Lecture 9, Introductions to the Nervous System (part 2)

Question 1

Nucleus

Answer 1

a circular or oval shaped structure found within the soma of a neuron
- contains genetic information necessary for cell maintenance and survival

Question 2

Nucleolus

Answer 2

the area within the nucleus that has a key role in protein synthesis (where the RNA transcription happens)

Question 3

Axon Hillock, Axolemma and Axoplasm

Answer 3

axon hillock: the branch point where the axon branches off the soma
axolemma: the plasma membrane of the axon (mostly fats but carbo and proteins)
axoplasm: the cytoplasm within the axon (gel-like structure)

Question 4

Nissi Bodies

Answer 4

clusters of rough endoplasmic reticulum (RER) and free ribosomes
- function in the synthesis and segregation or proteins

Question 5

Neurofilament

Answer 5

filaments that serve to maintain and support the structure and size of a neuron

Question 6

Telodendria

Answer 6

the terminal branches of an axon that eventually interact with other neurons or cells at a synapse (final branches point of axon before it becomes axon terminals)

Question 7

Synapse

Answer 7

synapse: the junction between one neuron and another neuron or cell
- mediates the transfer of information from the neuron to the other cell
a signal is passed from the presynaptic cell to the postsynaptic cell via movement of neurotransmitters (chemicals that serve as messengers pre to post) across the synapse
- neurotransmitters (like ACh) bind to receptors on the postsynaptic cell, which passes on the signal, or action potential, to the postsynaptic cell

Question 8

Neuronal Development

Answer 8

the development of neurons and glial cells being with neural stem cells, which can differentiate into neuronal or glial progenitor cells
- differentiation depends on the absence/presence of neurogenic growth signals
plasticity: the ability of the brain to continue to modify its structures and function throughout the lifespan, in response to stimulation or injury
- influences neurogenesis and gliogenesis
- can continue to undergo these processes
- found that neural stem cells are still present in adults

Question 9

Which glial cell secretes growth factors (neurogenic signals) to facilitate neuronal development?

Answer 9

astrocyte

Question 10

Order of Neuroglia Cell Differentiation

Answer 10

neuronal stem cell -> glial progenitor cell -> glial cell (ex. astrocyte, microglia etc.)

Question 11

Order of Neuron Differentiation & Neuron Steps

Answer 11

neuronal stem cell -> neuronal progenitor cell -> neuron
1. neuron migrates to the correct location
2. neuron forms projections that will eventually become dendrites/axons
3. a growth cone forms at the end of each axon, which helps guide the axon’s growth in the right direction (interacts with glial cells to help guide the growth of axon)
4. when the growth cone reaches its target, the synapse forms

glial cells help guide this process
- secretion of molecules that will promote or inhibit neuron growth
- physical guidance (axon growth may follow along the cell surface of glial cells)

Question 12

Axon Rengeneration (in CNS & PNS)

Answer 12

axons in the CNS do not have the capacity to spontaneously regenerate after an injury (injuries to brain and spinal cord and pretty dendrimental and cannot simply be fixed)
- oligodendrocytes do NOT have the ability to direct the regrowth of severed/damaged axons
◦ damaged astrocytes may form scar tissue, and/or
release chemicals that block axonal regrowth
(blood-brain-barrier) (occupies space that doesn’t
allow axons to grow)
- result = loss of sensation or paralysis in the corresponding area that was innervated (severe injuries)
axons in the PNS are able to readily regenerate following an injury
- schwann cells are able to direct the regrowth of severed/damaged axons

Question 13

Steps to Axon Regeneration in the PNS (4)

Answer 13

step 1: damaged schwann cells and cellular debris is broken is exposed to the extracellular fluid
step 2: schwann cells extend from the proximal and distal stumps to bridge the gap left by the damage
(microphages remove the cellular debris)
step 3: the axon regrows due to help/guidance of schwann cells
step 4: as axon growth continues, schwann cells form the myelin sheath around new axon segments

Question 14

Neuronal Injury in the CNS

Answer 14

in the CNS, injuries to the spinal cord are often crushing, rather than cutting, of the nervous tissue
- axons are intact, but supporting cells in the surrounding areas are damaged
example: damage to the surrounding oligodendrocytes will impair the maintenance of the myelin sheath
- loss of the myelin sheath
- decreased transmission of the action potential down the axon (as myelin helps transmit ap)
severed axons in the CNS are able to regrow small axonal extensions
- without the help or guidance of Schwann cells, the growth doesn’t enable the return of function
new research technologies are investigating the use of stem cell therapy to assist in regeneration of CNS tissue
- significant implications for individuals with spinal cord injury (SCI)