Neurophysiology

Question 1

Neurophysiology

Answer 1

the study of life processes within neurons that use electrical and chemical signals.

Question 2

How does communication between neurons work?

Answer 2

-For information to be processed by the nervous system, it must first be gathered (e.g. from the sensory system) and then relayed from neuron to neuron
–Each neuron in the chain (circuit) sequentially processes the signals given to them

Question 3

Inter-cellular Communication

Answer 3

-signals travel from one cell to another

-Movement of information BETWEEN cells/neurons

-Information is transmitted through circuits from neuron to neuron to neuron

-A neurotransmitter is a chemical messenger between neurons

Question 4

Intra-cellular communication

Answer 4

-signals travel within a single cell

-Movement of information WITHIN cells/neurons

-Information is received – dendrites

-Integrated and processed – axon hillock

-Transmitted / conducted – axon

-An action potential is a rapid electrical
signal that travels along the axon of a
neuron.

Question 5

Extracellular Fluid

Answer 5

-A phospholipid bilayer separates extracellular fluid (outside the cell)

Question 6

Intracellular fluid

Answer 6

-fluid inside the cell

Question 7

Phospholipid Bilayer

Answer 7

-Hydrophilic region of the protein, on the ends of the bilayer

-Hydrophobic region of the protein, in the middle of the bilayer

Question 8

Membrane Voltage Differential

Answer 8

-Not unique to neurons

-Inside of the cell is more negatively charged than the space immediately outside of the cell

-Ions are dissolved in intracellular fluid,
separated from the extracellular fluid by the cell membrane

Question 9

Concentration of ions is different inside vs. outside the cell

Answer 9

-Ions are charge carrying molecules
–Dissolved in intracellular fluid, separated from the extracellular fluid by the cell membrane
–Hydrophilic
–Lipophobic
–Cations
–Anions

Question 10

Higher concentration outside (vs. inside
the cell)

Answer 10

-Cations: Na+, Ca++
-Anion: Cl

Question 11

Higher concentration inside (vs. outside
the cell)

Answer 11

-Cations: K+
-Negatively charged proteins

Question 12

Concentration force

Answer 12

Ions move from high concentration to low
concentration

Question 13

Electric force

Answer 13

-Opposite charges attract
-Like charges repel
-concentration and electrical force can collaborate or oppose one another

Question 14

Resting membrane potential

Answer 14

-Rest/resting means in the absence of any other external input

• -60 to -70 mV (more negative inside
  than outside)

-At resting membrane potential, K+ channels are open and Na+ channels are closed

Question 15

How is resting membrane potential maintained?

Answer 15

-Sodium-Potassium pump
–“Pump” proteins are within membrane expend energy against their gradient
–Na+/K+ - ATPase pump
–This protein moves 3 Na+ ions out and 2 K+ ions in for every molecule of energy that is utilized

Question 16

Ions moving across the membrane

Answer 16

-If membrane becomes transiently permeable, ions will move in the direction governed by the concentration and electrical forces
–Move down their electro-chemical
gradient

-This is possible because of opening and
closing of ion-selective channels that
span the membrane

-K+ reaches equilibrium when the movement
out is balanced by the movement in

Question 17

Ligand-Gated Ion Channels

Answer 17

-Axon terminals of other cells secrete
chemicals that can regulate the opening of
channels
–Gated by neurotransmitter / ligand
–Also called ionotropic receptors

-When ligand-gated/ionotropic receptors
open …
–Ions flow through respective channel
–Membrane potential around the
channel changes
–Membrane potential change travels
with them
–Ions flow and then travel – as they move, their effect (de-/hyperpolarization) weakens

Question 18

Upon channel opening…

Answer 18

-If cations enter the cell, the membrane voltage potential becomes less negative
–Depolarizes (less polarized)
–Excitatory post-synaptic potential

-If anions enter the cell (or cations exit),
the membrane voltage potential becomes
more negative
–Hyperpolarizes (more polarized)
–Inhibitory post-synaptic potential

Question 19

Summation

Answer 19

-the job of combining these signals together

-Neurons receive inputs from many sources
(neurons) and must put all of that information
together – there are two types of summation

-Spatial summation

-Temporal summation

Question 20

Integration

Answer 20

-the job of translating those signals into a decision to send an output to the next neurons in the chain (circuit) or not

Question 21

Spatial Summation

Answer 21

the summing of potentials that come from different parts of the cell

Question 22

Temporal Summation

Answer 22

the summing of potentials that arrive at the axon hillock at different times

Question 23

What are they summing to?

Answer 23

-Many inputs are summed

-If the sum reaches threshold potential, an
action potential begins
–Action potentials begin at the axon hillock
(initial segment of the axon)

-Begin traveling actively through the cell,
including down the axon

Question 24

Action Potentials

Answer 24

-brief (transient) but large changes in the membrane potential

-They originate at the axon hillock
and propagate along the axon

Question 25

Threshold

Answer 25

the voltage (-40 to -55 mV) that the membrane needs to reach before an action potential is generated

Question 26

Depolarization

Answer 26

-occurs when the interior of the cell becomes less negative

-This increases the potential towards threshold
further increasing the probability of the occurrence of an action potential.

Question 27

Repolarization

Answer 27

occurs as the membrane potential becomes negative

Question 28

Hyperpolarization

Answer 28

occurs when the interior of the membrane becomes even more negative than the resting state, relative to the outside. During this phase
the cell is in a refractory period– it cannot
generate another action potential

Question 29

The strength of an action potential is defined by..

Answer 29

the number of action potentials generated–
not by the peak height of the action potential

Question 30

Temporal Occurrence of the action potential

Answer 30

-indicates that action potentials travel in one
direction– from the soma to the axon terminal

-This is because of the refractory state of the membrane after a depolarization

Question 31

Voltage-Gated Na+ Channels Active

Answer 31

-When the membrane potential reaches threshold:
–Voltage-gated Na+ channels open
–The membrane voltage, not a chemical, is the trigger
–Channels activate: Na+ ions rush into the cell
–Membrane potential moves towards positive range

Question 32

Voltage-Gated Na+ Channels Inactive

Answer 32

-After a fixed period of time, the Na+ channels
inactivate
–Inactivation = state in which channel is closed and temporarily unable to open again
–Absolute and relative
refractory period

Question 33

Voltage-Gated K+ Channels Active

Answer 33

-As the inside of the cell becomes more positive, voltage-gated K+ channels open
–They open more slowly
–“Delayed activating” K+ channels

-K+ moves out, and the resting potential is restored

-Membrane becomes more
negative (inside relative to
outside) again

Question 34

Action Potential Ends

Answer 34

-After a short period, K+ channels close

-Na+ channels transition from inactive to deactive (closed but capable of opening)

Question 35

Possible Series of Events

Answer 35

-Neuron is “at rest”
–No inputs active (EPSPs and IPSPs)
–Na+ concentration is high outside the cell
–K+ concentration is high inside the cell
– - 60 to -70 mV; most channels are closed

-Axon terminal releases neurotransmitter onto dendrite causing the opening of LIGAND-gated ion channels
–Na+ rushes inwards; EPSP
–EPSP moves down the dendrite towards the cell body, passively propagating, getting weaker as it travels

-EPSP reaches cell body/axon hillock in weak state, but spatially sums with other EPSPs arriving at the same time from other dendrites, causing cell to reach membrane threshold potential

Question 36

Possible Series of Events Pt. 2

Answer 36

-VOLTAGE-gated Na+ channels rapidly open in response to threshold
–Membrane potential climbs towards 0 mV, and even becomes more positive inside than outside

-Na+ channels inactivate (close and are unable to open)

-K+ channels open after a short delay

-K+ rushes outwards, bringing the membrane potential back into the negative range, often more negative than at rest

-K+ channels close, Na+ channels transition from inactive to deactive (closed and ABLE to open again) state

-Na+/K+ Pumps restore ion concentration gradients

-The cell is at rest again

Question 37

Active and Passive Propagation

Answer 37

-Active propagation of action potential is slow (10 m/s) but it does not weaken

-Takes many small steps down the axon – some chance of failure at every step

-Passive propagation (not dependent on voltage changes) is fast, but it weakens

Question 38

Saltatory Conduction

Answer 38

-Action potential starts at the axon hillock, moving passively through the myelinated
segment – quick but weakening

-When it reaches first Node of Ranvier, it regains full charge through active means

-Then moves passively through next myelinated segment