Module 4 - Nerves

Question 1

excitable cells

Answer 1

• All neurons and muscle cells are excitable
• Use resting membrane potential to create an electrochemical impulse (action potential)

Question 2

non-excitable cells

Answer 2

• Cells that do not generate action potentials
• Most cells in body are non-excitable

Question 3

voltage dependant channels

Answer 3

• Movement of ions across membrane (sodium Na+ & potassium K+)
• Sensitive to changes in membrane potential
• Open when cell becomes more positive (depolarization)
• Sodium channels open immediately & close with inactivation gate
• Potassium channels open after brief pause (when sodium enters inactivation period)

Question 4

permeability during action potential

Answer 4

• Na+ peaks rapidly
• K+ leave slowly
• Repolarization, K+ leave cell (return to membrane resting potential)
• Depolarization, Na+ enters the cell

Question 5

depolarization in action potential

Answer 5

• Membrane potential rapidly changes from resting (-70mV) to (+35mV)

Question 6

repolarization in action potential

Answer 6

• After depolarization
• Membrane potential returns to -70mV

Question 7

threshold in action potential

Answer 7

• Point that must be reached in depolarization to fire an action potential
• -55mV is considered the standard threshold

Question 8

overshoot in action potential

Answer 8

• Peak of action potential where membrane potential is positive
• Between 0mV and the peak of amplitude

Question 9

hyperpolarization in action potential

Answer 9

• Membrane potential becomes briefly more negative before returning to resting potential (-90mV)

Question 10

direction of flow of action potential

Answer 10

• Specific regions where action potentials can occur (cell body/1st node of ranvier)
• Travels in one direction, towards axon terminal
• Refractory period prohibits flow in backwards direction

Question 11

action potential propagation

Answer 11

• Generated on axon hillock
• Travel down nerve to axon terminal
• Movement of action potential down axon
• Current is carried by positively charged ions (Na+)
• From positive to negative areas (unlike charges attract)

Question 12

saltatory conduction

Answer 12

• Much faster than unmyelinated nerve fibers (jumping nodes of ranvier)
• Action potential cannot back up
• Channels are closed behind moving action potential (refractory period)

Question 13

all or nothing mentality of action potential

Answer 13

• If threshold isn’t reach repolarization returns membrane potential to resting state
• If threshold is reached action potential propagates down axon at full height & size

Question 14

steps of neuromuscular junction

Answer 14

• Action potential on presynaptic motor nerve fiber triggers voltage-gated Ca++ ion channels to open
• Ca++ flows into cell, down concentration gradient
• Influx of Ca++ trigger the fusing synaptic vesicles to the membrane
• Release of Ach into synaptic cleft via exocytosis
• Ach diffuses across synaptic cleft & attaches to Ach (ligand) receptors on muscle cells membrane
• Ligand-gated ion channels open
• Lots of Na++ in, few K+ leave
• Triggers local depolarization (end plate potential EPP)
• Depolarization of EPP spreads to adjacent cell membrane
• Voltage gated channels are open (for action potential)
• Allow large amounts of Na+ into muscle cell & trigger action potential
• Ach is broken down into acetic acid & choline by AChe enzyme
• Choline is taken back to axon terminal to be recycled

Question 15

dendrites

Answer 15

• receive incoming signals
• increase overall surface area to communicate with more neurone
• thin branching processes of cell body

Question 16

cell body (soma)

Answer 16

• control centre
• contains nucleus
• all necessary organelles for directing cellular activity

Question 17

axon

Answer 17

• carries outgoing signals of action potential

Question 18

myelin sheath

Answer 18

• insulator
• forces action potential to only take place at nodes of ranvier
• layered phospholipid sheath rapped tightly around axon

Question 19

nodes of ranvier

Answer 19

• action potential jumps from node-node
• quickly down axon

Question 20

collaterals

Answer 20

• increase number of target cells
• branching of axon near terminal end

Question 21

terminal bouton (axon)

Answer 21

• chemical facilitate transmission of signals across synapse to target cell
• swelling at axon collateral
• contains mitochondria & membrane bound vesicles