CTB Nerve Histology

Question 1

What cell types make up nervous tissue?

Answer 1

neurons and glia (nerve glue-supporting cells)

Question 2

Nissl stain

Answer 2

• stains RER in neurons

- stain cell body and dendrites, but not axons

Question 3

EM of gray matter composition shows…

Answer 3

gray matter is filled completely by cell bodies, cytoplasmic processes, and glial cells
-No connective tissue: all cytoplasmic processes of neurons fill all available extracellular space

Question 4

4 morphologically distinct regions of neurons

Answer 4

cell body
dendrites
axon (including the spike initiation zone)
presynaptic terminal

Question 5

proximal vs. distal part of axon hillock

Answer 5

-axon hillock is the proximal part of axon- tapered extension of cell body that lacks nissl stain

• distal part of axon hillock is initial segment of axon. this is untapered, unmyelinated, and contains numerous voltage-gated Na channels
• calls spike initiation zone- site where AP are generated

Question 6

What does the cytoplasm of an axon contain and not contain?

Answer 6

Axons do not have free polysomes, Nissl substance, or golgi, but they do have mitochondria and elements of cytoskeleton

Question 7

Cytoskeleton of neurons (3 components and where they are found within a neuron)

Answer 7

Microfilaments (actin): form matrix in periphery of neuron; prominent in dendrites

Neurofilaments: provide structural support for the neuron and are most numerous in the axon and proximal parts of dendrite. Part of intermediate filament family

Microtubules: found in all parts of the neuron.

Question 8

Role of dendritic spines and their cytoskeletal components

Answer 8

• Increase surface area of dendrites
• contain actin in neck, no microtubules
• lost with aging

Question 9

Glial cells of CNS and PNS

Answer 9

CNS: oligodendrocytes, microglia, and astrocytes (most numerous)
PNS:Schwann cells and Satellite cells

Question 10

Astrocytes are linked by? special roles?

Answer 10

• extensively by gap junctions
• store virtually all of the glycogen in the brain
• foot processes contribute to BBB by forming glial-limiting membrane
• form astroglial scar

Question 11

How are astrocytes similar to neurons? different?

Answer 11

Similar: negative Vm, NT receptors and transporters, ultrastructurally similar by both having prominent intermediate filaments (GFAP in astrocytes, neurofilament in neurons)

different: astrocytes are not polarized, cannot generate APs, lack chemical synapses, produce lactic acid as energy source from glycogen

Question 12

Microglia

Answer 12

CNS macrophages
smallest glial cells in CNS
not derived from neuroectoderm, from bone marrow precursor
act as antigen presenting cells
flat morphology

Question 13

Pericytes

Answer 13

-microglia that contribute to BBB

Question 14

Microglia and CNS disorders

Answer 14

• targeted by HIV1 virus in patients with AIDS
• affected microglia may produce cytokines that are toxic to neurons
• can also become phagocytic in response to neuronal tissue damage and may secrete toxic free radicals that can lead to disruption of ca2+ homeostasis of neurons

Question 15

PNS glial cells

Answer 15

Satellite cells and Schwann cells

Question 16

Role of PNS glial cells

Answer 16

Satellite cells: control microenvironment, provide electrical insulation, allow metabolic exchange, surround neuron cell bodies in autonomic and sensory ganglia

Schwann cells: make PNS myelin, more important cell in PNS

Question 17

Schwann Cells vs Oligodendrocyte function

Answer 17

S: work in PNS, can only myelinate one segment of one axon, compaction of myelin coincides with expression of P0, MBP (myelin basic protein), PMP22, and Nrg1

O: work in CNS, can myelinate up to 50 segments of 50 different axons, myelin expresses PLP and MOG

Question 18

MS and Guillain-Barre Syndrome

Answer 18

MS: affects CNS myeline, auto immune, marked by presence of plaques (sharply demarcated areas of demyelination), tend to form in axons near lateral ventricle surface

GBS: affects PNS myelination, myelin formed by schwann cells in PNS undergo acute inflammatory reaction after a respiratory or GI illness. motor axons always affect, leading to weakness in limbs

Question 19

Ways to increase axonal conduction velocity

Answer 19

• increase diameter
• as diameter increases, both membrane resistance and internal resistance decrease, but internal resistance decreased more
• myelination: increase membrane resistance
• thicker myelin: reduce capacitance

Question 20

What signal causes glial cells to myelinate axons?

Answer 20

Neuregulin- derived from axon; epidermal growth factor-like

Question 21

Where are voltage-gated ion channels found in an axon?

Answer 21

• Nodes of ranvier
• Na/K pumps found here too, as opposed to entire length of nonmyelinated cells which means myelinated cells also use less energy

Question 22

In both CNS and PNS, axon degenerates distal to cut in what fashion? What happens to the cell body?

Answer 22

• Anterograde or Wallerian degradation

- cell body undergoes retrograde chromatolysis

Question 23

Why can PNS axons regenerate but CNS cannot?

Answer 23

• Myelin and axonal debris quickly cleared by macrophages, schwann cells provide tube down which axon sprouts can re-grow. Slow process (1-4 mm/day)
• In CNS, debris not clearly, astrocytes form scar, oligodendrocytes undergo apoptosis, inflammation, inhibitory molecules on myelin and astrocytes

Question 24

3 known growth-inhibiting molecules of myelin

Answer 24

• Nogo
• Myelin-associated glycoprotein MAG
• Oligodendrocyte- myelin glycoprotein (OMgp)