Lecture 6: Neurons Flashcards
What are neurons?
Cells in neuronal tissues (e.g. neuropiles, nerves, chord, brain) where they form interconnected neural networks
What is the input zone of a neuron?
Where neurons collect and integrate information, either from the environment or from other cells
- dendrites
- cell body
What is the integration zone of a neuron?
Where the decision to produce a neural signal is made
What is the conduction zone of a neuron?
Where information can be transmitted over great distances
- axon
What is the output zone of a neuron?
Where the neuron transfers information to other cells
- axon terminals
What is the flow of information in a neuron?
Input zone -> integration zone -> conduction zone -> output zone
How are neurons similar to a typical animal cell?
Has similar organelles as any other cell
- a nucleus
- mitochondria
- cytoplasm
Its cell membrane however is special
What is electrophysiology?
Electrodes (electrical conductors) make contact with non-metallic (conductive) parts of an electric circuit in living specimen or cells
- recording electrode is places inside or outside the neuron (micro-electrodes), or further away from the body surface (e.g. EEG, ECG and EMG electrodes)
- Ground electrode is placed in/on tissue/ body as a further distance
What is resting potential?
- There is zero potential difference when the two electrodes are in a bath
- But when the electrode enters the axon, it records a negative potential (the inside of the axon is more negative than the outside)
Hodgkin and Huxley (1952)
- Measured the electric signals by directly inserting sharp glass electrodes into the squid’s giant nerve cell
- The isolated axon was laid in a bath of sea water. A recording micro-electrode was placed inside of the axon and a reference one outside
- They recorded the resting potential of the neuronal mebrane in the inactive neuron
What is hyperpolarisation?
a change in a cell’s membrane potential that makes it more negative, effectively increasing the difficulty for the cell to reach the threshold needed for an action potential or impulse
What is depolarization?
a biological process where a cell’s membrane potential becomes less negative (more positive), often due to an influx of positively charged ions, and is crucial for processes like action potentials and muscle contraction
What is action potential?
a rapid, brief change in the electrical potential of a cell membrane, especially in neurons and muscle cells, that transmits signals throughout the body
What are leak channels?
Allow a specific ion type to freely diffuse
What are the three ways in which ion channels remain closed until activation for a very brief period of time?
- Electrical signals (voltage-gated)
- Drugs and neurotransmitters (ligand-gated)
- Mechanical signal (mechanical-gated)
What is the function of ion pumps?
Actively transport ions (NA+, K+, or Ca2+) from one side of the membrane to the other
What is diffusion?
Particles move from areas of high concentration to areas of low concentration. That is, they move down their concentration gradient
What does it mean that the neural membrane is semi-permeable?
Brief opening of membrane lets some ions through
What are closed channels?
Ions accumulate near the membrane due to the electrostatic forces
What are open channels?
Ions cross the membrane (in or out of the neuron) at a rate and in a direction that depends on both forces (diffusion and electrostatic)
What happens when the neuron generates a signal?
Ion channels in the membrane briefly open.
Depending on the type of channel that opens, the respective ions are pushed into the cell (Na+ and CI- ions) or leave the cell (K+ ions) the neuron
What is the Hodgkin-Huxley model?
Action potentials are mediated by Na+ and K+ voltage-gated channels.
What is resting potential - Hodgkin-Huxley model?
Voltage-gated Na+ and K+ channels are closed
- Below -55mV threshold
- Both depolarisation and hyperpolarisation can take place
What is depolorisation - Hodgkin-Huxley model?
Changes in Ligand-gated or mechanical-gated ion channels (e.g. by stimulus)
Action potential - rising phase - depolarisation - Hodgkin-Huxley model
Action potential - crossed -55mV
Rising phase - depolarisation caused by the opening of voltage-gated na+ ion channels
What is action potential: overshoot?
The membrane potential becomes positive as more and more Na+ flow into the cell (positive feedback loop)
What is the action potential: falling phase - repolarisation?
Na+ ion channels become inactivated and close, while K+ channels open leading to a reduction of positive charge inside of the cell
What is action potential: undershoot - hyperpolarisation?
K+ ions flow out of the cell through the open K+ channels (hyperpolarisation)
What is action potential: recovery?
Refractory period during which all channels are closed and membrane potential returns to resting value
What is unidirectional transmission of the action potential?
Due to the refractory period, the voltage gates Na+ channels can open on only one side.
The action potential travels along the axon way towards the output zone
What is the difference between the action potential of a myelinated and unmyelinated axon?
Myelinated axons conduct action potentials much faster than unmyelinated axons due to a process called saltatory conduction, where the signal “jumps” between gaps in the myelin sheath (nodes of Ranvier), while unmyelinated axons require continuous depolarization
