Neuroscience Chapter: Membrane Permeability

Action Potentials and Graded Potentials

• Gated sodium channels open in response to a stimulus, increasing Na+ permeability.
• Graded potentials generate small electrical currents that dissipate over distance along the membrane.
• An action potential involves a significant voltage change, characterized by depolarization that hits a threshold.
• Refractory period occurs when sodium channels are inactivated, preventing the initiation of a second action potential.

Conduction of Action Potentials

• At the axon hillock, Na+ influx during the rising phase creates an electrical current, depolarizing adjacent axon regions.
• Action potentials are all-or-none; their magnitude and duration remain consistent along the axon.
• Myelin sheath, formed by oligodendrocytes in the CNS and Schwann cells in the PNS, insulates axons and facilitates faster action potential propagation.

Electrical Synapses and Neuronal Communication

• Electrical synapses have gap junctions allowing direct electrical current flow between neurons.
• The insulating lipid layers of myelin act as poor electrical conductors.
• Synaptic vesicles hold neurotransmitters, while the synaptic cleft is the gap between pre- and postsynaptic neurons.

Postsynaptic Potential

• Postsynaptic potentials occur when receptor proteins bind to neurotransmitters, triggering responses in the postsynaptic cell.

Cell Membrane and Potential

• The membrane potential is the voltage difference between the intracellular and extracellular environments, typically around -60 mV.
• Gated ion channels respond to voltage shifts across the plasma membrane, contributing to resting potential.

Resting Potential and Ion Transport

• Resting potential represents the voltage in an unstimulated neuron.
• The sodium-potassium pump uses ATP to transport Na+ out and K+ into the cell, maintaining concentration gradients: higher Na+ outside and higher K+ inside.
• Resting neurons have more open potassium channels, leading to a more negative interior compared to the outside.

Membrane Permeability and Transport

• The selectively permeable membrane regulates the transport of materials in and out of the cell.
• Diffusion processes can be passive or active, influenced by concentration gradients and temperature.
• Electric charge can impact diffusion rates and patterns.

Cell Surface Markers

• Glycoproteins are involved in self-recognition, creating unique protein/carbohydrate chain shapes per individual.
• Glycolipids contribute to tissue recognition through characteristic lipid/carbohydrate chain shapes.