Properties Of Sensory and Motor Neuronz

Question 1

What are passive electrical properties of neurons

Answer 1

Wires conduct current by electron Flow, neurons conduct current by ion flow, in both cases, current flow is impeded by resistance

Question 2

Neuron can be modelled as a wire

Answer 2

.each segment in model has a resistance
.this causes an applied voltage to decay as it travels along neuron
.ultimately the voltage will decay to zero

Question 3

How do we define the decay of the voltage

Answer 3

By 2 peramiters

1.space constant (how far the voltage travels)
2.time constant (how fast)

Question 4

Describe passive conduction velocity

Answer 4

Anything that increases the space constant or reduces the time constant will therefore increase conduction velocity

Question 5

What is the voltage across a cell membrane determined by

Answer 5

A balance between electrical charge and osmotic force i.e balance between electrical charge and osmotic force

Question 6

Describe chemical and electrical gradients

Answer 6

1. Net extrecellular positive charge under resting condition
   2.hyper polarisation increases this potential (action potential less likely)
   3.de polarisation reduces potential (making action potential more likely)

Question 7

What is the sodium pump crucial for

Answer 7

Establishing the membrane potential necessary for the action potential.

Otherwise sodium and potassium would leak across the membrane, causing the potential to drop to zero

Question 8

Describe action potential: voltage-gated ion channels

Answer 8

1.Ap is mediated by voltage gated ion channels embedded in cell membrane
2.open when a threshold is reached
3.sodium and potassium channels are the primary mediators of action potential

Question 9

Sodium channel has 3 states:

Answer 9

1.open
2.closed
3.deactivated

Question 10

Potassium channel has 2 states:

Answer 10

1.open
2.closed

Question 11

What is the action potential positive feedback cycle

Answer 11

1.cell membrane becomes depolarised

2.once depolarisation reaches a thresh hold sodium channels open

3.causes more sodium to pass through the osmotic gradient and leads to more depolar

4.this opens all adjacent channels causing a chain reaction

5.potassium channels open more slowly and this resulting outflow repolarises membrane potential

6.sodium channels close and temporarily deactivated

Question 12

What different dynamics do sodium and potassium channels have

Answer 12

Na channels open quickly, K channels open more slowly, and this difference is crucial for action potential

Question 13

What does the refractory period do

Answer 13

Prevents the positive feedback continuing indefinitely, this ensures the action potential travels in one direction

Question 14

What are the effects of neuron diameter

Answer 14

Time constant is barely affected

Space constant becomes larger therefore a faster space constant

Question 15

What is myelin

Answer 15

Essentially an insulator wrapped around the axon and neuron

Question 16

What are the affects of myelin

Answer 16

1.increases the space constant

Question 17

What are the effects of myelin and neuron diameter

Answer 17

Large diameter axons are faster for both myelinated and unmyelinated fibres