BIO1022 Lecture Notes - Lecture 5: Neurotransmitter, Cell Junction, Saltatory Conduction
6 Jun 2018
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o Flow determined by concentration and electrical charge
· Sodium-potassium pump transports these ions against their concentration gradients
o Equilibrium not achieved
o K+ principal intracellular, NA+ principal extracellular cation (an atom that has lost an electron to
become positively charged)
Graded potentials
· Hyperpolarisation
o Stimulus triggers increase in magnitude of membrane potential
o Opening of Cl- channels
· Depolarisation
o More positive
o Stimulus triggers decrease in magnitude of membrane potential (less negative)
o Opening of Na+ channels
o Magnitude dependent on stimulus strength
Action potentials
· All or nothing depolarisations
· Threshold membrane voltage (-55mV)
o Beyond threshold, action potential triggered
· Carry information along axons
· Very rapid (1 – 2 milliseconds)
· Magnitude always the same
1. Resting state
· Na+ and K+ gates closed
· Resting potential: -70mV
Document Summary
Flow determined by concentration and electrical charge. Sodium-potassium pump transports these ions against their concentration gradients: equilibrium not achieved, k+ principal intracellular, na+ principal extracellular cation (an atom that has lost an electron to become positively charged) Hyperpolarisation: stimulus triggers increase in magnitude of membrane potential, opening of cl- channels. Depolarisation: more positive, stimulus triggers decrease in magnitude of membrane potential (less negative, opening of na+ channels, magnitude dependent on stimulus strength. Threshold membrane voltage (-55mv: beyond threshold, action potential triggered. Magnitude always the same: resting state. Membrane potential less negative: rising phase. Eventually some na+ activation open to balance. Action potential in one region depolarises neighbouring regions. Cell junctions between a neuron and another cell: neuron-neuron, motor neuron-muscle cell, neuron-gland cell. Neuron-neuron conducts signals from axon presynaptic cell: electrical synapse (direct contact very rapid, chemical synapse (synaptic cleft most)
