Embryology I

Question 1

Primary axes of the central nervous system

Answer 1

• rostral (“towards the nose”) vs. caudal (“towards the tail”)
• ventral vs. dorsal
  
  • below the cephalic flexure
    
    • ventral = “towards the stomach”
    • dorsal = “towards the back”
  • above the cephalic flexure
    
    • ventral = towards the chin
    • dorsal = towards the top of the head

Question 2

Cephalic flexure definition

Answer 2

• initially straight neural tube ==> 80^o turn during development between the brain and brainstem (=diencephalon & mesencephalon)

Question 3

Planes used to discuss CNS

Answer 3

• horizontal/transverse/cross-section
• coronal
• sagittal

Question 4

Primary cerebral vesicles

Answer 4

• proencephalon (forebrain) = most rostral
• mesencephalon (midbrain)
• rhombencephalon (hindbrain) = most caudal
• 3 primary cerebral vesicles ==> 5 secondary cerebral vesicles

Question 5

Secondary cerebral vesicles (+ primary vesicle origins)

Answer 5

• prosencephalon ==> telencephalon (paired enlargements cranially) & diencephalon (more caudal)
• mesencephalon ==> mesencephalon
• rhombencephalon ==> metencephalon (more rostral) & myelencephalon (more caudal)

Question 6

Secondary vesicles ==> Adult brain structures

Answer 6

• telencephalon ==> cerebrum: cerebral hemispheres (cortex, white matter, basal nuclei)
• diencephalon ==> diencephalon: thalamus, hypothalamus, epithalamus
• mesencephalon ==> brain stem: midbrain
• metencephalon ==> brain stem: pons & cerebellum
• myelencephalon ==> brain stem: medulla

Question 7

Secondary vesicles ==> adult neural canal regions

Answer 7

• telencephalon ==> lateral ventricles
• diencephalon ==> third ventricle
• mesencephalon ==> cerebral aqueduct
• metencephalon ==> fourth ventricle
• myelencephalon ==> cerebral canal

Question 8

Rhombomere location/development

Answer 8

• rhomboencephalon = 8 morphologically distinct rhombomeres
  
  • r1 = posterior to mesencephalon
  • r8 = anterior to spinal cord
  • rhombomeres = similar size/number of cells
• each rhombomere develops uniquely ==> different morphologies, axonal trajectories, NT synthesis, etc.
  
  • HOX genes expressed differently ==> differentiation

Question 9

Common dorsoventral patterning w/in neural tube

Answer 9

• dorsal = sensory
• ventral = motor

Question 10

Neural tube development of dosoventral patterning

Answer 10

• neural tube develops sulcus limitans = separates ventral and dorsal population
  
  • ventral = “basal plate”
  • dorsal = “alar plate”
• @ basal plate ==> axons grow out to myotomes
• @ alar plate ==> dorsal root ganglia (sensory neurons from neural crest cells) grow to innervate neurons

Question 11

Modifications of dorsoventral pattern @ midbrain, pons, medulla, & spinal cord

Answer 11

• development of dorsoventral patterning is unique to each section of the midbrain

Question 12

Basic scheme of dorsoventral patterning of prosencephalon

Answer 12

• Before the telencephalic vesicles the rostral neural tube (forebrain) develops regionally restricted sonic hedgehog DV markers,
• DV markers ==> three discrete proliferative zones.
  
  • cortex (dorsally)
  • lateral ganglionic eminence
  • medial ganglionic eminence