11 B Flashcards
How do neurons respond to being excited?
Generating an action potential (nerve potential)
What is always the same no matter the stimuli in action potential?
Impulse
What are the two main types of ion channels?
Leakage (nongated channels) Gated channels (protein changes shape to open and close channel)
What are the three main types of ion gated channels?
Chemically gated (ligand gated) channels Voltage-gated channels Mechanically gate channels
What opens a chemically gated channel?
Binding of a specific neurotransmitter
What opens and closes a voltage gated channel?
A response to changes in membrane potential
What opens and closes mechanically gated channels?
In response to physical deformation of receptors (sensory receptors)
What happens when gated channels are open?
Ions diffuse quickly across membrane along electrochemical gradients
What does ion flow across the membrane create in open gated channels?
electrical current and voltage changes across the membrane
How do solutes move in response to concentration gradients?
from higher concentration to lower concentration
How do solutes move in response to electrical gradients?
Toward the opposite charge
What is the resting membrane potential?
Potential difference across membrane of resting cell
What is the approximate resting membrane potential of the neurons?
-70 mV
What is the term for a resting membrane?
Polarized
What is the resting membrane potential generated by?
Differences in ionic makeup of intracellular fluid and extracellular fluid
Differential permeability of the plasma membrane
What solute/ion plays the most important role in membrane potential?
K+ (the membrane is more leaky to potassium ions)
What is the Na+ concentration of the ECF balanced by?
Chloride ions
What balances the positive charge created by the K+ ions in the ICF?
Negatively charged proteins
What is the membrane impermeable to?
Large anionic proteins
What is the membrane slightly permeable to?
sodium ions through leaky channels
What is the membrane quite permeable to?
Chloride ions
Why is the cell more negative on the inside of the cell?
More potassium diffuses out than sodium diffuses in
What protein stabilizes resting membrane potential?
The sodium-potassium pump
How many sodium ions are pumped in by the sodium potassium pump and how many potassium out of the cell?
3 sodium in to 2 potassium out
What are changes in the membrane potential used for?
Communication signals (signals to receive, integrate and send information
When does the membrane potential change?
Concentrations of ions across the membrane change
Membrane permeability to ions change
What two types of signals are produced when membrane potential changes?
Graded potentials
Action potentials
Where do graded potentials occur?
At the dendrite region
What happens during graded potentials?
Incoming signals operate over short distances
What happens during action potentials?
Long distance signals across the axon
What happens in depolarization?
A decrease in membrane potential (to zero and above)
The inside of the membrane becomes less negative than the resting membrane potential
What increases the probability of producing a nerve impulse?
Depolarization
What happens during hyperpolarization?
An increase in membrane potential (away from zero and below)
Inside of the cell is more negative than Resting membrane potential
What reduces the probability of producing a nerve impulse?
Hyperpolarization
What are graded potentials and what do they vary in?
They are short-lived localized changes in membrane potential that vary in magnitude with various strengths of stimulus
What are graded potentials stimulated by?
Stimulus that opens gated ion channels
What happens to the current over distance with graded potentials?
It dissipates quickly and decays
Where in a neuron does an action potential pass through?
The axon
What is the principle way neurons send signals?
Action potentials
What is the principal means of long distance neural communication?
Action Potentials
Where do action potentials occur in the body?
Muscle cells and axons of neurons
What is an action potential?
A brief reversal of membrane potential with a change in voltage of around 100 mV
What are the two voltage sensitive gates for Na+ channels?
Activation gates
Inactivation gates
What gate of an Na+ channel is closed at rest?
Activation gates (when open they allow Na+ to enter the cell)
What gates of the Na+ channels are open at rest?
Inactivation gates (Block the channel when open to prevent more Na+ from entering the cell)
Is the voltage sensitive gate of K+ channels closed or open at rest?
Closed
What gates are open and which ones are closed during the resting state?
The leakage channels are open to maintain RMP
THe Na+ and K+ channels are closed
What happens to the gated channels during depolarization?
The local currents open voltage-gated Na+ channels to allow Na+ into the cell and this makes the ICF less negative
What happens at threshold to the Na+ channels?
At threshold, positive feedback causes opening of all Na+ channels
Spike of action potential
What happens to the channels during repolarizing phase?
Na+ channels slow inactivation gates close
Membrane permeability to Na+ declines to resting state
Slow voltage-gated K+ channels open so that K+ can exit the cell so negativity of the inside is restored
What happens during hyperpolarization to gates?
Some K+ channels remain open and allows excessive K+ efflux
Na+ channels begin to reset
What is the role of the sodium potassium pump?
After repolarization this pump restores the ionic conditions
What must happen for an axon to fire?
Depolarization must reach threshold
What is threshold?
Voltage at which AP is triggered
What happens at threshold?
Membrane has been depolarized 15-20 mV
Na+ permeability increases
Na+ influx exceeds K+ efflux
Positive feedback cycle begins
What is the all or none phenomenon?
An action potential either happens completely or not at all
What does progagation allow for?
Action potential to serve as a signaling device
What is propagation?
When the local currents cause depolarization of adjacent membrane areas in direction away from the origin (the depolarization spreads across the membrane)
TF: Once initiated, an AP is self propagating?
True
What happens to membrane depolarization in nonmyelinated axons?
Each successive segment of membrane depolarizes then repolarizes
What does a stronger simuli cause for action potentials?
It causes action potentials to occur more frequently
How does the central nervous system determine the stimulus intensity of action potentials?
The frequency of impulses (higher frequency means a stronger stimuli)
What is the absolute refractory period?
When voltage-gated Na+ channels open and the neuron cannot respond to another stimuli
(time from opening Na+ channels until resetting of the channels)
What does the absolute refractory period ensure?
That each ap is all or none
What does the absolute refractory period enforce?
One way transmission of nerve impulses
What happens during the relative refractory period?
Some K+ channels are still open
Most Na+ channels are resting state
Repolarization occurs
What kind of stimuli could stimulate an Action potential in the relative refractory period?
Only exceptionally strong stimuli to reach threshold (remember hyperpolarization is occurring so that means the inside of the membrane is more negative than in resting state)
What does the rate of action potential propagation depend on?
Axon diameter (larger diameter = less resistance to local current flow so faster) Degree of myelination (more myelination = faster)
Where does continuous conduction occur?
In nonmyelinated axons
Where does saltatory conduction occur?
In myelinated axons (faster)
Where are action potentials generated in saltatory conduction?
Only in the gaps (no channels in the myelin)
What kind of disease is multiple sclerosis?
An autoimmune disease where the myelin sheath in the CNS is destroyed
What helps prevent MS?
High blood levels of vitamin D
What are the treatments for MS?
Drugs that modify immune system’s activity
What happens in MS?
The immune system attacks the myelin sheath in the CNS
Causes the myelin to create lesions called scleroses
Impulse conduction slows and eventually ceases
What are the symptoms of MS?
Visual disturbances Weakness Loss of muscular control Speech disturbances Urinary incontinence
How can nerve fibers be classified?
Diameter
Degree of myelination
Speed of conduction
What are the three groups of fibers?
A B C
What group of fibers have a large diameter, myelination and are found in the joints and skeletal muscle?
Group A fibers
What group of nerve fibers has the slowest impulse conduction?
Group C fibers
Smallest diameters
Unmyelinated ANS fibers
