2.2.1 The Nerve Impulse 2

Question 1

By increasing a negative charge within a neuron we see a change called ____, which means increased polarisation.

Answer 1

hyperpolarisation

Question 2

Reducing the negative charge with a neuron towards zero is called ____.

Answer 2

depolarisation

Question 3

Stimulation beyond the ____ of ____ produces a massive depolarisation of the membrane. When the potential reaches the threshold, the membrane opens the sodium channels and permits sodium to flow into the cell.

Answer 3

threshold of excitation

Question 4

Any stimulation beyond the threshold, regardless of how far beyond, produces a big response. That response, a rapid depolarisation and then reversal of the usual polarisation, is the ____ ____.

Answer 4

action potential

Question 5

The action potential always starts in an ____ and propagates without loss along the ____.

Answer 5

axon

Question 6

For a given neuron, all action potentials are approximately equal in ____ and ____.

Answer 6

amplitude and velocity

Question 7

According to the ____ law, the amplitude and velocity of an action potential are independent of the intensity of the stimulus that initiated it, provided that the stimulus reaches the threshold.

Answer 7

all-or-none

Question 8

To signal the difference between a weak and a strong stimulus the axon sends more ____ action potentials to signal ____ ____ of stimulus.

Answer 8

frequent : greater intensity

Question 9

Immediately after an action potential, the cell is in a ____ ____ during which it resists the production of further action potentials.

Answer 9

refractory period

Question 10

In the first part of the refractory period, the ____ ____ ____, the membrane cannot produce an action potential, regardless of the stimulation.

Answer 10

absolute refractory period

Question 11

During the second part, the ____ ____ ____, a stronger tun usual stimulus is necessary to initiate and action potential.

Answer 11

reflective refractory period

Question 12

The refractory period has two mechanisms. The ____ channels are closed, and ____ is flowing out of the cell at a faster than usual rate.

Answer 12

sodium : potassium

Question 13

It is important for axons to convey impulses without any loss of ____ over distance.

Answer 13

strength

Question 14

In a motor neuron, an action potential begins on the ____ ____, a swelling where the axon meets the soma.

Answer 14

axon hillock

Question 15

During the action potential, sodium ions enter a point on the axon. Temporarily, that spot is positively charged in comparison with neighbouring areas along the axon. The positive ion flows within the axon to neighbouring ____. The positive charges slightly ____ the next area of the membrane, causing it to reach its threshold and open its voltage-gated sodium channels. Therefore, the membrane ____ the action potential at that point. In this manner, the action potential travels along the axon.

Answer 15

regions : depolarise : regenerates

Question 16

The term ____ of the ____ ____ describes the transmission of action potential down an axon.

Answer 16

propagation of the action potential

Question 17

Myelinated axons are those covered with a ____ ____.

Answer 17

myelin sheath

Question 18

Myelinated axons, found only in vertebrates, are covered with layers of ____ and ____.

Answer 18

fats and proteins

Question 19

The myelin sheath is interrupted periodically by short sections of axon called ____ of ____, each one about one micrometer wide.

Answer 19

nodes of Ranvier

Question 20

The jumping of action potentials from node to node is referred to as ____ ____.

Answer 20

saltatory conduction

Question 21

In addition to providing rapid conduction of impulses, saltatory conduction conserves energy: instead of admitting sodium ions at every point along the axon and then having to pump them out via the sodium-potassium pump, a myelinated axon admits sodium only at its ____.

Answer 21

nodes

Question 22

An axon that never had a myelin sheath conducts impulses ____ but steadily.

Answer 22

slowly

Question 23

In axon that has lost its myelin is not the same. After myelin forms along an axon, the axon loses its sodium channels under the myelin. If the axon later loses it’s myelin, it still lacks sodium channels in the areas previously covered with myelin, and most action potentials die out between one node and the next. Associated with _____ ____.

Answer 23

Multiple sclerosis

Question 24

Many small neurons have no axon. Neurons without an axon exchange information with only their closest neighbours. We therefore call them ____ ____.

Answer 24

local neurons

Question 25

When a local neuron receives information from other neurons, it has a ____ ____, a membrane potential that varies in magnitude in proportion to the intensity of the stimulus.

Answer 25

graded potential

Question 26

In a graded potential, the change in the membrane potential is conducted to adjacent areas of the cell, in all directions, gradually decaying as it travels. Those various areas of the cell contact other neurons, which they excite or inhibit through ____.

Answer 26

synapses