Lec 4 Flashcards
Who suggested the possibility that animal movement may involve electricity?
Luigi Galvani: Galvani noted that a dead frog’s legs could be made to twitch by touching them with a metal probe.
Luigi was studying the nerves that feed the major quadricep muscles of the leg
Had cut open the skin of the frog to expose the muscle –his assistant drew a spark from the scalpel and touched the scalpel to the frogs legs and it twitched. Luigi told the assistant to do it again and it happened again. Luigi concluded from that that nerves must conduct electricity.
Who elaborated on Luigi Galvani’s research?
Alessandro Volta –his name is used to describe voltage. He correctly suggested it was due to a small electrical current. He said that while muscles could be directly simulated it was even more powerful if that nerve was directly simulated. This was a burgeoning theory but until the development of atomical theory this method was not really well understood
What is electricity?
electricity is simply the movement of electrically charged particles from one place to another.
The tendency to move is called electrical potential and is measured in volts
What is equilibrium?
A general rule of nature is that if you separate things, or move them out of equilibrium, they will tend to re-equilibrate.
It doesn’t really matter what type of force is involved. The tendency toward equilibrium applies to the effects of gravity, heat, electricity, and more.
As things move toward equilibrium, their movement can be used to do work or carry a message.
What is the electrophysiology of the neuron?
- Neurons have more negatively charged ions inside their membrane and positively charged ions outside the membrane. For this reason, we say that the neuron is polarized.
- This means it can change (we have POTENTIAL energy; we can move it to a more negative direction, or we can move it to a more positive direction)
What is the neutrons resting potential?
-70mV
What molecules are inside/outside the neuron that allows polarization?
Positively charged sodium ions (Na) outside the cell as well as some negatively charged chloride ions (Cl)
Inside the cell tends to have a larger quantity of negatively charged protein and lesser quantity of positively charged potassium ions (K+)
How do we know we evolved from sea water?
This extracellular fluid is NaCl (salt water) because we emerged from the sea water as species. We were once unicellular organisms that evolved.
How does a neuron die?
(apoptosis)=cell death
Because the neuron requires energy to use active mechanisms to maintain resting potential, when it dies, this process stops and ions quickly re-equilibrate. The resting potential is lost, just like a dead battery
But, as long as the neuron is alive, it will continually work to return to its resting potential of -70mv.
How does a neuron maintain resting potential?
The neuron uses a combination of active and passive mechanisms
Any changes in the membrane potential would be _________
temporary (this is a good thing -signals are supposed to be temporary)
What is the action potential?
The action potential is what’s generated at the axon hillock following a change in excitatory potential energy at across the cell membrane in the soma and the dendrites. The main communication from one end of the neuron to the other is called the action potential.
The action potential is a short-lived, spreading, localized change in membrane polarity.
What happens to the membrane potential during an action potential?
membrane potential briefly goes from -70-mV up to around +30mv.
How is an action potential triggered?
- Action potentials take place when ion channels in the neuron’s membrane open, allowing positive ions to flood in.
- Ion channels are called voltage gated ion channels which mean they only open when the voltage hits a certain amount (around +30 to +50mv)
- All these sodium ions rush into the cell and they change that patch of tissue right around the ion channel to be more positive. This triggers the next ion channel to open, and that allows more sodium ions in, and so on and so forth. It travels all the way down the length of the axon opening up those sodium channels in succession. This causes a temporary change in positive charge and this takes about 1 millisecond to complete
- Sodium channels open but potassium ones open too and start to try to re- equilibrate. They start to pump out potassium to try to return the inside of the cell to be more negative
Why are action potentials short lived?
action potentials are local and very short lived because
ion channels quickly clamp shut, and the original resting potential re-establishes itself.
What is depolarization?
Since the neuron is said to be polarized when it’s at the -70mv resting potential, any change that reduces this is called a depolarization.
When the membrane is depolarized, it moves toward being positively charged.
Action potentials are spreading ___________
depolarization
What is an example of a positive feedback loop in the brain?
depolarization in one area stimulates adjacent areas to depolarize as well – a single point of depolarization can trigger a chain reaction that spreads across the entire membrane
How fast do action potentials travel?
Action potentials travel at a speed of 30-120m/s. Myelinated axons have a faster rate of conduction
Action potentials are fast, directional, and can travel virtually limitless distances.
How does information flow in neurons?
Dendrites > Cell body > Axon > Axon terminal
What are synapses?
- “to clasp” – are the points of contact between two neurons. The site of inter-neuron information transfer.
- While action potentials transfer signals rapidly by altering membrane electrical potential, synapses transfer signals by passing chemicals from neuron to neuron
Where is the target for exogenous chemical stimulation (drugs)?
Because synaptic communication relies on chemical interactions, synapses are frequent targets for exogenous chemical stimulation
