What was the big thing in the 16th century and how did it relate to the brain?
-electricity -people were discovering that you could contain it (Leyden jars) -animals like stingray can produce it so people wondered if electricity was the way nerves communicated
Who was Luigi Galvani and what did he do?
- 18th century Italian doctor, proved that elctricity was central to how infromation travels in the nervous system -when you generate electricity you can activate a nerve and then contract a muscle not just contracting a muscle by using electricity
What are nerve cells specialized to do?
-for transmission of electrical signals -nerve cells are little bioelectric devices (like batteries) -the electrical activity can be measured by inserting very small electrodes into the cell
What would you see when recording the difference of potential across a membrane?
-stereotypic event= the same size only thing that changes is how many and how close to each other
How is the difference in membrane potential achieved in the nerve cell?
-by selective movement of ions via ion transporters
What is an ion channel?
-allows ions to diffuse down concentration gradient -usually specific to only one ion -have opening and closing behaviour, may be voltage gated etc.
What is an ion transporter?
-it moves ions against concentration gradient (electrogenic)
What is electrochemical equilibrium?
-ions are free to travel will be equally distributed and no difference in membrane potential -if there are selective channels that let the ion go only one way then with every k+ leaving it leaves behind a more negative environment and goes into more positive= results in change in membrane potential
What is the key to using the membrane potential to create the nerve impulse?
-voltage dependence of the ion channels -Na+ open when depolarisation and will open and close really quickly under a millisecond -some Na goes in and some K goes out every action potential -this is how neurons communicate
How does the membrane potential difference travel through the axon?
-all of the current exchanges occur across membranes -one depolarisation activates the membrane next to it to depolarisation
How does nerve impulse conduction differ in vertebrates and invertebrates?
-vertebrates we have a better way of conducting nerve impulses faster= insulate (whereas invertebrates can only make longer bigger nerves with less resistance) -myelin sheath, then really concentrated channels in the node of ranvier = saltatory conduction
What is the function of a synapse?
-the cells of the nervous system must also integrate, process and store information -covergence and divergence of signals= the Synapse
What percentage of synapses in humans are electrical and what are they good for?
-less than 1% -good for synchronization of neuronal groups (eg. respiratory group)
What is the only effect an electrical synapse can have?
What type of transmission occurs in electrical synapses?
-passive transmission, no complex energy-dependent release machinery -fast, no long latency due to complex energy-dependent machinery, diffusion, and post-synaptic receptor activation
What do electrical synapses look like?
-like they're sort of joined together trough the channels
What type are majority of synapses in a human?
How wide is the synaptic cleft?
How fast are chemical synapses?
-slow, due to complex energy-dependent release machinery, diffusion, and post-synaptic receptor activation
Are chemical synapses energy dependent?
-yes. -synthesis, release and re-uptake all require energy
What signal can chemical synapse transmit?
-huge variety as there are over 100 neurotransmitters, huge variety of receptors. -what effect a transmitter has is determined by what the postsynaptic receptor does and how this affects the membrane potential
WHat do chemical synapses look like?
How many connections does a neuron typically have?
-1 neuron will have 1000-10 000 synaptic connections with other neurons
How does the process that is started by membrane potential spreading through the synaptic terminal go?
1.Transmitter is synthesized and then stored in vesicles 2.An action potential invades the presynaptic terminal 3.Depolarization of presynaptic terminal causes openings of voltage gated Ca2+ channels 4.Influx of Ca2+ through channels 5.Ca2+ causes vesicles to fuse with presynaptic membrane 6.Transmitter is released into synaptic cleft via exocytosis 7.Transmitter binds to receptor molecules in postsynaptic membrane 8.Opening or closing of postsynaptic channels 9.Postsynaptiic current causes excitatory or inhibitory postsynaptic potential that changes the excitability of the postsynaptic cell 10.Retrieval of vesicular membrane from plasma membrane
How was the presence of neurotransmitters discovered?
-scientist Loewi, stimulate a parasympathetic nerve stimulating the heart (vagus nerve) -he stimulates the heart loaaaads and the vagus stuff was so abundant due to the excessive stimulation so leaked= he caught it and tried to put the thing on another heart and it stimulated it too without the nerve doing anything= acetylcholine -called the released stuff vasgusstoff
What is the process of neurotransmitter synthesis when it is a small-molecule transfer?
1.Synthesis of enzymes in cell body 2.Slow axonal transport of enzymes 3.Synthesis and packaging of neurotransmitter 4.Relase and diffusion of neurotransmitter 5. Transport of precursors into terminal
What is the process of neurotransmitter synthesis when it is a peptide transmitter?
1.Synthesis of neurotransmitter precursors and enzymes 2.Transport of enzymes and peptide precursors down microtubule tracks 3.Enzymes modify precursors produce peptide neurotransmitter 4.Neurotransmitter diffuses away and is degraded by proteolytic enzymes
What does a vesicle really look like?
What were the three theories of how the nervous system worked in the early 1700s and why were they incorrect?
-Spirits running through hollow nerve fibres, conveying impressions to the brain and activating muscles =wrong because limbs do not increase in volume when muscles are activated -Mini explosions caused by fermentation upon the mixing of fluid droplets from the nerve ends and blood, activating muscle =wrong because nerves cut underwater did not result in bubbling ferment. Ligation of nerves did not cause them to accumulate fluid, and it was suspected that fluid of any sort could not move fast enough to explain the speed of nervous system function -Vibrations, light of different energies transferred vibrations to nerves, conveying sensations to the brain =wrong because nerves too floppy to transmit vibrations