2.1 The Cells of the Nervous System

Question 1

astrocytes

Answer 1

large glial cells with round or radially symmetrical forms; they surround neurons and are in close contact with the brain’s vasculature (vaatstelsel). An astrocyte makes contact with blood vessels at specializations called end feet, which permit the astrocyte to transport ions across the vascular wall.

Question 2

blood-brain barrier (BBB)

Answer 2

The astrocytes create a barrier between the tissues of the CNS and the blood. The BBB restricts the diffusion of microscopic objects (such as most bacteria) and large hydrophilic molecules in the blood from entering the neural tissue, but it allows the diffusion of small hydrophobic molecules, such as oxygen, carbon dioxide, and hormones. The astrocytes also have an active role in brain function. They may either directly or indirectly regulate the reuptake of neurotransmitters.

Question 3

oligodendrocytes

Answer 3

form myelin in the CNS

Question 4

Schwann cells

Answer 4

form myelin in the PNS

Question 5

Microglial cells

Answer 5

which are small and irregularly shaped, are phagocytes that devour and remove damaged cells. Unlike many cells in the CNS, microglial cells can proliferate even in adults (as do other glial cells).

Question 6

Ion channels

Answer 6

are proteins with a pore through the center, and they allow certain ions to flow down their electrochemical and concentration gradients

Question 7

Ion pumps

Answer 7

use energy to actively transport ions across the membrane against their concentration gradients—that is, from regions of low concentration to regions of higher concentration.

Question 8

permeability

Answer 8

ion channels who only allow one, or small subset of ions to pass through

Question 9

gated vs nongated ion channels

Answer 9

They open or close in response to changes in nearby transmembrane voltage, or to chemical or physical stimuli.
vs
ion channels that are unregulated, and hence always allow the associated ion to pass through

Question 10

electrical gradiant (resting state)

Answer 10

NA+ (sodium/natrium) and the Cl- (chloride) concentrations are greater outside the cell, and K+ (potassium/kalium) concentrations are greater inside the cell. So more postive charged ions outside the cell relative to the inside.

Question 11

electrochemical equilibrium

Answer 11

the concentration gradient and the electro gradient for each ion is equal and opposite.

Question 12

voltage-gated channels vs ligand-gated channels vs mechanically-gated channels

Answer 12

only open when the membrane potential reaches a certain value (mostly allow only a single ion to pass through)
vs
are triggerd to opne when they are bound by a specific molecule
vs
open in response to physcial forces such as changes in length or pressure

Question 13

graded potential

Answer 13

small change in membrance potential, can be either positive or negative

Question 14

sodium-potassium pump

Answer 14

uses the energy generated by ATP hydrolysis, to actively transports ions across the membrane against their concentration gradient. NA+ (sodium) is transported outside the cell where it’s concentration is higher, and K+ (potassium) is transported back into the cell where its concentration is higher. (3 NA+ outside, 2 K+ inside). Thus restoring the gradients.

Question 15

depolarization

Answer 15

is an all-or-nothing event that is initiated by the opening of NA+ (sodium) ion channels within the plasma membrane.

Question 16

repolarization

Answer 16

The subsequent return to resting potential, repolarization, is mediated by the opening of K+ (potassium) ion channels.

Question 17

hyperpolarization

Answer 17

Hyperpolarization is a phase where some K+(potassium) channels remain open and NA+ (sodium)channels reset. A period of increased potassium permeability results in excessive potassium efflux before the potassium channels close. This results in hyperpolarization as seen in a slight dip following the spike.

Question 18

absolute refractory period

Answer 18

The period of time when a nerve cannot fire another action potential, no matter how strongly it’s stimulated.

Question 19

relative refractory period

Answer 19

Is the period of time during which only a large stimulus will generate an action potential.

Question 20

1saltatory conduction

Answer 20

describes the way an electrical impulse skips from node to node down the full length of an axon