Topic 4: Nerve Conduction

Question 1

Give the 2 major regulatory systems

Answer 1

1) Nervous system
2) Endocrine system

Question 2

Describe neural communications

Answer 2

• Neurons specialized = rapid electrical signaling
• Allows rapid control of body muscles + exocrine secretions

Question 3

Describe hormonal communications

Answer 3

• Chemical messengers secreted = endocrine gland to blood
• Regulate process = require duration instead of speed e.g. metabolic activities + water/electrolyte balance

Question 4

Define resting potential

Answer 4

• Constant membrane potential = cell electrically at rest

Question 5

Describe basic neural communication in nerve/muscle tissues

Answer 5

• N/M cells are excitable tissues = rapidly change membrane potentials = produce electrical signals
• Neurons use electrical signals to receive + process + initiate + transmit messages
• Electrical signals critical to function of nervous system + muscles

Question 6

Give the 4 zones of neuron

Answer 6

1) Input zone = Dendrites
2) Trigger zone = axon hillock
3) Conducting zone = Axon
4) Output zone = Terminals

Question 7

Describe the 4 zones of neuron

Answer 7

1) Input: receives + processes signals from other neurons
2) Trigger: signals to be sent to other neurons
3) Conducting: transfers signals to output zone
4) Output: conveys signal to other neurons/muscles/glands

Question 8

Define depolarization

Answer 8

• Membrane potential = less negative
• Potential = less polarized than resting potential

Question 9

Define hyperpolarization

Answer 9

• Membrane potential more negative
• Potential = more polarized than resting potential

Question 10

Define polarization

Answer 10

• Membrane potential not 0mv

Question 11

Define repolarization

Answer 11

• Potential = returns to resting potential post depolarization

Question 12

What’s the value of resting potential?

Answer 12

-70mv

Question 13

Explain how electrical signals are produced

Answer 13

-

Question 14

Explain how electrical signals are produced

Answer 14

• Via ion movements across membrane
• Ions cannot pass lipid bilayer = only via channels
• Trigger in change of membrane potential = alters permeability = alters ion flow

Question 15

Give the 2 types of membrane channels for ion movement

Answer 15

1) Leak channels
2) Gated channels

Question 16

Describe leak channels

Answer 16

• Continuous ion movement
• Via electrochemical driving forces

Question 17

Describe gated channels

Answer 17

• Ion movement only when gates open
• Triggering event causes change in conformation = gate opens

Question 18

Give + define 4 types of gated channels

Answer 18

1) Voltage gated = change in membrane potential
2) Chemically gated = specific messenger binding to surface receptor
3) Mechanically gated = repond to stretching/mechanical shape change
4) Thermally gated = temp change

Question 19

Define graded potential

Answer 19

• Local changes in membrane potential = spread over short distances
• Can initiate action potentials = turn into long distance signals

Question 20

Explain graded potentials

Answer 20

• Produced by specific trigger = gated ion channels open = in specialized confined region of membrane
• Occurs at different grades = depending on stimulus strength

Question 21

What is the relationship between triggering event + resultant GP?

Answer 21

• Stronger TE = larger resultant GP
• More gated channels open = more Na+ enters = greater depolarization → greater magnitude of GP

Question 22

Describe the loss of graded potential

Answer 22

• Loss of charge over space due to K+ leakage from leak channels = GP die out

Question 23

Give 5 examples of GP

Answer 23

1) Postsynaptic potentials
2) Receptor potentials
3) End-plate potentials
4) Pacemaker potentials
5) Slow-wave potentials

Question 24

Define action potential

Answer 24

• Brief/rapid/large changes in membrane potentials
• If GP depolarizes membrane to threshold = AP otherwise no AP

Question 25

Describe AP

Answer 25

- Potential reverses = inside cell becomes more positive than outside - Like GP = specialized small region of membrane BUT AP propagated throughout entire axon nondecrementally - AP = accurate long-distance signals

Question 26

Describe channel states + ion flow during AP

Answer 26

- Resting potential -70mv = all voltage gated channels closed - Threshold = Na+ activation gate opens = PNa+ rises - Na+ enters cell = depolarization → +30mv = generates rising phase of AP - Peak AP = Na+ inactivation gate closes = PNa+ falls = net movement of Na+ into cells stops - At same time as Na+ inactivation K+ activation gate opens = PK+ rises - K+ leaves cell = repolarization to resting potential = generates falling phase of AP - Return to resting potential = Na+ activation gate closes + inactivation gate open → resetting channel for another trigger - K+ moving out through still open channel = hyperpolarization - K+ activation gate closes = returns to resting potential

Question 27

Explain how we get from GP to AP

Answer 27

- GPs = increasing depolarization - Membrane reaches threshold potential - Na+ voltage-gated channels open→ rising phase - Na+ flows into cell = reverses membrane potential from -70mV to +30 mV = depolarization and reversal phase - At peak of AP = Na+ voltage-gated channels close + K+ voltage-gated channels open→ K+ flow out of cell→ falling phase - K + flow eventually restores membrane potential to resting state = repolarization - Brief after hyperpolarization = K+ voltage-gated channels still open - Eventually the resting potential is restored = K+ voltage-gated channels close - Na+/K+ pump gradually restores concentration gradients

Question 28

Describe all or nothing response

Answer 28

- If neuron reaches threshold = full AP - If threshold not reached = no AP - Stronger/weaker stimulus doesn't affect magnitude of AP just GP - Stronger stimulus = larger GP = Threshold reached more often = higher AP frequency

Question 29

Describe refractory period + 2 types

Answer 29

- AP cannot be initiated in region just undergone AP 1) Absolute: no further AP possible 2) Relative: further AP possible with much stronger triggering

Question 30

Give the 2 types of propagation

Answer 30

1) Contiguous 2) Saltatory conduction

Question 31

Describe contiguous

Answer 31

- Slow conduction in unmyelinated fibers - AP regenerated at every portion of membrane = spreads along neighbouring portions tell end terminal reached

Question 32

Describe saltatory conduction

Answer 32

- Rapid conduction in myelinated fibers - AP jumps over sections of fibers covered with insulating myelin = only regenerated at myelin-free parts until terminal reached

Question 33

Define myelin

Answer 33

- Composed of lipids = acts as insulator

Question 34

Describe myelination

Answer 34

- Formed by oligodendrocytes in CNS - Formed by Schwann cells in PNS - Axon have voltage-gated channels = Nodes of Ranvier - AP only regenerated at NOR = rest of axon insulated - AP jumps from node to node

Question 35

What factors increase speed of AP propagation?

Answer 35

1) Myelination = saltatory faster than contiguous propagation 2) Nerve fiber diameter = larger→lower electrical resistance - E.g. large fiber skeletal muscles = 120 m/s - E.g. small unmyelinated fibers to stomach = 0.7 m/s

Question 36

Describe what occurs at each location of a neuron

Answer 36

1) Input zone = summation of GP 2) Trigger zone = initiation of AP 3) Conduction zone = propagation of AP 4) Output zone = releases neurotransmitters