Lecture 8 - Neurophysiology Flashcards
What is a gated ion channel?
An ion channel that can open or close in response to a stimulus
What is a leak channel?
A channel that is always open
What is a voltage gated ion channel?
A channel whose open or close state depends on the value (polarity) of membrane potential
What is a ligand gated ion channel?
a. A channel in which a ligand (chemical) binding to a receptor opens the channel
b. Can also be called a receptor mediated ion channel
What is a mechano-gated ion channel?
a. Mechanical stimulus opens or closes the ion channel
b. E.g. stretch receptors, touch receptors, baroreceptors
What are the three key types of V-gated channels?
a. Voltage gated Na+ channels
b. Voltage gated K+ channels
c. Voltage gated Ca+ channels
Voltage gated Na+ channels
a. Has three possible conductance states
i. Open, closed, inactive
b. Vna transition
i. Must close before they can repoen
ii. Refractory
c. Notable structural features of Vna
i. Voltage sensory
ii. Inactivation gate
d. Relative fast opening
Voltage gated K+ channels
a. Two possible conductance states
i. Open and closed
b. Dynamics
i. Slow opening, slow closing
Threshold potential positive-feedback cycle
a. Triggering event
b. Depolarization (decreased membrane potential)
c. Opening of some voltage-gated Na+ channels
d. Influx of Na+ (which further decreases membrane potential)
The cell membrane permeability at rest
75 x more permeable to K+ relative to Na+
Cell membrane during depolarization
a. Vna is open
b. The membrane is permeable to Na+ sp Na+ enter the cell
c. Na+ entering the cell bring positive charge into the cell
d. Vk remains closed
Cell membrane during repolarization
a. Vna become inactive and gate closes so Na+ can no longer enter the cell
b. Vk opens the membrane becomes very permeable to K+
c. K+ leaves the cell to positive charge leaves the cell and the membrane potential falls
Cell membrane during hyperpolarization
a. Vk remains open while Vna remains closed
b. Membrane even more permeable to K+ than it would be at rest
c. Fall in membrane potential “overshoots” and the membrane potential becomes even more negative than RMP
What are refractory periods?
During and immediately after an action potential their periods when it is hard to generate new action potential
Properties of action potentials
a. All or none (i.e. no half action potentials)
b. Self-regenerating
c. Travel down the axon
d. Initiated in one segment
e. Driven by voltage-gated ion channels
f. Travel the entire length of an axon without diminishment
g. High fidelity
h. No summation
What are graded potentials?
a. Any change in the membrane potential below threshold
b. They occur because gated ion channels are open or closed causing influx or efflux of ions
What is myasthenia gravis?
a. An autoimmune disease leading to destruction of nicotinic acetyl-choline receptors at the neuromuscular junction
i. Leads to muscle weakness
ii. Nerve function intact
What is EPSP
a. Excitory post synaptic potential
b. Movement of ions across the cell membrane at the synapse depolarizes the membrane
c. Membrane potential moves closer to the threshold
What is IPSP
a. Inhibitory post synaptic potential
i. Movement of ions across the cell membrane at the synapse hyperpolarizes the membrane
ii. Membrane potential moves further away from threshold
Temporal and spatial summation
a. Temporal summation occurs in time
b. Spatial summation occurs when PSPs at two different synapses summate
c. Summation occurs at the trigger zone
Describe the events that occur at the synapse
a. Action potential invades axon terminal
b. Depolarization of the axon potential leads to opening of Vca
c. Diffusion from high to low concentration triggers the movement of neurotransmitters
d. Neurotransmitters bind to receptors
e. Neurotransmitter function is terminated
The membrane potential can be calculated using the Goldman-Hodgkin-Katz equation. What would be altered by the opening of a gated cation channel?
a. The permeability value for potassium
b. The permeability value for sodium
Why is the relative permeability of the cell membrane to potassium 75 time greater than that of sodium?
due to the presence of K+ leak channels on the cell membrane
Summary of absolute refractory periods
After an action potential, the absolute refractory period of a cell occurs due to the voltage-gated sodium channels being in the inactive state. This prevents the initiation of further action potentials. As the cell repolarises, sodium channels re-enter the closed state. However, the initiation of further action potentials is rendered difficult due to the cells continued permeability to potassium which will tend to hyperpolarise the cell
What are two consequences of opening a ligand gated cation channel on a post-synaptic neuron?
- Na+ influx
- generation of an EPSP
