Topic 3 (chemical synapses) Flashcards
what mv causes the voltage gated calcium channels to open?
voltage gated calcium channels open when the membrane depolarises to -60 to -40 mv
is the calcium influx in the presynaptic termial down or against the concentration and electrical gradients?
calcium flows in down the concentration and electrical gradient
how does the neurotransmitter release vescicles?
Vescicles have v-SNARE proteins and the membrane has t-SNARE proteins
Each snare protein has a lipophilic section inside the membrane and a hydrophilic section outside the membrane
When calcium binds to these protein it allows them to link together and enable the vescicle to dock on, the membranes to fuse and the vescicle contents to be released into the extracellular space
what is an axospinous synapse?
a small presynaptic axon terminal contacts a postsynaptic dendritic spine
What is an axosomatic synapse?
- axons contact the postsynaptic syanpse
What is the synapse in the Calyx of Held?
- the unusually large axon terminal surrounds the post synaptic soma
- this allows a quick transmission of action potentials
- it is found when the auditory sensory neurons connect to neurons in the pons
what is translocation of neurotransmitters
when vescicles move in and out of the synaptic bouton
what role do astrocytes play in synapses
clear up neurotransmitters
how do astrocytes clear up excess glutamate?
they ustilise excitatory amino acid transporters (EAAT’S)
glutamate transporters in the astrocyte hoover up all of the glutamater
This is then converted to glutamine and sent back to the neurons
What are 7 excitatory neurotransmitters?
Glutamate Acetylcholine Histamine Dopamine Norepinephrine Noradrenaline
What are 3 inhibitory neurotransmitters
GABA
serotonin
dopamine
What are 3 glutamate receptors and what are they permeable to?
AMPA- Na+ and K+
Kainate- Na+ K+ and Ca2+
Nmda- Na+ K+ and Ca2+
What are GABAa receptors permeable to?
Cl-
What ions are excitatory and inhibitory receptors permeable to?
Excitatory:
k+ leaves the cell and Na+ / Ca2+ enters
Inhibitory:
Cl- enters
what are the two types of EPSP summation
temporal and spatial
where in the neuron is it important that the membrane potential is sufficiently depolarized for an action potential?
at the axon hillock
what codes information inside cells and between cells?
inside cells= frequency of action potentials
between cells= amount of NT release
How does visual processing occur in the lateral geniculate nucleus and visual cortex neurons?
LGN NEURONS
- respond to a dot of light in a particular part of the visual field
- no response to a general illumination over a wide area
VISUAL CORTEX NEURONS
- Get input from several LGN neurons
- Fires an action potential when there is a line in a particular part of the visual field
How do different types of neurotransmitter pathways modulate each other?
an inhibitory synapse may connect to a excitatory neuron, so the excitatory and inhibitatory systems can modulate each other
how does the hippocampus encode memories?
- the hippocampus is an association network
- cells that fire at the same time become associated
- when some of these cells are reactivated they can reactivate the whole network leading to memory recall
What are 4 mechanisms of synaptic plasticity?
- changes in amount of neurotransmitter released
- Biophysical changes to receptors and channels
- Modulation by other transmitters, proteins and channels
- morphological changes to the dendrites and spines of the postsynaptic neurons
- synapse loss or sprouting
- Changes in gene transcription
what was Hebbs postulate?
cells that fire together wire together
What is long term potentiation
before LTP a small input creates a small current
After LTP the same input can create a much larger current
So the synapses are essentially stregthened
what are changes in synaptic structure that may promote learning?
- increased axonal transport
- increase in terminal size or area
- increase in number of synaptic vescicles
- change in size of synaptic cleft
- change in dendrite stem length and width
- increase in density of contact zones
- increase in spine size or area
- increase in protein transport for spine construction
how did Eric Kandel discover changes in synapses
- they squirted water at a sea slug
- they discovered that the number and size of sensory synapses changed in the trained slugs
- they found that synapse number is decreased in habituated animals and increased in sensitised animals
how was CAMP shown to be related to learning?
- cAMP was shown to be important for learning
- mutations that either increased or decreased cAMP levels reduce the learning capacity of drosophilia
what are the 3 parts of the autonomic nervous system?
Sympathetic, Parasympathetic and enteric nervous system
What does the enteric nervous system control?
The gut
what activities is the parasympathetic nervous system involved in?
digestion, sexual arousal, salivation, crying, urination, defecation,
what nerves does the parasympathetic nervous system involve?
cranial nerves, vagus nerve, pelvic spinchial nerves
outline neurotransmission in the sympathetic nervous system
-Preganglionic neurons release Acetylcholine
-Postganglionic neurons express Nicotinic acetylcholine receptors
-stimulation of postganglionic neurons makes them release norepinephrine
the
- The norepinephrine then activates adrenergic receptors on peripheral targets
OR
- the adrenal medulla is stimulated to release norepinephrine into the blood system
Outline neurotransmission in the parasympathetic nervous system
- preganglionic neurons release acetylcholine at the ganglion
- this acts on nicotinic receptors of post-ganglionic neurons
- the postganglionic neuron then releases acetylcholine to stimulate the muscarinic receptors of the target organ
- different muscarinic receptors are expressed by different targets
