Exam 2 - Lecture 27 (Devel. of Nervous System)

Question 1

What is another name for monozygotic twins?

Answer 1

identical twins

Question 2

What are the 3 ways/stages in which monozygotic twins can occur?

Answer 2

1. Early blastomeres split apart (2-8 blastomeres when divided)
2. 2 inner cell masses develop in the blastula
3. 2 primitive streaks form in the same inner cell mass

Question 3

In the earliest possible stage that monozygotic twins develop, what is the state of amniotic cavities and placenta?

Answer 3

Separate amniotic cavities, no placental overlap

Question 4

In the middle stage that monozygotic twins develop, what is the state of amniotic cavities and placenta?

Answer 4

Shared placenta (surrounded by same trophoblasts), separate amniotic cavities

Question 5

In the latest possible stage that monozygotic twins develop, what is the state of amniotic cavities and placenta?

Answer 5

Same placenta (surrounded by same trophoblasts), same amniotic cavities

Question 6

Which stage of monozygotic twin formation is the most common in humans?

Answer 6

2nd stage (2 inner cell masses develop in the blastula)

Question 7

What is the least common and worst stage of monozygotic twin formation?

Answer 7

3rd stage (2 primitive streaks form); one twin almost always dies; can lead to cojoined twins

Question 8

What is an amorphous globosus?

Answer 8

Free, asymmetrical twins

• Amorphous glob surrounded by hair
• Inside has c.t. and a tooth

Question 9

What matter is on the inside portion of the spinal cord?

Answer 9

Gray

Question 10

What matter is on the outer portion of the spinal cord?

Answer 10

White

Question 11

What cells are in the grey matter?

Answer 11

Neuronal cell bodies and glial cells

Question 12

What structures are predominantly found in white matter?

Answer 12

Axons and myelin

Question 13

What gives white matter its white appearance?

Answer 13

High lipid content of myelin

Question 14

What two things join to form a spinal nerve?

Answer 14

Dorsal root and ventral root

Question 15

Where do ascending tracts of the nervous system go?

Answer 15

Spinal cord –> brain

Question 16

Where do descending tracts of the nervous system go?

Answer 16

Brain –> spinal cord

Question 17

What is the first organ system to initiate differentiation?

Answer 17

CNS

Question 18

What forms postnatally in puppies and kittens that form prenatally in foals and calves?

Answer 18

cerebellum

Question 19

If there is a disruption in the formation of the brain and spinal cord, what other 3 things can be affected?

Answer 19

vertebrae, head, face

Question 20

When does the neural tube begin developing?

Answer 20

2-3 days after gastrulation

Question 21

From what germ layer is the neural tube derived?

Answer 21

ectoderm

Question 22

What are the 4 steps of neural tube formation?

Answer 22

1. Notochord releases factors to begin differentiation of surface ectoderm
2. Surface ectoderm differentiates into the neural plate
3. Neural folds come up to meet each other while neural groove descends into embryo as a neural tube
4. Neural crest cells separate and also descend into the embryo

Question 23

What is the purpose of the cavity of the neural tube?

Answer 23

Communicates with amniotic cavity via rostral and caudal neuropores; helps get rid of waste and bring in nutrients

Question 24

What is derived ONLY from cranial neural crest cells?

Answer 24

Sensory ganglia of cranial nerves V VII, and X.

Question 25

What 3 things are derived from BOTH cranial and spinal neural crest cells?

Answer 25

1. Schwann cells 2. Enteric ganglia 3. Parasympathetic ganglia

Question 26

What 3 things are derived ONLY from spinal neural crest cells?

Answer 26

1. All dorsal root ganglia 2. Sympathetic ganglia 3. Adrenal medulla

Question 27

What is a ganglion?

Answer 27

Collection of neuronal cell bodies outside of the CNS.

Question 28

Where are ependymal cells located in the neural tube?

Answer 28

Line the cavity

Question 29

Where is the neural canal located in the neural tube?

Answer 29

In the center

Question 30

Where is the mantel layer located in the neural tube?

Answer 30

Includes alar plates and basal plates on either side of the neural canal

Question 31

Where is the alar plate located in the neural tube and what is its function?

Answer 31

Mass of cells closest to the roof plate; sensory

Question 32

Where is the basal plate located in the neural tube and what is its function?

Answer 32

Mass of cells closest to the floor plate; motor and autonomics)

Question 33

What is the marginal layer of the neural tube?

Answer 33

Axons projecting out from mantel layer

Question 34

What plate is the dorsal horn derived from?

Answer 34

Alar plate

Question 35

What plate is the ventral horn derived from?

Answer 35

Basal plate

Question 36

What two plates do not really move that much and what is the result?

Answer 36

Roof and floor plates; result in the dorsal median sulcus and ventral median fissure

Question 37

Where is the dorsal root ganglion derived from?

Answer 37

Neural crest cells

Question 38

What are the steps of ventral root formation?

Answer 38

Neurons in the ventral horn project their axons out to meet a target.

Question 39

What are the steps of dorsal root formation?

Answer 39

Neuronal cell bodies in the dorsal root ganglion project their axons to the dorsal horn and also out to the periphery to meet a target.

Question 40

How can multiple nerves innervate the same muscle?

Answer 40

Muscle bundles of the early spinal cord can fuse together to form a single muscle, but each bundle is attached to its own spinal nerve.

Question 41

What are the 4 steps to how the spinal cord changes in position?

Answer 41

1. Root of sacral nerves join with bundles of muscle just on the outside of the vertebrae 2. Vertebral column begins to grow faster than the spinal cord 3. Spinal cord moves cranially 4. Roots of nerves elongate, forming "cauda equina"

Question 42

What are the 3 types of spina bifida discussed in class?

Answer 42

1. Spinal bifida occulta 2. Meningomyocele 3. Myeloschisis

Question 43

What is the most benign form of spina bifida and what happens?

Answer 43

Spinal bifida occulta; vertebral arch is missing, typically on one vertebrae (can sometimes be on 2 consecutive vertebrae)

Question 44

What happens in spina bifida?

Answer 44

Development of vertebral arch is impacted

Question 45

What is the most common type of spina bifida in animals and what happens to the animal?

Answer 45

meningomyocele; paralysis

Question 46

What happens in meningomyocele?

Answer 46

Spinal cord and meninges protrude up into the space where the vertebral arch should be

Question 47

What is the most severe form of spina bifida and what happens?

Answer 47

Myeloschisis; neural tube doesn't close (animal can never walk)

Question 48

What is the fate of animals with spina bifida?

Answer 48

Are typically euthanized because of the difficulties associated with the condition.