Neuro-2 Flashcards
How do action potentials propagate along an axon?
The positively charged ions taken in during an action potential diffuse along the axon which causes another local depolarisation to generate an action potential further along the axon this process will repeat itself until the action potential reaches the end of the axon
Myelin sheaths can make this process faster by covering regions of the axon in an insulating sheath
What happens when an action potential reaches the end of the axon?
It opens a Ca channel in the nerve terminal triggering a Ca influx which allows vesicles containing neutransmitter to fuse with the cell membrane via exocytosis so the neurotransmitter is released into the synaptic space where it can produce its effect transiently as it will not remain there for long due both reuptake mechanism by the presynaptic nerve and enzymes which can break the neurotransmitter down
What are the two actions a presynaptic cell can have on a post synaptic cell?
It can cause that neuron to either depolarize (excitatory) or hypopolarize (inhibitory)
What is summation/
When multiple inputs combine to produce depolarisation above the threshold level
This may be spatial (close together) or temporal (occur at the same time)
This also applies for the combination of inhibitory inputs etc
What are the differences between vertebrate and invertebrate nervous systems?
Invertebrates typically have a distributed nervous system with a few large neurons the presence of inhibitory motoneurons and non-spiking interneurons
Vertebrates have a central nervous system and the presence of many nerves, only contain excitatory motoneurons and no evidence has yet been seen of non-spiking interneurons
What are non-spiking interneurons?
Neurons that don’t produce action potentials but continually leak neurotransmitter
What is Aplysia?
This is a sea slug which is commonly used as a classical preparation for studying neuroethology
They have simple, large neurons making them easy to study
What is the gill withdrawal reflex seen in Aplysia?
If the mantle which covers the gill of the sea slug is peeled back and then there is a tactile stimuli which comes into contact with the syphon the sea slug will rapidly withdraw the gill to protect it
How does Aplysia show habituation?
If the syphon of the sea slug is continually tapped to activate the gill withdrawal reflex then the slug will eventually become used to this stimulis and the reflex will stop working
What are the two neurons involved in the gill withdrawal reflex of aplysia?
There is a sensory neuron which connects to the syphon and will alter its rate of firing in response to touch and a motor neuron which drives the contraction of the gill
What change in the neural activity of aplysia generates the habituation of the gill withdrawal reflex?
The motoneuron stops responding to signalling from the sensory neuron (though the sensory neuron will continue to fire in response to the stimulis)
It is believed that this is partially due to the deactivation of Ca channels
How does aplysia show sensitization?
Even if the gill withdrawal reflex has been habituated to syphon tactile stimulus a tactile stimulus to the tail will still generate a gill withdrawal response
This can occur because the sensory nerve from the tail of the aplysia is axo-axonal (rather than axonal-dendritic as with the syphon sensory nerve) and releases serotonin allowing it to close K+ channels on the motoneuron and prolong the action potential allowing enough Ca in to allow activation of the motoneuron
