Title: Physiology 2130 / Module 4: Nerves

Q: Excitable cells use [...] to generate electrochemical impulses.
A: membrane potential
Extra: Electrochemical Impulses (aka. Action Potentials)

Q: Electrochemical impulses are called [...].
A: action potentials

Q: Dendrites are thin branches of cell body thats function is to [...] and  increase [...] to [...].
A: recieve incoming signals; surface area; communicate with many neurons

Q: The [...] is the control center of the nerve cell, containing the nucleus and all organelles required for directing cell activity.
A: cell body

Q: [...] are a projection of the cell body which carries the outgoing signal to a target cell in the form of an AP.
A: Axons

Q: The [...] is a layered phospholipid sheath that acts as an insulator and covers the axon, forcing the ionic changes that comprise the AP to take place only in small exposed regions of the axons (Nodes of Ranvier).
A: myelin sheath

Q: Myelination forces ionic interactions to occur at the [...]
A: nodes of ranvier

Q: The [...] are small, exposed areas of an axon that action potentials jump to.
A: Node(s) of Ranvier

Myelination makes transmission of action potentials faster since they  jump from node to node.
Extra: This jumping of the AP from node to node results in an increased transmission speed down the length of the axon.

Q: [...] are branches of axon near the terminal end that increase the possible target cells neurons can interact with.
A: Collaterals

Q: The [...] aka the [...] is a swelling at the end of the collateral that facilitate transmission of action potential across the synapse to the target cell.
A: terminal bouton; axon terminal

Q: Axon terminals contain [...] and [...] with neurochemical molecules.
A: mitochondria; vesicles
Extra: The chemicals here facilitate the transmission of the signal from the synapse to the target cell.

Q: Action potential causes a rapid reversal of the resting membrane, going from [...] to [...]mV.
A: -70mV; +35

Q: [...] is the sudden change of electric potential (membrane) to a more positive value.
A: Depolarization

Q: [...] is when membrane potential becomes more negative.
A: Repolarization
Extra: That is, repolarization restores the RMP (-70 mV).

Q: Repolarization occurs and reaches about [...]mV, this is called [...].
A: -90; hyperpolarization
Extra: Hyperpolarization = A state in which the MP is more negative than the default MP...but soon after that, the membrane establishes again the values of MP.

Header: Label the following:

Q: Voltage gated channels are found on the [...].
A: axon

Q: Voltage gated channels are sensitive to changes in membrane potential. They open when the membrane is [...] to [...]mV.
A: depolarized; -60

Q: Sodium voltage gated channels open [...] after depolarization.
A: immediately
Extra: Sodium = Na+

Q: The voltage gated sodium channels have an [...] and [...] gate.
A: activation; inactivation
Extra: Sodium = Na+

Q: When the inactivation gate is closed, the channel will [...]. This is called the [...].
A: never open; absolute refractory period
Extra: It's impossible to have have another AP on that part of the membrane because the inactivation gates have blocked those Na+ channels so you can’t get any more Na+ in to produce an AP.

Q: K+ voltage gated channels open slowly after a [...].
A: brief pause

Q: The [...] does not have an inactivation period.
A: K+ voltage gated channel

Q: K+ voltage gated channels start to open as the Na+ channels begins to enter their [...].
A: inactivation period

Q: Depolarization begins at the [...].
A: axon hillock

Q: When Na+ rushes into the neuron, the membrane depolarizes to [...]mV.
A: +35

Q: When K+ rushes out of the cell, it begins to repolarize to [...]mV but it continues to rush out which causes [...]  to [...]mV.
A: -70; hyperpolarization; -90

Q: When K+ channels begin to close is when the cell slowly returns to [...]mV.
A: -70
Extra: Resting Membrane Potential = -70 mV

Q: The 2 refractory periods are [...] and [...] refractory.
A: absolute; relative

Q: The relative refractory period occurs when the membrane is [...].
A: hyperpolarized

Q: The relative refractory period is caused by the [...].
A: K+ voltage-gated channels

Q: During [...] it's possible to fire another action potential, but it would require a stronger stimulus to reach threshold.
A: relative refractory,
Extra: That is, it’s a portion of time when the membrane is hyperpolarized (i.e., more negative than -70 mV) and you can have an AP, it’s just relatively more difficult.

Q: Small depolarization within the cell can be repolarized to resting by [...] leaving and [...] entering the cell.
A: K+; Cl-

Q: The threshold to fire an action potential is depolarization to [...]mV.
A: -55

Q: Na+ moving in while K+ moves out causes an [...] aka the [...] of the action potential.
A: overshoot; rounded top

Q: The depolarizing phase is due to [...] entering, and the repolarizing phase is due to [...] leaving.
A: Na+; K+

Q: The [...] voltage-gated channels are beginning to close as the [...] voltage-gated channels begin to open.
A: Na+; K+

Q: [...] of action potentials can be generated before the concentration gradients from Na+ and K+ break down enough to prevent the generation of further APs.
A: Thousands

Q: The [...] is not required for repolarization.
A: Sodium/potassium pump

Q: Note that as a standard, current is carried by [...] ions.
A: positively charged
Extra: ex., Na+

Q: Direction of current flow is generally [...] to [...].
A: positive; negative

Q: [...] conduction is much faster than conduction in unmyelinated fibers.
A: Saltatory
Extra: Saltatory =  Myelinated

Q: Action potentials are propogated down the axon at their [...] height.
A: full
Extra: If the threshold isn’t reached, the natural repolarizing forces of the membrane will return the MP to normal (-70 mV). Once the threshold is reached, you’ll generate an AP & this AP will be propagated down the axon at its full height without decreasing in size. This is the all-or-nothing principle.

Q: Action potentials always have fixed [...].
A: height/amplitude

Q: Action potentials follow an [...] principle.
A: all-or-nothing
Extra: That is, you either have a full AP or none at all.

Q: Due to the [...] 2 actions potentials cannot be fired ontop of each other.
A: absolute refractory period

Q: When the myelin sheath is attacked by the body's own immune system this causes the disease [...].
A: Multiple Sclerosis
Extra: Multiple Sclerosis = MS

Q: A chemical synapse is a point where the [...] almost comes in contact with another [...] or [...].
A: axon terminal; neuron; muscle cell

Q: The synapse between a neuron and muscle cell is called a [...].
A: neuromuscular junction
Extra: Neuromuscular Junction = NMJ

Q: The damaging of the myelin sheath can disrupt the natural flow of action potentials, to the point that [...] occurs. If the nerve that’s damaged is connected to a muscle, that muscle will not contract & the person can suffer [...].
A: no transmission; paralysis

Q: Neurons that contact muscle cells are called [...].
A: motor nerve fibers

The presynaptic axon terminal has mitochondria, Ca++ voltage gated channels and vesicles containing acetylcholine (ACh).
Extra: The chemicals here facilitate the transmission of the signal from the synapse to the target cell.

Q: Acetylcholinesterase (AChE) is contained in the [...] of the presynaptic [...].
A: basement membrane; axon terminal

Q: The muscle cell membrane is also called the [...].
A: sarcolemma

Q: The [...] is the region where the sacrolemma folds.
A: end plate

Q: The end plate contains [...] receptors.
A: ACh

Q: ACh receptors are associated with [...].
A: ligand-gated Na+ channels

Q: The gap between the [...] and [...] is called the synaptic cleft.
A: motor nerve fiber; muscle cell

The events at the neuromusclar junction (NMJ) are:
1. The action potential from the presynaptic neruon triggers the Ca++ voltage gated channel so Ca++ flows into the cell.
2. Ca++ triggers the fusion of synaptic vesicles to the membrane and releases ACh into the synaptic cleft.
3. ACh diffuses and binds to receptors on the muscle membrane.
4. The ligand gated sodium ion channel opens. Na+ flows into the cell and triggers depolarization called end plate potential.
5. The action potential is triggered by the EPP spreading to adjacent cells.
6. ACh is broken down into acetic acid and choline by AChE. The choline is taken back to the axon terminal.

Q: Action potentials to muscle cells cause the muscle to [...].
A: contract

Propogation of action potential down an unmyleinated neuron:
1. The inside of membrane is positive; about +35 mV due to influx of Na+.
2. This positive charge is attracted to and moves toward an area of the membrane that is adjacent and resting which creates a local current.
3. Because of the buildup of the positive charge, the adjacent area of the membrane depolarizes.
4. Depolarization of that area triggers the opening of Na+ gates.
5. Na+ rushes into the cell, depolarizes the region and creates a new action potential.
6. Repetition = Propogation.

Propogation of an action potential down a mylelinated axon:
1. The positive charge from the exisiting action potential is attracted to the the adjacent Node of Ranvier which is negative.
2. The Node of Ranvier then depolarizes.
3. Depolarization triggers Na+ gate to open.
4. Na+ rushes into the cell and depolarizes the region to threshold which generates a new action potential.
5. Repetition = Propogation.