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Physiology of Cells 2002 > Lecture 11: Action Potential Generation. > Flashcards

Lecture 11: Action Potential Generation. Flashcards

1
Q

Understanding Electrical Conductivity in the Heart:

A
  • Within the atria and ventricles MYOCARDIAL CELLS areCONNECTED BY GAP JUNCTIONS .
  • Gap junctions allow the CARDIAC ACTION POTENTIAL to PROPAGATE from cell to cell through a LOW RESISTANCE PATHWAY..
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1
Q

What are GAP JUNCTIONS?
ROLE?
FOUND?
FORMED FROM? = 5

A

1 ➢ Gap junctions are PORES between cells.

2 ➢ Allow small polar molecules to diffuse directly between cells.

3 ➢ Common in Heart, gastric smooth muscle.

4 ➢ Formed from transmembrane protein CONNEXON

5 ➢ Conenexon binds connexon of next cell forming tube.

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2
Q

Gap Junctions – pacemaker smooth muscle cell process

A
  1. Sponatenous action potential induced by pacemaker potential
  2. Action potential spread to nonpacemaker cell
  3. gap junction
  4. Non pacemaker smooth muscle cell
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3
Q

Initiation of Action Potentials = 5

A
  1. Action Potentials can start at pacemaker cells
  • e.g. in the heart or intestine
  1. Potential can spread from cell to cell by GAP JUNCTIONS
    - e.g. cardiac and smooth muscle cells
  2. Electrical synapses of nerves are very rare
  3. Action potential in most tissues started by RECEPTOR POTENTIAL OR NEUROTRANSMITTERS.
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4
Q

INITIATION OF ACTION POTENTIALS IN …. Receptor potential specialised afferent ending

A

STIMULUS

  1. Sensory receptor (modified ending of afferent neuron)

2.Stimulus sensitive nonspecific cation channel

  1. Na+ enters through VOLTAGE gated Na+ channel
  2. Action Potential
  3. SUMMARY = DEPOLARISE afferent nerve ending – local current flow from receptor potential triggers action potential by opening voltage gated Na+ channels.
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5
Q

INITIATION OF ACTION POTENTIALS IN …. Receptor potential in SEPARATE receptor cell.

A

SUMMARY : Neurotransmitter binds to ligand-gated ion channels causing depolarization which opens voltage gated Na+ channels triggering an action potential.

  1. STIMULUS (Na+ entry depolarises)
  2. Separate receptor cell
  3. Stimulus sensitive nonspecific cation channel.
  4. Ca+2 enters through voltage gated Ca+2 channel
  5. Neurotransmitter via vesicle to afferent neuron via passing through cleft palate.
  6. Chemically gated receptor-channel
  7. Na+ goes inside the post synaptic neuron
  8. Action potential
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6
Q
  • Action potentials: 3
A

carry neural signals along the axon.

  • All the same size and actively regenerated.
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7
Q

Receptor potentials: 3

A
  • generated in sensory cells in response to a stimulus.
  • Stretch gated ion channels in touch receptors.

Graded potentials

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8
Q

synaptic potentials: 3

A
  • are produced by neurotransmission.
  • Binding of a neurotransmitter open ligand gated ion channels
  • Graded potentials
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9
Q

Stimuli vs Permeability vs Potential

A

Stimuli open non-selective cation channels Receptor potential is graded

INCREASE stimulus - INCREASE permeability - INCREASE potential

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10
Q

Receptor Potential, How is is graded?

A

graded:
- in amplitude
- and duration,
- proportional to the stimulus.

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11
Q

what is integrative action?

A

transforms receptor potential to action potential.

—- Coded into frequency of AP firing.

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12
Q

Action potential is a …..

A

all- or-none response.

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13
Q

Understanding Output signal:

A

transmitter release from synaptic terminal.

Amount released is determined by the AP’s frequency.

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14
Q

Slide 10: Look at the various ways they are shown/ graphed.

A
  • Receptor potential
  • integrative action
  • action potential
  • Output signal
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15
Q

Diverse Neural Behaviour: Action potential,

Adaptation vs Rhythmic bursts

SLIDE 11

A
  1. Action potentials firing at steady frequency throughout the stimulus
  2. Adaptation: rapid firing frequency that slows over time
  3. Rhythmic Bursts:
    rapid burst of firing followed by brief pause
  4. Response of sensory receptor to sustained stimulation
16
Q

Action Potential Initiation - sensory nerve ending

= 3

A
  1. Axon hillock or sensory nerve ending
  2. Spike Generating Zone or Trigger Zone
  3. High density of voltage gated Na+ and K+ channels

eg. Pyramidal cell
- spike-initiation zone: axon hillock

Sensory neuron
- initiation zone: sensory nerve ending

MEMBRANE WITH HIGHEST DENSITY OF VOLTAGE-GATED SODIUM CHANNELS.

17
Q

Understanding Passive Potential decay….2

A
  1. Receptor & synaptic potentials decays away from source (length constant)
  2. Some neurons have voltage gated channels in dendrites to “boost” travelling synaptic potential
18
Q

Understanding Synaptic Potentials …3

A
  1. High density voltage gated Na+ and K+ channels
  2. Lower threshold for action potential generation
  3. An action potential is generated where the amplitude of the synaptic potential crosses the threshold
19
Q

understanding Excitatory Post-Synaptic Potentials
= 3

A
  1. Excitatory post-synaptic potentials – EPSP
  2. e.g. ACh-gated N-receptor or glutamate-gated ion channels
  3. Increase Na+ permeability
20
Q

UNDERSTANDING Skeletal Muscle Nicotinic Receptors = 4

A
  1. In SKELETAL muscle ACh stimulates N-cholinergic receptors.
  2. Nicotinic receptors are LIGAND GATED cation channels.
  3. Produces a motor endplate potential (like an EPSP).
  4. DEPOLARISATION open Voltage gated sodium channels
21
Q

UNDERSTANDING Inhibitory Post-Synaptic Potentials = 2

A
  1. Inhibitory post-synaptic potentials – IPSP
  2. e.g. Glycine-gated or GABA-gated ion channels Increase Cl- permeability
22
Q

Synaptic Potentials: define

A

Synaptic potentials occur when a neuron signals another neuron

23
Q

Post-synaptic potentials: 3

A

are the change in voltage produced in the post synaptic cell.

  • EPSP are excitatory post synaptic potentials.
  • IPSP are inhibitory post synaptic potentials
24
Q

Junction potentials: 5

A
  • are just the same as synaptic potentials but at a junction.
  1. Neuron to neuron connections are SYNAPSES
  2. Neuron to muscle or gland connections are called JUNCTIONS
  3. Neuron to skeletal muscle is called a MOTOR END PLATE
  4. END PLATE POTENTIALS in skeletal muscle
25
Q

Summation of Synaptic Potentials:

SPATIAL SUMMATION VS TEMPORAL SUMMATION.

A
  1. Presynaptic action potential triggers a small EPSP in the postsynaptic neuron
  2. Spatial summation:
    — 2 or more presynaptic inputs active at same time, individual EPSP’s add together
  3. Temporal summation:
    —Same presynaptic fiber fires AP’s in quick succession, individual EPSP’s add together
26
Q

UNDERSTANDING Summation of Synaptic Potentials

A
  1. Summation of synaptic potentials can drive membrane potential to threshold (action potential)
  2. Synaptic potentials have long time course and summate readily
  3. Action potentials cannot summate
27
Q

Summation of Synaptic Potentials:

Integration of EPSPs and IPSPs = 2

A
  1. EXCITATORY INPUT causes an inward postsynaptic current that spreads to the soma and recorded as an EPSP
  2. INHIBITORY SYNAPSE allows depolarizing current to leak out before it reaches the soma
28
Q

Features of Cell Potentials:

Receptor Potential

A

size: SMALL (0.1 -10mV)

duration: Moderate (5-100ms)

Variability: Graded

Direction: Hyper- or depolarising

Propagation: PASSIVE

Typical channel: Stretch gated or specialised sensor

Origin: Sensory cell response to stimulation.

29
Q

Features of CELL POTENTIALS:

SYNAPTIC POTENTIAL

A

size: SMALL (0.1 -10mV)

duration: WIDE RANGE (5ms - 20min)

Variability: Graded

Direction: Hyper- or depolarising

Propagation: PASSIVE

Typical channel: LIGAND GATED

Origin: Post synaptic cell response to neurotransmission

30
Q
A

size: Large (70-110mV)

duration: Brief (1-10ms)

Variability: ALONE OR NONE

Direction: depolarising

Propagation: ACTIVE

Typical channel: VOLTAGE GATED

Origin: Axon hillock or spike generating zone, response to depolarization

31
Q

Functional Circuit Example

A

Stretch Reflex pathway

  • A receptor – muscle spindle
  • An afferent fibre–muscle spindle afferent
  • An integration centre – lamina IX of spinal cord
  • An efferent fibre – α-motoneurones
  • An effector – muscle
32
Q

Summary: 5

A
  1. PACEMAKER cells, in gut or heart, can cause depolarisation and action potentials.
  2. Action potentials can spread from cell to cell through GAP JUNCTIONS, e.g. In the heart
  3. Activation of a receptor produces RECEPTOR POTENTIALS, neurotransmitters produce POSTSYNAPTIC (or post junctional) potentials
  4. SUMMATION of postsynaptic potentials at the SPIKE GENERATING or TRIGGER ZONE causes action potentials to form.
  5. Inhibitory transmitters produce INHIBITORY POST SYNAPTIC POTENTIALS potentials that hyperpolarize the neuron suppressing AP formation.

Physiology of Cells 2002 (24 decks)

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