Nervous Coordination 6.2

Question 1

Name the structures in the myelinated neurone

Answer 1

Dendrites
Nucleus
Cell body
Myelin sheath
Node of rancher
Axon
Axon terminal

Question 2

Explain how resting potential of a neurone is achieved

Answer 2

• sodium potassium pump actively transports sodium ions out of the neurone and potassium ions into the neurone
• the membrane is more permeable to potassium ions than sodium ions
• higher conc of potassium ions inside and sodium ions outside neurone
• membrane polarised more positive on inside more negative in outside maintaining resting potential

Question 3

Give the step by step stages of how an action potential is produced

Answer 3

• neurone stimulated voltage gated sodium ion channels open
• na+diffuses into axon down electro chemical gradient causing depolarisation
• more VGSI channels open threshold is reached depolarises to about +40mV
• sodium ion channels close, potassium ion channels open k+ diffuses out
• down electrochemical gradient repolarising neurone becomes more negative
  -to many diffuse out hyper polarisation becomes to negative
• k+ channels close sodium potassium pump returns neurone to resting potential

Question 4

What is happening at each stage of a graph showing changes in voltage across the membrane during an action potential

Answer 4

• flat line at -70 resting potential
  -sharp rise followed by peak at +40 , depolarisation
  -sharp fall down to resting potential, repolarisation
• membrane potential becomes lower than resting potential, hyperpolarisation

Question 5

What channels are open and closed, what is the moment of ions when
1. Resting
2. Depolarisation
3. Repolarisation

Answer 5

1. K+ channels open sodium potassium pump active sodium out potassium in
2. Na+ open k+ closed sodium ions in
3. Na+ closed K+ open potassium ions out

Question 6

What is the refractory period

Answer 6

Time during which no action potentials can be generated
Due to na+ channels staying closed

Question 7

What are the 3 functions of the refractory period?

Answer 7

-action potentials move in only one direction
- produces discrete impulses
- limits the maximum frequency of action potentials

Question 8

What is meant by the all or nothing principle

Answer 8

Action potentials are always the same size
If threshold reached you get an action potential
If threshold not reached no action potential

Question 9

How does an action potential travel across a non myelinated neurone

Answer 9

An action potential occurs at a section of the axon membrane
Membrane adjacently in-front detects depolarisation no adjacent voltage gates na+ ion channels open also forming an action potential
Action potential moves forward. Refractory period behind action potential prevents impulse moving backwards

Question 10

Describe how an action potential spreads across a myelinated axon by saltatory conduction

Answer 10

Myelin electrically insulates axon preventing na+ moving in
Depolarisation only takes place at nodes of ranvier
Action potentials jump from node to node know as saltatory conduction
Less depolarisation across whole length of membrane faster

Question 11

Why is nerve transmission slower in an unmylinated axon?

Answer 11

Unmylinated- more depolarisation across whole length of axon taking more time for channels to open and close

Question 12

What are 3 methods to increase conductance of an action potential

Answer 12

Myelination saltatory conduction
Higher temp increase kinetic energy faster diffusion
Greater axon diameter reduces resistance to ion flow

Question 13

Name the structures in the cholinergic synapse and draw it

Answer 13

1. Mitochondria
2. Synaptic vesicles
3. neurotransmitter
   4.. synaptic cleft
4. Neurotransmitter receptor
5. Calcium ion channels
6. Presynaptic membrane
7. Neurotransmitter reuptake pump

Question 14

Describe the steps of a transmission of an impulse across a cholinergic synapse

Answer 14

1. An action potentials depolarises pee synaptic membrane, voltage gated calcium ion channels open and diffuse in
2. Calcium ions cause synaptic vesicles with pre synaptic membranes and release ACh into the synaptic cleft
3. ACh diffuses across the synaptic cleft and binds to receptors in the post synaptic membrane
4. Sodium ion channels open and sodium ions diffuse into the post synaptic neurone, depolarising the post synaptic membrane causing an action potential
5. Acetylcholineesterase hydrolysis acetyl choline. Sodium ion channel closes no more action. Potentials generated

Question 15

Why is synaptic transmissions have unidirectionality?

Answer 15

-action potentials travel in one direction from pre-synaptic neurone to post-synaptic neurone
Due to: neurotransmitter only released from presynaptic neurone
Receptors only on post synaptic neurone

Question 16

Explain how a synapse can be inhibitory?

Answer 16

Chloride ion channels in post synaptic neurone
Makes neurone membrane more negative hyper polarised
More sodium ions needed to reach threshold

Question 17

Define temporal summation?

Answer 17

Repeated action potentials arrive in short time from presynaptic nerve to provide enough neurotransmitter to reach threshold in post synaptic nerve

Question 18

Define spatial summation

Answer 18

• more than one presynaptic neurone connected to the same post synaptic neurone

Question 19

What are the differences between a cholinergic synapse and a neuromuscular junction?

Answer 19

Cholinergic
-neurone to neurone
-less ACh receptors on post synaptic membrane
-can be excitory or inhibitory
-No clefts in post-synaptic membrane
Neuromuscular junction
-neurone to muscle fibre
-More ACh receptors on muscle fibre
-only excitatory
-contains clefts in muscle fibre membrane which stores acetychosine

Question 20

What is a motor unit?