Neurophysiology: From Cells to Networks

Question 1

Neurones

Answer 1

• The basic unit of structure and function in the nervous system
• Cells that conduct impulses
• Process information
• Sense environmental changes
• Communicate changes to other neurons
• Command body response
• High energy usage, constant need for glucose and oxygen

Question 2

Cell Body

Answer 2

• Contain nucleus and cellular

activity

Question 3

Axons

Answer 3

• Single extension of the

neurones providing output.

Question 4

Dendrites

Answer 4

• Branch like extensions that

receive messages from other neurones.

Question 5

Neuronal types:

Answer 5

• Motor
– carry impulses away from the brain and spinal cord
• Sensory
– carry impulses from inside / outside the
body to brain / spinal cord.
• Relay
– process incoming impulses and pass them on to motor neurons

Question 6

Neuronal Networks:

Answer 6

Neurones exist within neural tissue, where multiple neurones synapse with each other to produce an active network.
Activity is a measure of summation of inhibitory and excitatory action.
Can be recorded through an electroencephalogram (EEG).

Question 7

Neuronal Networks: EEG

Answer 7

Sub-dermal electrodes placed at specific locations on the dog skull, corresponding to regions of the canine cortical lobes.
• Pre-frontal (Fp)
• Frontal (F)
• Parietal (P)
• Occipital (O)
• Temporal (T)

EEG rhythm is a combination of local field potentials (LFP).
LFP is a measure of the underlying ionic environment, and therefore activity.

Question 8

action potential

Answer 8

a rapid reversal of the resting membrane potential

Question 9

how is an action potential generated

Answer 9

different ions with different electric charges are dissolved in the brain
movement of these ions across the membrane through specialised proteins is how an action potential is generated

Question 10

sphere of hydration

Answer 10

ions are atoms with a net electric charge
water molecules “stick” electrostatically to ions and form a sphere of hydration
this sphere of hydration increases the relative size of the atom

Question 11

an ion surrounded by a sphere of hydration is…

Answer 11

Much too large to pass through the membrane

Question 12

main ions dissolved in the brain

Answer 12

calcium
sodium
potassium
chloride

Question 13

ion channels

Answer 13

allow ions to pass in and out of a neuron
made form multiple subunits
a subunit is a protein that has been shaped into a tertiary structure
acts as a door to allow ions to pass through the membrane
come in a wide range of shapes and sizes
can open and close
highly selective

Question 14

a portion of the channel may have an electric charge.

only ions that are…

Answer 14

small enough to fit through the pore and carry an opposite charge may pass

Question 15

resting state

Answer 15

a neuron is integrating incoming signals and not generating an action potential. it is at rest

Question 16

action state

Answer 16

a neuron has been excited past threshold and fires an action potential

Question 17

negative charge inside of a neuron is

Answer 17

an absolute requirement for a functioning nervous system

Question 18

membrane potential

Answer 18

the voltage across the membrane at iny moment (in millivolts)
represented by Vm
at rest, Vm = -65 mV
potential arises becuse of differences in electrical charge across the membrane
the inside of a cell is more negative to the outside

Question 19

the resting membrane potential is determined by two forces

Answer 19

concentration
electrostatic pressure
a balance between these two forces creates the resting membrane potential

Question 20

ohms law

Answer 20

I = gV
where:
I= the movement of ions across the membrane
G= whether there are channels open for the ions to pass
V= whether there is a difference across the membrane to move them

Question 21

equilibrium potential

Answer 21

a balance of forces
the electrical potential that exactly balances an ionic concentration gradient if the membrane were permeable only to that ion
the point where diffusion and electrostatic pressure are exactly equal and there is no net movement of the ion across the membrane

Question 22

resting membrane potential is largely determined by

Answer 22

the equilibrium potential

Question 23

to balence all the K+ and A- inside the cell…

Answer 23

there needs to be an ion outside that cant cross the membrane
there is a high concentration of Na+ outside of a neuron that cannot get in
lots of Na+ lowers the concentration outside the cell creating an osmotic balance

Question 24

at rest there are open channels for

Answer 24

K+ but not na+

Question 25

describe the sodium potassium pump

Answer 25

binds three Na+ ions and ATP inside the cell
this changes the conformation of the protein
it releases the Na+ outside and picks up 2K+ ions
binding of K+ into the neuron

Question 26

describe how the action potential is mediated by the movement of ions

Answer 26

resting state
rising phase
overshoot
falling phase
undershoot

Question 27

resting state

Answer 27

membrane is at RMP (-65mV)

Question 28

rising phase

Answer 28

a rapid depolarisation of Vm

positive interior repels voltage sensor thereby opening the voltage gated Na+ channel

Question 29

overshoot

Answer 29

inside of the neuron is now positive relative to the outside

inactivation of the Na+ channels

Question 30

falling phase

Answer 30

rapid repolarisation of Vm
voltage gated K+ channels activate at threshold too but take 1ms longer, known as delayed rectifiers
K+ flows out of the neuron down both its concentration and voltage gradients

Question 31

undershoot

Answer 31

inside the neuron is now more negative than at rest (hyperpolarised)
K+ slow to close as well
the permiability of the membrane to K+ is even higher than at rest causing Vm to reach Ek

Question 32

depolarisation

Answer 32

change in Vm positive to rest

Question 33

repolarisation

Answer 33

change in Vm back to rest

Question 34

Hyperpolarisation

Answer 34

change in Vm Negative to rest

Question 35

injection of postitive current into a neuron will…

Answer 35

depolarise the membrane potential (vm)

Question 36

unless the membrane potentia can depolarise sufficintly to the threshold…

Answer 36

no action potential will be generated

Question 37

if the stimulus is strong enough the neuron will

Answer 37

fire action potentials

the stronger the stimulus the more action potentials a neuron will generate

Question 38

absolute refractory period

Answer 38

Na+ channels still inactivated therefore making it impossible to generate another action potential

Question 39

relative refractory period

Answer 39

Na+ channels have deinactivated and it takes more positive current to bring the neuron to firing threshold
since Vm = Ek

Question 40

Voltage gated channels at rest

Answer 40

Negative interior attracts positive voltage charge of sensors on Na+ and K+ channels
Background k+ channels still open to maintain Rmp

Question 41

If the neuron is depolarises to threshold then…

Answer 41

Both voltage gated Na+ and voltage. Gated K+ channels are activated
Increased positive charge on the neuron repels the voltage gated sensors. On both the channels
The channels pop open and Na+ immediately flows into the neuron bringing Vm close to Ena. K+ channels slowly start to open

Question 42

Voltage gated NA+ channels inactive before Vm reaches Ena due to

Answer 42

the pore becoming blocked from the inside
VMware nearly reaches Ena but voltage gated Na+ channels inactivate. K+ channels have yet to fully open
Na+ channels still open but are inactivated due the block by the globular portion of the channel
Voltage gated K+ channels are slowly opening

Question 43

Describe what happens when Voltage-Gated K’ channels finally pop open and leaves the neuron and repolarises Vm to a more negative value

Answer 43

During repolarisation, Na channels are open, but inactivated, and K+ is pushed out of the neuron down its concentration and voltage gradients