Week 1: Overview of nervous system: development, adult structures and ventricles

Question 1

Describe the basic events involved in embryological development of the CNS

Answer 1

• week 4: formation of neural crest and tube
• neural tube develops into spinal cord, brain, and brain stem
• day 25: 3 vesicle stage- tube has three dilations, the forebrain (prosencephalon), midbrain (mesencephalon), hindbrain (rhombencephalon)
• 5 weeks: 5 vesicle stage.
  forebrain: telencephalon and diencephalon
  midbrain: Mesencephalon
  hindbrain: metencephalon and myelencephalon

Question 2

List the major components of the adult CNS and its subdivisions

Answer 2

• cortex, brain stem, and spinal cord
• transition between brain stem and spinal cord is at foramen magnum (through which you can have tonsilar herniation due to intracranial pressure increases)

Question 3

Explain the production the CSF

Answer 3

• formed by choroid plexus: pial connective tissue and capillaries
• in body, inferior horn, and atrium (glomus) of lateral ventricles
• in roof of 3rd and 4th ventricles
• 500mL/day, only 150mL capacity in ventricles and subarachnoid (3x turnover/day)

Question 4

Know the sites of occlusion along the CSF pathways that can lead to hydrocephalus

Answer 4

1. obstructions within ventricular system
   - turmor of choroid plexus can occlude 3rd ventricle , cause stenosis of aqueduct
   - results in ventricle enlargement proximal to obstruction
2. obstructions in subarachnoid space impairing CSF absorption
   - tumor causes lateral shift of brain due to unilateral mass (post infectious or post hemorrhagic meningitis)

Question 5

List the adult derivatives of the CNS from the 5 vesicle stage

Answer 5

• Telencephalon: cerebral cortex and basal ganglia
• Diencephalon: retina, Thalamus, hypothalamus, subthalamus
• Mesencephalon: midbrain, sup and inf collicullus
• Metencephalon: Pons and cerebellum
• Myelencephalon: medulla

Question 6

What are the subdivisions of the diencephalon?

Answer 6

• Thalamus: relays sensory info from PNS to cortex. Integrates motor fxns of cortex with cerebellum and basal ganglia
• hypothalamus: regulating homeostasis
• Subthalamus: motor control
• epithalamus (pineal gland): circadian rhythms

Question 7

What are the subdivisions of the brain stem?

Answer 7

• midbrain
• pons
• medulla oblongata

Question 8

What is the cerebellum for and what are its subdivisions?

Answer 8

• coordinates motor activity and involved in motor learning

- divided into two hemispheres and a midline vermis

Question 9

How does the ventricular system develop?

Answer 9

• at around 5 weeks
• telencephalon expands, lateral ventricles enlarge with it
• third ventricle forms from central cavity of diencephalon and cerebral aqueduct from lumen of mesencephalon
• 4th ventricle from shape change in floor of met encephalon and myelencephalon to form diamond like depression

Question 10

Describe the ventricular system.

Answer 10

Lateral ventricles
-divided into anterior, body, posterior, and inferior horn
-lateral ventricles communicate with third ventricle through inter ventricular foramen
Third ventricle:
-extends into optic chasm, infundibulum, pineal body-called recesses
cerebral aqueduct
-connects 3rd and 4th ventricles
fourth ventricle:
-between cerebellum and pons, upper medulla ventrally
-communicates with subarachnoid space through 3 openings

Question 11

Explain the flow of CSF

Answer 11

lateral ventricle–>3rd ventricle–>cerebral aqueduct–>4th ventricle–>median and lateral apertures–>subarachnoid space around brain and spinal cord

Question 12

Explain the drainage of CSf

Answer 12

-CSF flows in upward direction form base of brain toward superior sagittal sinus. Absorbed via arachnoid granulations into cerebral venous sinuses

Question 13

Explain the functions of CSF

Answer 13

• prevent injury
• blood-CSF barrier by epyndemal cells in chord plexus
• transports micronutrients, e.g. vitamins, trace elements to brain
• remove products of metabolism of some neurotransmitters