Chapter 2 Flashcards
Discuss how neurons communicate
What is resting potential?
The neuron’s voltage at rest (-70mV)
How is information being relayed to a neuron transmitted?
This information is transmitted electrically
How is information being relayed from neuron to neuron transmitted?
This information is transmitted chemically
What is the charge of a neuron compared to its environment?
A neuron is negatively charged compared to outside the cell
What is an ion?
An electrically charged particle
What are ion channels?
Special passageways in the cell membrane of a neuron that allows or controls ion flow
What is special about ion channels?
They are selective; they only allow certain ions to flow through them, therefore there are several types of ion channels to accommodate for this
What does the sodium-potassium pump do?
It actively prevents an equal distribution of ions, in order to maintain a negative charge compared to outside the cell
- it sends out Na+ and allows fewer K+ in, keeping the net charge negative
Where is potassium in higher concentrations - outside the cell membrane or inside?
Inside; this causes potassium to flow out when a channel is open
Where is sodium in higher concentrations - outside the cell membrane or inside?
Outside; this causes sodium to flow into the cell when an ion channel is open
What does depolarization mean?
The peak of electrical charge; +40mV
What is the cell’s firing threshold? What happens when this threshold is crossed?
The cell’s firing threshold is -55mV after which point the cell will fire
What is repolarization?
The electrical charge of the cell retreats to the baseline
What is hyperpolarizaiton?
The overcompensation of the cell to try to reach resting membrane potential once more
What are the 3 properties of an action potential?
- action potentials are self-propogating (once it starts, there is nothing left for the cell to do)
- The action potential’s strength does not dissipate in the distance it travels
- action potentials are all-or-nothing responses (they either happen or they don’t, there is no in between)
Where do the production of APs begin?
At the axon hillock
Where does an AP end?
At the terminal bouton
- this is where the signal turns from an electrical one to a chemical one
What are receptors?
Specialized protein configurations
What chain of events is triggered by an AP?
The AP causes the synaptic vesicles to release their contents (neurotransmitters) into the synaptic cleft, where these are then taken in by receptors in the post-synaptic neuron
What are the two main types of receptors?
Ionotropic receptors and metabotropic receptors
What do ionotropic receptors do?
They work at opening and/or closing an ion channel
What does the bonding of a NT to a receptor do to the post-synaptic neuron?
When a NT bonds to a receptor, it changes the configuration of the receptor and causes an electrical signal to continue down to the next axon
What do metabotropic receptors do?
These receptors indirectly control ion channels
What are metabotropic receptors linked to? What happens when a NT bonds to it?
A protein called guanyl nucleotide-bonding protein (aka G-Protein)
- when a NT bonds to this receptor, a subunit of the G-protein (the alpha subunit) breaks away and either binds directly to an ion channel, causing it to open, or activates the channel by activating an enzyme
What is an enzyme?
It is any molecule that controls a chemical reaction
Explain the step-by-step process from when an AP reaches the axon terminal to the post-synaptic reaction
- action potential reaches axon terminal
- calcium channels open, allowing Ca2+ ions in
- Ca2+ causes synaptic vesicles to release from microtubules
- synaptic vesicles fuse with axon membrane at release site
- vesicles open and release NTs into the synaptic gap
- vesicle material is recycled
- vesicles return to neuron cell body or are refilled at the axon terminal
What does rate refer to?
The code the neuron’s transmit depends on how often the cell fires (i.e. what signal is coded depends on the rate of firing of the neuron)
What is an absolute refractory period?
This refers to the fact that an ion channel becomes blocked after allowing for the flow of ions, causing it to need a reset before functioning again
In what 3 ways are post-synaptic potentials different from action potentials?
- they are graded (meaning that the farther they travel, the weaker they become)
- their magnitude is much smaller than APs
- they can be excitatory (EPSP) or inhibitory (IPSP)
What is the relative refractory period?
When a much larger stimulus is needed to generate an AP during hyperpolarization
Where are excitatory synapses located?
on the dendridic tree
Where are inhibitory synapses located?
on the cell body (this makes IPSPs stronger)
How do neurons code the intensity of a stimulus?
By their rate of firing
- the neuron has an upper firing rate of 200 fires per second (this ceiling effect exists because an AP cannot begin until the previous one has finished)
How can NTs be cleared? (4)
- reuptake
- enzymatic deactivation (mostly for ACh via acetylcholinesterase)
- by astrocytes destroying the NT
- by diffusion
What do autoreceptors do?
They decrease the activity of the pre-synaptic neuron
What are amino acids?
They are the building blocks of proteins
Do all neurons only release one kind of NT?
No; many neurons can release two or more NTs
What are the 4 characteristics of a NT?
- they are synthesized in the neuron
- they are released when the cell is activated by an AP
- the same response can be obtained artificially (via medication or drugs)
- blockage of a NT results in no AP
What are the two major classes of NTs in the CNS?
- amino acids (the most common type)
2. NTs that are organized into systems
What are the two amino acid NTs?
glutamate and GABA
Describe glutamate.
- it is the main excitatory NT in the CNS
- it has three ionotropic receptors and one metabotropic receptor
- an overabundance of glutamate can cause epilepsy
Name the ionotropic and metabotropic glutamate receptors. Specify if they are ionotropic or metabotropic and mention what kind of effect each has.
- NMDA, AMPA (excitatory), kainate (excitatory) (all of these are ionotropic)
- glutamate receptor (this one is a metabotropic receptor)
What happens when glutamate binds on to an NMDA receptor?
it triggers a cascade, causing some ions to act as second messengers to change biochemical and structural properties of a cell (this structural reorganization is hugely important for the production of new memories)
What are agonists?
These are synthetic substances that mimic the natural effects of a NT
What are antagonists?
These are synthetic substances that oppose or diminish the effect of a NT
Describe GABA
- it is the main inhibitory NT in the CNS
- it has one ionotropic (GABAa) and one metabotropic (GABAb) receptor
- it reduces activity of the CNS
- benzodiazepines and barbiturates bind on to GABA receptors
What are the four neurotransmitter systems?
- cholinergic system
- dopaminergic system
- noradrenergic system
- serotonergic system
Of the neurotransmitter systems, which are included in the monoamine category?
Dopamine, Noradrenaline (aka Norepinephrine) and Serotonin
What role does tyrosine play, especially with Noradrenaline and Dopamine?
Tyrosine can change into dopamine (through a chemical process), which can then turn into noradrenaline
Why are there systems for certain neurotransmitters?
Because each of the monoamines is released by a different set of neurons that together make up a system
What are the two types of ACh receptors?
- nicotinic receptor (ionotropic)
2. muscarinic receptor (metabotropic)
What does the cholinergic system play a role in?
Maintaining cortical excitability and is linked to REM sleep
- this includes attention (overall arousal and vigilance)
as well as selective attention and memory (depletion of ACh is linked to Alzheimer’s)
What are the three sub-systems of the dopaminergic system?
- nigrostriatal
- mesolimbic
- mesocortical
How are the three dopaminergic sub-systems differentiated?
By the location of their cell bodies, the regions to which the project and the effect they have on behaviour
What are the overall characteristics of the dopaminergic sub-systems?
- all of the dopamine receptors are metabotropic
- the two main receptor families are D1-like and D2-like
- post-synaptic dopamine can either have an excitatory or inhibitory effect depending on which receptor it binds to
What is D1 and D2 activity linked to?
Schizophrenia
- many antipsychotics act as D2 agonists
- D1 has been linked to the cognitive and affective deficits associated with schizophrenia
Why is it difficult to treat both the psychotic effects as well as the cognitive and affective symptoms of schizophrenia?
Because blocking D2 receptors decreases D1 receptor activity
Describe the family of D1-like receptors?
This family includes D1 and D5 receptors and increase the production of cAMP
Describe the family of D2-like receptors?
This family includes D2 and D4 receptors and decreases the production of cAMP
What has the expression of the D4 receptor been linked to?
The personality trait, novelty seeking (i.e. exploratory behaviour, excitability and impulsivity)
Where are the cell bodies of the nigrostriatal subsystem located?
In the substantia nigra, and their axons project to the neostriatum (i.e. the basal ganglia)
What is the primary role of the nigrostriatal subsystem?
Important for selecting, initiating, and ceasing motor behaviour (this is the subsystem affected by Parkinson’s disease)
Where are the cell bodies of the mesolimbic subsystem located?
In the ventral tegmental area, and their axons project to several parts of the limbic system (i.e. the nucleus accumbens, ventral striatum, ventral amygdala, ventral hippocampus and the prefrontal cortex)
What is the mesolimbic subsystem linked to?
Reward related behaviour (it codes for whether a reward exceeds or falls short of an expectation)
Where are the cell bodies of the mesocortical subsystem?
Their cell bodies are also located in the VTA, but their axons project to motor, premotor and prefrontal cortices
What is the mesocortical subsystem linked to?
It influences the areas that its axons project to in terms of working memory
Where does the noradrenergic system originate? Where does it then project to?
It originates in the locus coerulus and then projects to the thalamus, the hypothalamus and the cortex (mainly the prefrontal cortex)
What are the 4 main types of noradrenergic receptors?
- are they metabotropic or ionotropic? what effect do they produce?
Alpha 1, Alpha 2, Beta 1 and Beta 2
- all are metabotropic and can have an excitatory or inhibitory effect
What does noradrenaline have an effect on?
Arousal and attention, as well as sleep (Alpha 2 receptors in the thalamus put the brain in sleep mode) and working memory (Beta receptor is linked to long term memories which have a strong emotional component)
- overall arousal is increased at Alpha 1 receptors in the thalamus and cortex; decreased arousal is associated with a decrease in NA in Alpha 2 receptors
Where are the cell bodies of the serotonergic system located?
Around the raphe nuclei of the midbrain, as well as the pons and medulla
- the most important clusters are found in the dorsal and medial raphe nuclei)
- these project to the hypothalamus, the hippocampus an the amygdala
- cells from the dorsal raphe nucleus project to the striatum, cortex, cerebellum and thalamus
What does the serotonergic system influence?
A large variety of behaviours:
- arousal
- mood
- anxiety and aggression
- control of eating
- sleeping and dreaming
- pain
- sexual behaviour
- memory
Describe the receptors of the serotonergic system?
They are all metabotropic except for 5-HT3
- LSD is a 5-HT2A and 5-HT2B agonist
