Module 4: Neuro > Physiology > Flashcards

Physiology Flashcards

(58 cards)

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1
Q

What are the three types of neurons? Where are they most often found (CNS vs PNS)?

A

Bipolar (PNS)

Multipolar (CNS)

Pseudounipolar (PNS)

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2
Q

What are glial cells?

A

Non-neuronal cells that maintan homeostasis, form myelin, and provide structural and metabolic support for neurons in the developing and mature nervous system

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3
Q

What do astrocytes do?

A

they are cells in the CNS that:

  • Provide scaffolds for growing axons and migrating neurons during development
  • have numerous projections that anchor neurons to their blood supply
  • maintain appropriate extracellular ion concentration
  • contribute to the formation of the BBB
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4
Q

What do microglia do?

A

They are specialized cells in the CNS that:

  • are capable of phagocytosis
  • protect neurons in CNS
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5
Q

What do ependymal cells do?

A

Line fluid-filled cavities (ventricles) of the brain and spinal cord

  • These cells create and secrete CSF and beat their cilia to help circulate CSF
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6
Q

What do oligodendrocytes do?

A
  • Coat axons in the CNS with their cell membrane, forming a specialized membrane differentiation called myelin ==> produces the myelin sheath
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7
Q

What is myelin sheath?

A

Insulation to the axon that allows electrical signals to propagate more efficienty

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8
Q

What are Schwann cells?

A

Myelin producing cells of the PNS

  • they also play a rone in nerve regeneration following injury
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9
Q

What do satellite cells do?

A

surround and support nerve cell podies in peripheral ganglia (in PNS)

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10
Q

What is unique about neurons in the CNS vs PNS?

A
  • *CNS:**
  • many presynaptic inputs to the postsynptic cell are required to activate a neuron
  • Excitatory and inhibitory inputs
  • various neurotransmitters (NT)
  • Many APs firing sychronously to attain an AP in the target neuron
  • *PNS:**
  • 1 prensynaptic input to 1 postsynaptic cell
  • Excitatory inputs ONLY
  • One NT
  • 1 AP in a motor neuron fires to attain an AP in target cell
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11
Q

How are CNS synapses mediated?

A

chemically

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12
Q

Where can neuron-neuron intereaction occur in CNS cells?

A
  1. Axon-dendrite interaction
  2. Axon-soma
  3. Axon-axon
  4. Dendrite-dendrite (rare)
  5. Soma-soma (rare)
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13
Q

What are factors influencing the size of the graded AP in the CNS?

A
  • Amount of neurotransmitter released into synaptic cleft
  • Density of receptors on postsynaptic membrane
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14
Q

How does integration of synaptic inputs occur in CNS neurons?

A
  • Graded postsynaptic potentials (both IPSP and EPSP) spread passively through the cell and decay over time and space
  • As the PSPs reach the axon hillock, the potentials are integrated and decision is made to trigger (or not trigger) an AP
  • PSPs are integrated by summation
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15
Q

What is temporal summation?

A

Conseutive EPSPs at the same site sum to depolarized the membrane toward the AP threshold

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16
Q

What is spatial summation?

A

Simultaneous EPSPs at different synapses on the same neuron sum to depolarize the membrane toward the AP threshold

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17
Q

What is it meant by divergence of local synaptic connections?

A

One neuron is able to influence many postsynaptic neurons

  • information is spread out to many cells
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18
Q

What is it meant by convergence of local synaptic connections?

A

Many presynaptic neurons converge and influence a single postsynaptic neuron

  • Increases influence and possibiltiy of postsynaptic cell’s abilty to fire
    (increase spatial summation)
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19
Q

What is an Axoaxonic Synapse Type 1?

A

When the presynaptic neuron influences the voltage at the axon hillock and alters the likelihood of generating an AP on the postsynaptic neuron

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20
Q

What is an Axoaxonic Synapse Type 2?

A

When the presynaptic neuron influences the voltage at the postsynaptic neuron at the axon terminal and alters the amount of Ca2+ present in the axon terminal of the postsynaptic cell

  • This results in altered amount of NT released by the postsynaptic cell (onto its postsynaptic cell)
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21
Q

How can an Axoaxonic Synapse Type 2 lead to presynaptic facilitation?

A

The “facilitating” neuron’s axon terminal activity results in increased Ca2+ in the axon terminal of the other neuron –> Increased NT release –> Increased EPSP or IPSP size in the final postsynaptic cell

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22
Q

How can Axoaxonic Synapse Type 2 result in presynaptic Inhibition?

A

The “inhibiting” neuron’s axon terminal activity results in decreased Ca2+ in the axon terminal of the other neuron –> Decreased NT release –> Decreased EPSP or IPSP size in the final postsynaptic cell

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23
Q

What is a feedforward excitation?

A

A –> B –> C

Neuron A Excites Neuron B –> Neuron B excites Neuron C

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24
Q

What is a feedforward inhibition?

Study These Flashcards
A

A –> B –> C

Neuron A excites Neuron B –> Neuron B inhibits Neuron C

25
What is disinhibition?
A --\> B --\> C --\> D Neuron A excites Neuron B --\> Neuron B inhibits Neuron C --\> Neuron C is inhibited from inhibiting Neuron D
26
What Amino Acids are used as Neurotransmitters?
GABA Glutamate (main excitatory NT in brain) Glycine
27
What amines are used as neurotransmitters?
Acetylcholine Dopamine Noepinephrine Histamine Serotonin
28
What neuropeptides are used as neurotransmitter?
Enkephalins Substance P (also endophins and dynorphins)
29
What is co-localization and how does it affect the postsynaptic neuron?
Many peptides like Substance P are co-localized with classical NTs in vesicles - Co-localization modulates the action of the NT on the PS cell
30
How do the CNS and PNS differ in healing and repair?
**PNS** has an intrinsic ability for repair and regeneration **CNS** is, for the most part, incapable of self-repair and regeneration
31
What is an anterograde reaction to injury?
If the axon is cut, the **part distal to the cut** degenerates (**wallerian degeneration)** - This is because materials for maintaining the axon are formed in hte ccell body and can no longer be transported down the axon * *PNS:** Schwann cells in the region dedifferentiate and divide - Schwann cells and macrophages phagocytose the degenerative debris **CNS:** Microglia , astrocytes, and macrophages phagocytose the degenerative debris
32
What is a retrograde reaction to injury?
Swelling of the cell body and nucleus - degredation of neuron opposite to AP propogation direction - Displacement of the nucleus from the center of the cell to an eccentric location - Dispersion of the Nissl substance into fine, homogenous particles of decreased basophilia - ribosome-studded ER are dispersed and replaced with polyribosomes
33
How does the PNS regenerate peripheral nerves?
**Sprouting:** tips of the proximal stumps form enlargements or growth cones - Growth cose sprout at nearest Node of Ranvier of the **proxima****l** segment, and must grow across teh injury site and into the schwann cell guidance tunnels - When the growing axons contact Schwann cells, a second wave of Schwann cell proliferation occurs - These Schwann cells form guidance tunnesl along the former course of the axon - Elongating axons innervate target tissue, myelinate, and functional recovery occurs
34
What is a neuroma?
Failure of regenerating axonal sprouts to cross the injury site (possibly due to formation of scarring or loss of large segement of nerve) results in a neuroma - the permanently denervagted muscle fibers demonstrate severe atrophy
35
How does the CNS regenerate its neurons?
Axonal regeneration is typically abortive --\> no regeneration occurs
36
How can a crush injury affect PNS regeneration?
Endoneurial sheaths remain intact, making it an easier injury to repair
37
How can a transection injury affect PNS regeneration?
Continuit of axoplasm is lost - misalignment of axons with original pathway can occur - if suture ends of nerve together, the chance of recoery increases
38
How can the site of injury affect PNS regeneration?
The closer to target site the nervev is damaged, the greater the likelihood for regeneration
39
How can age affect PNS regeneration?
Younger = Greater regenerative activity
40
Why are CNS neurons unable to regenerate?
Many factors: - loss of molecules that promote axonal growth - Expression of molecules taht inhibit axonal growth - Oligodendroglia do not form "guidance tunnels" - Development of glial scar at injury site impedes growth of axons due to proteoglycan production that inhibits sprouting
41
What is Cerebral Spinal Fluid?
Clear, colorless fluid that forms a crucial component of the CNS environment - Bathes the brain and spinal cord - CSF production, circulation, and absorption affect the homeostasis of CNS - Percolates through ventricles and out into subarachnoid space
42
Where is CSF produced?
It is actively secred into ventricles by the choiroid plexus epithelium
43
How does CSF leave the subarachnoid space and enter the veinous system?
Through Arachnoid granulations
44
What is the subarachnoid space?
Space between the arachnoid and pia mater - filled with CSF - in certain regions, subarachnoid space is expanded to form cisterns, which contain a considerable volume of CSF
45
What is the choroid plexus?
Area in the ventricles that form and secrete 70-75% of CSF Consists of: - Capillary network core lined with fenestrated endothelium - Choroid epithelium, (simple cuboidal), surrounding the interstitial fluid and vascular core Separates CSF in the ventricles from blood of the vascular plexus
46
What are extrachoroidal sources of CSF?
Cerebral capillary walls Metabolic generation of water by teh complete oxidation of glucose
47
What are the functions of CSF?
- **Maintains constant external environment** for neurons and glia - **Removes harmful brain metabolites** **- Distributes neuroactive hormones** throughout the nervous system - **Protects CNS from trauma via the bouyant effect**
48
How does CSF composition differ from blood in: Protein Glucose, K+, Ca2+, pH Mg2+, Cl-, lactate, H20 Na+
**less** protein (200x less) **less** glucose, K+, Ca2+, pH **More** Mg2+, Cl-, lactate, H20 **Equal** Na+
49
What do you have to take into account when doing a lumbar puncture to assess cranial CSF?
Lower spine CSF is slightly different from cranial CSF
50
What are the blood-brain-CSF barriers?
- the communication/transport of chemical substances between these compartments occurs through specific barrieres: - Blood Brain Barrier - Blood-CSF barrier - CSF-brain barrier
51
What is the purpose of the blood brain barrier?
To maintain the microenvirontment of the brain and CNS
52
What is transported across the BBB?
Glucose Certain Amino Acids Ribonucleotides \*Note: two different transporters are often required for most molecules: 1. from blood --\> brain 2. from brain --\> blood
53
What are transport mechanisms across the BBB?
1. Diffusion for lipid soluble, hydrophobic compounds 2. passive and actie carrier-type transporters 3. Ion channels and ion-exchangers for ions and other lipid insoluble hydrophilic compounds
54
What are general features of carrier-type transporters of the BBB?
- saturability - stereospecificity - enhancement of transport velocity
55
What are circumventricular organs?
Areas of specialized tissue that lack a BBB located in close proximity to the ventricular system Include: Subfornical organ Subcommissural organ Pineal Area postrema Median eminance Neuropypophysis Organum vasculosum of the lamina terminalis
56
What is brain edema?
Increased brain volume due to increased water content Two Types: **vasogenic cytotoxic**
57
What is vasogenic edema?
**Cause:** ischemia, head trauma, meningitis ** Mechanism:** Increased permeability of BBB and capillary walls **Manifestations:** Increase in brain interstitial fluid increased intracranial pressure Smaller ventricles
58
What is Cytotoxic edema?
**Cause:** Drug poisoning, hyponatremia, water intoxication, hypoxia from asphyxia **Mechanism:** net shift of water from extracellular space to the interior of brain cells **Manifestations:** cell swelling, decrease in brain interstitail fluid and water diffusion, increased intracranial pressure, marked reduction of ventricles
Module 4: Neuro
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