Module 4- Nerves

Question 1

what is a dendrite

Answer 1

• thin branches that extend from the cell body

- receive msgs from other neurons

Question 2

what is the cell body (soma)?

Answer 2

-where the nucleus is, directly neuron action

Question 3

what is the axon

Answer 3

carries the AP to the receiving neuron cell

usually myelinated

Question 4

what is the purpose of myelin

Answer 4

insulates the axon so the AP travels faster

Question 5

what is the axon terminal

Answer 5

terminal ‘bouton’

-a swelling at the end of the axon (split into collaterals) to synapse to receiving dendrites of other cells

Question 6

what are nodes of ranvier

Answer 6

the spaces between myelin on the axon that transfer the AP faster along the axon

Question 7

describe the formation of an action potential

Answer 7

1) membrane potential starts at -70mv (resting)
2) depolarizes (more +ve) to +35mv
- triggered na channels to open, na rushes IN (+ve)
- na channels deactivate, k channels start to open, k exits (+ve leaves so inside more -ve)
3) membrane repolarizes to resting -70mV
4) membrane hyperpolarizes to -90mV (bc k keeps rushing out)
5) membrane returns again to resting -70mV after k channels close

Question 8

what are the two types of voltage gated channels

Answer 8

1) sodium channels
- na flows into the cell to make more +Ve
- gate open triggered by depolarization
- has an activation gate AND an inactivation gate to close channel
- has an absolute refractory period where cannot open

2) potassium channels
- only activation gate, NO refractory period
- triggered to open when na begins to close
- k flows out of the cell to make more -ve

Question 9

whats the difference between the absolute refractory period and the relative refractory period?

Answer 9

• absolute is when na channels close and cannot open for a while
• relative is when it hyperpolarizes (-90), k is still leaking out so its harder to make an AP at this time

Question 10

whats the minimum depolarization to trigger an AP?

Answer 10

• 55mV

- enough NA has to enter the cell to build up enough +ve charge

Question 11

how is an AP propogated along an axon?

Answer 11

IF UNMYELINATED
-the +ve 35mv is attracted to the -ve membrane parts at rest so it depolarizes the one next to it and moves along
-the absolute refract period stops its from going backwards
IF MYELINATED
-called saltatory conduction–> ap jumps from node to node
-myelin made by SHWANN cells in PNS
-myelin made by OLIGODENDROCYTES in CNS

Question 12

what causes MS

Answer 12

• immune system attacks myelin on nerves

- interrupts APs so you dont get the message

Question 13

what is a neuromuscular junction NMJ?

Answer 13

• the chemical synapse between nerve and muscle cell
• presynaptic axon terminal has lots of ca that open, which open vesicles that have neurotransmitter in them to be released into the cleft
• the end plate has receptors for neurotransmitter which open ligand channels and receive the msg