BIOL 273 - Unit 2.3 Flashcards
Graded potentials
could be depolarizations or hyperpolarization across the membrane
- occur in the dendrites or cell body of neurons
How are graded potentials triggered
by the opening or closing of ion channels, allowing ions to enter from the ECF
Why are graded potentials called graded
depends on how strong/weak the neuron becomes depolarized/hyperpolarized
(the amplitude of the potential is proprotional to the strength of the triggering event)
Describe the travelling distance of graded potentials
short distance
Why do graded potentials travel a short distance (2)
Graded potentials lose their strength due to
1. current leak (positive charges leak back w depolarization wave)
2. cytoplasmic resistance (cytoplasm restrcits flow of the current )
What causes the ions to enter the cell (4)
- Events after neurotransmitter binding
- Signal strength (determined by number of ions entering the cell)
- Depolarizing graded potentials
- Hyperpolarizing graded potentials
What happens after neurotransmitter binds to membrane receptors (3)
Used to start up graded potentials
1. Ion channels open
2. Ions move into or out of neuron along the elctrochemical gradient
3. A wave of depolarization and hyperpolarization spreads though the cell
Describe depolarizing graded potentials
- coming closer to threshold potential (-55mV) by making the energy less negative from resting (-70mV)
- by doing this, it will increase the chance of exciting the axon to fire an action potential
What is the depolarizing stimuli called
Excitatory Post synaptic Potentials (EPSPs)
Describe hyperpolarizing graded potentials
When the neurons membrane potential becomes more negative, leading it farther away from the threshold
- which decreases the chance of exciting axon to fire and inhibit action potential
What is the hyperpolarizing stimuli called
Inhibitory Post synaptic Potentials (IPSPs)
Unlike graded potentials, how can a neuron carry a signal over long distances
via action potentials (for long distance transmission)
Give two way action potentials differ from graded potentials
- Action potentials are all identical, there is no volume control
- They do not diminish in strength as they travel long distances through the neuron
Describe the location of the initiation of action potentials and how does it work
start at the TRIGGER ZONE , to determine if a firing action will occur
(aka integrating center of the neuron)
Integrate signals from different places to determine if a firing action will occur
Describe the location of the trigger zone of action potential in SENSORY NEURONS (afferent neuron)
adjacent to the receptor
Describe the location of the trigger zone of action potential in EFFERENT NEURONS and INTERNEURONS
in axon hillock and the initial segment
What is the minimum depolarization critical to trigger an action potential , what is it called
-55mV , called Threshold potential
How can graded potentials initiate action potentials
graded potentials can sum together at the trigger zone to ultimate reach the threshold potential
How can graded potentials sum to potentially become action potentials? (2)
- Over space: spatial summation
- Time: Temporal summation
Phases of action potential: How does a membrane depolarize to threshold
voltage gated Na+ and K+ channels begin to open
rapid Na+ entry to depolarize cell (to a max of 30+ mV)
Phases of action potential: what contributes to the peak of the action potential
Na+ channels close and slower K+ channels open
Phases of action potential: what contributes in the repolariztion and hyperpolarization phase after reaching its peak AP
K+ exits results in membrane potential travelling towards resting membrane potential
Phases of action potential: how does the membrane return to resting ion permeability
retention of K+ and leak of Na+ into the axon brings membrane potential back to -70 mV
What are the two gates of the voltage gated sodium channels needed to regulate ion movement during an action potential
- Activation gate: closed at resting membrane potential to prevent Na+ influx (opens quickly)
- Inactivation gate: ball and chain of amino acids on cytoplasmic side of the membrane is open at resting membrane potential (close slowly)
Describe how the voltage gated Na+ channel stimulate a positive feedback loop
- Resting membrane potential
- Depolarizing stimulus to -55mV stimulates the entire channel (both gates)
- Activation gate opens: Na+ enters the cell
- The Na+ entry causes further depolarization, causing more voltage gates Na+ channels to open
- Inactivation gate closes to prevent further Na+ influx and end positive feedback (representing peak of action potential)
How does the membrane potential return to the resting level?
K+ ions leave the cell - falling phase of action potential
When does the refractory period occur
during the hyperpolarization phase
What are the two parts that make up the refractory period
- Absolute refractory period
- Relative refractory period
Describe the absolute refractory period
(lasts for approx 1 msec)
- found in the initial part of AP, the moment threshold potential is hit
- no other action potentials can be triggered at all (no matter how large the stimulus)
Why are there no other action potential triggered during absolute refractory period
because sodium channels is in inactive state (closed gate)
Describe the relative refractory period
another action potential can be fired if it is above the threshold (-55mV) called a suprathreshold
Why is a suprathreshold needed to fire another action potential
because the potassium channels are still open so an excess of sodium is needed to reach threshold stimulus (more depolarization needed)
Why is the refractory period important? (3)
- Set the direction of current flow (trigger zone to axon)
- Prevent sumation (more changes in membrane potential)
- Prevents backward movement of action potential
How can conduction of action potential occur in long distances without decreasing in strength
the positive feedback loop of sodium channels (new AP generated is identical to previous AP)
What determines the speed of action potential along neuron (2)
- Diameter of axon: giant axons lower resistance to speed conduction
- Resistance of axon membrane: insulating axon reduces ion flow out of the cell which speeds conduction using myelin sheath
How does axon become insulated to speed conduction of action potential (2)
axon insulated using myelin sheath :
1. in PNS: Schwann cells
2. in CNS: oligodendrocytes myelinating axons within interneurons
What do you call the section of neuron that is not myelineated , what do they consist of
Node of ranvier, they are concentrated with voltage-gated sodium channels and potassium channels
