NERVOUS SYSTEM (LECTURE 14)

Question 1

How many functions does the nervous system have?

Answer 1

3

Question 2

Name the 3 functions of the nervous system.

Answer 2

Sensory input, integration, motor output.

Question 3

Sensory input is the response to…

Answer 3

external and internal stimuli, made possible by sensory neurons.

Question 4

Describe integration.

Answer 4

It is the interpretation of sensory input - decides the appropriate response.

Question 5

Describe motor output.

Answer 5

It is the conduction of signals from the central nervous system to the effector cells, made possible by motor neurons.

Question 6

Neurons are cells specialized for…

Answer 6

transmitting electrical and chemical signals.

Question 7

Neurons are comprised of what 2 structural components?

Answer 7

The cell body and fiber-like extensions.

Question 8

What are the 2 classes of fiber-like extensions found on neurons?

Answer 8

Dendrites and axons.

Question 9

Describe dendrites.

Answer 9

These convey signals towards the cell body - they are short and numerous.

Question 10

Describe axons.

Answer 10

These conduct impulse away from the cell as long, single processes. Some are insulated by a myelin sheath and they all end in an axon terminal.

Question 11

What do axon terminals do?

Answer 11

They relay signals to other cells by releasing neurotransmitters.

Question 12

Neurons communicate via…

Answer 12

synapses.

Question 13

Neurotransmitters are released from a ____ neuron and act on a ____ neuron.

Answer 13

Neurotransmitters are released from a pre-synaptic neuron and act on a post-synaptic neuron.

Question 14

Nerve signals/impulses are changes in…

Answer 14

voltage across the plasma membrane.

Question 15

Nerve signals/impulses (changes in voltage) are caused by…

Answer 15

the movement of ions across the membrane.

Question 16

What (positively charged) ions move across a neuron’s membrane to cause changes in voltage?

Answer 16

Na+ and K+.

Question 17

What is the membrane potential of a resting neuron?

Answer 17

About -70 mV.

Question 18

Is the inside or outside of a resting neuron more negative?

Answer 18

The inside is more negative than the outside.

Question 19

What determines membrane potential?

Answer 19

The ion distribution across the membrane.

Question 20

What negatively charged molecules (anions) can cause a change in membrane potential? (5)

Answer 20

Negatively charged proteins, amino acids, sulfate and phosphate, Cl-.

Question 21

Charged molecules can cross a neuron membrane using what 2 ways?

Answer 21

Either through passive ion channels or gated ion channels.

Question 22

What are passive ion channels important for? When do they close?

Answer 22

These are important for maintaining -70mV membrane potential. They are open all the time.

Question 23

Describe gated ion channels.

Answer 23

These require a stimulus to open.

Question 24

Give an example of a stimulus that can open a gated ion channel.

Answer 24

A change in voltage.

Question 25

What does the Na+/K+ ATPase pump do?

Answer 25

These maintain concentration gradients of Na+ and K+ across the membrane (High [Na+] outside and high [K+] inside).

Question 26

For every 1 ATP used, how many Na+ / K+ are pumped into / out of the neuron?

Answer 26

3 Na+ pumped out. 2 K+ pumped in.

Question 27

There are many passive ____ ____ channels that are always ____.

Answer 27

There are many passive K+ channels that are always open.

Question 28

What does K+ do with the help of the many passive K+ channels?

Answer 28

K+ diffuses down its concentration gradient out of the cell (gradient created by the Na+/K+ ATPase pump).

Question 29

Stimuli can cause changes in ____ ____.

Answer 29

Stimuli can cause changes in membrane potential.

Question 30

Stimuli opens ____ ____ ____, changing the ____ ____ across the membrane.

Answer 30

Stimuli opens gated ion channels, changing the charge distribution across the membrane.

Question 31

Hyperpolarization is occurring when...

Answer 31

the inside of the neuron becomes more negative due to gated K+ channels opening, allowing K+ to diffuse out of the cell.

Question 32

Depolarization is occurring when...

Answer 32

the inside of the neuron becomes more positive due to Na+ channels opening, allowing Na+ into the cell.

Question 33

When is an action potential generated?

Answer 33

When a depolarizing stimulus is strong enough to pass the threshold potential.

Question 34

What does an action potential do if it is generated?

Answer 34

Action potential moves along the entire length of the axon and stimulates the release of neurotransmitters from the axon terminal.

Question 35

Name the steps to generate (propagate) an action potential. (5)

Answer 35

(1) Resting state. (2) Threshold. (3) Depolarization. (4) Repolarization. (5) Undershoot.

Question 36

Describe the resting state. (2)

Answer 36

No gated channels are open; -70mV resting potential.

Question 37

Describe threshold - what occurs at threshold?

Answer 37

Stimuli causes gated Na+ channels to open ; Na+ flows in causing depolarization.

Question 38

Describe depolarization.

Answer 38

If depolarization reaches threshold, an action potential will begin. At threshold, voltage-gated Na+ channels open causing a large depolarization.

Question 39

Describe repolarization.

Answer 39

Na+ channels close AND K+ channels open - K+ moves out of the cell.

Question 40

Describe undershoot.

Answer 40

K+ channels are slow to close allowing more K+ to leave. Membrane potential is more negative than resting potential.

Question 41

Why is the neuron's membrane insensitive to stimuli during repolarization and undershoot?

Answer 41

Na+ channels are closed and thus membrane is insensitive to stimuli.

Question 42

An action potential is a ____ ____ event.

Answer 42

An action potential is a localized electrical event.

Question 43

Describe the propagation (path) of the action potential.

Answer 43

If stimulation is strong enough to reach threshold, an action potential will be initiated and move along the length of the axon to the axon terminal.

Question 44

How does the action potential propagate along the axon?

Answer 44

Depolarization in one part of the axon causes depolarization in the region right next to it by opening voltage gated Na+ channels.

Question 45

Why can an action potential only move in one direction?

Answer 45

Since during repolarization and undershoot (processes directly following depolarization), a membrane cannot be depolarized - so action potential can only move in one direction.

Question 46

What is a synapse?

Answer 46

It is a space between presynaptic (transmitting) cell and a postsynaptic (receiving) cell.

Question 47

What occurs at chemical synapses?

Answer 47

Neurotransmitters are released from the axon terminal of a presynaptic cell and act on a postsynaptic cell.

Question 48

Describe what happens at a synapse in 4 steps.

Answer 48

(1) Action potential arrives at the axon terminal. (2) Ca2+ stimulates the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane. (3) Neurotransmitters bind to ligand-gated ion channels on the postsynaptic membrane. (4) Neurotransmitters are quickly degraded or taken back up by the presynaptic cell.

Question 49

How does the arrival of the action potential at the axon terminal result in the introduction of Ca2+?

Answer 49

Depolarization of the presynaptic membrane causes voltage-gated Ca2+ channels to open and Ca2+ to move into the axon terminal.

Question 50

How does the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane lead to the release of neurotransmitters in to the synapse?

Answer 50

Neurotransmitters are released into the synaptic cleft via exocytosis.

Question 51

A postsynaptic neuron will form ____ (____ to ____) with many ____ ____.

Answer 51

A postsynaptic neuron will form synapses (hundreds to thousands) with many presynaptic neurons.

Question 52

What is excitatory postsynaptic potential (EPSP)?

Answer 52

Where Na+ and K+ channels are involved in depolarization.

Question 53

What is inhibitory postsynaptic potential (IPSP)?

Answer 53

When K+ and Cl- channels are involved in hyperpolarization.