11-3. Nerve Impulses

Question 1

resting neuron

Answer 1

not conducting an impulse

Question 2

There is an ____ distribution of __ and ___ inside and outside the neuron.

Answer 2

unequal; Na+, K+

Question 3

Na+ levels are higher ____; K+ levels are higher ___

Answer 3

outside; inside

Question 4

Why is the distribution of ions unequal?

Answer 4

Na+/K+ Pump - uses ATP to actively transport Na+ out and K+ in (3 Na+ out for every 2 K+ in)

Question 5

A resting neuron is 75x more permeable to ___.

Answer 5

K+ - greater number of + charges diffusing out

Question 6

What other ions are found inside and outside the membrane?

Answer 6

large protein anions (A-) are trapped inside; negative Cl- ions outside

Question 7

What causes the difference in charge across the membrane of a resting neuron?

Answer 7

more positive ions moving out of the neuron than into the neuron (Na+ is being pumped out, some K+ is also diffusing out)

Question 8

resting potential

Answer 8

difference in charge across the resting membrane

Question 9

A resting neuron is ___ charged inside, and is referred to as being ___.

Answer 9

negatively; polarized

Question 10

The nerve impulse is also referred to as a(n) ____.

Answer 10

action potential

Question 11

If a threshold stimulus is applied to the neuron, the membrane becomes 1000x more permeable to ___.

Answer 11

Na+

Question 12

What happens to a neuron at the point of stimulation?

Answer 12

The sodium channels open and sodium rushes into the neuron by diffusion and attraction to negative charges inside

Question 13

A stimulated neuron is ___ charged inside, and is referred to as being ___.

Answer 13

positively; depolarized

Question 14

wave of depolarization

Answer 14

area of permeability to Na+ spreads down the neuron:

the local electrical current spreads to adjacent areas of the membrane, causing the Na+ channels to open > Na+ diffuses in > these areas are now also depolarized

Question 15

The charge on a stimulated nerve membrane is called a(n) ___.

Answer 15

action potential

Question 16

After the depolarization wave passes: ____.

Answer 16

Na+ channels close and K+ channels open, causing more K+ to diffuse outside the neuron

Question 17

The outer surface of the neuron becomes ___ charged after the impulse passes, referred to as ___.

Answer 17

positively; repolarization

Question 18

What happens after repolarization?

Answer 18

The Na+ that leaked in and the K+ that diffused out are returned to the original sides of the membrane by the Na+/K+ Pump.

Question 19

How is an impulse conducted down a unmyelinated neuron?

Answer 19

continuous conduction

Question 20

How is an impulse conducted down a myelinated neuron?

Answer 20

saltatory conduction

Question 21

continuous conduction

Answer 21

step-by-step depolarization of each adjacent area of an axon in an unmyelinated neuron

Question 22

myeline sheath

Answer 22

fatty insulated around some axons that doe snot conduct electrical current

Question 23

node of Ranvier

Answer 23

unmyelinated gaps where depolarization can occur, and action potentials can be generated

Question 24

saltatory conduction

Answer 24

the nerve impulse jumps from node to node along a myelinated axon - greatly increasing the speed of nerve impulse conduction

Question 25

Speed is ___ stimulus strength

Answer 25

independant of

Question 26

All-or-none Principle

Answer 26

an action potential either happens completely or not at all - if a stimulus is strong enough to cause an action potential, a stronger stimulus will not make it travel faster

Question 27

What affects the speed of nerve impulses?

Answer 27

1. temperature - warm neurons conduct at faster speed
2. size of axon - larger diameters conduct impulses faster (less resistance)
3. presence/absence of myelin - myelinated axons conduct faster (biggest effect on speed)

Question 28

synapse

Answer 28

junction between two neurons - transfers information from one neuron to another

Question 29

synaptic cleft

Answer 29

tiny space between the 2 neurons filled with ECF

Question 30

presynaptic neuron

Answer 30

brings the nerve impulse to the synapse

Question 31

postsynaptic neuron

Answer 31

carries the nerve impulse away from the synapse

Question 32

When a wave of depolarization reaches the end of a presynaptic neuron: _____.

Answer 32

synaptic vesicles in the synaptic knobs fuse with the membrane and release their contents into the cleft

Question 33

neurotransmitter

Answer 33

the chemical released from the synaptic vesicles in response to an action potential

Question 34

Neurotransmitters ___ across the cleft and bind to ___ on the ____.

Answer 34

diffuse; receptors; postsynaptic membrane

Question 35

Why does the synapse result in one-way impulse conduction?

Answer 35

only axon terminals have neurotransmitters - not in the cell body

Question 36

Each neuron releases ___ of neurotransmitter.

Answer 36

one type