Class 2 Flashcards
What are the major functions of the cell membrane?
- Protect cell
- Move chemicals in and out
What are cell membranes made from?
- Large protein molecules
- Lipid bilayer (fatty acids: phosphoglycerides)
What two layers does the cell membrane separate?
- intracellular fluid (cytosol)
- extracellular fluid (interstitial)
What ions are highly concentrated on the inside of the cell?
- Organic anions (A-)
- Potassium (K+)
What ions are highly concentrated on the outside of the cell?
- Sodium (Na+)
- Chloride (Cl-)
- Calcium (Ca++)
What is the average resting potential?
60 - 75 mV
A reduction of the charge separation is called _____.
depolarization
(Heading toward zero.)
An increase in the charge separation is called _____.
hyperpolarization
(Becoming more negatively charged.)
Describe non-gated (open) ion channels.
- Always open
- Not influenced significantly by extrinsic factors
- Maintain the resting membrane potential
Describe gated (closed) ion channels.
Open and close In response to specific electrical, mechanical, or chemical signals.
Most K+ channels are (open / closed).
open
Most Na+ channels are (open / closed).
closed
Most Cl- channels are (open / closed).
open
What factors affect movement of ions across membranes?
- Electrochemical force / ionic flow due to passive force
- Diffusion force: high to low concentration
- Electric force: toward opposite charge
- Semipermeable membrane
- Many open channels for K+; half as many for Cl-; fewer for Na+
- Na+ K+ pump (some sites: CA++ pump)
- Active transport of K+ into cell and Na+ out of cell (using biological energy ATP)
absolute refractory period
During initial phase of AP, another cannot be fired
relative refractory period
During repolarization, larger than normal stimulus (depolarization) can trigger AP
Defining characteristics of action potentials
- Wave of depolarization is self-propagated, therefore non- decremental in space or time
- All-or-None change in potential, large amplitude (70-110 mV) of same magnitude at each point along the axon
- Brief in duration (1-10 msec)
- Code for transmission is frequency or rate of impulses (also timing: inter-AP intervals)
Steps in the release of NT
- Impulse streams into terminals, CA++ channels open, CA++ flows into axon terminal
- CA++ implicated in release of neurotransmitter-bind with vesicles
- Exocytosis
- Vesicles containing neurotransmitter (NT) move towards active zones in presynaptic membrane of terminals
- Membrane of vesicle fuses with terminal
repeated synaptic inputs close together in time will sum
temporal summation
synaptic inputs on adjacent parts of membrane occurring close together in time will lead to summation of effect
spatial summation
A change in the resting potential that results from opening or closing chemically-gated channels altering the flow and transmembrane distribution of a specific ion.
Post-Synaptic Potential (PSP)
Excitatory Post-Synaptic Potential
- Depolarization: break down of the polarized state across membrane (resting potential) resulting from opening NA+ channels or closing K+ channels
- Increase the likelihood of neural impulse being triggered
Inhibitory Post-Synaptic Potential
- Hyperpolarization: increase in resting potential resulting from opening Cl- or K+ channels (or closing Na+)
- IPSPs decrease the likelihood of an impulse being generated
Interaction of receptor site and NT:
fast, direct synaptic process
Receptor sites are ion channels that open or close gates as a consequence of interaction with NT. These channels are referred to as
Interaction of receptor site and NT:
slow, indirect synaptic process
- Receptor site is not the ion channel; sets up a cascade of events within the membrane that leads to the activation of gated channels.
- These slow receptors are coupled to G-proteins (guanine nucleotide-binding proteins) which act to set off the series of chemical events (“
pinocytosis
uptake of NT or components by presynaptic terminal
Analytic capabilities of the neuron
(carried out by dendrites and soma)
- Discern different inputs (EPSP/IPSP; fast/slow synaptic processes)
- Add inputs (spatial & temporal summation)
- Preference: Location of synapse (proximity of input to initial segment of axon has potential effect)
- Decision rule: summation of inputs to determine if AP
