BIOSCI 107 ET: Neurons Flashcards
What is the Nervous System Comprised of?
CNS and PNS.
What are Neurons (Nerve Cells)?
The principal building blocks and instruments of communication in the brain.
What 2 Communication Types are used by Neurons?
Electrical signals, chemical signals.
Where are Electrical Signals Used?
Dendrites, cell body, axon.
Where are Chemical Signals Used?
Synapses.
What is the Resting Membrane Potential?
Electrical potential difference (50 to 70 mV) across the cell membrane which results from separation of charge.
What is the Typical Resting Membrane Potential of Cells?
Almost all cells have a negative resting membrane potential.
Which 3 Areas are Excitable?
Neurons, muscle fibres, some endocrine cells.
What does Excitable Mean?
Ability to suddenly respond with a transient change of the resting membrane potential in response to a stimulus.
Which 2 Techniques are used to Measure Intracellular Potentials Today?
Microelectrode recording technique, patch-clamp technique.
What is an Important Convention to Remember about RMP?
The potential outside the cell is defined as zero.
Which 3 Factors Cause the RMP?
Unequal concentrations of Na and K inside/outside the cell, unequal permeability of cell membrane to these ions, electrogenic action of Na/K pump (minor).
What are the Approximate Concentrations of K and Na Outside the Cell?
K: 5 mM
Na: 150 mM
What are the Approximate Concentrations of K and Na Inside the Cell?
K: 100 mM
Na: 15 mM
How are the Concentration Gradients for K and Na Maintained?
By the Na/K pump.
What are the 2 Main Types of Ion Channel in Ions?
Non-gated channels, gated channels.
What are Non-Gated Channels in Neurons?
‘Leak’ channels open at rest.
What are Gated Channels in Neurons?
Voltage/ligand (chemical)/mechanically gated - closed at rest.
How do the Numbers of K Channels compare to those of Na?
At rest: Pk / PNa = 40 / 1.
P = membrane permeability.
How can we Calculate Equilibrium Potential for Each Ion?
Using the Nernst Equation.
What is an Equilibrium Potential?
An intracellular potential at which the net flow of ions is zero, in spite of a concentration gradient and permeability.
What is Unique about Glia Cells?
They only have leak channels for K.
What is an Important Rule about Cell Membranes and Permeability?
Higher the permeability of the cell membrane to an ion, the more this ion can shift RMP towards its equilibrium potential.
What is the Goldman Equation?
Calculates value of RMP, including both concentration gradients and relative permeability to K and Na ions.
When does Neuron Potential Change?
When membrane permeability or ion concentrations change.
What is Hyperpolarisation?
When potential becomes more negative.
What is Depolarisation?
When potential becomes less negative.
What is the Action Potential?
A brief fluctuation in membrane potential.
What causes the Action Potential?
A transient opening of voltage-gated ion channels, which spreads like a wave, along axon.
When do Action Potentials Occur?
After the membrane potential reaches certain voltage - threshold (55 mV).
Why are Action Potentials Important?
Information coded in their frequency - language, also a key element of signal transmission along axons.
What are the 3 Stages of Action Potentials?
Fast depolarisation, repolarisation, after-hyperpolarisation.
How do we Group the 3 Stages of Action Potentials?
1 + 2 are the absolute refractory period.
3 is the relative refractory period.
What can the Stimulus of an Action Potential be?
Physical or chemical.
What are some Examples of Physical Stimuli for the Action Potential?
Electric current, light, stretch.
What are some Examples of a Chemical Stimuli for the Action Potential?
A drug, synaptic excitation.
What Happens when MP Reaches the Threshold?
A sudden activation (opening) of voltage-gated Na channels (increased permeability).
What Happens After MP Reaches the Threshold?
Pk / PNa is 1:20 instead of 40:1, so MP shifts towards ENa causing overshoot.
What Happens After Overshoot?
Transient opening of voltage-gated K channels - repolarisation and AHP.
Why does MP Shift Towards Ek after Overshoot?
Since Pk / PNa becomes 100 : 1.
What Happens when Voltage Threshold is Reached?
Sodium channels open and Na ions move into cell (both gradients).
When does Influx of Na Slow Down in a Voltage-Gated Channel?
When inside potential becomes positive, Na channels inactivate.
What is Important to Remember about the Amplitude of Action Potentials?
It is usually constant and doesn’t depend on stimulus intensity.
When does Hyperpolarisation occur in Electrical Currents?
When the current generated by an outside source flows through membrane from outside to inside.
When does Depolarisation occur in Electrical Currents?
When the current generated by an outside source flows through membrane from inside to outside.
Where are APs First Generated?
In the axon initial segment which has the lowest threshold - trigger zone.
What Evokes Depolarisation to Threshold?
Excitatory postsynaptic potentials, which spread passively from dendrites.
Where do Generated APs go?
Transmitted actively along the axon, away from the cell body.
What are the 2 Types of Axon?
Unmyelinated and myelinated.
What are Unmyelinated Axons?
Small diameter, transmission of APs slow, continuous.
What are Myelinated Axons?
Larger diameter, transmission of APs fast, saltatory.
What are the 2 Stages of Actions Potential Transmission?
Passive spread, generation of action potentials.
How is Local (Subthreshold) Depolarisation Induced?
By current injected into an axon by a glass microelectrode.
Why is Conduction Velocity Slow in Unmyelinated Axons?
AP must be regenerated at every point on the membrane.
Which 2 Components Form the Myelin Sheath?
Oligodendrocytes in the CNS, Schwann cells in the PNS.
What is Myelination?
Discontinuous; interrupted at nodes of Ranvier.
What is Important to Remember about Passive Conduction?
It occurs in both directions.
Why is there Less Dissipation during Myelination?
Due to the insulating properties.
How does Myelination increase Speed of SP Conduction?
By increasing efficiency of passive spread.
Where in APs Generating in Myelinated Axons?
At nodes of Ranvier only - flowing passively between them.
Why does AP Conduct in only One Direction?
Due to absolute refractory period - once this is over, AP has already moved down the axon.
Where is Information about the Strength of the Stimulus Coded?
In the amplitude of the receptor potential and the frequency of APs.
What are the 2 Ways Messages can be Transmitted between Excitable Tissues?
Synaptic transmission between neurons or between a neuron and a muscle fiber.
What is an Example of a Neurotransmitter?
Acetylecholine.
What are the 2 Main Types of Chemical Synapses in the CNS?
Excitatory and inhibitory synapses.
What is an Excitatory Synapse?
Depolarisation of the postsynaptic membrane, called the Excitatory Postsynaptic Potential.
What is an Inhibitory Synapse?
Hyperpolarisation of the postsynaptic membrane, called the Inhibitory Postsynaptic Potential.
What are the Neurotransmitters of Excitatory Synapses?
Glutamic acid or ACh.
What are the Neurotransmitters of Inhibitory Synapses?
GABA or glycine.
What is the Ionic Mechanism of EPSPs?
Transient opening of channels for Na, K and Ca (sometimes).
What is the Ionic Mechanism of IPSPs?
Transient opening of K channels.
What are the 2 Classifications of Neurotransmitters?
Small molecule neurotransmitters, neuropeptides.
How do we Identify Small Molecule Neurotransmitters?
Fast action, direct on postsynaptic receptors.
How do we Identify Neuropeptides?
Large, have an indirect action on postsynaptic receptors, or modulatory action on effects of other neurotransmitters.
What are Some Examples of Small Molecule Neurotransmitters?
Amino acids, acetylcholine, amines.
What are Some Examples of Neuropeptides?
NPY, substance P, kisspeptin, enkephaln.
Which 3 Factors Determine Synaptic Action?
Type of neurotransmitter/modulator, type of receptor, amount of receptor.
What is Excitotoxicity?
Excessive Ca entry that damages neurons.
What Happens if too much Glutamate is Released?
Excessive depolarisation and over-activation of neurons.
Which 3 Factors can Cause Neurotransmitter Inactivation?
Diffusion from synapse, enzymatic degradation in synaptic cleft, re-uptake/recycling.
What must Take Place for Depolarisation?
To depolarise initial segment to threshold, EPSPs need to be enhanced.
