Chapter 8 Neurons & NT Flashcards
What is the most widely used NT?
What releases this NT and where is it used?
Acetylcholine (ACH)
Released by cholinergic neurons
Used in the Brain and ANS; used at all neuromuscular junctions (skeletal muscle control)
What receptors use ACh and what types of receptors and what are their function?
Receptive tissues contain either nicotinic or muscarinic receptor subtypes
- nACh- receptors are ion channels
- mACh - receptors are G-protein linked Receptors that turn on a cascade effect to amplify the secondary signal molecule.
This is found on the target cell that is innervated by a cholinergic neuron, and its a channel?
What is its gate
Nicotinic ACh receptor
The channel is gated by acetylcholine meaning it needs ACh for the channel to open
After binding ACh to the nicotinic receptor what ions flow through and what dominates?
After binding ACh, both Na+ and K+ flow though the electrochemical gradient for Na+ efflux into the cell predominates
After the Efflux of Na+ at a nACh receptor what takes place?
This causes a depolarizing effect at the target tissue is called an excitatory post-synaptic potential (EPSP)
What is the difference of the muscarinic ACh Receptor from the nicotinic?
What is its main purpose
When ACh binds mACh it activates a G-protein enzymatic cascade that causes a series of chemical rxns to tun on an amplification.
This is an amplification of the signal
These second messengers are what control cellular events
How are NT shut off?
Can be reuptaken back into the axon terminus
Destroyed by enzymes with in the synapse
Removed by glial cells
What class of NT are derived from tyrosine?
What do they include?
Catecholamines (Monamines)
Include:
Serotonin
Norepinephrine
Dopamine
What are the amino acid NTs that are excitatory NT
Glutamic acid
Aspartic Acid
What amino acids are inhibitory NT’s
Glycine
GABA (gamma-aminobutyric acid) - most common NT in brain
What NT make up a large class that share the property that they are small proteins?
What are some examples and how are they activated
Peptide NT’s
Ex. Endorphins, enkephalins, endogenous opioid NT’s
Activated by stressors: analgesia and euphoria
Include pain sensations
What is the major gaseous signal factor
How is this released?
Nitric Oxide is major transmitter
Can be released by endothelial cells in response to elevated pressure with an arteriole
What is the function of NO?
Causes smooth muscle relaxation - in blood vessels this reduces the resistance to flow
What drug increases NO?
What does it do?
Viagra increases NO (Smooth muscle relaxation in arterioles)
This increases blood flow through blood vessels supplying external genitalia
What is the resting membrane potential?
What is the average RMP
The resting membrane potential is a voltage within a cell
The average RMP is -70mV
How this the RMP derived? Meaning what makes the RMP?
What maintains the RMP?
It arises from passive ion flux across the plasma membrane
K+ efflux, Na+ influx
Concentration difference across the membrane is maintained by the Na+/K+ ATPase.
If the membrane potential becomes less negative than the RMP what is happening?
What is the membrane potential used to do?
The cell depolarizes
Use the membrane potential to do work
Work is associated with the changes in the MP
What are the two changes that are associated with the membrane potential?
Depolarization
Hyperpolarization
The RMP is controlled by what?
However a neuron experiences a change in MP what is involved in this and how is this change accomplished?
RMP is established by open channels that are constantly open
The change in membrane potential involves gated channels
The gated channels open in response to what?
Stimuli
NT
Voltage disturbances
What are the three states that the voltage gated Na+ channels exhibits?
When does sodium influx through the channel
Closed
Activated
Inactivated
When it’s depolarized
There are two parts to the Na+ voltage gated channel, what are they and when do they open and close
The activation gate and the inactivation gate (ball and chain)
The activation gate is closed at RMP, when a depolarizing stimulus arrives the activation gate opens
At the peak of the AP it shuts off and the inactivation gate (ball and chain) closes and blocks the channel
During repolarization caused by K+ leaving the cell the two gates reset
What are Action Potentials? Where are they triggered?
AP’s are electrical signals that travel through a neuron
The trigger zone is the axon hillock
How do AP’s travel down the neuron?
The are regenerated along the length of the axon at the nodes of Ranvier
What are the features of an AP
Usually does not change in size or shape.
Regenerates itself along as it is propagated.
Doesn’t waken with distance.
What are the events of activation of voltage-gated channels during an AP?
- RMP. 2. Depolarizing stimulus. 3. Membrane depolarizes to threshold, voltage gated Na+ and K+ begin to open. 4. Rapid entry of Na+ entry into the cell causes depolarization. 5. Na+ channels close and slower K+ channels open. 6. K+ moves from cell to extracellular fluid. 7. K+ channels remain open and additional K+ leaves the cell causing hyperpolarization. 8. Voltage gated K+ channels close, less K+ leaks out if the cell. 9. Cell returns to RMP.
What type of cycle governs the activation of the Na+ channels?
Positive Feedback cycle
What are the two types of refractory periods?
Absolute refractory period
Relative refractory period
When doe the absolute refractory period take place and what is happening?
It begins when the Na+ channels open and when the Na+ channels reset and the K+ channels remain open
During this period no stimulus can trigger another action potential
What is the relative refractory period and what is taking place?
The Na+ channels have reset, while the K+ channels remain open
During the RRP only a larger than normal stimulus can initiate an new AP
Once the Na+ inactivate what happens the channels
Once inactivated, the channels won’t open until the cell returns to the RMP
What increase the velocity of an AP in a neuron? How fast is it?
About 2m/sec
Velocity increases with the increase of the diameter of the neuron
The resistance of the axon membrane to ion leakage. Lower the resistance the father the velocity
Neurons wrapped in what increases speed and ho w much faster?
Myelin
100m/sec
What does the myelin sheath help with and what is this called.
The myelin sheath creates resistance to current leak across the membrane
This is called Saltatory Conduction
Where are the voltage gated Na+ channels found?
What takes place at this area?
Nodes of Ranvier is where the voltage gated Na+ channels are
AP’s appear to jump form one node to another
How do Neurons communicate with their target? Where does this communication take place?
What is the main type of communication?
Neurons communicate with their target downstream target via synapses. The synapses is the presynaptic cell and the postsynaptic cell for the synapse. The space between is called the synaptic cleft
The major type of communication is called a Chemical Synapse
What does a Chemical synapse use to communicate between cells?
What happens during the communication between cells?
Neurotransmitters
NT’s are released from presynaptic vesicles and diffuse to the postsynaptic cell where they bind to their specific Postsynaptic cell receptor
What triggers the NT to be released from the presynaptic cell?
An AP depolarizes the axon terminal, and this caused voltage gated Ca+ to open. Ca+ enters the presynaptic axon terminus and triggers the exocytosis of the NT into the synaptic cleft.
NT binding to the postsynaptic cell triggers a cellular response.
There are two types of postsynaptic communication once the NT bins to the receptor, what are they?
(EPSP) Excitatory postsynaptic potentials
(IPSP) Inhibitory postsynaptic potentials
Where do AP’s go? Where is NT released from?
What part of the postsynaptic neuron does the NT have an effect on by opening voltage gated channels chemically?
Axon Terminus
Dendrites and cell bodies
If the synaptic potential is depolarizing it is called?
What does it make the cell do?
Excitatory postsynaptic potential (EPSP)
It makes the cell more likely to fire an action potential.
If the synaptic potential is hyperpolarization it is called?
What is hyperpolarization?
Inhibitory postsynaptic potential (IPSP)
It moves the membrane potential away from threshold and makes the cell less likely to fire and AP.
The combination of several nearly simultaneous graded potentials is called?
What does this mean?
Spatial summation
Spatial means that the graded potential originate at different locations (spaces) on the neuron
Summation that occurs from graded potential overlapping in time is called?
Temporal summation
Two sub threshold graded potentials from the same presynaptic neuron can be summed if they arrive at the trigger zone close enough together in time.
