the action potential

Question 1

what is a neuron?

Answer 1

a specialized type cell that is electrically excital

Question 2

what kind of signals do neurons send?

Answer 2

electrical and chemical signals that permit fast communication

Question 3

explain reticulor theory

Answer 3

believed that the brain was a physically connected network

Question 4

explain neuron doctrine

Answer 4

believed that the brain was composed of individual cells communicating

Question 5

name and explain different parts of neuron

Answer 5

1. soma
   cell body: location of the nucleus and other organelles
2. dendrites:
   sites for receiving chemical or sensory input
3. axon
   electrical signals (action potentials) are sent down the axon. only one axon, but that axon can branch many times.
4. axon terminal:
   end of axon, where the action potent triggers the release of neurotransmitters

Question 6

describe the neuron anatomy

Answer 6

phospholipid bilaye: cell membrane
ions cannot move across
what’s inside?
- cytosol
salty water-like solution
filled with potassium (K+), chlorine (Cl-), and sodium (Na+)

Question 7

what makes a cell specialized?

Answer 7

• all cells within an organism have the same DNA
• not all cells read the same sections of DNA
• a section of DNA (the gene) codes for a certain protein
• neurons are filled with proteins that determine the cell’s respiration

Question 8

how does transcription happen?

Answer 8

dna:
- string of nucleic
- in the nucleus (where it’s safe)
- strings of DNA = gene

mRNA:
- string of nucleic acid
- moved out nucleus to cytosol

Question 9

how does translation happen?

Answer 9

mRNA:
- read by ribosome to make strings of amino acids (proteins)

Protein:
- string of folded up amino acids
- made in cytosol
- a functional protein = folded up amino acid chains

Question 10

give examples of proteins

Answer 10

channels, pumps, receptors, transporters, messengers, scaffolds

Question 11

how do neurons communicate?

Answer 11

electrical:
relies on membrane potential (Vm; difference in charges between inside and outside of cell)
down the axon

chemical:
- relies on neurotransmitters
- release from axon terminal onto other neurons
- at the synapse

Question 12

what are ions?

Answer 12

molecules carrying electrical charge

Question 13

name the cations (4)

Answer 13

• sodium (Na+)
• potassium (K+) (more abundant inside cell)
• calcium (Ca2+)
• magnesium (Mg+)

Question 14

anion (1)

Answer 14

chloride (Cl-)

Question 15

name the ion channels that set the resting potential

Answer 15

sodium potassium pump
potassium leak channel

Question 16

explain the sodium potassium pump

Answer 16

sets the concentration gradient (the gradual change in the concentration of solutes in a solution as a function of distance through a solution) sends Na+ out the cell and K+ into cell

Question 17

explain the potassium leak channel

Answer 17

channel allows K+ to move freely in/out of cell; K+ leaking out sets negative Vm (membrane potential). if there is a greater concentration gradient of K+ outside the cell, K+ will travel into the cell using these channels

Question 18

what starts an action potential?

Answer 18

• when different ions cross the neuron membrane
  -we then have a negatively charged cell - positive ions want to come because of electrostatic pressure (the force on two ions with similar charge to repel each other and the force of two ions with opposite charge to attract to one another).
• sodium also wants to come in to move down the concentration gradient
• some depolarizing stimulus:
  eg; neurotransmitters released from another cell, sensory stimulus . receptor binding opens ion channels, allowing initial influx of Mv

Question 19

name the ion channels during the action potential

Answer 19

voltage-gated sodium channel
voltage-gated potassium channel

Question 20

explain the voltage-gated sodium channel

Answer 20

Opens when the cell is slightly depolarized
(~-40 mV); responsible for initiation of action potential

Question 21

explain the voltage-gated potassium channel

Answer 21

Opens when the cell is very depolarized
(~+60 mV); responsible for return to baseline Vm

Question 22

name the ion channel at axon terminal

Answer 22

voltage-gated calcium channel

Question 23

explain the function of voltage-gated calcium channel

Answer 23

Ca2+ into the cell triggers neurotransmitter
release

Question 24

how does the action potential travel down the axon?

Answer 24

The arrival of positive ions at this node depolarises this section of the axon as well, initiating another action potential. This process is repeated, allowing the action potential to propagate rapidly along the axon, effectively ‘jumping’ between nodes. This ‘jumping’ mechanism is known as saltatory conduction.

Question 25

why doesn’t the action potential work backwards?

Answer 25

• an action potential involves an influx positive charge into the cell
• the influx of positive ions pushes other positive ions away (down the concentration gradient)
• previously active voltage-gated Na channels are in refractory period (a period of time during which a cell is incapable of repeating an action potential.) (ball clogging pore)
• influx of positive ions cannot reopen them

Question 26

how do we make the propagation of action potential more efficient?

Answer 26

myelination: the production of the myelin membrane that wraps axons in the central and peripheral nervous systems.

Question 27

describe the glia and its components

Answer 27

astrocytes:
janitors of the cell
break down and clean up waste
provides scaffolding for other cellular functions

microglia:
provide immune support
regulate cell development and response to injury

oligodendrocy:
create myelin , wrapped around nearby axon
can provide sheath for 50 axons
Schwann cells = equivalent in peripheral nervous system

Question 28

explain the saltary conduction

Answer 28

• insulation means the ion inside myelinated axon segments are insensitive to charge differences outside
• positive charge quickly travels down axon and in repropagated a nodes of Ranvier *(unmyelinated segments of membrane at which the action potential is repropagated)

Question 29

what happens at the axon terminal?

Answer 29

Voltage-Gated Calcium Channel – open following depolarization, permit
Ca2+ entry

Question 30

name the two main types of receptors

Answer 30

I O N O T R O P I C
 Ion channels
 Direct, fast effect on cell
potential

Excitatory
EPSP
Na+ permeable

Inhibitory
IPSP
Cl- permeable

M E TA B O T R O P I C
 G-protein coupled receptors
 Can act indirectly on ion
channels
 Slower modification of cell
excitability

Question 31

name the two way neurotransmitters get removed

Answer 31

reuptake and enzymatic deactivation

Question 32

explain reuptake

Answer 32

Reuptake proteins transport
neurotransmitter back across
the membrane of the
presynaptic cell
 Neurotransmitter can then be
repackaged into a vesicle for
another round of release

Question 33

explain enzymatic deactivation

Answer 33

Enzymes (proteins dedicated to
destruction) break down
neurotransmitter in the synapse

Question 34

explain metabotropic receptors

Answer 34

Metabotropic receptors
have lots of different
effects on the cell –
depends on the receptor
and the signalling cascade
its activation causes