Chapter 12 Worksheet

Place a single word into each sentence to make it correct in describing the repair of a peripheral nerve fiber.

- A damaged PERIPHERAL nerve fiber may regenerate if its soma is intact and some neurilemma remains. - When a nerve fiber is cut, the fiber distal to the injury CANNOT survive. - Near the site of injury, the basal lamina and the neurilemma form a REGENERATION tube. - The tube guides the growing sprout back to the original target cells, reestablishing SYNAPTIC contact. - When contact is established, the SOMA shrinks, and reinnervated muscle fibers regrow.

Indicate the summative effect that brings the initial segment closest to threshold.

Two EPSPs in proximity to each other

Place a single word into each sentence to make it correct.

- An unmyelinated fiber has voltage-gated ion gates along its entire LENGTH. - An action potential at the TRIGGER zone causes sodium to diffuse into the cell. - This results in membrane DEPOLARIZATION. - The depolarization causes a REPETITION that excites the entire membrane. - This continues until the traveling signal reaches the end of the AXON.

What are the three general classes of neurons that correspond to the three major aspects of nervous system function? Check all that apply.

- Motor neurons that send signals predominantly to muscle and gland cells - Interneurons that lie between, and interconnect the incoming sensory pathways and the outgoing motor pathways of the CNS - Sensory neurons that are specialized to detect stimuli such as light, heat, pressure, and chemicals and transmit information about them to the CNS

Which types of glial cells are found in the central nervous system? Check all that apply.

- Oligodendrocytes - Ependymal cells - Microglia - Astrocytes

Complete each statement by using the appropriate word or phrase from the list.

- Prior to the arrival of a signal from a presynaptic input, the post-synaptic membrane is polar with a greater relative POSITIVE charge in the ECF. - In somatic neurons, an action potential arrives at the synapse causing synaptic vesicles to fuse with the PRESYNAPTIC membrane. - The presynaptic membrane releases (via exocytosis) acetylcholine (ACh) into the ECF OF SYNAPTIC CLEFT. - The ACh diffuses across the cleft and binds to the LIGANG-REGULATED SODIUM channels. - Activated (open) sodium channels allow a rapid diffusion of SODIUM down its electrochemical gradient towards the ICF. - The movement of positive charges to the ICF causes the relative charge across the membrane to become positive on the inner surface.

Complete each statement by using the appropriate word or phrase from the list.

- Resting membrane potential is created as a result of a greater net flow of positive charges from the ICF TO THE ECF. - Though potassium (+1) and sodium (+1) both leak through the membrane at rest, there is a greater diffusional flow of POTASSIUM at rest. - The diffusional movement of sodium and potassium across the membrane is driven at all times by the ELECTROCHEMICAL GRADIENT. - The electrical and chemical gradients for SODIUM are both high during resting membrane potential which results in a very high electrochemical gradient towards the inside of the cell. - In order to maintain the electrochemical gradients for sodium and potassium, ATPase pumps move these ions AGAINST their respective gradients.

Why is myelin important? Check all that apply.

-It speeds up signal conduction in the nerve fiber. -It is formed to assist in the regeneration of damaged fibers. -It insulates the nerve fiber.

Complete each statement by using the appropriate word or phrase from the list. Then, place the statements in the order of an action potential repolarization event.

1. As the membrane potential RISES TOWARD ZERO, the voltage-regulated sodium channels begin closing which, in turn, reduces the sodium movement to the ICF. 2. With membrane potentials approaching +35 mV, the VOLTAGE-REGULATED POTASSIUM channels become fully activated. 3. Through the activated channels, POTASSIUM now flows outwards causing the membrane to repolarize back towards RMP. 4. With a larger duration of activation than sodium channels, the potassium channels allow for a greater movement of potassium to the ECF causing a short period of HYPERPOLARIZATION.

Place the following statements in the correct order for an action potential to be generated.

1. a neuron starts at its resting membrane potential 2. excitatory postsynaptic potentials (ESPS's) are received 3. Na+ flows into the cell making the inside more positive 4. the cell reaches threshold 5. voltage-gated Na+ channels open 6. an action potential is generated

If acetylcholinesterase became mutated and nonfunctional, what would be the immediate result?

Acetylcholine would build up in the synaptic cleft.

Which term describes all neurons that carry signals towards the CNS?

Afferent

If a drug was developed that interfered with the proper functioning of the microtubules found within the axons of neurons, how would you expect this to impact axonal transport processes?

Both anterograde and retrograde transport processes would cease.

The enzyme choline acetyltransferase catalyzes the reaction between acetyl-CoA and choline resulting in the formation of the neurotransmitter acetylcholine. This enzyme is produced within the cell body of neurons, but the synthesis of acetylcholine occurs within the axon terminals. Which statement best describes the axonal transport mechanism associated with this process?

Choline acetyltransferase is transported in the anterograde direction.

Choose the correct statement about myelin.

It is best not to give children under two years of age a low-fat diet because myelin formation requires lipids.

Acetylcholine has which effect on the postsynaptic neuron?

Ligand-gated sodium ion channels open, and sodium diffuses in.

Why does depolarization occur?

More Na+ diffuse into the cell than K+ diffuse out of it.

During depolarization, which of the following statements about voltage-gated ion channels is true?

Na+ gates open before K+ gates.

_______________ the time between signals sent from the same presynaptic terminal increases the strength of the graded potential. This is an example of ________________ summation.

Reducing; temporal

Suppose that a new virus is discovered that specifically infects motor neurons. Assume that this virus enters neurons in conjunction with choline molecules. Once inside the cell, the virus enters the nucleus and replicates. Which direction describes the axonal transport route taken by this virus?

Retrograde transport

What happens as a result of ion flow at a presynaptic terminal?

Synaptic vesicles migrate to the plasma membrane and release acetylcholine.

Which of the following statements about the resting membrane potential is true?

The exterior of the cell has a net positive charge, and the interior has a net negative charge.

The resting membrane potential is negative due to which of the following?

There are more negatively charged particles on the inside of the membrane than on the outside.

If demyelination occurs, why don't action potentials occur at regions of the axon that were previously myelinated?

These regions lack the appropriate concentration of voltage-gated sodium channels.

An action potential arriving at the presynaptic terminal causes what to occur?

Voltage-gated calcium ion channels open, and calcium ions diffuse into the cell.

Pair each type of axonal transport with its definition.

anterograde transport- movement down the axon away from soma slow anterograde transport- movement of enzymes and cytoskeleton components down the axon to renew worn-out axoplasmic components fast retrograde transport- returns used synaptic vesicles and other materials to the soma fast anterograde transport- movement of enzymes and small molecules toward that distal end of the axon axonal transport- two-way passage of proteins, organelles, and other material along an axon

At the synaptic knob, voltage-gated ______________ channels open, thereby stimulating the synaptic vesicles to release their neurotransmitters by exocytosis.

calcium

Substances that cause facilitation of a neuron ____________________________.

cause the neuron to fire that may not fire under the same circumstances in the absence of the facilitator

A resting membrane potential of -70 mV indicates that the ________________.

charges lining the inside of the plasma membrane are negative compared to the charges lining the outside

Assume all of the presynaptic synapses identified produce EPSPs. If two of these synapses fired simultaneously, which synaptic combination brings the initial segment closest to threshold based on spatial summation? Click on the appropriate synapses.

choose synapses 3 and 4

Demyelinating diseases cause a(n) ______________ in the conduction velocity of action potentials.

decrease

Acetylcholine is actively transported from the presynaptic membrane to the postsynaptic membrane.

false

Action potentials occur ____________________________.

in the unmyelinated regions of an axon

When voltage-gated sodium channels are open, sodium flows _____________ the neuron, making the inside of the cell more _______________.

into; positive

Graded potentials result from the opening of ________________.

ligand-gated channels

Assume in a laboratory you were able to isolate a neuron and remove the Acetylcholine receptors from the postsynaptic membrane. The substance _________________ would no longer cause facilitation of this neuron.

nicotine

An inhibitory postsynaptic potential results from the opening of____________________.

potassium and/or chloride channels

Graded potentials are produced within the _______________________ segment of a neuron.

receptive

The following information best describes the _____________ phase of an action potential. • A membrane potential reading of +10 mV • Inactivated voltage-gated sodium channels • Open voltage-gated potassium channels

repolarization

Normally, sodium and potassium leakage channels differ because ___________________.

sodium ions diffuse through leakage channels into the cell, but potassium ions diffuse through leakage channels out of the cell

If the postsynaptic membrane potential reaches threshold level, an action potential will be produced.

true

The enzyme acetylcholinesterase, located in the synaptic cleft and on the postsynaptic membrane, breaks ACh down into acetate and choline, thereby stopping the stimulation of a postsynaptic cell.

true

The nerve impulse is an electrical current that travels along dendrites or axons.

true

The physical basis of memory is a pathway through the brain called a memory trace, in which new synapses have formed or existing synapses have been modified to make transmission easier.

true

The sodium-potassium pump is involved in establishing the resting membrane potential.

true