Nervous Communication

Question 1

Motor neurone goes from _______ to ______

Answer 1

CNS

To effector tissues

Question 2

What connects motor and sensory neurones?

Answer 2

Relay neurones

Question 3

What do sensory neurones do?

Answer 3

Connect receptors to the CNS

Question 4

In four points describe the structure of a neurone

Answer 4

Long
Ion channels (Ca2+ , Na+ , K+)
Sodium potassium pump
Mitochondria

Question 5

What are dendrites ?

Answer 5

Long branched elongations coming off the dendron

Question 6

What is the dendron part of the neurone?

Answer 6

From the dendrites to the cell body

Question 7

What is the axon of a neurone?

Answer 7

From the cell body to the end of the neurone

Question 8

What is meant by myelination?

Answer 8

Several layers of membranes and cytoplasm wrapped around a neurone

Question 9

In-between myelinated Schwann cell you find?

Answer 9

Nodes of ranvier

Question 10

The fact that current can only be generated in the Schwann cells is given the term?

Answer 10

Saltatory conduction

Question 11

Describe how a resting potential is formed

Answer 11

Na+/K+ pump pump three Na+ out for two k+ in
Some potassium leak through channel proteins
Proteins have negtive charges
Therefore there is an overall negative charge inside the neurone of -60mV

Question 12

Describe how a current is formed at the generator region of a neurone

Answer 12

Synapse triggers the Na+ channels to open
Na+ goes into the cell
Causes a generator potential
If enough generator potentials occur they can be summed and meet the threshold
Overall depolarisation will occur

Question 13

Describe how the inital opening of sodium ion channels leads to positive feedback

Answer 13

The depolarisation from the generator potential causes the opening of the voltage gated sodium channels
Causes more depolarisation

Question 14

After a set delay since gated sodium channels have opened what happens?

Answer 14

They close again

Question 15

Describe how re polarisation occurs why there is a refrcactory period and how the resting potential is regained

Answer 15

K+ ion channels open
K+ diffuse out of the cell
Causes hyperpolarisation as sodium potassium pumps take time to start working so the voltage drops down very qucikly
Once sodium potassium pump is working it will regain the resting potential

Question 16

Explain how the propagation of an action potential is Unidirectional

Answer 16

[Na+] is high behind the action potential still

Na+ is far more likely to diffuse forward than backward

Question 17

In a myelinated neurones where can Na+ and K + channels be found?

Answer 17

In the nodes of ranvier

Question 18

Explain how myelination increases the speed of nervous communication

Answer 18

Myelin acts as an insulator
Depolarisation only occurs at the nodes of ranvier which elongates the local circuits and results in saltatory conduction

Question 19

An action potential is an all or nothing response

How therefore is the intensity of the signals coded for?

Answer 19

By the frequency of signals

Question 20

Describe the movement of nervous signals across a synapse

Answer 20

Action potential arrives at the synaptic knob
Voltage gated Ca2+ channels open and ions diffuse into the synaptic knob
Cause vesicles with acetylcholine to fuse to the membrane of the pre synaptic knob. Exocytosis then occurs
Acetyl choline binds to recptor sites on Na+ channels on the post synaptic membrane
Na+ ions diffuse through the post synaptic membrane
Excitatory post synapctic membrane potential

Question 21

How is acetylcholine removed from receptors?

Answer 21

Acetylcholineesterase is an enzyme that braks acetylcholine down into ethanoic acid and choline

Question 22

Once broken down by acetylcholinease what happens to the products of this reaction?

Answer 22

Ethanoic acid and choline diffuse back to the synaptic bulb where they are recombined using ATP to form acetylcholine

Question 23

Why must the Ca2+ ions be gated?

Answer 23

Otherwise Ca2+ would be released all the time and would bind to the receptors sending inappropriate impulses