Signal Transduction Mechanisms: Electrical & Synaptic Signalling (PDF)

Signal Transduction Mechanisms: I. Electrical & Synaptic Signalling in Neurons Course instructor: Alvin Hee, Ph.D BGY 3002 Cell & Molecular Biology  Learning Outcomes Upon completing this lecture, you are expected to be able to: 1. Describe the structure o...

Signal Transduction Mechanisms: I. Electrical & Synaptic Signalling in Neurons Course instructor: Alvin Hee, Ph.D BGY 3002 Cell & Molecular Biology  Learning Outcomes Upon completing this lecture, you are expected to be able to: 1. Describe the structure of a nerve cell. 2. Explain the terms resting membrane potential and action potential. 3. Describe the transmission of an action potential along a myelinated axon. 4. Describe the transmission of a signal across a synapse. Structure of a Typical Motor Neuron  Resting Membrane Potential Potential differences exist when charges are separated between inside and outside of cell (i.e. positive ion excess on one side of membrane and a negative ion excess on the other). Electrical potential (voltage) across the plasma membrane or an unstimulated nerve cell. K+ gradients maintained by the Na+/K+ ATPase are responsible for the resting membrane potential.  Action Potential When cells are stimulated, there is a brief change in membrane potential involving an initial depolarization followed by a rapid return to the normal resting potential. Caused by inward movement of Na+ followed by the subsequent movement of K+; serves as the means of transmission of a nerve impulse. Na+ cannot reopen immediately following an action potential, producing a short refractory period when the membrane cannot be stimulated. All-or-none behaviour.  Propagation of Action Potential as an Impulse Action potentials produce local membrane currents depolarizing adjacent regions of the membrane that propagate the action potential. Speed is important- the speed of a neural impulse depends on the axon diameter and whether the axon is myelinated. - Resistance to local current flow decreases as the diameter increases; - Myelin sheaths cause saltatory conduction. Transmission of an Action Potential Along a Myelinated Axon  Chemical Synapse Neurotransmission & Synaptic Cleft Presynaptic neurons communicate with postsynaptic neurons (synapses) or muscles (neuromuscular junctions) across a gap (synaptic cleft). Chemical transmitters released from the presynaptic cell diffuse to receptors on the postsynaptic cell. The bound transmitter can depolarize (excite) or hyperpolarize (inhibit) the postsynaptic cell. Transmission of a Signal Across a Synapse