Case 2 - introduction to neurotransmission Flashcards
what are neurones made up of
- cell body
- axon terminals
- dendrites
- axon
what is the cell body made up of
nucleus, stores DNA and rough ER which builds protein and mitochondria
what are the dendrite region
the input region; receives input from other neurones
what are the axon terminals
the output region; release of neurotransmitter
what is the axon region
main conduction unit. carries information in the form of electrical signal known as the action potential
what starts and initiates all transmission
the dendrites
what can electrical signals not transfer through
the synaptic gap
what two things can synaptic transmission be
electrical or chemical
what are the pre and post synaptic elements int he chemical synapse separated by
the synaptic cleft
what are majority of signals carried in
chemical format
what two clusters of cell bodies, dendrites and axons project to different parts of the brain
the substantial nigra and the ventral tegmental
when does an action potential occur
when a neurone sends information down an axon
how do neurones act as a signalling mechanism
by altering their resting membrane potential
what happens at the presynpatic terminal
the action potential opens Ca2+ channels and initiates neurotransmitter release
what does the myelin sheath do
speeds up conduction and are an insulator for the axon
what happens when you reach threshold
you get the opening of the sodium channels.
what gradients does sodium have
electrical and chemical
what is the benefit of sodium having two gradients
cause more sodium channels to open and therefore get a huge depolrisation and get a very fast influx of sodium ions
what happens once inside the cell is positive
the sodium channel closes and get repolarisation
what is repolarisation due to
potassium channels
how does potassium move
we know that there is more potassium ibnsde the cell, and at this point It is positive inside the cell swell. therefore potassium leaves the cell and this is repolarisation.
what is hyoerpolarisation due to
potassium channels being a little slower to close
what is the neurotransmitter released into the synapse by
exocytosis
where are neurotransmitters stored
the synaptic vesicle
what is exocytosis
where the presynaptic vesicles bind to the presynaptic membrane, then the neurotransmitter is pushed out into the synaptic cleft
why is there no excess excitation
enzymes break down the transmitter in the cleft
what determines wether it is an excitatory or inhibitory signal
the receptor
what is an ionotropic receptor
receptor that is part of ligand gated ion channel protein and activation results in ion conductance changes.
what are inotropic receptors opened by
the transmitter to allow the passage of Na+ (excitatory) or K+/Cl- (inhibitory) and are involved in fast transmission - milli seconds
what are examples of inotropic receptors
acetylcholine, glutamate and GABA
what are metabotropic receptors
receptor protein in membrane that is coupled to effector mechanism via G proteins. in this signalling mechanism, agonist molecule combines with receptor proteins in the membrane
what does this result in
conformational change causes activation of a membrane associated enzyme via G protein
an example of a metabotropic receptor
dopamine receptor - they are a lot slower
receptors summary
what is the rate determining step in dopamine synthesis
tyrosine hydroxylase as it is normally saturated by substrate
what is dopa decarboxylase
high activity and nonselective
diagram showing synthesis of dopamine
how is dopamine stored
in the synaptic vesicles in the axonal terminal
where is dopamine released
into the synaptic cell upon the arrival of an action potential and influx of Ca2+
what 2 postsynaptic receptors does dopamine bind to
D1 family: D1&D5 - excitatory
D2 family: D2,3,4 - inhibitory
what enzymes metabolise dopamine
COMT and MAO
what is the reuptake process
catecholamines have a highly specific active transport mechanism to remove the transmitter from the synapse into presynaptic terminal
what is the dopamine transporter
DAT
what pathway is drug overuse focused on
the mesolimbic pathway
description of the mesolimbic pathway
- ventral tegmental area in the midbrain to limbic regions associated with reward, motivation, affect and memory.
- include ventral striatum (Nucleus accumbens), amygdala, hippocampus and medial prefrontal cortex
which pathway does Parkinson’s affect
the nigrostriatal pathway
what would you give to someone with Parkinsons
L-dopa because if you give L tyrosine it doesn’t matter how much you have because the tyrosine hydroxyls is the limiting factor as it is saturated.
or an agonist at D1 receptors
what is the major excitatory neurotransmitter in the CNS
glutamate
summary of dopamine pathways
order of signalling pathway in brain
- spinal cord
- medulla
- thalamus
- cortex
what are the 5 regions of the basal ganglia
- caudate nucleus
- putamen
- globus pallidus
- sub thalamic nucleus
- substantia nigra
the direct pathway
what is the major inhibitory neurotransmitter
GABA
where is acetylcholine released
at the neuromuscular junction
