Nervous System Formation

Embryology

The notochord is the primary signaling center of the early embryo

True

The notochord signals neural fold closure via NCCs

True

What process seals up the neural tube

invagination of the neural folds

What are the three main regions of the nervous system

CNS (brain + spinal cord)
PNS (neurons external to the CNS, cranial nerves, spinal nerves, etc that connect brain and spinal cord to peripheral structures)

ANS (parts of CNS and PNS that innervate smooth muscle, cardiac muscle, etc.)

The development of what two structures marks the beginning of NS development?

Week 3 dev of neural plate and neural groove

What are the two divots found on the cranial and caudal end of the embryo?

The cranial and caudal neuropores

Which region of the NS does the neural tube differenciate into?

The CNS

What is neurulation?

The formxn of the neural plate and neural tube at the 4th and 6th somite pairs

Neural fold fusion is when the folds seal around the heart

False; when they fold to form the neural tube

Which dxn does neural fold fusion occur after starting in the 5th somites?

both the cranial and caudal dxn

The neuropores close before the vascular system for the neural tube is formed

False; at the same time

Which structure is the “groundwork for the entire NS”?

The neural plate

What structure does the neural folds eventually form?

Spinal Cord

What do the dorsal crests of the neural tube become?

They break off and differentiate into NCCs

What are the 3 zones of the Spinal Cord?

1. Ventricular (inner)- give rise to ALL neurons

2. Intermediate- Mantle layer, gray matter and neuroblasts

3. Marginal (outer)- White matter of the spinal cord (axons grow into it from neuroblasts in mantle)

T/F: Crest Cells give rise to cells that form most of the PNS and ANS

True

2 Major Cell Types that form from NT Neuroepithelial Cell Sheet

1. Glioblasts- CNS support cells

2. Microglia- derived from mesenchyme cells, originate in bone marrow, scattered throughout gray and white matter in spinal cord

Meninges are the membranes covering the spinal cord

True

What week do CSF form (cerebral spinal fluid)

Week 5

What are the 3 layers of the Meninges

1. Dura Mater: tough outer layer (protective mother)

2. Arachnoid Mater: web-like middle layer, filled with CSF

3. Pia Mater: soft innermost layer, lines the CNS structures (bc they delicate)

Filim Terminae is a delicate, thread-like fibrous extension of the pia mater that anchors the inferior tip of the spinal cord to the coccyx

True

T/F: The myelin sheaths stop forming at birth

False, they continue to form up to the 1st year after birth

T/F Motor Roots are myelinated before sensory roots

True!

What does the sacral dimple indicate?

Closure of the caudal neuropore at the end of the 4th week

What cells form the myelin sheath?

Oligodendrocytes

The myelin sheath wraps around the neurons

False, they form a coating around the axons

Neural Tube Defects (NTDs) are more common in countries with an excess of folic acid in their diets

FALSE; lack of folic acid

You can lower risk of NTDs if you take supplements after conception

FALSE; before conception and maintained until 1st trimester

What is the primary cause of tube defects?

Defective closure of the rostral and caudal neuropores

Defective closure of the caudal neuropore is more severe than the rostral neuropore

FALSE; defective rostral leads to incomplete dev of brain & degen of brain tissue

Defective caudal neuropore closure is most commonly associated with what condition

Clubfoot

NTDs are ONLY caused by external factors

False; nutritional (b12) and environmental (antiepileptic meds + uncontrolled diabetes) are the primary causes, but they can RARELY be caused by genetic/chrom disorders

What is the MOST common NTD?

Spina Bifida (1/1000-1/500)

Spina Bifida (an NTD) comes in 3 forms

FALSE;

1. Meningocele- CSF + meninges

2. Meningomyelocoele- spinal cord + nerve roots inside cyst

3. Myeloschisis- Spinal cord in aff completely open

4. Occulta- no major issues; hair tuft

Spina Bifida Occulta is the most severe form

False; Spina Bifida Myelochisis; completely open spinal cord; flat mass of nerve tissue

Pallister-Killian Syndrome (an NTD) is caused by nutritional factors

FALSE; rare chrom disorder caused by TETRASOMY of 12p; only compatible w life in mosaicism

There are 3 primary brain vesicles that appear at wk5

True;

1. Forebrain (prosencephalon)

2. Midbrain (mesencephalon)

3. Hindbrain (rhombencephalon)

What are the 2 pieces of the prosencephalon?

Telencephalon (front) & Diencephalon (back)

There is only 1 section of the mesencephalon

True; it does NOT divide

T/F the Pontine Flexure breaks up the Mesencephalon into 2 secondary vesicles

FALSE; it breaks up the rhombencephalon

The rhombencephalon is made up of 2 secondary vesicles

TRUE

1. Metencephalon: diffs into the pons and cerebellum

2. Myencephalon: diffs into the medulla oblongata

The telencephalon of the forebrain eventually form the cerebral hemispheres

TRUE

The line that splits the cerebral hemispheres is called the falx

TRUE

What are the grooves in the brain called?

Sulci

The Diencephalon forms what 3 “swellings”?

1. Thalamus

2. Hypothalamus

3. Epithalamus

Why isn’t the pituitary gland included in the diencephalon swellings?

It’s technically ectodermal in origin

The choroid plexus secretes fluid that becomes CSF

TRUE

Cysts of the choroid plexus are always clinically significant

False; almost never. However, they can be signs of chrom aneuploidy when they co-occur with other abnormal US findings

CP cysts are typically permanent

FALSE; they usually disappear at 28wks

Birth defects of the brain are much less common than NT defects

FALSE; slightly more common at 1/333; mostly detected via US

Cerebral Palsy is a Brain Disorder

TRUE; most common via maternal infection, rarely genetic; wide range of intensity (hypo/hypertonic)

Developmental Delay is due to NT Defects

FALSE; Birth Defects of the Brain

There is an increased risk in developmental delay for families with Hx

FALSE; most often caused by teratogens (rubella, CMV, maternal alc abuse, radiation)

A typical sign of Agenesis of the Corpus Callosum is tear drop shaped ventricles

TRUE; can be complete/partial and symptomatic/asymptomatic

Chiari Malformation is signified by a medulla tongue that penetrates thru the vertebral canal

TRUE

There are 4 types of Chiari Malformation

TRUE

1. T1: asymptomatic and most common; found in adolescence

2. Arnold-Chiari: semi-evere w/hernia, occipital encephalocele, and lumber myelomeningocele

3. T3: most severe; hernia of cerebellum and brainstem into vertebral canal

   1. T4: cerebellum absent; lethal

Microcephally leads to small brain, small calvaria, and a small face

FALSE; face size is normal; underdev’d brain

Microcephaly is never genetic

FALSE; AR microcephaly; small brain w/o affected calvaria/head structure

ZIKA is a primary cause of Hydrocephaly

FALSE; microcephaly

Encephaloceles typically form on occipital region

TRUE (hernia that contains meninges + and some brain + and some ventricular system depending on the severity of the condition)

Hydrocephaly is caused by imbalance in CSF production

TRUE; excess CSF in ventricular system

Hydrocephaly CANNOT be caused by mutations

FALSE; L1CAM X-linked mutation

Hydrocephaly is commonly associated with Spina Bifida

TRUE

Holopresencephaly is most commonly associated with environmental factors

FALSE; mostly associated with genetic abnormalities (trisomy 13, 18, etc.)

Holopresencephaly refers to the failure of the rostral NT in dividing into hemispheres

TRUE

There are 4 types of holopresenchephaly

TRUE

1. Alobar (no forebrain + facial issues (proboscis) + cyclopia

2. Semi-lobar

3. Lobar

4. Middle

Anancephaly (macroencephaly) is caused by the inability of the rostral neuropore to close

TRUE'

Multifactorial Inheritance; no fore/mid/hindbrain (more common in girls than boys 2x) and always associated with acrania

Development of the PNS is marked by the formation of the Cranial + Spinal nerves as well as the cranial, spinal, and autonomic ganglia

TRUE

Anencephaly is very commonly associated with other defects

FALSE

PNS starts as one nerve process that becomes two processes

FALSE; bipolar cells that unite!

Spinal Nerve fibers destined for a particular muscle group arrange in bundles

TRUE

The spinal cord neurons form a single bundle that grows into the spinal cord

TRUE

There are 9 pairs of cranial nerves that form in wk5/6`

FALSE; 12 pairs that form 3 groups

Moebius Syndrome is a common cranial nerve defect

FALSE; very rare. Paralysis of cranial muscles

Marcus Gunn Jaw Winking Syndrome is a trigeminal nerve defect

TRUE; only 300 cases

The ANS develops into 2 parts of the system

TRUE

1. Sympathetic: fight/flight response

2. Parasympathetic: homeostasis and body at rest