Spikes Flashcards
What do neurons do? (In general terms)
Receive, process and transmit electrical signals
What is a spike?
Brief, pulse like electrical event
How does a spike travel?
Propagating
What happens to the membrane potential during a spike?
Is reversed, inside becomes more positive than outside (briefly)
What is the all-or-nothing principle?
When an electrical voltage stimulus reaches a certain threshold, only then will a spike be released
What do dendrites do?
Collect signals from other neurons
Do not spike, make much smaller signals
If signals summed together from dendrites reach threshold, spike triggered
What is the function of a spike?
Carries electrical excitation along an axon
Amplifies small electrical signals that would not make it along the axon
What is the speed of a spike?
From 1m/s up to 100m/s
What 3 factors affect spike speed?
Axon width
Temperature
Myelination
What does a myelin sheath do?
Saltatory conduction - conducts spike from node to node
What is the mechanism for a spike?
If excited, voltage gated Na+ channels open, Na+ enters axon by diffusion (making inside less negative)
This opens more Na+ channels (regenerative process)
Na+ channels close and inactivate
Voltage gated K+ channels open, K+ exits axon by diffusion (making inside negative again)
One spike has very small effect on ion concentrations, however…
Continuous excitation of a neuron can fatigue it
How do we know the mechanism for a spike? (Who and what on)
Huxley and Hodgkin - conducted experiments on giant axon in regular squid
What did Huxley and Hodgkin show?
Cytoplasm ion composition
Intracellular recordings: polarity reverses
Sequence of events
Do all neurons have axons? What does a lack of axons suggest?
No, many neurones in retina do not.
Lack of an axon suggests that these neurons do not send messages far in the nervous system
