Week 1 Lecture 3 Flashcards
What happens when a patch of excitable membrane generates an action potential?
An influx of Na+ and reverses the potential difference across the membrane.
Are most cells excitable?
No, most cells are not excitable however they conduct passive current, but not generate action potentials.
Why are most cells not excitable?
They lack voltage-gated Na+ channels (and axons)
What cells generate action potentials?
Is biological tissue conductive?
No, when voltage is measured, 1/2 of the amplitude is loss indicating some signal is lost.
length constant (lambda)
how far a signal can be carried before the signal is lost, larger potential difference = longer length constant = signal will be carried out w/o being lost
How is the length constant increased?
Increasing the diameter of the axon results in less internal resistance and therefore less voltage is lost as the currents travel down the membrane
Increasing membrane resistance results in less current being leaked out while traveling across membrane
How is the length constant defined?
it is defined with internal resistance, extracellular fluid resistance, and membrane resistance however since extracellular fluid resistance is not adjustable and relatively low, only internal resistance and membrane resistance is considered
What is the most efficient way of increasing conduction velocity?
Increasing membrane resistance i.e. myelination
What cells are involved in myelination?
Schwann cells (in the PNS) and oligodendrocytes (in the CNS) which are specialized glial cells.
What are glial cells?
Cells that assist the nervous system that are required for nutrition and increased membrane resistance
How does myelination occur?
Layers (50-100) of myelin are wrapped around sections of the axon by Schwann and oligodendrocytes in nervous system to create myelin sheath
Are all axons myelinated?
Only some axons are myelinated since they add bulk and take up space
Is an entire axon myelinated?
No, small gaps are left between adjacent portions of the myelin sheath by glial cells
What are the small gaps left between adjacent glial cells?
Nodes of Ranvier