lecture 4 LOs Flashcards
my/met and mesencephalon
house many of the cell bodies of neurons that use distinct NTs and send long projections that influence multiple brain regions
basal ganglia
involved in motor controls and action selection
most prominent nuclei in basal ganglia
dorsal striatum (caudate/putamen), and ventral striatum (nucleus accumbens)
dorsal striatum key role
motor learning and action selection. recieves input from sensor/motor cortex and dopamine input from substantia nigra
ventral striatum imp for
reward and motivated behavours
recieves input from limbic system and dopamine input from the ventral segmental area (mesencephalon)
telencephalon limbic system
integrates emotional responses and regulates motivated beh and learning
in charge of the 4 Fs
key regions o the telecephalon
hippocampus: associated with establishment of new long term memories and relational /spatial memory
amygdala: coordinates various components of emotional responses (esp fear) through profuse connections with other brain areas
other areas considered part of limbic system
hypothalamus, nucleus accumbens, preforntal (cingulate) cortex
most relevant region of cerebral cortex
frontal lobes. esp for many of the interesting actions of psychoactive drugs
brodmanns areas: partitioning of different cortical regions based on cytoarchitecture, or histological structure and organization of cells
prefrontal cortex
critical for making decisions, planning actions, evaluating different strategies
this area is disrupted in many psychiatric disorders
also in frontal lobes: primary/secondary motor cortex that mediates voluntary and well learned motor sequences
what is the PFC interconnected with
different nuclei in the limbic system and the striatum
all telencephalon regions contain receptors for ___
numerous NT systems affected by psychoactive drugs
three major types of synapses
axodendritic: terminal connects with a dentrite of the postsynaptic cell. most common type of synapse. synapses typically connect to dendritic spines, but occasionally connect to dendritic shafts
axosomatic: axon terminal forms connection with neuron cell body
axoaxonic: an exon synapsing on another axon terminal. can reduce (pre synaptic inhibition) or enhance transmitter release (presynaptic facilitation) of receiving terminal. work via heteroreceptors (receptor on axon terminal that responds to transmitters different from those released by those terminals)
where are most transmitters made
in terminals, but peptides are made in soma and then transported to terminals
where do many peptide transmitters reside
in terminals that also contain classical small molecule transmitters
neuromodulators def
may enhance, reduce, or prolong the action of another NT
cannot easily be seen as excitatory or inhibitory, can have different effects depending on multiple factors
volume transmission
neuromodulators may diffuse away from the site of release to influence other cells
rate and pattern of neuron firing
in general, higher firing rates means more NT release
burst firing leads to release more transmitter than rapid cont firing
many neurons that use classical NTs (DA, NE, 5-HT(serotonin)) switch to burst firing modes in response to motivationally or emotionally relevant stimuli
autoreceptors def
receptors for the same transmitter released by neuron
autoreceptor presynaptic terminal activated and inhibited by
activated by NT, inhibit further transmitter release
somatodendritic autoreceptors, where are they and what do they do
reside on cell bodies/dendrties when activated, they slow firing, reduces transmitter release
drugs that block autoreceptors ___ transmitter release
increase
drugs that stimulate autoreceptors ___ transmitter release
reduce
transmitters can be removed from the synapse by
enzymatic degradation
being taken up by presynaptic neurons (reuptake)
reuptake by nearby glial cells (astrocytes)
reuptake mediated through ___
transporter proteins
typically work via active transport
some transporters are sloppy and can uptake other types of NTs with similar chemical structure
NTs have multiple receptor subtypes that can differ in:
expression of different subtypes can vary across and/or within brain regions
all subtypes bind some ligand, but may do so with different affinities
sometimes, different receptor subtypes can exert opposite cellular effects (via different 2nd messengers)
two major categories of transmitter receptors
ionotropic: aka ligand gated ion channels
metabotropic: aka 2nd messenger or G-protein coupled recetors
ionotropic receptors:
consist of 4 or 5 subunits with an ion channel in center
some conduct Na+: opening excites (depolarizes) neurons
others allow flow of Na+ and Ca2+. Ca2+ entry can depolarize neuron and act as a second messenger
others conduct Cl- leading to hhyperpolarization (inhibitory)
metabotropic receptors:
act more slowly, effects last longer relative to ionotropic
work by activiating G proteins that act in one of two ways:
inhibit/activate ion channels (eg opens K+ channels, outflow causes hyperpolarization)
stimulate/inhibit effector enzymes that synthesize or break down second messenger molecules
protein kinases
second messengers are molecules inside cell that activate protein kinases that phosphorylate other proteins
phosphorylation of ion channels/eceptors can change their function
phosphorylation of nuclear proteins can turn gene expression off
second messenger pathway cyclic adenosine monophosphate (cAMP)
stimulates protein kinase A (PKA). some second messengers stimulate this pathway via a G-s protein), others inhibit cAMP (via G-i protein). controlled by some receptors for DA, NE, 5-HT (serotonin), endorphins
phosphoinositide second messenger pathway
breaks down a phospholipid in cell membrane, liberates two second messengers: diacylglycerol (DAG) and inositol triphosphate (IP3). DAG and IP3 increase concentration of Ca2+ ions in postsynaptic cell and activate protein kinase C (PKC). controlled by receptors for ACh, NE, 5-HT (serotonin)
