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MBBCh 1- APES1001A > Histology: Nerve Tissue > Flashcards

Histology: Nerve Tissue Flashcards

1
Q

Information processing:
• sensory neurons-
• interneurons-
• motor neurons-

A
  • sensory neurons- sensory input (external or internal cues)
  • interneurons- integration of signals
  • motor neurons- motor output
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2
Q
  • Coordination and control

* mainly nervous (____ impulses) & endocrine (_____) systems

A

nerve

hormones

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3
Q

Two main components of nervous tissue:

A

Neurons

Glial cells

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4
Q

What is the function of neurons?

A

• generate electrical signals (conducted nerve impulses / action potentials)

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5
Q

What is the function of glia?

A

Non-neuronal cells that mainly support neuronal function. `

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6
Q

What is the function of glia?

A

Non-neuronal cells that mainly support neuronal function. `

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7
Q

What are the glia types? (5)

A

Astrocytes, Oligodendrocytes, Microglia, Schwann cells & Ependymal cells

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8
Q

What are astrocytes?

A

Information transfer, regulate extracellular ion concentrations, promote blood flow to neurons, help form the blood-brain barrier, and act as stem cells to replenish certain neurons.

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9
Q

What are Oligodendrocytes?

A

Oligodendrocytes- myelinate axons in the CNS (myelination increase the conduction speed of action potentials)

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10
Q

What are microglia?

A

Microglia- immune cells in the CNS that protect against pathogens.

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11
Q

What are schwann cells?

A

Schwann cells- myelinate axons in the PNS

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12
Q

What are Ependymal cells?

A

Line the ventricles of the brain, promote circulation of the cerebrospinal.

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13
Q

What are dendrites?

A

Receive messages from other neurons at specialised junctions called synapses.

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14
Q

What is the function of the axon hillock?

A
  • Serves as junction between cell body and axon

* Integrates signals from multiple synapses

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15
Q

What is the function of the axon?

A

Propagate integrated signal to axon terminals.

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16
Q

What is the function of an axon terminal? (2)

A
  • Synapse on other neurons, muscles, or target organs

* Chemicals released, signals communicated to cells of target tissue

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17
Q

What are the Nodes of Ranvier? (2)

A
  • Gaps between the myelin insulation of Schwann cells

* Sites where signal is recharged

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18
Q

How does a neuron transmit information?

A

A neutron receives information, transmits it along an extension called an axon, and transmits the information the information to other cells via specialised junctions called synapses.

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19
Q

How do animals repsond to environmental stimuli?

A
  • animals respond to environmental stimuli using specialized cells—> neurons
  • stimulus is detected by sensory receptors & the body responds through motor effectors
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20
Q

How does the pain you experience when you burn your hand results so quickly in an action by your muscles? (2)

A
  • the cells working together allow you to respond very quickly to threats when you touch something hot—> heat receptors of a sensory neuron detect the stimuli and send the information of heat to an inter-neuron in your central nervous system -from there
    —> motor neuron sends a response from your central nervous system to the skeletal muscles in your arm causing them to contract and pull your hand away
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21
Q

The fundamental process of neural transmission that underlies this action occurs in all neurons of the body. How do neurons transmit this information and how is an action potential triggered? (2)

A
  1. neurons transmit this information through changes in the electrical potential of the membrane by the movement of ions across the membrane and an electrochemical gradient governs the movement of these ions resulting in an electrical impulse
  2. the resting membrane potential in a neuron when the cell is not firing an impulse is established by
    —> unequal distribution of sodium ions outside of the cell and potassium ions inside the cell making the outside of the cell more positively charged compared to the inside
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22
Q

How is the action potential triggered? (5)

A
  1. The electrochemical gradient is established—> maintained by an enzyme—>s odium potassium ATPase
  2. When the neuron is stimulated—>sodium ion channels open and sodium ions flow into the cell
    —> leads to a change in the electrical potential across the membrane called —> depolarization
  3. Depolarizing electrical potential travels down the dendrites and over the cell body
  4. Multiple electrical potentials will combine at the axon hillock in a process called —>summation
  5. If the depolarization is large enough—>action potential is triggered
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23
Q

What are action potentials?

A

-action potentials are all or non-electrical impulses that maintain their amplitude and strength down the length of the axon -the action potential travels down the axon when the deep polarization of an area of the membrane causes adjacent voltage-gated sodium ion channels to open

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24
Q

How does an action potential work? (4)

A
  1. the influx of sodium ions result in membrane depolarization along the membrane
  2. after a short delay potassium ion channels open and potassium ions flow out repolarizing the membrane
  3. for the neuron to fire again the resting membrane potential needs to be reestablished
  4. sodium potassium ATPase is used to move sodium and potassium ions against their concentration gradient reestablishing the resting membrane potential
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25
Q

What happens when the action potential moves down the axon? (6)

A
  1. As the action potential moves down the axon —> ions are diffusing only a short distance allowing the signal to move quickly
  2. At the axon terminal the electrical impulse passes to another cell at a cellular connection called a synapse —> the space between the presynaptic neuron and a postsynaptic cell is called the synaptic cleft
  3. the presynaptic neuron contains signal molecules called—> neurotransmitters that are packaged inside vesicles
  4. when an action potential reaches the end of a neuron —> neurotransmitters are released by exocytosis from the neuron into the synaptic cleft —> neurotransmitters bind the adjacent cell at receptor sites attached to ion channels
  5. the channels open allowing the movement of ions into or out of the effector cell which alters its membrane potential by transmitting the signal from the neuron to the effector cell
  6. because nerve impulses move very rapidly down the axon of a neuron and move from cell to cell across synapses —> you react quickly to a stimulus like burning your finger
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26
Q

What is the function of dendrites?

A
  • dendrites: receive signals from neighboring neurons (like a radio antenna)
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27
Q

What is the function of an axon?

A
  • axon: transmit signals over a distance (like telephone wires)
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28
Q

What is the function of an axon terminal?

A
  • axon terminal: transmit signals to other neuron dendrites or tissues (like a radio transmitter)
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29
Q

What is the function of the myelin sheath?

A
  • myelin sheath: speeds up signal transmission along the axon
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30
Q

Concentration ______ are key behind how action potentials work.

A

gradients

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31
Q

What is the function of the concentration gradient in terms of the action potential? (4)

A
  1. In terms of action potentials, a concentration gradient is the difference in ion concentrations between
    the inside of the neuron and the outside of the neuron (called extracellular fluid)
  2. If we have a higher concentration of positively charged ions outside the cell compared to the inside of the cell—>there would be a large concentration gradient.
  3. same if there were more of one type of charged ion inside the cell than outside.
  4. The charge of the ion does not matter—> both positively and negatively charged ions move in the
    direction that would balance or even out the gradient.
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32
Q

What is an ion channel?

A

A protein complex penetrates a cell membrane, allow specific ions through membrane

33
Q

What is a membrane potential?

A

Difference in electrical potential across membrane.

34
Q

What is resting potential?

A

Membrane potential of inactive cells.

35
Q

What is negative potential?

A

More sodium ions outside cell than potassium ions inside the cell.

36
Q

What is the function of potassium ions?

A

Potassium ions: diffuse out at a much faster rate than sodium ions diffuse into the cell because more
potassium leakage channels than sodium

37
Q

What is function of the sodium-potassium?

A

Sodium-potassium: pumps move two potassium ions inside the cell as three sodium ions are
pumped out to maintain the negatively-charged membrane inside the cell; this helps maintain the
resting potential

38
Q

What concentration gradient do neurons have most of the time?

A
  • Neurons have a negative concentration gradient most of the time—> there are more positively
    charged ions outside than inside the cell—>regular state of a negative concentration gradient is called
    resting membrane potential.
39
Q

During the resting membrane potential there are:

  • more _____ ions outside than inside the neuron
  • more _____ ions inside than outside the neuron
A

sodium

potassium

40
Q
  • The concentration of ions isn’t static though! —> Ions are ____ in and out of the neuron constantly
    as the ions try to equalize their concentrations.
A

flowing

41
Q
  • The cell however maintains a fairly consistent negative concentration gradient (between -40 to -90
    millivolts) . How ? : (3)
A
  • The neuron cell membrane is super permeable to potassium ions, and so lots of potassium leaks
    out of the neuron through potassium leakage channels (holes in the cell wall).
  • The neuron cell membrane is partially permeable to sodium ions, so sodium atoms slowly leak
    into the neuron through sodium leakage channels.
  • The cell wants to maintain a negative resting membrane potential, so it has a pump that pumps
    potassium back into the cell and pumps sodium out of the cell at the same time.
42
Q

How do action potentials work?

A

• Action potentials: forms when a stimulus causes the cell membrane to depolarize, causing all
sodium ion channels to open.

43
Q

What happens when potassium ion channels are opened, and sodium ion channels are closed?

A

• potassium ion channels are opened, and sodium ion channels are closed: cell membrane becomes
hyperpolarized as potassium ions leave the cell; the cell cannot fire during this refractory period

44
Q

Action potential travels down the axon as the membrane of the axon ______ and ______.

A

depolarizes

repolarizes

45
Q

What is the function of myelin?

A

Insulates the axon to prevent leakage of the current as it travels down the axon.

46
Q

What is the function Node of Ranvier?

A

Nodes of Ranvier: contain sodium and potassium ion channels, allowing the action potential to
travel quickly down the axon by jumping from one node to the next.

47
Q

What are action potentials?

A
  • Action potentials (those electrical impulses that send signals around your body) —> are nothing
    more than a temporary shift (from negative to positive) in the neuron’s membrane potential caused by
    ions suddenly flowing in and out of the neuron.
48
Q

What happens during the rest state?

A
  • During the resting state (before an action potential occurs)—> all of the gated sodium and
    potassium channels are closed—> gated channels are different from the leakage channels—> only open once an action potential has been triggered.
49
Q

How are these channels gated? (2)

A
  • These channels are “voltage-gated” —> open and closed depends on the voltage difference across the cell membrane.
  • Voltage-gated sodium channels have two gates (gate m and gate h), while the potassium channel only has one (gate n).
50
Q
  • Gate m (the activation gate) is normally closed, and ____ when the cell starts to get more
    _____.
  • Gate h (the deactivation gate) is normally open, and swings ____ when the cells gets too
    _____.
  • Gate n is normally closed, but slowly _____ when the cell is _____ (very positive).
A 
opens
positive
shut
positive
opens
depolarized
51
Q
  • Voltage-gated sodium channels exist in one of three states:
A

1.) Deactivated (closed) - at rest, channels are deactivated. The m gate is closed, and does not let
sodium ions through.
2.) Activated (open) - when a current passes through and changes the voltage difference across a
membrane, the channel will activate and the m gate will open.
3.) Inactivated (closed) - as the neuron depolarizes, the h gate swings shut and blocks sodium ions
from entering the cell.
-Voltage-gated potassium channels are either open or closed.

52
Q

What triggering event occurs that depolarizes the cell body? (2)

A
  • A triggering event occurs that depolarizes the cell body—> signal comes from other cells connecting to the neuron —> causes positively charged ions to flow into the cell body.
  • Positive ions still flow into the cell to depolarize it, but these ions pass through channels that open when a specific chemical—> neurotransmitter, binds to the channel and tells it to open.
53
Q
  • Neurotransmitters released by cells near the _____ —>as the end result of their own action
    potential!
  • incoming ions bring the membrane potential closer to 0, which is known as ______.
A

dendrites

depolarization

54
Q

What happens if an object is polar?

A
  • An object is polar—> if there is some difference between more negative and more positive
    areas—>As positive ions flow into the negative cell, that difference, and thus the cell’s polarity —> decrease.
55
Q
  • If the cell body gets positive enough that it can trigger the ____-____ sodium channels
    found in the axon—>the action potential will be sent.
A

voltage-gated

56
Q

What happens during depolarisation? (5)

A
  1. Depolarization - makes the cell less polar (membrane potential gets smaller as ions quickly
    begin to equalize the concentration gradients) .
  2. Voltage-gated sodium channels at the part of the axon closest to the cell body activate, thanks
    to the recently depolarized cell body
  3. lets positively charged sodium ions flow into the negatively charged axon—> depolarize the
    surrounding axon
  4. think of the channels opening like dominoes falling down - once one channel opens and lets
    positive ions in, it sets the stage for the channels down the axon to do the same thing
  5. stage is known as depolarization—>the neuron actually swings past equilibrium and becomes
    positively charged as the action potential passes through
57
Q

What happens during repolarisation? (4)

A
  1. Repolarization - brings the cell back to resting potential.
  2. The inactivation gates of the sodium channels close—>stopping the inward rush of positive
    ions
  3. At the same time—> potassium channels open—> much more potassium inside the cell than
    out—>so when these channels open, more potassium exits than comes in.
  4. This means the cell loses positively charged ions—>returns back toward its resting state
58
Q

What happens during hyperpolarization? (4)

A
  1. Hyperpolarization - makes the cell more negative than its typical resting membrane potential.
  2. As the action potential passes through—>potassium channels stay open longer—>continue to
    let positive ions exit the neuron.
  3. cell temporarily hyperpolarizes/gets even more negative than its resting state.
  4. As the potassium channels close—>sodium-potassium pump works to reestablish the resting
    state
59
Q

What basis do action potentials work on?

A

Action potentials work on an all-or-none basis. This means that an action potential is either triggered, or it isn’t – like flipping a switch. A neuron will always send

60
Q

There is a maximum frequency at which a single neuron can send action potentials, and this is determined by its ____ _____.

A

refractory periods

61
Q

What is absolute refractory potential?

A
  • Absolute refractory period: during this time it is absolutely impossible to send another action potential.
62
Q

What does the inactivation (h) gates of sodium channels lead to? (2)

A
  • The inactivation (h) gates of the sodium channels lock shut for a time, and make it so no sodium will pass through.
  • No sodium means no depolarization—> no action potential
63
Q

What do absolute refractory periods help direct?

A
  • Absolute refractory periods help direct the action potential down the axon, because only channels further downstream can open and let in depolarizing ions.
64
Q

What happens during the relative refractory period? (2)

A
  • Relative refractory period: during this time, it is really hard to send an action potential —> the period after the absolute refractory period, when the h gates are open again —> the cell is still hyperpolarized after sending an action potential.
  • It would take even more positive ions than usual to reach the appropriate depolarization potential than usual—> the initial triggering event would have to be bigger than normal in order to send more action potentials along.
65
Q

What do relative refractory periods helo us figure out? (3)

A
  • Relative refractory periods can help us figure how intense a stimulus is - cells in your retina will send signals faster in bright light than in dim light, because the trigger is stronger.
  • Refractory periods also give the neuron some time to replenish the packets of neurotransmitter found at the axon terminal—>so that it can keep passing the message along.
  • While it is still possible to completely exhaust the neuron’s supply of neurotransmitter by continuous firing—> refractory periods help the cell last a little longer.
66
Q

What are the benefits of an axon with a larger diameter? (3)

A
  • Larger diameter —> axons have a higher conduction velocity—> able to send signals faster because there is less resistance facing the ion flow
  • A lot of ions flooding into the axon—> the more space they have to travel, the more likely they will be able to keep going in the right direction
  • An axon is still part of the cell—> it’s full of cytoplasmic proteins, vesicles, etc—> The larger the
    diameter of the axon—>the less likely the incoming ions will run into something that could bounce
    them back
67
Q

The action potential depends on positive ions continually traveling away from the cell body, and that
is much easier in a _____ axon.

A

larger

68
Q

What complications would arise with axons with smaller diameters?

A
  • A smaller axon—> found in nerves that conduct pain, would make it much harder for ions to move
    down the cell because they would keep bumping into other molecules.
69
Q

What is the second way to speed up a signal in an axon?

A

-The second way to speed up a signal in an axon—>insulate it with myelin—>a fatty substance

70
Q
  • PNS ____ is found in Schwann cell membranes

- CNS—> __________ are responsible for insulation, these cells wrap around the axon—> creating several layers insulation

A

myelin

oligodendrocytes

71
Q

How does myelin help preserve the action potential?

A
  • action potential travels down the membrane, sometimes ions are lost as they cross the membrane and exit the cell—> The presence of myelin makes this escape impossible—> helps to preserve the action potential
72
Q

What does the myelin sheath decrease?

A

-A myelin sheath—>decreases the capacitance of the neuron in the area it covers

73
Q

Hwo does a myelin sheath decrease the capacitance of the neuron in the area it covers? (7)

A
  1. A myelin sheath —> decreases the capacitance of the neuron in the area it covers
  2. Since the neuron is at a negative membrane potential, it’s got a lot of agitated negative ions that don’t have a positive ion nearby to balance them out
  3. Like charges repel —> negative ions spread out as far from each other —> to the very outer edges of the axon near the membrane
  4. This then attracts positive ions outside the cell to the membrane as well > helps the ions calm down
  5. end up with thin layers of negative ions inside of the cell membrane and positive ions outside the cell membrane —> where myelin wraps around the cell—> provides a thick layer between the inside and the outside of the cell
  6. Fewer negative ions gather at those points because it is further away from the positive charges
  7. there are parts of the axon that are still negative —> contain fewer negative ions —> as the action potential comes rushing by —> it is easier to depolarize the areas that are sheathed, because there are fewer negative ions to counteract.
74
Q

What do the Nodes of Ranvier help with?

A

Nodes of Ranvier—> brimming with voltage-gated ion channels to help push the signal along.

75
Q
  • unsheathed—> ____ ions gather to help balance out the _____ ions
  • When the channels open—>positive ions swarm inside—>looks like the signal jumps from node to node—>process known as ____ _____.
A

positive
negative ions
saltatory conduction

76
Q

What does saltate mean?

A

-To saltate means to move by leaps or jumps—>like the action potential seems to do down the axon.

77
Q

What is the function of the internal current?

A
  • In reality, the internal current of flowing positive ions is activating the opening of the gates down the axon
78
Q

What is Sporadic amyotrophic lateral sclerosis (sALS)? (3)

A
  • Progressive neurodegenerative disease that affect nerve cells in brain and spinal cord
  • “Sporadic”- cause of disease unknown
  • Motor neurons die- ability of brain to initiate and control muscle movement lost
79
Q

What do Microscopic changes of sALS include? (2)

A
  • neuronal and axon loss
  • loss of myelinated axons in lateral and anterior columns of spinal cord and decrease in size of anterior horn of spinal cord

MBBCh 1- APES1001A (38 decks)

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