Chapter 4 Flashcards
Electricity
A flow of electrons from a body that contains a higher charge to a body that contains a lower charge
Negative pole
The source of electrons- higher charge
Positive pole
Location to which electrons flow- Lower charge
Do nerves carry electrical stimulation
Yes (Galvani 18th century)
Electrical stimulation
Passing a electrical current from the tip of an electrode through the brain tissue, changing the electrical activity in the tissue
Fritsch and Hitzig found
Electrical stimulation of the neocortex causes movement
Bartholow found
First report of human brain stimulation
Caton studies
First attempt in measuring electrical currents of the brain using a voltmeter and electrodes to the skull
Electroencephalogram
Graph that records electrical activity through the skull or from the brain and represents graded potentials of many neurons
von Helmholtz studies
Flow of info in the nervous system is too slow to be a flow of electricity
Bernstein found
Ions don’t travel along the axon but rather a wave of charge
Electrical potential
An electrical charge measured in volts: stored energy
Volt
A measure of a different in electrical potential
Voltmeter
A device that measures volts
What was used to measure a neuron’s electrical activity
A giant squid because of its large axon
Microelectrodes
A set of electrodes small enough to go into an axon. Can be used to measure a neurons neural activity or deliver a current to a single neuron
DIffusion
Movement of ions from higher concentration to lower
Concentration gradient
Differences in concentration of a substance that allow substances to diffuse
Voltage gradient
Difference in charge between two regions that allows a flow of current if the two regions are connected
Equilibrium
Occurs when concentration gradients and voltage gradients are balances
Resting potential
Electrical charge of the membrane in the absence of stimulation. The inside of the membrane is at rest (-70mV) relative to the outside
What four charged particles take part in a resting potential
Na+, Cl-, K+, and large proteins (A-)
Ion distribution across a resting membrane
A- ions and K+ ions have higher concentration inside the axon while Na+ and Cl- have higher concentration outside the axon
Na+-K+ pumps
Intrude Na+ from the intercellular fluid and extrude K+
Graded potentials
Small voltage fluctuations across the cell membrane
Hperpolarization
- Increase in electrical charge across a membrane (more negative)
- Usually due to the inward flow of Cl- (signalled by GABA) and outward flow of K+
Depolarization
- Decrease in electrical charge across a membrane
- Due to inflow of sodium
Action potential
Large brief reversal in polarity of an axon
Threshold potential
Voltage of neural membrane at which an action potential is triggered. Opening of Na+ and K+ voltage activated channels to -50mV leads to it
Voltage activated ion channels
Gated channels that open or close only at specific membrane voltages. Na+ channels are more sensitive and open sooner and both are closed at resting
Repolarization
Returning to a polarized state (K+ out)
Tetrodotoxin
Blocks sodium channels and causes a slightly different action potential due to an efflux of potassium recorded
TEA on action potential
TEA surrounding the axon blocks the potassium channels, a smaller than normal but longer action potential is recorded
Absolute refractory period
The state of an axon in the repolarizing period in which a new action potential cannot be fired because the channels are closed
Relative refractory period
The state of an axon in the later phase of an action potential, during which a stronger current is required to produce another action potential, Potassium channels are still open
Nerve impulse
Propagation of an action potential down an axon and only down. Refractory periods produce a single discrete impulse that travels along the axon in one direction only. Size and shape of potential remain constant along the axon
Myelin
Produced by oligodendroglia in the CNS and Schwann cells in the PNS, speed up nerve impulses
Node of Ranvier
Part of an axon that is not covered in myelin, enables interaction with the extracellular fluid and leads to action potentials
How many connections can dendritic spines create for a neuron
Over 50k
Excitatory postsynaptic potential (EPSP)
Brief depolarization of a neuron membrane in response to stimulation, making the neuron more likely to fire an action potential (Influx of Na+)
Inhibitory postsynaptic potential (IPSP)
Brief hyper-polarization of a neuron membrane in response to stimulation, making it less likely to fire an action potential (Efflux of K+ or influx of Cl-)
Summation
Cell body adding IDSP and EDSP impulses, need both temporal and spatial summation to increase action potential
Temporal summation
Pulses that occur approximately the same time on a membrane that are summed
Spatial summation
Pulses that occur at approximately the same place on a membrane are summed
The axon hillock
Junction of the cell body and axon, rich in voltage activated channels, EDSPs and IPSPs and action potentials are initiated here
Where do action potentials not occur
On its dendrites although some neurons have voltage activated channels on the dendrites that do enable action potentials
Back propagation
Reverse movement of an action from the axon hillock into the dendritic field
Optigenetics
Some ion channels respond to light rather than voltage
Ways we receive information about the world
- Bodily sensations
- Auditory sensations
- Visual sensations
- Chemical sensations
Neurons in relation to the ways we receive info
All neurons related to the way we receive info have ion channels on their cell membrane, these ion channels initiate chain of events that produce a nerve impulse
Touch neuron example
Hair displacement when touched opens stretch-activated channels in the dendrites membrane allow for an action potential
How nerve impulses produce movement
Spinal motor neurons send nerve impulses to synapses on muscle cells, axon of each motor neuron makes on or more synapses with target muscle and sends to end plate (Part of the muscle membrane that is contacted by the axon terminal)
Acetylcholine
Chemical transmitter that the axon terminal releases at the muscle end plate. This allows channels to open causing a membrane to depolarize the muscle to the threshold, which then leads to an action potential causing muscle contraction
