Lecture 5 - Membrane Potential Flashcards
- functional units of nervous system
- receive, process and transnit infromation ot other cells
neurons
parts of neurons
- soma
- dendrites
- axons
- body of a neuron
- metabolic miantenance
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
detect sensory information from receptors
Afferent (sensory) neurons
carry impulses or motor commands to muscles and glands.
efferent (motor) neurons
located inside the central nervous system and are in between afferent and efferent neurons
Interneurons
Transmission of signals in a single neuron
- surface membrane innervated
- action potential initiation
- AP carried from spike-initiating zone to axon terminal
nerve impulse
action potential
corresponds to the site where action po- tentials are initiated
spike initiation zone (SIZ)
- localized electrical gradient
- electrical potential difference across cell membrane caused by different concentrations of K+, Na+, and Cl- ions
membrane potential
membrane potential of neurons is usually between
-60 to -80 mV
where are excess negative charges found
plasma membrane side
where are excess positive charges found
other side
membrane potential is the source of __ __ to move molecules across membranes
potential energy
how do excitable cells use changes in membrane potential
communication signals
membrane potential is critical for what?
coordinated movements of cells and organisms
what do every cell have
voltage or membrane potential
more concentrated within a cell
anions (negative)
more concentrated in the extracellular fluid
cations (positive)
factors affecting potential difference
- concentration gradient of ion
- membrane that is permeable to that ion
resting potential of unstimulated cell
-70mV
the magnitude of membrane potential __ until an equilibrium is reached
increases
equal numbers of anions and cations
electroneutral
as more potassium leaves the cell , what happens to the electrical force
increases to level that balance driving force from potassium concentration gradient
draw positive charges into the cell
excess negative charge inside
cations in membrane potential
- K+
- Na+
K+
principal intracellular cation
Na+
principal extracellular cation
anions in membrane potential
- proteins, amino acids, sulfates, phosphate
- Cl-
proteins, amino acids, sulfates, phosphate
prinicpal intracellular anions
Cl-
prinipal extracellular anion
concentraiton of K+ is greater inside the cell, wile concentration of Na+ is greater outside the cell
resting potential
use ATP to maintain K+ and Na+ gradients
sodium-potassium pump
converts chemical potential to electrical potential
opening of ion channels
what does the neuron at resting potential contain
- many open K+ channels
- fewer open Na+ channels
- allow ions to diffuse across the plasma membane
- always open
non-gated ion channels
can generate large changes in their membrane potential
excitable cells
open or close in response to stimuli
gated ion channels
Types of gated ion channels
- chemically-gated ion channels
- voltage-gated ion channels
open or close in response to a chemical stimulus
chemically-gated ion channels (ligand-gated ioni channels)
open or close in response to a change in membrane potential
voltage-gated ion channels
changes in membrane potential
graded potentials
graded potentials
- hyperpolarization
- depolarization
membrane potential becomes more negative as gated K+ channels open and K+ diffuses out of the cell
hyperpolarization
membrane potential becomes less negative as gated Na+ channels open and Na+ diffuses into the cell
depolarization
all or nothing depolarization
action potential
what is triggered if graded potentials sum to ~-55mV
action potential
~-55mV of graded potential sum
threshold potential
Two volted gates of Na+ channels
- closed activation
- open inactivation
open rapidly in response to depolarization
closed activation gates
close slowly in response to depolarization
open inactivation
Five steps on action potential
- resting state
- depolarization
- rising phase of action potential
- falling phase of action potential
- undershoot
what happens in depolarization
- voltage-gated Na+ channels open first
- Na+ flows into cell
what happens in rising phase
- threshold is crossed
- membrane potential increases
what happens in the falling phase
- voltage-gated Na+ channels inactivate
- voltage-gated K+ channels open
- K+ flows out
what happens during undershoot
- membrane permeability to K+ is first higher than rest
- voltage-gated K+ close
- resting potential restored
- result of a temporary inactivation of Na+ channels
- second action potential cannot be initiated
refractory period
different period in changes in ion channels on membrane potential
- depolarizing stimulus
- absolute refractory period
- relative refractory period
where is action potential repeatedly regenerated
along length of axon
how is action potential generated
Na+ ions flow inward across membrane at one location
rapid method by which nerve impulses move down a myelinated axon with excitation occurring only at nodes of Ranvier
Saltatory conduction
where does excitation occur
nodes of Ranvier
action potential travels directly from the presynaptic to the postsynaptic cells via gap junctions
electrical synapses
how does electrical synapses travel from presynaptic to postsynaptic cells
via gap junctions
- information is transferred via the release of a neurotransmitter from one cell that is detected by an adjacent cell
- more common than electrical synapses
chemical synapses
region where neurons nearly touch and where nerve impulse is transferred
synapse
small gap between neurons
synaptic cleft
carries out transmission across a synapse
neurotransmitters
what happens during transmission across a synapse by neurotransmitters
- sudden rise in calcium at end of one neuron
- stimulates synaptic vesicles to merge with presynaptic membrane
- neurotransmitter molecules released to synaptic cleft
Three primary factors influencing impulse transmission
- axon diameter
- myelination
- temperature
diameter of axon
typically around 1 micrometer
formation of myelin sheath around nerve
myelination
the lower the temperature, the __ the impulses move
slower
what is affected by axon diameter and myelination
velocity of impulse propagation
how fast the membrane ahead of the active regions is brought to threshold by the local-circuit current
conduction velocity of AP
large axon diameter conduct __ due to less resistance
faster
how far a change in voltage will spread
length constant
greater the length constant the __ the conduction velocity of AP
faster
evolutionary adaptation to increase the length constant of invertebrates
increase in axonal diameter
evolutionary adaptation to increase the length constant of vertebrates
myelination
composition of myelin sheath
layered glial cell membrane
increase the transmembrane resistance and decrease the effective neuronal membrane capacitance
myelination
by definition a material which is able to hold an electrical charge
Capacitance
by definition is a measurement of the difficulty to pass an electric current through a materia
resistance
- where action potential is usually triggered
- region of a neuron that controls the initiation of an electrical impulse based on the inputs from other neurons or the environment
axon hillock