Nervous System 2 - Membrane Potentials Flashcards
What is resting membrane potential?
The voltage (charge) difference across a cell membrane at rest
What is variation of resting membrane potentials?
Resting membrane potential varies: -70mV - +5mV
What is the resting membrane potential of a neuronal membrane?
Neuronal membrane - Polarised with respect to charge
Extracellular fluid - Positive at rest
Intracellular fluid - Negative at rest
Size of resting membrane potential governed by 3 factors. What are they?
Unequal distribution of ions in intracellular & extracellular fluid
Inability of molecules to leave the cell
Relative permeability of neuronal membrane to different ions
In resting membrane potentials, what is the concentration in extracellular fluid?
High concentration of sodium & chloride ions
In resting membrane potentials, what is the concentration in intracellular fluid?
High concentration of potassium, phosphates & protein
Negatively charged proteins are too big to leave the cell. True or False?
True
What does the sodium potassium pump do?
Pumps more positive ions out of the cell membrane than it pumps in (Electrogenic)
Most ion channels are gated. What does that mean?
They are either open or closed
What factors control the gates ion channels?
Membrane potential (voltage)
Neurotransmitters (chemical)
What are the 4 types of channel?
Leakage channel
Ligand-gated channel
Mechanically gated channel
Voltage-gated channel
What are leakage channels?
Alternate between open & closed positions (randomly)
Found in all cells
Higher number of potassium leakage channels than sodium leakage channels in membrane
What are ligand-gates channels?
Open & close in response to chemical stimuli
Found on dendrites & motor neurons
Opened via various chemical stimuli – Neurotransmitters | Hormones | Ions
E.g. Acetylcholine permits inward flux of sodium & calcium which is paired with outward flux of potassium
What are mechanically gated channels?
Open & close in response to vibration (sound), pressure or stretching
Found on sensory neurons e.g. Touch receptors | Pressure receptors
What are voltage gated channels?
Open in response to a change in membrane potential (voltage)
Enabler of action potentials
Found on all neurons e.g. Potassium gated channel
Membrane is more permeable to Potassium. True or False?
True
Membrane relatively impermeable to Sodium. True or False?
True
K+ ions (i.e. positive charge) diffuses out of
neuron until K+ equilibrium potential is reached. True or false?
True
Changes in membrane potential occur due to the movement of ions across the membrane. True or False
True
What are the 4 terms used to describe the state of a membrane?
Local potential - Small changes in membrane
potential in response to stimulus
Action potential - Large & rapid depolarisation to nerve cells
causing the cell membrane potential to reverse
Inhibitory - Hyperpolarisation
Excitatory - Depolarisation
Do local potentials travel short or long distances?
Short
Can local action potentials add together?
Yes
What are Inhibitory local potentials?
Opening of small number of K
+ or Cl- channels in membrane
What are Excitatory local potentials?
Opening of small number of Na+ channels in membrane
What are the 3 main phases of an action potential?
Phase 1 - Depolarisation
Phase 2 - Repolarisation
Phase 3 - Hyperpolarisation
Nerve impulse travels the length of axon towards terminals. True or False?
True
Resting membrane potential - Inside of neuron is negative
& outside is positive. True or false
True
Threshold potential (-55mV) – Action potential takes
place due to a transient reversal in membrane polarity. True or False?
True
Peak of action potential (+30mV) - Inside of neuron is
positive, outside negative. True or false?
True
What are Hyperpolarisation?
Overshoot in membrane potential that makes the membrane more polar
An action potential can be generated from what?
Electrical stimulation of neuron
Sensory receptors receiving stimulus
from other neurons
The action potential threshold can also be called the All or Nothing Law. True or false?
True
For action potentials to be generated, neuronal membrane must
depolarise to threshold potential (-55mV) True or false?
True
What is subthreshold?
No action potential produced
(local potential will be produced)
What is threshold?
Action potential produced
What is supra-threshold?
Action potential produced (same size as threshold)
What is the refractory period?
Neuron is less excitable during & immediately after generation of an action potential than it is at
rest
What are the 2 phases the refractory period occurs in?
Absolute and Relative
What is absolute refractory period?
Occurs from start of depolarisation to end of repolarisation
A second action potential cannot be generated
during absolute refractory periods
During depolarisation – All Na+ channels open
During initial repolarisation - Na+ gates are inactivated
(closed) and cannot be opened by another stimulus
What is relative refractory period?
Occurs immediately after absolute refractory period
Possible to generate a 2nd action potential -
Only in response to a stronger stimulus
Some K+ channels remain open beyond repolarisation
phase (temporary hyperpolarisation)
It is ‘harder’ to depolarise the neuron but a stronger
stimulus is required
What are the 2 types of axons?
Unmyelinated and Myelinated
What is Continuous propagation?
Conduction in unmyelinated axons
What is Conduction in unmyelinated axons called?
Resting state
What are myelinated neurons covered by?
Myelin Sheath
Local potentials travel short distances & can be excitatory or inhibitory. True or false?
True
Action potentials travel long distances & are only generated following threshold potential. True or false?
True
True or false? Local & action potentials are underpinned by the movement of Na+ & K+ across the membrane?
True
Action potentials propagate more quickly along myelinated axons. True or false?
True
