Introduction to Neurophysiology Flashcards
The first cellular characterizations of the brain:
Camillo Golgi and Santiago Ramón y Cajal
- Golgi and Cajal allowed the anatomy of the nervous system to be observed by staining the cels and only a small fraction did or else it will all be black.
Golgi
Developed the silver impregnation method, which allowed him to see the entire nerve cell, including its dendrites and axon.
Cajal
Used Golgi’s method to study the nervous system and support the neuron theory, which states that nerve cells are structurally, functionally, and developmentally distinct.
MRI: Diffusion tensor imaging (2)
how + what
- reveals axon tracts in white matter
- measures the movement of water along axons
Serial electron microscopy (2)
how + what
- reveals micro-circuitry
- a method to generate high resolution three-dimensional images from small samples. The sample is enclosed in resin and theres a razor. The razor slices off thin slices and electron beam laser is used to scan it and produce pic becfore that is shaved off. The picture is then reorganized to 3D volume.
Unipolar neuron
structure + found
- Unipolar neurons have only one structure extending from the soma/cell body
- Commonly found in the olfactory epithelium and retina (cone and rod cells have this morphology)
Bipolar neuron
structure + found
- a type of neuron that has one dendrite and one axon, with the cell body located between these two structures
- Commonly found as sensory neurons (neuron that connects peripheral NS to the central NS)
Pseudounipolar neuron
structure + found
- Pseudounipolar neurons are sensory neurons that have no dendrites, the branched axon serving both functions. The peripheral branch extends from the cell body to organs in the periphery including skin, joints and muscles, and the central branch extends from the cell body to the spinal cord.
- Commonly found as sensory neurons (neuron that connects peripheral NS to the central NS)
What are the specs?
Synaptic spines where synapse comes in
Mltipolar neuron
The classical neuron
Explain the role of ion channels
Ion channels facillitate and control the flow of ions through the neuronal plasma membrane to control excitability. They are usually gated by voltage or gated by molecule (ligand). Amino side chains project into the ion channel pore creating ion selectivty filter.
What drives the movement of ions across the plasma membrane?
- Concentration gradient
- Voltage gradient aka electrochemical gradient
Reversal potential (2)
What + equation
The point at which the direction of net current flow reverses is called the reversal potential and is the same as the equilibrium potential.
Determined by Nerst equation.
Explain how an action potential occurs:
A triggering event occurs that depolarizes the cell body. This signal comes from other cells connecting to the neuron, and it causes positively charged ions to flow into the cell body. Positive ions still flow into the cell to depolarize it, but these ions pass through channels that open when a specific chemical, known as a neurotransmitter, binds to the channel and tells it to open. Neurotransmitters are released by cells near the dendrites, often as the end result of their own action potential! These incoming ions bring the membrane potential closer to 0, which is known as depolarization. An object is polar if there is some difference between more negative and more positive areas. As positive ions flow into the negative cell, that difference, and thus the cell’s polarity, decrease. If the cell body gets positive enough that it can trigger the voltage-gated sodium channels found in the axon, then the action potential will be sent.
Depolarization - makes the cell less polar (membrane potential gets smaller as ions quickly begin to equalize the concentration gradients) . Voltage-gated sodium channels at the part of the axon closest to the cell body activate, thanks to the recently depolarized cell body. This lets positively charged sodium ions flow into the negatively charged axon, and depolarize the surrounding axon. We can think of the channels opening like dominoes falling down - once one channel opens and lets positive ions in, it sets the stage for the channels down the axon to do the same thing. Though this stage is known as depolarization, the neuron actually swings past equilibrium and becomes positively charged as the action potential passes through!
Repolarization - brings the cell back to resting potential. The inactivation gates of the sodium channels close, stopping the inward rush of positive ions. At the same time, the potassium channels open. There is much more potassium inside the cell than out, so when these channels open, more potassium exits than comes in. This means the cell loses positively charged ions, and returns back toward its resting state.
Hyperpolarization - makes the cell more negative than its typical resting membrane potential. As the action potential passes through, potassium channels stay open a little bit longer, and continue to let positive ions exit the neuron. This means that the cell temporarily hyperpolarizes, or gets even more negative than its resting state. As the potassium channels close, the sodium-potassium pump works to reestablish the resting state.
Neurons are electrically excitable cells that can propagate quickly across:
neuronal membranes (down axons primarily but even all over the cell)
Alan hodgkin
Andrew Huxley
Sir. John Eccles
what + eccle’s work
- Worked with squid giant axon: Used a stimulus and provided a stimulus and prived AP propagated very rapily down the axon
- Eccle’s work showed how similar the AP is in all sort of animals (rat, frog, cat). The basic phenomenal are the same but the kinetics are different.
Explain the Na+- dependence of the AP experiment
- When you decrease the Na+ of the extracellular component to 1/3 the AP is really slow and much less. This is because channel opens and less sodium can diffuse.
- When you increase the NA+ sodium to 50% in the ECM you see a higher AP peak and rise quicker.
Synapse
- communication point between neurons.
Electrical signal converted to chemical briefly before turning back to electrical.
synaptic plasicity
Glial cell: Astrocycte
Homeostatic cell help regulate synapses and synaptic plasicity
Glial cell: microglia cell
Resident immune cell. Helps the brain be healthy, free of pathogens and damage
Glial cell: Oligodendrocytes
Myelin forming cells. Helps AP propagate long distance, fast neurotransmission in the CN.
Neurovascular unit
- The brain has big need for energy due to neurons using alot of ATP through AP firing, synaptic transmission and remodeling.
- Rely on O2 and glucose at high rate from blood supply. They also regulate how much they are getting depending on activity.
Explain what Nerst Equation means
This equation defines the relation between the concentrations of an ion on either side of a membrane that it perfectly selective for that ion and the potential difference (voltage) that will be measured across that membrane under equilibrium conditions.
As we discussed in the practical class, the Nernst equation is able to give a value for the voltage that must exist across the membrane in order to balance a chemical gradient that exists for the ion in question.
