Chapter 12-Part 3 Flashcards
(18 cards)
What is the all-or-none law?
If threshold reached, action potential generated and propagated down axon without any loss in intensity; if threshold not reached, voltage-gated channels stay closed, no action potential.
What is spatial summation?
Summation occurs across space and time; multiple locations on cell’s receptive regions receive neurotransmitter simultaneously and generate postsynaptic potentials.
What is temporal summation?
A single presynaptic neuron repeatedly releases neurotransmitter and produces multiple EPSPs within a very short period of time.
Define graded potentials.
Small, short-lived changes in the RMP established by the opening of chemically gated ion channels; they vary in degree and direction of change.
What are the two types of signals in neurons?
- Graded potentials (incoming short-distance signals)
- Action potentials (long-distance signals of axons)
What is the resting membrane potential (RMP)?
Typically –70 mV; it exists because ions are concentrated on different sides of the membrane.
What role do Na+/K+ pumps play in neurons?
They contribute about –3 mV to the RMP and maintain the concentration gradients for Na+ and K+.
What is the primary factor in setting the resting membrane potential?
K+ diffusion is the most important factor; it diffuses out of the cell due to its concentration gradient.
What causes an excitatory postsynaptic potential (EPSP)?
Depolarizations caused by Na+ entry.
What causes an inhibitory postsynaptic potential (IPSP)?
Hyperpolarizations caused by K+ exit or Cl− entry.
What are the three states of voltage-gated Na+ channels?
- Resting state: Activation gate closed; inactivation gate open
- Activation state: Activation gate open; inactivation gate open
- Inactivation state: Activation gate open; inactivation gate closed
What is Ohm’s law in the context of neurons?
Current = voltage/resistance; current increases with larger voltage and smaller resistance.
What types of channels are present in the plasma membrane of a neuron?
- Leaky channels
- Chemically gated channels
- Voltage gated channels
What is the role of the membrane surrounding the neuron?
It is composed of lipid and protein and contains transport proteins for moving substances across the plasma membrane.
Fill in the blank: The threshold for initiating an action potential is typically about _______.
-55 mV
True or False: The degree of change in RMP depends on the amount of neurotransmitter bound per unit of time.
True
What is the difference in ion concentration across the plasma membrane of a resting neuron?
- Higher K+ concentration in cytosol
- Higher concentrations of Na+, Cl−, Ca2+ in interstitial fluid
What happens at the axon hillock?
Summation of EPSPs and IPSPs occurs; if threshold is reached, voltage-gated channels open, and an action potential is generated.
