Midterm 2 Flashcards
Luigi Galvani
Observed that a frog leg twitched during an electrical storm. He concluded that the NS used electricity to communicate and he was partially correct
Otto Loewi
First evidence of chemical communication involvement in neurocommunication
- Stimulated the vagas nerve (slows rate of heart contractions. He found that another heart in the same solution also had a reduced rate of contraction even though its vagus nerve was not directly stimulated.
- He concluded that there must be a chemical release in the first heart that was affecting the other heart
- NEEDS BOTH ELECTRICAL AND CHEMICAL COMMUNICATION
chemical - ACh
What are the only excitable cells types?
neurons and muscle cells
these are the only cells with voltage gated sodium ion channels
What factors can lead to a graded potential occurring ?
Chemical (NT receptors)
Mechanical (stretch receptors)
What is the strength of the stimulus coded by?
The number/frequency of action potentials
Hodgkin-Huxley Model
Described the ionic basis of the AP - considered the most important achievement in cellular neurophysiology.
Mathematical + biophysical model of the AP
- the textbook model
- used squid axons
Graded potentials
Are variable with magnitude and duration which depends on strength and duration of the triggering event
Spread passively (no channel opening outside the point of origin, decreminating with distance from point of initiation
Travel over short distance
Channels during Resting
Na+ voltage activated gate is closed, Na+ inactivation gate is open. Channel is closed but not inactivated
Channels during depolarization.
Na+ flows into the cell because both the Na+ voltage activated gate and inactivation gate are open.
Channels during repolarization
Na+ voltage activated gate is open but the inactivation gate is closed and thus Na+ no longer flows into the cell.
K+ voltage gate is open and K+ moves out of the cell
Absolute refractory period
Channels during hyperpolarization
Na+ voltage activate gate is closed, the Na+ inactivation gate is open. No Na+ flows. K+ voltage activated gate is open.
Relative refractory period
Due to the K+ activation gate still being open and letting K+ out. The neuron needs more of a depolarizing stimulus to reach threshold for an AP to be generated during this period
How to speed up the nerve impulse?
Make the ions bigger in diameter or prevent ions from the leaving the axon by covering much of it with myelin
Group C fibres
Carry sensory information. They are unmyelinated, small diameter, and thus slow conducting
Include postganglionic fibres in the ANS and nerve fibres at the dorsal roots.
How do neurons generally make signals from distant synapses on dendrites for meaningful?
Larger PSP generated as distant synapses
signal boosters - VG Ca2+ channels - allow Ca2+ in to further encourage the cell to reach threshold
Where is an action potential initiated in neuron?
In the axon hillock - dense area of ion channels. There are no ion channels in the soma
How do touch sensory receptors work?
There is a dendrite wrapped around hairs. Displacement of hairs open stretch-activated channels in the dendrites membrane. When the channels open they allow an influx of Na+ ions sufficient to depolarize the dendrite to its threshold level
What is a renshaw loop ?
The axon collaterals of motor neurons will synapse with a renshaw cell (interneuron) . which then innervates the motor neurons
Indirect inhibition through renshaw interneuron controls motor neurons
Electrical synapse
Direct cytosolic (electrical conducting) bridges between cells (Na+ flows through)
Very fast but not very plastic (not a lot of modulation going on.
Not common in the mammalian brainy,
although invertebrates have many. Heart has many.
Chemical synapse
Not as fast as electrical synapse but very plastic (in the number of receptors, amount of NT, etc)
How many classical NTs are there versus neuropeptides?
7 diff classical NT’s
100 diff chemicals that are neuropeptides
How does the release of NT from the presynaptic neuron occur?
AP arrives at the axon terminal –> depolarization from the sodium influx activates voltage gated calcium channels – leads to calcium influx. Increase in intracellular calcium triggers the vesicles to fuse with the presynaptic neuron membrane – get exocytosis of NT
When more action potentials occur - what happens at the synapse?
Get MORE calcium influx which means MORE NT is released
Why can magnesium chloride be used as an anaesthetic?
When applied to body, it will be influxed into the cell instead of calcium – don’t get fusion of the NT vesicles with the membrane - don’t get exocytosed
Ionotropic receptor?
Ligand gated ion channel
Faster than metabotropic
Metabotropic receptor?
GPCR
The receptor type and ligand bind ultimately determines what effect the NT will have on the cell
Slower than ionotropic
Neurotransmitter
Chemical messenger used by neurons
A NT must be made or present in the cell that is releasing it.
The released chemical must be capable of producing an effect on its target (
Neurotransmitter
Chemical messenger used by neurons
A NT must be made or present in the cell that is releasing it.
The released chemical must be capable of producing an effect on its target (so the target MUST have receptors)
Effect of the chemical must be able to be mimicked by the exogenous application of the same or similar substance (response mimicked)
There should be a mechanism to remove or inactivate the NT when its work is done
Neuropeptide
Peptides that do not act directly as NTs but rather increase or decrease the action of an NT
Synthesized in the cell body of a neuron
Act usually as neuromodulators
>100 have been identified
Often co-localized with classical NTs and act as neuromodulators
Dale’s Exclusion Principle
States that although different NT’s can be produced at different synapses within the brain, idvl neurons are capable of releasing only one classical NT
A couple rare exceptions - co-release of GABA-glycine, Ach - glutamate, dopamine-glutamate
