Spread of Nerve Impulse

Question 1

Describe the functional structure of a neuron

Answer 1

Information travels via dendrites to the cell body (soma) where is it processes
Signal is then transmitted along the axon
At the end of the axon, information is passed onto the target (muscle of neruron) via boutons,

Question 2

Describe the variation seen in neuron phenotype

Answer 2

Multipolar Neuron - These are most common and look like the typical neuron, mainly found in the CNS
Bipolar Neuron - Have the cell body in the centre of the neuron and are found in the retina
Psudounipolar neuron - Have the cell body in the centre but off to one side, these are mainly found in spinal ganglia

Question 3

How do neurons send information

Answer 3

They encode and transmit informationa as electical activity

Question 4

What are the two types of conduction and define them.

Answer 4

Passive conduction - Electrical signals passing along the axon freely
Active - Generation of action potential by opening ion channels

Question 5

What is an issue with passive conduction

Answer 5

There is a loss of conduction as the signal travels down the axon due to pores in the axon that allow charge to leak out.

Question 6

Why is it essential that nerve impulses travel a long distance? and how does it do this?

Answer 6

So the neuron can transmit a signal along the full length of its axon. It involves both active depolarisation of membrane and passive conductance of charge.

Question 7

Describe the process of sodium channels in generation of an action potential

Answer 7

At rest, sodium channels are closed. An increase in membrane potential is sensed by voltage sensors within the channels which become activated at the threshold potential.
This causes a conformation change and the channels open allowing sodium ions to travel along its electo-chemical gradient.
At peak membrane potential a delayed component of voltage dependent activation blocks the channel by the inactivation gate.
Repolarisation re-sets the sodium channel to its original conformation.

Question 8

Describe the propagation of the action potential

Answer 8

Voltage gated sodium channels open and the action potential is generated.
Passive current of charge flows to the next voltage gated sodium channel. The passive current causes the next sodium channel to open and another action potential is generated.

Question 9

What are the two refractory periods

Answer 9

Absolute refractory period - when sodium channels are inactive and no action potential can be generated
Relative refractory period - An action potential could be generated but it would require a larger electrical signal as the membrane potential is lower then the resting membrane potential.

Question 10

What is the effect on a refractory period on the action potential?

Answer 10

It ensures that the impulse moves in one directions and there is no back flow opening of sodium channels

Question 11

What is the injected current proportional too?

Answer 11

The frequency of action potentials

Question 12

Describe the effect of resistance on charge movement

Answer 12

The larger the diameter of the axon, the lower the resistance is. The passive movement of charge along an axon is easier with lower resistance meaning charge movement will be faster

Question 13

Describe the effects of capacitance on charge movement

Answer 13

In larger axons, the membrane surface areas is larger which means it has a higher capacitance to store charge. However the higher the capacitance, the more energy is required to move all this charge. It is still faster but more energy intensive

Question 14

Describe the effects of myelination on axons

Answer 14

Myelination allows for larger axons to conduct faster however at smaller diameters it can be more efficient to have them unmyelinated.

Question 15

Describe some of the features of the nodes of ranvier

Answer 15

These are regions on the axon that are unmyelinated. Here are where sodium channels are found so they are the site where action potentials occur

Question 16

Describe the effects of multiple sclerosis

Answer 16

It attacks the oligodendrocyte myelin and so the CNA is affected.

Question 17

What type of conduction occurs through myelin?

Answer 17

Passive conduction. This is quick conduction

Question 18

Describe salatory conduction

Answer 18

It is passive to active conduction jumping.
The local passive currents can extend further as the myelin sheath prevents current leakage.
Conduction of the nerve impulse flows rapidly along the inside of the axon node, where it slows and ionic depolarisation takes place.
Fast conduction along the axon resumes.