In the cortex there are 20% 40%( 20%, 40% ) of all neurons, but it contains 80% 30%( 80%, 30% ) of the brain's mass.
In the cerebellum there are 50% 20%( 50%, 20% ) of all neurons, but it contains 10% 50%( 10%, 50% ) of the brain's mass.

10% 40%( 10%, 40% ) of all neurons are lost over time.

The brain represents only 2-3% 4-5%( 2-3%, 4-5% ) of the body's mass but needs 20% 25%( 20%, 25% ) of the energy.

The problem with intracellular recordings is that they cannot be recorded in behaving animals look different than normal action potent( cannot be recorded in behaving animals, look different than normal action potent ).

The sodium-potassium pump (Na-K ATPase) transports 3 2 1 4( 3, 2, 1, 4 ) Na+ out in( out, in ) and 2 1 3 4( 2, 1, 3, 4 ) K+ in out( in, out ).
It uses 1 2 3( 1, 2, 3 ) ATP.

The depolarization is due to the influx outflux( influx, outflux ) of sodium potassium calcium( sodium, potassium, calcium ).
The hyperpolarization is due to the outflux influx( outflux, influx ) of potassium sodium calcium( potassium, sodium, calcium ).

The absolute refractory period can be explained by the inactivation activation( inactivation, activation ) of sodium potassium calcium( sodium, potassium, calcium ) channels.
The relative refractory period can be explained by the extended opening closing( opening, closing ) of potassium sodium calcium( potassium, sodium, calcium ) channels.

An action potential can only travel in one direction due to the inactivated sodium potassium calcium( sodium, potassium, calcium ) channels.

A large length constant means a higher lower( higher, lower ) speed.

The length constant can be increased by:
(a) decreasing increasing( decreasing, increasing ) the internal resistance by thicker thinner( thicker, thinner ) axons
(b) increasing decreasing( increasing, decreasing ) the membrane resistance by improved poorer( improved, poorer ) insulation

The highest observed speed of an action potential happened in a shrimp and was about 200 150 100 250( 200, 150, 100, 250 ) m/s.

Most electric synapses are bidirectional unidirectional( bidirectional, unidirectional ).
The synaptic transmission happens almost instantaneous with a delay( almost instantaneous, with a delay ) and also sub-threshold potentials only sup-threshold potentials( also sub-threshold potentials, only sup-threshold potentials ) can be transmitted.

Signal transmission at a chemical synapse:

(1) The arrival of an action potential opens voltage-gated calcium sodium potassium( calcium, sodium, potassium )-channels.
(2) The increase of calcium-ions triggers the release of neurotransmitters through exocytosis endocytosis( exocytosis, endocytosis ) of synaptic vesicles into the synaptic cleft synaptic gap synaptic fissure( synaptic cleft, synaptic gap, synaptic fissure ).
(3) The neurotransmitters bin to receptors and open close( open, close ) channels.

The used neurotransmitters get either reabsorbed into the presynaptic postsynaptic( presynaptic, postsynaptic ) cell or broken down metabolically.

The signal transmission through transmitter-gated ion channels happens fast and transient slow and is long lasting( fast and transient, slow and is long lasting ). This is also called direct indirect( direct, indirect ) gating.

There is also G-protein-coupled F-enzyme-coupled H-molecule-coupled( G-protein-coupled, F-enzyme-coupled, H-molecule-coupled ) receptors, which is slower, longer lasting faster, more transient( slower, longer lasting, faster, more transient ) and can have more diverse effects (e.g. an amplification of the signal).
This is also called indirect direct( indirect, direct ) gating.

Postsynaptic potentials are graded fixed( graded, fixed ).

The most important neurotransmitters for EPSPs are:
- glutamate GABA glycine( glutamate, GABA, glycine ) in the CNS
- acetylcholine glutamate glycine( acetylcholine, glutamate, glycine ) for skeletal muscles

The most important neurotransmitters for IPSPs are:
- GABA glutamate( GABA, glutamate )
- glycine glutamate( glycine, glutamate )
- acetylcholine glutamate( acetylcholine, glutamate ) for smooth muscles (e.g. the heart)

The membrane potential is a consequence of an ion imbalance balance( imbalance, balance ) on both sides of a selectively permeable impermeable permeable( selectively permeable, impermeable, permeable ) membrane.

The properties of an action potential result from the dynamics of ion channels the synapses the axon Schwann cells( ion channels, the synapses, the axon, Schwann cells ).

(Chemical) synapses transmit electric potentials chemical signals neurotransmitters( electric potentials, chemical signals, neurotransmitters ) from the pre- to the postsynaptic cell by triggering a gating mechanism of specialized ion channels in the postsynaptic membrane.