Section 7 Flashcards
True or False:
Graded potentials are transient changes in the membrane potential. GPs travel only as mall distance from their point of origin and as they move, they decay in size.
True
Postsynaptic membrane graded voltage potentials (activated ligand gated channels) occur at the:
- Spinal cord in dendrites
- Spinal ganglia in dendrites
- NMJ in the motor end plate
Positive or depolarizing graded potentials
EPSPs
Negative or hyper polarizing graded potentials
IPSPs
Occurs when successive discharges of neurotransmitter from 2 or more (different) presynaptic anon terminals cause successive postsynaptic potentials (EPSPs and/or IPSPs) to overlap or summate
Spatial summation
Occurs with successive discharge of neurotransmitter from the same presynaptic axon terminal that results in successive postsynaptic potentials (EPSPs and/or IPSPs) that overlap or summate when they occur at sufficiently high frequency
Temporal summation
True or False:
Axon membrane’s permeability to Na+ in the activated region is 10 x greater than permeability in the resting region
False; its several 1000 times greater
True or False:
Membranes have the ability to move action potentials in either direction.
True
Share movement without ionic current flow through the membrane; initially depolarizes inactive membrane
Capacitive current
Currents in non-myelinated nerve axon; intracellular current flows from the active region through the intracellular fluid to the inactive region; when the - charge is replaced by a + charge, the + charge inside repels the + charge outside, which is replaced by a - charge on the outside
Eddy currents
Ions or charges move across the membrane
Ionic current
The current that changes the amount of charge on the membrane
Capacitive current
___ current is responsible for depolarization, while ___ current is responsible for repolarization.
Na+; K+
Summarize 3 steps of an action potential
- Capacitive current initially depolarizes membrane (opens voltage gated channels)
- Na+ channels open and close quickly; Na+ flows down its concentration gradient with a large driving force (upstroke of an action potential)
- K+ channels open slowly for delayed increase K+ current (downstroke of an action potential)
Action potential propagation in myelinated axons; nerve impulse leaps along the axon during conduction from node to node
Saltatory conduction
Where are charges found in myelinated axons?
At the nodes of Ranvier
True or False:
Nodes of Ranvier are spaced farther apart in smaller diameter axons than in small diameter axons.
False; nodes are space farther in larger diameter axons, which allows for even greater conduction velocity
Period where no matter how large the stimulus is, an AP cannot be produced - Na+ channels completely closed
Absolute refractory period
Period where a very large stimulus can produce an AP - some Na+ channels are still closed; K+ channels wide open
Relative refractory period
Period where a very small stimulus can produce an AP; membrane is slightly depolarized and Na+ channels are ready to open
Supernormal period
Graded potentials are _______ to stimulus strength
Proportional
State the 4 steps of how capacitive current works.
- Na+ current moves from active to inactive region of membrane inside the cell
- Positive charge displaces negative charge in the inactive region
- positive charge on the outside membrane is repel off by the positive charge on the inside membrane; initially exciting the membrane with the removal of the positive charge
- Replacement of the positive charge with a negative on the outside membrane is capacitive current
What is the Hodgkin Cycle?
Upstroke of an AP (occurs at each point along the membrane); membrane depolarization, incr. Na+ conductance, Na+ influx
Occurs at the leading edge of the traveling nerve impulse activating resting membrane
Hodgkin cycle
