4.9 - The Nervous System

Question 1

neuroglia (glial cells) (3)

Answer 1

1. help to support/protect neurons
2. supply nutrients
3. remove wastes
   (at least as many glia as neurons)

Question 2

types of glial cells (6)

Answer 2

1. astrocyte (astroglia)
2. microglia
3. satellite cells
4. myelinated glia
5. oligodendrocytes
6. Schwann cells

Question 3

astrocyte (astroglia) role

Answer 3

provide physical and nutritional support for neurons)

Question 4

microglia role

Answer 4

digest parts of dead neurons

Question 5

satellite cell role

Answer 5

physical support to neurons in the PNS

Question 6

oligodendrocyte role

Answer 6

provide myelin to neurons in the CNS

Question 7

Schwann cell role

Answer 7

provides myelin to neurons in the PNS

Question 8

Na+/K+ ATPase role

Answer 8

pumps Na+ out/K+ into cell against conc gradient

Question 9

Types of ion channels in neurons (3)

Answer 9

1. leak channels
2. ligand-gated channels
3. voltage-sensitive channels

Question 10

K+ leak channels role

Answer 10

at rest neurons permeable to K+ but not Na+ due to K+ leak channels

Question 11

role of Na+/K+ ATPase (2)

Answer 11

1. maintenance of resting membrane potential
2. maintains concentration gradient (Na+ high outside, K+ high inside)

Question 12

movement of Cl- into neuron

Answer 12

hyperpolarisation

Question 13

resting membrane potential

Answer 13

-70mV

Question 14

change making membrane potential more positive

Answer 14

depolarisation

Question 15

changes making membrane potential more negative

Answer 15

hyperpolarisation

Question 16

first response

Answer 16

small, localised charge alterations in cell’s membrane

Question 17

how can a first response become a cascade effect?

Answer 17

if enough ligand-gated ion channels activated -> voltage sensitive Na+ channels activated -> action potential

Question 18

graded potentials (3)

Answer 18

1. small stimulus (change in voltage)
2. decays along axon or dendrite (some current leaks across membrane)
3. can’t be propagated along axons by passive conduction alone

Question 19

threshold

Answer 19

enough depolarisation -> V-gated Na+ channels open -> more Na+ enters -> action potential

Question 20

pathway of action potential

Answer 20

electrical signal from cell body (axon hillock) down axon to terminal boutons (presynaptic points)

Question 21

refractory period

Answer 21

V-gated Na+ briefly inactivated
- prevents second action potential occurring during one action potential

Question 22

problems with unmyelinated axons (3)

Answer 22

1. signals at risk of dispersing across membrane
2. energy demanding
3. quite slow (<1.5m/s)

Question 23

what can improve unmyelinated axons?

Answer 23

larger axon diameter (squid giant axon - invertebrate approach to potential problem of signal decay/dispersal)

Question 24

myelin

Answer 24

multiple layers of glial cell membranes -> electrical insulation

Question 25

role of myelin

Answer 25

speeds up signals due to saltatory conduction

Question 26

saltatory conduction

Answer 26

signal jumps between sections of myelin

Question 27

nodes of ranvier

Answer 27

voltage-sensitive channels present in myelin gaps

Question 28

local depolarisation -> spread of actionnpotential

Answer 28

jumps from node of ranvier to node of ranvier (where channels are located)