Flashcards in Neurophysiology (2) Deck (55)
What causes the stimulus for the AP fired in response to testing a tendon reflex response?
Stretch of muscle spindle fibers is transduced into a graded electrical signal, called a receptor potential
Where does the AP originate in response to the monosynaptic or myostatic stretch reflex?
In the peripheral process of a sensory neuron ( the cell body of which lies in the dorsal root ganglion)
What nerve is the signal transferred to from the sensory neuron in the stretch reflex? Where in the spinal cord is this located
Alpha-motoneuron, located in the spinal cord ventral horn
Other than the alpha motoneuron, what nerve does the afferent sensory nerve synapse on in the spinal cord?
Interneuron. May inhibit firing of the motoneuron
What provides the stimulus for activation of a voltage-charged gate?
Charged amino acids
What are two mechanisms that can contribute to the selectivity pore of ion channels?
1. Narrow pore (only certain molecules can pass; steric hindrance)
2. Charged region in pore
What is Ohm's Law?
Voltage = current X resistance. V= IR
How do resistance and conductance (G) relate?
Resistance = 1/ conductance
Which biological structures act as resistors in a neuron? How then is resistance controlled?
Ion channels. Act like variable resistors and resistance is controlled by channel gating.
What biological structure serve as a capacitator in neurons? What are the consequences of having capacitators?
Lipid bilayer. Electrical signals are slowed by the storage of charge in the membrane (capacitative element)
What is the time constant? What does it determine?
Time for membrane potential to fall to 1/e of original potential charge. Determines time period over which electrical signals can be integrated in a cell. Voltage is maximal at the point of stimulation and decays exponentially with distance from that point.
At rest, what ion are neuronal cell membranes permeable to?
What does the Nernst equation determine?
The membrane potential at equilibrium if the membrane were only permeable to one ion.
What is the equilibrium potential in neurons for K+? Na+? Cl-?
K+ = -100 mV
Na+ = +50 mV
Cl- = -60 mV
What is the resting membrane potential for neurons typically?
What does the Goldman-Hodgkin-Katz equation predict?
The membrane potential at equilibrium when all permeant ions are taken into account
What two active pumps are responsible for maintaining the necessary ion concentration for the resting membrane potential?
1. Na/K ATPase
2. Ca2+ ATPase
What does the complicated geometry of neurons mean for the membrane potential?
It is not the same at all points in the membrane (not isopotential) at a given time
Increasing what parameter will increase the time constant in electrotonic or passive signal propagation?
Increasing diameter of cable. Larger diameter means less contact with the membrane, so charge doesn't leak as much
What causes the progressive decay in amplitude in passive (electrotonic) signal propagation?
Leakage of charge across membrane
There is also a slowing of response in passive signal propagation, what is responsible for this?
Charging of the membrane capacitance along the neuron
What type of signal is an active signal, that cannot be modeled by a simple RC circuit?
Firing of an AP
What is the undershoot, in which the membrane potential falls to less than the original called?
What indicates that selectivity is maintained but but that a different ion species dominates membrane permeability during depolarization, compared to K+ at rest?
The fact that membrane potential overshoots 0 mV. (Goes up to + 30)
What are the two major types of neural electrical signals?
1. Graded potentials
2. Action potentials
Graded potentials are ________ responses. Action potentials are ______ responses.
Why are action potentials/active responses voltage-dependent?
Because they rely on the opening of voltage-gated ion channels
What is responsible for the upstroke in an AP?
Increase in membrane permeability to Na+
What is responsible for the downstroke in an AP?
Inactivation of Na+ channels