Neurophysiology Flashcards
The transfer of information along and between the neurons can be done in two ways.
Electrical : Action potential
Chemical : Neurotransmitters
The cell body communicates with its terminal using electrical impulses: action potentials
Action potentials are ‘all-or-none’ signals
Action potentials cause ________________
depolarization of the terminal and release of neurotransmitters
Steps in propagation of AP through a synapse:
- impulse arrives at pre-sm
- VGCC open, Ca2+ enters pre-sn
- synaptic vesicles carrying nt’s arrive at pre-sm and bind to docking protein.
- they release their nt’s into the synaptic cleft
- nt’s diffuse and bind to receptor at post-sm
- impulse continues
RMP concentrations of ions:
Na+ (and Cl-) are concentrated outside
K+ (and A-) are concentrated inside.
The ionic charge between inside and outside is unequal
Inside is negative to outside (-60 to -90mV)
Neurones are special because _______
they can rapidly alter their membrane potential.
This depends on voltage-gated ion channels
Electrical signalling importance:
Physiological:
- Transfer along neurones (long distance/fast)
- Summation/integration of inputs
Pharmacological:
1. Site for drug action (local anaesthetics, anticonvulsants)
Puffer fish contains tetrodotoxin (TTX). Why is it bad?
TTX is very potent toxic, works by blocking VGNC necessary to produce action potential!
Chemical transmission by -
Ligand-gated channels i.e. eg neurotransmitters
Not all synapses are chemical. they can also be
Electrical synapses.
action potential can move through gap junction channel and become coupling potential
Process of chemical transmission:
Action potential arrives at axon terminals and depolarizes the membrane
Voltage-gated Ca2+ channels are opened and Ca2+ flows in
Ca2+ influx triggers the synaptic vesicles to release neurotransmitters
Neurotansmitters binds to the target receptor on postsynaptic neuron
Chemical transmission importance
Physiological:
Communication between neurones (short distance/slow)
Complex signalling
Pharmacological:
Sites for drug action
Myelination is the process of ____________ to allow ________________
Process of forming a myelin sheath around a nerve to allow nerve impulses to move faster.
Myelin is formed by: _____1_____
in the peripheral nervous system (PNS)
and by __________ in the central nervous system (CNS)
- Schwann cells
2. Oligodendrocytes
Difference between Schwann cells and oligodendrocytes?
Each Schwann cell forms a single myelin sheath around an axon. In contrast, each oligodendrocyte forms multiple sheaths (up to 30 or more) around different axons. Along the same axon, sequential myelin sheaths are formed by different oligodendrocytes.
How is myelination done?
Schwann cellsin the PNS form individual myelin sheaths (blue) aroundaxons(orange), whereasoligodendrocytes in the CNS form multiple myelin sheaths (purple), each on separate axons. Schwann cell nuclei are located on the outside of the sheath. One myelinating Schwann cell is shown partially unrolled: the light central area is the topological equivalent of the compact myelin sheath, and the darker edges represent belts of cytoplasm along the cell border. In the CNS, a stretch of unmyelinated axon is shown in agreement with recent evidence that some axons are inconsistently myelinated.
A cross-section of a myelin sheath is illustrated at the bottom demonstrating the origin of the intraperiod line, formed by apposition of the extracellular leaflets of theglialplasma membrane, and the major dense line, formed by the tight apposition of the cytoplasmic leaflets. Myelin grows by the spiral wrapping of the inner turn (arrow) around the axon.
