Communication between excitable cells Flashcards

1
Q

How does the diameter of an axon affect AP propagation?

A

Increase in diameter increase speed

Increases in axon diameter decreases axoplasm resistance, allowing local currents to flow more easily so speed increases.

For unmyleinated axons: V is proportional to the root of the diameter

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2
Q

How does myelination of axons affect AP propagation?

A

Myelination increases speed

Myelinated regions of axon membrane lack v-g ion channels forcing local currents to ‘jump’ from node of ranvier to the next - ‘Saltatory Conduction’.

Myelination increases axon diameter, increasing the internodal distance so ‘jumps’ are longer thus speed increases.

For myelinated axons: V is proportional to the diameter

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3
Q

How does temperature influence AP propagation?

A

As temperature decreases, speed of AP also decreases.

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4
Q

What is the range of conduction velocities for:

unmyelinated, small diameter axons?

myelinated, small diameter axons?

myelinated, large diameter axons?

A

0.5 - 2.5 ms

2 - 15 ms

60 - 100 ms

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5
Q

What is the conduction velocity range for autonomic axons?

A

5-25 ms

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6
Q

What stimuli are sensed by fast sensory axons?

A

touch
vibration
muscle length

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7
Q

What stimuli are sense by slow sensory axons?

A

temperature

‘ache’ (poorly-localised pain)

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8
Q

How can conduction of APs along an axon be blocked?

A

Reversible or Irreversible blockade of axonal sodium channels

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9
Q

Give an example of a local anaesthetic that reversibly blocks axonal sodium channels?

A

Lidocaine

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10
Q

What are the 2 ways in which APs are transmitted from cell to cell?

A
  1. At chemical synapses
    - between neurons; between motor neurons and muscle
  2. At low-resistance electrical gap junctions
    - between cardiomyocytes; between SMCs; between neurons via electrical synapses
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11
Q

Binding of transmitter to post-synaptic receptors results in what 2 events?

A
  1. Opening or closing of integral ion channel

2. Activation of enzyme system which modulates opening of nearby ion channels

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12
Q

What is the delay (in ms) of neuromuscular transmission in setting up of an AP receiving cell?

A

0.5 - 1 ms

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13
Q

At low-resistance electrical gap junctions, what connects the cytoplasms of each cell to allow the continuous flow of electrical current between cells?

A

Aligned Connexons that have water-filled pores.

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14
Q

Because of the direct connection between cells using low-resistance electrical gap junctions to propagate APs, what are the differences compared to synaptic transmission?

A

The direct connection means that no transmitter is required and there is no delay in transmission.

Bi-directional transmission is possible.

Gap junctions make poor pharmacological targets.

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15
Q

Where are the cell bodies of sensory neurons located?

A

Just outside the spinal cord (still part of the PNS)

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16
Q

Where are the cell bodies of motor neurons located?

A

In the spinal cord (CNS)

17
Q

Where are APs initiated in a neuron?

A

At the axon hillock

between the nucleus/cell body and the start of the axon

18
Q

Where are dendrites found and what is their function?

A

Dendrites are extension from the cell body of a neuron.

Inputs from other CNS neurons are received by the cell body via dendrites.

19
Q

Define Orthodromic and Antidromic.

A

Orthodromic - Normal direction of AP propagation

Antidromic - AP propagation in a non-physiological/opposite direction