NEUROTRANSMISSION ALONG THE AXON Flashcards
What is resting potential
When the neurone is at rest
-70mV
What is the neural membrane impermeable to
Most polar molecules (sugars and amino acids)
Charged molecules
How can ions cross the neural membrane
Simple diffusion Channel mediated diffusion Carrier mediated diffusion Active transport Electrostatic pressure
What maintains resting potential of the neurone
The sodium potassium pump- continuously pushes Na+ out of axon- requires atp
3Na+ out= 2k+ in
What is an action potential
Are generated when he membrane is depolarised beyond the threshold point (-55mV)
All or nothing principal
Are generated in trigger zone (there is a high density of Voltage gated Na+ channels here)
What are the phases of an action potential
- Once above threshold , VG Na+ channels open - Na+ into cell
- K+ channels open- K+ out of cell
- Na+ channels become refractory, no more Na+ into cell
- K+ keeps leaving cell causing membrane potential to return to resting level
- K+ channels close, Na+ channels reset
- Extra K+ outside diffuses away
What does the speed of propagation of an action potential across an axon depend on
- temperature
- diameter of axon
- Myelination (myelinated= faster) in PNS= Schwann cells in CNS = oligodendrocytes
What are the different types of nerve fibres
- Type a fibres
- type b fibres
- type c fibres
Decribe type a nerve fibres
Thickest
Fastest conducting
Myelinated
Describe type b nerve fibres
Medium diameter
Myelinated
Slower conducting than a but faster than c
Describe type c nerve fibres
Unmyelinated
Smallest diameter
Slowest conducting
What are graded potentials
Brief local changes in membrane potential that occur in neuronal dendriites and/or cell bodies but not in axons
-no threshold
-summmation can occur
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