Module 3: Lecture 5

Question 1

True of False
Contiguous conduction is in the UN-myelinated nerves?

Answer 1

True

Question 2

How does the saltatory conduction work?

Answer 2

• in myelinated cells
• gated channels cause depolarization allowing a high concentration of sodium ions into the cell
• this causes a trigger event when the threshold is met, opening the voltage-gated sodium and potassium channels and causing an action potential
• as the action potential is being restored and the insides of the cell are hyperpolarized the leftover sodium into the cell will travel along the membrane to an inactive area where the membrane is unmyelinated and causes another triggering event aka reaching the threshold to allow continuous action potentials are the nodes of Ranvier.

Question 3

What is the conduction velocity?

Answer 3

how quickly can the action potential travel the length of the axon

Question 4

True or False
myelinated nerve cells will have there conduction velocity be 50 times faster than unmyelinated nerve cells

Answer 4

true

Question 5

How does the diameter affect the velocity of action potentials?

Answer 5

the larger the diameter the more space for the ions to diffuse freely

Question 6

What is the rate at which myelinated fibres can communicate with the nerves in muscle?

Answer 6

120m/sec or 432 km/h

Question 7

What is the rate at which unmyelinated fibres can communicate with the nerves in the digestive tract?

Answer 7

0.7 m/sec or 2.5 km/h

Question 8

Why would we want big myelinated fibres for muscles and smaller unmyelinated fibres for digestion?

Answer 8

• depends on the importance of the signals
• digestion does not need to occur fast
• our muscles are part of our motor skills and we need them immediately to move

Question 9

What is “multiple sclerosis?” What happens as a result of it?

Answer 9

• neurodegenerative condition
• loss of myelin on the nerves
• which slows/blocks the chance of action potentials

*results in poor coordination, lack of sensation and possibly partial paralysis

Question 10

What is a synapse?

Answer 10

• the connection between two nerves and how they communicate together

Question 11

What is the “scientific” definition of the synapse?

Answer 11

the junction between axon terminals (onput zone) from a pre-synaptic neuron and the dendrites from a post-synaptic neuron (input zone)

Question 12

True or False?
One nerve cell can have 100,000 synaptic inputs.

Answer 12

True

Question 13

What are the 2 types of synapses?

Answer 13

1. Electrical (pre and post-synaptic cells)
2. Chemical (neurotransmitters) (WE ONLY TALKING ABOUT CHEMICAL)

Question 14

What is the space between your pre and post-synaptic neuron called?

Answer 14

synaptic cleft

Question 15

What are the 5 components of the chemical synapse?

Answer 15

1. Pre-synaptic neuron
2. Axon terminal
3. Synaptic cell
4. Post-synaptic neuron
5. Dendrites, cell body

Question 16

How are neurotransmitters released into the synaptic cleft?

Answer 16

• In the synaptic knob
• Neurotransmitters are stored in small synaptic vesicles enclosed by a bilipid membrane
• Once an action potential reaches the pre-synaptic axon terminal the neurotransmitter fuses with the cell membrane through the process of exocytosis to then be released out of the cell, into the synaptic cleft

*Calcium voltage-gated channels are activated in the synaptic knob region, the increased concentration of calcium trigger the fusion of synaptic vesicles to the pre-synaptic docking site where the neurotransmitters are released by exocytosis

Question 17

What are chemically or ligand-gated-ion channels?

Answer 17

They are channels that are opened by the binding of neurotransmitters allowing for ions to pass through

Question 18

What generates graded potential in nerve-to-nerve communication

Answer 18

The chemical synapse, the neurotransmitter binding to the ligand-gated channels opening them to allow for graded potentials

*if the graded potential is strong enough it will lead to action potential

Question 19

What are the 5 steps of nerve-to-nerve communication?

Answer 19

1. An action potential is carried out to the axon terminals of a presynaptic neuron causing a local depolarizing event
2. Causing Ca2+ enters the synaptic knob (through voltage-gated calcium channels) of the presynaptic neuron
3. Casing the release of neurotransmitters by exocytosis into the synaptic cleft
4. These neurotransmitters bind to receptor sites on the ligand-gated-ion channels in the subsynaptic membrane
5. Allowing sodium to enter the cell causes graded potentials, which may reach the threshold causing an action potential

Question 20

How does calcium allow for the process of exocytosis?

Answer 20

• calcium is the signal that allows for the neurotransmitters to be released in the synaptic cleft
• The vesicles are loosely docked in the ICM through SNARE proteins
• Once calcium comes into the cell it binds to a protein called Synaptotagmin
• The Synaptotagmin will undergo a conformational change and allow the vesicle to fuse with the membrane

Question 20

What does Synaptotagmin do?

Answer 20

• senses the amount of calcium in the nerve
• once there’s a high concentration of Calcium in the cell it will sense this and undergo a conformational change and hold the snare proteins together allowing the vesicle membrane to fuse with the cell membrane