Human Physiology Chapter 11: The Nervous System Part 3

Front 1

What is the refractory period?

Back 1

The refractory period is the time when neuron is unable to fire a second AP

Front 2

What is the absolute refractory period?

Back 2

The absolute refractory period is the time when a second AP is not possible

Front 3

When does the absolute refractory period take place? Are Na+ channels open or closed?

Back 3

The absolute refractory period takes place during depolarization. Na+ channels are either completely open or closed and locked

Front 4

What does the absolute refractory period ensure?

Back 4

It ensures that each AP is an all-or-none event

Front 5

What does the absolute refractory period enforce?

Back 5

It enforces one-way transmission of nerve impulses

Front 6

Why is a second AP not possible during the absolute refractory period?

Back 6

Because the first AP is still occurring

Front 7

During the relative refractory period, what is occurring?

Back 7

Hyperpolarization is occurring

Front 8

During the relative refractory period, which channels are open and which are closed?

Back 8

Most Na+ channels are closed but ready to open and some K+ channels are still open

Front 9

During the relative refractory period, what may occur?

Back 9

If there's a exceptionally strong stimulus opening enough Na+ channels, a second AP may occur

Front 10

During one AP, what is occurring at time = 2 ms?

Back 10

AP peak is at the recording electron

Front 11

During one AP, what is occurring at time = 4 ms?

Back 11

AP peak has passed and recording electrode is recording hyperpolarization

Front 12

Why doesn't NA+ travel the other way in AP?

Back 12

Na+ does go the other way but the channels are closed and locked immediately after AP passes

Front 13

You only see continuous conduction on what kind of neurons?

Back 13

Unmyelinated neurons

Front 14

What is conduction velocity?

Back 14

Conduction velocity is how fast the axon conducts an AP

Front 15

Unmyelinated axons propagate by what?

Back 15

Continuous Conduction

Front 16

Is the conduction velocity fast or slow with continuous conduction?

Back 16

Slow: 1 m/s

Front 17

What does continuous conduction require?

Back 17

Requires voltage-gated channels all along entire axon

Front 18

Why is continuous conduction inefficient?

Back 18

Because it must depolarize and repolarize each patch of membrane

Front 19

What does myelination of the axon prevent?

Back 19

Prevents leak of charge

Front 20

What does myelination of the axon do to the conduction velocity?

Back 20

Speeds it up

Front 21

What are the Nodes of Ranvier?

Back 21

Nodes of Ranvier are bare patches of axon

Front 22

In myelinated axons, voltage gated channels are located where?

Back 22

They are only clustered at the nodes of Ranvier

Front 23

What is saltatory conduction?

Back 23

Saltatory conduction is where APs appear to jump rapidly from node to node on myelinated axons

Front 24

In a bare plasma membrane, voltage decays why?

Back 24

Because current leaks across the membrane

Front 25

On myelinated axons, conduction velocity with saltatory conduction can propagate APs how fast?

Back 25

Up to 150 m/sec

Front 26

What is Multiple Sclerosis?

Back 26

MS is an autoimmune disease that mainly affects young adults

Front 27

In MS, what is occurring?

Back 27

Immune system is destroying myelin in the CNS

Front 28

What are some symptoms of MS?

Back 28

Loss of muscular control, disturbances of vision of speech

Front 29

What does the presynaptic neuron do?

Back 29

Conducts APs toward the synapse

Front 30

What does the postsynaptic neuron do?

Back 30

Transmits APs away from the synapse

Front 31

Neurons are separated by what?

Back 31

The synaptic cleft

Front 32

What is the synaptic cleft?

Back 32

Fluid-filled space through which NT diffuses

Front 33

What does the cleft do?

Back 33

Keeps presynaptic AP from directly reaching postsynaptic neuron

Front 34

What are the 5 events at the Chemical Synapse?

Back 34

1. Action potential arrives at axon terminal.
2. Voltage-gated Ca+2 channels open and Ca+2 enters axon terminal
3. Ca+2 entry triggers exocytosis of NT
4. NT diffuses across the synaptic cleft which binds to specific receptors on the postsynaptic neuron
5. Binding of NT opens chemically-gated ion channels which sets of GP

Front 35

What 3 ways are NT effects terminated?

Back 35

1. Diffusion away from the synapse
2. Enzymatic degradation
3. Reuptake by transport proteins (NE, or serotonin)

Front 36

What does EPSP stand for?

Back 36

Excitatory Post-Synaptic Potentials

Front 37

What do EPSPs do?

Back 37

Graded depolarization, excites AP

Front 38

What does IPSP stand for?

Back 38

Inhibitory Post-Synaptic Potentials

Front 39

What do IPSPs do?

Back 39

Graded hyperpolarizations, inhibits AP

Front 40

How are post-synaptic potentials graded?

Back 40

Amount of NT released and how long NT is in the area

Front 41

The amount of NT released depends on what?

Back 41

Depends on number of ion channels opened

Front 42

How long NT is in the area depends on what?

Back 42

How long channels stay open

Front 43

Graded potentials may last for how long? How long do APs last?

Back 43

Seconds to minutes. APs last only 2 msec

Front 44

A single EPSP cannot do what?

Back 44

A single EPSP cannot set off an AP

Front 45

A neuron receives input from one or many other neurons?

Back 45

Many other neurons

Front 46

What can EPSPs do to reach threshold?

Back 46

Summate

Front 47

When IPSPs and EPSPs summate, what occurs?

Back 47

They cancel each other out

Front 48

What are the two types of summation?

Back 48

Temporal summation and Spatial summation

Front 49

What is temporal summation?

Back 49

Temporal summation is when one or more pre-synaptic neurons transmit impulses in rapid fire order

Front 50

What is spatial summation?

Back 50

Spatial summation is when the neuron is stimulated by a large number of pre-synaptic neurons at the same time

Front 51

Most neurons make how many NTs?

Back 51

2 or more

Front 52

What does Acetylcholine do?

Back 52

Excites skeletal muscle to contract and inhibits cardiac muscle and slows heart

Front 53

What does norepinephrine do/

Back 53

Excites cardiac muscle (speeds heart up, stronger contractions)

Front 54

What is Tetrodotoxin?

Back 54

Tetrodotoxin is a powerful poison that selectively blocks voltage-gated Na+ channels.

Front 55

What does Tetrodoxin cause?

Back 55

After it blocks the Na+ channels, APs can't occur and then muscles everywhere can't contract. Death ensues

Front 56

How far do EPSPs and IPSPs travel?

Back 56

1-2 mm

Front 57

On what are EPSPs and IPSPs carried?

Back 57

Carried by local currents along dendrites