Class 6

Question 1

Chapter 9

Answer 1

The nervous and endocrine systems

Question 2

Neurons

Answer 2

Neutrons are specialized cells that transmit and process information from one part of the body to another.

Question 3

Action potentials

Answer 3

Information takes the form of electrochemical impulses known as action potentials.

Question 4

synaptic transmission

Answer 4

action potential reaches the end of an axon at a synapse, the signal is transformed into a chemical signal with the release of neurotransmitters into synaptic cleft, a process called synaptic transmission.

Question 5

Neuron

Answer 5

The basic structural and functional unit of the nervous system is the neuron.

These cells neurones) transmit and process action potential.

Question 6

Soma

Answer 6

Neutrons have a mental cell body called soma.

It contains the nucleus, and this is where most of the biosynthetic activity of the cell takes place.

Question 7

Neutrons have only ____ axon but many ____

Answer 7

One

dendrites

Question 8

bipolar

Answer 8

Neutrons with one dendrite are termed bipolar.

Question 9

Multipolar

Answer 9

neutrons with many dendrites are multipolar.

Question 10

direction of action potential in axon

Answer 10

away from the cell body

Question 11

What is the difference between neutron and nerve?

Answer 11

neutron is a single cell.

a nerve is a large bundle of many different axons from different neutrons.

Question 12

kinesin

Answer 12

a motor protein called kinesin is one of the several different proteins that drive movement of vesicles and organelles along microtubules in axons.

Question 13

anterograde movement

Answer 13

movement from the soma toward the axon terminus.

This is how kinesin drives movement.

Question 14

atrophy

Answer 14

(of body tissue or an organ) waste away, typically due to the degeneration of cells, or become vestigial during evolution.

Question 15

If a chines inhibitor is added to neutrons in culture, what is the likely result?

Answer 15

If materials can not be transported through through the axon from the cell body, atrophy of axons will occur.

Question 16

The resting membrane potential

Answer 16

the resting membrane potential is an electric potential across the plasma membrane of approximately - 70 millivolts (mV), with the interior of the cell negatively charged with respect to the exterior of the cell.

Question 17

What are the two primary membrane proteins that are required to establish the resting membrane potential?

Answer 17

The Na+/K+ ATPase and

the potassium leak channels

Question 18

Na+/K+ ATPase

Answer 18

The Na+/K+ ATPase pumps three sodium ions out of the cell and two potassium ions into the cell with the hydrolysis of one ATP molecule.

Question 19

What form of transport is carried out by the Na+/K+ ATPase?

Answer 19

The Na+/K+ ATPase uses ATP to drive transport against a gradient; this is primary active transport.

Question 20

What is the result of pumping three sodium ions out of the cell and two potassium ions into the cell?

Answer 20

The result is a sodium gradient with high sodium outside of the cell and a potassium gradient with high potassium inside the cell.

Question 21

Leak channels

Answer 21

Leak channels are channels that are open all the time. This allows the ions to leak across the membrane based on their gradient. Eg. Potassium leak channels allow potassium but no other ions to flow down their concentration gradient.

Question 22

If the potassium leak channels are blocked, what will happen to the membrane potential?

Answer 22

The flow of potassium out of the cell makes the interior of the cell more negatively charged. Blocking the potassium leak channels would reduce the magnitude of the resting membrane potential, making the interior of the cell less negative.

Question 23

What would happen to the membrane potential if sodium ions were allowed to flow down their concentration gradient?

Answer 23

Sodium ions would flow into the cell and reduce the potential across the plasma membrane, making the interior of the cell less negative and even relatively positive if enough ions flow into the cell.

Question 24

Why are the cells described as polarized?

Answer 24

The resting membrane potential establishes a negative charge along the interior of axons.Thus the cell can be described as polarized; negative on the inside and positive on the outside.

Question 25

What is an action potential?

Answer 25

An action potential is a disturbance in the membrane potential, a wave of depolarization of the plasma membrane that travels along an axon.

Question 26

What is depolarization?

Answer 26

Depolarization is a change in the membrane potential from the resting membrane potential of approximately -70mV to a less negative, or even positive potential. After depolarization, repolarization returns the membrane potential to normal.

Question 27

Voltage -gated sodium channels are _____

Answer 27

proteins located in the plasma membrane of the axon.

Question 28

What is the effect of opening the voltage - gated sodium channels on the membrane potential?

Answer 28

Sodium ( positively charged) flows into the cell, down its concentration gradient, making the interior of the cell less negatively charged, or even positively charged.

Question 29

resting potential is

Answer 29

-70mV

Question 30

Threshold potential is approximately

Answer 30

-50mV

Question 31

What happens when the threshold is reached?

Answer 31

Once the threshold is reached, the channels are opened fully, but below the threshold, they are closed and do not allow the passage of any ions through the channel. When the channels open, sodium flows into the cell, down its concentration gradient, depolarizing that section of the membrane to about +35 mV before inactivating.

Question 32

If an action potential starts at one end of an axon, can it run out of energy and not reach the other end?

Answer 32

No it cannot. Action potentials are continually renewed at each point in the axon as they travel. Assuming there are enough voltage gated channels, once an action potential starts, it will propagate without a change in amplitude until it reaches a synapse.

Question 33

What opens a voltage-gated ion channel?

Answer 33

voltage - gated ion channels require a threshold depolarization to open. A depolarization below threshold will produce no response. This is called an all or none response.

Question 34

What happens when voltage gated sodium channels open?

Answer 34

sodium flows into the cell and depolarizes the membrane to positive values.

Question 35

Repolarization

Answer 35

Voltage gated potassium channel open more slowly than voltage gated sodium channel and stay open longer.

Voltage gated sodium channels open in response to membrane depolarization.

As potassium leaves the cell down its concentration gradient, the membrane potential returns to negative values, actually overshooting the resting potential by about 20mV ( i.e to about -90mV). At this point, the voltage gated potassium channels close.

potassium leak channels and the Na+/K+ ATPase continue to function ( as they always do) to bring the membrane back to resting potential.

All these depolarize the membrane potential even without the voltage-gated potassium channels, but it would take longer.