organ systems III: neuroanatomy

this lecture covered some basic ideas in the anatomy of the brainstem and cerebellum as well as introducing a little bit of the embryology of the brain. neurulation is the process in the 4th week by which the neural plate, which is the central part of the ectoderm, folds into the neural tube. primary neurulation occurs when the top layer of the neural plate transitions to columnar epithelium, then folds inwards to form a cylinder. secondary neurulation occurs near the sacral region and involves condensation of mesenchymal cells, followed by an epithelial transition that hollows the mass of cells into a tube. the neural folding happens in 5 "waves"- starting at the brainstem, upper spinal cord, head, neck, and lower spinal cord. some conditions such as anencephaly can be due to failure of closure of a specific wave (in the case of anencephaly, failure of wave 2 closure, leading to a lack of cerebrum and skull).

the spinal cord anatomy is looked at in some detail [see diagram]. the grey matter that was introduced in previous semesters was differentiated further into laminas, which are areas within the grey matter that contain neurons that are relatively distinct functionally. in general, the ventral laminas receive sensory afferents, the intermediate laminas contain autonomic neurons, and the dorsal laminas project motor efferents to muscles. the white matter, described as the "freeway" system for axons, is made up of ascending and descending tracts of neurons and can also be divided into discrete functional groupings called funiculi. the dorsal funiculi mainly contains tactile and proprioceptive information up to the brainstem. within the lateral funiculi, there is the lateral corticospinal tract, which is the main pathway for descending motor information from the cortex, the spinocerebellar tract, which sends tactile and proprioceptive information to the cerebellum, and the anterolateral system, which sends pain and temperature information to the thalamus. finally, the ventral funiculi contains the ventral corticospinal tract, which is another pathway for descending motor information from the cortex, and the vestibulospinal and reticulospinal tracts, which receives descending motor information from the brainstem.

next is the brainstem: the midbrain, pons, and cerebellum. the midbrain includes cranial nerves, regulatory centers, sensory and motor pathways, and the reticular formation, which is a system of neurons that projects to the cortex and spinal cord and is central to states of arousal, attention, motivation, and wakefulness, among other things. the cerebellum is described as an outgrowth of the pons and cerebellar peduncles are thick axonal bundles that are the communication channel between the pons and the cerebellum. within the midbrain, there are different nuclei that are involved in different physiological functions: the substantia nigra is involved in dopamine modulation of motor control, the periaqueductal gray nucleus is involved in the stress response, the superior/inferio colliculi are involved in looking and listening, and the red nucleus is part of the descending motor pathway.

next, different areas of the cerebral cortex are looked at: frontal lobe contains the primary, premotor, and association motor cortex. parietal lobe contains the primary, secondary, and association somatosensory cortex. temporal lobe contains the primary, secondary, and association audition cortex. occipital lobe contains the primary, secondary and association visual cortex. finally, the insula is contained within the lateral sulcus and contains the gustatory and visceral cortices.

lastly, we looked at the diencephelon, basal ganglia, and limbic systems. the diencephelon is made up of the thalamus (which is involved in sending sensory and motor information to the cortex), hypothalamus (involved in autonomic and hormonal regulation, and stereotypic behavior), and epithalamus (which houses the pineal gland). the basal ganglia includes the structures: caudate nucleus, putamen, globus, pallidus, substantia nigra, subthalamus. the limbic system includes the structures: limbic cortex, anterior/medial dorsal thalamic nuclei, hippocampus, amygdala, and ventral striatum.

neurulation...
1. what is the neural plate derived from?
2. when does the neural plate begin neurulation?
3. how does the neural tube differentiate along the dorsal/ventral axis?
4. what is the difference between the mechanisms of primary vs. secondary neurulation?
5. describe primary neurulation.
6. describe secondary neurulation.
7. describe the sequence of closure of the neural tube.
8. CNS formation is complete when...
9. what is anencephaly and what is it caused by?
10. what is spina bifida and what is it caused by?
11. where is the caudal neopore?
12. describe the beginning of differentiation of different CNS regions.
13. what is the cephalic flexure and what is its purpose in humans?
14. where is the pontine flexure and what is its significance?

spinal cord...
15. spinal cord can be divided into...
16. grey matter is divided into...
17. white matter is divided into...
18. what are rexes lamina?
19. in general what are the functions of the dorsal, intermediate, and ventral lamina?
20. afferents in the dorsal horn convey...
21. what becomes of afferent neurons in the dorsal column?
22. what sort of neurons are contained within the ventral horn and where do they project?
23. what are the three divisions within white matter?
24. what type of neurons does the dorsal funiculi carry and where do they project?
25. within the lateral funiculi, which is the major descending tract from the cortex?
26. what types of neurons does the spinocerebellar tract convey and where do they project?
27. what type of information does the anterolateral system convey?
28. what is the propriospinal tract and what does it do?
29. what type of neurons does the ventral funiculus convey?

midbrain, pons, cerebellum...
30. brainstem consists of...
31. what are some major structures contained within the brain stem?
32. cerebellum is an outgrowth of...
33. what is the function of the medulla and pons?
34. where is the cerebellum located?
35. what are cerebellar peduncles?
36. what are some functions that the cerebellum is responsible for?
37. what are cerebral peduncles?

which midbrain nuclei are responsible for...
38. dopamine modulation of motor control?
39. pain and stress response?
40. looking and listening?
41. part of the descending motor pathway?

diencephelon...
42. the thalamus contains several nuclei that...
43. what is the hypothalamus responsible for?
44. epithalamus contains...

cerebral cortex: describe what is contained within the...
45. frontal lobe
46. parietal lobe
47. temporal lobe
48. occipital lobe
49. insula

other structures of the brain...
50. what is the reticular formation?
51. what are the components to the basal ganglia?
52. what are the components to the limbic system?
53. describe the interconnection between the cortical regions.

answers
1. central part of ectoderm.
2. the 4th week.
3. via the Shh and BMP growth signalling factors.
4. primary neurulation involves folding a flat surface into a column whereas secondary neurulation is the hollowing out of a solid mass.
5. primary neurulation involves the "columnarization" of existing epithelium following by the folding into a tube.
6. condensation of mesenchyme to form a rod, which then undergoes epithelial transition to form a tube.
7. the neural tube closure occurs in waves in 5 distinct regions. it begins in the brainstem and upper spinal cord, followed by the head and neck, followed by the lower spinal cord.
8. rostral and caudal neuropores close.
9. lack of cerebrum and skull formation due to dysfunctional wave 2 closing.
10. lack of development of spinal cord and overlying vertebrae due to incomplete closure of caudal neopore.
11. at the junctions of wave 1 and 5, the site at which the primary and secondary neurulations join.
12. dilations and flexures of different sections of the neural tube differentiates into different regions of the CNS.
13. the cephalic flexure is a bending forward of the neural tube such that the brain is at a right angle to the spinal cord; an adaptation for upright animals that evolved to let the vision be parallel to the ground.
14. located at the 4th ventricle and pons. significant because at this point the cerebellum is differentiated from the edge of the pons.

15. white and gray matter.
16. sensory, autonomic, motor areas.
17. ascending and descending tracts.
18. functionally distinct areas of grey matter.
19. dorsal is sensory, intermediate is autonomic, ventral is motor.
20. tactile, temperature, proprioceptive, pain sensations to neurons in lamina 2-4
21. afferent axons split and send processes rostrally and caudally.
22. efferent neurons that project to muscle groups.
23. dorsal, ventral, lateral funiculi.
24. tactile, proprioceptive to the brainstem.
25. lateral corticospinal tract.
26. tactile and proprioceptive to the cerebellum.
27. pain and temperature to thalamus.
28. surrounds grey matter and interconnects different spinal levels.
29. descending tracts from the cortex via the ventral corticospinal tract, and descending motor pathways from the brainstem via the vestibulospinal and reticulospinal tracts.

30. medulla, pons, midbrain
31. cranial nerves, sensory and motor pathways, reticular formation, regulatory centers. (mem: brain regulates the cranium through ridiculous S+M)
32. the pons
33. they contain the regulatory centers for respiratory, CV, GI systems.
34. dorsal side of pons and medulla.
35. large axon bundles that interconnect the pons and cerebellum. contain input and output tracts between the two areas.
36. muscle coordination, motor planning, procedural memory, balance, and eye movements. (mem: muscles plan balance procedures with their eyes)
37. axonal bundles that carry sensory and motor pathways to and from the cerebral cortex and the midbrain.

38. substantia nigra.
39. periaqueductal gray
40. superior and inferior colliculi
41. red nucleus

42. process and distribute sensory and motor information to and from the cerebral cortex.
43. autonomic and hormonal regulation and stereotypic behavior.
44. the pineal gland.

45. motor cortex: primary, premotor, association. also has broca's area.
46. somatosensory cortex: primary, secondary, association, wernicke's language area.
47. auditory cortex: primary, secondary, association.
48. visual cortex: primary, secondary, association.
49. contains gustatory and visceral cortex within the lateral sulcus

50. the system in the brain that runs through the medial brainstem and projects to the cortex, limbic structures and spinal cord, and is associated with arousal, attention, motivation, wakefulness, and many other physiological states.
51. caudate nucleus, putamen, globus pallidus, substantia nigra, subthalamus.
52. limbic cortex, anterior and medial dorsal thalamic nuclei, hippocampus, amygdala, ventral striatum
53. white matter axon bundles interconnect different cortical regions: longitudinal, occipitofrontal fasciculi interconnect cortices longitudinally. arcuate fibers interconnect local gyri. corpus callosum interconnects left and right hemispheres.