Chapter 4: Neuron's Use of Electrical Signals to Transmit Information Flashcards
Electrical stimulation
passage of electrical current from an uninsulated tip of an electrode through tissue, resulting in changes of the electrical activity of the tissue
Electroencephalogram (EEG) and a discovery by them
graph that records electrical activity of the brain and indicates graded potentials of many neurons; shows that the activity is too slow to be actual electricity –> it is a wave of charge of ions
Oscilloscope
device that serves as a sensitive voltmeter by registering changes in voltage over time
Microelectrodes
microscopic insulated wire or salt water-filled glass tube whose uninsulated tip is used to stimulate or record from neurons; can be on outside, inside or suctioned to it
Diffusion
movement from an area of higher concentration to lower
Concentration gradient
relative abundance of a substance in space or solution
Voltage gradient
difference in charge between 2 regions
How Ion movement produces electrical charges
difference of chloride on the 2 sides of a membrane produces a difference in charge or voltage; at equilibrium the concentration gradient and voltage gradient are equal
Resting potential
store of potential energy produced by a greater negative charge on the intracellular relative to extracellular side (-70mv)
Maintaining resting potential (3)
1) Proteins stay in the cell
2) K+ and Cl- flow more freely across the membrane. Na+ more restricted
3) Na+-K+ pumps extrude Na+ and inject K+ (3 Na for 2 K)
Maintaining resting potential inside the cell
K+ inside in large numbers to counteract the negative charge of A-; not all K+ goes in because of the concentration gradient of inside vs outside so the inside stays a bit negative relative to outside
Maintaining resting potential outside the cell
a few K+ outside to contribute to relative negative charge of the inside; 10x Na+ outside; Cl- contributes little to the potential (12x Cl- outside)
Graded potentials
small voltage fluctuation across cell membrane
Hyperpolarization
increase in electrical charge across a membrane, usually due to the inward flow of Cl- or Na+ or outward flow of K+; Ex. -70 to -73
Depolarization
decrease in electrical charge across a membrane, usually due to inward flow of Na+; Ex. -70 to -65
3 Channels for Graded Potentials
1) K+ channels: efflux of them causes hyperpolarization
2) Cl- channels: influx of Cl- hyperpolarizes
3) Na+: influx of sodium depolarizes
Action Potential
large brief reversal in polarity of the axon membrane; lasts 1ms; Na+ flows in, shortly after K+ flows out; from -70 to -50 to +30 to -100 then slowly to -70 again
Threshold potential
voltage on a neural membrane when action potential is triggered (usually -50mv)
Voltage sensitive channel
gated protein channel that opens or closes at certain voltages
Absolutely refractory
state of an axon in the repolarizing period, new action potential cannot be elicited (some exceptions), because gate 2 of the Na+ channels, which are not voltage sensitive, are closed
Relatively refractory
more stimulation needed for action potential because it is hyperpolarized; K+ channels still open
Nerve impulse
propagation of an action potential on the membrane of an axon; each action potential propagates another on an adjacent part of the membrane (all or none)
Saltatory (jumping) conduction
fast propagation of an action potential at successive nodes of Ranvier
Nodes of Ranvier
part of an axon not covered by myelin; these allow for less energy to be used and for the nerve impulse to travel faster
What happens during an Excitatory Post Synaptic Potential (EPSP)?
Na+ channels open; results in a brief depolarization of a neuron membrane in response to stimulation, the neuron is more likely to produce an action potential
What happens during an Inhibitory Post Synaptic Potential (IPSP)?
K+ channels open or Cl- open; results in a brief hyperpolarization of a neuron membrane in response to stimulation, as a result is less likely to produce an action potential
What is the Initial Segment and why is it significant in transmitting neural impulses?
it is the area near or overlapping the axon hillock that is rich in voltage sensitive channels; because of this it is the area where the action potential begins (usually); dendrites closest to the initial segment influence it more
Temporal Summation
it is the addition of one graded potential to another that occur close in time
Spatial Summation
the addition of one graded potential to another that occur close in space on the membrane
What is back propagation and what process does it play a role in?
the reverse movement of an action potential into the soma and the dendritic field of a neuron; perhaps it plays a role in plastic changes critical in learning as it lets the dendrites know when an action potential has occured down the axon
Optogenetics
a transgenic technique that combines genetics and light to excite or inhibit targeted cells in living tissue
Where does the conduction of information begin?
ion channels
Stretch sensitive channels
an ion channel on a tactile sensory neuron that respond to the stretching of a membrane, activating a nerve impulse
What is an end plate and what neurotransmitter does it receive?
a receptor-ion complex on a muscle that is activated by the release of the neurotransmitter acetylcholine from the terminal of a motor neuron
What are transmitter sensitive channels, why are they important and where are they located?
a receptor complex that has both a receptor site for a chemical and a pore through which ions can flow; it is important because acetylcholine attaches to it and allows for the flow of Na+ and K+ through the same pore that leads to the contraction of muscles; located on the end plate
Mysathenia Gravis
acetylecholine receptors are blocked and muscles cannot depolarize (slow eye opening example)
At resting potential each ion is: (3)
1) Na+: driven in by electrostatic forces and concentration gradient
2) K+: driven in by electrostatic forces and out by concentration gradient
3) Cl- driven out by electrostatic and by concentration gradient
