lumbar Tap

43. Spinal Cord
Figure 12.29a

44. The Spinal Cord Spinal nerves: Cervical and lumbar enlargements:
31 pairs attach to the cord by paired roots
Cervical and lumbar enlargements:
Sites where nerves serve the upper and lower limbs emerge
Cauda equina:
Collection of nerve roots (horse-tail appearance)
Found at the inferior end of the vertebral canal

45. Cross-Sectional Anatomy of the Spinal Cord
Figure 12.31a

46. Gray Matter and Spinal Roots
Gray matter consists of:
Soma
Unmyelinated processes
Neuroglia
Gray commissure:
Connects masses of gray matter
Encloses the central canal

47. Gray Matter and Spinal Roots
Figure 12.31b

48. Biol2401.5039 Break Slide Mon, Nov 5, ’12

49. Gray Matter and Spinal Roots
Posterior (dorsal) horns:
Consists entirely of Interneurons
Anterior (ventral) horns:
Consists mostly of somatic motor neurons
With some interneurons
Lateral horns:
Contain sympathetic nerve fibers

50. Gray Matter and Spinal Roots
Figure 12.31b

51. Gray Matter: Organization
Dorsal half:
Sensory roots and ganglia
Ventral half:
Motor roots
Dorsal and ventral roots:
Fuse laterally to form spinal nerves
Four evident zones within the gray matter:
Somatic sensory (SS)
Visceral sensory (VS)
Vsceral motor (VM)
Somatic motor (SM)

52. Gray Matter: Organization
Figure 12.32

53. White Matter in the Spinal Cord
Fibers run in three directions:
Ascending:
Sensory inputs
Ascend up to the higher centers
Descending:
Motor outputs
Descend down to the cord (from brain or within)
Transversely:
Commissural fibers
Run across the sides of the cord

54. White Matter in the Spinal Cord
The white matter is divided into 3 columns
These columns are called funiculi
They include:
Posterior funiculus
Lateral funiculus
Anterior funiculus

55. Gray Matter and Spinal Roots
Figure 12.31b