Basics

In the cortex there are [blank_start]20%[blank_end] of all neurons, but it contains [blank_start]80%[blank_end] of the brain's mass. In the cerebellum there are [blank_start]50%[blank_end] of all neurons, but it contains [blank_start]10%[blank_end] of the brain's mass.

[blank_start]10%[blank_end] of all neurons are lost over time.

The brain represents only [blank_start]2-3%[blank_end] of the body's mass but needs [blank_start]20%[blank_end] of the energy.

Local graded potentials

Action potentials

The problem with intracellular recordings is that they [blank_start]cannot be recorded in behaving animals[blank_end].

The membrane is a [blank_start]lipid bilayer[blank_end].

Kation channels have a [blank_start]high[blank_end] specificity, anion channels have a [blank_start]low[blank_end] specificity.

Ion channels can be activated by

Ohm's law: I = [blank_start]V/R[blank_end]

The opposite of the resistance is called [blank_start]conductance[blank_end].

The conductance depends on

The equilibrium potential is the potential at which the [blank_start]ion flux[blank_end] due to [blank_start]concentration[blank_end] difference and ion flux due to the [blank_start]electrical potential[blank_end] gradient balance each other so that there is no [blank_start]net[blank_end] movement of ions and no net current.

The Nernst equation depends on

The [blank_start]osmotic balance[blank_end] is the state in which the total concentrations of soluble particles is equal inside and outside of the cell.

Since the charges collect at the membrane it has the properties of a [blank_start]capacitor[blank_end], while [blank_start]cytoplasm[blank_end] and [blank_start]extracellular[blank_end] space remain neutral.

The driving force: [blank_start]V-E[blank_end]

In the equilibrium state there is no [blank_start]net current[blank_end], therefore the different ion-currents add up to [blank_start]0[blank_end].

The sodium-potassium pump (Na-K ATPase) transports [blank_start]3[blank_end] Na+ [blank_start]out[blank_end] and [blank_start]2[blank_end] K+ [blank_start]in[blank_end]. It uses [blank_start]1[blank_end] ATP.

I_Na / I_K = -[blank_start]3[blank_end]/[blank_start]2[blank_end]

The depolarization is due to the [blank_start]influx[blank_end] of [blank_start]sodium[blank_end]. The hyperpolarization is due to the [blank_start]outflux[blank_end] of [blank_start]potassium[blank_end].

The absolute refractory period can be explained by the [blank_start]inactivation[blank_end] of [blank_start]sodium[blank_end] channels. The relative refractory period can be explained by the extended [blank_start]opening[blank_end] of [blank_start]potassium[blank_end] channels.

An action potential can only travel in one direction due to the inactivated [blank_start]sodium[blank_end] channels.

The length constant depends on the [blank_start]internal[blank_end] resistance per unit length and the [blank_start]membrane[blank_end] resistance per unit length.

A large length constant means a [blank_start]higher[blank_end] speed.

The length constant can be increased by: (a) [blank_start]decreasing[blank_end] the internal resistance by [blank_start]thicker[blank_end] axons (b) [blank_start]increasing[blank_end] the membrane resistance by [blank_start]improved[blank_end] insulation

In the CNS myelin is formed by [blank_start]oligodendrocytes[blank_end]. In the PNS myelin is formed by [blank_start]Schwann cells[blank_end].

?

The fact that the action potential in an insulated axon jumps from node to node is called the [blank_start]saltatory[blank_end] propagation of action potentials.

The highest observed speed of an action potential happened in a shrimp and was about [blank_start]200[blank_end] m/s.

Electric synapses are formed by [blank_start]gap junctions[blank_end].

Most electric synapses are [blank_start]bidirectional[blank_end]. The synaptic transmission happens [blank_start]almost instantaneous[blank_end] and [blank_start]also sub-threshold potentials[blank_end] can be transmitted.

Chemical synapses contain [blank_start]mitochondria[blank_end] for energy supply and [blank_start]synaptic vesicles[blank_end] that carry neurotransmitters.

Signal transmission at a chemical synapse: (1) The arrival of an action potential opens voltage-gated [blank_start]calcium[blank_end]-channels. (2) The increase of calcium-ions triggers the release of neurotransmitters through [blank_start]exocytosis[blank_end] of synaptic vesicles into the [blank_start]synaptic cleft[blank_end]. (3) The neurotransmitters bin to receptors and [blank_start]open[blank_end] channels. The used neurotransmitters get either reabsorbed into the [blank_start]presynaptic[blank_end] cell or broken down metabolically.

The signal transmission through transmitter-gated ion channels happens [blank_start]fast and transient[blank_end]. This is also called [blank_start]direct[blank_end] gating. There is also [blank_start]G-protein-coupled[blank_end] receptors, which is [blank_start]slower, longer lasting[blank_end] and can have more diverse effects (e.g. an amplification of the signal). This is also called [blank_start]indirect[blank_end] gating.

Postsynaptic potentials are [blank_start]graded[blank_end]. The most important neurotransmitters for EPSPs are: - [blank_start]glutamate[blank_end] in the CNS - [blank_start]acetylcholine[blank_end] for skeletal muscles The most important neurotransmitters for IPSPs are: - [blank_start]GABA[blank_end] - [blank_start]glycine[blank_end] - [blank_start]acetylcholine[blank_end] for smooth muscles (e.g. the heart)

Which figure represents spatial summation and which represents temporal summation?

The membrane potential is a consequence of an ion [blank_start]imbalance[blank_end] on both sides of a [blank_start]selectively permeable[blank_end] membrane. The properties of an action potential result from the dynamics of [blank_start]ion channels[blank_end]. (Chemical) synapses transmit [blank_start]electric potentials[blank_end] from the pre- to the postsynaptic cell by triggering a gating mechanism of specialized ion channels in the postsynaptic membrane.

[blank_start]10[blank_end] % of the cells in the brain are neurons, [blank_start]90[blank_end] % are glia cells.

Each neuron receives input and sends output from/to approximately [blank_start]10,000[blank_end] neurons.

The [blank_start]axon hillock[blank_end] is the last site in the soma where membrane potentials propagated from synaptic inputs are summated before being transmitted to the axon.