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Absolute-refractory period
Period of time after an action potential where a small section of the axon cannot have an overlapping action potential. (About 1-2 mili seconds)
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Relative-refractory period
- Period of time (usually 2-4 mili seconds after action potential) where a larger than normal graded potential can force open a few already reset voltage gated Na+ channels and cause a second Action potential.
- Requires a larger than normal graded potential
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Why don't dendrites show a refractory period?
Dendrites lack voltage gated channel protiens
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What prevents "backwards" conduction?
- The absolute refractory period
- This period ensures a "one-way" conduction of action potentials from the trigger zone towards the synapse.
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How can a neuron transmit information about the size of a particular stimulus?
- The frequency of action potentials over a period of time
- Frequency is proportional to the size of the stimulus.
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Do action potentials move?
- NO! They are just a measurment at a small specific spot on the axon membrane!
- Action potentials move like dominos. One simply triggers another down the line, etc.
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Continuous conduction:
Sequential segments of axon membrane each having an action potential. One after another.
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What factors speed up conduction on the axon?
- Larger diameter (less resistence to current ion flow)
- Myelinated axons (saltatory conduction)
- Higher temperature
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Why is continuous conduction slower?
Because it requires more action potentials to occur
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What disease is caused by damage to myelination on the axon?
Multiple sclerosis
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What is Hyperkalemia?
An increase in potassium ion in ECF
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What is Hypokalemia?
A decrease in potassium ion in the ECF
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Hypernatremia
Increase of sodium ion in ECF
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Hyponatremia
Decrease of sodium ion in ECF
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What is an Electrical synapses?
- Gap junctions
- Very fast conduction
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What is a Chemical Synapses?
- Pre-synaptic terminal: synthesis of neurotransmitters & CA++ triggers release of neurotransmitters.
- Synaptic cleft
- Postsynaptic cleft: Neurotransmitter receptors
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Each synapse is a ___________ where information is recieved and a decision is made.
Site of intergration
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What does Acetylcholine effect?
Skeletal, smooth, cardiac muscle, glands, autonomic neurons and CNS
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What does Norepinephrine and Epinephrine effect?
smooth, cardiac muscle, glands, SNS autonomic neurons and CNS
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What does Serotonin & Dopamine effect?
CNS
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What does Gamma-aminobutyric acid (GABA) effect?
Inhibitory to CNS
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What does Substance P, enkephalins, and endorphins effect?
Alters pain sensory information
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Excitatory Post-Synaptic Potential (EPSP)
When a positive ion flows in, or if a negative ion flows out, it depolarizes the membrane, which brings it closer to the action threshold.
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Inhibitory Post-Synaptic Potential (EPSP)
When the post synaptic cell is further from threshold due to an inhibitory response from a positive ion flowing out or a negative ion flowing in.
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Divergence
- When one pre-synaptic neuron has axon collaterals that form synapses with multiple post-synaptic neurons.
- Used to have a stimulus detected by the pre-synaptic neuron cause an action potential that "turn ons" responses in multiple neurons.
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Convergence
- When multiple pre-synaptic neurons all synapse on the same post-synaptic neurons.
- Used to have multiple stimuli detected by multiple pre-synaptic neurons.
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Summation
When graded potentials are all added together
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Temporal Summation
When one neuron causes two graded potentials to be summed together in time on the post-synaptic neuron.
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Space Summation
When the graded potentials from two or more neurons are summed together in space on the post-synaptic neuron.
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Parkinson's Disease
- Disorder of the Basal Ganglia
- Death of neurons in the substantia nigra that secreates Dopamine.
- Difficulty starting or stopping movement
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