Neurons, Glia, & Brain Tissue

Question 1

Nucleus: grey vs. white matter?

Answer 1

grey

Question 2

Lemniscus: grey vs. white matter?

Answer 2

white

Question 3

Ganglions: grey vs. white matter?

Answer 3

grey

Question 4

Funiculus: grey vs. white matter?

Answer 4

white

Question 5

Fasciculus: grey vs. white matter?

Answer 5

white

Question 6

Tract: grey vs. white matter?

Answer 6

white

Question 7

Peduncle, cortex, body: grey vs. white matter?

Answer 7

• peduncle = white
• body = grey
• cortex = grey

Question 8

Astrocyte physical characteristics

Answer 8

• resemble small stars
• large cells w/numerous processes extending between neuronal processes/@ synapses
• “end-feet” envelop all CNS vessels

Question 9

Astrocyte functions

Answer 9

• Maintain ionic equilibrium: taking up K⁺ out of ECF
• Helps recycle neurotransmitters @ synaptic clefts
  
  • Takes up GABA and glutamate
  • converts glutamate to glutamine ==> axon terminals
• Envelop CNS blood vessels:
  
  • tranport nutrients from blood vessels to nearby neurons
  • help regulate blood floow
• Aid w/separation/isolation of neurons

Question 10

Microglia physical characteristics/distribution

Answer 10

• Small cells originating from bone marrow
• Small processes extend from cell bodies and run between nerve cells
• Spread w/even distribution throughout brain
  
  • cells never overap

Question 11

Microglia functions

Answer 11

• Respond to environmental changes in brain parenchyma
  
  • react by proliferation or behavioral change
• Phagocytic actions ==> Macrophages of brain

Question 12

Fate of severed/injured neuron (initial)

Answer 12

• Axon distal to cut is destroyed/degenerates (w/help of microglia)
  
  • Microglia migrate and proliferate
• Myelin withdraws/degenerations

Question 13

Oligodendrocytes: function & distribution

Answer 13

• location: CNS
• function: myelinates axons ==> speed conduction
  
  • one oligodendrocyte ==> myelinate many axons
  • cell type = glial cell

Question 14

Schwann cells: function & distribution

Answer 14

• location: PNS
• function:
  
  • myelinates axons ==> saltatory conduction
  • one schwann cell ==> myelinates only one axon

Question 15

Dendrite function vs. Axon function

Answer 15

• Dendrites
  
  • receptors receive NTs from synapse
  • send message from NTs to soma
• Axons
  
  • electrical conduit (of action potentials)
  • conduit for macromlx

Question 16

Axon terminal function

Answer 16

1. Receives action potential
2. Opens voltage-gated Ca²⁺ channels ==> release synaptic vesicles w/NTs
3. NTs (glutamate=most common, next is GABA) bind to receptors @ subsequent neuron
4. Receptors @ receiving dendrite determine whether the rxn to a NT is excitatory or inhibatory

Question 17

Types of dendritic receptors

Answer 17

• ionotropic
• metabotropic

Question 18

Ionotropic receptor characteristics

Answer 18

• dendritic receptor
• ion-gated channel
  
  • NT binding ==> channel opens ==> ions flow down gradients
• fast, direct-function
  
  • 1 ms rxn times

Question 19

Metabotropic receptor characteristics

Answer 19

• dendritic receptor
• NT binding ==> activation of second-messenger systems (e.g. G-proteins)
• Slow, indirect action
  
  • several ms rxn times

Question 20

Nissl substance composition and function

Answer 20

• composition: rough endoplasmic reticulum of neuron
• function: produce and modify proteins

Question 21

PET vs. fMRI scan

Answer 21

• both ~track cerebral blood flow
• PET
  
  • imaging that tracks movement of radio-labeled marker (e.g. water or glucose)
  • movement of water or glucose follows flow of blood
• fMRI
  
  • baseline image subtracted from image taken while performing some function/activity
  • reveals active portions of the brain

Question 22

Blood-brain barrier function

Answer 22

• tight junctions @ cerebral endothelium ==> prevent substances from in circulatory from freely entering extracellular space of brain
• allows for strict control of ECF composition w/in brain via active transport

Question 23

Astrocyte blood flow regulation mechanism

Answer 23

• Glutamate taken up by astrocytes ==> release of intracell stores of arachidonic acid
  
  • glutamate = commonly excitatory NT
• P450 enzyme acts on arachidonic acid ==> epoxy-eicosatrienoic acid (EET)
• EET is released ==> hyperpolarizes arteriolar membrane ==> decreased vascular tone = dilation = increased blood flow

Question 24

Peripheral nerve damage: peripheral & central response

Answer 24

• peripheral response
  
  • schwann cells clear myelin debris and line up to provide growth surface
  • nerve damage ==> initiation of growth program @ cell body ==> distal end of axon regrows
• central reponse
  
  • microglia proliferate and change shape ==> after 2-3 days, strip synapses & reorganize connection ==> can lead to neuropathic states
  • activate astrocytes

Question 25

Central nerve damage: central regeneration response

Answer 25

• damage ==> neuronal degeneration
• oligodendrocytes do not clear myelin debris or aid in regeneration
  
  • upregulate expression of mlx that actively inhibit axonal outgrowth
  • activate local astrocytes ==> form glial scar = chemical & physical barrier to regeneration