NEUROPHYSIOLOGY Flashcards
(23 cards)
Define Membrane Potentials
the difference in the electrical charge between the inside and outside of the cells membrane
What is the cell membrane
the boundary between the internal and external environment of the cell
What is the cell membrane made up of
phospholipids and proteins
explain phospholipids and proteins
Phospholipids: each molecule has a hydrophilic (water-attracting) “head “ and 2 hydrophobic (water-repelling) “tails”
Proteins: embedded withing the phospholipid (bilayer) membrane, that allow certain membranes to pass through them.
What is the resting membrane potential
-70mV (when at rest, it is polarised)
What is the difference between hyper polarisation and depolarisation
H: if the neutron is inhibited, the inside is even more negative than at rest
D: if the neuron is stimulated, the inside of the neuron becomes more positive and moves closer to 0
Define diffusion gradient
when particles move from a region of high concentration to a region of low concentration
Define Dynamic equilibrium
once the molecules are equally distributed, the concentration is same throughout the fluid and the molecules continue to move around randomly
What is an ion
If an atom loses or gains an electron, it becomes an ion
Opposite ions attract and generate electrostatic forces
Sodium and Potassium ions are essential for action potentials.
Ions in neurons
The resting membrane potential is mainly due to the movement of (K+) out of the cell
The action potentials is mainly due to the movement of (Na+) into the cell
Explain the permeability to Potassium (K+)
At rest the membrane is only permeable to K
Ions will leak out of the cells for a diffusion gradient
This will happen until it reaches an equilibrium
The equilibrium potential is -90mV
Explain the permeability to Sodium (Na+)
If the membrane is only permeable to Na, it will diffuse into the cell and the membrane will depolarise.
The equilibrium potential is +60mV
What are the voltages for: resting membrane potential, if the membrane is equally permeable to both, equilibrium potential for K and Na
RMP: -70mV (negative because it is more permeable to K)
Equally for both: -15mV
Potassium: -90mV
Sodium: +60mV
Resting membrane potential
The RMP and AP depend on the levels of Na and K
Potassium is 40x higher inside the cell
Sodium is 10x higher outside of the cell
What are Action potentials
the way that neuron’s communicate
How long does an action potential last and what is the direction of polarisation
only lasts 2ms
it is rapidly depolarised and repolarised depending on the voltage-gated ions
explain the voltage-gated ions
they are closed at rest and only open when the neuronal membrane is depolarised (change in potential difference across the membrane), the subunits of the ion channel have a voltage sensor (S4)
Exciting a neuron depolarises the membrane and open voltage-gated sodium channels very immediately but voltage-gated potassium channels open after a 1ms delay
When does the action potential fire
-55mV as the neutron needs to be stimulated enough
the nerve impulse propagates along the axon as a series of separate action potentials
The membrane depolarises up to the threshold due to the Na+ channels, generating the action potential.
Describe the process of the action potential firing
Depolarisation to threshold (-55mv) due to the opening of sodium channels
Rising phase: membrane becomes more positive and is depolarising +60mV
Overshoot: when the neuron is close to the equilibrium potentially for sodium, sodium channels close and K channels open.
Falling phase: When the K channels open, this allows the membrane to become more negative to the equilibrium for potassium (-90mV)
Undershoot: K flows in, hyperpolarisation occurs and the K channels close when it reaches –90mV, returning to the resting state.
Return to resting state: K channels close and the membrane returns to rest. The sodium-potassium pumps help the membrane to return to its resting state.
Refractory period: Another action potential cannot occur until the membrane reaches equilibrium.
What is conduction
once the action potential is generated, it will spread across the axon to reach the axon terminal as a series of action potentials. This depends on the properties of the axon
what are the two types of axons
myelinated and non-myelinated
What are the characteristics of myelinated axons
- Segments of the axon are wrapped in myelin (Myelin sheath), a fatty layer formed by glial cells.
- This insulates the axon and prevents current leakage. The myelin sheets are separated by gaps called the ‘nodes of Ranvier’, in which the action potentials occur and spread.
- These can be up to 120 m/s
- The action potential “jumps” from one NoR to another – saltatory conduction
- Found in more critical areas, such as motor neurons
What are the characteristics of non-myelinated axons
- Do not have any insulation
- The action potentials are close together because the electric current can only reach short distances, which trigger the next action potential – continuous conduction
- Nerve impulses are slower at 0.5-2 m/s
- Found in less critical areas, such as digestion
