Module 2 Flashcards
What are the three rules regarding injected current
- If injected current does not depolarize the membrane to threshold, no action potential will be generated
- If injected current depolarizes the membrane beyond threshold, action potentials will be generated
- The action potential firing rate increases as the depolarizing current increases
Explain the role of the separate gates in Voltage-gated Na+ channels
As the membrane potential depolarizes, the inactivation gate will slowly close, while the activation gate quickly opens.
Explain the role of gates in Voltage gated K+ channels
First, it only has one gate. That gate opens as the membrane depolarizes
What main purpose do K+ channels play in an action potential?
When the cell depolarizes, they open, causing a hyper-polarization, and bring the action potential back down towards rest.
Defined the K+ channel called the Delayed Rectifier
opens slowly in response to changes in membrane potential, closes slowly. Responsible for repolarizing axonal membrane following an action potential
Defined the K+ channel called the A-channel
Opens when the membrane is depolarized, closes rapidly, influences neuron excitability
Defined the K+ channel called the Inward Rectifier
Opens when membrane is hyperpolarized, influences duration of action potential
Defined the K+ channel called the Ca2+ activated channel
Opens in the presence of Ca2+, influences the excitability of the neuron
Defined the K+ channel called the M-channel
Opens when the membrane is depolarized, closes slowly. Regulated by neurotransmitters
Defined the K+ channel called the ACh channel
Opens when membrane is exposed to ACh, involved in regulation of heartbeat
Defined the K+ channel called the Kv3 subfamily
Activated only at high voltages, they have fast recovery (deactivation).
Result is fast repolarization without compromising AP amplitude
In terms of electrochemical significance, define Ca2+
Located in large conc. outside the cell. Therefore, it generally causes cell depolarization when it’s channels open, like Na+
Define Voltage-gated Ca2+ channels
Open with similar time dependence as voltage-gated channels
Ca2+ current is more sustained
What are the four steps of an action potential in a neuron
- Signal reception
- Signal integration
- Signal conduction
- Signal transmission
Where does the signal integration (initiation of AP in cell) usually occur?
Axon hillock
What are the four steps of a graded potential?
- Neurotransmitter binds to ligand-gated Na+ channel
- Na+ enters the cell
- Current spreads through the cell
- Strength of the signal decreases with distance
What are Five differences between graded potentials and action potentials?
Graded potentials
- Vary in magnitude
- Vary in duration
- Decay with distance
- Occur dendrites or cell body (as opposed to axons)
- Caused by opening and closing of many kinds of channels (APs are controlled just by voltage-gated ion channels)
Define a threshold potential
Found with APs, it is the minimum level of membrane depolarization required for an AP to be generated
What is the length constant (lambda) in a neuron?
The length constant is a measure of how far the voltage travels down the axon before it decays to zero.
When will length constant be highest?
When Ri is low, and Rm is high
What kind of conduction speeds do squid giant axons have?
High
Define myelin
An insulating wrapping around axons that increases membrane resistance by decreasing current loss through leak channels
How does myelin differ between CNS and PNS
CNS: oligodendrocytes
PNS: Schwann cells
Define the nodes of Ranvier
Areas of exposed axonal membrane in between insulated regions that are rich in ion channels. they are required to continue the propagation of the AP.
