2 - Intro to Neurotransmission Flashcards
what is the input region of a neuron?
dendrites
what is the main conduction unit of a neuron?
axon
what is the output region of the neuron?
axon terminal
what type of synapses are very rare in the adult brain?
electrical synapses
what is the gap in a chemical synapse called?
synaptic cleft
what initiates neurotransmitter release from the presynaptic terminal?
action potential opening Ca2+ channels
what are the 4 main stages of neurotransmitter activity across the synapse?
- synthesis
- storage
- release
- inactivation/reuptake
exocytosis
process of presynaptic vesicles binding to presynaptic membranes and releasing neurotransmitters directly into the synapse
agonist
substance which stimulates the receptors and mimics the natural ligand
antagonist
subtances that block the receptor and prevents the effects of the natural ligand
partial agonist
agonist that is unable to induce maximal activation of a receptor population, regardless of the amount of drug applied
which class of receptors are most important in neurotransmission due to their rapid conduction?
ionotropic receptors
receptors for what hormones are ionotropic receptors?
ACh
Glutamate
GABA
what is the mechanism of inotropic receptors?
- neurotransmitter binds to receptors that is part of ligand-gated ion channel proteins
- activation causes conformational change
- allows passage of Na+ (excitatory) or K+/Cl- ions (inhibitory)
- makes membrane potential more +ve or -ve which moves it closer or further from threshhold
how are metabotropic receptors coupled to effector mechanism?
via G-proteins
what is the mechanism of metabotropic receptors?
- agonist molecule combines the receptor proteins in membrane
- associated G proteins cause conformational change
- ions move in or out of cell
list these receptors in order of speed (fastest to slowest):
* kinase-linked receptors
* ionotropic receptors
* intracellular receptors
* metabotropc receptors
- ionotropic -msecs-secs
- metabotropic - secs-mins-hours
- kinase-linked - mins-hours
- intracellular - hours-days
where are ionotropic receptors used?
fast neurotransmission (nerve to nerve, somatic nerve to skeletal muscle)
where are metabotropic receptors used?
slower neurotransmission processes such as hormone action or growth factor action
agonist efficacy in iontropic receptors relates to what?
mean channel open time
agonist efficacy in metabotropic receptors relates to what?
ability to activate G-proteins
where are kinase-linked receptors used?
regulation of growth
differentiation and responses to metabolic signals
where are intracellular receptors used
used by lipid-solube steroid hormones, affecting DNA transcription processed
how is dopamine synthesised?
- L-Tyrosine converted to L-Dopa by tyrosine hydroxylase
- L-Dopa converted to dopamine by dopa decarboxylase (DDC)
what converts L-tyrosine to L-dopa
tyrosine hydroxylase
what converts L-dopa to dopamine?
dopa decarboxylase
what is the rate-determining step in dopamine synthesis?
tyrosine hydroxylase, as it becomes saturated by the substrate
what postsynaptic receptors can dopamine bind to?
- D1 family (D1 & D5) - excitatory
- D2 family (D2/3/4) - inhibitory
how is dopamine inactivated/reuptaken?
- metabolised by enzymes - COMT or MAO
- reuptake process - dopamine transported (DAT)
what are the 4 major dopamine pathways?
- nigrostriatal pathway
- mesolimbic pathway
- mesocortical pathway
- tuberoinfundibular pathway
which dopamine pathway is associated with parkinson’s disease?
nigrostriatal
which dopamine pathway is associated with +ve symptoms of SZ
nigrostriatal
which dopamine pathway is associated with drug abuse?
mesolimbic
which dopamine pathway is associated with -ve symptoms of SZ?
mesocortical
which dopamine pathway is associated with the side effects of drugs/medication?
tuberoinfundibular
what is parkinsons diseas?
- loss of dopamine neurons in the motor circuit
- when 60-70% of neurones are lost = symptoms
thinking about the synapes involved in parkinsons, what are two potential targets of drug treament?
- give patient L-dopa
- give pt agonist that could activate D1 receptors
what does the basal ganglia consist of?
5 large subcortical nuclei that participate in the control of movement
what are 4 important neurotransmitters in the basal ganglia?
GABA
Dopamine
glutamte
ACh
nodes of ranvier?
gaps on unmyelinated neurones between sections of myelin sheath
where do pain pathways cross the midline?
spinal cord
where do proprioceptive pathways cross the midline?
medulla
Label the AP
Label the neuronal body
Label the dopamine pathways
Draw a diagram illustrating the dopamine and motor circuit in the basal ganglia
What are the intracellular and extracellular levels of :
Na
K
A
Cl
Draw a diagram showing what happens when there is increased dopamine in the motor circuit of the basal ganglia
