Lecture 4 - Transmission between neurons Flashcards
Transmission between neurons
- Neurons send messages via synaptic transmission
- Neurotransmitters are released from one neuron and attach to another neuron
- This (neurotransmitter) initiates a reaction that ultimately results in postsynaptic potentials
- Chemical process
Presynaptic
Produces neurotransmitter
Postsynaptic
Receives neurotransmitter
Synapse
- The junction between two neurons (terminal buttons of one neuron and membrane of another neuron – normally a dendrite)
- One neuron connects to 50,000 other neurons (estimate)
- Vesicles within terminal buttons which contain neurotransmitters (made in soma or terminal button themselves)
- Presynaptic membrane and postsynaptic membrane
- Synaptic cleft = gap between the two membranes (don’t actually touch)
- Gap is 20 nanometres wide
- Astrocytes clear away neurotransmitters floating around in the synaptic cleft
Process of synaptic transmission
- AP arriving at terminal buttons
- -> Ca channels open and Ca2+ enters
- -> vesicles fuse with membrane and fusion pore opens (and widens)
- -> release of NT into cleft (exocytosis)
- -> NT diffuses across cleft and binds to postsynaptic membrane
- -> postsynaptic channels open
- -> ions flow (excitatory or inhibitory PSPs)
EPSP
Excitatory postsynaptic potential
IPSP
Inhibitory postsynaptic potential
Binding
- Neurotransmitter binds to binding site on post-synaptic membrane (alters membrane)
- Specific neurotransmitter and specific receptor site
- Postsynaptic potential depends on which ion channel (lock) is opened
- E.g. if sodium channels opened – sodium moves in – excitatory
- E.g. if potassium channels opened – potassium moves out – inhibitory
Ionotropic receptor
Contains a binding site and an ion channel. This opens when molecule attached to binding site. Direct way of opening ion channel
Metabotropic receptor
Contains a binding site. Initiates a chain reaction that eventually opens ion channels. Requires energy. Indirect way of opening ion channel
- G-proteins and secondary messengers
- PSPs slower than those produced by ionotropic receptors
Termination
- Terminate PSPs so other neurotransmitters can be taken up by receptor sites (could be either or combination of both)
Reuptake
Transmitter is taken back by the presynaptic terminal via transporter molecules. Astrocytes involved in reuptake e.g. reuptake glutamate
Enzymatic deactivation/degradation
Transmitter broken down by an enzyme e.g. acetylcholinesterase breaks down Ach into choline and acetic acid
Neural integration
- Excitatory = increased likelihood of neuron firing
- Inhibitory = decreases likelihood
- Neuron decides with these messages whether it fires or not
- Integration = summation of PSPs in control of neuron firing
- *Inhibitory PSPs do not always inhibit behaviour (inhibition of inhibitory neurons makes behaviour more likely and excitation of inhibitory neurons makes behaviour less likely)
- E.g. when asleep, some neurons stop you getting up and walking around when you’re asleep
GABA
- Most abundant (common) inhibitory neurotransmitter in CNS (reduces chance of neuronal firing)
Glutumate
- Most abundant (common) excitatory neurotransmitter in CNS
- Can bind to a number of receptors
- Important for learning and memory
Acetylcholine
- First neurotransmitter discovered
- Direct action small-molecule working primarily in muscles to translate our intentions to move into actual actions as signals are passed from the neurons into muscle fibre
- Other roles = helping direct attention, helps facilitate neuroplasticity across the cortex
- Found at neuromuscular junction
Serotonin
- Regulation of mood, eating, sleep
Dopamine
- ‘Pleasure chemical’
- Released when mammals receive a reward in response to their behaviour
- Diverse role in human behaviour and cognition
- Involved with motivation, decision making, movement, reward processing, attention, working memory and learning
- New research suggests it also plays a role in Parkinson’s disease, addiction, SZ, and other neuropsychiatric disorders
- Motor control, reward, addiction
Antagonist
- A drug that blocks a neurotransmitter
- E.g. Botulinum toxin (Botox) blocks the release of acetylcholine and prevents muscle contraction so paralyses muscles
Agonist
- A drug that mimics a neurotransmitter and enhances synapse function
- E.g. muscarine (naturally occurs in mushrooms) imitates acetylcholine
