Exiteable cells 2 Flashcards
What neurones do we have in the brain?
What is their function?
- Most sensory neurons are pseudounipolar, which means they only have one axon which is split into two branches
- Motor neurons and interneurons are multipolar, each with one axon and several dendrites
Compare the function of Neuronal cells and Glial cells.
- Neurons – (signaling cells) electrically excitable cell that communicates with other cells via specialized connections called synapses
- glial cells – (support cells) non-neuronal cells in the CNS (microglia, astrocytes, and oligodendrocyte) and the PNS (Schwann cells) that do not produce action potentials
> control CNS environment within which neurons function
Function of Astrocytes?
What is the PNS glia?
Function of oligodendrocytes?
What is the PNS glia?
Function of Microglia?
Function of Ependymal cells?
How do ion channels work?
- Select either cations or anions to permeate
- Non-gated or gated (voltage-gated ion channels & ligand-gated)
> So that ions flow only when needed, the pathway through an ion channel can be opened and closed by conformational changes that displace an obstruction called a gate
How do Ion pumps work?
- Expending energy to slowly move ions thermodynamically uphill
- Primary active transport - hydrolyze ATP to produce energy in order to transport ions across the membrane
- Secondary active transporters - use electrochemical gradient created across the membrane by pumping ions in or out of the cell
E.G. Na+/K+ ATPase
What is the membrane potential?
- Distribution of charge across the cell membrane
> expressed by its value inside the cell relative to the extracellular environment
What is the electrostatic gradient?
- Movement of the cation from inside to outside cell leaves behind a negative anion, & thus the inside of the cell becomes more negative, while the outside of the cell becomes more positive
- The negative charges inside the cell start to exert a force to keep the positively charged K+ ions inside the cell, a force that opposes the movement of the ions down the concentration gradient.
> When this negative electrostatic charge is opposite the force of the concentration gradient, there is no movement of the ions
How is a resting membrane potential brought about?
- Na+-K+ pump actively transports 3Na+ out of and 2K+ into the cell keeping the concentration gradient of Na+ high in the ECF and the concentration gradient of K+ high in the ICF.
- K+ drives the membrane potential to K+’s equilibrium potential (-90mv), whereas Na+ drives the membrane potential to Na+’s equilibrium potential (+60mv)
- However, K+ exerts the dominant effect on the resting membrane potential because the membrane is more permeable to K+.
- The resting membrane is slightly permeable to Na+ and the relatively small net diffusion of Na+ inward neutralizes some of the potential that would be created by K+ alone.
- Bringing the resting membrane to -70mV
How is RMP achieved?
- At rest, the concentration of Na+ ions outside of the cell is higher or lower than the concentration inside of the cell?
- At rest, the concentration of K+ ions outside of the cell is higher or lower than the concentration inside of the cell?
- uneven distribution of ions between the inside and the outside of the cell, and by
the different permeability of the membrane to different types of ions - Extracellular concentrations of Na+ & Cl− > intracellular concentrations
- Extracellular concentration of K+ < intracellular concentration
What is equilibrium potential? How can it be expressed?
- Electrical potential difference across the cell membrane that exactly balances the concentration gradient for an ion is known as the equilibrium potential
(Potential level across a membrane that will exactly prevent net diffusion of an ion) - can be expressed by the Nernst equation
Describe Action potentials.
- What they are
-Underlying mechanism
- means of…
- type of phenomenon
- Electrical impulses, or changes in membrane potential, that travel along the surface of a neurone.
- Change in membrane permeability for different ions, first Na+ & then K+ in the recovery phase.
- APs are the means of communication between neurons.
- APs are an all-or-nothing phenomenon
What are the two types of refractory periods?
The action potential moves along the axon in one direction because of the…
- Absolute refractory period - no stimulus can cause second action potential
- Relative refractory period - stronger stimulus needed (strength needed reduces as membrane reduces)
> Refractory period as an AP cannot be generated in this time as it requires a greater influx of Na+ to reach threshold again until MP returns back to resting potential
What does pre-synaptic inhibition involve and what does post-synaptic inhibition involve?
Pre synaptic: decreases release of neurotransmitter
Post-synaptic: Decreased post-synaptic A.P
- all targets inhibited equally
- inhibitory neurone modulates excitatory neurone signal below threshold
What are the 2 types of inhibition?
- feed-forward inhibition
* excitatory neurons excite inhibitory cells, which then inhibit a group of postsynaptic excitatory neurons - feedback inhibition
* excitatory neurons to drive the inhibitory cells, which in turn inhibit the same population of excitatory cells can limit excitation in a pathway
Explain the type of inhibition involved in patella reflex.
