CH. 7 Nerve Cells and Electrical Signaling

Question 1

What are the cells of the nervous system?

Answer 1

1. neurons - excitable cells

2. glial cells - support cells

Question 2

What are the 5 components of a neuron?

Answer 2

1. soma
2. dendrites
3. axon
4. axon hillock
5. axon terminal

Question 3

What is the function of the soma?

Answer 3

contains nucleus and most organelles

Question 4

What is the function of dendrites?

Answer 4

reception of incoming information

Question 5

What is the function of the axon?

Answer 5

transmits electrical impulses called action potentials

Question 6

What is the function of the axon hillock?

Answer 6

where axon originates and action potentials are initiated

Question 7

What is the function of the axon terminal?

Answer 7

releases neurotransmitter

Question 8

What are the two types of neuron transport?

Answer 8

1, anterograde transport - from soma to axon terminal (A to B)

2. retrograde transport - from axon to soma (B to A)

Question 9

What is a synapse?

Answer 9

site of communication between two neurons or between a neuron and an effector organ

Question 10

What is synaptic flexibility?

Answer 10

with continued use, synapse changes anatomically which produces a different synapse

Question 11

What are the 3 ion channels of a neuron?

Answer 11

1. leak channels

2, ligand-gated channels

3. voltage-gated channels
   - sodium and potassium channels
   - calcium channels

Question 12

What are the characteristics of leak channels?

Answer 12

• always open
• located throughout the neuron
• has a resting membrane potential

Question 13

What are the characteristics of ligand-gated channels?

Answer 13

• open or close in response to ligand binding
• located on dendrites and cell body
• synaptic potentials?

Question 14

What are the characteristics of voltage-gated channels?

Answer 14

• open or close in response to changes in membrane potential
• sodium/potassium channels are found throughout but more in the axon (action potentials)
• calcium channels found at axon terminal (releases neurotransmitter)

Question 15

What are the three structural classes of neurons?

Answer 15

1. bipolar
2. pseudo-unipolar
3. multipolar

Question 16

What are the three functional classes of neurons?

Answer 16

1. afferent neurons
2. efferent neurons
3. interneurons

Question 17

What are the four types of glial cells?

Answer 17

1. astrocytes
2. microglia
3. oligodendrocytes
4. schwann cells

Question 18

What are the characteristics of oligodendrocytes?

Answer 18

• located in the central nervous system

- one oligodendrocyte forms several myelin sheaths and myelinates sections of several axons

Question 19

What are the characteristics of schwann cells?

Answer 19

• located in the peripheral nervous system

- one schwann cell forms one myelin sheath and myelinates one section of an axon

Question 20

Why do resting membrane potentials exist?

Answer 20

there are more negative charges inside the cell and more positive charges outside the cell

Question 21

What is the resting membrane potential of neurons?

Answer 21

-70 mV

Question 22

What are the two factors that are critical in determining resting membrane potential?

Answer 22

1. ion concentration gradients

2. membrane permeability to these ions (ion channels)

Question 23

What is a graded potential?

Answer 23

relatively small change in the membrane potential produced by some type of stimulus that triggers the opening or closing of ion channels

Question 24

What is the concentration gradient produced by the Na+/K+ pump?

Answer 24

high sodium outside, low inside

low potassium outside, high inside

Question 25

How does electrical driving force respond when K+ diffuses out of cell that is permeable to potassium only?

Answer 25

wants to pull K+ back into the cell to make less negative

Question 26

When is an ion at equilibrium?

Answer 26

when there is no net force for it to move across the membrane i.e chemical force = negative electrical force or electrochemical force = 0

Question 27

What is the ion permeability of neurons?

Answer 27

neuron is 25 times more permeable to potassium than sodium - more potassium leaves the cell than sodium enters - makes the inside of the cell more negative

Question 28

What are the chemical driving forces of a typical neuron?

Answer 28

potassium out | sodium in

Question 29

What is the steady state of a neuron?

Answer 29

inflow of sodium is balance by outflow of potassium | - creates a resting membrane potential of -70mV

Question 30

What are the different types of gated channels in neurons?

Answer 30

1. voltage gated 2. ligand (chemically) gated 3. mechanically gated

Question 31

What are the phases of an action potential?

Answer 31

resting - depolarization - repolarization - hyperpolarization

Question 32

What does it mean when graded potentials are decremental?

Answer 32

magnitude decays as it spreads

Question 33

What is temporal summation?

Answer 33

a graded potential where the same stimulus is repeated close together in time

Question 34

What is spatial summation?

Answer 34

a graded potential where different stimuli overlap in time

Question 35

What is an action potential?

Answer 35

rapid large depolarization is used for communication

Question 36

How do action potentials travel in neurons?

Answer 36

along axons from cell body to the axon terminal | - if afferent neuron, from receptor to terminal

Question 37

What occurs that prevents an action potential from reaching the equilibrium constant of sodium?

Answer 37

the slow opening of potassium channels and the slow closing of sodium channels

Question 38

What restores the resting membrane potential when an action potential has reached hyperpolarization?

Answer 38

sodium/potassium pump

Question 39

What are the two gates associated with the voltage gated sodium channel?

Answer 39

activation gate and inactivation gate

Question 40

What is the "all-or-nothing" principle?

Answer 40

a threshold depolarization needs to be met in order to induce the regenerative mechanism for the opening of sodium channels i.e for action potential to occur

Question 41

What is the refractory period?

Answer 41

period of time following an action potential 1. absolute 2. relative

Question 42

How long does the absolute refractory period last?

Answer 42

spans all of depolarization and most of the repolarization phase - second action potential cannot be generated

Question 43

How long does the relative refractory period last?

Answer 43

spans the last part of the repolarization phase and hyperpolarization - second action potential can be generated but with a stronger stimulus

Question 44

What are the 3 consequences of refractory periods?

Answer 44

1. all-or-nothing principle 2. frequency coding 3. unidirectional propagation of action potentials

Question 45

What needs to be present for the propagation of action potentials?

Answer 45

myelin