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)
- 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
Why don't dendrites show a refractory period?
Dendrites lack voltage gated channel protiens
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.
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.
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.
Sequential segments of axon membrane each having an action potential. One after another.
What factors speed up conduction on the axon?
- Larger diameter (less resistence to current ion flow)
- Myelinated axons (saltatory conduction)
- Higher temperature
Why is continuous conduction slower?
Because it requires more action potentials to occur
What disease is caused by damage to myelination on the axon?
What is Hyperkalemia?
An increase in potassium ion in ECF
What is Hypokalemia?
A decrease in potassium ion in the ECF
Increase of sodium ion in ECF
Decrease of sodium ion in ECF
What is an Electrical synapses?
- Gap junctions
- Very fast conduction
What is a Chemical Synapses?
- Pre-synaptic terminal: synthesis of neurotransmitters & CA++ triggers release of neurotransmitters.
- Synaptic cleft
- Postsynaptic cleft: Neurotransmitter receptors
Each synapse is a ___________ where information is recieved and a decision is made.
Site of intergration
What does Acetylcholine effect?
Skeletal, smooth, cardiac muscle, glands, autonomic neurons and CNS
What does Norepinephrine and Epinephrine effect?
smooth, cardiac muscle, glands, SNS autonomic neurons and CNS
What does Serotonin & Dopamine effect?
What does Gamma-aminobutyric acid (GABA) effect?
Inhibitory to CNS
What does Substance P, enkephalins, and endorphins effect?
Alters pain sensory information
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.
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.
- 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.
- When multiple pre-synaptic neurons all synapse on the same post-synaptic neurons.
- Used to have multiple stimuli detected by multiple pre-synaptic neurons.
When graded potentials are all added together
When one neuron causes two graded potentials to be summed together in time on the post-synaptic neuron.
When the graded potentials from two or more neurons are summed together in space on the post-synaptic neuron.
- Disorder of the Basal Ganglia
- Death of neurons in the substantia nigra that secreates Dopamine.
- Difficulty starting or stopping movement