C2.2 Neural signalling

Question 1

Define neurons

Answer 1

• cells of the nervous system

Question 2

Name all the parts of a neuron and its function

Answer 2

1. Dendrites - gain signals or information
2. Axon - to trasmit signals from the cell body to the branches at the end of the axon
3. cell body - to process information
4. nucleus
5. myelin sheaths (not shown here) - to insulate for myelination
6. schwann cells (inside the MS) - to produce myelin sheaths
7. nodes of Ranvier

Question 3

Describe how action potential is achieved

Answer 3

• via a response to a stimulus which causes sodium channels to open

NOTE: this card was not previously filled out for some weird reason

Question 4

What is an electrical signal

Answer 4

• movements of ions or electrons

nerve impulse is a type of electrical signal because pf the movements between positively charged ions

Question 5

Define nerve impulse

Answer 5

• reversal of resting potential of a neuron’s membrane as a result of the faciliated diffusion between Na+ and K+ ions

facilitated by the Na+ K+ pump

Question 6

Give a brief overview of the process of action potential

Answer 6

1. Depolarization
2. Repolarization
3. Rebuilding gradients (not a stage)

Question 7

Depolarization

Answer 7

1. Sodium channels in the membrane open, Na+ ions in neuron (concentration gradient)
2. Change of the charge in the membrane (relatively negative -> relatively positive)*
3. Membrane rises from -70 mV to around + 40 mV (change of charge)

*compared to the outside of the neuron

Question 8

Repolarization

Answer 8

• This occurs immediately after depolarization, MP triggers the opening of these channels
  1. The voltage gated sodium channels close
  2. Voltage Potassium channels open
  3. Potassium ions diffuse out of neuron*
  4. Neuron becomes relatively negative again (- 70 mv-80 mV)

sodium channels, voltage gated -> first to open due to membrane depolar.

• the K should still be inside of the neuron — this will be ffixed when the gradients are rebuilt

Question 9

Rebuilding gradients

Answer 9

• after an action potential
  1. the Na+K+ pump re-establishes the Na+ and the K+ gradients

Question 10

Describe resting potential

Answer 10

• the** plasma membrane of a cell **maintains the concentration gradient
• generally, the inside of cell electrically negative compared to the outside
• membrane potential at -70 mV for neurons during resting potential
  -** Na+K+ pump lets 2 K+ ions, 3 K+ out**
  -** Na+K+ pump uses ATP**

Question 11

Why is the inside of the neuron relatively more negative than the outside?

Answer 11

• because the Na+K+ pump lets 2 K+ in only while 3 Na+ goes out

Question 12

List two other factors contribute to resting potential

Answer 12

• K+ ions more permeable to the membrane to leakage of K+ ions is faster*
• there are negatively charged proteins inside the neuron

*The ions leack back across the membrane by diffusion. K+ being permeable means that the K+ can get in easily

Question 13

Define synapse

Answer 13

• a junction between two neurons

Question 14

Where are the synapses mostly located?

Answer 14

• the brain and the spinal cord

Question 15

Define presynaptic neuron

Answer 15

• the neuron that is transmitting the signal to another neuron

Question 16

Define postsynaptic neuron

Answer 16

• the neuron that receives a signal from another neuron

Question 17

Which parts of the neuron(s) does synaptic transmission occur

Answer 17

1. the axon terminal/end of the axon (presynaptic)
2. the synaptic cleft
3. the membrane of the dendrites (postsynaptic)

*NOTE THIS OCCURS IN THE MEMBRANES OF THE FOLLOWING EXCEPT SYNAPTIC CLEFT AS THEY HAVE NO MEMBRANE

Question 18

Define synaptic cleft

Answer 18

• the gap between the post-synaptic and presynaptic membranes

Question 19

Define synaptic transmission

Answer 19

• the sequence of events of how an impulse is passed from the presynaptic membrane to the post-synaptic membrane

Question 20

Outline the process of synaptic transmission

Answer 20

1. Action potential reaches axon terminal of the presynaptic neuron
2. Hence opens the voltage gated ion channels
   3.calcium ions diffuse into the cell, promote the exocytosis of the vesicles which contain NTs
3. NTs released into the synaptic cleft
4. NTs bind to receptors on thepost-synaptic membrane
5. The ligand-gated ion channels hence open
6. The ion channels generates an impulse (action potential), letting the pre-synaptic signal travel through the post-synaptic neuron

Question 21

Explain saltatory conduction

Answer 21

• some axons are coated with myelin sheaths
• myelin sheaths are created by schwann cells
• myelin sheaths insulate parts of the axon
• the gaps in the axon not covered by myelin sheaths = nodes of ranvier
• the nerve impulse jumps from one node of ranvier to the next
• transmission of nerve impulses now more rapid

Question 22

Explain excitatory postsynaptic potential

Answer 22

• a change in membrane voltage
• likely to create action potential
• this happens during synaptic transmission
• if the potential rises from -70 mV to -50 mV

Question 23

How long is the neurotransmitter bound to the receptor

Answer 23

• for a short time
• then quickly removed from the synpatic gap

Question 24

Acetylcholine

Answer 24

• widely used neurotransmitter at synapses between neurons
• used at synapses between neurons and muscle fibres

Question 25

From where is acetylcholine synthesized?

Answer 25

• from choline and acetyl groups

Question 26

To where does acetylcholine bind to?

Answer 26

• Acetylcholine binds to a receptor in the postsynaptic membrane which also actss as the channel for Na+ ions

Question 27

Which enzyme breaks down acetylcholine?

Answer 27

• acetylcholinesterase