Chapter 8

Question 1

Dev. Stage Conception to 2 weeks

Answer 1

egg gets fertilized, finds energy, starts to multiply. Inner cell mass is suspended in a big water balloon that will surround, protect and nourish them as they develop. It is what will be known as the placenta.

Question 2

Dev. Stage 2nd week to 8th week

Answer 2

Developing embryo and embryonic disc. disc has 3 layers.

• Outside layer- ectoderm (sensory receptors/organs, and outer covering (epidermis), and cells of nervous system (the neural plate))
• Inside the disc- mesoderm- (dermis, skin underneath the outer layer, muscles, skeleton, circulatory).
• Inside layers- endoderm- (gut, liver, pancreas, respiratory)

Question 3

Dev. Stage (fetal) 8th to birth

Answer 3

Swell head (number of cells in the head multiply exponentially) NS tissue grows within it. A lot of migration of skin, bone, and muscle cells take place (away from the neural tube out to the developing body) drags NS tissue with it.

Question 4

Neural tube formation- Day 18-26

Answer 4

Neural plate is the part of ectoderm that becomes the nervous system (NS).
Flat plate starts to roll up on itself like a tube. some of the light purple becomes the tube (spinal cord, brainstem, and interior of your brain) and the dark purple part is the NS tissue that gets placed right next to the tube.
Tube then completely forms. Dark purple cells are pushed out to the side (clusters of dark purple cells are dorsally located along the tube).
Superior and inferior neuropore take place to completely close tube at base of brain and at the coccyx)
Dark purple clusters of cell bodies are located just posterior to the neural tube and become the dorsal root ganglia (sensory in nature) are pseudounipolar cells of the peripheral sensory innervation. (light purple cells are multipolar).
Inside the neural tube, cells segregate further into concentric circles.
Inner circle=mantel layer
Outer circle=marginal layer (protects and myelin of mantel layer)

Question 5

Superior neuropore

Answer 5

closing towards the top (brain forms around it)

Question 6

Inferior neuropore

Answer 6

zips closed at the caudal end (zips up spinal cord all the way down to the coccyx)

Question 7

Mantel layer

Answer 7

multipolar cells. the cell bodies of motor neurons. Inner most circle of the neural tube.

Question 8

Marginal layer

Answer 8

a white covering around the mantel layer. cells of the myelin sheath. there to protect the axons of the mantle layer. Oligodendrocytes.

Question 9

Somite

Answer 9

31 pairs of somites on each side of neural tube. balls of mesoderm (cells of skin, bone, and muscles)

Question 10

Somite subdivision

Answer 10

Sclerotome- Harden- part that makes the bones (our skeleton)
Myotome- Piece of the somite that makes our muscles.
Dermatome- part of the somite that makes our skin.

All grab on to an axon and drag it with them (may be motor or sensory) from the neural tube out to their developed position.

Question 11

Motor plate

Answer 11

anterior aspect of spinal cord, have cells of peripheral motor function.

Question 12

Association plate

Answer 12

cells of sensory function and is the posterior aspect of spinal cord.

Question 13

Dorsal root ganglion

Answer 13

house the cells of the peripheral somatosensory function.

Question 14

Dermatome

Answer 14

Embryologic tone (the piece of every somite that will become skin,

Our definition- as the skin innervated by 1 of the 31 spinal nerves/a single spinal nerve

Arm bud pokes out taking C7 and dragging the bands above and below it out into the formation of the arm. C7 led the way. dragging C6 and C8 which drag C5 and T1.

Leg bud poked out and goes down to the knee then rotates 90 degrees internally which is why we have the strange dermatome angels

Question 15

Myotome

Answer 15

Piece of somite that becomes muscle cell.

Our D: All muscles innervated by a single spinal nerve.

All muscles in our body started out as two different somites on the left and two on the right besides the intrinsic muscles of the hand.

Cells of the C5 biceps and C6 biceps merge to become big biceps muscle when close to final destination. Still innervated by two different spinal nerves. C5 and C6 spinal nerves get collected up into the musculocutaneous brachial plexus nerve.
General rule* spinal nerve injuries will weaken but not paralyze muscles.

If musculocutaneous nerve gets sectioned and taken away the biceps muscle becomes paralyzed because the peripheral nerve will paralyze it. no peripheral nerve=paralyzed.

Question 16

Dermatome formation and growth.

Answer 16

Dermatomes grow out away from the neural tube. C6 has to merge with C5 so there are not open spaces without innervation. They mesh together which creates some unclear boundaries. At the boundaries where C5 and C6 mesh you will get the “I don’t know” answers when testing sensation due to this mixing of dermatomes.

At 3rd month in utero, the spinal cord is as long as the spinal column.
Birth, spinal cord has stayed same size and spinal column has continued to grow,
Adult, spinal cord ends about L1

Question 17

Brain formation

Answer 17

Forebrain- All structures rostral to midbrain, (most rostral spot)

• Midbrain- dividing line between the forebrain and the hindbrain
• Hindbrain- pons, medulla, and cerebellum (helps to control autonomic function and can grossly move around, our primitive or reptile brain, what keeps us alive from moment to moment).

Question 18

Migration of mantel layer cells

Answer 18

Gray matter is inner ring of neural tube, but the outer layer of cerebral and cerebellar cortex. All brain cells in the head need to go to the outside. Climb along “radial glia” like climbing a scaffold from inside to surface. (the neurons differentiate after reaching final location)
*Astrocytes provide the framework needed for migration of mantel layer.
Take on motor and sensory roles one they get to where they are going.

Question 19

Fast motor neuron (fast twitch muscle)

Answer 19

Axons are large diameter, heavily myelinated. Connect to muscle cell turned into fast twitch (high force, short duration)

Question 20

Slow motor neuron (slow twitch muscle

Answer 20

Smaller diameter, less myelinated (low force, long duration).

Question 21

Myelination

Answer 21

• Begins in 4th fetal month (have to myelinate centrally and peripherally).
• Ends at about 3 years of age
• Different rates in different areas.
• • Peripheral motor neurons around 1 month of age
• • Central motor neurons around 2 years of age.