Chapter 11 - Part 2 Flashcards
______ should be used to separate the positive and negative charges
Energy
A measure of potential energy generated by separated charge; Measured between two points in V or mV
A.k.a - Potential difference
Voltage
Greater the difference between two points______
Greater the voltage (potential difference) ________
Higher voltage, greater current
Charge difference in plasma membrane
Negative reading = more negative inside than outside
Membrane potential
Flow of electrical charge (ions) between two points
Can be used to do work
Flow is dependent on voltage and resistance
Current
Hindrance to charge flow
Insulator: substance with high electrical resistance
Conductor: substance with low electrical resistance
Conductor
Nongated channels; Always open
Leakage channels
Part of protein changes shape to open/close the channel
When opened, ions diffuse quickly towards opposite charge
3 types: Chemically, voltage, mechanically
Gated channels
Open only with binding of specific chemical
Chemically gated channel
Open and close in response to changes in membrane potential
Voltage gated channel
Open or close in response to physical deformation of receptors, as in sensory receptors
Mechanically gated channel
Combination of electrical and chemical gradients; Determines which way ions flow
Electrochemical gradient
Voltage that exists across the plasma membrane during the resting state of an excitable cell
Approx. -70mV
Membrane = polarized ( inside - )
Resting membrane potential
- Differences in ion composition of intra/extracellular fluids
- Differences in plasma membrane permeability to ions
Generating Membrane Potential
When concentrations of ions across membrane change
Used as signals to receive, integrate, and send infomation
2 types: hyperpolarization, depolarization
Changing membrane potential
Increase in membrane potential; Further from zero
Inside of membrane becomes more negative than resting potential
Probability of nerve impulse decreases
Hyperpolarization
Decrease in membrane potential; Moves towards zero
Inside of membrane becomes less negative than resting membrane potential
Probability of producing nerve impulse increases
Depolarization
Incoming signals operating over short distances; Results in depolarization
Short-lived; stronger the stimulus, the more the voltage changes and further the current goes
Occur at cell body and dendrites
Graded potentials
Long-distance signals of axons
Action potentials
Type of graded potential; Stimulus is a form of energy (heat, light, etc.)
Receptor potential
Type of graded potential; Stimulus is a neurotransmitter from another neuron
Excitatory (EPSP) - Brings the neuron closer to AP threshold
Inhibitory (IPSP) - IPSPs drive the neuron away from AP threshold
Postsynaptic potential
Transient (short) depolarization event along the cell membrane; Voltage changes from -70mV to +30mV
Principal way neurons send signals
Do not decay over distance
Action potential
Action pontential sheet for other facts
First part in action potential
All Na+ and K+ channels are closed; only leakage channels are open
Voltage gates are closed
-70mV
Resting state
Voltage sensitive gate in Na+ channel
Closed at rest, opens with depolarization, allowing Na+ to re enter cell
“Activates” action potential
Activation gates
Voltage sensitive gate in Na+ channel
Block channel once it is open to prevent more Na+ from entering cell
Inactivation gates
How many voltage sensitive gates does K+ have?
- Closed at rest
- Opens slowly with depolarization
One
Second step in action potential; Na+ channels open; Local currents depolarize the axon membrane
Na+ rushes into cell, and intracellular fluid becomes (+)
(-55mV to +30mV)
Depolarization
For axon to “fire” depolarization must reach -55mV to trigger action potential
Na+ permeability increases
Na+ influx exceeds K+ influx
Positive feedback cycle begins
Threshold voltage
Action potential either happens completely, or does not happen at all
If number of Na+ ions that enter the cell is too low to achieve threshold, no action potential will occur
All or none response
Third part in action potential; Na+ channels are inactivating, K+ channels open
AP spike starts to decline
Na+ permeability declines
Resting potential restored
Repolarization
Fourth part in action potential; Some K+ channels remain open, Na+ channels reset
Inside of membrane becomes more (-) than resting state
-80mV
Hyperpolarization
Transmission of action potential from it origin down entire length of the axon toward axon terminals
Depolarization in one area causes depolarization in the next
Propogation
Once initiated, APs are _______
Self propogating
AP only occurs in the ______ direction
Forward
Time in which neuron cannot trigger another action potential
Voltage gated Na+ channels are open, so neuron cannot respond to another stimulus
Two types:
1. Absolute refractory period
2. Relative refractory period
Refractory period
Time from opening of Na+ channels until resetting of the channels
Absolute refractory period
Most Na+ channels have returned to their resting state
Some K+ still open
Repolarization occuring
Relative refractory period
- Axon diameter: larger = faster
- Degree of myelination: Continuous conduction/Saltatory conduction
Factors of AP rate propagation
Slow conduction that occurs in unmyelinated axons
Continuous conduction
Occurs only in myelinated axons and is 30x faster
Myelin sheaths insulate and prevent leakage of charge
Channels located at sheath gaps; AP only generated here
Electrical signal jumps from gap to gap
Saltatory conduction
Autoimmune disease that affects primarily young adults
Myelin sheaths are destroyed when immune system attacks myelin
Symptoms: Visual disturbances, weakness, loss of muscular control, speech disturbance
Treatment: drugs to modify immune system activity
Multiple sclerosis (MS)
Junctions that mediate information transfer; Neuron to neuron
Two types:
1. Electrical - less common, neurons electrically coupled
2. Chemical - Specialized release of chemical neurotransmitter
Synapse
Neuron conducting impulses toward synapse (sending info)
Presynaptic neuron
Neuron transmitting electrical signal away from synapse (receives info)
Postsynaptic neuron
Synaptic connection between axon terminals of one neuron and dendrites of others
Axodendritic
Synaptic connection between two axon terminals of one neuron and soma (cell body) of others
Axosomatic
Fluid-filled cavity that prevents nerve impulse from directly passing from one neuron to the next
Synaptic cleft
“Language of the nervous system”
Classified by either chemical structure or function
Chemical passed through synptic cleft
Neurotransmitters
Excitatory vs. inhibitory
Inhibitory - Hyperpolarization
Excitatory - Depolarization
Effect neurotransmitter
Direct vs. indirect
Direct - Neurotransmitter binds directly to and opens ion channels
Indirect - Neurotransmitter acts through intracellular second messengers
Action neurotransmitter
Secreted in PNS; All neuromuscular junctions with skeletal muscle
Effects prolonged when AChE blocked by nerve gas, leading to muscle spasms
Acetylcholine
Plays a role in sleep, appetite, nausea, migraine headaches, and regulating mood (happiness)
Anti-depression/anxiety medications block function
Activity blocked by LSD and enhanced by ecstasy
Serotonin
