Chapter 7 (Electrical Signals)

Question 1

electrical gradient vs. concentration gradient

Answer 1

• electrical gradient: # of charges

- concentration gradient: # of a certain ion

Question 2

signal integration occurs at the ___

Answer 2

axon hillock

Question 3

signal transmission occurs at the ___

Answer 3

axon terminal

Question 4

Schwann cells

Answer 4

• form myelin sheath
• type of glial cell
• associated with motor neurons and many sensory neurons
• only in PNS
• wrap around a single neuron

Question 5

oligodendrocytes

Answer 5

• form myelin sheath
• only in CNS
• protection and support
• may wrap around axons of many neurons

Question 6

astrocytes

Answer 6

• large, stellate (star-shaped)
• shortcuts between neurons and blood vessels
• in CNS
• transport nutrients, support, development, debris removal

Question 7

microglia

Answer 7

• macrophages of CNS

- maintenance

Question 8

ependymal cell

Answer 8

• line fluid filled cavities of CNS

- have cilia that circulate cerebrospinal fluid

Question 9

depolarization

Answer 9

• membrane potential becomes more positive

- opening of Na+ channels causes Na+ inflow

Question 10

hyperpolarization

Answer 10

• membrane potential becomes more negative

- opening of K+ channels causes K+ outflow

Question 11

repolarization

Answer 11

any change that returns membrane potential to normal resting potential (-70 mV)

Question 12

What determines the strength of a graded potential?

Answer 12

stronger stimulus = higher concentration of neurotransmitter = more ion channel opening = larger change in membrane potential = larger magnitude of graded potential

Question 13

subthreshold potential

Answer 13

• graded potential that is not large enough to produce an action potential
• less than +15 mV

Question 14

supratheshold potential

Answer 14

• graded potential that is larger than what is required to trigger an action potential
• greater than +15 mV

Question 15

threshold potential of most neurons is __

Answer 15

-55 mV

Question 16

temporal summation

Answer 16

• two subthreshold potentials building on each other
• can trigger action potential if subthreshold depolarization occur at slightly different times and combine to reach threshold potential

Question 17

Describe the phases of action potentials: depolarization phase, repolarization phase, absolute refractory period, and relative refractory period.

Answer 17

• depolarization phase: membrane potential at axon hillock reaches threshold potential and adjacent part of membrane rapidly depolarizes (+30mV)
• repolarization phase: rapid return to resting membrane potential (hyperpolarization phase follows, becomes more negative)
• absolute refractory period: axon incapable of generating new AP
• relative refractory period: new AP can be generated only if stimulus very large

Question 18

spatial summation

Answer 18

• subthreshold potential occurs in different dendrites

- they combine at axon hillock to produce suprathreshold potential

Question 19

Hodgkin cycle

Answer 19

• Na+ influx from first depolarization triggers further opening of Na+ channels
• positive feedback loop
• accounts for rapid membrane depolarization

Question 20

How does the action potential only travel in one direction?

Answer 20

the previous segment is in refractory period; its voltage gated Na+ channels are inactivated

Question 21

Exposed portions of axons of myelinated neurons are called ___ and myelinated regions are called ___

Answer 21

nodes of Ranvier; internodes

Question 22

How do myelinated axons propagate action potentials faster than nonmyelinated?

Answer 22

• voltage gated Na+ channels only occur at nodes of Ranvier; depolarization can only occur at these nodes
• myelination prevents ions from leaking out so spread of charge through internodes is very fast

Question 23

synaptic transmission

Answer 23

relaying of info from one neuron cell to another via synapse (junction between cells)

Question 24

electrical vs chemical synaptic transmission

Answer 24

• electrical: direct flow of electric current from one cell to another via gap junctions (rare)
• chemical: secretion of neurotransmitter molecules that bind to and activate receptors

Question 25

Describe the synthesis and recycling of acetylcholine.

Answer 25

• Acetyl CoA synthesized in mitochondria
• Acetyl CoA and choline converted to ACh, catalyzed by choline acetyl transferase
• ACh packaged into synaptic vessicles
• ACh released into synapse
• ACh binds to postsynaptic cell receptors
• Acetylcholinesterase (AChE) breaks down ACh into choline and acetate (signal terminates)
• choline taken back up into presynaptic neuron and acetate diffuses out of synapse

Question 26

function of acetylcholine (ACh)

Answer 26

primary neurotransmitter at vertebrate neuromuscular junction

Question 27

Describe the events of signal transmission at a chemical synapse.

Answer 27

• AP arrives at axon terminal
• voltage gated Ca2+ channels open and Ca2+ enters cell
• Ca2+ triggers vesicle movement to membrane; vesicles fuse with membrane and release neurotransmitter by exocytosis
• neurotransmitter diffuses across synaptic cleft and binds to receptors, activating signal transduction pathway

Question 28

ionotropic neurotransmitter receptors vs. metabotropic receptors

Answer 28

• ionotropic: ligand gated ion channels; rapid change
• metabotropic: signal sent via second messenger; slower
• both operate via conformational change caused by binding of neurotransmitter