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Neuroanatomy > Neurons and Glial Cells > Flashcards

Neurons and Glial Cells Flashcards

1
Q

What are connections between neurons called?

A

synapses

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2
Q

What is the nucleus?

A

a cluster of neurons with similar functions (ganglia)

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3
Q

How many more glial cells are there than neuronal cells?

A

10x

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4
Q

What is nervous tissue specialised for?

A

to receive and generate stimuli (excitable) and transmit impulses (conductive)

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5
Q

What are neurons made up of?

A

cell body (soma) with extensions of axons and dendrites

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6
Q

What do neurons do?

A

create and maintain a potential difference from the inside to the outside (inside is more negatively charged compared to the outside)

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7
Q

What are the structural and functional units of the NS?

A

neurons; they can generate and conduct APs and are excitable

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8
Q

What is the inside of the neuron separated from the outside by?

A

the neuronal membrane

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9
Q

How much longer are axons than dendrites?

A

2000x

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10
Q

What is the diameter of the cell body of a typical neuron?

A

20µm

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11
Q

Which organelles are within the cell body of a neuron?

A
  • nucleus
  • RER
  • SER
  • Golgi apparatus
  • mitochondria
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12
Q

What does the neuronal membrane serve as?

A

a 5nm barrier to enclose the cytoplasm inside the neuron and to exclude certain substances that float in the fluid that bathes the neuron

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13
Q

What gives structure to neurons?

A

the cytoskeleton

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14
Q

What are most axons and where do they arise and branch?

A

long, slender processes that arise from the axon hillock in the cell body and branch at the distal (terminal) end

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15
Q

What is the main function of an axon?

A

to relay the electrical signal to the next cell

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16
Q

How does the axon differ from the soma?

A

the axonal cytoplasm (axoplasm) does not contain any RER that is usually found in the soma i.e. no protein translation can occur

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17
Q

What must happen since there is no protein translation in the axon?

A

all the proteins, nutrients and cytoskeletal elements found in the axon have to be transported from the soma to the far end of the axon

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18
Q

What are the 2 types of axonal transport?

A
  • anterograde - forward (cell body to axon)
  • retrograde - backward (axon to cell body)
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19
Q

What are the 2 types of anterograde transport?

A
  • fast transport, where cargo is moved at the rate of 50-1,000 mm/day
  • slow transport, where the cargo moves at a speed of 1-10 mm/day
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20
Q

What are the cargoes in fast and slow anterograde transport respectively?

A
  • fast = metabolites and receptors
  • slow = building blocks that are required for maintenance of the axon
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21
Q

What are dendrites?

A

specialised structures that arise from the soma and branch

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22
Q

What do dendrites do?

A

conduct impulses toward the cell body

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23
Q

How do electrical signals move through neurons?

A
  1. receptors sense the incoming neurotransmitters and convert them into electrical signals
  2. the signal is passed down to the soma and further into the axon and to the next cell
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24
Q

What is the direction of information flow in axons?

A

unidirectional; from dendrites and cell body down to the axon

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25
Q

How are impulses transmitted?

A

from one neuron (presynaptic) to another neuron (postsynaptic)

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26
Q

What are the 2 types of synapse?

A

chemical and electrical

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27
Q

How does communication occur at chemical and electrical synapses?

A
  • chemical = chemical neurotransmitter release
  • electrical = electricity
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28
Q

What is a synapse?

A

a junction where the axon from one cell meets the dendrite from another cell, so as to relay the message the first cell (presynaptic cell) to the second cell (postsynaptic cell)

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29
Q

Give examples of neurotransmitters

A
  • GABA
  • glutamate
  • ACh
30
Q

Where is the only place where transmission is chemical in nature?

A

synaptic cleft

31
Q

What do the pre and post synaptic terminals have respectively?

A
  • pre = vesicles and voltage gated ion channels
  • post = receptors
32
Q

Where is an AP generated and where does it go?

A

axon hillock of cell 1 then travels down the axon to synapse mediated by depolarisation via sodium channels

33
Q

What follows the cleft?

A

the postsynaptic density (dendroplasm) which contains all of the receptors

34
Q

What happens in excitatory synapses?

A
  1. binding of neurotransmitter to its receptors opens sodium channels in the postsynaptic membrane
  2. depolarisation of the membrane to ~-45mV
  3. AP in the postsynaptic cell
35
Q

What happens in inhibitory synapses?

A
  1. binding of neurotransmitter to its receptors opens chloride or potassium channels in the postsynaptic membrane
  2. hyperpolarisation of the membrane to ~-45mV
  3. no AP in the postsynaptic cell
36
Q

Why can neurons in the CNS not undergo further cell division?

A

they are postmitotic and cannot regenerate

37
Q

What is the first thing that happens when CNS axons are cut due to an accident?

A

the nucleus moves away from the cell body to the periphery and the Nissl body moves away from the nucleus and are dispersed

38
Q

What are the 7 stages of axon regeneration after an accident in the PNS?

A
  1. Nissl bodies disperse which leads to loss in the cytoplasmic basophilia
  2. Wallerian degeneration occurs in the distal portion of the axon
  3. the axon begins to swell and degenerate, the myelin sheath fragments, and phagocytes remove cellular debris
  4. after ~3 weeks, Schwann cells proliferate and form a tube of cells distal to the injury
  5. if the lesion in a peripheral neuron is sufficiently distant from the cell body, the nerve may recover
  6. axonal sprouts are produced at the distal end of the axon stump
  7. the axon stump elongates, and the sprouts seek the tubes formed by Schwann cells
39
Q

What happens when the axon is not completely able to reattach?

A

it makes random connections which can sometimes lead to phantom pain

40
Q

What are the 3 types of glial cells?

A
  • oligodendrocytes
  • astrocytes
  • microglia
41
Q

What is the percentage and function of oligodendrocytes?

A
  • 60-80%
  • myelin sheath formation
42
Q

What is the percentage and function of astrocytes?

A
  • 25%
  • blood-brain barrier, structural support, scar formation, secretion of nerve growth factors, water transport
43
Q

What is the percentage and function of microglia?

A
  • 5-10%
  • brain macrophages, secretion of proinflammatory cytokines, antigen-presenting function and immunocompetent cells of the CNS
44
Q

What can excess transport by oligodendrocytes lead to?

A

cerebral oedema

45
Q

What are the largest neuroglial cells?

A

astrocytes

46
Q

What do the processes of astrocytes do?

A

terminate on capillaries near the pia mater

47
Q

Where are fibrous astrocytes located?

A

white matter

48
Q

Where are protoplasmic astrocytes located and what are they?

A

grey matter and are thick, lightly branched processes that are closely opposed to neuron cell bodies

49
Q

What do astrocytes express?

A

potassium channels that release potassium, increasing the local extracellular concentration when neurons are active

50
Q

What do synapses contain?

A

glycogen for gluconeogenesis

50
Q

What happens upon injury to nerve cells within the CNS?

A

astrocytes rush to the injury site and fill up the space to form a glial scar

50
Q

What can happen if potassium is not cleared from the extracellular space?

A

epileptic seizures

51
Q

What are the 2 most important functions of astrocytes?

A
  • regulate blood flow in the brain by end feet i.e. they control the supply of oxygen and nutrients to the brain
  • regulate homeostasis of neurotransmitter
52
Q

What is a tripartite synapse?

A

a presynaptic terminal synapsing on a post synaptic terminal

53
Q

What does the tripartite synapse do?

A

mop up excess neurotransmitter at the CNS only, mostly at excitatory synapses

54
Q

What are the most important type of neuroglia cells?

A

oligodendrocytes

55
Q

What do oligodendrocytes in grey matter do?

A

act as satellite cells to neurons

56
Q

What do myelin sheathes allow?

A

increased conductivity and AP velocity via APs jumping from one node of Ranvier to another skipping the unnecessary channels in the internode

57
Q

Where do microglia originate from?

A

peripheral monocytic precursor cells

58
Q

Why do microglia cells have to act as antigen presenting cells?

A

most of the antibodies that the body makes do not cross the blood brain barrier into the nervous tissue, so it is up to the microglia to be able to recognise foreign particles and activate immune T cells

59
Q

What do microglia cells secrete?

A

cytokine-like TNF α and IL1 β that signal more microglia to be activated

60
Q

When are cytokine-like TNF alpha and interleukin 1 β secreted?

A

in response to a foreign particle or debris

61
Q

What are microglia cells implicated in?

A

a wide variety of diseases associated with degeneration of neurons, including Parkinson’s, Alzheimer’s disease etc.

62
Q

What are the 3 components of the PNS?

A
  • neuron processes and cell bodies located outside the CNS
  • neuroglial cells (Schwann cells and satellite cells)
  • nerve endings
63
Q

What is a peripheral nerve comprised of?

A

bundles (fascicles) of nerve fibres (axons) that are surrounded by myelin sheathes or Schwann cells

64
Q

What are the 3 connective tissue elements of a peripheral nerve?

A
  • epineurium - surrounds the entire nerve
  • perineurium – dense layer around each fascicle of nerve fibres
  • endoneurium – thin, reticular layer that surrounds each individual nerve fibre and contains Schwann cells
65
Q

In myelinated fibres, where does the endoneurium lie?

A

outside and encloses the myelin sheath

66
Q

What do Schwann cells form?

A

the myelin sheath around myelinated axons

67
Q

How does myelination work in the CNS and PNS respectively?

A
  • CNS = oligodendrocytes myelinate portions of several axons
  • PNS = individual Schwann cells myelinate portions of only a single axon
68
Q

What are ganglia?

A

encapsulated collections of neuron cell bodies, located outside the CNS

69
Q

What do ganglia contain?

A

satellite cells and connective tissue elements along with neurons

70
Q

What do satellite cells do?

A

form a capsule of cells around neuron cell bodies located in the peripheral ganglia

Neuroanatomy (17 decks)

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