Question

1. what is the fatty layer that surrounds some axons?

a. nissl body
b. dendrite
c. gray matter
d. myelin sheath

1. what do neuroglial cells not do?

a. fill spaces
b. support neurons
c. carry out phagocytosis
d. conduct impulses

1. which ion is represented by the symbol k⁺?

a. sodium
b. calcium
c. chloride
d. potassium

1. which ion passes easily through the nerve cell membrane?

a. na⁺
b. cl⁻
c. ca²⁺
d. k⁺

1. when a nerve cell is at rest, where are there more na⁺ ions?

a. inside the cell
b. in the nucleus
c. equally inside and outside
d. outside the cell

1. which ion is more concentrated inside a resting nerve cell?

a. sodium
b. calcium
c. chloride
d. potassium

1. what causes the inside of the nerve cell to be negatively charged at rest?

a. excess na⁺
b. excess cl⁻ outside
c. presence of schwann cells
d. non - diffusible negative ions inside

1. what is the term for the difference in charge across the membrane at rest?

a. action potential
b. equilibrium
c. synaptic charge
d. resting potential difference

1. what term describes the resting state of a nerve cell?

a. hyperactive
b. neutral
c. diffused
d. polarized

1. what must be reached before a nerve signal starts?

a. resting level
b. potential energy
c. synaptic potential
d. threshold potential

1. when threshold is reached, what ion moves inside the neuron?

a. potassium
b. chloride
c. calcium
d. sodium

1. what happens immediately after sodium enters during an action potential?

a. sodium gates close permanently
b. schwann cells remove ions
c. cell becomes neutral
d. potassium exits the cell

1. how long does an action potential take?

a. 1 second
b. 1/10 second
c. 1/100 second
d. 1/1000 second

1. where does the nerve impulse jump from node to node?

a. myelin sheath
b. schwann cell
c. dendrite
d. nodes of ranvier

Explanation:

1. Myelin sheath is the fatty insulating layer around axons.
2. Neuroglial cells support neurons but do not conduct electrical impulses (neurons do this).
3. The symbol K⁺ represents the potassium ion.
4. Potassium ions (K⁺) have high permeability across resting nerve cell membranes.
5. At rest, sodium ions are more concentrated outside the nerve cell due to ion pumps.
6. Potassium ions are more concentrated inside a resting nerve cell.
7. Trapped non-diffusible negative ions inside the cell create a negative resting charge.
8. Resting potential difference is the charge difference across a resting neuron membrane.
9. A resting nerve cell is polarized, with a negative internal charge relative to the outside.
10. Threshold potential is the minimum stimulus needed to trigger a nerve signal.
11. When threshold is reached, sodium ions rapidly move into the neuron to start an action potential.
12. After sodium enters, potassium exits the cell to repolarize the membrane.
13. An action potential lasts approximately 1 millisecond (1/1000 second).
14. Nerve impulses jump between Nodes of Ranvier (gaps in myelin) in saltatory conduction.

Answer:

1. D. Myelin sheath
2. D. Conduct impulses
3. D. Potassium
4. D. K⁺
5. D. Outside the cell
6. D. Potassium
7. D. Non-diffusible negative ions inside
8. D. Resting potential difference
9. D. Polarized
10. D. Threshold potential
11. D. Sodium
12. D. Potassium exits the cell
13. D. 1/1000 second
14. D. Nodes of Ranvier