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Physiology > Unit 4: Principles of Neural and Hormonal Communication > Flashcards

Unit 4: Principles of Neural and Hormonal Communication Flashcards

1
Q

What is polarization?

A

Any time the membrane potential is different than 0mV, in the positive or negative direction.

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2
Q

What is depolarization?

A

When the membrane potential inside the cell becomes more positive.

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3
Q

What is repolarization?

A

When the membrane potential drops back to resting membrane potential (movement in the neg. direction)

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4
Q

What is hyperpolarization?

A

When the membrane potential jumps past resting membrane potential (becoming more negative)

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5
Q

What are graded potentials?

A

Local changes in membrane potential that occur in varying degrees or strengths.
*usually due to ion changes in selective regions of the cell that become excitable. This specialized region is called the Active Area.

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6
Q

How is current lost throughout the membrane?

A
  • Charge- carrying ions leak through un-insulated parts of the membrane through open leak channels.
  • Explains why graded potentials are only beneficial over short distances.
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7
Q

What are Action Potentials?

A
  • Brief, large changes in membrane potential where the inside of the cell becomes more positive than the outside. (depolarization of the membrane)
  • occur in a non-decremental fashion.
  • Changes in ion permeability through voltage-gated ion channels.
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8
Q

Can graded potentials turn into action potentials?

A

Yes! The depolarization must go from resting potential to the Threshold Potential (-55/-50mV), in which a HUGE upward deflection of +30mV occurs (depolarization).
–>Hyperpolarization can occur, around -80mV, as the cell reaches back to its resting membrane potential of -70mV.

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9
Q

What is the Threshold Potential, before the cell becomes very depolarized (positive) ?

A
  • 55 to -50 mV

* All or Nothing type response.

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10
Q

What is Overshoot?

A

The portion of the action potential where the membrane lies within 0mV–> 30 mV.

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11
Q

What are sodium activation and inactivation gates?

A

Activation gates operate like a hinge.
Inactivation gates operate like a ball and chain.
*Both must be open for the passage of Na+ ions.
The inactivation gate must always be open, but the activation gate is capable of opening.

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12
Q

What is the potassium gate?

A

K+ only has 1 gate in comparison to Na+’s 3 gates.

*Additional to leak channel gates

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13
Q

What is the rising phase of an action potential?

A

From resting potential to +30mV

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14
Q

What is the falling phase of an action potential?

A

From +30mV back to -70mV.

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15
Q

What three parts make up a neuron?

A

A cell body, a dendrite and an axon.

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16
Q

What is the function of dendrites?

A

-receive electrical impulses from other cells.

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17
Q

What is the function of the cell body?

A

Contains nucleus and other organelles.

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18
Q

What is the function of the axon?

A

To conduct electrical signals along the neuron.

-Axons often branch off into collaterals.

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19
Q

What is the most easily excitable portion of the axon?

A

The Axon Hillock

  • Can trigger action potentials from graded potentials if the impulse is strong enough.
  • Impulses are sent to axon terminals where they influence surrounding cells.
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20
Q

Where are action potentials stimulated?

A

In areas of high abundance Na+ channels that can stimulate changes in membrane potential (depolarization)

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21
Q

What is Contiguous Conduction?

A
  • A current, active action potential spreads down the length of an axon, which depolarizes inactive areas by local current flow.
  • ->Brings inactive areas to threshold, and allows old areas to return to resting potential.
  • Occurs until the end of the axon.
  • Unmyelinated fibres**
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22
Q

What is the Refractory Period?

A
  • A new action potential cannot be initiated by normal events in a region where an action potential just occurred.
  • Ensures one-way propagation of impulses.
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23
Q

What is the Absolute Refractory Period?

A

-One part of the membrane in undergoing potential, and no other part of the membrane can be stimulated- regardless of the strength.

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24
Q

What is the Relative Refractory Period?

A

-A second action potential is produced by a triggering event considerably stronger than usual.

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25
Q

What is the All-or-Nothing Law?

A

-An action potential spreads non-decrementally throughout the cell at maximum, or not at all.

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26
Q

Does a stronger stimulus produce a larger action potential?

A

No, it only produces more frequent action potentials.

27
Q

What effects the speed of an action potential?

A
  1. Myelination

2. The diameter of the fibre.

28
Q

What is Saltatory Conduction?

A

The spread of action potentials down myelinated fibres; spreads impulses faster.
*Jumps from node to node

29
Q

Myelin properties?

A
  • composed of lipids

- great insulator (prevents leaks)

30
Q

What are Oligodendrocytes?

A

Myelin cells in the brain and spinal cord

31
Q

What are Shwann Cells?

A

Myelin cells in the nerves of the PNS

32
Q

What are the Nodes of Ranvier?

A

Spaces in between myelinated sections of the axon where current flows.
*Contain an abundance of Na+ channels.

33
Q

True or False: Larger axons produce more frequent action potentials?

A

True.

34
Q

True or False: Cut axons in the CNS CAN regenerate, and cut axons in the PNS can’t.

A

False. This is reversed.

35
Q

How do PNS nerve cells regenerate?

A

If the axon is cut in the nerves, the portion of the axon furthest from the cell body degenerates, and the surrounding Shwann cells phagocytize the debris.
–A regeneration tube guides new nerve fibres to form at their proper destination.

36
Q

What is a neural synapse?

A

-Involves the junction between one neuronal terminal (pre-synaptic neuron) and the dendrites of another neuron (post-synaptic neuron)

37
Q

What are the 5 critical steps of a synapse?

A
  1. An action potential of the pre-synaptic neuron is propagated to the axon terminal. This leads to the opening of Ca2+ ions.
  2. Ca2+ flows into the synaptic knob through open channels.
  3. Ca2+ releases a neurotransmitter into the synaptic cleft, done by exocytosis.
  4. The neurotransmitter binds with specific protein receptor sites on the subsynaptic membrane.
  5. Binding triggers the opening of ion channels, altering the ion permeability of the subsynaptic membrane.
38
Q

How many neurotransmitters can individual neurons release?

A

1

39
Q

What is an Excitatory Post Synaptic Potential (EPSP)

A

-When non-specific cation channels open, allow for an influx of Na and K into the membrane. This allows for depolarization of the membrane, bringing it closer to threshold AKA closer to excitation.

40
Q

What is an Inhibitory Post Synaptic Potential (IPSP)

A

When potassium or chloride ions enter the cell and cause hyperpolarization (more neg.) , this leads the cell further away from excitation (further than resting potential)

41
Q

What is a synaptic delay?

A
  • Conversion of an action potential in the presynaptic neuron to an electrical signal in the postsynaptic neuron by chemical means TAKES TIME!
  • ->0.5-1.0 mseconds.
  • The more complex, the larger the delay.
42
Q

What are some different neurotransmitters released at synapses?

A

EPSP= glutamate
IPSP= GABA
*continues as long as the neurotransmitter is bound

43
Q

What is the Grand Post Synaptic Potential?

A
  • The total sum of EPSP’s and IPSP’s occurring at approx. the same time.
  • Determines if the post synaptic cell will reach threshold!
44
Q

What is Temporal Summation?

A

-If an excitatory post synaptic potential is stimulated a second time before the first time has died off, the second EPSP adds to the first one, which many bring the post-synaptic cell to threshold.

45
Q

What is Spatical Summation?

A
  • The summation of EPSP’s originating simultaneously from several different pre-synaptic inputs.
  • Adding inputs to bring the post-synaptic cell to threshold.
46
Q

Can IPSP’s and EPSP’s cancel one another out?

A

Yes, depending on relative magnitude.

47
Q

What are Classical Neurotransmitters?

A
  • Small, rapid acting molecules that typically trigger the opening of specific ion channels
  • ->Bring about a change in potential of the post synaptic neuron.
  • Synthesized & packaged in synaptic vesicles in the cytosol of the axon terminal.
48
Q

What are Neuropeptides?

A
  • Large molecules of amino acids.
  • Synthesized in neuronal cell body’s in the ER and golgi.
  • Moved by axonal transport.
  • *Can be co-secreted with neurotransmitters.
49
Q

What are Neuromodulators?

A

-Chemical messengers that modulate the action at the synapse.

50
Q

What is Presynaptic Inhibition?

A
  • Refers to a decrease of neurotransmitter released at a central synapse.
  • If release of neurotransmitter is enhanced, the effect is called presynaptic facilitation.
51
Q

What is Converging input?

A

-A single cell is influenced by thousands of other cells.

52
Q

What is Diverging Input?

A

-Refers to the branching of axon terminals so that a single cell synapses with/ influences other post-synaptic neurons.

53
Q

What are Paracrines?

A
  • Effect only cells in the immediate environment.
  • Short distances/ local areas
  • distributed by simple diffusion- inactivated by enzymes
54
Q

What are Neurotransmitters?

A
  • Short range chemical messengers released in response to action potentials.
  • ->Act locally on adjoining target cells.
55
Q

What are Hormones?

A

LONG RANGE.

  • Specifically secrete into the blood by endocrine glands in response to appropriate signals.
  • Only target cells can bind hormones.
56
Q

What are Neurohormones?

A
  • Hormones released into the blood by neurosecretory neurons.
  • Only effect target cells.
57
Q

Signal Transduction Mechanisms?

A
  • Binding of appropriate chemical messengers triggers a sequence of intracellular events that ultimately controls cellular activity.
  • ->Can operate by 2 means:
    1. Activating a channel (FAST SYNAPSES)
    2. Activating secondary messengers (SLOW SYNAPSES)
58
Q

What is Endocrinology?

A

-The study of homeostatic chemical adjustments and other activities accomplished by hormones, which are secreted in the blood by endocrine glands.

59
Q

What are Hydrophilic Hormones?

A
  • Highly water soluble- low lipid soluble
  • Chains of peptides or proteins
    ex. include epinepherine and norepinepherine
  • Transported and dissolved in blood plasma.

Function by either:

  1. Affecting ion permeability of channels
  2. Activating secondary messengers.
60
Q

What are Lipophilic Hormones?

A
  • High lipid solubility
  • Thyroid/ steroid hormones
  • derived from cholesterol
  • Can’t dissolve into watery plasma
  • *instead, bind to plasma proteins and circulate the blood.

Function by:
Activating specific genes in the target cell, which causes the formation of new intracellular proteins–> produces hormones desired effect.

61
Q

How do hydrophilic hormones pass through the bilayer?

A

-Because they are water loving, they bind with specific receptors located on the outer plasma membrane surface of the target cells.

62
Q

How do Lipophilic hormones pass through the lipid bilayer?

A

Easily, they pass right through their target cell and bind with receptors inside the cell.

63
Q

How are specific genes activated in Lipophilic hormones?

A

One the hormone is internalized and bound to its receptor, the hormone complex binds with DNA at a specific attachment site called the Hormone Response Element (HRE), which turns on the gene in the target cell.

Physiology (12 decks)

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