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Systems > unit 3: Neurophysiology and neural communication > Flashcards

unit 3: Neurophysiology and neural communication Flashcards

1
Q

Chemical gradient

A

responsible for the movement of particles from one side to other of a semipermeable membrane. It depends on the final concentration of each particle on both sides

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2
Q

Electrical gradient:

A

responsible for the movement of charged particles from one side to the other of a semipermeable membrane. It depends on the final balance of electrical charges in each compartment

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3
Q

Electrochemical gradient:

A

Responsible for the movement of particles from one side to the other of a semipermeable membrane. It depends on the final balance of charges and concentration, on both compartments

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4
Q

ionic channels

A

Membrane proteins that allow the passing of ions (NA+, K+, Cl, etc) from one side of the membrane to the other

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5
Q

2 types of ionic channels

A

two types depending on the conformation of the inner pore

  1. Passive channels: they are always open
  2. Gated channels:
    They can be either open or closed
    Gating depends on the type of channel
    Ligand-gated channels
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6
Q

Semipermeable membrane

A

only allows the passing of certain molecules

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7
Q

Selective permeability
Depends on

A

The electrochemical gradient of ions
The channels present on the membrane
The open or closed state of those channels

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8
Q

excitable cells

A

can change their membrane potential in response to stimuli

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9
Q

how do ionic movement across the membrane happen - 3

A

Chemical or concentration gradients elicit ionic movement across the membrane. This induces an uneven charge distribution across the membrane, generating also an electrical gradient

Chemical gradient + electrical gradient = electrochemical gradient

The electrochemical gradient generates an electrical potential that is called resting membrane potential

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10
Q

Equilibrium potential:

A

Potassium moves outwards according to its concentration gradient but this is against its electrical gradient (is + and goes to the positive side)

K+ equilibrium potential: potential value when the concentration and electrical gradients are even

Sodium moves inwards according to its concentration gradient, and this is also down its electrical gradient (is + and goes to the negative side)

Na+ equilibrium potential: potential value when the concentration and electrical gradients are even

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11
Q

Characteristics of the action potential:

A

Excitable cells (neurons, muscle cells) are able to modify their resting membrane potential
These cells can generate an action potential in response to a stimulus that reaches a certain threshold
Threshold: voltage limit that has to be reached in the membrane to trigger an action potential

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12
Q

what is action potential

A

The action potential is a depolarizing voltage change (potential reaches more positive values than -70mV) but:
* Not all voltage changes are depolarizing
* Not all depolarizations are action potentials

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13
Q

how can potential change happen

A

The potential changes due to changes in the permeability of the membrane: gated channels open altering the basal permeability

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14
Q

types of potential changes

A

Depolarization: voltage change that turns the potential more positive than -70mV

Hyperpolarization: voltage change that turns the potential more negative than -70mV

Repolarization: voltage change that returns the potential to resting values -70mV

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15
Q

voltage gated channels

A
  • located on the axon
  • only open when a neuron needs to propogate info to the following cell (neuron or not)
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16
Q

“All or none” principle: - 2

A
  • Once the threshold is reached, the shape, amplitude and duration of action potentials is always the same, disregarding the intensity of the stimulus. Stronger stimuli increase the triggering frequency, not the amplitude, that is always 100 mV
  • The amplitude does not diminish with the propagation
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17
Q

label

A
  1. Resting membrane potential
  2. Depolarizing stimulus (effect of the neurotransmitters received by the dendrites, enough depolarization to reach the threshold)
  3. At the threshold (-55 mV) voltage-gated Na+ channels open increase permeability
  4. Rapid Na+ entry (down electrochemical gradient) depolarize the neuron up to + 30mV
  5. Voltage gated Na+ channels close and voltage-gated K+ channels open. K+ moves outwards down its chemical gradient. Repolarization begins
  6. K+ moves outwards looking for its equilibrium potential (-90mV)
  7. When the potential reaches the resting value (-70 mV), K+ channels close but slowly, so K+ can still move out of the neuron, driving the hyperpolarization
  8. Slow voltage-gated K+ channels are already closed, so less K+ goes out of the neuron. The Na+/K+ pump drives a second repolarization
  9. The neuron recovers its resting permeability (only non-gated channels are open now) and the Na+/K+ pump restores the resting membrane potential
18
Q

refractory period:

A
  • minimum period of time that prevents the generation of a second action potential before the first one has finished
  • When an area of the membrane is triggering an action potential, it becomes refractory: unable to respond to a second stimulus
19
Q

2 sub periods within the refractory period

A
  1. Absolute: (blue)
    a. Voltage gated NA+ channels are closed and inactive (unable to open)
    b. There can’t be a depolarization so the neuron cant trigger a second action potential
  2. Relative: (orange)
    a. Due to continuous outflow of K+ during hyperpolarization.
    b. Voltage gated Na+ channels are closed but can be opened
    c. The neuron can trigger a second action potential if the stimulus is stronger than the first one (enough to reach the threshold, that is now farther)
20
Q

propagation or conduction

A

After an action potential is triggered in the axon hillock, it has to travel along the axon until it reaches the axon terminal, where the neurotransmitter vesicles are stored

21
Q

Propagation of the electrical signal:

A

only happens in one direction (from axon hillock to axon terminal) thanks to the refractory period
Propagation speed is directly related to:
* Axon diameter. More diameter higher speed
* Myelination - coats axon to speed up the propagation of the action potential

22
Q

myelin
- what it is
- produced where
- the different cells that produce myelin and why

A
  • coats axon to speed up the propagation of the action potential
  • produced by certain glial cells
  • Oligodendrocytes (CNS) prudces myelin for : the axons in the white matter - Each oligodendrocyte coats several axons
  • schwann cells (pns) produces myelin: for motor axons - Each schwann cells coats only one axon
23
Q

unmyelinated axons

A

he action potential has to regenerate in each portion of the axon, as the sodium-gated channels are equally distributed along. Slower propagation speed

The propagation follows one direction, down to the axon terminal, because the axon membrane proximal to the soma remains in refractory period, so depolarization can only occur distally

24
Q

myelinated axons:

A

Myelin has insulating properties that prevent current leaks. Thus, where a myelin sheath is placed, the action potential can move from one naked area (node of ranvier) to the next without losing properties. Sodium-gated channels concentrated on these nodes to reinforce the depolarization and make the signal “jump” to the next node. This increases the propagation speed, as less action potentials are needed to reach the action

25
Q

Definition of synapse

A

communication mechanism between a neuron and a target cell. It involves and action potential in a neuron releasing neurotransmitters into the synaptic space, reaching the target cell and inducing a response
When a synapse occurs between two neurons, the neuron triggering the action potential is called presynaptic and the neuron receiving the neurotransmitters is called postsynaptic.

26
Q

types of synapses:

A
  1. electrical: cells are physically coupled
    * Cells are electrically coupled through GAP junctions, pores that allow the flux of ions directly between cytoplasms
    * Occurs in:
    a. Cardiac cells
    b. Smooth muscles

chemical: cell do not touch each other
* Abundant in the CNS, where neurons do not touch each other or target cells
* A presynaptic neuron releases a chemical messenger (neurotransmitter)
* The NT binds specific receptors located on the target cell, inducing a response (changes in membrane potential when it is a postsynaptic neuron)
* Unidirectional

27
Q

Chemical synapse mechanism: 2

A
  • The presynaptic cell is always a neuron
  • The postsynaptic cell is either a neuron or other target cell
28
Q

depolarization and hyperpolarization

A

Binding of the NT to its receptor may induce changes in the membrane potential of the postsynaptic neuron

29
Q

when are NT vesicles released

A

When the action potential of a presynaptic neuron reaches the axon terminal, exocytosis is triggered by calcium entrance

Nt cross the synaptic space until they reach the postsynaptic membrane with their receptors (Rc)

30
Q

Outcome of the synaptic transmission:

A

Binding of the NT to its receptor (ligand-gated channel) changes the basal permeability and induces a voltage change in the postsynaptic neuron: unitary postsynaptic potential

31
Q

Postsynaptic potentials can be:

A
  1. Excitatory postsynaptic potential (EPSP) : the NT binds a receptor that is a Na+ channel, causing depolarization. NT such as glutamate or acetylcholine produce EPSP
  2. Inhibitory postsynaptic potential (IPSP): the NT binds a receptor that is either a K+ or a CL- channel and induces hyperpolarization. The main inhibitory NT is GABA

The same postsynaptic neuron will receive EPSP and IPSP through its dendrites as several NT can be released at the same time over it. The soma integrates these unitary changes so that if the intensity of EPSP overcomes IPSPs and is enough to reach the threshold (-55mV), the postsynaptic neuron will trigger an action potential, becoming a presynaptic neuron for the following synapse

32
Q

what needs to happen after the tramssion is over

A

It is important to completely remove the NT from the synaptic cleft once the transmission is over (When the action potential at the axon terminal finishes). Three mechanisms:
1. Diffusion of the NT to adjacent flail cells or blood vessels
2. Enzymatic degradation of the NT in the synaptic cleft
3. Re-uptake into the presynaptic terminal (active transport)

At least 3 mechanisms are needed to ensure rapid removal, and normally all three can be found at the synapses in CNS

33
Q

Signal integration: neural circuits

A

Linear circuits: chain-like. A single neuron synapses with another one, and this one with another one
But a presynaptic neuron can contact with several postsynaptic neurons

34
Q

types of linear circuits

A

Covering circuits: many incoming fibers send impulses to the same neuron (Spatial summation)
Goal: integration of information from different areas (Sensory info coming into the spinal cord

Diverging circuits: one incoming fiber triggers responses in increasing numbers of neurons
Goal: amplify the signal (motor control / neurons of the motor cortex

35
Q

classical neurotransmitters: 5

A
  1. acetylcholine
  2. cetacholamines (dopamine, adrenaline, noradrenaline)
  3. serotonin
  4. histamine
  5. amino acids
36
Q

acetylcholine

A

NT from the neuromuscular junction
Synthesized by all the neurons of the spinal cord
Specific roles in both CNS and PNS

37
Q

Catecholamines (dopamine, adrenaline, noradrenaline):

A
  • Synthesized in areas of the NS that participate in movement, mood, attention, visceral function
  • They can act as neurohormones and travel in the blood flow
38
Q

seratonin

A
  • Widely distributed in the CNS
  • Participates in processes such as the sleep-wake cycle, emotions, satiety, circadian rhythms
39
Q

Histamine

A

Produced by the hypothalamus
Distributed to all the CNS
Participates in attention, analgesia, satiety, neuromodulator

40
Q

Amino Acids:

A

Participate in most of the synapses within the CNS
Glutamate (Glu): excitatory amino acids (EPPs)
GABA and Glycine (Gly): inhibitory amino acids (IPPs)

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