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Neuro > Alterations > Flashcards

Alterations Flashcards

1
Q

What is the critical period?

A

postnatal time during which a given behavior requires specific environmental influences in order to develop normally.
-failure to be exposed to appropriate stimuli during the CP is difficult or impossible to remedy.

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2
Q

Define plasticity

A

ability of an experience to influence neural activity in such a way that it alters neural circuitry and thus determines behavior.
-Differs in different regions and throughout the lifetime (most during critical period)

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3
Q

What is the significance of plasticity?

A
  1. potential for plasticity of the relatively stereotyped units of the nervous system endows each of us with our individuality
  2. plays a role in the recovery (or lack of) of function following brain trauma.
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4
Q

What are functional alterations in terms of plasticity?

A

typically short term

-changes in the effectiveness of existing synaptic connections

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5
Q

what are anatomical alterations in terms of plasticity?

A

typically long term

consist of growth of new synaptic connections between neurons

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6
Q

What are the two categories of the adjustment of synaptic connections (functional alterations)?

A
  1. short term-lasts a few minutes

2. long term- lasts hours to years

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7
Q

How are short term adjustments of existing synaptic connections facilitated or depressed?

A

Facilitation: prolonged elevation of presynaptic Ca++ levels results in increase in neurotransmitter release in response to subsequent APs

Depression: progressive depletion of synaptic vesicles that are available for release results in a decrease of neurotransmitter release in response to high frequency stimulation.

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8
Q

What are the two categories of long term adjustments to existing synaptic connections?

A
  1. Long term Potential

2. Long term depression

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9
Q

What are the features of long term potential

A
  1. state dependent
  2. input specificity
  3. associativity
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10
Q

define state dependent.

A

the state of the membrane potential of the post synaptic cell determines whether or not LTP occurs

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11
Q

Define input specificity.

A

LTP induced by activation at one synapse does not occur in other, inactive synapses that contact the same neuron.

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12
Q

Define associativity

A

if one synapse is weakly activated at the same time that an adjacent synapse onto the same cell is strongly activated, both synapses undergo LTP

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13
Q

What are the steps to long term potential?

A
  1. high frequency stimulation with release of sufficient glutamate from presynaptic cell.
  2. simultaneous depolarization through non-NMDA receptors AND activation of NMDA receptors of the postsynaptic cell.
  3. Ca++ enters the post synaptic cell through NMDA receptors. Large and fast increase of Ca++.
  4. Activation of Ca++ dependent enzymes in the post synaptic cell.
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14
Q

What are the effects of long term potential?

A
  • increase in sensitivity to neurotransmitter in the postsynaptic cell, leading to an increase in excitatory postsynaptic potential size.
  • changes in gene expression and synthesis of proteins.
  • potential cellular and molecular mechanisms of Hebb’s Postulate: cells that fire together, wire together.
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15
Q

What are the steps of long term depression?

A
  1. low frequency stimulation for long periods (10-15 min) with release of sufficient levels of glutamate from the presynaptic cell.
  2. simultaneous depolarization through non-NMDA receptors AND activation of NMDA receptor of the post synaptic cell.
  3. Ca++ enters the postsynaptic cell through NMDA receptors. (Small and slow increase of Ca++)
  4. Activation of Ca++ dependent enzymes in the postsynaptic cell.
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16
Q

What are the effects of long term depression?

A
  • decrease in sensitivity to the neurotransmitter in the postsynaptic cell, leading to a decrease in excitatory postsynaptic potential size.
  • changes in gene expression and synthesis of proteins
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17
Q

What does the growth of new synaptic connections involve?

A

pruning of preexisting synapses, production of new dendritic spines, axonal sprouting, formation of new synapses, and/or activation of previously inactive connections.

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18
Q

What are some examples of plasticity?

A
  1. memory

2. reorganization of cortical maps

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19
Q

Describe memory as an example of plasticity

A

long term potentiation in the hippocampus is thought to play an important role in consolidating explicit memories of events and facts.
- not known how adjustments of existing synaptic connections encode memories.

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20
Q

Describe reorganization of the primary somatosensory cortex (study example)

A

Following an amputation of a digit, the cortical map in the primary somatosensory cortex of an owl monkey changes substantially so that the area dedicated to the amputated digit now is dedicated to the adjacent digits.

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21
Q

Describe the reorganization of the primary motor cortex.

A

following amputation of (B) UE, cortical map in primary motor cortex changes so areas dedicated to hangs become dedicated to feet

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22
Q

describe reorganization of intermodal area

A

blind humans reading Braille have increased blood flow to primary visual and visual association areas. Same areas are activated in such individuals by verbal language tasks and learning lists of words.

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23
Q

What is thought to play an important role in reorganization of cortical maps?

A

previously inactive connections (alterations in the strength of synapses already present) is thought to play an important role.

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24
Q

Define regeneration

A

regrowth of original tissue, thereby restoring normal tissue structure and function.
-occurs only if the parenchymal cells can undergo cell mitosis AND the surround CT matrix is intact.

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25
Q

Define repair.

A

replacement of non-regenerated parenchymal cells with CT. Formation of a CT scar thereby restoring the structural integrity of the tissue.
-occurs with necrosis of permanent parenchymal cells or excessive necrosis of tissues

26
Q

What is nerve tissue composed of?

A

cells (neurons) that are specialized to receive stimuli from other cells and to conduct impulses, and their support cells (glial).

27
Q

When can axons and dendrites regenerate?

A

If their cell bodies, basement membranes, AND endoneuriums are intact.

28
Q

What are 2 cells that are capable of regeneration?

A
  1. Stem cells

2. Olfactory neurons

29
Q

What does neurogenesis require?

A

population of neural stem cells.

30
Q

Where are neural stem cells located in humans?

A

Adjacent to the lateral ventricles, and only give rise to interneurons in the olfactory bulb and hippocampus.

31
Q

What are glial cells?

A

capable of regeneration and are responsible for repair in the CNS

32
Q

Where do most injuries to the peripheral and central nervous system involve?

A

damage to axons

33
Q

Define necrosis

A

refers to a sequence of morphologic changes that occur in irreversibly injured cells within living tissue

34
Q

define apoptosis

A

programmed cell death

35
Q

What does CNS repair occur in response to?

A

neuronal cell death through the processes of necrosis/apoptosis

36
Q

What are the steps to CNS repair?

A
  1. Breakdown and removal of Necrotic tissue
  2. migration and proliferation of cells
  3. Gliosis (Glial Scar Formation)
37
Q

What does the breakdown and removal of necrotic tissue involve?

A
  • Formation of an empty cavity
  • microglia and macrophages become involved in phagocytosis and produce and secrete chemical mediators and growth factor (initiate 2nd step)
38
Q

What occurs during migration and proliferation of cells?

A
  • Endothelial cells are involved in angiogenesis
  • Fibroblasts are only present if meninges are penetrated. involved in the synthesis of extracellular matrix components to provide a framework for other cells.
  • astrocytes are involved in gliosis and produce and secrete many molecules that serve structural, neuromodulatory, and other functions.
39
Q

What occurs during gliosis?

A

Astrocytes form a dense aggregate with their cytoplasmic processes with the empty cavity

40
Q

What are examples of axon damage

A
  1. transection of an axon either acutely by laceration OR more slowly by crushing (axotomy)
41
Q

What is Axotomy?

A
  • crushing of axons

- divides the axons into proximal (attached to cell body) and distal segment (no attachment)

42
Q

What are the 2 processes that can occur during axonal degeneration?

A
  1. Proximal segment

2. distal segment

43
Q

What occurs during proximal segment degeneration?

A

cell body and organelles undergo REVERSIBLE ultrastructural changes, including swelling and nuclear alterations.

44
Q

What is distal segment degeneration?

A

undergoes Wallerian degneration, a process by which the axon, associated glial cells, and myelin sheath degenerate.
-The nerve terminals fail rapidly

45
Q

What occurs during the breakdown and removal of necrotic tissue?

A

Macrophages (and Microglia in CNS) are involved in phagocytosis and produce and secrete chemical mediators and growth factors.

46
Q

What are the steps involved in axonal regeneration?

A
  1. Axonal degeneration
  2. breakdown and removal of necrotic tissue
  3. Migration and Proliferation of cells
  4. Axonal Sprouting
47
Q

What occurs during the migration and proliferation of Schwann cells in the PNS?

A

produce and secrete molecules that promote axon regeneration

48
Q

What occurs during migration and proliferation of cells in the astrocytes of the CNS

A

Astrocytes form glial scars that impede axon growth beyond the site of the lesion and produce and secrete molecules that are inhibitory to axon regeneration.

49
Q

What is the job of oligodendrocytes?

A

produce myelin that is inhibitory to axon regeneration

50
Q

What occurs during axonal sprouting?

A

cell body expresses genes that restore it to a growth state

51
Q

Explain axonal sprouting in PNS

A

Axonal sprouts grow from the proximal segment, enter the CT elements of distal segment, and grow toward target.

  • once they return to their target, regenerated axons can form new functional nerve endings.
  • process is largely directed by molecules secreted by schwann cells.
52
Q

Explain axonal sprouting in the CNS.

A

as axonal sprouts approach glial scars, the axonal growth cones develop bulbous abnormalities and are unable to migrate through the glial scar.

53
Q

What is axonal sprouting dependent on?

A

the presence of CT elements (scaffolding) to guide the axonal sprouts.

54
Q

Where is axon regeneration greater? PNS or CNS?

A

PNS- schwann cells are critical

55
Q

What is the hypothesis of aging?

A

may result from changes in informational macromolecules (DNA, RNA, and proteins)
-errors in the duplication of DNA increase with age because of random damage that occurs over time. When a significant number of genetic errors accumulate, aberrant mRNA and proteins are formed, leading eventually to aging.

56
Q

What are structural alterations that occur in the CNS during aging?

A
  1. decrease in brain volume and weight- due to loss of tissue and neuron shrinkage
  2. decrease in nerve conduction velocity- due to fragmentation and loss of myelin
  3. decrease in some receptors and neurotransmitters
  4. decrease in alterations of synapses
  5. increase in concentration of plaques and tangles
57
Q

What are senile plaques?

A

extracellular deposits of beta-amyloid protein surrounded by degenerating neuronal and glial cell processes

58
Q

What are neurofibrillary tangles?

A

filamentous inclusions in neuronal cell bodies and proximal dendrites

59
Q

What are the structural alterations that occur in the PNS due to aging?

A
  1. decrease in number of unmyelinated and myelinated nerve fibers - loss of motor units
  2. decrease in nerve conduction velocity
  3. alterations of density and morphology of sensory receptors
  4. decrease in alterations synapses
60
Q

What are the motor functional alterations that occur due to aging?

A
  • posture is less erect and reflexes are slowed.
  • Gait is slower and stride length is shorter
  • increases in risk of falls
61
Q

What are the cognitive functional alterations due to aging?

A

-decrease in speed of learning, problem solving, retention of new information, visuo-spatial ability, verbal fluency, and general intelligence.

Neuro (31 decks)

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