Neurophysiology (scavma) Flashcards
Neurons
Functional units of the nervous system
Primary function of nervous system
To receive information form the environment and act on this information
Signal information pathway through nervous system
Environment- sensory receptor- receptor (generator) potential- CNS- action potentials- output, muscle contraction
CNS signal information
Action potential reaches CNS
then have synaptic transmission, post synaptic potentials, integration and action potentials which then leave
Sensory transduction
Physical or chemical signal from environment is changed to an electrical signal known as receptor potential or generator potential which can lead to a potential
Transient electrical signals
Generator potentials, Postsynaptic potentials also and action potentials
Convey info within and between the cells of the nervous system , all result in brief membrane changes
Membrane potential
Exchange of ions across the membrane is responsible for this potential and bioelectrical activity of the neuron
Extracellular Na and Cl
Higher than intracellular and reverse for K, higher intracellular
Electrical Potential
Difference between intracellular and extracellular fluid compartments
Intracellular is negative vs extracellular= membrane potential
Depolarizing
Towards 0 and extracellular potential
Hyperpolarization
More negative
Resting potential
Resting, steady state
Excess of + along outside of membrane and - along inside
3 influential factors in ion movement
Concentration gradient, voltage gradient, membrane permeability
Voltage gradients
For Na and K are inside because cell is negative
For Cl is outwards because attracted by outside +
Net flux
Movement of ions across a membrane dependent on both the forces or gradients acting on that ion and permeability of the cell membrane to that ion
Flux= Pion x driving force
Anions
Driving force is large but permeability is zero so no net flux
At rest permeability
More permeable to K and Cl vs. Na
Steady state transfer
3 Na in for every 2 K out
To offset passive movement cells like neurons have developed ATP dependent ion pumps which transport 3 Na out for every 2 in
So in steady state no net transfer
Electrochemical potential gradient
Sum of 2 passive forces, concentration gradient of ion and voltage of electrical gradient
At rest this should be zero
Potassium equilibrium potential
Membrane potential at which inward electrical flux is counterbalanced by outward diffusional flux
NERNST equation: Ek= RT/zF lnKo/Ki
At body temp: 61mVlog Ko/Ki
Driving potential
Difference between the membrane potential and the Nernst potential for an ion is called this
Resting potential -equilibrium potential
Change to relative permeability
When this changes for various ions this is the basis for electrical signals used by the nervous system for information processing
Membrane potential in resting condition
Determined primarily by the K+ gradient
So that at body temp resting potential can be determined
If ratio of K and Na permeability changes this is what happens with electrical signal
Na-K pump
In most excitable cells the active effluent of Na and active influx of K are coupled because move simultaneously
Phosphate bond of ATP provides energy
Mediated by enzyme which hydrolyzes ATP and activated by an increase in intracellular Na or extracellular K : Na, K activated ATPase
Energy for transport
To transport Na and K against electrochemical gradients is 20% excess of energy capacity of neuron
