LECTURE 5: MEMBRANE POTENTIAL Flashcards
-Functional Units of Nervous System
-receive, process and transmit information to other cells
Neurons
Components of Neurons
-Soma
-Dendrites
-Axons
metabolic maintenance
Soma
receptive surface that brings signals from other neurons toward the cell body
Dendrites
- conduct signals away from the cell
- carry information for long distances with high fidelity and without loss
Axons (nerve fibers)
Types of Neurons
-Sensory Neurons or Afferent Neuron
-Motor or efferent Neuron
-interneuron
they are nerve fibers that transmit sensory information from the body to the brain and spinal cord
Sensory Neurons or Afferent Neuron
hey are responsible for carrying signals from the brain to the body to initiate an action
Motor or efferent Neuron
neurons that connect sensory and motor neurons in the central nervous system (CNS), including the brain and spinal cord.
Interneuron
-surface membrane of motor-neuron dendrites & soma – innervated
-Soma integrates input to initiate an action potential (AP – nerve impulse)
-AP is carried from the spike-initiating zone (near axon hillock) to the axon terminal – skeletal muscle cell or gland
Transmission of Signals in a Single Neuron
Soma integrates input to initiate an _________
action potential (AP – nerve impulse)
AP is carried from the ____________ (near axon hillock) to the axon terminal – skeletal muscle cell or gland
spike-initiating zone
Electrical potential differences across the cell membrane cause by different concentrations of K+, Na+ and Cl- ions on each side of the membrane.
Membrane Potential
Membrane potential is usually between ____ and ____ mV.
-60 and -80 mV
-fundamental property of cells resulting from an excess of negative charges on side of the plasma membrane and an excess of positive charges on the other side
-source of potential energy to move molecules across membranes
-excitable cells use changes in membrane potential as communication signals
-critical for allowing the coordinated movements of cells and organisms
Membrane Potential
Nature of Nerve Signals
-every cell has a voltage or membrane potential across its plasma membranes
-a membrane potential is a localized electrical gradient across membrane
every cell has a _______________ across its plasma membranes
voltage or membrane potential
a ____________-is a localized electrical gradient across membrane
membrane potential
What is more concentrated within a cell and what is more concentrated in the extracellular fluid?
Within cell: Anions
Extracellular Fluids: Cations
Factors (potential difference)
-Concentration gradient for an ion
-Membrane that is permeable to that ion
___________ connected to a reference electrode via a voltmeter (voltage drop across the circuit) - measures membrane potential
microelectrode
an unstimulated cell usually has a resting potential of ____
-70mV
KCl
-100mM inside
-10mM outside
NaCl
– 10mM inside;
- 100mM outside
K+
- outward movement
Na+
- inward movement
Cl-
no gradient for the movement
equal numbers of anion and cations
Electroneutral
with __________ – potassium ions move out of the cell along concentration gradient
potassium channels
potassium ions move out of the cell along concentration gradient resulting to?
region of electronegativity (inside) and electropositivity (outside)
Excess ___________ inside – draw positive charges into the cell
negative charge
as more potassium leaves the cell, the electrical force_________ to a level that balances the driving force from the potassium concentration gradient
increases
potassium ions continue to move, inward and outward fluxes exactly balance each other
equilibrium potential (E ion )
Nernst Equation
Ex = RT/zF · ln [X]out/[X]in
Goldman-Hodgkin-Katz equation:
Vm = RT/F · log Pc[C]out + Pa[A]in_
Pc[C]in + Pa[A]out
-represents the sum of the equilibrium potentials of all the relevant ions
-relative permeability of the ions
-influence of each ion over the overall membrane potential is proportional to its permeability
-e.g.
resting neurons are more permeable to potassium than the other ions
Potassium – setting the resting membrane potential of neurons
Goldman-Hodgkin-Katz equation:
Cations
K+ and Na+
Principal intracellular cation
K+
principal extracellular cation
Na+
proteins, amino acids, sulfate, and phosphate are the principal intracellular anions
Anions
Principal intracellular anions
Cl-
at resting potential the concentration of K+ is greater ______ the cell, while the concentration of Na+ is greater _____ the cell - chemical potential energy
-inside (K+)
-outside (Na+)
______________ use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane
Sodium-potassium pumps
opening of ion channels in the plasma membrane converts _________ to _________
chemical potential to electrical potential
A neuron at _______________ contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell
resting potential
Anions trapped inside the cell contribute to the ____________ within the neuron
negative charge
-allow ions to diffuse across the plasma membrane
-these channels are always open
Ungated ion channels
-have the ability to generate large changes in their membrane potentials
-gated ion channels open or close in response to stimuli
-opening or closing of ion channels alters the membrane ‘s permeability to particular ions, which in turn alters the membrane potential
excitable cells
open or close in response to stimuli
Gated ion channels
Types of gated ions:
- Chemically-gated ion channel
- Voltage-gated ion channel
open or close in response to a chemical stimulus
chemically-gated ion channels
open or close in response to a change in membrane potential
voltage-gated ion channels
changes in membrane potential of neuron give _____ to nerve impulses
rise
Graded Potentials
-Hyperpolarization
-Depolarizations
changes in membrane potential
graded potentials
magnitude of the change in membrane potential varies with the __________________-
strength of the stimulus
Gated K+ channels open —-> K+ diffuses out of the cell —-> the membrane potential becomes more negative
Hyperpolarization
Gated Na+ channels open ——> Na+ diffuses into the cell —–> the membrane potential becomes less negative
Depolarization
What type pf grade potential is action potential?
All or Nothing Depolarization
if graded potentials sum to _____ a threshold potential is achieved it triggers an action potential
approximately -55mV
approximately -55mV is considered as
Threshold Potential
In the resting state closed voltage-gated K+ channels open slowly in response to __________
depolarization
2 gates of Voltage-gated Na+
-closed activation gates open rapidly in response to depolarization
-open inactivation gates close slowly in response to depolarization
Most voltage-gated Na+ and K+ channels are ____, but some K+ channels (not voltage-gated) are _____
-closed
-open