Chapter 12 - Neurophysiology Flashcards
Electrical signals
only travel along membranes (axolemma & sarcolemma); membranes carry electrical signals
Ions involved in generation of electrical signals
- Na+
- K+
when they go thru a membrane they change. they charge across membrane & generate electrical signals
axolemma & sarcolemma
phospholipid; ions have a hard time crossing membranes; protein channels allow ions thru
ion channels
places on the membrane that allows a specific ion thru & it begins to generate signals
Types of Ion channels
- Leakage channels
- Gated channels
a. ligand-gated i.c.
b. mechanically gated i.c.
c. voltage gated i.c.
Leakage channels
ions leak thru a little at a time & it’s not regulated
Gated channels
when gate is open, ion can move thru; when closed, there is no movement; responds to stimulus to open or close
Ligand-gated ion channels
respond to special chemicals (neurotransmitters);
ligand = specific chemical that binds;
acetylcholine-specific binding that opens after it binds & ions can go thru & charge across membrane changes;
can only produce graded potentials;
located–plasma membrane of dendrites or cell body
Mechanically gated ion channels
responds to physical force (pressure, touch, stretching) & signal generated;
can only produce graded potentials;
located–plasma membrane of dendrites or cell body
Voltage gated ion channel
if voltage changes it can open the ion channel; responds to changes in membrane potential;
voltage = charge difference;
only one to produce action potentials;
located-axolemma & sarcolemma
Membrane potential
charge difference across a membrane
Volt meter
can measure charge difference across membrane
Resting membrane potential
no signal is being generated;
approx: -70 mV (million volts); cell at rest; charge on inside is more negative than outside of cell
Explanation of why inside of cell is more negative outside of cell
Na+ K+ pump–pumps ions from low to high; pumps Na+ out of cell & K+ into cell; exists in every single cell’s membrane; fluid outside cell has lots of Na; for every 3 Na+ out in pumps 2 K+; so more charges are on outside; inside has fewer positive charges, so more negative on inside
Electrical Signals (2 types)
- Graded potentials
2. Action potentials
Graded potentials
caused by decreasing w/distance; short distance electrical signals; ligand-gated or mechanically gated i.c.
Electrical signals
move resting membrane potential to more positive position
Action potentials
voltage-gated channels; only occurs on axolemma & sarcolemma; long-distance electrical signals; do not decrease effect over long distance, signal stays just as strong
Action Potentials (characteristics)
- Long distance electrical signal
- Transient reversal of membrane potential; flips membrane potential to neg on inside to pos on inside; depolarization, repolarization, hyperpolarization
- Mediated by movement of ions
- All-or-none event - either 100% or 0%
- Fast - travels quickly so our NS responds quickly
threshold
certain membrane potential that must be reached in order for action potential to start; very important #; ex. if it doesn’t reach threshold, nothing happens
3 Phases of Action Potentials
- Depolarization
- Repolarization - returns to resting
- Hyperpolarization
Polarized
negative
Action Potentials:
Phase / Caused by / Membrane potential
- Phase: Depolarization
Caused by: Na+ channel opens; Na+ enters cell;
Membrane potential: more positive - Phase: Repolarization
Caused by: K+ channel opens; K+ leaves cell
Membrane potential: more negative - Phase: Hyperpolarization
Caused by: K+ channels close slowly;
Membrane potential: more neg than resting
Action potentials occur…
at axon hillock; all we need is threshold for action potential to start; goes away from cell body to axon terminal
Refractory period
action potentials don’t go backwards; explains why action potentials move forward; it can’t respond backwards
Factors affecting rate of Action potentials
- Diameter of axon - thick axon travels faster; increase diameter, increase rate
- Increase temp, increase rate
- Increase amount of myelination, increase rate
Myelinated axon move faster than unmyelinated axons bc
action potentials jump over schwann cells to next node; saltatory conduction–faster than continuous conduction bc you are skipping spots
fastest moving action potential in body
very thick & myelinated; travels 300 mph by saltatory conduction
Synapses
junction between 2 neurons or between a neuron & an effector cell; how neurons talk to other neurons; how signal gets to another cell
